St. Croix River Crossing Preliminary Engineering Concept Refinement Report

Prepared for: Minnesota Department of Transportation and Wisconsin Department of Transportation

Prepared by: Parsons Brinckerhoff

June 2010

St. Croix River Crossing Preliminary Engineering Concept Refinement Report

Table of Contents 1 Executive Summary ...... 1‐1 1.1 Pier Configuration ...... 1‐1 1.2 Box Girder Configuration ...... 1‐2 1.3 Pedestrian Trail Location ...... 1‐2 1.4 Cable Anchorage Details ...... 1‐2 1.5 Approach and Ramps Span Arrangement ...... 1‐2 1.6 Approach and Ramps Columns ...... 1‐3 1.7 Bridge Lighting ...... 1‐3 2 Introduction ...... 2‐1 2.1 Project Description ...... 2‐1 2.1.1 Proposed River Crossing Description ...... 2‐1 2.2 Report Purpose and Objective ...... 2‐2 2.3 St. Croix River Crossing Development ...... 2‐3 2.4 General Definition of an Extradosed Bridge ...... 2‐4 3 Acknowledgement of Commitments ...... 3‐1 3.1 Reference Documents ...... 3‐1 3.2 Commitments ...... 3‐1 4 Risk Evaluation ...... 4‐1 4.1 Risk Matrix and Summary ...... 4‐1 4.2 Investigation and Evaluation of Risk Factors ...... 4‐2 4.2.1 Structural Analysis ...... 4‐2 4.2.2 Bridge Lighting and Signing ...... 4‐3 4.2.3 Visual Quality ...... 4‐4 4.2.4 Construction...... 4‐5 4.2.5 Maintenance and Inspection ...... 4‐6 5 Division I Structural Analysis ...... 5‐1 5.1 Introduction ...... 5‐1 5.2 Objectives ...... 5‐1 5.3 Base Modeling ...... 5‐2 5.4 Longitudinal Analysis ...... 5‐2 5.5 Transverse Analysis ...... 5‐4 5.6 Superstructure Cross‐section Investigation ...... 5‐5 5.7 Inboard Pedestrian Trail ...... 5‐6 5.8 Box Girder Depth ...... 5‐7 5.9 Single Box Girder Feasibility ...... 5‐8 5.10 Transverse Diaphragm investigation ...... 5‐9 5.11 Pier Investigation ...... 5‐9 5.12 Fixity/Longitudinal Movement Investigation ...... 5‐12 5.13 Grade Induced Movement Investigation ...... 5‐13 5.14 Two Box Girder Load Distribution Investigation ...... 5‐13 5.15 Wind Load—Vibration Analysis Investigation ...... 5‐15 5.15.1 Back span Uplift/Maximum Back span Length Investigation...... 5‐17 5.16 Extradosed Stay Cable Analysis ...... 5‐17 5.17 Points of Interest—Local Analysis ...... 5‐19

June 2010 i St. Croix River Crossing Preliminary Engineering Concept Refinement Report

6 Division II Structural Analysis ...... 6‐1 6.1 Introduction and Objectives ...... 6‐1 6.1.1 Box Girder Width Transition Investigation ...... 6‐1 6.1.2 Box Girder Depth Economy Investigation ...... 6‐1 6.1.3 Fixity/Longitudinal Movement Investigation ...... 6‐2 6.1.4 Grade Induced Movement Investigation ...... 6‐2 6.1.5 Box Girder Depth Transition Investigation ...... 6‐2 6.2 Investigation Methods: Longitudinal Analysis...... 6‐2 6.3 Baseline Model Description ...... 6‐4 6.3.1 Piers ...... 6‐4 6.3.2 Box Girders ...... 6‐6 6.3.3 Transition Span ...... 6‐7 6.3.4 Pedestrian Trail ...... 6‐7 6.4 Alternative R1 Investigation ...... 6‐10 6.4.1 Grade‐Induced Movement Investigations ...... 6‐15 7 Bridge Lighting and Signing ...... 7‐1 7.1 Review of Requirements for Architectural and Roadway Lighting ...... 7‐1 7.2 Lighting Criteria ...... 7‐1 7.3 Lighting Alternatives Analysis ...... 7‐5 7.3.1 Source Selection ...... 7‐5 7.4 Architectural Lighting ...... 7‐11 7.4.1 Option 1A ...... 7‐12 7.4.2 Option 2A ...... 7‐13 7.4.3 Option 2AA ...... 7‐14 7.4.4 Option 3 ...... 7‐15 7.4.5 Option 4 ...... 7‐16 7.4.6 Preferred Option ...... 7‐16 7.5 Roadway Lighting ...... 7‐17 7.6 Loop Trail Lighting ...... 7‐18 7.7 Navigation and Obstruction Lighting ...... 7‐18 7.8 Light Trespass / Glare / Environmental Impacts ...... 7‐18 7.9 System Maintenance ...... 7‐19 7.10 Box Section Inspection Lighting ...... 7‐19 7.11 Signing ...... 7‐20 7.11.1 Review of the Visual Quality Manual ...... 7‐20 7.11.2 Additional Concept Refinements ...... 7‐20 8 Visual Quality ...... 8‐1 8.1 Introduction ...... 8‐1 8.2 Objectives ...... 8‐2 8.3 Refinement Process ...... 8‐2 9 Construction ...... 9‐1 9.1 Introduction ...... 9‐1 9.2 Construction Staging Areas ...... 9‐1 9.3 Casting Yard ...... 9‐1 9.4 Precast vs. Cast‐in‐place Construction ...... 9‐1 9.4.1 Precast Construction ...... 9‐2 9.4.2 Cast‐in‐ Place Construction ...... 9‐3

ii June 2010 St. Croix River Crossing Preliminary Engineering Concept Refinement Report

9.5 Permitting Requirements ...... 9‐3 9.6 Erosion Control and Environmental Compliance ...... 9‐4 9.7 Foundation Construction Methods ...... 9‐4 9.8 Substructure Pier and Tower Construction ...... 9‐5 9.9 Reinforcing steel arrangements congestion and detailing ...... 9‐5 9.10 Post‐tensioning tendons and grouting ...... 9‐6 9.11 Stay Installation ...... 9‐6 9.12 Special architectural forming and finishing ...... 9‐6 9.13 Industry forum ...... 9‐7 10 Maintenance and Inspection ...... 10‐1 10.1 Introduction ...... 10‐1 10.2 Critical Elements ...... 10‐1

List of Figures Figure 4‐1. Risk Assessment ...... 4‐1 Figure 5‐1. Stick (top) and Rendered (bottom) Isometric View of Global Model ...... 5‐2 Figure 5‐2. Rendered Isometric View of Global Model Showing Construction Sequence ...... 5‐3 Figure 5‐3. Box Girder Stress along Length of Bridge ...... 5‐4 Figure 5‐4. Transverse Framing at Cable Connection ...... 5‐5 Figure 5‐5. Baseline Box Girder Superstructure ...... 5‐6 Figure 5‐6. Proposed Box Girder Showing the Reduced Depth and Integrated Pedestrian Trail ...... 5‐7 Figure 5‐7. Typical Sections ...... 5‐9 Figure 5‐8. VQM Baseline Pier Configuration ...... 5‐10 Figure 5‐9. Proposed Pier Configuration ...... 5‐12 Figure 5‐10. Deflected Pier Shape ...... 5‐13 Figure 5‐11. Superstructure between Cable Supports ...... 5‐14 Figure 5‐12. Transverse Analysis ...... 5‐14 Figure 5‐13. Closure Pour Detail ...... 5‐15 Figure 5‐14. Mode Shapes from the Eigenvalue Dynamic Analysis ...... 5‐16 Figure 5‐15. Extradosed Stay Cable Configuration ...... 5‐18 Figure 5‐16. Live Load Stress Range ...... 5‐19 Figure 5‐17. Local Model of Integral Pier (Bottom View) ...... 5‐20 Figure 5‐18. Local Model of Integral Pier (Top View) ...... 5‐20 Figure 5‐19. Pier Cross Girder Interface Model ...... 5‐21 Figure 5‐20. Pier 8 Elevation Showing Widened Superstructure and Full Super Elevation ...... 5‐22 Figure 5‐21. Span 8 Typical Section ...... 5‐23 Figure 5‐22. Isometric View of Precast Truss ...... 5‐23 Figure 5‐23. Isometric View of 3D Analysis ...... 5‐24 Figure 6‐2. Detail of Segments on Pier and Accurate Section Property Input ...... 6‐3

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Figure 6‐1. Balanced Cantilever Construction Method (Modeling of Construction Stage 6, Bridge 82048) ...... 6‐3 Figure 6‐3. Stress Output Checked at 10 Locations in the Cross‐section ...... 6‐4 Figure 6‐4. Pier 1 on TH 36 (Bridge No. 82045) ...... 6‐5 Figure 6‐5. Typical Pier on TH 36 Approaches (Others Similar) ...... 6‐6 Figure 6‐6. Baseline Approach Box Girders...... 6‐7 Figure 6‐7. Baseline Model 82045E‐r0A, Bridge 82045 EB (EB TH 36) ...... 6‐8 Figure 6‐8. Plan and Elevation of Baseline Model, Bridge 82045 EB (EB TH 36) ...... 6‐8 Figure 6‐10. Model 82045E‐r1A—Double‐stem Columns in Alternative R1 Span Arrangement ..... 6‐11 Figure 6‐9. Plan and Elevation of Alternative “R1” Models for EB and WB TH 36...... 6‐11 Figure 6‐11. Model 82045E‐r1B—Single‐stem Columns in Alternative R1 Span Arrangement ...... 6‐12 Figure 6‐12. Plan and Elevation of Model 82045W‐r1B—WB TH 36 with Single‐stem Columns in Alternative R1 Span Arrangement ...... 6‐12 Figure 6‐13. Bridge No. 82047 (NE Ramp) Stick Model and Rendered Model ...... 6‐13 Figure 6‐14. Bridge No. 82047 Rendered Plan and Elevation from Structural Model with Details ...... 6‐13 Figure 6‐15. Bridge No. 82048 (SE Ramp) Stick Model (Left) and Rendered Sectional Model (Right) ...... 6‐14 Figure 6‐16. Bridge No. 82048 (SE Ramp) Plan and Elevation View of Rendered Model ...... 6‐14 Figure 6‐17. Models Used in Investigating Grade‐induced Deflection ...... 6‐15 Figure 7‐1. Typical LED ...... 7‐6 Figure 7‐2. Schematic of LED Operation ...... 7‐6 Figure 7‐3. Typical Representative Spatial Radiation Pattern for White Lambertian ...... 7‐8 Figure 7‐4. Typical Polar Radiation Pattern for White Lambertian ...... 7‐8 Figure 7‐5. Typical Luminous Flux ...... 7‐9 Figure 7‐6. Typical Light Output Characteristics Over Temperature (Cool‐White at Test Current) ...... 7‐10 Figure 7‐7. Typical Lumen Maintenance Values for Various Light Sources ...... 7‐11 Figure 7‐8. Base Architectural Lighting Option ...... 7‐11 Figure 7‐9. Lighting Option 1a ...... 7‐12 Figure 7‐10. Lighting Option 1b ...... 7‐12 Figure 7‐11. Lighting Option 2a ...... 7‐13 Figure 7‐12. Lighting Option 2b ...... 7‐13 Figure 7‐13. Lighting Option 2aa ...... 7‐14 Figure 7‐14. Lighting Option 2bb ...... 7‐14 Figure 7‐15. Lighting Option 3 ...... 7‐15 Figure 7‐16. Lighting Option 4a ...... 7‐16 Figure 7‐17. Lighting Option 4b ...... 7‐16 Figure 7‐18. Preferred Option—View from Sunnyside Marina ...... 7‐16 Figure 7‐19. Preferred Option—View from Stillwater ...... 7‐16

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Figure 7‐20. Preferred Option—View Looking North ...... 7‐17 Figure 7‐21. Roadway Lighting ...... 7‐17 Figure 7‐22. Loop Trail Lighting Using Linear Luminaires ...... 7‐18 Figure 7‐23. Navigation and Obstruction Lights ...... 7‐18 Figure 7‐24. LED Utility Light ...... 7‐19 Figure 7‐25. Typical Inspection Lighting ...... 7‐20 Figure 8‐1. Section View Illustrates Curved Outside Edges of Cross Girder ...... 8‐3 Figure 8‐2. Tangent Segments Have Been Introduced Along Vertical Faces of Tower Forms for Ease of Construction ...... 8‐4 Figure 8‐3. View along pedestrian trail located inside of tower line ...... 8‐5 Figure 8‐4. Section view of trail located on north edge along west bound travel lanes ...... 8‐6 Figure 8‐5. Typical Pedestrian Overlook outside of tower on north elevation of bridge ...... 8‐7 Figure 8‐6. View of underside of Pedestrian overlook surrounding tower ...... 8‐7 Figure 8‐7. Higher curb height with 6” vertical picket spacing and integral LED light fixtures incorporated into post on pedestrian hand railing...... 8‐8 Figure 8‐8. North elevation view of structure with covered cable connections ...... 8‐9 Figure 8‐10. View of Battered Abutment (Left) and Typical Single Stem Pier (Right) along Minnesota Approach ...... 8‐10 Figure 8‐9. Enlarged view of covered cable connections ...... 8‐10

List of Tables Table 4‐1. Summary of Risk Assessment ...... 4‐2 Table 5‐1. Box Girder Depth Cost Comparison ...... 5‐8 Table 6‐1. Baseline Span Arrangement ...... 6‐9 Table 6‐2. Span Arrangement “R1” ...... 6‐10 Table 6‐3. Grade‐induced Movement Results ...... 6‐15 Table 7‐1. Illuminance Levels for Floodlighting Buildings and Monuments ...... 7‐2 Table 7‐2. Illuminance Method—Recommended Values ...... 7‐2 Table 7‐3. Luminance Method—Recommended Values ...... 7‐3 Table 7‐4. Illuminance and Luminance Design Values (English) ...... 7‐4 Table 7‐5. Recommended Illumination (Values in lux) ...... 7‐5 Table 7‐6. Flux Characteristics for LUXEON K2 with TFFC Junction and Case Temperature = 25C ...... 7‐9

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St. Croix River Crossing Preliminary Engineering Concept Refinement Report

Acronyms and Abbreviations 2D two dimensional 3D three dimensional AASHTO American Association of State Highway and Transportation Officials ASBI American Segmental Bridge Institute avg average BMP best management practice(s) cd/m2 candelas per square meter CSL Crosshole sonic logging cy cubic yards DB design build EB eastbound EoR engineer of record f’c Concrete 28‐day compressive strength fc Footcandles FEIS Final Environmental Impact Statement

FGUTS Prestressing strand guaranteed ultimate tensile strength FHWA Federal Highway Administration fpu Prestressing strand specified ultimate tensile strength ft feet I severity of impact IES Illuminating Engineering Society IESNA Illuminating Engineering Society of North America InGaN indium gallium nitride kips thousand pounds ksi thousands of pounds per square inch LED light emitting diode Lpile A Program for the Analysis of Piles and Drilled Shafts Under Lateral Loads LRFD Load and Resistance Factor Design lux SI unit of illuminance and luminous emittance mA milliamps max maximum min minimum Mn/DOT Minnesota Department of Transportation NDE Nondestructive evaluation NE northeast P probability of occurrence PB Parsons Brinckerhoff (PB Americas, Inc.) PGL Profile grade line

June 2010 i St. Croix River Crossing Preliminary Engineering Concept Refinement Report

PTI Post‐Tensioning Institute RFP request for proposal RGB Red green blue color model SE southeast sf square feet SFEIS Supplemental Final Environmental Impact Statement Tj junction temperature UP R/R Union Pacific Railroad USCG U.S. Coast Guard UV ultraviolet VE value engineering VQAC Visual Quality Advisory Committee VQM Visual Quality Manual VQRC Visual Quality Review Committee WB westbound WisDOT Wisconsin Department of Transportation

Certification I hereby certify that this report was prepared by me or under my direct supervision, and that I am a duly Licensed Professional Engineer under the laws of the State of Minnesota.

Paul J. Towell PE No. 42965 June 30, 2010

ii June 2010 St. Croix River Crossing Preliminary Engineering Concept Refinement Report

1 Executive Summary This Concept Refinement Report has been developed by Parsons Brinckerhoff (PB), under contract with the Minnesota Department of Transportation (Mn/DOT). PB is providing concept design and associated services for the proposed new St. Croix River Crossing that is within the overall St. Croix River Crossing Project. These services are part of the Preferred Alternative Package for the St. Croix River Crossing Project as documented in the 2006 Supplemental Final Environmental Impact Statement (SFEIS). The purpose of the report is to document the results of investigations of the following aspects of the bridge:  Structural Analysis  Bridge Lighting and Signing  Visual Quality  Construction  Maintenance and Inspection The report separates the structural analysis portion of the study into two divisions. Division I is for the extradosed portion of Bridge 82045, and Division II is for the approach spans of Bridge 82045 and the ramps designated Bridges 82047 and 82048. The other areas of study are reported in combined sections that cover both divisions. The starting point for the concept refinement is the concept design presented in the Visual Quality Manual (VQM). This concept is based on the use of concrete segmental bridges for the mainline and ramp structures. In addition, the river crossing portion of the mainline structure is an extradosed bridge with short towers above the roadway and cable support of the girder. The objective of the concept refinement effort is to confirm the feasibility of the VQM concept and to develop and refine the concept prior to advertising for final design and construction. A key component of the concept refinement effort was coordination with the Visual Quality Advisory Committee (VQAC). Meetings with the committee, consisting of a subset of the stakeholder groups involved in the SFEIS process, were used to present and discuss proposed concept refinements. Based on the results of the various studies undertaken, and input from the committee, a number of refinements were incorporated. A summary of the results of the concept refinement effort are as follows: 1.1 Pier Configuration The VQM concept three‐column pier with a center column under the box girder girders was revised to a two‐column pier by eliminating the center column. Structural analysis determined that the center column was not necessary, and with post‐tensioning the cross girder between the two columns had sufficient strength to support the box girders. From a visual quality aspect, the removal of the center

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column had been the desire of the Visual Quality Review Committee during the development of the VQM, but structural feasibility needed to be confirmed before this goal could be attained. In addition the form of the pier columns was refined to improve constructability. 1.2 Box Girder Configuration Two box girder configurations were studied for the roadway deck, a two‐box girder configuration as shown in the VQM, and a one‐box girder configuration. Structural analysis and constructability studies determined that both configurations were viable. 1.3 Pedestrian Trail Location The VQM concept with the pedestrian trail outboard of the box girders and passing around the north pier column was revised to an inboard configuration with the pedestrian trail located on the box girder and passing inside of the north pier column. This configuration was a recommendation of the CRAVE Study completed in November 2008. Various studies confirmed that this arrangement was similar in cost to the concept, but with the benefit of improved constructability and long‐term durability. With the trail located inboard of the column, pedestrian overlooks were at the piers to permit people to stop and view the scenic river while removed from through bicycle traffic. After review by the VQAC, it was determined that three overlooks located at alternating piers within the river would be appropriate. 1.4 Cable Anchorage Details The VQM concept with the anchorages exposed along the side of the box girders was revised to cover the side face of the anchorages providing a smooth line along the roadway edge. This was a recommendation of Sumitomo Mitsui Construction Co., Ltd., the technical advisor for the project. The saw tooth appearance of the exposed anchorages did not seem to be in harmony with the smooth curving forms of the bridge. Visually the covered anchorage gives the bridge a much cleaner appearance and the added vertical face provides additional protection from the elements for the cable anchorage. 1.5 Approach and Ramps Span Arrangement The VQM concept assumed typical spans of approximately 300 feet for the Minnesota approach spans and ramps to minimize the number of piers at the approach spans that extend from the bluff toward the shoreline in Minnesota. The approach spans and two ramp structures cross four wetland areas, with the primary impacts from construction in Basin Q and Basin Q Forested. The 300‐foot span arrangement proposed in the concept design would have required extensive falsework. To reduce the impacts from construction on falsework, an alternate span arrangement was developed that permitted a greater amount of balanced cantilever segmental construction and reduced the wetland impacts. The long spans proposed

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in the concept design are not conducive to segmental construction, specifically at spans adjacent to expansion joints and at bridge sections that vary in width. Both of these conditions occur over the Basin Q wetlands. 1.6 Approach and Ramps Columns The VQM concept has twin stem piers with a 10‐foot space between the stems. Visually the piers had a heavy look and structurally the piers stiffness could not be reduced without the stems becoming overly slender. To resolve these issues, an alternate twin stem arrangement with a 5‐foot space between the stems and a single stem pier were studied. The structural results proved that the single stem pier was feasible and based on review by the VQAC, the single stem pier was selected. In addition to structural and aesthetic benefits, the single stem column is more economical and improves constructability. 1.7 Bridge Lighting Bridge lighting studies were performed for both functional lighting and architectural lighting. Functional lighting consists of roadway lighting, pedestrian trail lighting, aerial obstruction lighting, and navigation lighting. In addition a number of options for architectural lighting were added to the functional lighting in photo visualizations for review by the VQAC. Based on input from the VQAC it was determined that lower lighting levels were preferred, and the proposed architectural lighting is limited to lighting of the pier columns below the roadway. In combination with the roadway and trail lighting, which provide low levels of light on the cables and columns above the roadway, the desired effect is achieved. This concept refinement report is not a final engineering report, and it is anticipated that final design will be performed by others under a separate contract.

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St. Croix River Crossing Preliminary Engineering Concept Refinement Report

2 Introduction

2.1 Project Description This Concept Refinement Report has been developed by PB, under contract with the MnDOT. PB will provide concept design and associated services for the proposed new St. Croix River Crossing that is within the overall St. Croix River Crossing Project: Minnesota S.P. 8214‐114, S.P. 8214‐(82045), S.P. 8214‐(82047), S.P. 8214‐(82048) and Wisconsin Project I.D. 1550‐00‐02. The overall St. Croix River Crossing Project termini are along TH 36/STH 64 from TH 5 in Minnesota to 150th Avenue in Wisconsin. These services are part of the Preferred Alternative Package for the St. Croix River Crossing Project as documented in the 2006 SFEIS. 2.1.1 Proposed River Crossing Description The proposed St. Croix River Crossing is comprised of three separate bridges that are identified as MnDOT Bridge Nos. 82045, 82047, and 82048. The alignment of the bridge follows a horizontally curved extension of the TH 36 alignment that will pass just to the south of the Oak Park Heights water treatment plant and north of the King Power Plant. The alignment continues on a tangent across and approximately perpendicular to the river intersecting the bluffs in Wisconsin, and continuing on to new alignment for STH 64. The bridge approach spans, which extend from the Minnesota bluff to the river cross both high quality wooded wetlands adjacent to the river and lower quality wetlands inland from the river. An eastbound entrance ramp structure and westbound exit ramp structure connect TH 36 to TH 95 in Minnesota. Requirements for these bridges have been developed and are documented in two reports, the 2006 SFEIS, and the VQM (January 2007). Those requirements are summarized as follows:  The extradosed river spans will have no more than 6 piers in the water.  The extradosed towers vary in height from approximately 220 feet on the Wisconsin side to approximately 170 feet on the Minnesota side (tower heights are above normal pool elevation and include approximately 60 feet of tower above the deck).  The extradosed span lengths are approximately 480 feet and the backspans approximately 290 feet.  The extradosed typical section consists of two 12 foot lanes in each direction, 6 foot inside shoulders, 10 foot outside shoulders, and a 12 foot sidewalk on the north side of the bridge.  Aesthetics, landscaping, and context sensitive designs are in the VQM.

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Mn/DOT Bridge 82045 (WisDOT Bridge B­55­224) (Mainline TH 36 and STH 64) Bridge No. 82045 spans Minnesota TH 95, the Union Pacific Railroad(UP R/R), wetlands, and the St. Croix River. Its west abutment is located immediately west of TH 95. Its east abutment is located on the Wisconsin river bluff. The total bridge length from abutment to abutment is approximately 5,040 feet. The bridge is comprised of main river spans with a length of approximately 3,460 feet and westerly approach spans with a length of approximately 1610 feet. The river spans have an extradosed superstructure that combines concrete box girders with cable stays. The approach spans have a concrete box girder superstructure. The transition from approach spans to river spans occurs at a common pier located just inland from the Minnesota shoreline. The Minnesota approach spans to the river crossing have lengths ranging from 180 to 300 feet. Mn/DOT Bridge 82047 (TH 36WB off­ramp to TH 95) Bridge No. 82047 spans the UP R/R, local roadways, and wetlands. This bridge has a concrete box girder superstructure that frames into an approach span of Bridge 82045. The structure depth is directly related to that of the Bridge 82045 river spans. The typical section has a variable lane width ranging from 16 to 32 feet, with 4 foot inside and outside shoulders. Mn/DOT Bridge 82048 (TH 36EB on­ramp from TH 95) Bridge No. 82048 spans the UP R/R, local roadways, and wetlands. This bridge has a concrete box girder superstructure that frames into an approach span of Bridge 82045. The structure depth is directly related to that of the Bridge 82045 river spans. The typical section has a variable lane width ranging from 16 to 32 feet, and 4 foot inside and outside shoulders. 2.2 Report Purpose and Objective The Concept Refinement Report that will look at a number of items for investigation described in further detail within the report. The content of the report is separated into two divisions:  Division I is for the extradosed portion of Bridge 82045 (B‐55‐224),  Division II is for the approach spans of Bridge 82045 (B‐55‐224) and the ramp Bridges 82047 and 82048. Items for study and evaluation will include:  Structural Analysis  Bridge Lighting and Signing  Visual Quality  Construction  Maintenance and Inspection

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The report provides the results of the investigation and evaluation of risk for each of the items listed above. The evaluation of risk for each item assesses and reports the impacts to design feasibility, constructability, costs, schedule, environmental risks, aesthetics, long term durability, maintenance, etc. In addition to detailed findings, a risk analysis matrix is provided that summarizes the risk assessment for ease of understanding. The report is arranged in the following format and content:  Table of Contents  Executive Summary  Introduction  Acknowledgement of Commitments—The Report will cite commitments made in project documents that affect the bridge. This includes such documents as the SFEIS, Visual Quality Manual, etc.  Risk Evaluation  Content—Divisions I and II Portions of the report may be incorporated into a future design build request for proposal (RFP) for the project. 2.3 St. Croix River Crossing Development A new river crossing near Stillwater to replace the aging lift bridge has been discussed for many years. The first formal effort to replace the existing bridge began in 1985 with a Draft Study and Scoping Document. The planning process moved forward until 1995 when FHWA approved and Final Environmental Impact Statement (FEIS). Final design began in 1995, but in 1996 the National Park Service reacting to federal permit applications determined that the proposed bridge would have an adverse effect on the St. Croix River, a part of the National Wild and Scenic River System. With this determination, the federal permits could not be issued and work on the new river crossing stopped. Beginning in 1998 efforts to revive the river crossing began culminating in the approval of an SFEIS in 2006. The visual appearance of the St. Croix River Crossing and the context of the bridge within the wild and scenic riverway were critical factors in the development of the new river crossing. As the SFEIS was developed between 2004 and 2006, the extradosed bridge type was select for the main river crossing through an extensive stakeholder process that involved local state and federal government agencies, as well as, local and national citizen organizations. In parallel with the SFEIS process, a VQM was developed to outline the aesthetic values for the project. A VQRC with member participation from all of the stakeholder groups was a key part of the visual quality process. In addition the VQM process included a public open house to gather public input for the aesthetic development of the bridge. For a complete history of the planning stages for the St. Croix River Crossing refer to Chapter 1 of the 2006 Supplemental Final Environmental Impact Statement.

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2.4 General Definition of an Extradosed Bridge The extradosed bridge concept was first proposed by French engineer Jacques Mathivat in 1988. In the past 20 years over 40 extradosed bridges have been built around the world, with the majority of the bridges built in Japan. The extradosed bridge combines a prestressed girder bridge with a cable stayed bridge. With a span to depth ratio of 30 to 35 compared to a typical prestressed girder bridge with a span to depth ratio of 20 to 25, the economy of a shallower girder is realized with the extradosed bridge. The tower height: span ratio of 1:8 compared to 1:4 for a cable stayed bridge gives a structure height that is much less imposing than a cable stayed bridge. Finally because of the relatively stiff girder, the extradosed bridge permits allowable cable stresses of 0.6 fpu compared to 0.45 fpu for a cable stayed bridge. This leads to the economy of fewer strands in the cables and a reduction in the number of post‐tensioning tendons needed to support the bridge.

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3 Acknowledgement of Commitments

3.1 Reference Documents 2006 Supplemental Final Environmental Impact Statement Visual Quality Manual 3.2 Commitments This Concept Refinement Report and associated Concept Drawings have been developed by PB, under contract with Mn/DOT. PB has performed this work in accordance with the concepts and commitments included in the 2006 Supplemental Final Environmental Impact Statement and the Visual Quality Manual.

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4 Risk Evaluation

4.1 Risk Matrix and Summary Risk management is an integral part of all phases of project delivery, from planning and preliminary engineering through final design and construction. Risk management is the systematic process of identifying, analyzing, and responding to project risk. Risk management must be conducted throughout the life of a project. A standard dictionary definition of risk is: “exposure to the chance of injury or loss; a hazard or dangerous chance”. In the design and construction of large transportation projects there are inherent risks that must be explored as the project develops. At the beginning, these variables, such as, subsurface geology, material quantities and costs, and material and labor availability, are uncertain. As a project develops, these risks begin to be to become less variable as information is gathered and engineering evaluation begins. Risk assessment is used to evaluate risks as part of risk management. The first step is to identify the risk factors. For the St. Croix River Crossing, eight specific risk factors have been identified. Each of the five report areas are to be assessed for these eight risk factors, with an additional risks assessed as a ninth risk factor. Assessment of risk is based on a scale from 1 to 3 for the probability of occurrence (P), and on a scale of 1 to 3 for the severity of impact (I). Scoring is qualitative, with low defined as 1, medium defined as 2, and high defined as 3. The risk score is the multiple of P x I, such that the lowest risk is 1 and the highest risk is 9. The process is illustrated in Figure 4‐1.

Significant Risk Area High Med Low

Low Med High

Probability (P) of Occurrence Impact (I)

Figure 4‐1. Risk Assessment

In some cases a category may not be applicable, in which case, a value of 0 will be applied. Table 4‐1 shows the summary of risk assessment.

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Table 4‐1. Summary of Risk Assessment Bridge Structural Lighting & Visual Maintenance Risk Factor Analysis Signing Quality Construction & Inspection Design feasibility 3 1 1 1 2 Constructability 2 1 2 1 1 Cost 4 1 2 6 1 Schedule 1 1 1 6 0 Environmental risks 1 1 1 3 1 Aesthetics 1 1 1 1 2 Long‐term durability 2 1 1 2 3 Maintenance 2 1 1 2 3 Total 16 8 10 22 13 Average 2.0 1.0 1.25 2.75 1.63

4.2 Investigation and Evaluation of Risk Factors 4.2.1 Structural Analysis Design Feasibility Probability (P): 1 Implementation of a QA/QC procedure in the design process will help confirm the design is feasible. Impact (I): 3 When a major error is found during construction, the impact to cost and schedule is severe. Constructability Probability (P): 1 Proper constructability reviews will significantly reduce the chance of construction problems. Impact (I): 2 Errors found during construction can be corrected. Costs Probability (P): 2 Overly conservative design and/or design errors will increase construction cost. Impact (I): 2 Conservative design will not significantly increase construction cost, but design error may. Schedule Probability (P): 1 Design may impact schedule. The design process should be clearly defined and the review process integrated into the design process, to permit timely reviews and issuing of construction drawings. Impact (I): 1 Lack of approved construction drawings can slow or stop construction.

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Environmental Risks Probability (P): 1 Low risk. Impact (I): 1 Low impact. Aesthetics Probability (P): 1 Low risk. Impact (I): 1 Low impact. Long­term Durability Probability (P): 1 Proper analysis and design detailing will ensure the long‐term durability of the structure. Impact (I): 2 Serviceability issues can be corrected with remedial work, but additional costs are incurred. Maintenance Probability (P): 1 Accessibility for inspection and maintenance must be considered throughout the design process. Impact (I): 2 Accessibility for maintenance and inspection is of critical importance. 4.2.2 Bridge Lighting and Signing Design Feasibility Probability (P): 1 Proposed bridge light and signing details are fairly standard. Impact (I): 1 Low impact. Constructability Probability (P): 1 Proposed bridge light and signing details are fairly standard. Impact (I): 1 Low Impact. Costs Probability (P): 1 Proposed bridge light and signing details are fairly standard. Impact (I): 1 Low impact. Schedule Probability (P): 1 Proposed bridge light and signing details are fairly standard. Impact (I): 1 Low impact. Environmental Risks Probability (P): 1 Spillover lighting can be assessed during lighting tests and adjustments made as needed. Impact (I): 1 Low impact.

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Aesthetics Probability (P): 1 Planned aesthetic lighting levels are minimized to subtly highlight the structure. Current modeling techniques allow accurate design and visualization of the lighting system Impact (I): 1 Low impact. Long­term Durability Probability (P): 1 LED fixtures have long operating life and are low cost to operate. Impact (I): 1 Low impact. Maintenance Probability (P): 1 LED fixtures have long operating life and are low cost to operate. Impact (I): 1 Low impact. 4.2.3 Visual Quality Design Feasibility Probability (P): 1 Preliminary engineering has vetted the design feasibility of the aesthetic design elements of the bridge. Impact (I): 1 Low impact. Constructability Probability (P): 1 The design features include many curved surfaces, but the concept refinement has conformed the various surfaces to standard geometric shapes. Impact (I): 2 The many curved surfaces will provide more of a challenge than construction with flat surfaces. Costs Probability (P): 2 The forming systems required for the various design elements will cost more than standard forming systems. Impact (I): 1 The repetitive use of these forming systems will minimize this additional cost. Schedule Probability (P): 1 Some reduction in production rates may occur due to curved form of the various design elements. Impact (I): 1 As with all construction operations, there is a learning curve, but as operations are repeated productivity increases.

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Environmental Risks Probability (P): 1 Visual impacts are addressed in the visual quality process, which provides guidance to ensure the bridge fits into the environment. Impact (I): 1 Low impact. Aesthetics Probability (P): 1 The visual quality process has developed aesthetic standards for the bridge. Impact (I): 1 Low impact. Long­term Durability Probability (P): 1 The aesthetic features do no impact long‐term durability. Impact (I): 1 Low Impact Maintenance Probability (P): 1 The aesthetic features do not impact maintenance. Impact (I): 1 Low Impact 4.2.4 Construction Design Feasibility Probability (P): 1 The planned construction methods are included in the design process using construction stage analyses to ensure that the construction methods are feasible. The planned construction methods are standard methods. Impact (I): 1 Coordinated construction planning during the design phase will limit design impacts. Constructability Probability (P): 1 The planned construction methods using concrete segmental construction with either cast‐in‐place or precast segments are standard methods used throughout the world. Impact (I): 1 Coordinated constructability reviews during the design phase will limit constructability impacts. Costs Probability (P): 2 Foundation construction costs are less defined than other costs, because preliminary foundation capacity is relatively low. Impact (I): 3 Foundation costs are significant, and cost reduction or increase can be significant. Schedule Probability (P): 2 Construction is the largest project activity and controls the contract duration. Proper scheduling is critical.

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Impact (I): 3 The construction schedule must be closely monitored to ensure that progress toward schedule completion is maintained. If the schedule begins to slip, work around schedules, or supplemental schedules must be developed to get the project back on track. Environmental Risks Probability (P): 1 Construction operations by their very nature impact the environment. Proper environmental standards and controls are necessary to ensure environmental compliance. Impact (I): 3 The Minnesota approach spans cross environmentally sensitive wetlands and the St. Croix River is a national scenic waterway with mussel beds near the Wisconsin shore. Uncontrolled and unmonitored construction operations can had serious environmental impacts. Construction debris, excavated soils, and petroleum products are among the numerous items that can cause environmental damage. Aesthetics Probability (P): 1 Proper workmanship is utmost importance to produce finished work of the specified quality. Impact (I): 1 Typical finishing methods will remedy minor workmanship errors. Long­term Durability Probability (P): 1 Material controls and construction QA/QC programs must be implemented and maintained to ensure that the requirements of the plans and specifications are incorporated into the work. Impact (I): 2 Incorporating specified materials using proper construction methods and workmanship are critical to long‐term durability. Out of specification metal products and/or concrete will have a detrimental effect on long‐term structure performance. Maintenance Probability (P): 1 See Long‐term Durability. Impact (I): 2 See Long‐term Durability. 4.2.5 Maintenance and Inspection Design Feasibility Probability (P): 1 Design details will affect maintenance and inspection. Maintenance and inspection should be considered throughout the design process. Impact (I): 2 Design that does not include consideration of maintenance and inspection access will impact operations.

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Constructability Probability (P): 1 Maintenance and Inspection have little impact on constructability. Impact (I): 1 Costs Probability (P): 1 Inspection and maintenance are directly related to cost. Impact (I): 1 The cost of future maintenance and inspection is directly linked to accessibility. Schedule Probability (P): 0 None. Impact (I): 0 None. Environmental Risks Probability (P): 1 The maintenance of the bridge drainage system is critical. Impact (I): 1 Leakage of bridge drainage must be repaired quickly. The overflow trough will limit leakage until repairs are made. Aesthetics Probability (P): 1 The architectural surface treatment is long lasting are requires little maintenance. Impact (I): 2 Lack of maintenance will have a negative impact on the structures appearance. Long­term Durability Probability (P): 1 The long‐term durability of the bridge depends on the inspection and maintenance programs, but concrete segmental bridges are among the most durable bridges. Impact (I): 3 Poor inspection and maintenance can greatly reduce the life span of the bridge. For a concrete segmental bridge the parts that are most vulnerable to wear and bearings and expansion joints. In addition the stay cables of an extradosed bridge are key structural components. The anchorages and cable sheathing need to be inspected on a systematic basis. Maintenance Probability (P): 1 See Long‐term Durability. Impact (I): 3 See Long‐term Durability.

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St. Croix River Crossing Preliminary Engineering Concept Refinement Report

5 Division I Structural Analysis

5.1 Introduction The extradosed river spans for the St. Croix River Crossing are designated Mn/DOT Br. No. 82045 (WisDOT Bridge B‐55‐224)(Mainline TH 36 and STH 64). For the purpose of this report, the baseline structure is defined as a structure that conforms to the structural configuration presented in the VQM. The baseline structure is an eight‐span, extradosed structure with a length of 3,460 feet, and a span arrangement of 290 feet—480 feet—480 feet—480 feet—480 feet—480 feet— 480 feet—290 feet. Of the seven piers, six are located in the river with one pier located on the Wisconsin bluff. The baseline structure’s configuration is such that the seven piers consist of three columns below roadway level, with the two exterior columns extending above the roadway as towers for anchoring of the extradosed cables. The baseline superstructure is comprised of two concrete segmental box girders connected by full‐depth diaphragms at the cable support locations. The cables are arranged in two planes and anchor in an anchor pod at the exterior edge of each box girder, with typical spacing of 20 feet between cables. There are a total of 252 cables, with 36 cables anchored at each pier. The exterior piers extend 60 feet above the roadway, thus giving a tower vs. span ratio of 1:8, which is ideal for an extradosed bridge. Various modifications to the baseline structure have been made in order to satisfy the goals of the objectives. These modifications to the baseline structure are described in the following sections of this report. 5.2 Objectives The specific concept refinement program consists of developing appropriate structural models and performing structural analyses to determine the adequacy and feasibility of the proposed concept design. As previously described, the baseline model conforms to the structural configuration presented in the VQM. The structural analysis utilizes a global model for longitudinal and transverse effects, and localized modeling performed at two “points of interest” identified during the global modeling. In addition to the general analysis task, specific investigations and evaluations will include the following:  Base Modeling  Superstructure Cross‐section Investigation  Pier Investigation  Fixity/Longitudinal Movement Investigation  Grade Induced Movement Investigation  Two Box Girder Load Distribution Investigation  Wind Load—Vibration Analysis Evaluation  Back span Uplift Investigation  Extradosed Stay Cable Analysis  Points of Interest—Local Analysis

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5.3 Base Modeling The base model is configured according to the structure previously defined in the VQM. The analysis of the bridge was carried out using a three‐dimensional (3‐D) structural model of the bridge, including explicitly modeled foundation elements with non‐linear springs to represent the soil properties. The superstructure and substructure components are modeled using beam elements with prismatic section properties. The stay cables are modeled as truss elements. The superstructure’s two box girders are modeled independently and are connected by transverse members at each cable connection location. The double stem portion of the pier columns are also modeled independently to more realistically simulate the longitudinal stiffness. The model simulates the anticipated construction sequence and duration to capture the locked‐in dead load forces from construction and to simulate the long‐term effects of creep and shrinkage on the structure. This model, as shown in Figure 5‐1, is used for all global longitudinal analyses, with modifications incorporated as preliminary results determined that proposed refinements were structurally feasible.

Figure 5‐1. Stick (top) and Rendered (bottom) Isometric View of Global Model

5.4 Longitudinal Analysis As with all segmental bridges, the design of a segmental extradosed bridge is dependent on the construction sequence used to build the bridge. For the St. Croix River Crossing, the structural arrangement conforms to a balanced cantilever construction sequence, as shown in Figure 5‐2. As with any segmental bridge built in balanced cantilever fashion, the substructure consisting of the foundation and pier is built first followed by construction of the superstructure girder. Segments of the

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girder are either cast on a form traveler for cast‐in‐place construction or erected using a deck mounted lifting system or land/water‐based crane for precast construction. As each segment is cast, or in the case of precast, as each pair of segments is erected, cantilever post‐tensioning tendons in the top flange that anchor at the ends of the two cantilevers are installed and stressed. In addition, for the extradosed structure, the cables are installed and stressed and cantilever construction progresses.

Figure 5‐2. Rendered Isometric View of Global Model Showing Construction Sequence

The construction at the various piers can proceed in a number of sequences, but typically construction either proceeds from one end of the structure to the other end, or from both ends toward the middle. As balanced cantilever construction is completed at a pier nearest to an abutment, a number of segments adjacent to the abutment are supported on temporary falsework. A closure segment is cast between the two sections of girder, and continuity post‐tensioning tendons in the bottom flange are installed and stressed to make the first continuous span. As cantilever construction is completed at subsequent piers, a closure segment is cast between adjacent sections of girder, and continuity post‐tensioning tendons in the bottom flange are installed and stressed to make the span continuous. In addition to the changing structural system as the cantilevers are constructed and the spans are made continuous, time dependent effects due to increasing concrete strength, concrete creep and shrinkage, and post‐tensioning steel relaxation must be considered in the design of segmental structures. Once the structure is completed, the time dependent effects continue to occur, and the analysis evaluates these

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effects for a predetermined time interval, typically to 10,000 days, which is defined as time infinity, when it is assumed all time dependent effects have occurred. Following the 10,000‐day analyses, external loads such as truck and wind forces are applied to the completed structure. Stresses are checked for conformance within AASHTO LRFD limits. These stress checks include limit states during and after construction. A girder stress profile displaying service load stresses is shown in Figure 5‐3.

Figure 5‐3. Box Girder Stress along Length of Bridge

5.5 Transverse Analysis The extradosed bridge configuration in the VQM consists of two cable planes, which are connected to the superstructure along the outside edge of each box girder. Transverse members between the box girders are required to transfer and balance the forces imposed by the stay cables in addition to transferring unbalanced live loads between the individual box girders, as shown in Figure 5‐4. The lower member primarily resists tension forces and the upper closure pour member resists compression forces as well as vertical shear forces caused by unbalanced live loads.

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Figure 5‐4. Transverse Framing at Cable Connection

To determine the demands on the transverse members, a 3D analytical model of a representative span was created. The box girders were modeled using plate elements and the transverse members were modeled using beam elements. Various live load conditions were studied as well as the forces induced in the members during the stressing of the stay cables during construction. As a result of the analysis, it has been determined that a post‐tensioning tendon of 24 strands is required and the 4 foot deep closure pour of the top flange is sufficient to resist compression and shear. 5.6 Superstructure Cross­section Investigation The superstructure of the baseline structure described in the VQM consists of two concrete segmental box girders connected by full depth diaphragms at the cable support locations, as shown in Figure 5‐5. The box girders are comprised of a 3‐cell cross‐section, with two vertical interior webs and two inclined exterior webs. The box girders are 20 feet deep and 42.25 feet wide at the top flange or roadway level, with a 16.0‐foot width at the girder soffit. The exterior webs and soffit have circular curved faces with a radius of 66.0 feet. The individual curves meet at the web‐soffit intersection, forming an angular break point. The exterior webs curve to vertical at roadway level by the addition of a smaller radius curve at the top 3 feet of the web. The top flange of the box girder is haunched adjacent to each web to provide room for post‐tensioning anchorages on either side of the interior webs, and on the interior side of the exterior webs. The bottom flange is similarly haunched adjacent to the interior webs to permit the top surface of the flange to follow the curved soffit face and reduce the flange thickness at the midspan between the webs.

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Figure 5‐5. Baseline Box Girder Superstructure

The baseline pedestrian trail cantilevers from the edge of the northern box girder, outside the north cable plane. The trail consists of a sidewalk slab supported by concrete brackets attached to the box girder at the same interval as the cable diaphragms. This trail curves outward and around the north column at each pier. Several aspects of the superstructure cross section were evaluated during the project, which include girder depth, feasibility of a single box girder superstructure and transverse diaphragm requirements. Another item investigated was the feasibility and possible benefits of integrating the cantilevered pedestrian trail with the box girder, as recommended in the Cost Reduction and Value Engineering (CRAVE) Study. 5.7 Inboard Pedestrian Trail After discussions with Mn/DOT, WisDOT and the VQAC, the cantilevered pedestrian trail has been integrated with the box section. The trail is now located inboard of the north cable plane. The recommendation is based on improved constructability, improved operations, ease of maintenance and inspection, and potential cost savings. More information regarding the benefits of integrating the pedestrian trail with the box girder can be found in the Visual Quality Section of this report. The overall shape and symmetry among the two box girders is maintained, however, the median barrier is no longer located at the centerline of the bridge. Each box girder is widened to a width of 49’‐3” and the median barrier is shifted 6’‐7” south of the centerline of the bridge. The proposed section showing the revised configuration is shown in Figure 5‐6.

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Figure 5‐6. Proposed Box Girder Showing the Reduced Depth and Integrated Pedestrian Trail

5.8 Box Girder Depth As previously mentioned, the box girder illustrated in the VQM has a constant depth of 20 feet. After evaluating the longitudinal demands on the girder, it was concluded that from a structural perspective, a 20 foot deep girder is not required. It has been determined that a box girder depth of 16 feet is more advantageous. The 16 foot deep girder was found to be more economical and more compatible with the approach spans, while still maintaining the architectural proportions described in the VQM. The shallower box girder is lighter and more efficient, especially since the girder has a constant depth along the length of the spans. Our studies also indicate that the 16‐foot deep girder alternative is approximately $12.50 per square foot of bridge area less expensive than the 20‐foot deep girder alternative, as shown in Table 5‐1. The overall shape and general dimensions of the shallower girder remain the same.

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Table 5‐1. Box Girder Depth Cost Comparison Bridge length ...... 3,460 ft Number of piers ...... 7 Pier cross girder width ...... 20 ft Girder length ...... 3,320 ft Bridge area ...... 354,000 sf Concrete unit cost ...... $700.00/cy Reinforcing, epoxy coated unit cost ...... $1.25/lb Reinforcing weight ...... 250 lb/cy Cross‐ Box Girder section Web Width Concrete Concrete Reinforcing Total Cost Depth (ft) Area (sf) (ft) Volume (cy) Cost ($) Cost ($) Reduction 20 175.140 1.25 43,071 30,150,027 13,459,833 16 157.313 1.50 38,687 27,081,142 12,089,795 Difference ‐4,384 (3,068,885) (1,370,038) (4,438,923.00) Difference per sf (12.54)

5.9 Single Box Girder Feasibility According to the VQM, both a single box girder and a double box girder superstructure are acceptable alternatives. The basic configuration of both superstructure alternatives is shown in Figure 5‐7. Both alternatives have been evaluated from structural, constructability, and architectural perspectives. Based on our analysis and engineering judgment, it has been concluded that the single box girder alternative is feasible. It has also been determined that the optimal superstructure depth for the single box girder alternative is 16 feet. From a constructability perspective, the double box girder alternative would most likely be constructed using precast segments and the single box alternative would most likely constructed by casting the segments in place using a form traveler, due to the size and weight of the segment as the weight of a single box girder is too large for typical erection equipment. In terms of construction duration, it is believed that the double box girder alternative would require less time to construct since the precast segments can be cast concurrently with the construction of the bridge substructure.

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Figure 5‐7. Typical Sections

5.10 Transverse Diaphragm investigation Although it is not explicitly stated, it appears that the structural systems shown in the VQM utilize full depth diaphragms located at each cable. After conducting a transverse analysis on the structure, it has been determined that full depth diaphragms are not required. Instead, a much lighter transverse tie member and partial depth diaphragms inside the girder are proposed. The post‐tensioned tie member will most likely be constructed as a precast element. For additional information on the transverse diaphragms, please see the Transverse Analysis section of this report. 5.11 Pier Investigation As shown in the VQM (baseline structure) and in Figure 5‐8, the deck is supported at each pier by the two outside columns, which extend above the deck for anchoring of the extradosed cables and one center column that terminates at the cross girder at deck level. The pier configurations shown in the VQM have a constant height of 60 feet above the girder, and so therefore vary in height above the water line from 170 feet at the pier closest to the Minnesota shore to 212 feet at the pier on the Wisconsin bluff. The pier columns are generally conical in shape with varying dimensions from top to bottom, with the smaller dimension at the top of the pier. The interior column is split into two stems below the girder, and combines into a single column 104 feet below the roadway level. The exterior columns are split into two stems from the top of the pier to 104 feet below the roadway level, with the

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exception of the tower anchor housing, which extends from just below the top of column to 17 feet above the girder. The exterior column stem connection occurs only at the upstream and downstream face of the column, creating a C‐shaped column in cross‐section. The three columns in the baseline structure are connected by a 20‐foot wide by 25‐foot deep rectangular shaped cross girder at the roadway level. The cross girder is a hollow section between columns with 5‐foot thickness for the top and bottom flanges, and the two webs. At the columns, the cross girder has a solid cross‐section comprised of a diaphragm infill in addition to the flange and web section. Since it has been determined to reduce the depth of the superstructure box girder from 20 feet to 16 feet, the cross girder depth has also been reduced the same amount to maintain similar proportions shown in the VQM. The proposed cross girder depth is 21 feet.

Figure 5‐8. VQM Baseline Pier Configuration

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The Visual Quality Advisory Committee’s preference is to have only the two stay tower columns at each pier (eliminate the center column) to maintain the “light and elegant” appearance of the chosen “Organic” design concept. The pier investigation evaluated the feasibility of a two column design in place of the three column design presented in the VQM. The evaluation considers the advantages and disadvantages of cost, constructability, and aesthetics including impact to the overall appearance of the two column option compared to the three column option. There are three critical components to be considered when determining the feasibility of the two column alternative. The first item is the location and number of the expansion joints on the bridge. It is preferred to have all eight extradosed spans be continuous with expansion joints only at Pier 7 and the East Abutment. Having the expansion joints only at the ends of the extradosed bridge create significant demands on Piers 8 and 14 due to the longitudinal displacements from the thermal loads and long term creep and shrinkage. The second item is the stiffness of the individual pier columns. The pier cross girder strength is the third critical component in determining the feasibility of tower bents consisting of two, rather than three, column legs. Since the superstructure is integrally connected to the substructure at all piers, the pier cross girder is subjected to sizeable shear, vertical bending and torsion. Based on our analysis and our engineering judgment, it has been determined that the two pier columns alternative is feasible. The two columns have adequate capacity to resist the imposed loads and deformations. The relatively tall and slender double stem section of the pier column provide adequate flexibility to accommodate the longitudinal displacement demands from thermal effects and long term creep and shrinkage. Although it is relatively minimal, additional flexibility of the substructure is provided by the drilled shaft foundation. Even though it is not the shortest pier, Pier 8 controls the design. This is due to shallow rock at the footing location, resulting relatively short, stiff drilled shafts. The double stem sections of the columns are the controlling component of the pier design. Utilizing the cracked section properties, the double stem section will require approximately 2% reinforcement, which is a feasible amount. It has also been determined that the proposed cross girder has adequate strength to resist the imposed loads. The proposed pier configuration is shown in Figure 5‐9. For additional information, please see the Fixity / Longitudinal Movement Investigation section of this report.

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Figure 5‐9. Proposed Pier Configuration

5.12 Fixity/Longitudinal Movement Investigation The fixity/longitudinal movement investigation evaluated the pier and bearing fixity requirements, pier stiffness effects due to thermal movements, and other issues unique to long, continuous bridges. As the superstructure shortens due to thermal effects and long‐term creep and shrinkage, the pier columns are deflected and the pier cross girders are subjected to torsional effects. Based on our analysis and our engineering judgment, it has been determined that the eight span extradosed portion of Bridge 82045 (B‐55‐224) can be made continuous with expansion joints only at Pier 7 and the East Abutment. The relatively tall and slender double stem section of the pier columns provide adequate flexibility to accommodate the longitudinal displacement demands from thermal effects and long term creep and shrinkage, as shown in Figure 5‐10. Although it is relatively minimal, additional flexibility of the substructure is provided by the drilled shaft foundation. Even though it is not the shortest (therefore stiffest) pier, Pier 8 controls the design. This

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is due to shallow rock at the footing location, resulting relatively short, stiff drilled shafts. The expected movement of the extradosed bridge due to thermal effects is approximately +/‐ 8 inches and the expected shortening of the superstructure due to creep and shrinkage is approximately 6 inches. This results in the expansion joint at the east abutment having a movement rating of 26 inches and the expansion joint at Pier 7 having a movement rating of 38 inches. The increased expansion joint size at Pier 7 accounts for the movement of the approach structure. Please see the Pier Investigation section of this document for more information.

Figure 5‐10. Deflected Pier Shape

5.13 Grade Induced Movement Investigation The bridge is on a constant +1.74% grade traveling toward Wisconsin. An investigation to evaluate the tendency of the bridge to move permanently in the downhill direction was conducted. It has been concluded that the bridge is not susceptible to grade induced movements. The frame action of the integral pier configuration alleviates this movement. 5.14 Two Box Girder Load Distribution Investigation The two box girder load distribution investigation evaluated the requirements for transfer of transverse loads in the regions along the bridge where cable stays and diaphragms do not exist, as shown in Figure 5‐11.

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Figure 5‐11. Superstructure between Cable Supports

Once the closure between the individual girders is complete, the two girders no longer act independently, but instead behave as if they are one. As shown in Figure 5‐12, the deflection of both box girders is approximately the same when only one box girder is subjected to full live load.

Figure 5‐12. Transverse Analysis

It has been determined that the closure pour between the two box girders is sufficient to transfer unbalanced live loads and to prevent differential deflection between the individual box girders. To improve the long‐term service performance of the closure, transverse post‐tensioning will be integrated into the design. A detail of the proposed closure pour is shown in Figure 5‐13.

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Figure 5‐13. Closure Pour Detail

5.15 Wind Load—Vibration Analysis Investigation Long span bridges tend to be excited by dynamic wind load. The St. Croix River Bridge River Crossing is a long span bridge with six 480’ spans. While the bridge is extradosed type, it is actually a box girder bridge with partially exposed post‐ tensioning tendons and therefore the bridge behavior is very close to traditional box girder bridges. There are long span box girder bridges in Japan and other countries that have experienced large vibrations under wind load and there is a possibility that this bridge might also experience wind induced vibration. A study for the vulnerability to excessive vibration has been performed and is discussed below. An Eigenvalue dynamic analysis was performed on the St Croix River Crossing and some modes of vibration are shown in Figure 5‐14. The period of the first vertical mode is approximately 1.0 second. The period of the first torsional mode is found to be approximately 0.5 second. The ratio of the first vertical mode to the first torsional mode is approximately 2. Based on previous experience, when this ratio is near the range of 2 to 3, the bridge has higher possibility of wind induced vibration. Therefore, a detailed wind study is deemed necessary during final design of this bridge.

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Figure 5‐14. Mode Shapes from the Eigenvalue Dynamic Analysis

Bridge structural dynamic response to wind is commonly studied by performing wind tunnel tests. An aero elastic model wind tunnel test can cover all modes of the bridge and provide a realistic prediction of the bridge dynamic response to wind. A partially completed structure is more vulnerable than a complete structure. The most vulnerable condition of this bridge is before the spans are closed and while the cantilever arms are the longest. Therefore, several critical construction conditions in addition to the complete bridge are recommended for detailed study. In accordance with these findings, it is recommended that the design criteria include aerodynamic evaluation of the bridge with the testing criteria listed as follows: 13.3.3.1.10 Aerodynamic Evaluation  A wind expert shall perform wind data collection and analysis to determine the design wind speed.  The aerodynamic stability of the structure shall be determined by performing wind tunnel tests on aero‐elastic models of the structure. A buffeting analysis shall be performed based on the data measured from the wind tunnel tests.  The buffeting analysis will generate equivalent static wind loads to the structure. Aero‐elastic model wind tunnel tests shall include critical construction conditions as well as the completed structure.

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Large amplitude vibration of some stay cables in light rain and low wind has been observed in of some cable stayed bridges around the world. This phenomenon is called rain‐wind induced vibration. The stay cable industry has developed several means to counteract this vibration. The most commonly used method is a spiral bar placed around the PE pipe. This has been proven a very effective Measure and it is recommended that this type of PE pipe be required for the St Croix River Crossing.  The allowable stress in the cables of the extradosed bridge is 0.6 FGUTS or 162 ksi. The allowable stress in the cables of cable‐stayed bridge is 0.45 FGUTS or 122 ksi. The higher allowable tensile stress in the extradosed bridge has the effect of lowering the possibility of excessive vibration.  The Contractor will be required to design the cables in accordance with PTI Guide Specifications Recommendations for Stay Cable Design, Testing and Installation, 3rd and 5th Editions. A properly designed cable is not expected to experience wind induced vibration. 5.15.1 Back span Uplift/Maximum Back span Length Investigation The back span uplift/maximum back span length investigation evaluated the potential for uplift at the back span piers. It has been determined that the current configuration of the spans does not result in uplift. One of the main reasons there is no uplift is that the live load to dead load ratio on the extradosed bridge is quite low. Another reason is that the proposed back span length is 290 feet, which is 50 feet longer than half of the main span. The additional 50 feet of span length on the back span effectively acts a counterweight to resist the uplifting forces when the main span is fully loaded. The integral framing of the superstructure to the substructure at the main piers is effective at resisting the longitudinal rotation of the superstructure caused by the fully loaded main span, which also limits the ability of the back span to uplift. It had been determined that the minimum service load bearing reaction at the back span support is approximately 800 kips, based on a two bearing per girder configuration. 5.16 Extradosed Stay Cable Analysis The cables of the baseline structure are arranged in two planes and anchor in an anchor pod at the exterior edge of each box girder, with typical spacing of 20 feet between cables, as shown in Figure 5‐15. There are a total of 252 cables, with 36 cables anchored at each pier.

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Figure 5‐15. Extradosed Stay Cable Configuration

The cables are connected to the tower starting 22 feet above the roadway level, with typical spacing of 4 feet between cables at centerline of pier. The cables are either anchored to the tower within a steel anchorage housing. The cables are connected to the box girder at anchorage pods spaced at 20 feet along the exterior edges of the two box girders. There are nine anchorage pods along each edge up station and down station from the pier. The first cable pair is located 55 feet from the centerline of pier, with the ninth cable pair located 215 feet from centerline of pier. This leaves a space of 50 feet in the midspan between the ninth cable pair of adjacent piers. The angle of the cables from the horizontal plane varies from 14 degrees to 22 degrees. At each anchorage pod there is a diaphragm connecting the box girders together. The extradosed cables were initially sized assuming that they would resist approximately 60% of the dead load moment of the cantilever prior to closure. Following this initial sizing, the average cable tension (1250 kips) was selected to be applied to each extradosed cable upon installation. According to the Cable Stays Recommendations of the French Interministerial Commission of Pre‐stressing, stay cables with a change in stress caused by live load of less than 7.2 ksi are considered extradosed. The standard limits the cable tension to 60% of the guaranteed ultimate tensile strength, that is, 0.6 GUTS, under the effects of maximum service loading. It has been determined that the stress variation caused by live load (HL‐93 with no pedestrian load) on the St. Croix River Bridge is approximately 4 ksi (as shown in Figure 5‐16), which defines the cables as extradosed. Utilizing the allowable tension limit of 0.6 FGUTS, all cables are comprised of 37 0.6‐inch diameter strands.

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Figure 5‐16. Live Load Stress Range

5.17 Points of Interest—Local Analysis Two “points of interest” were identified during the global modeling. The first location is the integral pier cross girder to column connection, which is a complex area and critical component to the feasibility of the structure. A localized finite element model was generated to study the force flow, stress concentrations and deformations within the integral connection. The forces input into the localized models have been derived from the global analytical model. The results of the localized analysis indicate that proposed integral connection is still feasible. However, there will be areas of stress concentration that will need to be addressed during final design. Various stress diagrams can be seen in Figure 5‐17 through Figure 5‐19.

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Figure 5‐17. Local Model of Integral Pier (Bottom View)

Figure 5‐18. Local Model of Integral Pier (Top View)

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Figure 5‐19. Pier Cross Girder Interface Model

The second area of interest is the configuration of the first two spans (spans 8 and 9) of the extradosed bridge, which have a variable width superstructure caused by the merging of Ramps SE and NE into the mainline. The majority of the width variation is within span 8, in which the width varies from 135 feet at Pier 7 to 110 feet at Pier 8. Special consideration of the framing of span 8 is required due to its increased width. It should also be noted that in addition to the increased width, the super elevation is also varying along the length of span 8. Although it doesn’t have a major impact on the framing, the varying super elevation must be considered in the cross girder and extradosed stay cable design. There are several viable alternatives, but one solution is shown in Figure 5‐20 through Figure 5‐22. The proposed configuration utilizes a precast truss member between the two precast box girders. This maintains a similar “open” appearance to the rest of the extradosed structure as well as maintaining the same geometry for the box girders.

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Figure 5‐20. Pier 8 Elevation Showing Widened Superstructure and Full Super Elevation

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Figure 5‐21. Span 8 Typical Section

Figure 5‐22. Isometric View of Precast Truss

To determine the demands on the transverse members, a 3D analytical model of a representative span was created as shown in Figure 5‐23. The box girders were modeled using plate elements and the transverse members were modeled using beam elements. Various live load conditions were studied as well as the forces induced in the members during the initial stressing of the stay cables during construction. Based on the results from the localized and global analysis, it can be concluded that the proposed precast truss alternative is feasible. The light weight strut design will also keep the extradosed stay cable force increase to a minimum.

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Figure 5‐23. Isometric View of 3D Analysis

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6 Division II Structural Analysis

6.1 Introduction and Objectives There are three bridges in this portion of the work: Bridge No. 82045 (Mainline TH 36 approach units), Bridge No. 82047 (TH 36WB off‐ramp to TH 95), and Bridge No. 82048 (TH 36EB on‐ramp from TH 95). The typical mainline superstructure is comprised of two parallel concrete segmental box girders connected by a closure pour at the top flange, while the ramp superstructures are a single concrete segmental box girder. The baseline model piers are twin stem wall type that is connected monolithically to the superstructure, with the exception of the mainline pier nearest to the abutment that is a single column with bearings. The approach span adjacent to the extradosed river spans is a transition span that has a wider cross‐section to accommodate the on‐ramp and off‐ramp lanes. The concept refinement program consisted of developing appropriate structural models and performing structural analyses to evaluate the adequacy of the proposed design concept. The baseline model conforms to the structural configuration presented in the VQM and the Mn/DOT‐provided roadway design files. Variations on the baseline model were developed as the layout and construction impacts were examined for reduction of impact and overall technical enhancement. These variations were designated R1, R2, etc., to indicate the layout version being modeled. Subsequent sections describe the baseline model and interpretation of the VQM. The modeling approach utilized global modeling for longitudinal and transverse effects, and localized modeling was performed at “points of interest” identified during the global modeling. In addition to the general analysis task, specific investigations and evaluations included the following: 6.1.1 Box Girder Width Transition Investigation The box girder width transition investigation evaluated the transition in box girder width at the ramp termini, on the Minnesota side, and investigated options for transitioning the box girders at the ramp termini. The transition was kept off of the back span of the extradosed portion of the river crossing to the greatest extent possible. 6.1.2 Box Girder Depth Economy Investigation The box girder depth economy investigation evaluated ways to economize the depth of the box girder section from the west abutment to pier 6. As referenced in the VQM, the depth of section of the first 6 spans varies from 10 feet to 20 feet. The 10‐ foot depth is required to provide vertical clearance over TH 95 in Span 1 and the 20‐ foot depth is required to match the depth of the extradosed spans.

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6.1.3 Fixity/Longitudinal Movement Investigation The fixity/longitudinal movement investigation evaluated pier and bearing fixity requirements, pier stiffness effects due to thermal movements, and other issues unique to long, continuous bridges. Continuous structures are desired with expansion joints only expected to be at the ends of the extradosed spans and the west abutment. 6.1.4 Grade Induced Movement Investigation The grade induced movement investigation evaluated potential of the bridge to move permanently in the downhill direction and provide performance requirements for a Design‐Build RFP. The Minnesota approach spans of Bridge 82045 (B‐55‐224) are on a ‐1.25% grade traveling toward Wisconsin. 6.1.5 Box Girder Depth Transition Investigation The box girder depth transition investigation evaluated recommendations regarding the location of the box girder depth transition. There are vertical clearance restrictions over TH 95 at the first span of the river bridge approach spans that necessitate a 10‐foot maximum structure depth. The structure depth must increase at some location after spanning over TH 95 to accommodate longer span lengths and to match the depth of the extradosed spans. In the concept plan shown in the VQM, the depth transition begins in Span 1 just east of TH 95 and terminates at Pier 2. 6.2 Investigation Methods: Longitudinal Analysis As with all segmental bridges, the design is dependent on the construction sequence used to build the bridge. For the St. Croix River Crossing, the structural arrangement conforms to a balanced cantilever construction sequence. The substructure consisting of the foundation and pier is built first followed by construction of the superstructure girder. Segments of the girder are either cast on a form traveler for cast‐in‐place construction or erected using a deck mounted lifting system or land/water‐based crane for precast construction. As each segment is cast, or in the case of precast, as each pair of segments is erected, cantilever post‐tensioning tendons in the top flange that anchor at the ends of the two cantilevers are installed and stressed. The construction at the various piers can proceed in a number of sequences, but typically construction proceeds from one end of the structure to the other end. As balanced cantilever construction is completed at a pier nearest to an abutment, a number of segments adjacent to the abutment are supported on temporary falsework. A closure segment is cast between the two sections of girder, and continuity post‐tensioning tendons in the bottom flange are installed and stressed to make the fist continuous span. As cantilever construction is completed at subsequent piers, a closure segment is cast between adjacent sections of girder, and

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continuity post‐tensioning tendons in the bottom flange are installed and stressed to make the span continuous. Cantilever construction and the span closures change the structural system. Coinciding with these changes are time dependent effects due to increasing concrete strength, concrete creep and shrinkage, and post‐ tensioning steel relaxation which must be considered in the design of segmental structures. Once the structure is completed, the time dependent effects continue to occur, and the analysis evaluates these effects for a predetermined Figure 6‐1. Balanced Cantilever Construction Method (Modeling of Construction Stage 6, Bridge 82048) time interval, typically to 10,000 days, which is defined as time infinity, when it is assumed all time dependent effects have occurred.

Figure 6‐2. Detail of Segments on Pier and Accurate Section Property Input

Following the 10,000‐day analyses, external loads such as truck and wind forces were applied to the completed structure. Stresses were checked for conformance within AASHTO LRFD limits. These stress checks include limit states before and after construction.

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Figure 6‐3. Stress Output Checked at 10 Locations in the Cross‐section

6.3 Baseline Model Description 6.3.1 Piers The VQM illustrates twin stem wall piers having a curved surface on the outward faces looking up station and down station. These double‐stem piers vary in width from top to bottom with the smaller dimension at the top of the stem walls. A diagonal cut on the side faces provides the taper. From the side, the outer and inner stem faces are plumb, but the diagonal cut provides a side face that decreases in dimension from top to bottom. The top width of the stem walls matches the bottom flange width of the box girder. The double stem piers were examined through initial visual renderings, bridge elevation views of each structure, approximate material quantities and an estimated construction impacts. Through discussions with Mn/DOT and the VQAC, there was general consensus that a single stem pier would be preferred to obtain constructability, economic and visual benefits. Since substructure geometry significantly affects the structural analysis, all models were suffixed with either an “A” or “B” to indicate whether double‐stem piers or single‐stem piers were modeled, respectively. In other words, structural model 82045_R1A was variation 1 on the baseline model and utilized double‐stem columns, whereas model 82045_R1B was baseline variation one with single‐stem columns.

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From our analyses it is apparent that a single stem column is a viable option with the caveat that expansion joint locations will require a wider platform for bearings and jack area for bearing replacement. This wider platform would equate to a single column with an approximately 14’‐6” longitudinal dimension at Ramp Pier 5R and the three columns of Pier 7. Alternatively, double‐stem columns connected with a pier cap may be utilized.

Figure 6‐4. Pier 1 on TH 36 (Bridge No. 82045)

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Figure 6‐5. Typical Pier on TH 36 Approaches (Others Similar)

6.3.2 Box Girders The baseline box girders along the TH 36 mainline are comprised of a 3‐cell cross‐ section, with two vertical interior webs and two inclined exterior webs. The bridge begins at the west abutment with 10‐foot deep box girders that transition to a 20‐ foot deep box girder from the end of span 1 throughout span 2. These girders are typically 42’‐8” wide at the top flange or roadway level, with a 16.0‐foot width at the girder soffit. The exterior webs and soffit have circular curved faces with a radius of 66.0 feet. The individual curves meet at the web‐soffit intersection, forming an angular break point. The exterior webs curve to vertical at roadway level by the addition of a smaller radius curve within the top 3 feet of the web. The baseline N.E. and S.E. ramp box girders emulate the shape of the mainline girders. The depth of these ramp girders was undefined prior to preliminary design, although there was some indication in the proposed railroad and Plant Access Road

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profiles that these girders would be 10 feet deep at these crossings. Considering this indication, preliminary design proceeded with the assumption that the approach ramp structures should also include a box girder depth transition from 10 feet to 20 feet. This assumption fit the ramp structures well because a constant 20’‐foot depth appeared visually too deep for the ramps, especially as these structures descended toward the respective exit or entrance intersection. The baseline ramp box girders are typically 27’‐4” wide at the top flange or roadway level, with a 12.0‐foot width at the girder soffit. The exterior webs and soffit have circular curved faces with a radius of 50.0 feet for the exterior webs and 36.0 feet for the soffit. The individual curves meet at the web‐soffit intersection, forming an angular break point. The exterior webs curve to vertical at roadway level by the addition of a smaller radius curve at the top 3 feet of the web.

Figure 6‐6. Baseline Approach Box Girders

The top flange of the box girder is haunched adjacent to each web to provide room for post‐tensioning anchorages on either side of the interior webs, and on the interior side of the exterior webs. The bottom flange is similarly haunched adjacent to the interior webs to permit the top surface of the flange to follow the curved soffit face and reduce the flange thickness at the midspan between the webs. 6.3.3 Transition Span The approach span adjacent to the extradosed river spans is a transition span that has a wider cross‐section to accommodate the on‐ramp and off‐ramp lanes. The cross‐section consists of two box girder similar to the mainline, but the box girder dimensions vary to accommodate the additional roadway width. 6.3.4 Pedestrian Trail A pedestrian trial cantilevers from the edge of the transition span and the northern ramp box girder. The trail consists of a sidewalk slab supported by concrete brackets attached to the box girder at approximately 20‐foot interval. The six bridges are divided into four baseline models as follows: The initial focus was on determining constructible and feasible box sections for use in modeling. These design sections made use of repeatable forms and were

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conceptually compatible with the VQM intent. Areas of wide variation were relegated to cast‐in‐place construction on falsework. Such sections were kept minimal to limit the environmental impacts and cost impacts, but nonetheless these areas were accurately modeled in the analyses for construction staging and tendon geometry. Bridge 82045 was modeled in a baseline model consisting of double‐stem piers in and five‐span configuration as illustrated in Figure 6‐7 and Figure 6‐8 and Table 6‐1. Consistent with the model naming convention, the analysis is termed 82045E‐r0A to indicate Bridge 82045, Eastbound in the baseline configuration with double‐stem columns.

Figure 6‐7. Baseline Model 82045E‐r0A, Bridge 82045 EB (EB TH 36)

Figure 6‐8. Plan and Elevation of Baseline Model, Bridge 82045 EB (EB TH 36)

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Table 6‐1. Baseline Span Arrangement

Length Span Arrangement from Bridge No. (feet) West to East (feet) Comment 82045 (EB) 1609 180‐229‐300‐300‐300 Mainline eastbound 82045 (WB) 1609 180‐229‐300‐300‐300 Mainline westbound, similar to eastbound and not uniquely modeled 82045 (EB) 300 300 Transition eastbound 82045 (WB) 300 300 Transition westbound, similar to eastbound and not uniquely modeled 82047 1031 125‐300‐300‐301 Off‐ramp TH 36WB/TH 95 82048 1296 91‐300‐300‐300‐300 On‐ramp TH 36EB/TH 95

Pursuant to the study’s objectives, the baseline box girder depth of 20 feet was investigated in both the extradosed and approach unit models and span arrangements. In the extradosed span, an optimal depth of 16 feet was determined by balancing girder and cable requirements. In the approach units, however, the 16‐ foot depth was not structurally viable in the transition span with the baseline span configuration. One reason for this is that the N.E. and S.E. ramp expansion joints force the transition span to be a single‐span, separate structure. Precast, balanced cantilever construction envisioned for much of the bridge construction is not possible in a single‐span configuration. Therefore, the baseline configuration would require a 20‐foot deep box girder in the 300‐foot transition span that would be entirely cast on falsework. This finding initiated a focus on the transition span and span alternatives. Four goals were set for the transition span investigation:  To enable construction via the precast balanced cantilever method  To minimize the falsework and associated permanent impacts in the wetlands below  To move the expansion joints over the support locations and eliminate hinges for maintenance reasons  To enable use of a 16‐foot deep structure that was compatible with the optimal structure depth found for the extradosed spans Decreasing the box girder depth to 16’ would also introduce savings in material and support structure costs due to the increased weight of the superstructure. Parallel to the girder depth investigation, the baseline spans were examined for feasibility. Results from these analyses indicated Bridge 82045 appeared to have a viable arrangement given the 20’ box girder depth, but the N.E. and S.E. ramps had baseline span arrangements that were not only inefficient but appeared impractical for the 10‐foot box girder depth near the end spans as suggested by the profiles. For this reason, no baseline model was developed for the N.E. and S.E. Ramps according

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to the VQM, or baseline, span arrangement. Instead, variations of span arrangements were investigated using engineering judgment which suited:  The VQM box girder section  Site constraints such as wetland avoidance and railroad clearances  Balanced cantilever construction method to minimize heavy duty falsework in sensitive areas The resulting span arrangements were drafted and presented at a wetland coordination meeting on September 2nd, 2009. The proposed changes to span configuration as suggested by PB were agreeable to the stakeholders and it was agreed to further advance these configurations as the preferred arrangement. These preferred arrangements are described in detail in the next sections. 6.4 Alternative R1 Investigation Alternative R1 is the result of girder depth investigations, span efficiency and site constraints. The R1 span arrangements are indicated in Table 6‐2.

Table 6‐2. Span Arrangement “R1”

Length Span Arrangement from Bridge No. (feet) West to East (feet) Comment 82045 (EB) 1909 184‐224‐300‐300‐183‐161 Mainline eastbound 82045 (WB) 1909* 184‐235‐300‐300‐183‐161* Mainline westbound 82047 1031 104‐195‐243‐233‐202 Off‐ramp TH 36WB/TH 95 82048 1296 126‐192‐199‐199‐199‐199‐168 On‐ramp TH 36EB/TH 95 *Indicates span measurement with respect to EB TH 36 alignment

Within the R1 span arrangement, various column configurations were investigated. These models were suffixed with a letter designation to indicate the column type used in the investigation. The suffixes to date are as follows:  A = baseline model with double stems typical except at Pier 1, Bridge 82045  B= single stem columns with an 8‐foot longitudinal dimension and f’c=4 ksi  C = single stem columns with an 6‐foot longitudinal dimension and f’c=5 ksi In all of these instances bridge modeling using true coordinates along the respective alignment. However, a horizontal datum of 70’ was established for a constant girder elevation while the column heights were correctly calibrated to the height from PGL to top of footing. At the top of footing, 3 rotational and 3 translational springs serve to emulate the group pile behavior. These springs were determined elastically from a refined piling arrangement and checked through the use of industry‐standard Lpile Group software.

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For all bridges it is assumed that a pair of bearings supports the superstructure at the West Abutments, Pier 1 and the end piers. The introduction of bearings at the West Abutment and Pier 1 are due to the short height of these support structures, which creates a high stiffness and resistance against thermal movements. The end pier bearings are necessary because they are expansion joint locations.

Bridge 82045 EB was modeled with Figure 6‐9. Plan and Elevation of Alternative “R1” both a double‐stem column and a Models for EB and WB TH 36. single‐stem column. These two models served as a basis for evaluating the viability of the single‐stem piers. Once verified, column option A (Double‐stem columns) were eliminated due to Mn/DOT preference and column option B was continued through analyses that included WB TH 36 and the N.E. and S.E. ramps. Figure 6‐10 through Figure 6‐12 illustrate the various analyses that were developed in this program.

Figure 6‐10. Model 82045E‐r1A—Double‐stem Columns in Alternative R1 Span Arrangement

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Figure 6‐11. Model 82045E‐r1B—Single‐stem Columns in Alternative R1 Span Arrangement

Figure 6‐12. Plan and Elevation of Model 82045W‐r1B—WB TH 36 with Single‐stem Columns in Alternative R1 Span Arrangement

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Bridge 82047, or the N.E. Ramp, includes a cantilevered sidewalk in the VQM which was integrated with the box section after discussions with Mn/DOT. With the inclusion of the sidewalk, this ramp has a width very comparable with the typical TH 36 approach unit segments and a consistent shape was utilized. At the West end, two turn lanes are added on the structure necessitating variable width sections up to 60’‐6” in width. A depth increase of 6‐foot is introduced in span four to match the depth of TH 36 box girder at Pier 5R. This depth increase suits the higher end span moments and provides a visually appropriate transition.

Figure 6‐13. Bridge No. 82047 (NE Ramp) Stick Model and Rendered Model

Figure 6‐14. Bridge No. 82047 Rendered Plan and Elevation from Structural Model with Details

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Bridge 82048 (SE Ramp) is the narrowest and the longer of the two ramps. The ramp width is largest at the beginning where the roadway would permit three 12‐foot lanes and narrows to a 24’‐0 roadway for two potential loading lanes. Although the roadway width is amenable to a single‐cell box girder, this bridge has been envisioned as a two‐cell box girder due to the lack of counter‐balancing overhangs. Without cantilever overhangs to decrease the top‐slab span, high restraint forces will develop directly under the barriers and necessitate more transverse post‐ tensioning and a thicker, heavier slab section. For these reasons, a two‐cell structure presents more efficiency than a single cell girder. The box girder depth transition is placed in the second span from the end of the ramp to enable the deeper girder’s effectiveness in the end span. Model R1B is illustrated in Figure 6‐15 through Figure 6‐16.

Figure 6‐15. Bridge No. 82048 (SE Ramp) Stick Model (Left) and Rendered Sectional Model (Right)

Figure 6‐16. Bridge No. 82048 (SE Ramp) Plan and Elevation View of Rendered Model

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6.4.1 Grade­Induced Movement Investigations Grade induced movement was examined by using two models that were identical in all respects except the grade. For this investigation the EB Bridge 82045 Alternative R1 was used. To exaggerate the effects, a grade of 5% was modeled in lieu of the actual 1.25% slope. Both models were run and the displacements at Pier 7, the downhill end support, were examined. As can be seen in Table 6‐3, no appreciable difference is observed. The results are taken at a time equal to 10,000 days after construction, which is an industry‐ standard time for which all construction‐induced load effects should be realized (Self‐weight, elastic shortening, creep, shrinkage, etc.).

Table 6‐3. Grade‐induced Movement Results Vector Sum, Net Model DX DY DZ movement Description Time (Feet) (Feet) (Feet) (Feet) Horizontal T_INFINITY ‐0.194 ‐0.236 ‐0.042 0.305 5% grade T_INFINITY ‐0.194 ‐0.236 ‐0.037 0.306

Figure 6‐17. Models Used in Investigating Grade‐induced Deflection

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St. Croix River Crossing Preliminary Engineering Concept Refinement Report

7 Bridge Lighting and Signing

7.1 Review of Requirements for Architectural and Roadway Lighting The Visual Quality Manual discusses many aspects of the different types of lighting for the bridge, roadway, and trail. These include specific concerns about the impact of lighting as well as the lighting approach to be used for different areas. Specific concerns included:  Design should minimize the negative impact that bridge lighting could have on the scenic river valley.  Lighting should meet the needs for required safety levels but minimize “spillover” into the riverway.  Architectural lighting must be thoughtfully designed to enhance the structure without intruding into the sensitive natural environment. Preliminary investigations were conducted during the preparation of the VQM into various types of lighting approaches. The results of these investigations arrived at the following recommendations.  Roadway lighting using davit poles with twin arms and contemporary style luminaires mounted in the median.  A “white” light source such as metal halide is preferred due to aesthetic and quality reasons  Trail lighting could use a low level lighting system to provide adequate pedestrian visibility with minimized light trespass.  Navigation channel lighting is not required but lighting identifying the piers locations for boaters is required for safety reasons.  FAA obstruction lights are required at the tops of the pier towers. These concerns and recommendation were carried into this phase of design and are addressed and discussed in the various lighting approaches in this report. 7.2 Lighting Criteria Aesthetic lighting for the St. Croix River Crossing will accent its unusual forms. These derive from the extradosed structural design and the biomorphic aesthetic concept. The effects under consideration include illuminating the cables from below with narrow beam floodlights, grazing the tower surfaces either inside or outside, and outlining selected features with direct view fixtures. For floodlighting options the criteria of the Illuminating Engineering Society (IES) will apply. The criteria recommended in IES RP‐33‐99 Lighting for Exterior Environments is shown in Table 7‐1 (excerpted from Table 2 of that document).

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Table 7‐1. Illuminance Levels for Floodlighting Buildings and Monuments Average Target Illuminance (Vertical) Area Description (lux/footcandles) Bright surroundings and light surfaces 50/5 Bright surroundings and medium light surfaces 70/7 Bright surroundings and dark surfaces 100/10 Dark surroundings and light surfaces 20/2 Dark surroundings and medium light surfaces 30/3 Dark surroundings and medium dark surfaces 40/4 Dark surroundings and dark surfaces 50/5

The vertical value on the structural elements will be designed to 20 to 30 lux (2 to 3 footcandles) associated with the categories of Dark Surroundings and Light to Medium Light Surfaces (note : RP‐33 has an error in the table description). For roadway lighting criteria the recommendations of IESNA Recommended Practice 8‐00 and AASHTO Guide for Roadway Lighting apply. The criteria recommended in ANSI/IES RP‐8‐05 Standard Practice for Roadway Lighting is shown in Table 7‐2 and Table 7‐3.

Table 7‐2. Illuminance Method—Recommended Values

Pavement Classification Veiling Pedestrian (minimum maintained average values) Uniformity Luminance Conflict R1 R2 & R3 R5 Ratio Ratio Road Area (lux/fc) (lux/fc) (lux/fc) Eavg/Emin Lmax/Lavg Freeway Class A 6.0/0.6 9.0/0.9 8.0/0.8 3.0 0.3 Freeway Class B 4.0/0.4 6.0/0.6 5.0/0.5 3.0 0.3 Expressway High 10.0/1.0 14.0/1.4 13.0/1.3 3.0 0.3 Medium 8.0/0.8 12.0/1.2 10.0/1.0 3.0 0.3 Low 6.0/0.6 9.0/0.9 8.0/0.8 3.0 0.3 Major High 12.0/1.2 17.0/1.7 15.0/1.5 3.0 0.3 Medium 9.0/0.9 13.0/1.3 11.0/1.1 3.0 0.3 Low 6.0/0.6 9.0/0.9 8.0/0.8 3.0 0.3 Collector High 8.0/0.8 12.0/1.2 10.0/1.0 4.0 0.4 Medium 6.0/0.6 9.0/0.9 8.0/0.8 4.0 0.4 Low 4.0/0.4 6.0/0.6 5.0/0.5 4.0 0.4 Local High 6.0/0.6 9.0/0.9 8.0/0.8 6.0 0.4 Medium 5.0/0.5 7.0/0.7 6.0/0.6 6.0 0.4 Low 3.0/0.3 4.0/0.4 4.0/0.4 6.0 0.4

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Table 7‐3. Luminance Method—Recommended Values Veiling Average Uniformity Uniformity Luminance Pedestrian Luminance Ratio Ratio Ratio Conflict Lavg Lavg/Lmin Lmax/Lmin Lmax/Lavg Road Area (cd/m2) (max allowed) (max allowed) (max allowed) Freeway Class A 0.6 3.5 6.0 0.3 Freeway Class B 0.4 3.5 6.0 0.3 Expressway High 1.0 3.0 5.0 0.3 Medium 0.8 3.0 5.0 0.3 Low 0.6 3.5 6.0 0.3 Major High 1.2 3.0 5.0 0.3 Medium 0.9 3.0 5.0 0.3 Low 0.6 3.5 6.0 0.3 Collector High 0.8 3.0 5.0 0.4 Medium 0.6 3.5 6.0 0.4 Low 0.4 4.0 8.0 0.4 Local High 0.6 6.0 10.0 0.4 Medium 0.5 6.0 10.0 0.4 Low 0.3 6.0 10.0 0.4

The American Association of State Highway and Transportation Officials (AASHTO) also have recommendations in the AASHTO Roadway Lighting Design Guide 2005 which, in general, are in agreement with the IES and are shown in Table 7‐4. Based on these recommendations considering the bridge roadway to be classified as a freeway, a average illuminance of 6 to 12 lux (.6 to 1.1 footcandles) and average luminance of 0.4 to 1.0 candelas/square meter (cd/m2) would be suitable design ranges. For the pedestrian area adjacent to the roadway, the lighting criteria described in IES DG‐5‐94 Recommended Lighting for Walkways and Class 2 Bikeways is most suitable. RP‐8 has a pedestrian area criteria but it applies to sidewalks and walkways adjacent to the roadway where pedestrian conflicts can occur. The bridge pedestrian walkway is separated and protected from the roadway so the recommendations of DG‐5 are more applicable. Using Table 2 of this guide and classifying the bridge walkway as a pedestrian overpass an average horizontal value of 2 lux (0.2 footcandles) and a vertical illuminance values of 5 lux (0.5 footcandles) should be used.

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Table 7‐4. Illuminance and Luminance Design Values (English)

Illuminance Method Luminance Method Veiling Off‐Roadway Average Maintained Illuminance Illuminance Average Maintained Luminance Luminance Light Uniformity 6 Ratio3 Roadway and Sources— Minimum Ratio Lavg Uniformity Uniformity Walkway General Land R1 R2 R3 R4 Illuminance avg/min cd/m2 Lavg/Lmin Lmax/Lmin Lv(max)/Lavg Classification Use (fc) (min) (fc) (min) (fc) (min) (fc) (min) (fc) (max) (min) (max) (max) (max) Interstate and Commercial 0.6 to 1.1 0.6 to 1.1 0.6 to 1.1 0.6 to 1.1 0.2 3:1 or 4:1 0.4 to 1.0 3.5:1 6:1 0.3:1 other freeways Intermediate 0.6 to 0.9 0.6 to 0.9 0.6 to 0.9 0.6 to 0.9 0.2 3:1 or 4:1 0.4 to 0.8 3.5:1 6:1 0.3:1 Residential 0.6 to 0.8 0.6 to 0.8 0.6 to 0.8 0.6 to 0.8 0.2 3:1 or 4:1 0.4 to 0.6 3.5:1 6:1 0.3:1 Other principal Commercial 1.1 1.6 1.6 1.4 3:1 1.2 3:1 5:1 0.3:1 arterials Intermediate 0.8 1.2 1.2 1.0 3:1 0.9 3:1 5:1 0.3:1 Residential 0.6 0.8 0.8 0.8 3:1 0.6 3.5:1 6:1 0.3:1 Minor arterials Commercial 0.9 1.4 1.4 1.0 4:1 1.2 3:1 5:1 0.3:1 Intermediate 0.8 1.0 1.0 0.9 4:1 0.9 3:1 5:1 0.3:1 Residential 0.5 0.7 0.7 0.7 4:1 0.6 3.5:1 6:1 0.3:1 Collectors Commercial 0.8 1.1 1.1 0.9 4:1 0.8 3:1 5:1 0.4:1 Intermediate 0.6 0.8 0.8 0.8 4:1 0.6 3.5:1 6:1 0.4:1 Residential 0.4 0.6 0.6 0.5 4:1 0.4 4.1 8:1 0.4:1 As Local Commercial 0.6 0.8 0.8 0.8 6:1 0.6 6:1 10:1 0.4:1 uniformity Intermediate 0.5 0.7 0.7 0.6 ratio allows 6:1 0.5 6:1 10:1 0.4:1 Residential 0.3 0.4 0.4 0.4 6:1 0.3 6:1 10:1 0.4:1 Alleys Commercial 0.4 0.6 0.6 0.5 6:1 0.4 6:1 10:1 0.4:1 Intermediate 0.3 0.4 0.4 0.4 6:1 0.3 6:1 10:1 0.4:1 Residential 0.2 0.3 0.3 0.3 6:1 0.2 6:1 10:1 0.4:1 Sidewalks Commercial 0.9 1.3 1.3 1.2 3:1 Intermediate 0.6 0.8 0.8 0.8 4:1 Residential 0.3 0.4 0.4 0.4 6:1 Use illuminance requirements Pedestrian and All 1.4 2.0 2.0 1.8 3:1 bicycle ways2 1Meet either the illuminance design method requirements or the luminance design method requirements and meet veiling luminance requirements for both the illuminance and the luminance design methods. 2Assumes a separate facility. For pedestrian and bicycle ways adjacent to roadway, use roadway design values. Use R3 requirements for walkway/bikeway surface materials other than the pavement types shown. Other design guidelines, such as IESNA or CIE, may be used for pedestrian and bicycle ways when deemed appropriate. 3 Lv(max) refers to the maximum point along the pavement, not the maximum in lamp life. The maintenance factor applies to both the Lv term and the Lavg term. 4There may be situations when a higher level of illuminance is justified. The higher values for freeways may be justified when deemed advantageous by the agency to mitigate off‐roadway sources. 5Physical roadway conditions may require adjustment of spacing determined from the base levels of illuminance indicated above. 6Higher uniformity ratios are acceptable for elevated ramps near high‐mast poles. 7See AASHTO publication entitled “A Policy on Geometric Design of Highway and Streets” for roadway and walkway classifications.

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Table 7‐5. Recommended Illumination (Values in lux) Average Conditions Special Conditions1 Avg Maintained Illuminance Min Levels Horizontal Maintained Horizontal Avg to Min Avg Vertical Avg to Min 2 3 Levels (Eavg) Avg Levels (Eavg) Ratio Sidewalks along streets by area classifications4 Commercial 10 4:1 20 5:1 Intermediate 5 4:1 10 5:1 Residential 2 10:1 5 5:1 Park walkways and class I bikeways 5 10:1 5 5:1 Pedestrian tunnels 20 4:1 55 5:1 Pedestrian overpasses 2 10:1 5 5:1 Pedestrian stairways 5 10:1 10 5:1

7.3 Lighting Alternatives Analysis 7.3.1 Source Selection Based on the direction of the Visual Quality Manual for the use of a “white” light source like metal halide, a review of possible sources meeting this criteria was evaluated. The types of lamps which were considered were:  Metal Halide  Fluorescent  Induction  LED Each of these sources has unique operating characteristics in terms of efficiency, lamp life, temperature impacts, and lumen depreciation, so a description of each is included below with an expanded description of LED’s. Because LED’s are a solid state device and not a conventional lamp type, more information is provided including some LED “basics”. Metal Halide Metal halide lamps are high intensity discharge lamps which operate by vaporizing various materials at extremely high voltages, stabilizing after ignition. Metal halide lamps are available in various color temperatures and are fairly efficient at about 70‐ 80 lumens per watt. The life of a metal halide lamp will range from about 12,000 to 20,000 hours depending on the lamp wattage used (rated life is determined as the time when 50% of the lamps have failed). Metal halide lamps do experience some color shift during their life and generally need to be in enclosed luminaires. The lamps are prone to shortened life in conditions encountering sustained vibration because of arc tube failure and mechanical failure of the lamp components.

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Fluorescent / Induction Fluorescent sources operate by generating an ultraviolet arc spanning over two ends of the lamp. As the ultraviolet energy comes in contact with phosphors it produces visible light. Induction technology uses coils, external to the lamp to generate an electric field to perform this function. The use of these external coils, operating at high frequency, help extend the lamp life of this source to over 100,000 hours. Linear fluorescent lamps are sometimes considered for bridge lighting because of their long life and efficiency. Typical arrangements are as linear rail lights or accent lighting. A T8 fluorescent lamp with reduced mercury content, operating in conjunction with a programmed start ballast will provide a lamp life of over 40,000 hours and a system efficiency of approximately 110 lumens per watt. The lamps with electronic ballasts are durable in high vibration environments when used in properly designed fixtures. Temperature however does effect lamp output. Typically optimized for a bulb wall temperature of 77 degrees F, the lamps output can be reduced by over half in very cold environments. Induction lamps have a lower efficiency than some linear fluorescent lamps, operating at approximately 75‐80 lumens per watt. Lamp life is very long at approximately 100,000 hours. The end of life of an induction system is typically when the high frequency driver fails to operate. LED (parts of the text included in this section are excerpted from the US Department of Energy documents at www.netl.doe.gov) LEDs differ from traditional light sources in the way they produce light. In an incandescent lamp, a tungsten filament is heated by electric current until it glows or emits light. In a fluorescent lamp, an electric arc excites mercury Figure 7‐1. Typical LED atoms, which emit ultraviolet (UV) radiation. After striking the phosphor coating on the inside of glass tubes, the UV radiation is converted and emitted as visible light. An LED, in contrast, is a semiconductor diode. It consists of a chip of semiconducting material treated to create a structure called

a p‐n (positive‐negative) junction. Figure 7‐2. Schematic of LED Operation When connected to a power source, current flows from the p‐ side or anode to the n‐side, or cathode, but not in the reverse direction. Charge‐ carriers (electrons and electron holes) flow into the junction from electrodes. When

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an electron meets a hole, it falls into a lower energy level, and releases energy in the form of a photon (light).

The specific wavelength or color emitted by the LED depends on the materials used to make the diode.

Red LEDs are based on aluminum gallium arsenide (AlGaAs). Blue LEDs are made from indium gallium nitride (InGaN) and green from aluminum gallium phosphide (AlGaP). “White” light is created by combining the light from red, green, and blue (RGB) LEDs or by coating a blue LED with yellow phosphor.

Color Characteristics Unlike incandescent and fluorescent lamps, LEDs are not inherently white light sources. Instead, LEDs emit light in a very narrow range of wavelengths in the visible spectrum, resulting in nearly monochromatic light. This is why LEDs are so efficient for colored light applications such as traffic lights and exit signs. However, to be used as a general light source, white light is needed. White light can be generated from LED’s by either coating a blue LED with a yellow phosphor, or by using monochromatic red, green, and blue (RGB), LED’s and operating them at different levels to “mix” and create white, or any other color light. For most applications were the light source is visible, white (coated) LED are used. For RGB configurations, unless using an intermediate optic material, when viewing the sources directly you can see the individual red, green and blue LED’s and the source does not appear white. When applied to a surface however the mix of the colors creates a white surface. LED’s with a high correlated color temperature (which are “cooler” or bluer in appearance) tend to be the more efficient LED’s in terms of lumens per watt of power consumed. “Warmer” LEDs are available but have a slightly lower efficiency..

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Photometric Characteristics LED’s are available in different emitting patterns. An example of a typical pattern (from Phillips Luxeon K2) is shown in Figure 7‐3 and Figure 7‐4.

Figure 7‐3. Typical Representative Spatial Radiation Pattern for White Lambertian

Figure 7‐4. Typical Polar Radiation Pattern for White Lambertian

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Effect of Electrical Variations The light output of an LED is related to the amount of current it is being operated. The greater the current, the higher the light output of the LED. These variations in current also alter the useable life and efficiency of the LED. It is important to look at the performance data provided for particular LED’s and the current that they will be actually operated.

Table 7‐6. Flux Characteristics for LUXEON K2 with TFFC Junction and Case Temperature = 25C Minimum Performance at Test Current Typical Performance at Indicated Current Minimum Typical Luminous Flux (lm) Luminous Flux Color Part Number (lm) at 100 mA at 1600 mA at 700 mA at 350 mA Cool White LXK2‐PWC4‐0200 200 275 170 95 LXK2‐PWC4‐0180 180 250 150 85 LXK2‐PWC4‐0160 160 220 135 75

Figure 7‐5. Typical Luminous Flux

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LED’s also require a driver, similar to the way a fluorescent and high‐intensity discharge (HID) light sources cannot function without a ballast, which provides a starting voltage and limits electrical current to the lamp. The driver converts line power to the appropriate voltage (typically between 2 and 4 volts DC for high‐ brightness LEDs) and current (generally 200‐1000 milliamps or mA), and may also include dimming and/or color correction controls. Currently available LED drivers are typically about 85% efficient. So LED efficacy should be discounted by 15% to account for the driver. Effect of Temperature The luminous flux figures cited by LED manufacturers are based on an LED junction temperature (Tj) of 25°C. LEDs are tested during manufacturing under conditions that differ from actual operation in a fixture or system. In general, luminous flux is measured under instantaneous operation (perhaps a 20 millisecond pulse) in open air. Tj will always be higher when operated under constant current in a fixture or system. LEDs in a well‐designed luminaire with adequate heat sinking will produce 10%‐15% less light than indicated by the “typical luminous flux” rating.

Source: Philips Luxeon K2—(10/07) Figure 7‐6. Typical Light Output Characteristics Over Temperature (Cool‐White at Test Current)

Estimated Life LED’s, much like the mercury lamp, will continue to operate for long periods of time but at a steadily deteriorating light output. For this reason the estimated life of an LED cannot be based on how long it is still operating but how long it is still being an effective lighting source. Research (ref. Mark Rea, Lighting Research Center, 2000) has shown that for general lighting, a majority of occupants can accept a lighting level reduction of up to 30%, when done gradually. For this reason, as well as for

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standardization, the life of an LED is established to be the time when its’ light level has been reduced to 70% of its initially rated value. This is called an L70 life.

Source: Adapted from Bullough, JD. 2003. Lighting Answers: LED Lighting Systems. Troy, NY. National Lighting Product Information Program, Lighting Research Center, Rensselaer Polytechnic Institute. Figure 7‐7. Typical Lumen Maintenance Values for Various Light Sources

By this method, most currently available LED’s are rated between 40,000 and 60,000 hours of life at rated current. Much longer operating life can be obtained by operating the LED’s at a lower forward current and just using more LEDs. LED life can be extended 120,000 hours or higher by driving the LEDs at reduced current. Because LEDs are solid state devices, without arc tubes, they are very stable in high vibration environments such as bridges assuming proper construction of the sold state elements and circuit boards. The advancement of LED technology is exponentially faster than conventional lamp sources. Based on current advancements and expected continuation, LEDs should surpass all other sources in terms of operating life and energy efficiency within the next 2 years. When looking at current technology and the future potential, the use of LEDs seem appropriate for the St. Croix River Crossing if used with lower drive currents and lower color temperatures to better compliment the proposed finishes of the bridge and eliminate the environmental impacts of higher color temperature sources. 7.4 Architectural Lighting The architectural lighting options for the bridge ranged from no accent lighting to either floodlighting or using point sources to accent most of the structure and cables. In this section of the report we will discuss the progression of each Figure 7‐8. Base Architectural Lighting Option option as designed and presented to the Visual Quality Committee and where consensus was reached.

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The base architectural lighting option looked at no accent lighting for the bridge structure using only required lighting for basic motorist safety. The roadway was illuminated to the required lighting levels discussed in the criteria section using metal halide lamps in standard cobra head style full cutoff luminaires on 35’ davit arm style pole with 8’ arms. The walkway area met the minimum required horizontal values. 7.4.1 Option 1A From the base option of just using the roadway lighting, the roadway lighting luminaires were replaced with LED luminaires having increased distribution/output to the front side of the luminaire. This allowed more lighting to be placed on the cables from the roadway lighting equipment. The roadway lighting however is mounted on the median which is not centered between the cables due to the addition of the walkway on one side of the bridge. Because of this, the

lighting on the cables is different Figure 7‐9. Lighting Option 1a depending on which direction the bridge is viewed. Looking south, the cables are mostly illuminated. Looking north, the illuminated section of the cables is not as high due the increased distance to the luminaire so the effect is less pronounced. Floodlights were added at the base of the piers which light the inside surface of the split pier. Four floodlights were used for each pier consisting of narrow beam LED floodlights. These floodlights were also RGB color change floodlights allowing the lower piers to change color for the purpose of special occasions or significant events. The RGB Figure 7‐10. Lighting Option 1b LED arrangement can be tuned to produce virtually any color. In addition, each group of floodlights on each pier and be individually controlled and set to different preset colors.

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7.4.2 Option 2A The next lighting alternative investigated was to add LED floodlights to the upper portion of the towers. The intent of the floodlighting alternatives analysis is to keep adding layers of light in an attempt to reach the proper balance and perspective. Two LED floodlights were used Figure 7‐11. Lighting Option 2a at the top portion of the pier directed down the face of the tower. These additional floodlights added the effect of visually lengthening the perceived height of the towers. It also has the effect connecting the bottom to the top of the towers. The negative effects of these lights include the addition of more lighting into the night Figure 7‐12. Lighting Option 2b environment at the bridge and it did somewhat compete with the cable lighting. Because the inside surface of the cables are illuminated, an observer sees the cable lighting on the opposite side of the bridge. Unless directly lined up with the bridge, the illuminated tower would not usually line up with the illuminated cables causing some clutter and potentially an unbalanced appearance.

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7.4.3 Option 2AA The next progression of surface floodlighting included another group of floodlights mounted at the top of the towers to light the inside face of the towers. These additional floodlights would add symmetry to the illuminated surfaces of the bridge and also increase the visual interest to the motorist passing over the bridge. Figure 7‐13. Lighting Option 2aa When using the white light the floodlights did seem to more evenly balance the bridge. From the roadway the lighting also helped accentuate the full tower height. The color change option however did not produce the same results. The roadway lighting, particularly with the higher angle forward distribution tended to wash out the color impact of the floodlights and make the effect somewhat muddy and inconsistent.

Figure 7‐14. Lighting Option 2bb

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7.4.4 Option 3 Option 3 investigated the use of a conventional method of cable lighting. Cable lighting for bridges can be done in two ways resulting in different effects. The most often used method is floodlights mounted at the base of the cable aimed along its length towards the tower. This type of lighting tends to uniformly light the cables regardless of the viewing direction. Cable grazing is another lighting method where the floodlights are arranged along the bridge and aimed vertically, grazing the cables. With this type of arrangement the cables appear more brightly lit on the side of the tower where the observer is located. When the observer changes, so does the location of perceived brightness for the cables. For this alternative however the first method was used aiming along the cables. This option can be done with standard metal halide floodlights or with LED Figure 7‐15. Lighting Option 3 floodlights. While this arrangement does give the towers a strong visual appearance from a driver’s perspective it ignores the lower portion of the towers and front faces by only illuminating the outside face.

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7.4.5 Option 4 The last option investigated was various arrangements of direct view sources. In this type of option, lower wattage sources using globes or opaque lenses are used to “dot” or line the structure with points of light. The most commonly used application of this type of Figure 7‐16. Lighting Option 4a lighting is the a necklace lighting system often used on suspension bridges. While useful as necklace lighting where the curving arch of the main cables are highlighted by the points of light, it only seemed to detract from the strong structural elements that make up the St. Croix Bridge design. Figure 7‐17. Lighting Option 4b 7.4.6 Preferred Option As a result of discussing the various options and considering the long standing concerns about environmental impacts, spill lighting, conflict with the natural beauty of the river and surrounding area, the simple and subtle approach seemed to be Option 1A. Also from a bridge Figure 7‐18. Preferred Option—View from aesthetic standpoint, the Sunnyside Marina organic and graceful design of the bridge seemed better complemented by a more natural “moonlit” glow than a strong “feature” type of lighting system.

Figure 7‐19. Preferred Option—View from Stillwater

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This option using lower pier LED floodlights as the only added lighting to the roadway and pedestrian lighting was generally agreed to be the correct approach. To arrive at the proper balance of lighting in this situation and environment will require a strict criteria and explicit specifications in the RFP Figure 7‐20. Preferred Option—View Looking North documents to achieve the desired results. This can be done by using the calculated results of the current design as the light level criteria for various surfaces of the bridge and specifying fixture output and distribution required for installation. The lower pier lighting would also be RGB color change lighting programmed with preset lighting colors which can be activated remotely. 7.5 Roadway Lighting The roadway lighting, as partially described in the architectural lighting section, is made up of median mounted 35’ poles, with 8’ davit arms, spaced at 160’ centers. The pole spacing is arranged to coincide with the 80’ tower spacing. The luminaires are 292 watt LED luminaires. For this initial analysis the luminaire used was a Beta LED 12 bar unit similar to the luminaire currently used on the St. Anthony Falls Bridge. It should also be noted that the lighting calculations were performed at the rated output and drive current of the luminaires and is therefore Figure 7‐21. Roadway Lighting higher than required. In order to extend the maintenance life of the LED’s a lower drive current will be specified in the design/build RFP so that the lighting levels are lowered to the criteria levels and the associated wattage will be reduced.

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7.6 Loop Trail Lighting The loop trail lighting consists of 40 watt LED linear luminaires, integrated into the bridge railing. The lighting levels with this added lighting meet the requirements of the IESNA for both standard and enhanced security by providing 5 lux minimum vertical illuminance. By providing this vertical illuminance, facial recognition is enhanced. This improves the pedestrian’s comfort level and sense of security while traveling over the bridge. It also helps increase object contrast in the walkway Figure 7‐22. Loop Trail Lighting Using Linear area which will aid cyclists in Luminaires seeing unexpected obstacles. 7.7 Navigation and Obstruction Lighting Even though there is no defined navigable channel by the Coast Guard in the area of the proposed bridge, concerns were raised about the visibility of the bridge piers by boaters. The current option includes pier accent lighting but those lights may not be in operation during all the hours of darkness. As a result, bridge navigation lights are proposed to be placed near the bottom of each of the piers, one on each side. These lights would utilize LED sources to increase their operating life. FAA obstruction lights will be required at the top of the towers. Two of these lights would be used on each of the towers. These lights are omni‐direction, red obstruction lights and would also use LED Figure 7‐23. Navigation and technology to lengthen their service life. Obstruction Lights 7.8 Light Trespass / Glare / Environmental Impacts Because of the concerns contained in the Visual Quality Manual and from the meetings discussing the project, minimizing light trespass, glare, and sky glow were key design elements. The use of LED luminaires allows for precise control of lighting both in the beam size but also by controlling the output of the LED’s. For this concept design the following approaches were used to minimize environmental impacts:  Lighting was designed to meet the minimum recommended values of the IESNA.  Lighting for the preferred option has limited uplight. The floodlights used at the bottom of the piers are narrow distribution LEDs with most light contained, and blocked, by the bridge deck.

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 The proposed control system for the lighting would leave the roadway lighting system on, but turn off both the architectural lighting and the pedestrian lighting at a predetermined time (possibly 12AM). By using the navigation lighting the pier lighting is not required throughout the night. For the trail lighting the basic horizontal illuminance requirements for the sidewalk can be met with the roadway lighting system. The enhanced vertical illumination however will not be met but it is anticipated that pedestrian volumes will be very low and therefore unnecessary.  Veiling luminance calculations have been performed to make sure the lighting system provided limits disability glare to the prescribed limits of the IES. 7.9 System Maintenance Maintenance was a strong consideration when evaluating proposed lighting systems and source types. The use of LED technology minimizes the relamping requirements. Also the use of reduced current operation extends the life and overall efficiency of the LEDs considerably. For the systems proposed we anticipate a minimum of a 10 year source life. After this time the LEDs and drivers would need to be replaced, with the next generation of LEDs gaining additional life expectancy and efficiency. Some key considerations when reviewing the proposed system include:  The lower pier floodlights and pier navigation lights will need to be maintained from the water level. That would mean the use of a boat or small barge with ladders/scaffolds when the LEDs have reached their end of life. The control system proposed and short “on” duration will likely yield a much longer than 10 year service cycle but maintenance predictions included in this report have been kept conservative.  The obstruction lights on the tower would be maintained by access through the towers  The roadway lighting would be maintained by conventional means, most likely requiring a lane closure on both sides of the roadway  The trail pedestrian lighting system would require replacement of the LED strip after the 10+ year expected life. Again the life is a very conservative estimate based on the proposed control system and hours of operation. 7.10 Box Section Inspection Lighting The interior of the box section of the bridge will be accessed for periodic inspection. In order to support these inspections, a lighting and control system, as well as maintenance receptacles, is used within the box. For Figure 7‐24. LED Utility this project, it is proposed to use LED utility lights within Light the box, controlled by 3 way switches and timer and/or occupancy sensors. The timer/sensors are used for turning the lighting off, if it has inadvertently been left illuminated after an inspection.

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7.11 Signing The signing limits for the St Croix River Crossing will include the entire bridge and approximately 100 feet beyond the ends of the bridge. The purpose of the signing is to convey the necessary information in a comprehensible manner allowing the driver adequate time to initiate any allowable action required in a safe manner. 7.11.1 Review of the Visual Figure 7‐25. Typical Inspection Lighting Quality Manual The location of signs will be based on current sign placement standards adopted by Mn/DOT and WisDOT and where possible, will be placed in the roadside consistent with the VQM. Mn/DOT has additionally stated that they did not want any large overhead signs mounted in the median of the bridge. Where overhead sign structures are required, they should be a neutral gray in color in accordance with the VQM. However, Mn/DOT, in contrast to the VQM, has specifically required that all overhead sign structures use the standard truss style configuration mounted onto a standard sign post or where possible connected directly to the pier columns in an unobtrusive acceptable manner. The exact elevation of the sign truss shall be consistent with adopted Mn/DOT standards for overhead signing and will be a function of the sign panel sizes being accommodated. The truss should also be mounted so as to allow for the possibility of adding a future walkway and sign lighting system. Where it is required that signs be mounted on a bridge overpass to serve the motorists on the under passing road, the signs should be attached in an unobtrusive manner consistent with the VQM. Where possible, that shall mean the top of the sign should not extend above the bridge rail and the bottom of the sign should not extend below the bottom of the structure. The current signing concept only depicts one sign to be mounted on each sign truss at each location. As a result there is no contradiction with the VQM requirement that all signs on the same structure have the same vertical dimension and are mounted at the same elevation. 7.11.2 Additional Concept Refinements All other signing beyond the limits of the project or not directly attached to the bridge structure itself shall be provided for by others under a separate contract.

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Additional signing for delineators, markers, speed limits, route confirmation signs, and trail signs shall be located as need and defined by the Contractor and approved by Mn/DOT. As a result of eliminating the median mounted overhead sign structures, the structure for the begin and end junction signs have not been defined at the time of this writing as to if they will be mounted overhead or mounted off to the side of the bridge or ground mounted. Further discussion is needed to finalize this element.

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St. Croix River Crossing Preliminary Engineering Concept Refinement Report

8 Visual Quality

8.1 Introduction The visual appearance of the St. Croix River Crossing and the context of the bridge environs are a critical factor in the design development of the bridge. As the SFEIS was developed between 2004 and 2006, the extradosed bridge type was select for the main river crossing through an extensive stakeholder process that involved local state and federal government agencies, as well as, local and national citizen organizations. In parallel with the SFEIS process, a VQM was developed to outline the aesthetic values for the project. A VQRC with member participation from all of the stakeholder groups was a key part of the visual quality process. In addition the VQM process included a public open house to gather public input for the aesthetic development of the bridge. Through the VQM process, a preferred architectural treatment was selected from a number of options. The preferred concept is called “Organic” to compliment the natural forms of the setting. The VQM describes the Organic concept as “characterized by curved planes, tapered forms, smooth surfaces, and expressed joints between parts.” In the preliminary engineering phase of the project, the stakeholder involvement has been continued with the formation of a VQAC. The VQAC is made up of a subset of the VQRC member organizations, and includes the following members:  City of Bayport, MN  City of Oak Park Heights, MN  City of Stillwater, MN  Town of St. Joseph, WI  Minnesota State Historic Preservation Office  National Park Service The purpose of the VQAC is to:  Perpetuate the work that has been accomplished through the Environmental Process and Visual Quality Process  Assist the Project Team through the interpretation of the Visual Quality Manual in areas where the intent is not fully defined.  Advise the Project Team regarding refinements to the conceptual design during the preliminary engineering phase  Assist the Project Team in evaluating how newly discovered aspects discovered during preliminary engineering relate to the previously developed concept design.  Attend VQAC Meetings to offer input and comment on visual quality issues related to the preliminary engineering.  Inform the agencies or organizations that are represented of information presented or discussed with regard to the relationship between the conceptual

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design documented in the Visual Quality Manual and the preliminary engineering design. In addition, public involvement was continued through two open houses, where the concept refinement was presented for public input and comment. 8.2 Objectives The specific objectives of the concept refinement through the preliminary engineering phase include:  Collaborate with the structural discipline to study and execute refinements of the concept design using the VQM for guidance.  Develop architectural drawings that support proposed structural design concepts and compliment the intent described in the VQM including: o 2D drawings showing the various concept refinements. o 2D lighting drawings showing the river bridge at night, on the river up and down stream and on the roadway from the Minnesota and Wisconsin sides. o 2D drawings to describe the design intent to both the professional and the layman. o 2D CAD drawings indicating accurate scale and proportion to be used for discussion purposes with the Design Team and the VQAC o 2D CAD drawings developed for formal presentations to the DOT’s, other agencies, and the public at large. o Refinements to the concepts presented in the VQM, such as further design refinement of the two‐column vs. three‐column piers, to be presented to obtain concurrence of the Design Team and input from the VQAC on the refinements.  Provide input to the Mn/DOT Visualization Unit for their preparation of photo‐ realistic renderings of the bridge in both daytime and nighttime simulations. 8.3 Refinement Process The VQM presents a concept design and visual, functional, and engineering guidance for the further development of the concept design. The VQM defines the selected “Organic” concept as:  The parts look as if they were found in nature, or shaped by natural forces.  The vertical pier forms are reed‐like; the girders are rounded and tapered like bones or tree branches; and walls, barriers and railings are curved and blended into the larger forms.  Transitions are gradual and smooth; edges are soft and curved; and colors are unified and natural expressions of their materials. In preparation for the concept refinement and as part of the preliminary engineering, the concept design was reviewed and evaluated to more fully understand these defining principles of the concept. The refinement of the concept required close collaboration between the architectural discipline and the structural

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discipline, so that the aesthetic values outlined in the VQM are coordinated with the structural requirements of a major river crossing. The outward appearance of the bridge and its relationship to the bluffs, wetlands, and river are of utmost importance, but the structural integrity of the bridge is the backbone that supports that visual experience. The bridge structure must be functional and economical while expressing the intended context sensitive design. With these values in mind, the focus of the Visual Quality effort was:  Pier Concept Refinement: The concept pier is a three‐column pier with two exterior columns that extend above the roadway to provide an attachment for the stay cables, while the interior column is under the bridge girders along the centerline of bridge. During development of the VQM, the preference of the VQRC was to have a two‐column pier, but a three‐column pier was included in the concept until structural investigation was performed to verify the feasibility of the two‐column pier. The “Organic” concept represents the light and elegant character desired of the river bridge, and the two‐column conveys these attributes to the fullest extent. Through technical analysis of the structure it was possible to confirm that the number of columns can be reduced from three to two. This was achievable without changing the size or form of the column while retaining the preferred shape and proportions. While the depth and width of the cross girder was also retained, it became necessary to modify the lower edge of the cross girder to provide greater contact area of the girder with the tower legs. The original concept of a curved outer edge along the cross girder was also retained though the radius of the curved edge had to be shortened to increase the necessary surface area. This has resulted in a slightly different but acceptable visual appearance of the cross girder.

Figure 8‐1. Section View Illustrates Curved Outside Edges of Cross Girder

 Pier Column Shape Refinement: The pier column shape depicted in the VQM has variable dimensions from top to bottom of column creating a tapered cylindrical cross‐section that is slightly canted toward the bridge centerline as the column extend upward from the water. The Cost Risk Assessment and Value Engineering

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(CRAVE) study undertaken in late 2008, recommended that the pier column shape be simplified to improve constructability and provide cost savings. A number of refinements were explored but the one chosen retains the visual character of the VQM column while providing a greater level of constructability. The chosen refined design consists of a uniform sloping and canted exterior on three outside column faces while the inboard face is vertical and uniformly tapered. To achieve this, short tangent segments were introduced into the column section on all four sides so that transitional blocking could be more easily introduced into the formwork. The interior face of the twin column sections above the roadway deck line where closed with a single tangent. This was in part to enhance constructability and to reduce cost. Near the base of the river columns, a sloped concrete fill is proposed. This fill area is to be located at the surface water elevation and slope upward closing the hollow column form. The purpose for the fill is to prevent unauthorized entry of small vessels or persons. It will also protect the columns from ice intrusion and reduce lodging of drift.

Figure 8‐2. Tangent Segments Have Been Introduced Along Vertical Faces of Tower Forms for Ease of Construction

Pedestrian Trail Location: In the VQM concept, the pedestrian trail cantilevers from the north edge of the bridge girder outboard of the north plane cable stays (outboard scenario). This requires the trail to curve outward and around the north column at each of the piers. The CRAVE study recommended that the pedestrian trail be relocated onto the bridge girder, placing the trail inboard of the north cable plane. The recommendation is based on improved constructability, improved

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operations, maintenance and inspection, and potential cost savings. With the trail inboard of the cables, interference between pedestrian/bicycle travel and the cables is eliminated, and pedestrians can be removed from the through traffic of the trail by placing overlooks at the piers. Both the outboard and inboard trail locations were evaluated for constructability, safety, operations and maintenance, cost savings and visual characteristics. The two scenarios were modeled and compared and contrasted. The analysis concluded that the inboard trail concept provides superior safety, operations and maintenance characteristics. These include ease of access for safety, emergency, snow removal and maintenance vehicles. Pedestrian movements are linear providing greater user safety as the alignment affords trail users a clear sight lines along the entire length of the bridge. Lighting is more easily and efficiently accomplished as roadway lighting systems are adequate to provide pedestrian lighting needs for certain use conditions and in times of higher use, it is easily supplemented with low level lighting located within the hand rail. The inboard trail separates users from the cable systems of the bridge yet still provides ample viewing of the structure and its’ components as well as views to the river beyond.

Figure 8‐3. View along pedestrian trail located inside of tower line

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Figure 8‐4. Section view of trail located on north edge along west bound travel lanes

 Pedestrian Trail Overlook: The VQM concept does not have specific locations designated for pedestrians to stop along the bridge and view the river. The inboard trail provides the opportunity to use the space adjacent to the north column at each pier as an overlook. This will provide space off of the through trail alignment for pedestrians to enjoy the scenic river valley, while separated from bicycle traffic. The overlook concept is the result of moving the trail inboard of the tower line. The overlook concept was developed to take advantage of the opportunity for non motorized bridge users to have an unobstructed view of the river north of the bridge. The overlooks are cantilevered platforms that extend out over the water from the tower locations. The overlooks provide a resting and viewing area which is out of the flow of non motorized traffic and away from the vehicular roadway and provide a commanding view of the river and bluffs. Because the overlooks are not part of the through trail facility, the option was explored to construct an overlook at alternating tower lines. This further refinement of the overlook concept has resulted in the recommendation to include four overlooks on the bridge. They are to occur at three locations, pier lines 9, 11, and 13. The underside of the overlook structure was also studied in detail. The design team considered the platform underside as an opportunity to provide a dynamic daytime element and to use lighting at night to accentuate this feature.

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Figure 8‐5. Typical Pedestrian Overlook outside of tower on north elevation of bridge

Figure 8‐6. View of underside of Pedestrian overlook surrounding tower

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 Pedestrian Trail Railing: The VQM concept is a full height metal railing with a short concrete curb. The pedestrian rail provides a number of opportunities for input from the VQAC related to curb height and railing details including trail lighting fixtures built into the railing. The pedestrian railing design was refined to simplify the rail as much as possible while still maintaining the principles identified in the VQM. Both a full height rail with short curb and a taller curb with shorter rail were evaluated. The taller rail was complicated in design. The rail has to meet safety requirement for containment up to a height of 27” with a 4” vertical bar spacing and then 6” minimum vertical bar spacing thereafter. Both a 4” spaced rail and a combined 4” and 6” spaced rail were modeled and illustrated. These designs resulted in complicated and or visually dense appearance. Both of these designs impeded the view to the river and increased construction cost. It was also noted that these full height rail options with small curb also would be subjected to greater mechanical damage from snow removal operations and other maintenance activities. The chosen rail consists of a taller concrete curb upon which the metal rail is attached. The added curb height of 21‐3/4 inches allows the metal railing to be constructed solely with 6‐inch center to center separation which reduces the amount of material, as well as visually “lightens” the railing making it more transparent and more easily seen through. The design of the rail can easily be fabricated in modules which will reduce cost, and enhance constructability and maintenance operations. To increase the levels of lighting on the trail, the railing posts have been designed in paired arrangement which provides a nesting location for the small LED lighting fixture. This design provides protection for the lighting while reducing the visual prominence of the fixtures.

Figure 8‐7. Higher curb height with 6” vertical picket spacing and integral LED light fixtures incorporated into post on pedestrian hand railing.

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 Cable Anchorages: The VQM Concept has portrayed individual cable anchor “pods” attached to the side of the box girder. This provides a certain texture to the side of the bridge and exposes the supporting elements as part of the overall visual appearance of the bridge. Refinement of the pods was performed to confirm the structural dimensions needed to support the bridge and to maintain the architectural details to provide a coordinated and smooth transition of the pod into the girders. Two alternative cable connection details were studied. The exposed connection as illustrated in the VQM and an alternative called a covered cable concept. The structural requirements for the anchorages were determined and can be easily met with either style. The motivation to evaluate alternative connection options was largely as a result of visual consistency concerns of the design team. Both alternatives were modeled and illustrated for the VQAC and Mn/DOT. The VQAC unanimously chose the covered cable alternative because it supported the linear form of the main bridge elements more effectively than the exposed cable connection scenario. There are also some construction, maintenance and operations benefits to the covered scenario as it easier to build, and provides a greater level of protection for the cable terminations on the underside of the deck without limiting inspection access to cable anchorages.

Figure 8‐8. North elevation view of structure with covered cable connections

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Minnesota approach Structures: The VQM design of the Minnesota Approach included a pier design composed of tapered columns in pairs. The columns are sloped at 1:33 and the pairs are separated by 10’. Two alternative column forms were studied and modeled. This included a paired column concept which reduced the slope to 1:66 and the separation between the pair to 5” Figure 8‐9. Enlarged view of covered cable between columns. The other connections concept was a single stem design utilizing the 1:66 taper and reveals along the edges of the single column form. The two alternatives were modeled and illustrated from various view points along the Minnesota shore and adjacent river locations. It was determined that the single tapered column form performed visually as well if not better than the pair alternative and it was easier to construct. The VQAC and Mn/DOT agreed the single column form was acceptable.

Figure 8‐10. View of Battered Abutment (Left) and Typical Single Stem Pier (Right) along Minnesota Approach

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9 Construction

9.1 Introduction This section discusses what are considered to be some of the more critical construction issues for both land based construction and construction of the river spans that will need to be addressed for the successful construction of the project. In addition, construction of major bridges requires that constructability be investigated and evaluated at every stage of design development as well as during construction as the successful Design‐Build (DB) Contractor plans the construction of the work. This constructability analysis is performed to ensure that the completed bridge will be fully compliant with the contract requirements and that acceptable standards for construction means and methods have been met. 9.2 Construction Staging Areas Construction staging areas will be required for the river crossing bridge work and for the approach structures. Some of these will fall within the construction limits while some may be located nearby. There are very limited areas for construction staging adjacent to the project area because of the complexity of the terrain, the wetlands, the river way, and numerous man‐made features. Therefore it may be necessary for the DB Contractor to make arrangements for additional staging areas as necessary to support his construction needs. The Contract documents should make clear what potential staging areas are available to the contractor as well as that he is responsible for any additional staging areas that he deems may be required. 9.3 Casting Yard In addition to construction staging areas, if the DB Contractor elects to use precast construction for the approach spans, the river spans, or both, it will be necessary to utilize an existing casting yard facility or to set up a new facility specifically for this project. Either way, the casting yard will need to have sufficient area for the precast operations, storage of materials and storage of an inventory for precast segments. It can be expected that for a project of this size, a parcel of land that is 20 acres or more may be needed for a new casting yard facility. It is not unusual that storage of approximately one third of the total number of segments may be required though this is clearly dependent on the planned and actual schedule for precasting and erection. 9.4 Precast vs. Cast­in­place Construction The DB Contractor may elect to utilize either precast or cast‐in‐place construction methods or a combination thereof perhaps differentiating between the approaches and the river crossing. Both methods are considered viable options and the selection will be made in consideration of the contractor’s experience and preference, availability of equipment, as well as precast plant considerations including transport, schedule and economics.

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Some of the pros and cons of each construction method include the following. 9.4.1 Precast Construction  With over 5000 linear feet of bridge deck there is an opportunity for cost effective utilization of precast segmental construction. The river crossing will have constant depth segments and the approaches will transition to a shallower depth consistent with the shorter spans. Maintaining a constant depth simplifies and reduces the cost of precast forms and allows for improved efficiency.  If the schedule allows, precast operations could be set up indoors to allow year round production of segments.  One advantage of precast construction is that precasting can proceed concurrent with construction of substructure elements to further shorten the schedule.  Dependent on the location of the casting facility, transport of segments to the erection site by barge and positioning the segments for lifting could be very efficient. The smaller approach segments would more likely be transported by truck.  Precast segment height is expected to be in a range from 10 feet to 16 feet, approximately 10 feet long and up to 52 feet wide.  Precast segment weights are expected to be in the range of 145 to 160 tons which would require use of special haulers. Haul routes from the proposed casting yard to the jobsite must be checked for any special restrictions or permits that may apply.  Utilizing precast segments would limit the amount of concrete to be delivered on the river to the piers, towers and some limited cast‐in‐place superstructure closure joints.  The repetitious nature of precasting segments in a “factory” style environment tends to lead to a higher quality of finished concrete product.  On the downside the precast method requires the use of either an existing precast facility or establishment of a new facility for the project.  Some existing casting yards known to exist within a 100 mile radius of the project site that could be considered include three commercial facilities constructing precast bridge beams and pipe products and one contractor owned facility previously utilized for precast segments.  Even if the precast method is selected, some cast‐in‐place work would still be required on approaches at the transition sections.  Erection can be ongoing at multiple locations and can share erection equipment.  Erection in winter months can proceed provided heated enclosures are used and provisions are made for curing of epoxy joints and cast‐in‐place joints. It can be expected that there may be times when it is simply too cold to proceed with erection even with such measures being taken.

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9.4.2 Cast­in­ Place Construction  Again, the large quantity of bridge deck construction offers efficiency if the DB Contractor elects to use travelers for cast‐in‐place construction, particularly for spans over the water.  Cast‐in‐place work on the approaches could, alternatively, be done on falsework rather than by use of travelers.  The travelers can be easily shipped to site by barge or truck.  Cast‐in‐place deck construction over water would be more likely to be restricted during severe low temperatures from mid‐December to mid‐March. Both methods require the use of specialized equipment and previous experience in this type of construction should be mandatory including PT tendon installation and tensioning and grouting. It is customary to require at least two previous projects or a minimum of 5 years experience. Given the limited construction of extradosed structures in the US, it may not be practical to include a similar requirement for the St Croix River Crossing, though, requiring supervisory personnel to have experience with the construction of at least two segmental or cable‐stayed structures in the last 10 years should be considered. In order to provide for segment erection to proceed through winter months, special attention must be paid to grouting of tendons. If allowed by the Specifications, tendon grouting may be postponed in the winter months by the use of a corrosion inhibitor until substrate temperatures rise again where freezing of freshly placed grout is no longer a concern. 9.5 Permitting Requirements The Minnesota side of the river bridge has environmental restrictions with a high quality wetland in the area, very limited access, and other bluff impacts. The Wisconsin side of the river has bluff impacts and mussel beds adjacent to the shore. It is essential that the permitting is established based on reasonable assumptions of how the bridge construction is to be carried out. Provisions need to be included for the delivery and site relocations of large pieces of equipment such as cranes, travelers, haulers, dirt moving equipment. This will require temporary haul roads throughout the project limits extending to the river from TH 36 and STH 35. Consideration needs to be given at this stage for permanent access typically in the form of a 12‐ to 15‐foot wide corridor paralleling each structure. Access to Pier 14 on the Wisconsin bluff will be particularly challenging as the grade drops approximately 200 feet from STH 35 to the river. It is important that the land acquisition on the Wisconsin side provide for switch backing of the access road as needed. It is noted that the concept drawing titled “Wetland Impact Details” includes an aerial view of the Minnesota approach spans area showing temporary and permanent access roads as well as areas that are expected to be impacted less than and greater than 6 months during construction. It is recommended that the

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Contractor be given some flexibility to develop his own means and methods that could affect those areas perhaps by defining a limiting impact assessment and the permitting requirements by the appropriate agencies for any DB Contractor proposed deviations from what has been indicated. 9.6 Erosion Control and Environmental Compliance Given the sensitivity of the wetland areas and watercourses that the project is to be constructed over, it is essential that erosion control measures be employed during construction. Erosion control must also be considered during design so that the contract documents adequately spell out the minimum requirements and restrictions with which the DB Contractor must comply. For the land based construction, this will be primarily based on standard best management practices (BMP) for erosion and sediment control, establishment of construction limits, signage, spill prevention and control, training of the workforce in environmental awareness and monitoring. For work over water, the Contractor must plan his operations and control the work to prevent contamination of the watercourse particularly during cofferdam installation, excavation, trestle construction, barge movements and spudding/anchoring, dredging, handling and disposal of drill shaft spoils, equipment fueling and accidental spillage. It is recommended that there be at least one individual on the contractor’s staff whose sole responsibility is environmental compliance. Consideration should also be given to creating a line item for environmental compliance items so that Mn/DOT and Wis/DOT can control and exactly what is required in this area. 9.7 Foundation Construction Methods A cofferdam is anticipated to be constructed at each pier for the construction of the drilled shaft foundation cap since the top of the structural cap is assumed to be at the mudline or approx 20 feet below waterline. The cofferdam could be installed before or after installing the steel casings and drilled shafts. If built prior to the drilling of the shafts, the cofferdam could serve as a template for shaft construction. Once the cofferdam frame work and steel sheeting is in place with several bracing tiers that act as a drilled shaft liner template, the drilled shaft operation can begin. Each drilled shaft casing will be placed by a large crane on a barge and driven by a vibratory hammer to just above the top of rock. All of the casings for each pier will be placed prior to any drilling of the shafts. Subsequent to placing the pier casings, a drill rig and the appropriate support equipment such as a mud plant, drilling tools and a scow will be mobilized to begin drilling the shafts and rock sockets. Once the rock socket is complete, an airlift can be used for cleaning the shaft by recycling the drilling fluid though the mud plant which separates the fluid from the suspended solids and allows the clean fluid to pass back to the drilled shaft. The placement of the reinforcing cage will follow the cleaning process and will require a

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large crane due to the weight of the reinforcing which will likely be spliced in several sections. Tremies and CSL tubes will be placed prior to the concrete placement in each drilled shaft. Due to the large quantity of concrete needed for each drilled shaft, a barge mounted concrete batch plant may prove economically feasible. Upon completion of the drilled shafts within the pier cofferdam, excavation for the tremie seal can take place by using a water jet and an airlift coupled with a mud plant and scow. Once excavated, concrete for the tremie seal will be placed up to an elevation just short of the bottom of the foundation cap. It will be necessary to trim the seal to remove laitance and humps from the tremie locations from protruding into the foundation cap. When the trimming of the seal is complete, forming and placement of the foundation cap and the bridge columns can then be constructed in the dry. 9.8 Substructure Pier and Tower Construction Access to the pier locations could be by barge as described above for drilled shaft operations, by a series of floating pontoons/car barges or by trestle. Floating pontoons would be quick to install and could be more easily reconfigured as work progresses. Trestle construction would have the advantage of being off the water and would not have to consider access and movements during winter months when the river will be frozen. Either of these methods might be considered for perhaps just one or two piers from either shore which would still leave the center spans open for navigation. Whichever option is selected, it will be subject to USCG approval and permitting. The pier and tower construction will require delivery of rebar and concrete and will require crane support. With the height of the towers exceeding 200 feet above the water level, it may be efficient to utilize tower cranes supported on the permanent pile caps. The tower cranes would also be able to service the towerhead assemblies, stay anchor boxes, cable installation and tensioning. The unique pier and tower cross section will pose some challenges in forming and may limit the amount of reuse that each form can fulfill on a single column but should permit reuse on other piers and towers. It can be expected that the pier/tower construction will be made in approximately ten lifts including three or four lifts for the towerhead incorporating the stay anchor assemblies. 9.9 Reinforcing steel arrangements congestion and detailing Since this is a Design‐Build project, it is to be expected that the DB Engineer of Record’s (EoR) design drawings will be detailed such that rebar shop drawings are not necessary. This would require that the detailer provide complete details and bar bending diagrams for construction and to verify and resolve conflicts with stay

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hardware, PT hardware and any other embeds required, such as ladders and platforms or mechanical and electrical installations in the towers. The DB EoR should also be responsible for identifying possible conflicts and for their resolution in the development of the design drawings. The design drawings should also identify any elements that are fracture critical such as components of the stay anchor assemblies in the tower heads and should provide clear requirements for all welds sizes, weld classification and NDE requirements. 9.10 Post­tensioning tendons and grouting Complete details of the post‐tensioning system must be provided by the post‐ tensioning supplier. This should include records of all testing and material test certificates that indicate compliance with the contract requirements. As stated in the previous section, it is the responsibility of the EoR to ensure reinforcement detailing is compatible with the post‐tensioning system and cable stay hardware and that dimensional conflicts are resolved on the design drawings, not in the field. Tensioning and grouting of the system should be performed by trained and experienced personnel. American Segmental Bridge Institute certification for the tensioning and grouting personnel is recommended. These operations also warrant close inspection by QC personnel to ensure that the work is performed in compliance with contract requirements to ensure that the life of the structure is not compromised by lack of attention to detail. Consideration should be given to inclusion of mock up tendon grouting to demonstrate adequacy of grouting equipment and methods and for training of grouting crews. 9.11 Stay Installation For an extradosed structure, cable tensioning more closely resembles post‐ tensioning tendon stressing than the operations that are unique to cable stayed bridge construction. The means and methods for the installation of the stay pipes and for installation of the tendons do however need to be carefully planned and carried out such that these critical elements are not damaged during construction. 9.12 Special architectural forming and finishing It is noted that special architectural forming and finishing has been identified for this structure. This relates to the form and shape of the piers, towers and the superstructure. These are the result of the findings and recommendations contained in the Visual Quality Manual (January 2007) as well as the ongoing concept refinement process It should be recognized that there will be a premium cost associated with the special architectural forming and finishing and the Contract documents must be clear on what opportunity the DB Contractor may have to propose alternate forms for any of these elements and the process for approval of any such deviations.

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9.13 Industry forum An industry forum was held during the ASBI annual convention on Oct 25, 2009. At the forum contractors were briefed on the conceptual details for the St Croix River Crossing project and the schedule for procurement and for construction. This served as a briefing to allow attending contractors to learn something about the Project. It is recommended that a more formal forum be held prior to issuing the RFP to gather additional contractor input.

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10 Maintenance and Inspection

10.1 Introduction Maintenance and Inspection are very critical considerations for any bridge project particularly so when the bridge may be outside of the typical bridge construction practice as is the case for the St Croix River Crossing utilizing extradosed spans that are relatively uncommon in the US. The extradosed river spans for the St. Croix River Crossing will require a specific maintenance and inspection strategy. Access to critical components of the structure for maintenance and inspection must be incorporated into the design development, and specific maintenance and inspection procedures must be developed for the long‐life expected for the structure. 10.2 Critical Elements Operation, inspection, maintenance and access requirements for each of the following items listed below must be addressed in the RFP documents. The Contractor will be required to address each of those requirements during the final design. Deliverables from the successful DB Contractor should also include an Operation, Inspection and Maintenance Manual prepared specifically for the St Croix River Crossing. The manual must include comprehensive details for each component of the bridge including a list of components likely to require replacement within the expected life of the structure. Items that will require ongoing operation and maintenance include:  Anti‐icing system  Bridge Lighting  Navigation Lighting  Aviation Lighting  Lighting inside the bridge  Lighting inside the towers  Drainage  Signage It is anticipated that these elements will be inspected at least once per year but may require immediate attention should something cease to function at any time. Life expectancy of these items is less than the structure life expectancy and will likely require full replacement a number of times over the life of the structure. Items that will require inspection and periodic maintenance include:  Bearings  Expansion joints  Overlay  Painted surfaces

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It is recommended that these items be inspected every two years and in the event that any unusual structure behavior or event has occurred. It can be expected that these elements or components of them such as bearing pads, will also have to be replaced a number of times over the expected life of the structure. Items that will require inspection and may require periodic maintenance include:  Cables and Protection Systems  Anchorage systems  Post‐tensioning systems  Concrete substructure elements  Concrete superstructure elements  Foundations including river piers below water These are critical support elements of the structure and if constructed with care and attention to detail should provide service for the life of the structure with little maintenance. They should however all be inspected bi‐annually to observe any changes in service and any indications of distress must be investigated and addressed. Access is a key aspect of any inspection program and it will be necessary to make sure that equipment is available for regular inspection as indicated above. This will be particularly the case for inspection of the exterior surfaces of the superstructure elements of the river spans and the towers above deck. It will be important that underbridge snoopers or manlifts that are currently in service will be able to reach to those areas. Substructure piers will require inspection from a manlift mounted on a barge. For the Approach structures it will be important that permanent access be constructed and maintained for future maintenance and inspection. This is particularly important where there are wetlands adjacent to the bridge.

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