s water leaves the south- ern tip of in Athe swift-moving Saint Clair River, it forms an interna- tional boundary between and . For almost 60 years international access between Port Huron, MI, and Point Edward, Ontario, has been provided by a cantilever built near the north end of the river. The Michigan Department of Transportation and The Bridge Authority in Ontario jointly own and operate this cantilever bridge - each col- lects tolls from traffic entering the bridge, and traffic leaving the bridge passes through cus- toms and immigration on each end. About 60 years ago, the firm of Modjeski and Masters, Inc. designed the river crossing and supervised its construction. This bridge is a Port Huron landmark and has become an integral part of the local heritage. The success of the crossing at this location has led to a steady growth of traffic and the anticipation of an additional bridge for a second crossing. Recent surges in the traffic volume led the Owners to begin work on the Second Blue Water Bridge years earlier than INTERNATIONAL anticipated. DESIGN OF THE NEW BRIDGE The Joint Venture of Modjeski CONNECTION and Masters, Inc. from Pennsylvania and Buckland & Taylor, Ltd. from British The Blue Water Bridge, which Columbia were retained in 1993 by the Owners to develop studies connects Port Huron in Michigan to and plans for the new bridge. The first phase of the work was Ontario, is one of the first major to prepare engineering studies for the new crossing and develop bridges to use LRFD and SI units a Study Report. In late 1993, a Study Report By Joseph E. Prickett, P.E., Brian D. Morgenstern, P.Eng., was issued indicating that six P.E., John M. Kulicki, P.E., P.Eng., Ph.D., bridge forms would be suitable and Roger A. Dorton, P.Eng., Ph.D. for the new crossing: • steel cable-stayed bridge; • concrete cable-stayed bridge; • a duplicate truss; • a parallel chord truss; • a simple span tied arch; and • a continuous tied arch.

Modern Steel Construction / October 1997 ed with approaches of box gird- ers and multi-girder spans. A requirement for the main bridge construction was that the work be divided equally between the Owners, and that the construc- tion be equally divided between a contractor from Canada and one from the United States in a joint venture contract, which dic- tated that at least two fabrica- tors and two steel suppliers would be required. A consider- able effort was required during the design to ensure that the details, materials, standards and procedures in the plans were proper for construction in both countries. The main span deck is rein- forced concrete for three traffic lanes and a pedestrian sidewalk. The slab thickness was set at 7” in order to reduce dead load on the main span. The roadway has a bituminous wearing surface, and the sidewalk has a latex modified concrete overlay. The stringers are rolled beam sec- tions, made continuous and com- posite with the deck slab. The floorbeams are welded I-sections with welded transverse stiffen- ers. Steep roadway grades (4.65 percent) and channel clearance Shown at top is the Second Blue Discussions, evaluations and requirements resulted in a shal- Water Bridge under construction with economics of each of these types low superstructure depth. This the First Blue Water Bridge pictured in were presented in the Study limited the available web depth the background. Pictured above is a for the floorbeams, resulting in line drawing of the First Blue Water Report to the owners with a Bridge. matrix recommended for evalu- the need for intermediate floor- ating and choosing a type to be beams between vertical loca- carried into final design. tions. Welded I-members were The preliminary cross-section used for the floor system lateral was established as a three-lane bracing. deck with sidewalk, traffic barri- Under dead load only, an ers and pedestrian railing. The uplift condition would occur at preferred alignment adjacent to the anchor span end bearings. A the existing bridge was set. All counterweight was added to pro- project documents would be com- vide a positive reaction under all pleted in S.I. units. The design loading conditions, except the would conform to the new most extreme live load case, and AASHTO LRFD Bridge Design the bearings here are designed to Specifications and major provi- resist the uplift resulting from sions of the Ontario Highway that case. The floor system at Bridge Design Code (OHBDC), the anchor end required modifi- with the LRFD being the prima- cation to accept a concrete coun- ry specification. terweight. Intermediate stringers were added to the typi- SELECTED STRUCTURE cal cross-section in the two end For the main river crossing, a panels. Stringer depth was continuous tied arch was select- increased to 36” in these two

Modern Steel Construction / October 1997 panels to support the concrete supports the bridge deck, was arch structure, then under mass. The stringers were coped chosen to be the principal mem- Federal moratorium, acceptable over the floorbeams to accommo- ber and it is proportioned to be to the Owners. Clearly, mitiga- date their increased depth. considerably stiffer than the tion measures translate into Power driven, rail-mounted arch rib. additional, but necessary, costs. platform travelers provide access This bridge layout consists of If the tie were a steel box assem- to the underside of the deck and several basic segments. The bled by welding, it is possible floor system. One traveler rests main support framing consists of that, under the impact of varying near the anchor piers at each the end segments made up of the loading, a crack might propagate end of the bridge, and each is anchor spans (85 meters) and across the entire member (using capable of traversing the entire those portions of the main span the welds as a path from one length of the arch structure. extending from the main pier to plate to the other). For this rea- Access to the remainder of the the knuckle joints (36 meters). son, it was decided that the tie bridge is provided by an inte- These support the middle seg- girder would not contain any grated system of crosswalks, lad- ment or main arch (209 meters) welding; rather, it would be ders, stairways, railings and between the knuckle joints. assembled by high-strength handropes. The special consider- These are basically independent, bolts. Even so, a potential crack ation given to access inside the closed units, except for the flex- could propagate across one of the tie girder resulted in forced ven- ural continuity of the tie girder plates or elements of the tie gird- tilation, adequate lighting and and arch rib at the knuckle joint. er. As a safeguard, the tie girder special surface finishing of the Steel vertical columns and hang- was proportioned so that it could interior. ers connect the arch rib and the withstand the loss of any one The arch has proven to be a tie girder. Steel floorbeams sup- plate or element. These mea- successful form of span for many porting the steel floor stringers sures gave the tie girder the years. The primary load path are attached to the tie girders. internal redundancy desired and used by an arch is the curve of removed the specter of Fracture the arch itself, where the shape ARCH DETAILS Critical fabrication require- of the arch is ideally the shape of The continuous tied arch ments. the moment diagram caused by requires a number of special Temperature changes and the loading. The load is basically design considerations, as do the loads on the bridge cause move- carried in compression by the LRFD requirements, and the ments at the supports. The main arch, and at the supports a hori- demands of the Owners for this arch bearing in Ontario is fixed zontal force is needed to resist crossing. against sliding, and all the oth- the compression of the arch. A The arch rib is a box about 1.2 ers are designed for longitudinal large number of steel arch bridge meters on a side made of welded sliding. The capacity for sliding spans have been built, and many steel plates, and near each end is is provided by incorporating of these are simple spans using a a welded closure plate to seal the Teflon on polished stainless steel horizontal steel tie member from main length of the arch rib mem- within the bearing. At the end-to-end of the arch to resist bers. These sealed sections are Michigan main pier, the bearing the horizontal force of the arch. not painted, but they have been design accommodates movement Less than a half dozen continu- partially evacuated, then filled of over 300 mm. contraction and ous tied arch bridges have been with dried air and sealed. over 400 mm. expansion. A previously used in North Pressure test points are located tough flexible disk in compres- America. in the end portions of the mem- sion is a part of the bearing’s When the vertical load on the bers for long-term monitoring of support for vertical load, and arch varies, some flexural the interior pressure. permits the small rotation which strength and stiffness is required The tie girder is a steel box takes place at the support joints. since the arch cannot change its built up by bolting and it con- In addition to the bolting used shape to accommodate the sists of steel plates with corner to assemble the tie girder, all the change. The tie member is com- connecting angles - it is about member connections are made monly supported by the arch so 1.2 meters wide by 2.5 meters with high- strength bolts, and all they can act together flexurally. deep. The tie girder is the ten- the high-strength bolts are gal- In a tied arch, the bridge floor is sion member that provides the vanized. The paint system used commonly attached to the tie. sole horizontal support for the on the bridge consists of a coat of Since the tie girder and arch entire arch. In addition, it pro- zinc-rich primer, a second coat of rib act together flexurally, it is vides most of the flexural resis- epoxy, and a top coat of light possible to choose, by selective tance of the arch segments. It is grey urethane. The primer was proportioning, the member the quintessential Fracture shop applied to all surfaces of which will carry most of the flex- Critical Member and mitigation completed members, and the ural stresses. For this design, measures were proposed in the final two coats were shop applied the tie girder, which directly Study Report to make this tied to all, except faying surfaces at field connections.

Modern Steel Construction / October 1997 SPECIAL DETAILS Several locations on the arch required special study to develop arrangements and details which satisfied the requirements of structural adequacy and orderly flow of forces, aesthetics, mainte- nance, and fabrication and erec- tion. At the ends of the bridge, the tie girder and the arch rib merge into a single variable-depth box member for several panels. In merging the two members, a large compression from the arch rib combines with a large tension from the tie girder to form a moment in the single member. The interrupted flanges of the rib and tie are continued well into the joint to help accomplish this transfer. The sizes of the plates became so large it was necessary to add a longitudinal field splice along the joint to make the sizes manageable. The support joint at the main pier was a location made difficult by the fact that it is a major sup- port for the bridge, and also because of the large angle change in the arch rib. The gen- eral arrangement provides conti- nuity for the heavily loaded arch rib plates in the large weldment at the base of the column. The vertical sides of the arch rib are backed up by the vertical plate of the column; the bottom flange of the arch rib bears on the bearing plate; and a special plate was added inside the column to back up the top flanges of the rib. Large welds at close spacing is used, and the plans required the Contractor to assemble and fab- ricate one joint just to evaluate the distortion from the welding. If satisfactory, the trial assembly could, in fact, be used on the bridge. Coming riverward from the main pier, the rising arch rib intersects the tie girder. This, again, is a location where large forces must be carefully carried. It was decided to carry the rib forces through the joint in a rib section, and build the tie girder Shown above, from top to bottom: arch and cross-sections; elevation of “Y” joint; to pass by it. At adjacent splices, and shop assembly of “Y” joint.

Modern Steel Construction / October 1997 the rib was reduced in width by two plate thicknesses so it would fit between the webs of the tie girder. Additional web plates were added to the tie girder, and special connections carried the flange strength and material outboard of the tie girder webs, so it was possible to create the opening in the tie girder needed by the rib. The forces during erection were evaluated in designing the arch, as required by the LRFD Specifications. It was found that several of the shorter verticals were overstressed when erected due to the flexure caused by the combination of shop camber and erection loads. It was decided to pin these several members dur- ing erection and then make the final bolted connections after the bridge had been swung.

ARCH ERECTION Erection from the water, which would have been difficult due to the speed of the current, was banned by the Coast Guard. In accordance with the LRFD Specifications, the design plans included a feasible erection pro- cedure. This plan first erected the anchor span using temporary bents and then placed a false- work tower over the main pier. Erection of the main span was accomplished by cantilevering from this point, using stays secured at the anchor pier and passing over the tower to sup- port the river span sections. Each half of the arch was erected by a contractor from that country, and each elected to use the basic procedure shown in the plans, with minor modifications. To handle the uplift created by the cantilevering special, tie rods were set into the anchor pier footing and for attachment to the tie girder at the point of the stay attachment.

APPROACHES Three continuous steel box girder spans are used for the flanking spans placed at each Shown at left, from top to bottom: main pier joint; intersection of rib and tie; and end of the tied arch to provide detail of column relief joint. visual continuity, and beyond alone specifications were pre- pared for the main bridge and flanking spans, which was the first contract completed, and these were appropriately modi- fied for the subsequent approach contracts. These specifications were prepared in S.I. coordinat- ing the requirements of Michigan and Ontario.

LRFD SPECIFICATION The bridge was designed using the AASHTO LRFD Bridge Design Specifications, S.I. Units, First Edition, 1994. The completed edition was released shortly before the start of final design began. Specific project that the approaches vary in their a hammerhead impracticable. Design Criteria, begun during makeup to suit local conditions. the Study Phase, were developed DIVISION OF WORK The flanking spans are support- and shown on the plans. These ed by three box tube girders The main river crossing and began by establishing the LRFD about 2.1 meters deep. These the flanking spans are in a sin- as the basis for the design and girders are composite with the gle set of plans and arranged so continued with further definition concrete deck, and a plane of that each Owner and each coun- and refinement, all specific to bracing is provided for the top try’s contractor is responsible for this project. flanges. The Michigan side has construction to the center of the The LRFD Specifications three spans of 61 meters, and main river crossing. A separate require designers to explicitly the Ontario portion has three plan set is prepared for each consider the importance, redun- spans of 54 meters. country’s approach for adminis- dancy and ductility of the struc- Beyond the flanking spans, tration by that country’s Owner. ture and its components. These the Michigan Approach contin- Thus, the construction of the features enter the design process ues with 1.8 meter deep precast main bridge and approaches through the load multipliers prestressed concrete girders in forms three separate contracts: shown in Table 1. spans ranging from 28 to 36 the Main Bridge and Flanking The loadings and traffic pat- meters. The girders are made spans; the Michigan Approach, terns on the existing bridge had continuous for live load in those and the Ontario Approach. It been studied by Modjeski and spans where the roadway and became necessary that some por- Masters, Inc. previously, and a cross-section are uniform. The tions of the contracts overlap fairly common condition had last span is a simple span of and the Contractors for each been observed—bumper-to- steel girders. Near the Michigan approach will continue some por- bumper traffic with a high pro- Plaza a special crossover ramp is tion of the work to the centerline portion of trucks over the full- provided to permit traffic to of the river: placing the bridge length of the main bridge and access the proper lanes under deck overlay, and installation of approaches, all waiting to pass specific conditions of operation, light standards and signal immigration and customs. The and this ramp is framed with devices. experience with this bridge was composite prestressed concrete A number of special provisions one of the reasons that the and steel girders. had been anticipated for the pro- LRFD Specifications contains a ject, as is common for a structure ‘STRENGTH II’ load condition SUBSTRUCTURE of this magnitude and complexi- where a special loading, applica- All the piers are of reinforced ty. After the project had been ble to a specific bridge is used. concrete founded on steel ‘H’ divided into three separate con- The special loading condition as piles driven to rock. The main tracts, for a number of indepen- selected and included in the piers have a column under each dent contractors working simul- Design Criteria consists of load- of the arches, and are connected taneously on the same bridge ing any two lanes uniformly with at the top by a strut. The performing overlapping opera- an intensity of 24 kN/m centered remaining are hammerhead tions, it was realized construc- in each lane with no concurrent piers, except at the crossover and tion coordination could present load in the third lane or side- locations adjacent to the Plaza special problems in the area of walk, no superimposed concen- where the bridge widens to make specifications. As a result, stand- trated loads, and no impact.

/ Modern Steel Construction / October 1997 Table 1: Load Multipliers Federally-funded highway pro- as megaPascals, degrees Celsius, jects. The requirement that this and kiloNewton-meters. A table Component ηηη η bridge be jointly designed by was provided for conversion D R l U.S. and Canadian engineers, between S.I. and customary U.S. Tied Arch and be jointly built by U.S. and values for this project. Since con- Superstructure 1.10 1.00 1.05 1.05 Canadian contractors was a com- version of values where ‘weight’ Tied Arch pelling reason that the plans is referred to in the customary Piers 1.05 1.00 1.00 1.00 would be presented in S.I. units. U.S. system may be somewhat Piles (groups Some recent projects have ambiguous, the plans define of 8 or more) been planned so that the field ‘weight,’ for this project as being Approach 1.00 1.00 0.95 1.05 measurements and the office synonymous with mass, to be Superstructure design work would be made in measured in kilograms or & Piers 1.05 1.00 1.00 1.05 customary English units, and tonnes, where a tonne equals the conversion to S.I. would be a 1000 kilograms. separate step to take place as One of the early considera- PREPARING FOR SI tions had to do with the singular the final drawings are made, so importance of the tie girder since that the completed drawings Several important steps it is a tension member essential contain S.I. units. For the required in starting design work to the entire bridge, and it must Second Blue Water Bridge pro- in S.I. include familiarization, have redundancy as described ject, it was decided that all the general re-tooling, and accumu- previously. engineering work, including lation of resource and availabili- In accordance with the LRFD measurements, studies, design, ty information. To some extent, requirements, the design includ- and plans would be in S.I. units. these involve repeating the ed the studies required to devel- The initial survey which set the stages engineers have gone op a satisfactory construction project monuments and the pro- through during the years of sequence for the tied arch. None ject coordinate system used S.I. accumulating experience and of the arch segments carries its units, as did the following geot- expertise. load as an arch until the seg- echnical and aerodynamic stud- Tables for converting between ment is ‘closed’, or joined with ies and reports. S.I. and English units, and gen- the tie. Until that is achieved, The timing of this project fell eral booklets describing the S.I. the members are all merely in the awkward interim stage system are good starting points beams requiring falsework and during which the engineering in familiarization, but the objec- temporary support. The detailed community of the United States tive is to develop a ‘feel’ for S.I. erection sequence is shown in was preparing to begin using S.I. units, and this is obtained by the plans and includes: the stag- units, and there was still some actually using S.I. values and ing; the falsework and tempo- differences of opinion as to the quantities. rary bracing locations and load- ‘standard’ way of presenting and In the design office and draft- ings; deflections; and procedures using the S.I. units. Therefore, it ing room, re-tooling has been rel- for making closures of the sever- was important that a consistent atively simple and inexpensive. al segments of the tied arch. The procedure or standard be adopt- The Architect’s scale with subdi- final design and detailing of the ed for this project in the begin- visions showing feet and inches permanent members of the tied ning, and that this standard be in fractions of an inch were arch was checked and adjusted, explicitly shown in the plans. replaced with S.I. scales for if required, to accommodate the The project plans define the reading and scaling from draw- loadings from the construction project dimensions and units, as ings. The 1/4-inch grids on the sequence. well as indicating some of the calculation pads were replaced The Design Criteria indicates conventions used in presenting with grids of 5 mm. The CAD the requirements for deck repla- these values. Project dimensions computer software was modified cability, and the plans include were given in millimeters (mm), for drafting in S.I. instead of feet staging diagrams for the feasible and values over five digits long and inches, and the design soft- procedure applicable to each part were written using a space ware was modified as required of the bridge. instead of a comma to break the for the different units, and the number in clusters of three. different format required. SI UNITS Elevations and coordinates were Designer’s work requires The S.I. system has been in given in meters (m) and stations resource information with data use in Canada for a number of were given in kilometers (km). and availability information years, and in the United States Forces were tabulated in about standard materials such many engineers are working kiloNewtons (kN), and mass was as, steel rolled shapes and toward adopting the S.I. system, given in kilograms (kg). The plates, reinforcing bars, fasten- which will soon be mandatory for units for stresses, temperature, ers, and the like. In the United and bending moment were given States documentation on prod-

Modern Steel Construction / October 1997 ucts in the English system have High-strength S.I. bolts are been accumulated over the not readily available from U.S. years. One method of presenting manufacturers. In addition, steel plans in S.I. units is to make a fabricators have not yet retooled design and selection of materials to accept S.I. fasteners. The con- in English units, and make a soft tractors requested that the near- conversion to S.I. values. In this est English equivalent bolt (1”) system, all the English units are be used in lieu of the bolt diame- multiplied by S.I. conversion fac- ter specified on the plans tors and used directly. Where (24 mm). The Owners approved possible, it is desired to use a the use of English equivalent hard conversion which uses fastener size with the stipulation rounded S.I. values. Tables, that all details be reviewed with brochures and other information respect to net section to ensure is available from professional no components were over- and trade organizations, and stressed with the larger diame- U.S. manufacturers and suppli- ter bolts. ers indicating construction mate- Although manufacturers fur- rials in hard converted S.I. units. nish catalogs, brochures and data on S.I. supplies for structur- WORKING IN SI al use, there has been very limit- In proportioning the bridge ed requirement for them to-date, members, the designers were and they are either in very short careful to choose from the pub- supply or non-existent in the Bridge Details lished list of plate thicknesses. United States. As the need and Total length The manufacturer’s published use of S.I. materials becomes a of bridge: 6,109 feet tables of S.I. rolled shapes were reality and starts to grow, their Number of spans: 39 at hand for selection of sizes. For availability will increase in the tied arch span, 24 mm dia. response. Total weight of H.S. bolt was chosen as a fasten- main span: 20,084 tons er. GRAND OPENING Structural steel While developing details for In mid-July 1997, the Second in river span: 14,000 tons the bridge contacts with the Blue Water Bridge opened with Bolts: 350,000 manufacturers revealed that a two-day celebration. By some Total design drawings: 760 they have not generally made estimates, as many as 300,000 Shop drawings: ~ 2,000 the changeover to standard S.I. people walked across the bridge. rolled shapes, and, therefore, the Several days later the bridge S.I. sizes indicated in their publi- was opened to two-way traffic Project Team cations are generally not, in fact, and the venerable First Blue actually available. For this rea- Water Bridge was taken out of • Owners: Michigan Department son, the rolled shapes used for service for rehabilitation. When of Transportation; The Blue Water the stringers and connection it returns to service in mid-1999, Bridge Authority angles were dimensioned based each bridge will be one way, and • Designers: Modjeski and on soft conversions of the the total lane capacity will be Masters, Inc.; Buckland & Taylor, English equivalent. increased from one lane each Ltd. A U.S. supplier of S.I.-sized way to three lanes each way. • Environmental Consultant: reinforcing was difficult to Giffels Associates, Ltd. locate. One major manufacturer Joseph E. Prickett, P.E., is a • General Contractors: explained that they exported a senior associate and John M. PCL/McCarthy Joint Venture great deal of S.I.-sized reinforc- Kulicki, P.E., P.Eng., Ph.D., • Fabricators: PDM of Wausau, ing, but this was all made to the president and chief engineer with Wisc., and of Eau Claire, Wisc.; foreign standards where the bar Modjeski and Masters, and Canron, Inc. (Canron/Midwest) diameter is in even S.I. units. Brian D. Morgenstern, P.Eng., • Erection: Midwest The CRSI standard S.I. sizes, as P.E., is a principal and Roger A. Constructors; Traylor Brothers used in Canada and the United Dorton, P.Eng., Ph.D., is manag- • Painting: Michigan Multi-Coat States, produce rounded S.I. er of the Ontario office of Shop System (shop coat by Blastetch Corportion and touch- areas, but the bar diameters are Buckland & Taylor. up/joints by Hartman Walsh Paint not in even S.I. units. A supplier Co.) was found in Pennsylvania who Bearings/Expansion Joints: is furnishing S.I. reinforcing for H.S.C. Canada, Inc.; D.S. Brown a new Federal building in Washington, D.C.