Montana Department of Transportation December 2017 RESEARCH PROGRAMS

Project Summary Report: 8226-001

Authors: Damon Fick, Ph.D., PE Michael Berry, Ph.D. Tyler Kuehl Jerry Stephens, Ph.D., PE

Montana State University - Bozeman, MT

Investigation of Prefabricated - Systems http://www.mdt.mt.gov/research/projects/structures/prefab.shtml

Introduction What We Did with the cost of plate alternatives Steel truss are The following four tasks were and 3) identify revised an efficient and aesthetic completed for this project: connection details option for crossings. 1. A literature review to improve fatigue Their relatively light weight performance. compared with plate girder state-of-practice related 3. A 205 ft. span steel systems make them a desirable toidentified the analysis, the current design, truss with bolted and alternative for both material and construction of welded connections savings and constructability. similar bridge systems was investigated as A prototype of a welded steel constructed on an an alternative to the truss constructed with an accelerated schedule. The proposed all-welded integral deck has review focused on four truss. The 205 ft. span been proposed by a steel primary topics pertinent was selected so that fabricator as a potential to the proposed bridge results could be readily alternative for accelerated system and this project: compared with the Swan bridge construction (ABC) 1) modular systems, River plate girder project projects in Montana. 2) concrete decks, 3) currently being designed welded connections by MDT. This system consists of a subjected to fatigue, and 4. A comparison was prefabricated welded steel 4) full-scale experimental made of materials and truss topped with a concrete studies. fabrication costs for deck that can be cast at the 2. An analytical evaluation both the steel truss fabrication facility (for ABC was conducted to 1) and plate projects) or in the field after identify any impacts on systems. Shipping, erection (for conventional the projected service life construction, and projects). This specific bridge of the prototype truss erection considerations and prefabricated construction for both accelerated technique are not well proposed by a steel and conventional represented in the literature, fabricatorbridge configurations based on construction methods and thus there is a need to fatigue of the welded were considered. identify potential bridge spans member-to-member and traffic volumes where the connections, 2) perform proposed system is viable and a cost analysis for the four tasks, conclusions were economical. proposed systems and madeBased relatedon findings to the from analysis, these compare the results design, and construction of a

Project Summary Report 8226-001 1 steel truss with bolted connections sources for the 148 ft. truss and a project (the Swan River project), and compared with a plate girder comparable plate girder suggested allowing for cost comparisons alternative. a welded steel truss would cost to be readily prepared between approximately 5% to 20% less than the two systems. To further a comparable plate girder. investigate the potential material What We Found and fabrication cost savings for the Based on discussions with steel truss system, a three-dimensional No documentation was found fabricators and the projected during the literature review fatigue performance of the was created to more accurately welded connections, a new truss estimatefinite element the distribution model (Figure of 2) proposed bridge structure, multiple lane and axle loads specifically addressing the i.e., a prefabricated welded to the in the system steel truss with a composite verticalconfiguration members was anddesigned bolted with and attendant individual truss concrete deck, cast-in-place diagonalmore economical member wideconnections. flange members. Results of this analysis at the fabrication facility. The The steel truss used a welded indicated that a distribution factor most common application for connection between the vertical for use with a 2D model could be modular prefabricated steel truss compression members and top lower than previously calculated systems has been for temporary and bottom chords. The new truss using the relatively simple and bridge crossings in through-truss members and bolted connection typically conservative lever rule (by approximately 25 percent), was also found on prefabricated and in further analyses, this new configurations. Some information bridge elements consisting of a andconfiguration fatigue requirements produced a systemfor distribution factor was used. concrete deck precast on steel that satisfied the strength stringers (note that one such connections of the proposed truss The 205 ft. steel structure was built by MDT over foran infinite-lifea 205 ft. span design. are shown The in was re-analyzed and designed Maxwell Coulee). This review Figure 1. A 205 ft. span was used of the available information in this re-design, as MDT had available a plate girder design distributionusing a two-dimensional factors. Conventional finite analysis/investigation of the at this span length from a recent andelement accelerated model with construction the refined proposedconfirmed system. the need for further

Subsequently, an analysis was conducted on a preliminary design of the proposed concrete deck/steel truss elements (with welded connections in the truss) under AASHTO’s Fatigue I load combination for a 148 ft. span. This analysis, performed using a

model, found that load-induced fatiguetwo-dimensional stresses exceeded finite element threshold

a factor of approximately 4.0. For avalues 75-year for designan infinite life usinglife design Fatigue by Figure 1: Proposed Steel Truss Panel II load combinations, calculated fatigue stresses exceeded threshold values by approximately 18% in a design scenario typical of that in which MDT would use this bridge system (for this purpose, measured

MT was used to determine fatigue demands).traffic on Hwy Material 200 East and of fabrication Jordan, cost estimates from three Figure 2: 3D Finite Element Model

Project Summary Report 8226-001 2 scenarios were considered in Plate Girder Truss 1 Truss 2 the design of the truss members, connections, and splices. The Allied Steel $135,000 $105,000 $94,000 conventional construction scenario AVEVA $95,000 $103,000 $85,000 assumed a single splice at mid- RTI Fabrication $126,000 $112,000 $84,000 span with a concrete deck cast Average $119,000 $107,000 $88,000 after the truss was erected. For the Table 1: Final Steel Price Estimates accelerated construction scenario, fabricators suggests a reduction in local contractors to receive the assumption was made that the cost of 10% and 26% for the two truss elements with integral concrete construction alternatives, respectively. successfully implementing a deck would bridge the span in three steelmore truss specific bridge suggestions system built for segments (resulting in two splices). Based on this investigation, a steel using conventional or accelerated The weights and spans of the two truss with integral concrete deck, construction methods. trusses are shown in Figure 3 with either precast on the truss for the splice locations and weight of the accelerated bridge construction, deck performance of the Maxwell Swan River plate . Estimated or cast-in-place for conventional • CouleeEvaluate bridge the joint that and utilized concrete a prices for the two truss scenarios and construction, are attractive the plate girder from three sources alternatives for bridge projects in integral concrete deck. are shown in Table 1. Although the Montana. For the case considered rolled wide-flange section with an costs of the splice connections were in this study, using a combination of methods for a steel truss bridge not included in the estimates, one bolted and welded connections in the • constructedInvestigate alternative with an integral contracting fabricator indicated additional cost trusses, this system was found to offer concrete deck. The Construction savings could be realized by building good performance at a potentially Manager/General Contractor camber into the truss through the lower cost than comparable plate method could provide a more bolted connections. Additional costs girder construction. not included with the plate girder alternative are the required weld aefficient steel truss and foreconomical a selected delivery. inspections for the full-penetration What the Researchers • bridgeComplete crossing a final with design input of welds between shop splices in the Recommend from an erector and fabricator, combined with Maxwell Coulee of the bolted and welded steel The following recommendations observations. trussesflange and assuming the web. conventional The steel weight and are made based on the results of the accelerated construction were 15% Prefabricated Steel Truss Bridge Deck evaluation program, including and 28% less than the steel weight of Systems project: • instrumentationImplement a monitoring and remote and data the Swan River plate girders. Using acquisition, for the constructed an average of the materials and crossing sites and geometries steel truss bridge. fabrication estimates from various • withDiscuss steel potential fabricators bridge and

(a) Plate Girder

(b) Truss 1

(c) Truss 2

Figure 3: Weight of each Splice Section for the (a) Plate Girder, (b) Truss 1 and (c) Truss 2

Project Summary Report 8226-001 3 For More Details . . .

The research is documented in Report FHWA/MT-17-009/8226-001, http://www.mdt. mt.gov/research/projects/structures/prefab.shtml.

MDT Project Manager: Sue Sillick, [email protected], 406.444.7693

Researcher’s Organization Project Manager: Damon Fick, , 406.994.6105

To obtain [email protected] of this report, contact MDT Research Programs, 2701 Prospect Avenue, PO Box 201001, Helena MT 59620-1001, [email protected], 406.444.6338.

MDT Implementation Status: December 2017

The implementation recommendations documented above were made to MDT. These recommendations, along with MDT’s response, are documented in the implementation report, which can be found at the above URL.

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Project Summary Report 8226-001 4