Steel Bridge Erection Practices (2005)

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3BACKGROUND The erection of steel bridges, depending on the complexity of the structure, may pose critical issues for owners. Because of this complexity, plus the great variety of practices currently being used, there are frequently concerns with the integrity, speed, safety, quality, delays, and claims related to steel bridge erection. The number of curved structures and structures with complex geometry that are being constructed adds consider- ably to the type of steel erection issues that owners, designers, fabricators, erectors, and contractors face. A compilation of the methods employed by those agencies or firms, involved in all phases of a project from design through construction, may minimize these difficulties. SYNTHESIS OBJECTIVES This synthesis examines and discusses issues relating to steel I-girder, tub-girder, and box-girder bridges; particularly curved, skewed, and staged structures. It addresses issues that influence steel bridge erection and the practices dealing with those issues. The key items to consider are: • Impact of design and analysis practices on erection; • Methods used to predict erection deflections as a func- tion of bridge type and complexity; • Shop-assembly practices and alternative methods of ensuring properly assembled geometry; • Sequencing of erection to ensure proper fit-up and to achieve desired girder profile and geometry; • Stability issues during all phases of bridge construc- tion, such as deck overhang, concrete placement, lift- ing and handling, and temporary or permanent bracing or supports; • Field connection practices and impact on final geometry; • Examples of structures where erection practices have caused problems; • Owner requirements for erection procedures, implemen- tation of requirements, and impact of procedures on the quality of the erection; and • Current and proposed future research. SYNTHESIS APPROACH This synthesis reports the responses of three different ques- tionnaires that were sent to U.S. states and Canadian prov- inces, steel bridge fabricators, and steel bridge erectors and contractors. Questionnaires were sent to all state depart- ments of transportation (DOTs) and Canadian provinces, 25 steel erectors/contractors, and 24 fabricators. Responses were received from 30 states, 2 provinces, 15 fabricators, and 4 erectors. See Appendix A for the questionnaires. The questionnaires requested “Yes” or “No” answers, dis- cussion type answers, additional contacts for follow-up infor- mation, and copies of construction specifications. The infor- mation provided in the completed questionnaires was then recorded. Follow-up telephone calls were made when appro- priate contact information was provided. Information gath- ered by telephone interviews was also recorded (see Appen- dix B for the results grouped by each category of survey respondent). TERMINOLOGY Terms that pertain to procedures and materials are provided in this section. Blocking dimensions: Offset dimensions that are mea- sured in shop assembly from a reference line to the girder’s bearing points, splice points, and camber points, to control the girder alignment when drilling or reaming the holes for the field splices (see Figure 1). Deck cantilever brackets or deck support brackets: Can- tilever brackets that attach to the outside girder to support the deck formwork and the concrete deck until it has cured (see Figure 2). Drift pins or pins: Hardened steel round tapered pins that are used to align the holes in steel members during erection (see Figure 3). Full girder assembly: The procedure consisting of shop assembling each continuous girder or rolled beam line to its full length (see Figure 4). No-load condition, steel dead-load condition, and full dead- load condition: The possible load conditions under which the girder webs will be vertical or plumb. For the no-load condition, the girders and crossframes will be detailed, fab- ricated, and erected such that the webs will be vertical as CHAPTER ONE INTRODUCTION

though gravity is turned off. For the steel dead-load condi- tion, the webs will be vertical after steel erection, and for the full dead-load condition, the webs will be vertical after all of the dead load has been applied. There is little uniformity of thought as to which load condition is appropriate for speci- fying plumb girder webs. Pinning: The process of using drift pins when erecting steel members (see Figure 5). Progressive girder assembly: The procedure in which a part of a continuous girder line is initially assembled and gird- ers are progressively added and removed as the field splices are reamed and/or drilled. Normally, at least three members must be included in each assembly unless bearing-to-bear- ing requirements are specified (see Figure 6). Shop assembly: The procedure of shop assembling indi- vidual girders in position to ream or drill holes for the field splices. 4 Special complete structure assembly: The procedure whereby the entire structure including crossframes, dia- phragms, and floor beams are shop assembled (see Figure 7). Stage construction: The construction condition where the deck on part of the bridge has been poured and cured and a transversely adjacent part, or second stage, has not been poured. This process is not to be confused with staged FIGURE 1 Measuring offset dimensions during shop assembly (Industrial Steel Construction, Inc.). FIGURE 2 Deck cantilever brackets (DeLong’s Inc.). FIGURE 3 Drift pin. FIGURE 4 Full girder assembly (DeLong’s Inc.).

5deck placement, in which the erection of girders has not been staged. REPORT ORGANIZATION This report is organized into a summary, seven chapters, and two appendixes. This first chapter is the introduction. Chapter two discusses owner-specified or preferred practices, chapter three is a summary of fabricator practices and views, chapter four is a summary of erector practices and views, chapter five lists problems cited, chapter six discusses the solutions to the problems, and chapter seven presents the conclusions. The appendixes contain all of the questionnaires, responses, sum- maries of the responses, and results of specification reviews. RESPONSES TO QUESTIONNAIRES A total of 111 questionnaires were distributed, with 51 re- sponses received. A slim majority of the owners (32 of 62) responded to the owners’ questionnaire. A larger, yet not overwhelming, majority of fabricators (15 of 24) responded to their questionnaire. Only 4 of the 25 erectors/contractors that were solicited responded to their questionnaire. The owners’ response rate may be misleading. Many own- ers, because of tradition and other cultural reasons, and to a lesser degree technical considerations, do not construct many steel bridges. For example, the Sun Belt and Western states do not construct nearly as many steel bridges as do the states of the Rust Belt and the Northeast. States that construct fewer steel bridges were among those not responding, possibly indi- cating less interest in the topic. Thus, if the percentage of steel bridges being constructed in a particular state is entered into the analysis, it is found that the response rate is relatively high for those actively constructing steel bridges. FIGURE 5 Drift pins used to erect a girder (Washington State DOT). FIGURE 7 Special complete structure assembly (Washington State DOT). FIGURE 6 Progressive girder assembly.