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3 CHAPTER ONE INTRODUCTION BACKGROUND inces, steel bridge fabricators, and steel bridge erectors and contractors. Questionnaires were sent to all state depart- The erection of steel bridges, depending on the complexity of ments of transportation (DOTs) and Canadian provinces, the structure, may pose critical issues for owners. Because of 25 steel erectors/contractors, and 24 fabricators. Responses this complexity, plus the great variety of practices currently were received from 30 states, 2 provinces, 15 fabricators, being used, there are frequently concerns with the integrity, and 4 erectors. See Appendix A for the questionnaires. speed, safety, quality, delays, and claims related to steel bridge erection. The number of curved structures and structures with The questionnaires requested "Yes" or "No" answers, dis- complex geometry that are being constructed adds consider- cussion type answers, additional contacts for follow-up infor- ably to the type of steel erection issues that owners, designers, mation, and copies of construction specifications. The infor- fabricators, erectors, and contractors face. A compilation of mation provided in the completed questionnaires was then the methods employed by those agencies or firms, involved in recorded. Follow-up telephone calls were made when appro- all phases of a project from design through construction, may priate contact information was provided. Information gath- minimize these difficulties. ered by telephone interviews was also recorded (see Appen- dix B for the results grouped by each category of survey respondent). SYNTHESIS OBJECTIVES This synthesis examines and discusses issues relating to steel I-girder, tub-girder, and box-girder bridges; particularly TERMINOLOGY curved, skewed, and staged structures. It addresses issues that influence steel bridge erection and the practices dealing with Terms that pertain to procedures and materials are provided those issues. The key items to consider are: in this section. · Impact of design and analysis practices on erection; Blocking dimensions: Offset dimensions that are mea- · Methods used to predict erection deflections as a func- sured in shop assembly from a reference line to the girder's tion of bridge type and complexity; bearing points, splice points, and camber points, to control · Shop-assembly practices and alternative methods of the girder alignment when drilling or reaming the holes for ensuring properly assembled geometry; the field splices (see Figure 1). · Sequencing of erection to ensure proper fit-up and to achieve desired girder profile and geometry; Deck cantilever brackets or deck support brackets: Can- · Stability issues during all phases of bridge construc- tilever brackets that attach to the outside girder to support the tion, such as deck overhang, concrete placement, lift- deck formwork and the concrete deck until it has cured (see ing and handling, and temporary or permanent bracing Figure 2). or supports; · Field connection practices and impact on final geometry; Drift pins or pins: Hardened steel round tapered pins that · Examples of structures where erection practices have are used to align the holes in steel members during erection caused problems; (see Figure 3). · Owner requirements for erection procedures, implemen- tation of requirements, and impact of procedures on the Full girder assembly: The procedure consisting of shop quality of the erection; and assembling each continuous girder or rolled beam line to its · Current and proposed future research. full length (see Figure 4). No-load condition, steel dead-load condition, and full dead- SYNTHESIS APPROACH load condition: The possible load conditions under which the girder webs will be vertical or plumb. For the no-load This synthesis reports the responses of three different ques- condition, the girders and crossframes will be detailed, fab- tionnaires that were sent to U.S. states and Canadian prov- ricated, and erected such that the webs will be vertical as
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4 FIGURE 1 Measuring offset dimensions during shop assembly FIGURE 3 Drift pin. (Industrial Steel Construction, Inc.). Special complete structure assembly: The procedure though gravity is turned off. For the steel dead-load condi- whereby the entire structure including crossframes, dia- tion, the webs will be vertical after steel erection, and for the phragms, and floor beams are shop assembled (see Figure 7). full dead-load condition, the webs will be vertical after all of the dead load has been applied. There is little uniformity of Stage construction: The construction condition where thought as to which load condition is appropriate for speci- the deck on part of the bridge has been poured and cured fying plumb girder webs. and a transversely adjacent part, or second stage, has not been poured. This process is not to be confused with staged 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. FIGURE 2 Deck cantilever brackets (DeLong's Inc.). FIGURE 4 Full girder assembly (DeLong's Inc.).