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15 CHAPTER SIX SOLUTIONS TO REPORTED PROBLEMS DISTORTION AT DECK CANTILEVER BRACKETS use a closure or construction pour between stages. One spec- ifies at least three lines of girders in the first stage, with a In regard to owners, three reported that additional analysis of strong preference for six lines where future redecking may be the fascia girder is required to solve the problem of distortion needed. Another owner requires at least three lines in any caused by the load of the cantilever brackets. One requires stage. Two owners use only a top and bottom strut between the designer to review the load condition on the fascia girder the girders of adjacent stages, and one of the owners adds caused by the cantilever bracket forces and, where necessary, cross bracing after the deck pour. Finally, one owner uses provide additional transverse stiffeners, require the bracket slotted holes to facilitate fit-up of adjacent stages. to be supported by the bottom flange of the fascia girder, or allow the contractor to propose an alternate solution. That Washington State cited a report by researchers from the owner also requires the designer to consider the effect of out- University of Washington of particular interest. "Methods of of-plane girder rotation. Controlling Stresses and Distortions in Stage-Constructed Steel Bridges" (4) describes six design and construction Two owners have developed software to analyze the fas- methods, including a procedure for determining the forces in cia girder under such conditions. In particular, the Kansas struts and/or crossframes for several of the methods, a design Bridge Office, in conjunction with Kansas State University, paradigm for the six methods, and typical strut and/or cross- developed the program Torsional Analysis of Exterior Gird- frame connection details. ers (TAEG 2.0), to predict the torsional resistance of the exterior girder eccentrically loaded with the screed machine and deck overhang concrete. Still another owner requires the contractor to submit his forming procedures for approval. Erectors Only one erector offered a solution for the problems of stage construction. That solution is field-drilling the holes in one THERMAL DISTORTION OF SUN HEATING side of the crossframe after the deck is poured in Stage 2. ERECTED MEMBERS Although owners noted distortions of the steel-only super- structure as a result of thermal radiation, no solutions such GIRDER STABILITY as general requirements were cited. One owner indicated that the problem was mitigated with the completion of the There were several measures that owners reported in regard deck formwork over the girders. Another employed tempo- to solutions. Two owners address the problem of girder sta- rary bracing when the problem was encountered on a spe- bility by placing more responsibility with the designer. One cific bridge. To avoid reporting a problem that does not owner requires checks of the stability of a cantilever girder, really exist, one erector suggested that the erector consider adding lateral bracing if required; adequacy of the cross- the position of the sun and temperature of the steel when frames to avoid flange buckling owing to the dead load of the checking the alignment of a structure. One line of girders girder and/or concrete; adequacy of the flanges for lateral may be longer than the other because of shading of one by bending or buckling; erectability of the girders; and effects the other. of the pouring sequence in the positive moment regions. The other owner requires the designer to show lateral bracing at middepth of the girders in either one or two bays (depending STAGE CONSTRUCTION on bridge width) on spans more than 45 m (150 ft), to con- trol instability owing to wind loads. Owners Two of the owners place more responsibility with the Several owners have developed strategies for successful stage erector. One requires that the erector show lateral bracing in construction based on past successful practice. Five owners the erection procedure, if needed. Another recommends that