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OCR for page 13
14 External forces are needed to force a girder out of plumb dur- reported problems include webs not vertical, difficulty con- ing erection so that it will be plumb after the deck is cast. necting crossframes, buckling of K-frame members, poor There will almost always be some distortion until all of the alignment, a dropped girder, and bolts popping. The prob- dead load is applied. lems often are a result of unanticipated differential deflec- tions between adjacent girders in sharply skewed or curved bridges, improper or inadequate use of falsework, poor hor- At Supports izontal and vertical alignment control, use of oversized holes, or detailing inconsistencies. Five owners reported problems resulting from unanticipated distortions at piers, abutments, or other supports. The unan- Four fabricators reported problems as a result of unantic- ticipated distortions cited at supports were either out-of- ipated distortions in the span of bridges. Two specifically plane movement of girder webs or end rotations of girders attributed problems to improper use of drift pins. or stringers. Those distortions resulted in a moveable bridge unable to close owing to dead-load stringer end rotations, concrete deck GENERAL COMMENTS ON PROBLEMS cracking as a result of dead-load girder end rotations, diffi- One fabricator reported that most problems are the result of culty in fitting box girders to bearings and loss of bearing pin human error and are not technical problems. Such prob- keeper plates owing to differential lateral movement of the lems include designers providing incorrect information on girder ends. Although some of these problems have occurred the plans, fabricators exceeding tolerances, or erectors not at skewed supports, that is not always the case. controlling geometry. Such reports suggest that more care is needed, not a change in practices. In the Span Another fabricator raised the issue of webs being cited as Twelve owners reported problems resulting from distortions out of plumb and the question of what the effect on the bridge that have occurred "in span" rather than at supports. The actually is.