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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.
