Title:
Excessive Deflections of Record-Span Prestressed Box Girder
Author(s):
Zdenek P. Bazant, Qiang Yu, Guang-Hua Li, Gary J. Klein, and Vladimir Kristek
Publication:
Concrete International
Volume:
32
Issue:
6
Appears on pages(s):
44-52
Keywords:
deflection, creep, shrinkage, finite element analysis
DOI:
Date:
6/1/2010
Abstract:
When completed in 1977, the Koror-Babeldaob Bridge in Palau held the world-record span of 241 m (790 ft) for segmentally erected prestressed concrete box girders. Within 18 years, its total deflection, compared with the design camber, reached 1.61 m (5.3 ft.) and the prestress loss was measured as 50%. In 1996, the bridge was retrofitted, but three months later the bridge suddenly collapsed. It wasn’t until 2008 that the technical data necessary for complete analysis were released. This article shows that the existing models for creep and shrinkage prediction grossly underestimate the deflections and prestress loss, although one model, model B3, does so much less than the others and, if calibrated by the 10-year tests of Brooks, matches the observations. The main lessons are that the use of a realistic creep and shrinkage model is paramount; three-dimensional finite element analysis is required; and the differences in drying rates among slabs of different thicknesses and exposures must be taken into account.