The Earthquake Engineering Online Archive

Redistribution of Stresses in Segmentally Erected Prestressed Concrete Bridges

Ketchum, Mark A.

UCB/SEMM-1986/07, Dept. of Civil Engineering, University of California, Berkeley, 1986-05, 248 pages

A study of time dependent moment redistribution in segmentally erected prestressed concrete bridges is presented. The phenomenon of moment redistribution due to changes in the structural system of the bridge, and an approximate approach commonly used for the prediction of such moment redistribution are discussed. The shortcomings of this approach and the need for a more precise approach are discussed. A numerical method and computer program for the time dependent analysis of segmentally erectred prestressed concrete bridges is developed. Girder segments can be either precast or cast in place. Prestressing tendons may be stressed, restressed, and removed. Traveling formwork can be modeled. Any statisically feasible construction sequence can be considered. The solution includes the effects of creep, shrinkage and aging of the concrete and relaxation of the prestressing steel. A mathematical model for creep of the concrete is developed, based on a refined integration over time, and is implemented for several differenct creep functions. The program is capable of the time dependent analysis of frame structure under time dependent force and displacement boundary conditions. Moment redistribution in bridges built using the cantilever method is investigated and discussed in detail. Numerical solutions are obtained using the program and are compared with the results of the approximate approach. The shortcomings of the approximate approach in predicting prestressing losses and moment redistribution under various loadings and prestressing are discussed. The capabilities of the program to predict the behavior under service loads of large segmental bridges are demonstrated. Based on this investigation, an approach for the design and analysis of segmentally erected bridges, using approximate methods for the preliminary design and the program for the final design checking and construction monitoring, is presented.

Available online: http://nisee.berkeley.edu/documents/SEMM/SEMM-86-07.pdf (18 MB)