Computer Analyses of Time-Dependent Behavior of Continuous Precast, Prestressed Bridges


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Title: Computer Analyses of Time-Dependent Behavior of Continuous Precast, Prestressed Bridges

Author(s): J. D. Glikin, S. C. Larson, and R. G. Oesterle

Publication: Special Publication

Volume: 106


Appears on pages(s): 1-24

Keywords: bridges (structures); computer programs; continuity (structural); cracking (fracturing); creep properties; girders; loads (forces); moments; precast concrete; prestressed concrete; Design

Date: 6/1/1988

Design and construction of bridges composed of simple-span, pretensioned girders made continuous for composite dead and live loads have become widespread. The design of these structures in the U.S. has been generally based on the procedure outlined in "Design of Continuous Highway Bridges with Precast, Prestressed Concrete Girders," published by the Portland Cement Association (PCA) in 1969. Although existing bridges designed by this procedure are generally performing well, it is believed that this method may not accurately predict the true behavior of these structures. One of the major uncertainties in the design of these structures is prediction of positive and negative moments in the cast-in-place connections at the piers. This uncertainty is due to the different loading and construction stages, time-dependent effects, and details used to make the connection. To resolve such uncertainties, an analytical study was conducted to develop guidelines for more rational design of the continuity connections. Paper summarizes results of an extensive parametric study to consider the effects of 1) construction sequence, including simple span behavior before and continuous behavior after casting the deck and diaphragms; 2) time-dependent behavior, including concrete creep and shrinkage, and steel relaxation; 3) live load applied at any stage of service life; 4) cracking resulting from both positive and negative moment, including "tension stiffened" stress-strain relationships for reinforcement; and 5) closing of cracks when combined dead load plus time-dependent moments are reversed by application of live loads.