Development of User-Guided Program for Predicting Time-Dependent Deformations in Prestressed Bridge Girders

Abstract

A Visual Basic (VB) computer program was developed to predict time-dependent deformations and associated material stresses in prestressed concrete bridge girders. The VB program allows the user to select a model for the development of the concrete modulus of elasticity (MOE) over time as well as the creep and shrinkage models used in the calculations. The program includes two test-based and three code-prediction models for MOE growth. The test-based models include the “Constant Ec” and “Two-Point Ec” models. The code-prediction models include AASHTO LRFD ’05(+)—2005 and later, ACI 209R-92, and CEB 90. The creep and shrinkage models include AASHTO LRFD ’05(+), AASHTO LRFD ’04(-)—2004 and earlier, ACI 209R-92, CEB 90, and Modified CEB 90. The Modified CEB 90 model is based on previous research by Kavanaugh (2008). Experimental data from three previous research studies at Auburn University were used to evaluate the strain- and camber-prediction capabilities of the program. Strain and camber measurements were collected from six full-scale AASHTO Type I girders and five AASHTO BT-54 girders. Camber measurements for sixteen 15-in. deep prestressed T-beams were also used. The AASHTO Type I girders and T-beams were constructed using conventional and self-consolidating concrete (SCC) mixtures. Four moderate- strength SCC mixtures and three high-strength SCC mixtures were used. The moderate-strength SCC mixtures had 28-day concrete strengths between 8500 and 9800 psi, while the high-strength SCC mixtures had 28-day concrete strengths between 13100 and 13600 psi. The 28-day concrete strengths of the conventional mixtures ranged from 6300 to 7200 psi. Various combinations of models for the concrete MOE development and creep and shrinkage calculations were used to predict the strain and camber of prestressed flexural members. The program results were compared to experimental measurements to evaluate the accuracy of the camber predictions. A sensitivity analysis was also performed to determine the effects of design parameters on strain and camber results.