Time-dependent nonlinear analysis of curved nonprismatic prestressed concrete box girder bridges

The accurate design and analysis of prestressed concrete (PC) bridges during their service life are very important issues. They affect public safety and economy. The behavior of prestressed bridges is complicated, i.e., it includes inelastic response, concrete cracking, steel yielding, creep, shrinkage, temperature, and tendon relaxation phenomena. This study considers the material nonlinearities (concrete, reinforcing mild steel, and prestressing tendon), and tension stiffening effect between concrete and reinforcement. The time-dependent material behavior is also included. Environmental conditions which influence concrete creep and shrinkage, thermal effect, and instantaneous and long term prestressing force losses are also included. In addition, a construction and a service load stage analyses are developed by accounting for the considerable changes generated during bridge construction and its service life. Another special feature considered in this study is the effect of curved geometry on the analysis of PC box girder bridges. To account for this effect, a finite element formulation based on thin-walled box beam theory including longitudinal warping mode and transverse distortion mode of the trapezoidal cross section is utilized. Nonprismatic concrete box section along the longitudinal axis as well as diaphragms, which reduce warping and distortional effects, are also considered in this analysis. The moment redistribution resulting from the construction and service load stage is also checked in tracking the actual behavior. A computer program (NTPBOX) is developed to implement the analysis of curved box girder bridges. The analysis capabilities of the developed program (NTPBOX), including time dependent nonlinear analysis, are compared with other programs and experimental results. The comparison is shown to be satisfactory.