Finite Element Method Calculation of A Prestressed Self Consolidating Concrete Beam

Abstract

In this study, a prestressed concrete box beam produced for the Stalnaker Run Bridge (SRB) replacement project using self-consolidating concrete (SCC) was simulated using finite element method (FEM) numerical technique. ANSYS, a commercial FEM software, was used to build the prestressed SCC box beam model. The FEM model was developed to understand the behavior of concrete and steel under prestressing loads, long-term effects, and superimposed loads. The SOLID65 and REINF264 element types were chosen to simulate the behavior of concrete and steel materials. Experimentally measured mechanical properties of concrete from the SRB project were used in the analysis allowing for direct comparison. The properties of Gr270 low-relaxation strands, specified by the manufacturer, were assumed in the FEM model for the prestressed steel. Vertical steel stirrups, provided in the box beams, were also simulated using wire elements. The first FEM model was developed to simulate the behavior of the beam shortly after release of prestressing forces, while the second FEM model - behavior of the beam two years later. The simulated stresses at the top and bottom surfaces of the beam compared well with the conventional prestressed concrete design calculations, except for a short length at the midspan, where the transition of the cross-section took place. Results show a 2.3% difference in longitudinal strains between the FEM model and experimental beam for the compression surface at 15 kips loading. The FEM model accurately describes the load-deflection of the physical beam before cracking, after cracking, and through yielding of the prestressed tendons. The load causing decompression of the beam, calculated by FEM and measured experimentally, had a difference of about 2.8%. The location of the neutral axis after cracking of the beam, determined using the strains calculated by FEM, compared well with results from the moment-curvature analysis. The FEM model was able to simulate the final failure of the box beam due to concrete compression failure observed in the experiment. The FEM prediction of the final failure load agrees within 1% of the experimental observation. The methodology shown in this study can provide an efficient and satisfactory prediction for both short-term and long-term behaviors of prestressed SCC box beams.