Optimal Force-Based Beam-Column Element Size for Reinforced-Concrete Piles in Bridges

The nonobjective disadvantages of the force-based frame element, such as the nonobjective curvature prediction, have been discussed by many researchers. The trial-and-error method is commonly used to determine element size, but it could cost tremendous computational efforts. This paper proposes and analytically studies the optimal element size for reinforced-concrete piles for bridges when using force-based beam elements. In this study, the relationship between the optimum element size and integration point number is investigated, and the equivalent plastic hinge length is used and correlated to the optimal element size, on the basis of which the moment-curvature and force-displacement responses are objective and the soil effects on the pile response could be simulated sufficiently as required. The results of a case study show that both the local and global responses can be very well predicted, and the nonobjective disadvantage of the force-based element could be eliminated using the proposed optimal element size. Additionally, the optimal element size with more than two integration points is suggested for modeling the plastic hinge in the pile above the ground.