A parametric study of optimum road frame bridges by threshold acceptance

Abstract

This paper examines the economic optimization of reinforced concrete road frame bridges by threshold acceptance. The formulation of the problem includes 50 discrete variables: three geometrical ones, three types of concrete and 44 reinforcement bars and bar lengths. Design loads are in accordance with the national codes for road bridges. An internal matrix method program computes the stress resultants and envelopes of the frame bridges. The evaluation module includes the ultimate limit state of fatigue plus other commonly specified limit states of service and ultimate flexure, shear and deflections. Solutions are evaluated following the Spanish code for structural concrete. This study reviews the main factors affecting the design of frame bridges. The study then presents a parametric study of commonly used road frame bridges from 8 to 16 m in horizontal span for different fills and earth covers conditions. The evolution of the total, concrete and steel cost is examined with regard to the key parameters, resulting in practical rules of thumb for optimum frames. Finally, it is shown that the steel-to-concrete cost has a fair influence on the characteristics of the optimum road frame bridges.