COST AND PERFORMANCE OPTIMIZATION OF PRECAST POST TENSIONED PRE-STRESSED GIRDER BRIDGE SUPERSTRUCTURES

Abstract

Bridges are the most costly components of a road transportation network. Pre-stressed concrete girders with cast in place concrete decks are widely used for short to medium span bridges. The design and subsequent cost of a bridge depends on key geometric variables such as bridge width, number of lanes, number and length of spans, slab thickness, number and spacing of girders. Some of these variables are dictated by traffic demands and highway geometry, while others are related to structural demands. Typically, designing a bridge usually involves experience and expert judgement of the bridge engineer. This study is aimed at cost and performance optimization of pre-stressed concrete girder bridges using a parametric study of the design variables and their effects on cost and performance of the bridge. A spreadsheet is developed for analysis and design of deck slab and girders using one dimensional beam line analysis and AASHTO LRFD distribution factors. The spread sheet also calculates the overall cost of the bridge superstructure. This spreadsheet is then used to perform a parametric study by iterating through all design parameters. It is shown that, contrary to conventional wisdom, the cost and performance of bridge superstructure are not necessarily competing factors. Relationships for slab thickness and girder spacing are presented that result in optimal performance and cost of the bridge superstructure.