Quantification of intermediate diaphragm effects on load distributions of prestressed concrete girder bridges

Abstract

Construction of intermediate diaphragms in prestressed concrete bridges impacts cost and schedule. The practice of providing intermediate diaphragms in prestressed concrete bridges is still controversial, and each state has a different practice. The American Association for State Highway and Transportation Officials' (AASHTO's) Standard Specifications for Highway Bridges specifies that intermediate diaphragms be used at the point of maximum positive moment for spans exceeding 12 m (40 ft), but clear reasons for this requirement are not given. While the AASHTO LRFD Bridge Design Specifications state that intermediate diaphragms can improve live-load distributions, this effect is not included in the calculation of load-distribution factors. Previous studies of intermediate diaphragms were limited to whether they increased or decreased the load-distribution factors. No significant work has been conducted to develop a formula to quantify the influence of intermediate diaphragms on load distributions. This study aims to quantify the intermediate diaphragm influence on load distributions and presents an approach to develop correction factors for load distributions. The correction factors are applied to the AASHTO LRFD specifications' load-distribution factors. This results in a revised load-distribution factor that accounts for the intermediate diaphragm influence on load distributions. The study illustrates how to apply these formulas in design. The presented information will help engineers examine the functions of intermediate diaphragms and develop their policies of intermediate diaphragm practice for prestressed concrete bridges.