Live-Load Distribution Factors in Prestressed Concrete Girder Bridges

TLDR

The study evaluates flexural live‑load distribution factors for three‑span prestressed concrete girder bridges. Finite‑element models of a tested bridge, calibrated against a static live‑load test, were used in 24 variations to assess code‑based distribution‑factor procedures and to examine the influence of lifts, diaphragms, continuity, skew angle, and load type. For geometries like those in AASHTO LRFD, FE‑model distribution factors were within 6 % of code values, but for the tested bridge they differed by 28 %; lifts, end diaphragms, skew angle, and load type significantly lowered factors, while continuity and intermediate diaphragms had minimal impact, and adopting FE‑model factors could reduce required concrete release strength by 6.9 MPa or allow a 39 % increase in live load.

Abstract

This paper presents an evaluation of flexural live-load distribution factors for a series of three-span prestressed concrete girder bridges. The response of one bridge, measured during a static live-load test, was used to evaluate the reliability of a finite-element model scheme. Twenty-four variations of this model were then used to evaluate the procedures for computing flexural live-load distribution factors that are embodied in three bridge design codes. The finite-element models were also used to investigate the effects that lifts, intermediate diaphragms, end diaphragms, continuity, skew angle, and load type have on distribution factors. For geometries similar to those considered in the development of the American Association of State Highway and Transportation Officials Load and Resistance Factor Design Specifications, the distribution factors computed with the finite-element models were within 6% of the code values. However, for the geometry of the bridge that was tested, the discrepancy was 28%. Lifts, end diaphragms, skew angle, and load type significantly decreased the distribution factors, while continuity and intermediate diaphragms had the least effect. If the bridge had been designed using the distribution factors calculated with the finite-element model rather than the code values, the required concrete release strength could have been reduced by 6.9 MPa (1,000 psi) or the live load could have been increased by 39%.