Simplified Live Load Distribution Factor Equations

The live load distribution factor is a very important parameter in both the design of new bridges and the evaluation of in-service bridges. Studies have shown that there can be large discrepancy between the actual load distribution factors of field bridges and the load distribution factors predicted by bridge design codes. In addition, the load distribution factor is always treated as a constant in bridge assessment even though it is a random variable with certain statistical properties. In this study, the reliability indexes of 15 prestressed concrete girder bridges designed following the AASHTO LRFD code are calculated by considering the randomness of the load distribution factors induced by the random vehicle transverse position. It is found that there is a considerable increase in the calculated bridge reliability indexes, especially for short-span bridges, when the load distribution factor is modeled as a random variable with the statistical properties obtained from numerical simulations. This suggests that vehicle transverse position is one important factor that can be considered if a refined analysis is desirable when traditional evaluation methods predict unsatisfactory bridge assessment results. The findings in this article also highlight the importance of considering the actual vehicle transverse position in the evaluation of existing bridges.

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Single-Lane Live Load Distribution Factor for Decked Precast, Prestressed Concrete Girder Bridges

Transportation Research Record Journal of the Transportation Research Board ◽

10.1177/0361198105192800116 ◽

2005 ◽

Vol 1928 (1) ◽

pp. 142-152 ◽

Cited By ~ 4

Author(s):

Jason L. Millam ◽

Zhongguo (John) Ma

Keyword(s):

Prestressed Concrete ◽

Load Distribution ◽

Live Load ◽

Distribution Factor ◽

Girder Bridges ◽

Girder Bridge ◽

Live Load Distribution ◽

Load Distribution Factor ◽

Precast Prestressed Concrete ◽

Bridge System

The live load distribution factor equations provided by AASHTO load and resistance factor design specifications for the decked precast, prestressed concrete (DPPC) girder bridge system do not differentiate between a single-lane or a multilane loaded condition. This practice results in a single-lane load rating penalty for DPPC girder bridges. This paper determines distribution factor equations that accurately predict the distribution factor of the DPPC girder bridge system when it is subjected only to single-lane loading. Eight DPPC girder bridges were instrumented. Each bridge was loaded with a single load vehicle to simulate the single-lane loaded condition. The experimental data were used to calibrate grillage models of the DPPC girder bridge system. The calibrated grillage models were used to conduct a parametric study of the DPPC girder bridge system subjected to a single-lane loaded condition. Four new equations that describe the single-lane loaded distribution factor for both shear and moment forces of these bridges are developed in this paper.

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