Load and resistance factors for prestressed concrete girder bridges

Andrzej S. Nowak

nowak@auburn.edu
Department of Civil Engineering; Auburn University; (United States)

Olga Iatsko


Department of Civil Engineering; Auburn University; (United States)
https://orcid.org/0000-0001-8380-9515

Abstract

There has been a considerable progress in the reliability-based code development procedures. The load and resistance factors in the AASHTO bridge design code were determined using the statistical parameters from the 1970's  and early 1980’s. Load and resistance factors were determined by first fixing the load factors and then calculating resistance factors. Load factors were selected so that the factored load corresponds to two standard deviations from the mean value and the resistance factors were calculated so that the reliability index is close to the target value. However, from the theoretical point of view, the load and resistance factors are to be determined as coordinates of the so-called “design point” that corresponds to less than two standard deviations from the mean. Therefore, the optimum load and resistance factors are about 10% lower than what is in the AASHTO LRFD Code. The objective of this paper is to revisit the original calibration and recalculate the load and resistance factors as coordinates of the “design point” for prestressed concrete girder bridges. The recommended new load and resistance factors provide a consistent reliability and a rational safety margin.

Supporting Agencies

This work was supported by the Highway Research Center at Auburn University.

Keywords:

design point, design formula, prestressed concrete girders, resistance factor, reliability index, bridge live load, safety margin

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Published
2020-09-30

Cited by

Nowak, A. S. and Iatsko, O. (2020) “Load and resistance factors for prestressed concrete girder bridges”, Budownictwo i Architektura, 19(3), pp. 101–111. doi: 10.35784/bud-arch.2120.

Authors

Andrzej S. Nowak 
nowak@auburn.edu
Department of Civil Engineering; Auburn University; United States

Authors

Olga Iatsko 

Department of Civil Engineering; Auburn University; United States
https://orcid.org/0000-0001-8380-9515

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