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Abstract

This report presents the relevancy of the allowable stress rating (ASR) and the load and resistance factor rating (LRFR) methods for timber bridges. Benchmark bridges constructed in the 1930s have been upgraded with hollow structural steel (HSS) beams and three-dimensional finite element models provide technical information necessary for examining their behavior and rating evaluations. Complying with published manuals, 17 rating vehicles are considered across three categories (design, legal, and permit) to generate the maximum responses of the bridges. The vehicles' position dominates the deflection profiles of the unrepaired bridges. After installing the HSS beams, the live loads are redistributed, and stiffness enhancement is noticed in the transverse direction of the bridges. The rating factors calculated with ASR exceed those with LRFR for the unrepaired bridges regardless of vehicle configurations, and the level of disparity between these rating approaches increases when the bridges are repaired owing to differences in load factors. In terms of sensitivity to average daily truck traffic, the LRFR factors of the bridges under the "legal" vehicles are more responsive than the factors subjected to other vehicle types. From a probability perspective, the compatibility of these rating methodologies varies contingent upon vehicle categories and the presence of the HSS beams. Practice guidelines are proposed to facilitate the conversion of rating factors between ASR and LRFR as a function of the present condition of constructed timber bridges.

How to Cite

Kim, Yail Jimmy. Transition of Allowable Stress Rating to Load and Resistance Factor Rating, MPC-24-546. North Dakota State University - Upper Great Plains Transportation Institute, Fargo: Mountain-Plains Consortium, 2024.