Safety assessment of steel-plate girder bridges subjected to military load classification

Abstract

This paper presents a safety evaluation of steel-plate girder bridges subjected to Military Load Classification (MLC). Three-dimensional finite element models are developed to predict the bridge response, including three different span lengths (L=12m, 24m, and 36m) that represent short- and medium-span bridges. A total of 36 load cases are considered to examine the flexural behavior of the bridges. Evaluation methodologies used here are a critical weight approach and load rating based on the allowable stress rating (ASR), load factor rating (LFR), and load and resistance factor rating (LRFR) methods. The gross weight of the MLC truck is a dominant parameter for the safety of the bridges, rather than longitudinal axle spacing. Load-sharing effects between the girders improve the behavior of the bridge superstructures. Existing empirical formulas developed for nonstandard civilian trucks (e.g., Formula B) exhibit noticeable errors for MLC applications with an average error ranging on the order of 6.7–17.9. The LFR (operating) and the LRFR methods show acceptable rating factors. A safety index of 2.5 is recommended for the evaluation of bridges subjected to MLC trucks. A simplified formula is proposed to promptly assess the critical weight of MLC trucks for short- and medium-span bridges.