Reliability-based assessment for load and resistance factored rating under NJDOT permit load for steel bridges
Creators: name: Srithaninrat, Thanachai
Publisher: name: No Publisher Supplied
Year: 2018

description: Nowadays, the aging bridges are exposed to much higher truck load than they were originally designed for, since trucks have the capacity to carry more weight. This becomes a major concern for engineers as they try to maintain the bridges and ensure that they remain safe. The engineers have come up with several load rating methods, such as Allowable Stress Rating (ASR), Load Factor Rating (LFR), and Load and Resistance Factor Rating (LRFR), that can evaluate and inspect the conditions and safety of the bridge structure. Load rating is the determination of the live-load carrying capacity and load limits of an existing bridge. Based on the AASHTO LRFR, a rating factor of equal to or greater than 1 means that the structure has sufficient capacity to carry the vehicle that weighs less than or equal to the loading vehicle. In New Jersey alone, there are 3,142 steel girder bridges and according to 2017 National Bridge Inventory (NBI), majority of those bridges were designed according to the Allowable Strength Design (ASD), whereas most of the modern bridges (after the year 2000) were designed according to the AASHTO Load and Resistance Factor Design (LRFD) Bridge Design Specifications. The LRFR is consistent with the LRFD philosophy and is the main focus of this thesis. The objective of this study is to perform a reliability-based assessment of the current AASHTO LRFR in terms of the reliability indices β of steel girder bridges versus the LRFR rating factors. In particular, attention is placed on the Strength II and Service II limit states using New Jersey Department of Transportation (NJDOT) design permit truck. The bridge database consists of two sets. The first dataset includes the existing bridges obtained from NJDOT bridge inventory and the previous research. These bridges are designed in accordance with the AASHTO Standard Specifications for Highway Bridges. The second dataset includes the new bridges that are designed in accordance with the AASHTO LRFD and they are invented just for this study. The current AASHTO Manual of Bridge Evaluation (MBE) indicates the live load factors for permit loads have been calibrated to achieve a target reliability of 2.5 with a minimum of 1.5 for the Strength II limit state when rating factor is equal to 1. However, the live load factors in Service II limit state have not been calibrated through similar procedures, particularly for a simply-supported steel girder bridge. Therefore, to ensure the same level of uniformity, there is a need to assess the serviceability levels for the current permit loads and their corresponding live load factors for the Service II limit state. This thesis presents the results of bridge load rating using the LRFR procedures and the corresponding reliability indices, specifically for Strength II and Service II limit state. The results of this study show that the current LRFR live load factors at the Service II limit state do not truly reflect the current level of serviceability of the steel girder bridges. Based on the review of the analysis results, the study suggested a recommendation on the load and the resistance factors for the Service II limit state.