Service life assessment of a steel girder bridge under actual truck traffic

Abstract

Fatigue behavior of a bridge is considered as a main concern for structural engineers especially for bridge construction due to the rapid growth of overloaded trucks. Truck traffic has increased significantly on bridge structures in Bangkok. Moving loads due to overloaded trucks on a steel girder bridge would cause fracture formation and propagation. The study is conducted to assess the safety of a steel girder bridge under actual truck traffic data. The study addresses the fatigue behavior of the bridge structure using FEM analysis. This will help to evaluate the remaining service life under the operational performance of several truck classes. The service life of this steel girder bridge was evaluated by S-N curve application based on Miner’s damage rule which is recommended by AASHTO LRFD standard specifications. The bridge consists of 19 spans with 1.75 m transverse width of each five longitudinal steel girders including reinforced concrete slabs. The dynamic behavior of the steel girders was validated by field instrumentation. The fatigue truck model was constructed using data of 102,546 truck movements in 2020. The data included gross weight, axle weight, and axle spacing. The number of stress cycles can be measured by analytical investigation at the midspan of each girder. The structure could be carried out for more than 75 years without consideration of truck traffic growth. The result obtained from analytical investigation revealed that the steel girder bridge would be affected fatigue failure with the expected growth of truck traffic. If that truck traffic growth would increase by 4% every year in Thailand, the service life of the structure exhibited a huge reduction less than 75 years. This study was conducted to estimate service life in three aspects: 1) service life estimation in accordance with the AASHTO specification, 2) categorized different truck types, and 3) categorized overloaded truck. Based on the results obtained from the investigation, it can be concluded that fatigue damage to a bridge depends on truck classification in stress range and number of cycles. IMPLICATION OF THESIS: This study shows that the importance of estimating service life, fatigue behavior and computational modelling to avoid fatigue cracking failures. Nowadays the movement of overloaded trucks on the bridge structure has increased in Thailand. It is more important to study the behavior of the bridge structure under dynamic live load to protect public safety and avoid economic loss. The results show the selected bridge in Bangkok performs safely with an acceptable probability with the reference of the AASHTO LRFD standard specification. However, with the consideration of the expected growth of truck traffic, it is found that the bridge structure would cause serious fatigue failures. As a main conclusion, this research study was implemented to distribute the results of the steel and composite highway girder bridge structure behavior subjected to dynamic live load actions to design engineers and structural engineers in Thailand in order to prepare the earliest precaution and improvement of the service life of the bridge under growing truck traffic conditions.