Revisiting of Three Bridge Failures in Sri Lanka

There are nearly 12,000 road bridges in the national bridge network of Sri Lanka and average life of these bridges are more than 50 years old. Further, there still exist bridges whose lives are more than 100 years. Condition assessment and maintenance strategy of bridges is based on visual inspection by the Road Development Authority (RDA). However, visual inspection of bridges tends to be labour intensive, personal bias, expensive and inconsistent. Further, increase traffic volume has gradually strained the residual structural capacities of these bridges. These reasons have led to a number of sudden bridge failures during last two decades such as Paragastota bridge failure (1999), Rakwana bridge failure (2014) and Kappitigala bridge failure (2015). Studying these bridges failures is useful in mitigating the incidences and potential of future failures. This study presents failure studies of above collapsed bridges. These bridges failed mainly as a result of overloading due to heavier loading vehicle. Finite Element (FE) analyses of the failed bridges were carried out using the STAAD. Pro general purpose softwares, where different FE models were developed for each bridge. Manual design calculations were also performed using the obtained results of FE models. Laboratory experiments such as uniaxial tensile test, Rockwell hardness test and microscopic examination test of the bridge materials were carried out to identify material and their engineering properties of each bridge. In this study the critical failure modes were identified for each bridge. The study reveals, Paragastota bridge failed in tension by exceeding the elastic capacity, Rakwana bridge failed due to slip at the support and Kappitigala bridge failed due to compression failure in top chord of the bridge truss. Understanding these bridge failures would assist bridge engineers to avoid catastrophic bridge failures in future.