Considerations for Retrofitting Existing Pipe Bridges

Abstract

Pipe bridges are widely used to cross over roads, highways, railroads and obstructions. Retrofitting of existing pipe bridges are required for many reasons such as additional levels, outriggers, and past modifications which were not considered in the original design. There are many items to consider when evaluating, analyzing and reinforcing existing pipe bridges such as operating loads, test loads, seismic loads, wind loads, analysis methods, and reinforcement plans. Pipe bridges are classified as pipe rack structures, which belong to non-building structures. The nature of pipe bridge structures are not similar to regular building structures, which have less redundancy to resist seismic or wind loads. Wind load determination can be a challenging topic due to the lack of research and design guidelines. In this paper, there is a comparative study of wind load determination, which is based on ASCE 7, ASCE Wind Loads on Petrochemical Facilities, a reference calculation performed in the 60s, current design practices and AASHTO wind pressures. The consideration of operating loads, test loads, seismic loads and load combinations for pipe bridges are also discussed in this paper. Usually, existing pipe bridge evaluations and retrofit plans will rely on a structural analysis of the existing bridge. In order to eliminate or minimize the extent of upgrades and satisfy client expectations, several design approaches and options need to be tried and compared. These efforts are also important to meet the project schedule and budget requirements. In some cases, obstructions will add to the difficulties of the retrofit project that requires additional efforts for passing code check, connection verifications and foundation reinforcement. Spring boundary conditions and analysis modeling options are discussed in this paper. It is found that the force redistribution among the structural members and foundations is important for retrofit projects, especially for pipe bridges located in congested areas. The enhancement for pipe bridge members, connections and foundations are also discussed and presented in this paper.