Structural Analysis of a Six Span Pratt Steel Truss Bridge under Vertical Load with a Damaged Member

Steel truss bridges are widely used in bridge engineering due to their high strength to weight ratio, structural efficiency, and suitability for medium spans. Among different truss configurations, the Pratt truss is one of the most commonly used systems because of its effective arrangement of tension and compression members. In this study, the structural behavior of a six span Pratt steel truss bridge subjected to vertical loading is investigated, with special emphasis on the bridge response under a critical damage scenario. A numerical finite element model of the structure was developed, and a vertical load was applied at the upper chord joints. To simulate a critical failure condition, one of the key truss members was intentionally removed from the model, representing a damaged or missing structural element. Internal member forces, displacements, and stress redistribution within the damaged structure were analyzed and compared with the expected behavior of an intact Pratt truss system. The results show significant changes in axial force patterns, particularly in the central spans where force redistribution becomes more pronounced due to the absence of the removed member. The bottom chord members still primarily experience tension, and the top chord members remain mostly in compression; however, the magnitudes of these forces increase substantially in the vicinity of the damaged region. The maximum internal forces and deformations occur near the middle spans, highlighting the sensitivity of multi span truss systems to localized member loss. Overall, the findings provide valuable insight into the structural performance and vulnerability of steel Pratt truss bridges under vertical loads when subjected to sudden member removal, contributing to improved assessment and resilience based design strategies.

کلیدواژه ها:

Steel truss bridges ، Pratt truss ، critical damage scenario