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

Steel truss bridges are widely used in bridge engineering due to their high strength to weight ratio, structural efficiency, and suitability for medium span applications. Among various truss configurations, the Pratt truss is one of the most commonly adopted systems because of its efficient 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 particular emphasis on the bridge response under a critical damage scenario involving the removal of two key structural members. A numerical finite element model of the bridge was developed, and a concentrated vertical load was applied at the upper chord joints to represent traffic loading conditions. To simulate a severe damage state, two critical truss members located in the central spans were intentionally removed from the model, representing missing or failed elements due to deterioration, fatigue, or accidental actions. 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 indicate substantial changes in axial force distribution, particularly in the middle spans, where force redistribution becomes more pronounced due to the simultaneous loss of two members. While the bottom chord members continue to predominantly experience tensile forces and the top chord members remain mainly in compression, the magnitude of these forces increases significantly in the vicinity of the damaged region. The maximum internal forces and deformations are observed near the central spans, highlighting the high sensitivity of multi span truss systems to multiple localized member losses. Overall, the findings provide valuable insight into the structural performance, redundancy, and vulnerability of six span Pratt steel truss bridges under vertical loading conditions with multiple damaged members, contributing to improved resilience based design and structural assessment strategies.

کلیدواژه ها:

Steel truss bridges ، Pratt truss ، maximum internal forces