Structural Evaluation of Tied-Arch and Truss Footbridges through a Case Study

Footbridges are usually slender structures with comparatively light load bearing requirements. These bridges are constructed over busy roads or other obstacles to provide a safe and easy passage for pedestrians and improve access. Footbridges are often less costly when compared to other bridges and structures. However, their aesthetics, appearance and practicability are also of high importance. The structure’s slenderness offer opportunities for engineering innovation, but these characteristics make designers pay more attention to issues, such as, wind, impact and collision loads. The main objective of this thesis is to propose some design alternatives for a footbridge crossing over Nicosia-Famagusta main road between the North and South Campuses of Eastern Mediterranean University. In this regard, two types of footbridges, tied-arch and truss bridges, with seven alternatives including the original bridge are investigated from four viewpoints; structural behavior, material usage, cost and aesthetics. Design and loading are according to AASHTO guidelines. Modeling and analyses of the structures are carried out by using the general purpose analyses and design program SAP2000, version 16.0.0 Ultimate. The footbridges studied in this research are to be constructed over a busy road, thus, the vulnerability of each alternative to impact and collision loads were investigated. For this purpose, progressive collapse analysis is carried out to study the behavior of design alternatives in case of damage to pier columns. The results showed that single span bridges have higher performances, and among them, arch type ones represent less deflection and lower compressive stress. In order to determine the bridge with the highest performance each of the investigated characteristics (structural behavior, material usage, cost and aesthetics) were first of all individually compared and then they were compared with each other. The results revealed that single span arch bridge that is designed to be constructed by using simple sections appear to be the best and most appropriate alternative if all parameters receive equal importance weights. However, assigning importance weights to the structural behavior, material usage, and cost, which are as three times as the one allotted to the aesthetics, resulted in selection of single span truss bridge as the most suitable option. Keywords: Footbridges, pedestrian bridges, structural behavior, progressive collapse analysis.