Comparative study of novel cold-formed steel sections for pedestrian bridges under varying structural configurations

Abstract

The use of Cold-Formed Steel (CFS) in bridge engineering has received considerable interest due to its favorable properties, including a lightweight structure, a high strength-to-weight ratio and affordability. As an innovative alternative to traditional materials such as hot-formed steel, timber, and reinforced concrete, CFS shows significant potential in pedestrian bridge construction. The research investigates the performance of CFS pedestrian bridges, with the aim of advancing lightweight, prefabricated, and environmentally sustainable infrastructure in New Zealand.

The research primarily focuses on evaluating the feasibility of using CFS for pedestrian bridges by investigating deflection behavior, stress distribution and overall structural performance under standard loading conditions via finite element analysis (FEA). In total, six types of bridge models --Flat Pratt Truss, Box Truss, Tub Girder, Flat Foot, Box Bridge, and the Modular Panel Bridge-- were thoroughly analyzed under a 5 kPa load. The mesh sensitivity study was conducted to ensure that the simulation results were independent of mesh size, achieving numerical convergence without excessive computational cost, and the simulation procedure is validated by comparing with experimental data sourced from an existing Glass Fiber Reinforced Polymer (GFRP) pedestrian truss bridge. In this study, six Cold-Formed Steel (CFS) pedestrian bridge models were investigated under identical 5 kPa loading, a span/200 deflection criterion as defined by the SNZ-HB-8630:2004 code, consistent boundary conditions, and a yield stress limit of 550 MPa, but with varying spans and geometries. (1) For the Flat Pratt Truss bridge spanning 6 meters, the effect of span on deflection and stress was investigated, revealing a maximum deflection of 0.8 mm and a maximum stress of 77.14 MPa, both well within allowable limits; however, the extremely low stress utilization indicates material overconsumption. (2) For the Modular Panel bridge spanning 7.2 meters, the influence of modular assembly on load distribution was examined, resulting in a higher deflection of 65.88 mm and stress levels reaching 639.4 MPa, exceeding the yield strength. (3) For the Box Truss bridge spanning 6.7 meters, the impact of closed-section geometry on stiffness was studied, demonstrating minimal deflection of 20.3 mm and uniformly distributed stress around 535 MPa. (4) For the Tub Girder bridge spanning 15 meters, the effect of large span on flexural performance was analyzed, identifying significant midspan deflection of 37.5 mm with stresses exceeding the yield strength. (5) For the Flat Foot bridge spanning 30 meters, the influence of extreme span on structural integrity was evaluated, showing excessive deflection of 58.92 mm, though still within the serviceability limits, while the maximum stress of 582.4 MPa surpassed the material yield strength. (6) For the Box Bridge spanning 10 meters, the effect of simple box-section design on structural efficiency was assessed, resulting in a deflection of 13.9 mm and stresses exceeding 550 MPa, demonstrating full material utilization. Among all, the Box Truss bridge was found to offer the most favorable balance between satisfying the deflection serviceability limit and achieving a more uniform stress distribution.