Experimental static resistance of cold-formed steel roof truss systems

Abstract

[EMBARGOED UNTIL 6/1/2024] Critical infrastructure vulnerable to attack or located in areas of high threat requires increased protection. U.S. facilities at home and abroad have seen disruption and destruction due to lack of capability to fully resist attack. Increasing effort to improve the building structure, particularly building envelope systems, can improve the life-safety and continued operability of critical infrastructure under adverse circumstances. The popularity of cold-formed steel (CFS) building components has seen a sharp rise in recent years due to its low cost, high strength, ease of construction, and design flexibility. Despite its extensive use, no design criteria exist for the design of cold-formed steel roof systems under blast load. While extensive studies have been conducted on blast load on CFS walls, sufficient research has not been done to develop adequate design procedures for CFS roof systems. Past research has explored the behavior of these truss systems up to ultimate capacity, but the full inelastic behavior was not fully captured. Since many structures are allowed to sustain permanent deformations in blast scenario, it is critical to the safety of building occupants to fully understand the non-linear response of building envelope systems. Dynamic testing and numerical analysis are uneconomical and tedious for every design variation, so the simplified single degree of freedom (SDOF) approach to dynamic analysis is commonly used to project blast resistance of complicated structural systems. In order to perform the SDOF analysis, a static resistance function is required. This study aims to analyze the full static resistance of full-scale cold-formed steel trusses commonly used in the industry and identify associated failure modes in order to more accurately predict dynamic response with simplified methods. Sixteen unique truss designs were tested under quasi-static loading up to ultimate failure using a mechanical testing system. Three select designs will be discussed in this thesis. A simplified finite element analysis was performed using SAP2000 non-linear analysis and compared to experimental results. Experimental results show that truss performance and absorbed energy are significantly affected by the truss configuration and thickness of truss elements. Results of this study will be used to validate advanced numerical models. The quantifiable application of system capacities will improve future designs of building systems and lead to a more safe and resilient infrastructure.