A Proposed Methodology to Analyze Cold-Formed Steel Trusses Subjected to Blast Loading Using Single-Degree-of-Freedom for Design and Assessment
The following thesis proposes a methodology for analyzing Cold-Formed Steel (CFS) trusses subjected to blast loading using a non-linear Single-Degree-of-Freedom (SDOF) approach. SDOF has proven to be an effective structural dynamic analysis tool for the design of common components such structural steel, reinforced concrete, and even CFS studs in flexure. Unlike typical components, the behavior of CFS trusses when loaded beyond their peak capacity is not well understood, but data sets from small experimental samples demonstrate that CFS trusses are capable of providing residual capacity even after buckling occurs. Based on this key observation, the scope of this thesis intends to leverage existing data to develop a simplified methodology for blast analysis using SDOF. Within this scope, Finite Element (FE) modeling assumptions and techniques are developed and validated against available experimental data for analysis using LS-DYNA. Advanced topics, such as buckling and imperfections, are considered when modeling techniques are developed; however, these topics are worthy of independent research efforts that are not included in the scope of this thesis. Quasi-static strength simulations are then performed on designed trusses in order to better characterize the extent of residual capacity after buckling. The data from strength simulations, along with principles of advanced structural analysis, are then leveraged to develop parameters for SDOF modeling. Finally, FE models and SDOF models are subjected to identical blast scenarios and the results are compared side-by-side. The resistance functions resulting from the proposed SDOF methodology compare favorably to the quasi-static simulation results performed in LS-DYNA. Similarly, the blast analysis results using the proposed SDOF models compare very well to the blast simulations performed in LS-DYNA. However, due to the limited amount of data produced within the scope of this thesis, it can be concluded that the results are encouraging, but only a framework for further development has been established. The conclusion section highlights several areas for improvement that were identified for additional research to ensure the methodology is better vetted. Also, design considerations and general guidance that are based on the findings from the work performed and backed by engineering principles are summarized as recommendations in the conclusions as well.