Dynamic analysis of cold-formed steel roof truss systems under blast loads
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[EMBARGOED UNTIL 05/01/2027] Cold-formed steel (CFS) roof truss systems are widely used in structural applications due to their high strength-to-weight ratio and construction efficiency. However, such systems are not explicitly addressed in existing blast-resistant design standards such as the Unified Facilities Criteria (UFC), and their complex failure mechanisms, ranging from local buckling to connection rupture, pose unique challenges under extreme dynamic loading. This dissertation presents a comprehensive investigation into the dynamic response of full-scale CFS roof trusses subjected to blast loading, combining experimental testing, finite element (FE) modeling, and analytical methods. A validated three-dimensional transient dynamic FE model, developed in ANSYS Workbench 2023, accurately predicted peak deflection with a deviation of less than 2% from full-scale experimental field data. Parametric studies were conducted to examine the influence of truss height, chord thickness and widths, web thickness, yield strength, and roof slope across symmetric, asymmetric, and inclined truss configurations. Key findings showed that increasing yield strength and chord thickness reduced peak deflection by up to 43% and 64%, respectively, with diminishing improvements beyond 600 MPa and 1.85 mm. Asymmetric trusses exhibited increased torsional deformation and local instability. Inclined roof trusses with a 14° slope experienced over 85% higher deflections compared to flat trusses, due to increased reflected pressures and complex dynamic behavior. An analytical framework for evaluating the blast response of Cold-Formed Steel (CFS) roof trusses through the development of a static resistance function and a Single-Degree-of-Freedom (SDOF) dynamic model has been developed. The analytical model incorporates material properties, geometric nonlinearity, and boundary conditions to capture the nonlinear resistance of CFS trusses, demonstrating strong correlation with experimental results, with deviations typically within 5--10%. The SDOF approach was successfully validated against experimental and finite element (FE) analysis results, demonstrating its effectiveness in predicting dynamic structural response under blast loads. Furthermore, the limitations of current blast load estimation methods were evaluated. The ASCE procedure overestimated response by up to 214.6%, whereas the proposed Calculated Pressure Wave (CPW) method achieved improved accuracy with a maximum error of 41%. These findings confirm the need for refined blast load modeling and structural response prediction in CFS systems. Overall, this work delivers validated modeling strategies, analytical tools, and design recommendations for CFS trusses under blast loads. It supports the advancement of blast-resistant design practices and provides a strong foundation for updating UFC and ASCE guidelines to better reflect the behavior of CFS roof systems in extreme dynamic environments.
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Ph. D.