Browsing by Subject "Progressive collapse"

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Experimental testing of a steel gravity frame with a composite floor under interior column loss
(2013-05) Hull, Lindsay A.; Engelhardt, Michael D.
Progressive collapse research aims to characterize and quantify the behavior of different structural systems in events of extreme local damage caused by bombings to improve the performance of targeted structures and to protect occupants. The focus of the research program described herein is the performance of steel gravity frame structures with composite floor systems in column loss scenarios. The goal of the project is to contribute to the development of rational design guidelines for progressive collapse resistance and to assess any potential weaknesses in current design standards. This thesis presents the results of a series of tests performed on a steel frame structure with simple framing connections and a composite floor slab under interior column loss. The specimen was designed and constructed in accordance with typical design practices and was subjected to increasing uniform floor loads after static removal of the central column. No significant structural damage was observed up to a load equivalent to the ultimate gravity design load. Further testing was performed after the deliberate reduction of the capacity of the steel framing connections, ultimately resulting in total collapse of the specimen.
Large-scale testing and numerical simulations of composite floor slabs under progressive collapse scenarios
(2015-05) Hadjioannou, Michalis; Williamson, Eric B., 1968-; Engelhardt, Michael D.; Jirsa, James O; Helwig, Todd A.; Kyriakides, Stelios
Two full-scale composite floor slabs were tested at Ferguson Structural Engineering Laboratory at The University of Texas at Austin under two different column removal scenarios. The removal of a column and the associated response of a structure is an index of its resiliency under abnormal loads, such as those due to a terrorist attack or a vehicle collision. Previous computational studies have shown that floor slab contributions are extremely important in mitigating collapse, but the limited experimental data currently available provide inconsistent results. The aim of the experimental testing program was to identify basic behaviors of floor slabs and to estimate their ultimate capacity under the absence of a critical column. The two test specimens were representative of isolated sections of the gravity-load resisting system of a typical steel-framed building. Thus, all steel members were joined using simple connections. During testing, the critical column was statically removed under service loads. Next, the load on the floor slab was increased at a slow rate until the specimens completely collapsed. Overall, the ultimate load carrying capacity of the two specimens under the absence of a single column exceeded the required capacity from progressive collapse provisions. Detailed finite element models were developed and validated against the collected experimental data in which all the components of the floor system were explicitly modeled. The explicit nonlinear finite element software LS-DYNA® was employed to simulate the response of the experimental tests. Initially, individual components of the floor system were modeled and validated against experimental data available in the literature. The two specimens were modeled using a similar approach. The main components of the floor system were modeled using three-dimensional solid elements for the concrete and steel members, shell elements for the corrugated steel deck, and beam elements for the shear studs and reinforcement in the slab. Bolts and other connection components were explicitly modeled using solid elements, and contact was specified to account for the interaction among the connected parts. Good agreement was found between the tests and numerical simulations. Further analyses provided information about the sensitivity of the numerical models to several design parameters.
Linear and nonlinear equivalency factors for progressive collapse analyses
(2007-08) Khandelwal, Akansha; Williamson, Eric B, 1968-
In recent years, progressive collapse as an engineering problem has become a topic of interest due to the observed performance of some structures following terrorist attacks. Due to its highly nonlinear and dynamic nature, rigorous analysis to resist collapse is not common in design offices. Current guidelines by the federal government and US military have addressed this issue and have provided simplified static analysis methods to help mitigate collapse. Past research, however, has suggested that these existing guidelines may be too conservative. This research study focuses on the estimation of equivalency factors for static linear and static nonlinear alternate load path analyses that can be used to achieve the same level of safety as computed from dynamic nonlinear analyses.
Progressive collapse resistance of steel-framed structures with composite floor systems
(2014-08) Moutsanidis, Georgios; Williamson, Eric B., 1968-; Engelhardt, Michael D
Progressive collapse research intends to evaluate and quantify the resistance of structural systems against local failures independent of how such failures may initiate. The present research program pertains to the simulation and analysis of a structural gravity frame with composite floor system under column loss scenarios. The ultimate goal of this research is to evaluate and possibly identify any potential deficiencies in the current progressive collapse guidelines. This thesis presents the construction, testing, and results of a test performed on a steel-concrete composite structure with shear connections under a perimeter column removal. The structure was designed based on typical design guidelines. After the column removal, the specimen was subjected to increasing uniform load and was found to resist the full progressive collapse design load without major failures. In addition, computational work pertaining to the composite floor system behavior and the interaction among the beams, the slab, and the shear connectors was conducted. The purpose of this work was to identify possible deficiencies in the current simulation techniques for composite structure modeling under progressive collapse scenarios. After the analyses were conducted, it was found that the majority of current simulation techniques are adequate for modeling composite floor systems, with the use of nonlinear springs being the most accurate and computationally efficient.
Simplified modeling for assessing collapse resistance of steel gravity frames with composite floor systems
(2014-05) Oksuz, Umit Can; Williamson, Eric B., 1968-; Engelhardt, Michael D.
Progressive collapse is a structural failure that is initiated by the failure of a primary structural member due to manmade or natural reasons and causes a disproportionately large portion of the structure to damage and/or collapse. This thesis is focused on the computational assessment of the performance of steel gravity frames with composite floor systems under column loss scenarios. The ultimate goal is to provide step-by-step guidance to practicing civil/structural engineers on modeling and analyzing full-size structures by using simple structural analysis software with the purpose of determining progressive collapse resistance. In this research project, a steel frame structure with simple framing connections and a composite floor system was tested, modeled, and analyzed under an interior column loss scenario. For the computational analysis part of the research, a simplified modeling approach was developed and verified by comparing the analysis results with detailed finite element model results and available experimental data. Next, the test specimen was modeled with the proposed approach using the SAP2000 software, and an analysis was performed. Results of the analysis were compared with the test data to verify that the model accurately simulates the measured behavior of the structure. In the end, it was concluded that steel gravity frame structures with composite floor systems can be accurately simulated by using the proposed simplified modeling approach up to the point of first element failure. Moreover, it was shown that practicing civil/structural engineers can do quick and simple checks for their structure’s ability to resist progressive collapse by using the methods and approaches that are described in this thesis.
Simplified modeling of shear tab connections in progressive collapse analysis of steel structures
(2010-05) Heumann, Eric Michael, 1985-; Williamson, Eric B., 1968-; Engelhardt, Michael D.
Recent tragedies involving the collapse of several large and prominent buildings have brought international attention to the subject of progressive collapse, and the field of structural engineering is actively investigating ways to better protect structures from such catastrophic failures. One focus of these investigations is the behavior and performance of shear tab connections in steel structures during progressive collapse events. The shear tab, a simple connection, is typically modeled as a perfect pin in standard design, but in progressive collapse analysis, a much more accurate model of its true behavior and limits is required. This report documents the development of a simple yet accurate shear tab model and its use in understanding the behavior and limits of shear tab connections in column removal scenarios. Particular attention is paid to the connections’ axial force limit state, an aspect of behavior that is typically unimportant in standard design.