Browsing by Subject "Blast"
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Item Analysis and response mechanisms of blast-loaded reinforced concrete columns(2009-05) Williams, George Daniel; Williamson, Eric B., 1968-; Williamson, Eric B., 1968-Terrorism has been an international threat to high occupancy civilian structures, government buildings, and military installations for many years. Statistical data from past terrorist attacks show that transportation infrastructure has been widely targeted, and a bombing of an ordinary highway bridge is a realistic scenario. Recent threats to bridges in the U.S. confirm this concern and have caught the attention of the bridge engineering community. Given that many ordinary highway bridges in the United States support critical emergency evacuation routes, military transportation plans, and vital economic corridors, the loss of a key bridge could result in severe national security, economic, and socioeconomic consequences. Therefore, in this research, a simplified procedure is developed to predict blast loads on bridge columns, and an understanding of the mechanisms that cause damage and ultimately failure of blast-loaded reinforced concrete bridge columns is advanced. To that end, computational fluid dynamics models are constructed and validated using experimental data. These numerical models are used to characterize the structural loads experienced by square and circular bridge columns subjected to blast loads, which is followed by the formulation of a simplified load prediction procedure. Additionally, nonlinear, three-dimensional, dynamic finite element models of blast-loaded reinforced concrete bridge columns are developed and validated using qualitative and quantitative data from recent experimental tests. The results of these analyses illustrate the fact that circular columns cannot be assumed to experience less base shear demand than a square column simply because they experience less net resultant impulse. Furthermore, the column response models developed in this research are used to identify and explain the mechanisms that lead to the spalling of side cover concrete off blast-loaded reinforced concrete members observed in recent experimental tests. Therefore, the results of this research advance the understanding of the structural loads on and the resulting response of reinforced concrete bridge columns subjected to blast loads, and as such these contributions to the structural engineering community enhance the security of the U.S. transportation infrastructure.Item Development of simplified dynamic response models for blast-loaded bridge components(2014-05) Sammarco, Eric Louis; Williamson, Eric B., 1968-; Bayrak, Oguzhan; Kallivokas, Loukas F; Engelhardt, Michael D; Ezekoye, Ofodike A; Stevens, David JInternational terrorist organizations have been active across the globe for decades, but attacks against public surface transportation infrastructure constitute a recent trend. Statistical data from past attacks, along with numerous threats received by United States (U.S.) Government authorities, support this claim and render U.S. transportation infrastructure security a national concern. Public highway bridges can be particularly vulnerable to a malevolent attack due predominately to their public accessibility and exposed nature. Furthermore, the sudden failure of a highway bridge located on a major transportation corridor has the potential to cause significant economic loss, human casualties, and societal distress. Motivated by the recent trend of increasing worldwide attacks and identified vulnerabilities associated with public highway bridges, considerable research in the area of bridge security has been carried out over the past decade. While much research is still needed, it is important to begin transitioning the existing knowledge and technology to the appropriate users within the bridge analysis and design community. Accordingly, the main objective of the research described in this dissertation is to facilitate this transition and advance the state of-the-practice in bridge-specific protective analysis and design by developing accurate yet fast-running dynamic response models for reinforced concrete (RC) bridge columns and tower panels subjected to blast loads. Given a threat scenario and bridge component of interest, the RC component response models characterize demand on a selected component and provide an estimate of peak dynamic response and incurred damage. Such fast-running, engineering-level models provide practicing bridge engineers with the ability to readily assess the performance of blast-loaded bridge components without having to rely on time-consuming, costly, and complex resources such as physical testing or high-fidelity finite element simulations. The proposed dynamic response models are also capable of facilitating anti-terrorist/force protection (ATFP) retrofits and rapid in-situ vulnerability assessments of existing bridge components, as well as safe designs of new bridge components. As part of a larger research effort that was chiefly managed by the author of this dissertation, the RC component response models were integrated with similar models for steel bridge towers and high-strength steel cable components to form a comprehensive, component-level vulnerability assessment software for blast-loaded bridges. Therefore, the results of this research synthesize the state-of- the-art in blast-resistant bridge analysis/design and put forth a practical, engineering-level tool to aid in the growing concern of domestic transportation infrastructure security. This contribution to the structural engineering community marks a step towards enhanced resiliency of existing and future U.S. highway bridges.Item Development of software architecture to investigate bridge security(2012-12) Bui, Joeny Quan; Williamson, Eric B., 1968-; Bayrak, OguzhanAfter September 11, 2001, government officials and the engineering community have devoted significant time and resources to protect the country from such attacks again. Because highway infrastructure plays such a critical role in the public’s daily life, research has been conducted to determine the resiliency of various bridge components subjected to blast loads. While more tests are needed, it is now time to transfer the research into tools to be used by the design community. The development of Anti-Terrorism Planner for Bridges (ATP-Bridge), a program intended to be used by bridge engineers and planners to investigate blast loads against bridges, is explained in this thesis. The overall project goal was to build a program that can incorporate multiple bridge components while still maintaining a simple, user-friendly interface. This goal was achieved by balancing three core areas: constraining the graphical user interface (GUI) to similar themes across the program, allowing flexibility in the creation of the numerical models, and designing the data structures using object-oriented programming concepts to connect the GUI with the numerical models. An example of a solver (prestressed girder with advanced SDOF analysis model) is also presented to illustrate a fast-running algorithm. The SDOF model incorporates the development of a moment-curvature response curve created by a layer-by-layer analysis, a non-linear static analysis accounting for both geometric non-linearity as well as material non-linearity, and a Newmark-beta-based SDOF analysis. The results of the model return the dynamic response history and the amount of damage. ATP-Bridge is the first software developed that incorporates multiple bridge components into one user-friendly engineering tool for protecting bridge structures against terrorist threats. The software is intended to serve as a synthesis of state-of-the-art knowledge, with future updates made to the program as more research becomes available. In contrast to physical testing and high-fidelity finite element simulations, ATP-Bridge uses less time-consuming, more cost effective numerical models to generate dynamic response data and damage estimates. With this tool, engineers and planners will be able to safeguard the nation’s bridge inventory and, in turn, reinforce the public’s trust.Item Numerical simulations of riveted connections under quasi-static and dynamic loadings(2016-05-02) Hill, Aaron Thomas, Jr.; Williamson, Eric B., 1968-; Engelhardt, Michael D.; Clayton, Patricia; Taleff, Eric M.; Crane, Charles K.Despite years of concerted effort in the war against terrorism, there still exist terrorist networks and lone wolf actors that continue to threaten people and infrastructure around the world. Among the potential targets of terrorists are the more prominent, high value, and symbolic locations that make up the United States’ critical transportation network. This is an urgent national security issue. While many organizations such as the Federal Highway Administration (FHWA) and the Association of State Highway and Transportation Officials (AASHTO) continue to sponsor experts from professional practice, academia, and other agencies to develop strategies to deter and disrupt such attacks, there is little known about the specific response of riveted connections under high rates of loading. A general lack of access and expertise with riveted connections, which have not been widely used in construction of bridges since the 1950s, and the expense and difficulty in replicating and collecting accurate data for close-in detonation testing on riveted steel connections make it a challenge to analyze and estimate the capacity and behavior of riveted connections. This research focuses on numerical simulation of riveted steel connections under high rates of loading. Finite element modeling using LS-DYNA (2013) is first developed to match the physical testing of A502 Grade 2 riveted structural connections subjected to dynamic and quasi-static shear loadings completed at the U.S. Army Engineer Research and Development Center (ERDC). This initial modeling serves as validation for the LS-DYNA (2013) model parameters for response. Subsequent analyses expand on the validated modeling to serve as a numerical prediction of additional riveted connections subjected to dynamic loads. Results from the testing and numerical simulations can serve to expand the capabilities of existing anti-terrorist planning software and serve as an addition to existing bridge protection guidelines. The numerical simulation modeling will fill an important gap in the current knowledge base on the performance of riveted connections under high loading rates that will be of value to the U.S. Army Corps of Engineers and the Federal Highway Administration. Understanding the capacity and behavior of these connections will assist future researchers in developing mitigation strategies against blast loadings.Item Predicting damage and blast load propagation due to internal detonations(2015-08-13) Strecker, Adam Michael; Williamson, Eric B., 1968-; Engelhardt, Michael D; Helwig, Todd A; Bayrak, Oguzhan; Ezekoye, Ofodike AIn recent years, the world has seen an increase in international terrorism. Terrorist attacks often involve explosive devices, and they frequently target non-military buildings constructed with typical details. The way in which the U.S. military currently trains and fights has also shifted in recent years from a conventional warfare focus during the Cold War, to a focus on military operations in urban terrain (MOUT). In these urban operations, military targets may include buildings constructed with typical details, and the employment of munitions can potentially cause excessive collateral damage. Most of the past research involving blast effects on structures has involved external detonations or internal detonations on hardened facilities. The current terrorist threat and the increase in MOUT have created a need to analyze internal detonations in buildings constructed with typical details. The goal of the research study is to develop an engineering-level model to predict the damage and blast load propagation through buildings constructed with typical details resulting from an internal detonation. The research focuses on full-height steel stud interior walls and develops a mechanics-based predictive model. Experimental tests performed by the Defense Threat Reduction Agency as well as concepts from an existing empirically-derived model created by Weidlinger and Associates, Inc., were used to develop the model for the research study. This model simulates blast loads in an interior detonation room and computes the structural response of the interior steel-stud walls by using an equivalent single-degree-of-freedom system to analyze each wall. The structural response is combined with air mass flow through openings to predict blast load propagation. Pressure and impulse histories are computed for each room within a building. The predictive capability of the model developed for the research study is validated using a different series of experimental tests conducted by the Air Force Research Laboratory. The research presented in this dissertation has created a predictive blast load propagation model for internal detonations for one specific scenario involving full-height steel-stud walls. This model can continue to be improved to encompass a broader spectrum of scenarios and become an extremely useful engineering-level tool for protective design and munitions employment