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International 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.
Damage to a pier column will take a bridge out-of-service, or worse, lead to a complete bridge failure. Besides the importance of civilian safety, maintaining bridge serviceability is imperative to civilian and military transport, while discontinuous transportation networks have rippling effects on economy and community. With the increase of blast attacks on transportation networks and structures, researchers and design engineers are seeking understanding of the behavior of transportation structures subject to blast loading.Increased numerical modeling capabilities allow researchers to consider material, structural, and load effects on structure response at limited expense. However, researchers must carefully consider modeling parameters to appropriately represent the nonlinear material and geometric behavior inherent to a blast event. Numerical model simulations vary vastly in complexity and are handicapped by programming assumptions. A balance of numerical model fidelity, simulation behavior accuracy and general applicability must be found to develop design criterion for blast loads on bridge components. This study considers the effects of four modeling parameters: aspect ratio, boundary conditions, longitudinal reinforcement ratio and standoff distance in a simplified and a complex numerical simulation. The simplified model considers several discrete mass elements connected by linear elements to model the subject column, whereas the complex model considers continuum elements, material models accounting for degradation and failure, and a built-in blast load application software. The scope of the project was to evaluate the performance of the simplified model considering the complex model as the baseline for comparison. It is believed that the differences in load application, material behavior, and stiffness have the largest impact on the simplified model. Implementation of the load application and stiffness must be carefully considered in the development of a simplified model.
Terrorist attacks and other destructive incidents caused by explosives have, in recent years, prompted considerable research and development into the protection of structures against blast loads. For this objective to be achieved, experiments have been performed and theoretical studies carried out to improve our assessments of the intensity as well as the space-time distribution of the resulting blast pressure on the one hand and the consequences of an explosion to the exposed environment on the other.This book aims to enhance awareness on and understanding of these topical issues through a collection of relevant, Transactions of the Wessex Institute of Technology articles written by experts in the field. The book starts with an overview of key physics-based algorithms for blast and fragment environment characterisation, structural response analyses and structural assessments with reference to a terrorist attack in an urban environment and the management of its inherent uncertainties.A subsequent group of articles is concerned with the accurate definition of blast pressure, which is an essential prerequisite to the reliable assessment of the consequences of an explosion. Other papers are concerned with alternative methods for the determination of blast pressure, based on experimental measurements or neural networks. A final group of articles reports investigations on predicting the response of specific structural entities and their contents.The book concludes with studies on the effectiveness of steel-reinforced polymer in improving the performance of reinforced concrete columns and the failure mechanisms of seamless steel pipes used in nuclear industry.
Explores code-ready language containing general design guidance and a simplified design procedure for blast-resistant reinforced concrete bridge columns. The report also examines the results of experimental blast tests and analytical research on reinforced concrete bridge columns designed to investigate the effectiveness of a variety of different design techniques.
[Truncated abstract] Efficiently and accurately predicting structural dynamic response and damage to external blast loading is a big challenge to both structural engineers and researchers. Theoretical investigation on this problem is complex as it involves non-linear inelastic material properties, effect of time varying strain rates, uncertainties of blast load calculations and the time-dependent structural deformations. Most of the theoretical methods are developed based on simplified models which makes their accuracy and application scope limited. Experimental investigation on this issue can provide valuable data for locating the damage and establishing the damage criteria. The damage curves generated from the extensive experimental study can provide quick assessment of the structural status. However, such blast experiments always involve concern about the safety and affordability. Besides this, because of the large nonlinear deformation, experimental data often cannot be extrapolated. Therefore the correlation of the experimental data with predictive method is difficult since it requires a large number of tests to generate damage curves. Compared with the theoretical and experimental study, numerical simulation does not involve any safety concern and it is proved to be cost-effective. With verified material model and element model, numerical simulation could be powerful supplement for the experiments and provide reliable structural response predictions. However, the numerical simulation of modern structures under impulsive loadings could be time and resource consuming. This is because in order to convert the blast energy into the structure and capture the transient wave propagation as well as the localized damage, refined mesh is always required and this requirement makes the simulation process slow and costly. In the first part of this thesis, a numerical method aimed at reducing the calculation cost and ease the numerical simulation effort is proposed. When compared with the natural vibration period of most structures, the blast loading duration is extremely short and there is no sufficient time for the overall structural response to develop during the loading phase, thus the large global deformation and damage usually occur in the free vibration phase. In the proposed method, the structural response is calculated in two steps. In the first step, the structural velocity and displacement response at the end of the blast loading duration is calculated using the theoretical SODF model, and such responses are used as the initial conditions for the second step free vibration analysis...
After 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.
[Truncated abstract] As a consequence of the increase in terrorist incidents, many comprehensive researches, both experimental and numerical modelling of structure and blast interaction, have been conducted to examine the behaviour of civilian structures under dynamic explosion and its impact. Nevertheless most of the works in literature are limited to response of simple structures such as masonry walls, reinforced concrete beams, columns and slabs. Although these studies can provide researchers and structural engineers a good fundamental knowledge regarding blast load effect, it is more likely for blast load to act upon entire structures in actual explosion events. The interaction between blast load and structures, as well as the interaction among structural members may well affect the structural response and damage. Therefore it is necessary to analyse more realistic reinforced concrete structures in order to gain an extensive knowledge on the possible structural response under blast load effect. Among all the civilian structures, bridges are considered to be the most vulnerable to terrorist threat and hence detailed investigation in the dynamic response of these structures is essential. This thesis focuses on the study of the response of a modern cable-stayed bridge under blast loadings. ... Firstly, analysis is conducted to examine the failure of four main components namely pier, tower, concrete back span and steel composite main span under close proximity dynamic impact of a 1000 kg TNT equivalent blast load. Secondly, based on such results, the remainder of the bridge structure is then tested by utilizing the loading condition specified in the US Department of Defence (DoD) guideline with the aim to investigate the possibility of bridge collapse after the damage of these components. It is found that failure of the vertical load bearing elements (i.e. pier and tower) will lead to catastrophic collapse of the bridge. Assuming that terrorist threat cannot be avoided, hence protective measures must be implemented into the bridge structure to reduce the damage induced by explosive blast impact and to prevent bridge from collapse. As such, a safe standoff distance is determined for both the pier and tower under the blast impact of 10000 kg TNT equivalent. This information would allow the bridge designer to identify the critical location for placing blast barriers for protection purpose. For the case of bridge deck explosion, carbon fibre reinforced polymer (CFRP) is employed to examine in respect of its effectiveness in strengthening the concrete structure against blast load. In this research, appropriate contact is employed for the numerical model to account for the epoxy resin layer between the CFRP and concrete. In addition, to ensure that the CFRP can perform to its full capacity, anchors are also considered in the numerical study to minimize the chance of debonding due to the weakening of the epoxy. The results reveal that although severe damage can still be seen for locations in close proximity to the explosive charge, the use of CFRP did reduce the dynamic response of the bridge deck as compared to the unprotected case scenario. Further investigation is also carried out to examine the change in damaged zone and global response through variation in CFRP thickness.
Original research on performance of materials under a wide variety of blasts, impacts, severe loading and fireCritical information for protecting buildings and civil infrastructure against human attack, deterioration and natural disastersTest and design data for new types of concrete, steel and FRP materials This technical book is devoted to the empirical and theoretical analysis of how structures and the materials constituting them perform under the extreme conditions of explosions, fire, and impact. Each of the 119 fully refereed presentations is published here for the first time and was selected because of its original contribution to the science and engineering of how materials, bridges, buildings, tunnels and their components, such as beams and pre-stressed parts, respond to potentially destructive forces. Emphasis is placed on translating empirical data to design recommendations for strengthening structures, including strategies for fire and earthquake protection as well as blast mitigation. Technical details are provided on the development and behavior of new resistant materials, including reinforcements, especially for concrete, steel and their composites.