Robert J. Dinan

Modeling blast wave propagation using artificial neural network methods

The paper reports on work concerned with the development of artificial neural network approaches to modeling the propagation of bomb blast waves in a built-up environment. A review of current methods of modeling blast wave propagation identifies a need for a modeling system that is both fast and versatile in its scope of application. This is followed by a description of a preliminary study that used artificial neural networks to estimate peak pressures on buildings protected by simple blast barriers, using data generated from, first, an existing empirical model and, second, miniature bomb-barrier-building experiments. The first of these studies demonstrates the viability of the approach in terms of producing accurate results very rapidly. However, the study using data from live miniature bomb-barrier-building experiments was inconclusive due to a poor distribution of the sample data. The paper then describes on-going research refining this artificial neural network approach to allow the modeling of the time-wise progress of the blast wave over the surfaces of critical structures, facilitating a three-dimensional visualization of the problem. Finally, the paper outlines a proposed novel method of modeling blast wave propagation that uses a coarse-grain simulation approach combined with artificial neural networks, which has the goal of extending modeling to complicated geometries while maintaining rapid processing.

Resistance of Concrete Masonry Walls With Membrane Catcher Systems Subjected to Blast Loading

This paper describes a methodology for analyzing the impulse pressure response of unreinforced concrete masonry walls that have been retrofitted with membranes that are not bonded to the masonry (catcher systems). Membrane catcher systems can be used to protect building occupants from secondary debris resulting from blast pressure, and the effectiveness of systems comprised of polymers, composites, geotextiles, and thin steel and aluminum sheets has been researched extensively over the past fifteen years. The methodology presented herein is based upon the large displacement response of the unreinforced masonry wall, with and without compression membrane arching, and the subsequent tension membrane resistance of the catcher system. The necessary equations are developed in the form of nonlinear resistance functions, which are then used in single-degree-of-freedom analyses to develop dynamic response predictions. The applicability of the approach is substantiated through comparison to full-scale blast test results, and demonstrations involving disparate materials and loading are made.

Boundary Connection Behavior and Connection Design for Retrofitted Unreinforced Masonry Walls Subjected to Blast Loads (Preprint)

Abstract : Over the past decade, extensive experimental and analytical research has been conducted on the behavior and resistance of unreinforced masonry (URM) walls retrofitted with methods for increasing ductility. This includes numerous experiments conducted by the Airbase Technologies Division of the Air Force Research Laboratory (AFRL). These retrofit materials varied from soft elastomeric coatings to very stiff composites and metal sheets. Some retrofit materials were strongly bonded to the masonry wall, which resulted in an integrated system response, while others were not bonded to the masonry and the membrane simply acted as a barrier that prevented secondary fragmentation from entering the occupied space. Previous research programs by AFRL and others have focused on the development of the retrofit materials, with the predominant exploratory measure focusing on the maximum inward transverse displacement. However, little emphasis was placed on the real behavior of the boundaries of these systems and the proper and efficient design of connections. This paper discusses an appropriate analytical methodology for the design of retrofit connections to resist impulse loads due to blast. In addition, typical support conditions for URM walls, and the shear, flexure and friction interaction of blast-impulse-loaded retrofitted URM walls at their support boundaries are discussed. The ideas and conclusions presented herein are based on component-level static testing, full scale explosion arena testing, and high fidelity finite element modeling.

Blast Resistance of Fully Grouted Reinforced Concrete Masonry Veneer Walls

AbstractThis paper describes the full-scale experimental evaluation of the out-of-plane flexural response of fully grouted RC masonry walls subjected to uniform static pressure and to dynamic pressure resulting from an explosion. The investigation was performed as part of a larger effort to improve the design methodologies for reinforced masonry subjected to blast loading. The masonry walls were non-load-bearing and vertically spanning, which represents a significant amount of common construction in the United States. Both single-wythe and veneer wall sections were evaluated. Two types of concrete masonry units were used, i.e., conventional and A-block concrete masonry units. The results of the program provide a better understanding of the ultimate dynamic capacities and ductility of reinforced masonry walls—both single-wythe and veneer walls—which will ultimately help engineers produce designs that are safer and more economical.

Blast-Retrofit of CMU Walls Using Steel Sheets

Blast resistant design has come to the forefront of engineering concerns in the wake of recent terrorist threats to the United States. Safety and security are of utmost concern when designing structures, and there has been a significant rise in the demand of researching new methods of reinforcing and retrofitting structures to provide better resistance to blast loading. The focus of this research paper is on the use of steel sheathing as a method of such retrofit. Research is done to ascertain the steel strength, analyze the response of the steel to static pressure, explore strength and ductility limits, investigate connection details, and develop an analytical model of the static resistance function, which will be verified by experimental data. The analytical model for the resistance function will be used in a single-degree of freedom (SDOF) dynamic model to predict the response of steel sheathing blast-retrofitted wall systems. Coupon tests were performed to establish the stress-strain behavior of the steel material, and component beam tests were used to determine the response of the sheathing under static pressure. In addition, connection methods were analyzed and tested in an effort to determine the most suitable blast-retrofit design for a given blast, without exceeding strength or ductility limits for the steel sheets, and to develop the limit states for the retrofit system. The results of the experimental program and the analytical static and dynamic models were incorporated into a user-friendly wall analysis code for the design of steel sheathing for blast retrofit of CMU walls.

Blast Design of Stay-In-Place PVC-Formed Concrete Walls

Blast resistant design and retrofit of wall systems is of current interest. After standoff, mass and ductility are the most important parameters for blast protection. Concrete walls has the mass necessary, but could lack in ductility if not properly designed. PVC-formed concrete walls are suitable for rapid construction and expeditionary structures. The ductility provided by the PVC layers is expected to enhance the energy absorption capability, and thus improve the blast mitigation capability of the wall system. The paper discusses the mechanics of materials approach for developing the static resistance function for PVC-filled concrete walls. Static tests using a full-scale loading tree to simulate uniform pressure were used to verify the mechanics of materials models. Compared to concrete walls, PVC-concrete wall systems exhibited better energy-absorption capabilities. PI diagrams are developed in this paper to enable blast response prediction of the PVC-concrete wall system.

Resistance Definition for Membrane Retrofit Concrete Masonry Walls Subjected to Blast

Mitigation techniques are currently being sought to ensure public safety in the event of intentional or accidental explosions. Building material fragmentation is a major cause of human injury during such events. One of the most common methods of construction in buildings is the use of unreinforced, ungrouted, infill concrete masonry walls. Concrete masonry provides a fast inexpensive way to construct buildings of various heights; however, these walls are extremely vulnerable to blast pressure resulting in collapse, fragmentation, and severe injury to occupants. Much research has been conducted using full scale blast tests as well as high fidelity computational methods to study the behavior of membrane retrofit masonry walls, but the cost is prohibitive. Design tools developed by other investigators in the field have been available for the past few years; however, they lack a direct definition of the membrane retrofit and their accuracy remains questionable when compared to actual blast test data. The research presented in this paper developed resistance function definitions for three different scenarios of membrane retrofit unreinforced concrete masonry walls. These functions include the bonded and unbonded membrane retrofit scenarios as well as the arching behavior of the masonry wall. The resistance functions were further coupled with single degree of freedom systems to predict the wall response to blast loads. This research gives the structural engineer a practical tool for the design of membrane retrofit masonry walls to resist blast pressures.

Performance of Polymer-encased Concrete Walls Subjected to Blast Loads

Military and diplomatic facilities are targets of terrorist bomb attacks. Unfortunately, terrorists also commonly target populated public facilities such as residential buildings, office buildings, and restaurants. Most casualties and injuries sustained during external explosions are not caused by the pressure, heat, or container fragments resulting from a bomb detonation. Rather, most injuries are blunt trauma and penetration injuries caused by the disintegration and fragmentation of walls, the shattering of windows, and by non-secured objects that are propelled at high velocities by the blast. Ensuring that the exterior walls of a structure are able to withstand a blast without producing deadly fragments is a critical part of minimizing injuries to building occupants. Most common building wall structures are not designed to withstand blast loading. The resistance of a wall to blast loads can be enhanced by increasing the mass and ductility of the wall with additional concrete and steel reinforcement, which can be time consuming and expensive. For these reasons among others, a need has arisen for cost effective methods of designing and constructing walls that can resist significant levels of blast pressure. The overall objective of the research described herein is therefore to investigate and describe the effectiveness mechanisms of walls comprised of permanent concrete formwork for resisting blast loads, and to develop an engineering definition of the resistance provided by polymer-encased concrete wall systems subjected to blast loading. Static flexural tests and full-scale explosive tests were conducted. Also, high-fidelity finite element simulations were used to further understand resistance mechanisms. Efforts thus far have focused on walls without internal steel reinforcement. Future efforts will involve other configurations of stay-in-place forms and resistance definitions that include internal steel, reinforcement. This paper highlights static testing, dynamic testing, finite element modeling approach, engineering resistance definitions, and implementation and accuracy of single-degree-of-freedom (SDOF) models.