Bryan T. Bewick

Performance and Characterization of Shear Ties for Use in Insulated Precast Concrete Sandwich Wall Panels

Insulated precast concrete sandwich wall panels are commonly used for exterior cladding on building structures. The insulation is sandwiched between exterior and interior concrete layers to reduce the heating and cooling costs for the structure. The panels can be designed as composite, partially composite, or noncomposite. Shear ties are used to achieve these varying degrees of composite action between the interior and exterior concrete layers. A variety of shear ties are available for domestic construction. An experimental study was conducted to assess the relative strength and response of these commercially available ties. Fourteen different shear tie types were examined, the failure modes and responses were quantified, and simplified engineer level multilinear strength curves were developed for each connection. The test results indicate that shear ties used in sandwich wall construction have considerable variation in strength, stiffness, and deformability. The maximum shear strength of the discrete tie...

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.

Evaluation of Conventional Construction Techniques for Enhancing the Blast Resistance of Steel Stud Walls

AbstractCold-formed steel stud walls are an attractive alternative to wooden stud walls because of their ductility, sustainability, and resistance to insects, mold, and rot. To date, engineers have faced challenges using steel stud walls to mitigate blast loads because of strict response limits set forth by existing standards that address blast-resistant design. Because of the limited past research on the response of steel stud walls subject to blasts, uncertainties exist regarding how these systems transition from elastic to inelastic response, particularly when lateral torsional buckling or local buckling of a section occurs. Existing standards used to design structures to mitigate blast loads penalize the use of steel stud walls by incorporating large safety factors that make the design of these systems uneconomical, which prevents engineers from taking full advantage of their benefits. The goal of the research described in this paper is to evaluate the suitability of conventional construction techniqu...

Blast Performance of Single-Span Precast Concrete Sandwich Wall Panels

AbstractA research program was conducted to assess the capability of conventional non-load-bearing insulated precast concrete exterior wall panels to withstand blast loadings. Typical construction details from the tilt-up and prestressed concrete industries were examined. The sensitivity of insulation type, reinforcement, foam thickness, and shear tie type on the flexural resistance was assessed. Forty-two single-span static experiments were conducted on 14 different panel designs. From the results of these experiments, resistance functions and deformation limits for insulated concrete sandwich panels were determined. The resistance functions were used to develop predictive dynamic models for panels subjected to blast demands. The models were found to be accurate in comparison to measurements from four full-scale blast detonations. The findings of the research indicate that both prestressed and non-prestressed insulated concrete wall panels meet current rotational limits defined by the U.S. Army Corps of ...

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.

Crumb Rubber Concrete Performance under Near-Field Blast and Ballistic Demands

To address the ever-increasing quantity of scrap tires produced in the United States, a study is conducted on the use of crumb rubber in concrete for use in structures against near-field blast and ballistic demands. Crumb rubber concrete (CRC) is produced by replacing a volume percentage of the traditional coarse and/or fine aggregate with crumb rubber particles. Crumb rubber is produced in various gradations from used vehicle tires through a variety of shredding processes. The influence of crumb rubber on the constitutive and structural performance of concrete under quasi-static loading has been examined in past research. CRC has been shown to have decreased strength and stiffness while still being a useable structural material. This research study examines the use of CRC for the specialized application of blast and ballistic protection. The program characterizes resistance of CRC to contact and near-contact high explosive detonations, and examines depth of penetration, and perforation using V50 methods. The results of the experimental and analytical investigation found that (1) the addition of crumb rubber results in decreased resistance to ballistic demands and near-field blast loads, (2) the reduction is less than that estimated by accepted predictor methods, and (3) when normalized by weight rather than thickness, the use of CRC results in an improvement in resistance to ballistic and near-field blast demands.

Simulation of Prestressed Concrete Sandwich Panels Subjected to Blast Loads

Abstract : This paper discusses simulation methodology used to analyze static and dynamic behavior of foam insulated concrete sandwich wall panels through ultimate capacity. The experimental program used for model development and validation involved component-level testing, as well as both static and dynamic testing of full-scale wall panels. The static experiments involved single spans and double spans subjected to near-uniform distributed loading. The dynamic tests involved spans up to 30 ft tall that were subjected to impulse loads generated by an external explosion. Primary modeling challenges included: (1) accurately simulating prestressed initial conditions in an explicit dynamic code framework, (2) simulating the foam insulation in the high strain rate environment, and (3) simulating shear transfer between wythes, including frictional slippage and connector rupture. After validation, the models will be used to conduct additional behavioral studies and parametric analyses, and assess and improve methodology currently used in the design of foam insulated precast/prestressed sandwich panels for blast loads.

A Neural-Network Model-Based Engineering Tool for Blast Wall Protection of Structures:

Blast barrier walls have been shown to reduce blast loads on structures, especially in urban environments. Analysis of existing test and simulation data for blast barrier response has revealed that a need still exists to determine the bounds of the problem and produce a fast-running accurate model for the effects of barrier walls on blast wave propagation. Since blast experiments are very time intensive and extremely cost prohibitive, it is vital that computational capabilities be developed to generate the required data set that can be utilized to produce simplified design tools. The combination of high fidelity model-based simulation with artificial neural network techniques is proposed in this paper to manage the challenging problem. The proposed approach is demonstrated to estimate the peak pressure, impulse, time of arrival, and time of duration of blast loads on buildings protected by simple barriers, using data generated from validated hydrocode simulations. Once verified and validated, the proposed neural-network model-based simulation procedure would provide a very efficient solution to predicting blast loads on the structures that are protected by blast barrier walls.

Computational Modeling of Steel Stud Wall Systems for Applications to Blast-Resistant Design

AbstractPast research has shown that blast-loaded steel stud walls exhibit a range of different failure mechanisms depending on the stud and track section properties, connection details, and sheathing characteristics. To date, few studies have addressed the computational modeling of these systems. Because large-scale blast tests are expensive and logistically difficult, computational models are needed to evaluate different design options prior to carrying out full-scale experiments. In this paper, the authors present finite-element models that capture the peak load and deformation capacity of steel stud wall systems, accounting for the failure modes observed in past testing. The proposed models strike a balance between level of refinement and computational efficiency. These models were validated against data collected from an extensive laboratory testing program. Based on observations from both the lab tests and computational simulations, recommendations are given for improving the large-deformation respo...