John M. Hoemann

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...

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 ...

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.

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.

Assessment of resistance definitions used for blast analysis of unreinforced masonry walls

Over recent decades, three distinct methods have evolved that are currently being used to generate resistance functions for single-degree-of-freedom analyses of unreinforced masonry walls subjected to blast loading. The degree of differences in these resistance definitions depends on whether the wall is assumed to be simply supported or whether compression arching forces result from rotation restraint at the supports. The first method originated in the late 1960s as a result of both experimental and analytical research sponsored by the US Department of Defense. That method, referred to as the Wiehle method, is the basis of Unified Facilities Criteria 3-340-02 and other derived analytical software such as the Wall Analysis Code developed by the US Army Corps of Engineers, Engineer Research and Development Center. The second method is based on elastic mechanics and an assumed linear decay function that follows and is the basis of the widely used Single-Degree-of-Freedom Blast Effects Design Spreadsheets software distributed by the US Army Corps of Engineers, Protective Design Center. The third method is largely based on concrete and masonry behavioral theories developed by Paulay and Priestly in the early 1990s. This article systematically compares the resistance methodologies for arching and non-arching scenarios, demonstrates the implications by plugging the disparate resistance functions into blast load single-degree-of-freedom models, compares the analytical results to full-scale blast test results, and offers conclusions about the accuracy and efficacies of each method.

Design Limits for Precast Concrete Sandwich Walls Subjected to External Explosions (PREPRINT)

Abstract : The use of precast/prestressed concrete and tilt-up concrete for exterior walls is common practice in the United States. This form of construction provides an economical, rapid, and high quality building technique making it ideal for military and government facilities. In most cases these building systems must be designed against a potential explosive demand. Current design recommendations are very restrictive when using precast concrete components due in large part to the lack of experimental research data. To address this issue, a series of over 50 experiments were conducted to assess the failure modes and load and deformation capacity of wall panel systems. Single span and multispan panels were examined. Foam type, tie type, and reinforcement were varied to provide a thorough understanding of the effects of these variables on the failure modes of the panels. The response of the systems was found to be sensitive to the insulation foam used and the failure mode of the shear ties. The results indicate that insulated precast concrete panels exceed the current response limits used by the Army for Anti-Terrorism and Force Protection (ATFP) applications.

Response Prediction of Foam-Insulated Concrete Sandwich Panels Subjected to Blast Loads using Bilinear Weighted-Resistance SDOF Models

This paper presents the development and validation of a single-degree-of-freedom (SDOF) methodology that can be used for the analysis and design of foam-insulated concrete sandwich panels subjected to blast loads. The experimental program used for validation involved both static and dynamic testing of full-scale wall panels. Static testing demonstrated that the degree of composite action provided depends greatly upon the shear connector used and that the internal shear resistance mechanisms change as the panel undergoes large deflection. Given the extreme complexities involved, a simplified bilinear resistance definition was developed using weighted averages between the composite and non-composite resistances. The weighting values were based upon equating the averaged energy absorption capacity measured during the large deflection static testing with that of the analytical definition. The analytical resistances were then used in SDOF models to examine their applicability through comparison to full-scale blast test responses. The weighted resistance SDOF approach was shown to be a viable option for analyzing foam-insulated sandwich panels subjected to blast loads.

Performance of steel stud walls subjected to blast loads

Abstract : Past research has demonstrated that steel stud walls can perform well when subjected to large blast events. The construction methods needed to achieve good performance that take advantage of the inherent ductility offered by steel, however, have been costly and have often required the use of specialized connection details that allow a stud to reach its full flexural and/or tensile capacities prior to connection failure. The goal of the current study is to develop techniques for mitigating large blast loads acting against steel stud walls using conventional construction materials and techniques. Two issues of concern for the current research are: 1) the performance under blast loads of typical connections, either commercial clips or the standard screwed-stud-to-track, has yet to be fully examined, and 2) current methods of design do not incorporate the mechanical interaction of veneer layers for potentially increasing the blast resistance of steel stud walls. To better understand the role played by connection design details and wall system construction details, research for this project includes laboratory testing, field testing, and computational modeling. In this paper, the authors provide an overview of the research program and a summary of the findings that have been developed to date. From the data collected during this project, designs that exhibit a balance of simplistic, economic, and adequate protection will be developed.

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.

Blast resistance of membrane retrofit unreinforced masonry walls with flexible connections

Unreinforced masonry infill walls are one of the most economical and widely used exterior wall systems. However, they can produce secondary fragments due to their brittle failure modes when subjected to an impulsive blast load. One retrofit to reinforce existing masonry walls is to install a membrane that prevents fragments from entering the building’s interior. Previous research focused on defining the resistance provided by the wall membrane system, but did not include flexibility of the attachments and their influence on the retrofitted wall system. This article addresses that issue through (1) a review of existing membrane retrofit resistance definitions, (2) a derivation of the resistance definition that includes connection flexibility, (3) validation of the derived resistance definition through nonlinear finite element analyses, and (4) comparison of the resistance in a single-degree-of-freedom framework against full-scale blast testing.