Sandwich Wall Panels Research Articles

Structural Performance of Sandwich Wall Panels with Different Foam Core Densities in One-way Bending

The flexural behavior of a new sandwich panel proposed for cladding of buildings is studied. The panel is fabricated by laminating two glass fiber-reinforced polymer skins to a prefabricated polyurethane foam core. Two different densities for the core are explored, namely; a 0.31 kN/m3, referred to herein as ‘soft’ foam, and a 0.63 kN/m3, referred to as ‘hard’ foam. Ten 1500 × 300 × 76 mm3 panels were tested in flexure. For each core density, three similar panels were tested to establish the reproducibility of test results as a measure of quality control of fabrication. The panels were tested in three-point and four-point bending as well as under uniform load. The effect of wind pressure and suction was simulated for some panels by applying cyclic bending. It was shown that flexural strength and stiffness increased substantially, by 165% and 113%, respectively, as the core density was doubled. The contributions of shear deformation of the soft and hard cores to mid-span deflection were 75% and 50%, respectively. Panels with soft cores were vulnerable to localized effects under concentrated loads, and suffered inwards wrinkling of the compression skin at a lower ultimate strength. Low cycle fatigue resulted in some residual deflection upon unloading but insignificant stiffness degradation.

Analysis and design guidelines of precast, prestressed concrete, composite load-bearing sandwich wall panels reinforced with CFRP grid

This paper presents newly developed design guidelines for precast/prestressed concrete wall panels reinforced with carbon-fiber-reinforced-polymer (CFRP) shear grid to achieve the composite interaction. The analytical approach provides a general methodology to determine the behavior of fully and partially composite wall panels. The effects of an imperfect connection between the two concrete wythes are considered by varying the total shear force transmitted through the shear connectors at the interface. The predicted strains along the thickness of the panel at different load levels compared well with recent test results conducted at North Carolina State University in Raleigh. The shear-flow capacity of the insulating materials and the CFRP shear grid are determined using the proposed approach. The influence of the degree of the composite interaction on the induced curvature and slip-strain behavior is presented. A simple design chart for estimating the flexural capacity of the wall panels with different shear-reinforcement ratios is proposed. The approach is also verified by using finite-element analysis up to the service-load level. The predicted displacement and strains compared well with the measured values reported by the experimental program.

Experimental evaluation of precast, prestressed concrete, three-wythe sandwich wall panels

This paper describes an experimental program designed to verify the behavior of 3-wythe panels under later load and at the time of prestress transfer. The general flexural behavior of the 3-wythe panels was investigated using lateral load tests. Load-deflection behavior, degree of composite action, flexural strength, and horizontal shear of the panels under the action of a uniform pressure over the panel span were evaluated in this study. Fabrication of the panels for the lateral load tests revealed that cracking at prestress transfer was a concern. Thus, additional tests were performed to evaluate stresses at prestress transfer. These tests examine the actual behavior of full-scale, 3-wythe panels under the action of prestress force. Experimental results presented in this paper are compared with FEM analysis results. Descriptions of FEM analyses and models were given in a prior paper, and complete details of the work presented in this paper were provided in 2 other earlier papers.

Analytical assessment of blast resistance of precast, prestressed concrete components

Protection against blast has become a high priority for many owners of structures. Blast retrofits/structural hardening, as with earthquake retrofits, can be costly. For this reason, it is important to understand that any structural element has an inherent capacity to absorb energy and resist some level of blast demand. A general evaluation that allows a designer to realize the absorption capacity of a structural element may preclude the need for a blast-specific retrofit. To illustrate this concept, blast resistances of non-loadbearing precast, prestressed concrete sandwich wall panels (PCSWP) are examined. These components are extensively used in modern construction for cladding of structural systems and often provide a significant level of protection from blast events. This paper examines the behavior of PCSWP subjected to blast loads. Four explosive experiments were performed on 4 sets of wall panels. An analytical model was developed and validated with the measured blast demands and peak displacements. The analytical model is used to predict wall-panel damage for varying levels of peak pressures and impulses. An extension of this method is proposed for assessing the blast resistance of horizontal diaphragm elements, such as double tees or hollow-core. An example analysis for a double-tee structural base system with a localized blast is provided.

Design and Analysis of Precast, Prestressed Concrete, Three­ - Wythe Sandwich Wall Panels

Precast concrete, three-wythe sandwich wall panels were developed with potentially improved thermal and structural performance compared with that of traditional two-wythe panels. A three-wythe panel has three concrete wythes and two insulation layers. All three concrete wythes are connected by solid concrete regions, and the connections between successive concrete wythes are staggered in location so that no concrete path extends directly through the entire thickness of the panel. This paper describes the design and analysis of the three-wythe panels. A series of two- and three-wythe panels were designed, and examination of the resulting panels' behavior provides insight into the anticipated capabilities of the three-wythe panels. Finite element analyses were performed to anticipate the behavior of the three-wythe panel at both the transfer of prestressing force and under service loads. It was found that three-wythe panels can be designed using current design codes with special consideration of stresses that develop at the panel ends. A three-wythe panel can be treated as a composite panel and is suitable for longer spans compared with spans typical for a two-wythe panel. Transverse bending occurs in a three-wythe panel at the panel ends, and several approaches to reduce the transverse bending were introduced and evaluated, such as using partially debonded strands and shear connectors.

Development of a Precast Concrete Shear-Wall System Requiring Special Code Acceptance

Precast, prestressed wall panels comprising thin concrete sections are not commonly used as seismic shear walls. Many engineers and code officials view prestressed materials as nonductile, and the connections between the sandwich wall panels and the foundation may suffer from brittle joint failures. The authors have designed a new load-limiting foundation connection for precast, prestressed panels used as shear walls that prevents the development of excessive uplift forces in the joint. This connection allows precast, prestressed concrete wall panels, such as hollow-core, to act as shear walls in resisting seismic loading without relying on wall ductility or causing an anchorage failure in a thin concrete section of the wall panel (where a connector is located). This unique connector allows the wall system to behave unlike that anticipated by building-code-defined design methods. Building codes require the behavior of new systems to be compared (and proven similar) with that of code-conforming behavior before being used. This paper describes the development and testing of the proposed load-limiting connector and wall system and the wall design approach needed to obtain special building code approval for its use.

Thermal performance evaluation of precast concrete three-wythe sandwich wall panels

Precast concrete sandwich wall panels are commonly constructed of two wythes of concrete separated by a layer of thermal insulation. In these two-wythe panels, solid concrete regions are often provided for embedded hardware for lifting, handling, and connections, or to provide composite action. These solid concrete regions can have a significant adverse impact on the thermal performance of the panels. This research was directed towards the development of precast concrete three-wythe sandwich wall panels with potential improved thermal and structural performance. A three-wythe panel has three concrete wythes and two insulation layers, and all three concrete wythes are connected by solid concrete regions. However, the connections between successive concrete wythes are staggered in location so that the total thermal path length through the concrete is extended. Practical panel configurations of the three-wythe panels were developed to reduce thermal bridge effects caused by regions of solid concrete. The thermal performance of the three-wythe panel was evaluated by estimating its thermal resistance ( R-value) using the finite element method. It was found that, in general, the thermal performance of three-wythe panels is better than that of two-wythe panels due to the increased thermal path length through the panel.

NU Precast Concrete House Provides Spacious and Energy Efficient Solution for Residential Construction

In 1990, the University of Nebraska-Lincoln began conducting research to develop a novel precast concrete alternative to traditional wood framing for residential homes in the United States. The main objective of this effort was to produce a new housing system, called the Nebraska University (NU) Concrete House, a precast concrete design that would offer superior benefits over conventional construction,. including resistance to fire, termites, high winds and storm damage; reduction in home maintenance, dust, and noise; and high energy efficiency for homeowners. Research focused on three new precast concrete systems-a patented fully insulated exterior sandwich wall panel, a floor joist panel, and an under-roof girder framing system designed for fast assembly. The NU Concrete House used only bolted connections, eliminating the need for welding or grouting during erection.

Analytical Investigation of Thermal Performance of Precast Concrete Three-Wythe Sandwich Wall Panels

Precast concrete sandwich wall panels are commonly constructed of two wythes of concrete separated by a layer of thermal insulation. In these two-wythe panels, solid concrete regions which extend directly through the entire thickness of the panel are often provided with embedded hardware for lifting, handling, and connections, or to provide composite action. These solid concrete regions have a significant adverse impact on the thermal performance of the panels. This research was directed towards the development of precast concrete three-wythe sandwich wall panels with improved thermal and structural performance. A three-wythe panel has three concrete wythes and two insulation layers, and all three concrete wythes are connected by solid concrete regions that are staggered in location so that no concrete path extends directly through the entire thickness of the panel. Practical panel configurations of three-wythe panels were developed, and their thermal performance was evaluated by estimating thermal resistance (R-value) using finite element method.

Experimental Evaluation of the Composite Behavior of Precast Concrete Sandwich Wall Panels

Lateral load tests were performed on four full-scale precast concrete sandwich wall panels. The first panel was a typical precast, prestressed concrete sandwich panel that had shear transfer provided by regions of solid concrete in the insulation wythe, metal wythe connectors (M-ties), and bond between the concrete wythes and the insulation wythe. The degree of composite action developed by each shear transfer mechanism (regions of solid concrete, wythe connectors, and bond) was then evaluated by testing three additional panels that included only one mechanism each. The panels were tested in a horizontal position with simple supports under the action of a uniform lateral pressure. It was found that, for the panel geometries and materials treated in this study, the solid concrete regions provide most of the strength and stiffness that contribute to composite behavior. Steel M-tie connectors and bond between the insulation and concrete contribute relatively little to composite behavior. For design purposes, it is recommended that solid concrete regions be proportioned to provide all of the required composite action in a precast sandwich wall panel.

Loadbearing Architectural Precast Concrete Wall Panels

Architectural precast concrete wall panels that act as loadbearing elements in a building are both a structurally efficient and economical means of transferring floor and roof loads through the structure and into the foundation. In many cases, this integration can also simplify construction and reduce costs. This article presents the many benefits that can be derived from using loadbearing architectural precast concrete walls in buildings. Discussed herein are the various shapes and sizes of wall panels, major design considerations, and when loadbearing or shear wall units should be the first design choice. The role of connections, shear walls, and the use of precast concrete as forms for cast-in-place concrete is explained. In general, the design methods and techniques presented in this article apply to buildings in both seismic and non-seismic areas. The latter part of this article shows how these design principles can be applied in practice in a variety of buildings. These examples illustrate the use of window wall panels, spandrels, and solid or sandwich wall panels as the loadbearing wall members. When all the advantages of using architectural precast concrete as loadbearing walls are added up, it makes good sense to use this structural form in building applications.

State-of-the-Art of Precast/Prestressed Sandwich Wall Panels

The purpose of this report is to present to the architect, engineer, contractor, precast/prestressed concrete producer and owner current [as of 1997] North American practices concerning uses, design, detailing, manufacturing and thermal performance of sandwich panels. An additional purpose is to share experience gained over the past decades, and by doing so, permit specifiers, suppliers and users to benefit.