Flexural behaviour of pre-cast concrete sandwich composite panel – Experimental and theoretical investigations

This paper describes newly developed precast concrete sandwich panels. The panels use a new system of fiber reinforced plastic (FRP) connectors, developed at the University of Nebraska's Center for Infrastructure Research, for transferring shear forces from one concrete wythe to the other The use of FRP as the connector material increases the thermal efficiency of the panels compared to panels that contain steel or concrete connectors. The geometry and material properties of the new connector provide sufficient strength and stiffness for a significant transfer of shear between the two concrete wythes. The results of structural tests are analyzed and design recommendations are presented. Description of an accompanying thermal performance testing of these panels is also included. For full-scale specimens were tested in a vertical position. Two of the specimens contain the new FRP connectors, and two contain steel truss connectors. Measurements of load versus panel deflection and load versus connector stress are provided. The ultimate strength of the panels containing the new connector were found comparable to the strength expected of fully composite panels. The design of panels containing the proposed FRP connecting system can be undertaken ina manner similar to that composite panels. Ultimate strength of the panels can be computed assuming full composite action between the concrete wythes, it sufficient shear connectors are provided and the panels are not over-reinforced.

Full scale testing of precast concrete sandwich panels

Two series of composite precast concrete sandwich panel (PCSP) systems containing various connector reinforcement and construction details were tested in flexure. Panels of one series utilized details similar to certain commercially produced panels, while the second series panels contained modified details to better evaluate interface shear transfer behavior. Results of static testing indicated that a high degree of composite stiffness and composite flexural capacity can be attained with truss girder connectors oriented longitudinally in the panels. Test results also showed that construction details can have a significant impact on the distribution of shear in elements crossing the interface. Results of fatigue testing indicated relatively minor stiffness loss over 55,000 loading cycles.

Flexural behavior of composite precast concrete sandwich panels with continuous truss connectors

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...

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

This paper describes the structural behavior of precast, prestressed concrete sandwich wall panels reinforced with carbon-fiber-reinforced polymer (CFRP) shear grid to achieve composite action. Use of CFRP as a shear transfer mechanism was intended to increase the thermal insulation efficiency, enhance the service life, and increase the overall structural capacities of the panels. This study included testing of six full-scale sandwich wall panels, each measuring 20 ft x 12 ft (6.1 m x 3.7 m). The panels consisted of two outer prestressed concrete wythes and an inner insulation wythe. The study included two types of insulation and several shear transfer mechanisms with different CFRP reinforcement ratios to examine the degree of composite action developed between the two concrete wythes. All panels were simultaneously subjected to applied gravity and lateral loads. Reverse-cyclic lateral loads simulated the effects of wind pressure and suction. All panels were subjected to approximately 4000 cycles of lateral loading with the presence of factored gravity load. Following each fatigue regime, the lateral loads were increased until failure was achieved. Test results of the experimental program were compared with theoretical predictions of fully composite and noncomposite actions to evaluate the percent composite action and to assess the optimum panel configuration.

Behavior of precast, prestressed concrete sandwich wall panels reinforced with CFRP shear grid

A new precast concrete sandwich panel system with a high thermal resistance and optimum structural performance has been developed. A hybrid truss provides the connector in this panel system - the diagonals are fiber-reinforced plastic bars and the chords are prestressed steel strands. Each connector consists of a fiber-reinforced plastic bar fabricated in a deformed spiral shape through which a pair of prestressing strands is threaded to provide anchorage in the concrete wythes. The developed shear connecting system is described together with its advantages. An experimental and analytical investigation of the connecting system was conducted. The experimental program included testing of small scale specimens by push-off loading, small scale panels by flexural loading. The analytical investigation included finite element modeling of the tested small scale specimens and comparisons with theory of elasticity solutions. Experimental and analytical results from finite element modeling and from theory of elasticity equations correlated well and showed that the developed panel system meets the objectives of the research and is expected to have a promising future.

A new structurally and thermally efficient precast sandwich panel system

Maher K. Tadros Cheryl W. Prewett Professor of Civil Engineering and Director Center for Infrastructure Research University of Nebraska Omaha, Nebraska Precast Concrete Sandwich Panels (PCSP), used as exterior walls in multi-unit residential, commercial, and warehouse buildings, are structurally and thermally efficient building elements, and they are in use worldwide; yet, there is very limited available information on the various design, production and construction philosophies. This paper presents the PCSP systems most widely used in North America and Europe as exterior walls for low rise commercial and warehouse buildings. The constituents of these panels are described, and some of the limited available research results are discussed. The theory of analysis for volume change effects is explained and numerical examples are given. A discussion of issues in need of further research is provided. Some widely used PCSP systems in North America and Europe are described in Appendix A, and the names of producers are included for further reference.

http://www.pci.org/uploadedFiles/Siteroot/Publications/PCI_Journal/1991/DOI_Articles/jl-91-november-december-8.pdf

State-of-the-Art of Precast Concrete Sandwich Panels

To make precast concrete sandwich panels, a first concrete slab is formed having embedded in it one end of connectors which extend from it's surface in two directions with the path between the two containing only thermally insulative material, a layer insulative material is positioned adjacent to a central portion of said connectors to form a solid layer and a second layer of concrete is cast so as to receive the upper ends of said connectors. The connectors provide resistance to shear in at least two directions and include insulative high tensile strength members extending in more than one direction between the concrete slabs.

Precast concrete sandwich panels

A continuum model for evaluating partially composite insulated concrete sandwich panel deflections with discrete shear connectors due to differential volume changes such as those caused by differences in temperature between the wythes is evaluated for accuracy by comparison with finite-element analysis. Design equations for computing these deflections are provided. Analysis of sample panels indicates that the continuum model provides acceptable accuracy for calculating thermal bowing of wall panels. The resulting equations show that, for long panels, the amount of thermal bowing in the panels is relatively insensitive to the stiffness of the connectors. This implies that long insulated sandwich panels with low connecting-layer stiffness will experience nearly the same amount of thermal bowing as fully composite panels.

David C. Salmon

Papers

Full scale testing of precast concrete sandwich panels

A new structurally and thermally efficient precast sandwich panel system

State-of-the-Art of Precast Concrete Sandwich Panels

Precast concrete sandwich panels

Partially Composite Sandwich Panel Deflections