Structural and thermal efficiency of precast concrete sandwich panel systems

Precast concrete sandwich panels (PCSP) are structurally and thermally efficient elements used for exterior walls in multi-unit residential, commercial, and warehouse buildings throughout the world. A typical PCSP consists of two precast reinforced concrete layers (called wythes) separated by a layer of insulation and connected with connectors which penetrate the insulation layer. The connectors used in the majority of available PCSP systems consist of concrete webs or blocks, steel elements, or a combination thereof. Because of their low thermal resistance, steel and concrete connectors can cause significant reduction in the effective thermal resistance of the panel through thermal bridging. The objective of this research is to develop a connecting system capable of improving the thermal and structural performance of PCSPs. This dissertation first presents a review of existing PCSP systems. Next, evaluation of selected fiber reinforced plastic (FRP) connectors is summarized. The structural performance of a few FRP connectors is evaluated through a series of pure-shear (push-out) tests performed on small scale specimens. The initial evaluation and the first phase of testing led to the selection of a FRP bent-bar connector. The bar is fabricated in a deformed spiral shape through which a pair of prestressing strands or reinforcing bars can be threaded to provide anchorage in the concrete wythes. Phase two (pure shear tests) and phase three (flexural tests) were performed on small scale specimens to evaluate the structural performance of the bent-bar connector. In addition, the structural performance of the connector was analytically evaluated by developing finite element models for panel behavior in testing phases two and three. Experimental and analytical results from finite element and differential equation analysis are in good correlation. This dissertation also includes a brief study of stresses and deformation due to differential volume changes. Volume changes often contribute a large portion of the stress or out-of-plane deflection of PCSPs. The finite element model, calibrated with the results of testing phase three, is used to evaluate the effectiveness of the differential equations for computing deflections due to differential volume changes. Both methods are compared with a practical design method for evaluating stresses and out-of-plane deflection due to differential volume changes