In-plane behavior of BFRP grid reinforced geopolymer concrete sandwich wall panels

Abstract

Prefabricated concrete sandwich wall panels (SWPs), composed of two reinforced concrete wythes and a thermal insulation layer in between, have been widely used in the precast industry as a facade or load-bearing wall. Connectors are used to laterally connect the two wythes to achieve sufficient composite action. With increasing attention to global warming and demand for reducing energy consumption, the SWPs provide thermal insulation to building envelopes in order to reduce energy consumption for heating and cooling the interior building space. The structural behavior of a SWP is very complex due to the non-linear behavior of materials, the uncertain role of connectors causing the partial degree of composite action, and the interaction between its various components. This thesis presents a study on the in-plane behavior of a novel type of SWP, proposed by the author’s group, consisting of Basalt FRP (BFRP) grid/bar reinforced geopolymer concrete wythes and hollow tubular Glass FRP (GFRP) connectors. Geopolymer concrete (i.e., clinker-free concrete) is produced by alkali-activation of solid aluminosilicate precursor materials (i.e., fly ash and slag), having comparable mechanical properties to OPC concrete. Replacement of OPC concrete with geopolymer concrete, steel reinforcement bar with BFRP grid/bar and use of tubular GFRP connectors makes the proposed SWP environmentally friendly, durable and structurally efficient. The thesis contains extensive experimental and numerical investigations covering the structural behavior of the followings – 1) concentrically axially loaded SWPs, 2) eccentrically axially loaded SWPs, and 3) SWPs subjected to in-plane cyclic shear loading. In the first part, ten full-scale concentrically axially loaded SWPs were tested to evaluate the effect of slenderness ratio, the thickness of insulation and spacing of connectors. The failure modes, load-deformation behavior, load-strain relationships, and ultimate axial loads were obtained and discussed. The test axial load capacities were compared with predicted theoretical load capacities while following the fully composite action assumption. The next part of the thesis presents the findings obtained from testing the six full-scale SWPs subjected to eccentrical axial load. The key test parameters included slenderness ratio, type of reinforcement (i.e., BFRP bar or grid), and load eccentricity. The failure modes, crack pattern, load-deformation behavior, and load-strain relationships were carefully studied and reported. Axial load-moment (N-M) interaction curves were obtained for squat and slender SWPs. The strain variation profiles across the sectional thickness of SWPs were obtained and discussed. Further, a numerical analysis, using a MATLAB script, was carried out to predict the axial load capacities of tested SWPs obtained while following the fully composite action assumption, and the predicted results were compared with the test results. A parametric study was conducted using the developed MATLAB program. A lower bound value of a parameter, £ (i.e., ratio of test capacity to predicted axial load capacity), is proposed based on a comparison of the test results of available experimental studies with the theoretically predicted results. In the last part of the thesis, eight full-scale quasi-static tests were conducted to understand the structural behavior of the proposed SWP subjected to in-plane cyclic shear loading, simulating the seismic loading. The role of the BFRP grid as web shear reinforcement was investigated. Test parameters considered were aspect ratio, solid vs sandwich wall panel, axial load ratio and web reinforcement type. Test data were analyzed to obtain the failure modes, drift capacity, hysteretic curve, energy dissipation, stiffness degradation, and shear and flexural components of lateral deformation. Further, a numerical analysis was conducted using OpenSees software using the available SFI-MVLEM module (i.e., Shear-flexure interaction multiple-vertical-line-element model) to predict the structural behavior of the solid equivalent of the proposed SWP subjected to in-plane cyclic shear loading. This thesis has contributed to understanding the in-plane behavior of proposed SWPs. An in-depth understanding of failure modes, load capacities, second-order effect, axial load-moment interaction curves, the role of connectors, seismic behavior (i.e., hysteresis curve, energy dissipation, shear and flexural deformations, etc.) of SWPs has been achieved. Comparing test results with numerically predicted results while assuming the full-composite action will help develop a simplified design methodology. However, more such tests with a wide range of parameters need to be conducted to develop a simplified empirical expression to predict the behavior of such SWPs for design purposes.