Abstract
abstract: Insulated pre-cast concrete wall panels, also called sandwich panels, consist in two external concrete layers, in which an internal layer of thermal insulation material is inserted between, aiming better acoustic and thermal performance. One of the main concerns regarding the performance of these panels refers to the elimination of thermal bridges caused by metallic connectors, which jeopardize the panels’ thermal efficiency. One of the proposals to solve this problem consists in the use of PERFOFRP connectors, which are plane plates with perforated holes through its thickness, which are embedded into the concrete plates, creating anchorage pins that enhance the shear strength and the layers’ debonding resistance. This research had the objective of evaluating the production quality of this type of connector, produced with a low-cost and easy-to-use vacuum assisted resin infusion system; considering the effects of: (a) resin plate homogeneity, by taking samples from various locations on the plate; (b) fabrication repeatability; and (c) raw production materials’ origin; on the results of: (I) ultimate tensile stress, (II) modulus of elasticity, and (III) volume fraction of fibre. Also, 18 specimens in the form of representative models of the shear connector in insulated pre-cast concrete wall panels, with six different hole configurations achieved by varying the holes’ diameter and spacing, were subjected to push-out tests, to assess the holes’ diameter and spacing effects on the mechanical performance of the connection in terms of ultimate load capacity and stiffness. The results indicated a production quality with a satisfactory level of characteristics variation, considering: the variability in different parts of a single composite plate, the variability between composite plates from different infusion process, and the variability between different production batches. Furthermore, the push-out tests demonstrated that the perforated connectors presented, when compared to non-perforated connectors: a gain in shear strength from 8% to 25%, lower relative displacements, and higher levels of stiffness. It was also observed that connectors with 25.40 mm diameter holes presented better performance than connectors with 31.75 mm diameter holes; and that the reducing the hole spacing from 2.00 to 1.75, for the 25.40 mm diameter specimens, caused a decrease in the load capacity of the connector. Thus, it was verified that variations on the hole’s diameter and spacing influenced the load carrying capacity of the connection.
Highlights
Insulated pre-cast concrete wall panels, called sandwich panels, consist in two external concrete layers, in which an internal layer of thermal insulation material is inserted between, aiming better acoustic and thermal performance
The evaluation of the production quality of the glass-fibre reinforced polymer (GFRP) composite plates encompassed three characterization procedures: (a) a dimensional homogeneity analysis, by measurement of the plate thickness (ε), which refers to geometric conformity; (b) the mechanical characterization of the main properties of interest (i.e., ultimate tensile stress, longitudinal (Ept.l) and transversal tensile modulus of elasticity (Ept.t), and Poisson’s ratio (υ)), which refer to composite strength conformity; (c) the determination of the volume fraction of fibre (Vf), which refer to the material composition conformity
4 CONCLUSIONS This work presented the evaluation of production quality and the mechanical behaviour of shear connectors manufactured with perforated GFRP plates for insulated pre-cast concrete wall panels, produced with an in-house developed low-cost vacuum assisted resin infusion system
Summary
Insulated pre-cast concrete wall panels, called sandwich panels, consist in two external concrete layers, in which an internal layer of thermal insulation material is inserted between, aiming better acoustic and thermal performance. Concerning the mechanical strength of FRP connectors, several tests have been conducted in order to assess the mechanical performance and composite action degree of this type of connector, such as: Naito et al [3], that used double-shear tests to evaluate the performance of 14 types of commercial connectors, including FRP connectors, and developed a simplified tri-linear model of force versus relative displacement for use in structural performance analysis of sandwich panels; Hodicky et al [15], that analysed the effect of connector spacing and insulation thickness in the strength of a CFRP grid connector, observing that an increase in insulation thickness leads to a decrease in the connector strength; and Tomlinson et al [16], that tested connectors composed by angled bars of basalt-fibre reinforced polymer (BFRP) and analysed the effects of varying the bar diameter, inclination angle, and orientation of the diagonal connector relative to loading in tension and compression cases, in the bond between concrete and insulation layers and the overall performance of the connector In this sense, the PERFOFRP connectors were developed aiming both better mechanical and thermal insulation performance. This research has two main objectives: (a) assess the production quality of a low-cost fabrication system of shear connectors for sandwich panels, produced from plane perforated plates of GFRP according to the PERFOFRP proposal; (b) asses the mechanical behaviour of the produced connectors, by means of double-shear push-out tests on representative models of the shear connector in insulated pre-cast concrete wall panels, with hole of various diameter and spacing
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