Precast Concrete Sandwich Panels Research Articles

Blast behaviors of precast concrete sandwich EPS panels: FEM and theoretical analysis

Precast concrete sandwich panel (PCSP) is widely used as the component of the precast concrete structure (PCS). Various numerical studies on PCSPs have been conducted to investigate their blast behavior. At first, a three-dimensional finite element model was established to study the blast resistance of PCSPs. An explosion tests were adopted to validate the accuracy and reliability of the numerical model developed in this study. Secondly, parametric analyses were carried out to investigate the influence of the thickness of expanded polystyrene (EPS) insulation layer, the spacing of connectors, layouts of connectors and the force transfer mechanism of connectors on maximum deflection and the effective plastic strain of PCSPs. Finally, a simplified numerical model is proposed to validate the derivation and simplify the calculation of the dynamic response of PCSPs under blast loads. Moreover, the comparisons of the anti-blast performance between the reinforced concrete (RC) slab and PCSP were also carried out. The results showed that the blast resistance of PCSP is weaker than the conventional RC slab.

Development of thin precast concrete sandwich panels: Challenges and outcomes

The development of thin precast concrete sandwich panels presents many structural, thermal and practical challenges. This study outlines the design, testing and production of novel panels constructed of two layers of high strength, fibre-reinforced concrete that sandwich a layer of high performance insulation. The layers are connected with fibre reinforced polymer grid connectors in an effort to achieve composite action. Thin precast concrete sandwich panels offer weight and material savings over standard reinforced concrete panels, that enable manufacturing, transport and onsite efficiencies, as well as reduced embodied energy. Much current research, focused on reduced concrete section thickness, prioritise the use of textile reinforced concrete which requires specialist equipment and manufacturing methods. This work instead presents a solution that is suitable for production in standard precast facilities. The design development and testing of different design iterations is outlined. Ten samples of 3 m high panels are tested structurally using flexural tests. The panels are tested thermally using experimental techniques and finite element analysis. A case study is presented on a demonstration building. It achieved bending moment capacities in excess of the design wind load requirements, a measured U-value less than 0.18 W∙m−2∙K−1 and post cracking residual strength ensuring a ductile failure. Hence, the final panel design is deemed to achieve both structural and thermal requirements of a high performing cladding element. The panel was developed at scale in a precast facility for practical implementation on a building in-use.

Experimental and Numerical Investigation of Novel I-Shaped GFRP Connectors for Insulated Precast Concrete Sandwich Wall Panels

Abstract Insulated precast concrete sandwich wall panels (IPCSWPs) are widely used in the thermal resistance systems of buildings. This paper proposes a novel I-shaped glass fiber-reinforced plasti...

Flexural performance of precast geopolymer concrete sandwich panel enabled by FRP connector

Precast concrete sandwich panel (PCSP), consisting of two concrete wythes and a thermal insulation layer in between, can improve greatly the energy efficiency in buildings. This study aims to investigate the structural performance of a new type of PCSP, for which reinforced geopolymer concrete is used as two wythes and connectors made of fiber-reinforced polymer (FRP) composites are used to realize the composition action. Eight so-formed precast geopolymer concrete sandwich panels (PGCSP) were fabricated and evaluated their flexural performance through four points bending test. The experimental parameters included connector type (plate-type and hexagonal tubular), connector spacing (300 and 525 mm), reinforcement type (basalt FRP reinforcement and steel reinforcement) and reinforcement ratio (0.30% and 0.43%). The load vs. mid-span deflection relationships, crack patterns, failure modes, reinforcement strain development relationships, and degrees of composite action of the panels were investigated in details. In addition, two-dimensional (2D) finite element (FE) analysis was conducted to reproduce the test results and to facilitate a better understanding on the panel’s performance particularly the connector’s behavior at different loading stages. It was concluded that a higher degree of composite action in the panels can be achieved through the use of FRP tubular connectors, besides, all the FRP tubular connectors can retain their load transfer capacities at the ultimate limit state owning to their ductile failure behavior.

Thermal-Structural Analysis and Thermal Bowing of Double Wythe UHPC Insulated Walls

Ultra-high performance concrete (UHPC) was recently introduced to the precast concrete sandwich panel (CSP) industry, resulting in significantly thinner and lighter panels than those with conventional concrete. As exterior walls, they are expected to endure a wide range of seasonal temperatures, causing thermal bowing. A robust thermal-structural coupled finite element (FE) model, capable of modeling the partial composite action, was developed for the UHPC CSPs to assess their thermal bowing behavior. Three CSP designs, differing mainly in configuration and quantity of shear connectors, have been studied. Thermal loading was introduced by subjecting one surface to a constant room temperature, and the other to a variable temperature range of -50 °C to +60 °C. The model predictions were validated using panels tested under thermal and structural loading. The analysis revealed that panel deflections increased with the degree of composite action but satisfied serviceability requirements for the full range of temperatures. Cracking of the UHPC wythe occurred when the temperature differential (ΔT) between the two surfaces was equal to or less than -7 °C. The maximum tensile stress in the connector was less than 12% of its tensile strength, and occurred in the first connector from the panel end, which is consistent with the maximum relative slip between wythes.

Structural shear performance of insulated precast concrete sandwich panels with steel plate connectors

Precast concrete sandwich panels are an increasingly popular means of building cladding. They can be designed with high thermal resistance by embedding abundant insulation between two concrete wythes. Steel, in the form of thin plate connectors, remains one of the most common tie materials to support the outer wythe of concrete vertically, and transmit lateral forces from the external rain-screen to the internal structural wythe. The optimum design of steel shear connectors must satisfy thermal and strength capacity constraints. An extensive experimental study analyses the structural shear performance of precast concrete sandwich panels with steel plate connectors of various dimensions that give rise to different load capacities, stiffnesses and failure modes.

Experimental study on precast concrete sandwich panel with cross-shaped GFRP connectors

Precast concrete sandwich panels (PCSPs) have been extensively used as a facade wall in buildings to improve thermal efficiency. The connectors that link the two concrete wythes are mainly used for in-plane shear transfer. In this study, two cross-shaped glass-fibre-reinforced polymer connectors with different section areas are proposed, with the aim of achieving optimal performance and easy construction in PCSPs. First, the pull-out and shear capacities of the connectors were evaluated. Then four PCSPs and two reinforced concrete solid panel counterparts were fabricated and tested under out-of-plane static loads in order to evaluate their flexural behaviour. The parameters investigated included the connector section area and spacing. Moreover, two-dimensional finite-element (FE) analysis was conducted to reproduce the test. The results indicate that: (a) the proposed connectors can provide considerable performance in terms of anchorage and shear capacity; (b) the failure mode of the PCSP specimens was governed by connector failure; (c) the degree of composite action in terms of ultimate strength can be obviously enhanced by increasing the connector section area and/or reducing its spacing; and (d) based on a comparison with the test results, the proposed FE model can predict the flexural behaviour of the tested PCSPs.

Mechanical behavior and composite action of two-wythe precast concrete sandwich beams via chemically hybridized intermediate layer

Composite action of two-wythe precast concrete sandwich beams are examined on the premise of an integrated thin intermediate layer that is suggested as a possible substitute candidate for industry-standard extruded polystyrene (XPS) in precast concrete sandwich panels (PCSP). Designable mechanical properties of a carbon-fiber reinforced interfacial epoxy-polyurea matrix (C-IEPM) may be tuned via the rate of reaction between epoxide and amine of a thermosetting epoxy network, controlled by the elapsed time of reaction tc, and its subsequent surface treatment via reaction with isocyanate and amine moieties, resulting in a thin covalently bonded IEPM layer. Thirteen concrete beams were tested under 4-point bending. A two-wythe beam with an intermediate C-IEPM layer (tc = 0.5 h) was compared to two-wythe beams that included the following intermediate layers: XPS, conventional carbon-fiber epoxy (CF/E), and no layer, where beams with a C-IEPM layer at lower tc showed substantial increase in peak strength and energy absorption: 54% and 97%; 47% and 143%; 27% and 46%, respectively. This indicates that C-IEPM that engenders a high-quality IEPM can substantially improve mechanical performance, energy absorption, and composite action. Finite element analysis of a two-wythe system with an assumed perfectly bonded C-IEPM intermediate layer (tc = 24) confirms that IEPM designed at tc ≤ 0.5 effectuates a perfect bond between wythes and also provides tremendous resiliency and strength sustainability in accordance with load-deflection response beyond the peak load, making C-IEPM a viable candidate as an intermediate layer in pre-cast multi-wythe constructions.

Thermal bridge effect of vertical diagonal tie connectors in precast concrete sandwich panels: an experimental and computational study

The purpose of this work was to quantify the thermal bridge effect of vertical diagonal tie connectors in precast concrete sandwich panels (PCSPs). Special interest was in cases where the use of rigid insulation (e.g. PIR) would leave air gaps between insulation boards and diagonal ties, thus intensifying the thermal bridge. A climate chamber experiment using 5 different joint types was performed to gather reference data for CFD model validation. In the experiment, natural convection was observed in joints where no additional insulation was used, i.e. in air cavities. Significantly larger heat fluxes were measured in these cavities compared to insulated joints. The thermal bridging effect was evaluated for a typical PCSP (thermal transmittance without thermal bridges U = 0.11 W/(m²·K)) using CFD software taking into account 3D heat conduction and convection. Simulation results indicate that diagonal ties without adjacent air cavities increased the average thermal transmittance (U-value) of the envelope by 8%, diagonal ties with a 6 mm air cavity – 19...33% and diagonal ties with a 10 mm air cavity – 45...56%. In conclusion, it was found that the joints in insulation caused by diagonal ties affect the overall thermal performance of the building envelope significantly when efforts are not made to fill the air cavities around the connectors.

Numerical study on through thickness shear capacity of insulated sandwich panels

In the world with ever decreasing natural resources and ever increasing need for structures along with global warming compel us to go for a less consuming and more environment friendly approach one of such is wall panel construction using precast sandwich panels. Precast concrete sandwich panels (PCSP) are as name suggests a type of precast wall panels with an insulated core sandwiched between two wire mesh reinforced concrete wythes. The core can be of any insulated material, in this study the core material used is Expanded Polystyrene (EPS). These panels can be used as both wall panels and roof panels. The two wythes are associated by the shear connectors through the EPS centre for transference shear forces (hence called as through-thickness shear) between the wythes and accomplishing composite activity in the panels. The shear connector that is considered for this study is a discreet truss shaped shear connector that are proven to be effective by previous experimental studies. Though various experimental studies are conducted in those panels the numerical study in this is scanty. In this paper the numerical study is conducted for the through thickness shear capacity of the sandwich panels using ABAQUS-CAE software (Finite Element Analysis software). The parameters varied in this numerical study include the effect of absence of EPS core and thickness of the EPS core. From the numerical model the stress strain relationship along with the load deflection curves are plotted and the results are discussed. The results from the numerical studies are similar to that of the experimental studies and are compared.

Early-Age Shrinkage Effects in Precast Concrete Sandwich Panels

Early-Age Shrinkage Effects in Precast Concrete Sandwich Panels

Load-Carrying Capacity of Composite Precast Concrete Sandwich Panels with Diagonal Fiber-Reinforced-Polymer Bar Connectors

Load-Carrying Capacity of Composite Precast Concrete Sandwich Panels with Diagonal Fiber-Reinforced-Polymer Bar Connectors

Accelerated ageing test and durability prediction model for mechanical properties of GFRP connectors in precast concrete sandwich panels

Glass fiber-reinforced polymer (GFRP) connectors are the key components in precast concrete sandwich panels, because they not only provide continuity between two concrete wythes but also promote thermal efficiency of the panels. This paper presents an experimental study on durability of GFRP connectors in alkaline solution (simulated concrete environment) with variable parameters of temperature (40, 60, and 80 °C) and conditioning time (3.65, 18, 36.5, 92 and 183 days). A total of 160 specimens were immersed in the alkaline solution with a composition specified in ACI 440.3R-12 at elevated temperatures. Scanning electron microscope (SEM) was used to observe the degradation mechanism of the specimens, and the phenomenon of debonding between fibers and resin could be observed more obvious with the increase of erosion time and temperature. The test results also showed that, after 183 days of immersion at 60 °C, tensile strength and modulus of elasticity of the specimens decreased about 38.85% and 21.45% respectively, while compressive strength and modulus of elasticity of the specimens decreased about 40.18% and 27.62%. Finally, a prediction model of tensile and compressive strength after conditioning over time at varied temperatures was proposed based on Arrhenius equation.

Lumped GFRP star connector system for partial composite action in insulated precast concrete sandwich panels

This paper introduces a novel composite shear connectors system used to transfer interface shear forces in a precast concrete sandwich panel. The shear connectors consist of non-proprietary non-composite commercial glass fiber reinforced polymer (GFRP) pin connectors that are laid out in a star pattern and clustered at the top and bottom of the panels. The testing program consisted of thirty-four push-off, twenty-three pullout, and eight full-scale flexural specimens was conducted to evaluate the structural performance of the new shear connectors. The effect of concrete wythe thickness, insulation wythe thickness, and concrete compressive strength was investigated throughout these tests. Additionally, the effect of bond between insulation and concrete wythes was investigated using push-off tests. The flexural test results were compared with predicted fully composite, non-composite, and partially composite values to evaluate the overall panel performance. The comparison showed satisfactory performance with a lower bound of 90% composite action for specimens with 100 mm thick insulation wythe and full composite action for most panels with 50 mm thick insulation. Idealized shear load-slip curves were also developed that account for various parameters to assist design engineers in designing insulated sandwich wall panels with the proposed shear connectors system.

Thermal investigation of thin precast concrete sandwich panels

Thin, lightweight alternatives to standard precast concrete sandwich panels have received much research and design focus in recent years. Some designs have been structurally tested and validated. Much less focus has, however, been given to their thermal performance. This study thermally investigates thin, lightweight precast concrete sandwich cladding panels that embed high performance insulation between two thin concrete wythes. A sample thin design is experimentally tested using a hot plate apparatus to evaluate its thermal performance. Finite element modelling is then used to further investigate the common features of thin panel designs and potential areas of heat loss. The analysed representative thin sample sandwich panel (150 mm thick) achieves an average U-value of 0.324 W m−2 K−1; this is 16% lower than that of a typical 315 mm thick sandwich panel with 100 mm of polystyrene foam insulation. Thermal bridging is identified as a major source of heat loss in the thin wall design, accounting for up to 71% of the total thermal transmittance of the tested thin sandwich panel. In standard walls this is usually less than 20%. Some of the features of the tested design can be improved to significantly reduce the effect of the thermal bridging and reduce the U-value by 59% to 0.13 W m−2 K−1 in an optimised panel design.

Composite behaviour of fibre-reinforced concrete sandwich panels with FRP shear connectors

The flexural behaviour of a precast concrete sandwich panel constructed of high performance fibre reinforced concrete wythes and foam insulation, connected together with carbon fibre reinforced polymer grid connectors, is investigated in this paper. This study tests and analyses the thin concrete cladding system which omits conventional steel reinforcement, the use of which requires concrete cover to the reinforcement layer that typically dictates the minimum thickness of the concrete wythes. A total of four full height panels are constructed in a precast concrete facility and are tested by way of three point bending. To complement the experimental study, finite element analysis is used to better understand the bending behaviour beyond what was discerned from the results obtained through experimentation. The experimental results showed that the thin concrete sandwich panel is a plausible solution for precast cladding systems with ultimate moment capacities in excess of those required to meet design wind loads. Ductile behaviour was observed in all of the four tested panels as a result of the high dosage of small 24 mm coated glass fibres used in the mix design for the concrete wythes. The experimental results showed no evidence of the FRP grid connector providing any significant degree of composite action. Finite element analysis suggests that this is due to, one or a combination of, the insulation′s stiffness being too low or because the tensile members in the grid connector being under an initial compressive strain and not fully engaged during initial loading.

Experimental studies on through-thickness shear behavior of EPS based precast concrete sandwich panels with truss shear connectors

Effective use of building materials for achieving sustainable construction is of prime importance today due to fast depletion of the natural resources by the construction industries for obtaining raw materials and aggregates. Precast insulated concrete sandwich panels (CSPs) consisting of two reinforced concrete wythes, an Expanded Poly-Styrene (EPS) core and truss-type shear connectors can be considered as an innovative construction material for acting as load bearing walls and floors in building systems. The two wythes are connected by the shear connectors through the EPS core for transferring shear forces (henceforth called as through-thickness shear) between the wythes and achieving composite action in the panels. In this paper, details of experimental studies conducted on small-scale precast CSP specimens under through-thickness shear loading are presented. The major parameters considered in the experimental program were the thickness of EPS core, gap between the wythes (in CSPs without EPS core), presence/absence of EPS core and number of shear connector lines. The effect of the major parameters on the failure mode, through-thickness shear strength, load vs relative displacement (between top and bottom wythes) behavior and load vs strain behavior of the CSPs are presented and discussed. The test results indicate that the through-thickness shear strength and behavior of the CSPs are significantly influenced by the parameters considered. Reduction in thickness of the EPS core and presence of the EPS core improved the through-thickness shear strength of the CSPs.

Nonlinear finite element analysis of composite precast concrete sandwich panels made with diagonal FRP bar connectors

Composite precast concrete sandwich panels made with diagonal FRP bar connectors have increasingly been used in the last few decades mainly due to their excellent thermal insulating properties. However, there is a lack of standards, design guidelines and reliable models that can be used for their analysis and design. In this paper, a finite element model is developed for investigating their structural behaviour, which aims to clarify their response and to provide a basis for establishing design guidelines. The model accounts for cracking and tension stiffening, material nonlinearity of concrete in compression, and geometric nonlinearity. The modelling challenges and assumptions are investigated, and the model is validated by comparing with other models and test results from the literature. The results explain the structural behaviour of these panels, which exhibit a partial composite action. The results also show that the failure mode of typical panels is ductile and dominated by yielding of the flexural steel reinforcement. A preliminarily investigation of the thermal effects shows that temperature gradients can lead to significant arching action in the panel and can affect its stability. The influence of the diameter and shape of the shear connectors and the stiffness of the insulation are investigated.

Research Progress of Precast Concrete Sandwich Panels

The wallboard is an important support and guarantee for the development of prefabricated buildings, and it is also the main development direction of green wall materials in China during the 13th five-year plan period. Precast concrete sandwich panels is composed of inner and outer leaf concrete board, sandwich insulation layer and connecting parts, which has good performance of fire prevention, heat preservation and heat insulation. On the basis of introducing the types and characteristics of precast concrete sandwich panels, this paper summarizes the research status of precast concrete sandwich panels at home and abroad, analyzes the existing problems of sandwich panels research, and prospects the research direction of precast concrete sandwich panels.

Experimental Study of Structural Performance of Precast Concrete Insulated Sandwich Panels with Cruciform Cross Section GFRP Connectors

This study investigated the structural performance of precast concrete insulated sandwich panels with cruciform cross section glass fiber-reinforced polymer (GFRP) connectors, based on tensile and shear tests. 5 tensile specimens and 4 shear specimens were fabricated and tested. The load-displacement relation and failure mode of the specimens were analyzed. The results revealed that the average ultimate tension load of the tested specimens with single GFRP connector was 13.14kN with concrete splitting or concrete partial cone failure. For the shear specimens, the average ultimate shear load was 14.83kN with rupture failure of GFRP connector. Furthermore, durability of sandwich panels was investigated, by fabricating and testing 48 tensile specimens with GFRP connectors immersed in tension load had sufficient safety in different design situations.