Concrete Sandwich Research Articles

Out-of-Plane Flexural Behavior of Insulated Wall Panels Constructed with Large Insulation Thicknesses.

Insulated concrete sandwich wall panels (ICSWPs) are gaining popularity as energy regulations become stricter worldwide. ICSWPs are now being constructed with thinner wythes and thicker insulation to keep up with the changing market, which is reducing material costs and increasing thermal and structural efficiency. However, there is a need for adequate experimental testing to validate the current design methods for these new panels. This research aims to provide that validation by comparing the predictions of four different methods with experimental data obtained from six large-scale panels. The study found that while current design methods adequately predict the behavior of thin wythe and thick insulation ICSWPs within the elastic region, they do not accurately predict their ultimate capacity.

Design equations for thermal bowing and composite degree of concrete sandwich panels

Concrete sandwich panels (CSPs) are oftentimes subjected to extreme exterior temperatures, causing thermal gradients between inner and outer surfaces, and eventually bowing. In addition, the composite degree (kp) of CSPs has been conventionally estimated using methods that require costly and time-consuming experimental tests or rigorous numerical models. The lack of research and understanding on the effects of kp and bowing oftentimes result in overly conservative and uneconomic design, particularly for partially composite (PC) panels. This study develops simple design equations for thermal bowing and kp in CSPs based on a comprehensive parametric study using a transient thermal-structural coupled finite element (FE) model developed earlier by the authors. Key parameters considered are span (L); connector configuration, material, and reinforcement ratio; wythe and insulation thicknesses; concrete strength and thermal differential (ΔT) on both sides. In panels with L larger than 13 m, particularly those featuring steel and CFRP truss connectors and subjected to temperature gradients (ΔT) higher than 30 °C, bowing was larger than the deflection serviceability limit of L/360. Cracking in concrete wythes and yielding of steel connectors were also observed and were mainly dependent on ΔT and kp. Two existing theoretical models were evaluated using results of the parametric analysis and were found to overestimate thermal bow, particularly for panels with low kp. A proposed bowing model is presented which incorporates the effects of composite degree and yields much better predictions than these from literature.

A review on the various factors influencing the structural behaviour of TRC sandwich elements

This review article discusses the structural performance of Textile Reinforced Concrete (TRC) sandwich structures consisting of two outer TRC faces and a rigid core insulation. Sandwich structures offer advantages such as lightweight construction and thermal insulation. Hence, the application of the non-corrosive TRC as the facings of sandwich panels helps in reducing the overall thickness and weight of the panels by replacing the reinforced concrete faces and eliminating the thick concrete cover. The strength, stiffness and load-carrying capacity of TRC sandwich panels are governed by several factors such as thickness of the face, density of the core material, reinforcement ratio, the use of shear stiffeners, etc. In this review article, the influence of various parameters such as face thickness, type of textile, number of textile layers, core thickness and core density are addressed. The effect of shear connectors on enhancing the composite behaviour of TRC sandwich panels is also discussed.

Shear Transfer Mechanism between CFRP Grid and EPS Rigid Foam Insulation of Precast Concrete Sandwich Panels

An experimental program was implemented to investigate the shear transfer mechanism of carbon-fiber-reinforced polymer (CFRP) grids and expanded polystyrene (EPS) rigid foam insulation in three wythe precast concrete sandwich wall panels. The purpose of the research was to measure the shear flow capacity and to observe the failure mode(s) of precast concrete sandwich panels manufactured with a CFRP grid shear transfer mechanism between wythes. Six precast concrete sandwich panels were examined by push-out tests in which the center concrete wythe was pushed downward with respect to two outer concrete wythes. It was observed that the average shear flow capacity of the specimens having 2 in (51 mm) thick foam was higher than that of the specimens having 4 in (102 mm) thick foam. In addition, stiffness decreased significantly when the thickness of the EPS insulation increased. The failure mode for the panels included relative displacement between the center concrete wythe and the outer concrete wythes. Test results showed that panels tended to fail by CFRP grid rupture, CFRP grid pull-out, and loss of bond at the concrete/foam interface. Further tests should be performed to fully comprehend the nature of the shear transfer mechanism between the specific CFRP grid used and EPS rigid foam insulation.

Thermal properties of multiple-wythe masonry overlayed with textile reinforced concrete sandwich panels

Thermal properties of multiple-wythe masonry overlayed with textile reinforced concrete sandwich panels

Flexural behaviors of sandwich panels with AR-glass textile reinforced concrete under low-velocity impact

Textile reinforced concrete（TRC）can be used as the face-sheet for sandwich panels due to its lightweight, excellent tensile strength, high energy absorption, and ductility. This study investigates the flexural behavior of alkali-resistant glass-textile reinforced concrete (ARG-TRC) sandwich panels with different textile layers, core thicknesses, and interface forms under various impact velocities. A new manufacturing technique for ARG-TRC sandwich panels is proposed. The sandwich panels with four textile layers have superior load-carrying capability and impact resistance than those with two layers. The impact load can be transferred more effectively for panels with a core thickness of 40mm, allowing the top and bottom face-sheets to bear the load simultaneously for better impact resistance. Ribbed panels can reduce the possibility of side core tensile fracture and core crushing while improving flexural stiffness. It was also found that TRC sandwich panels typically exhibit four failure modes under the impact load, including face-sheet fracture, core shear fracture, side core tensile fracture, and core crushing fracture. The findings of this study can provide some insights into promoting the design and application of TRC sandwich panels in residential and industrial structures.

A Review on Textile Products for Reinforcing Concrete Sandwich Panels

Concrete sandwich panels have gained considerable popularity in the construction industry. Based on their structural and thermal performance, sandwich panels have been employed in industrial, residential, and commercial structures. Two concrete outer layers are connected by connections that run through the interior insulating material, which is isolated from the exterior layers by an insulating stiff foam core to increase thermal effectiveness. There are numerous issues with the steel used for reinforcement including corrosion, high cost, heavy weight, increased thickness, and thermal bridges. Textile reinforcing concrete (TRC) is a solution for these issues, for that; researchers have attempted to replace steel with various textile goods to improve the quality of sandwich panels. Many researchers used textile’ grides for enhancing sandwich panels’ thermal isolation and reinforcing properties as nets or as a connector. This article reviews and observes methods of reinforcing concrete sandwich panels with TRC with different materials, constructions, behavior and application of textiles for investigating sandwich panels’ performance as well as textile reinforcing of concrete and discussing differences between these applications. It was found that TRC can be used for reinforcing concrete sandwich panels as core, as grid or as a connector, All these shapes of TRC effect on the performance of concrete sandwich panels positively.

Experimental study on seismic behaviour of an unreinforced precast wall-slab structure based on UHPC sandwich panels

Heavy prefabricated components and complex reinforcement arrangements are regarded as main problems affecting the construction efficiency of traditional precast concrete structures. This study proposes a new wall-slab structure based on prefabricated ultra-high performance concrete (UHPC) sandwich panels, which features with light weight, no reinforcement, fast bolt-based dry connection and insulation system integrated. A large-scale two-story substructure is prefabricated and assembled, which consists of eight sandwich walls and four sandwich slabs. Vertical load test and lateral cyclic load test are conducted to investigate the mechanical behavior of the wall-slab structure. The cracking patterns, failure modes, bearing capacity, stiffness, energy dissipation capacity, and strain distribution are analyzed. Test results demonstrate that the maximum and cracking base shear forces are about 10 and 7 times the sum of gravity and live load of the specimen, respectively. The various connections between precast panels are all reliable without obvious damage during the test. Therefore, the new wall-slab structure has excellent seismic performance, which can even avoid cracking under severe earthquake. In addition, design suggestions are proposed based on the test results, regarding the design principle, inter-story drift ratio limit and panel connections.

Bending Performance of Concrete Sandwich Walls with Actual Boundary Conditions

Concrete sandwich walls are commonly used as the exterior wall panels of a structure, in which the wall suffers out-of-plane bending under strong wind conditions. This paper aims to investigate the bending performance of concrete sandwich walls under actual boundary conditions through experimental and analytical methods. In total, four concrete sandwich walls were tested to detect the influence of openings and loading direction. Typical failure patterns were characterized and discussed. The load-displacement curves of four test specimens were analyzed. It was indicated that the bearing capacity of the walls under negative bending conditions was higher than that under positive bending conditions, owing to the additional constraints provided by the steel beams. Strain distributions of wall specimens were also discussed in order to obtain the composite action of the sandwich walls between the upper and lower layers of concrete. In addition, the finite element model (FEM) was developed by ABAQUS to provide insights into the bending performance of the sandwich walls. Through comparison with the test results, the FEM was verified with a good level of accuracy. Subsequently, the degree of composite action of the sandwich walls was assessed in terms of both the moment of inertia and bearing capacity. From the experimental and numerical results, it demonstrated that the bearing capacity of concrete sandwiched wall under negative direction was higher than that under positive direction owing to the constraints of steel beam. The derived composite action degree could be employed to evaluate the out-plane bending stiffness and strength of sandwiched concrete wall. Both the experimental and analytical results in this paper are beneficial for the design of sandwich walls under bending conditions.

Experimental and analytical study on the double steel plates-UHPC sandwich slabs under low-velocity impact

The upgrading of protective structures can be realized through the application of new materials or the innovation of structural forms. A novel double steel plates–concrete (DSC) sandwich structure constructed with an ultra-high-performance concrete (UHPC) core forming a DSUHPC sandwich structure could be applied in Arctic offshore platforms as protective layers. This structure can withstand dynamic pressure derived from impacting ice sheets and vehicles in serve cold regions. This paper presents the dynamic behavior of these DSUHPC sandwich slabs subjected to drop-weight impact load. The superiority of protective performance of DSUHPC sandwich structure was revealed in contrast with the perforation failure mode of reinforced concrete (RC) slabs subjected to the same impact energy. Moreover, the brittleness of concrete material under dynamic load was alleviated by adding steel fibers compared with double steel plates–normal strength concrete (DSNC) sandwich slabs, showing effectiveness in the improvement of material utilization and energy dissipation. Further, the diverse dynamic response of DSUHPC sandwich slabs with different steel plate thicknesses and under different impact velocities was also studied. Finally, a two-degree-of-freedom model was established to predict the time–history curves of impact force and displacement. The acceptable accuracy of the proposed analytical model was demonstrated.

Shaking table tests and seismic assessment of a full-scale precast concrete sandwich wall panel structure with bolt connections

A novel, light-weight, sustainable, repairable and cost-effective precast concrete sandwich wall panel structure system is proposed in this paper, including the dry bolt connections and the precast concrete sandwich panels. To evaluate the seismic performance of precast structure system, a sequence of shaking table tests is carried on the full-scale precast concrete sandwich wall panel structure, and the dynamic characteristics, damage pattern, dynamic responses and seismic fragility are investigated and analyzed by the test results under service level earthquake, design based earthquake, and maximum considered earthquake. The seismic fragility curves and failure probability curves are analyzed by the shaking table test results, which quantitatively describes the seismic performanceexpressed by probability. The results show that the precast concrete sandwich wall panel structure performs high lateral stiffness, large safety margins and high strength reserves. The precast concrete sandwich wall panel structure system presents a good seismic performance. The damage of the structure is slight under maximum considered earthquakes, and the structure has begun to enter the plastic stage. The light-weight characteristic reduces the dynamic responses, and the mild sliding between precast components consumes a fraction of seismic energy.

Experimental study on the in-plane response of cast-in-situ reinforced concrete sandwich walls under combined vertical and horizontal load

Cast-in-situ Reinforced Concrete Sandwich Panel (cRCSP) technology represents a viable and increasingly popular solution for the construction sector to face recent crucial challenges, such as great housing demand or environmental sustainability. Recently, cRCSP-based buildings are being widely used also in earthquake-prone countries, like Italy. Nevertheless, so far, the available studies in the literature studies focused on the seismic response of this structural typology are not-exhaustive and, besides, relevant structural technical codes do not provide specific design rules. The present study deals with an experimental campaign carried out on four full-scale cRCSP walls subjected to increasing in-plane cyclic lateral loading. Two wall configurations have been considered different for shape and openings: the first has no openings and a squat profile; the second has a central door-type opening and a square profile. Two levels of uniformly distributed vertical load have been applied and kept constant during the test. Materials, specimens, and test set-up are described. The main experimental outcomes in terms of recorded force-displacement curves and observed damage states are discussed in detail. In particular, different failure modes and seismic performances have been observed.

Structural performance of a façade precast concrete sandwich panel enabled by a bar-type basalt fiber-reinforced polymer connector

Structural performance of a façade precast concrete sandwich panel enabled by a bar-type basalt fiber-reinforced polymer connector

Experimental and numerical study of blast resistance of geopolymer based high performance concrete sandwich walls incorporated with metallic tube core

To reduce the disastrous consequences caused by explosion, increasing attention has been paid to the blast mitigation of structures while keeping their adequate functions in recent years. In this study, an innovative multi-layer sandwich wall has been developed to provide blast mitigation for protective structures. Such a multi-layer sandwich wall consists of three layers including two steel wire mesh (SWM) reinforced geopolymer based high performance concrete (G-HPC) layers and a metallic tube core (MTC) layer. The blast behavior of the multi-layer sandwich walls under 1.0 kg contact explosion was investigated experimentally and numerically. A total of five sandwich walls were tested to explore the influence of different factors (including the thickness of the front/rear G-HPC layer and MTC layer) on their performance. Subsequently, a finite element model was developed and validated by comparing the numerical results with the experimental data. The findings indicated that the well-designed sandwich walls exhibited excellent anti-blast performance and the rear G-HPC layer remarkably affected the anti-blast performance. In addition, the numerical results could fairly predict the experimental phenomenon.

A concrete sandwich wallboard damage identification method based on strain energy density increment

During the loading process of concrete members, the identification of characteristic damage states is not sensitive enough. This paper investigates the damage evolution of four concrete sandwich wallboards subjected to vertical compression by employing the strain energy density increment to enhance identification sensitivity. First, the equivalent elastic modulus model for a wallboard subjected to vertical compression is established based on the material stress–strain relationship. Then, the strain data of concrete, obtained from experiments and numerical simulations, are modeled as the normalized unit approximate strain energy density increments (NUASEDIs), which follow the damage evolution of the wallboard as a more sensitive index. The first cracking formation of wallboard corresponds to the first high NUASEDI. The failure damage state corresponds to the final high NUASEDI, which reflects the process changing from the local to the global failure. Finally, the strain energy density increment theory improves averagely the cracking identification sensitivity of concrete members by 13.32% and the failure identification sensitivity by 3.01%.

Study on impact resistance of precast light-weight concrete sandwich panels

To investigate the dynamic impact resistance of precast lightweight sandwich panels (PLCSP) composed of non-sintered coal ash ceramsite concrete and self-developed thermal blocking shear connectors, drop hammer impact tests with different impact energy were carried out in the central area of the exterior wythe. The dynamic response of PLCSP under different steel fibers content, wythe thickness, and the different number of shear connectors was compared and analyzed. The numerical simulation was carried out by LS-DYNA. The results show that 2% volume fraction of steel fibers enhance the stiffness of the panel by improving the overall impact toughness, while the increase in wythe thickness slows down the panel amplitude to enhance the stiffness. The exterior wythe of the PLCSP has penetrated failure, and the failure mode of the interior wythe changes from bending failure to collapse failure with the increase of the number of shear connectors. Therefore, the arrangement spacing of shear connectors can be appropriately reduced to reduce the risk of collapse failure. The ratio of maximum displacement and residual displacement of the panel under different impact energies ranged from 3.37 to 5.94, and the maximum erosion depth of the hammer was twice the displacement of the bottom of the panel, indicating that the unique sandwich structure and material of the PLCSP have good impact resistance. The research results can provide reference for the design and application of PLCSP.

Retrofit of Building Façade Using Precast Sandwich Panel: An Integrated Thermal and Environmental Assessment on BIM-Based LCA

The study conducts a comprehensive life cycle assessment (LCA) of precast sandwich panels by integrating operational and embodied phases detailing thermal efficiency and environmental impacts. The analytical regression model is developed for climatic diversity and design variables using the energy rating tool FirstRate5 to compare with a conventional brick veneer construction. LCA is performed on the building information modeling (BIM) platform to connect operational energy and express the relative embodied impacts of insulation constituents, compressive strength, reinforcement, and mix design. Monte Carlo simulation shows significant advantages of concrete sandwich panels in reducing operational H/C loads over building service life. LCA reveals a 100 mm thick external precast concrete wall with 50% fly ash reduces CO2 emission and energy demand by 54.7% and 75.9% consecutively against the benchmark. Moreover, it comprises 84.31% of the total building mass, accountable for only 53.27% of total CO2 emission and 27.25% of energy demand, which is comparatively lower than other materials. In the case of selecting lining insulation, a broader benefit is identified for extruded polystyrene (XPS) and expanded polystyrene (EPS) boards due to their relative weight, thickness, and environmental impacts. Representative equations of energy efficiency and impact assessment will assist in adopting sandwich panels for new construction and refurbishment with relative dimensions.

The Development and Application of Prefabricated Buildings

This essay will start at the development of construction area, including the detailed introduction of the meaning and features of prefabricated buildings, as well as its general situation and requirements and policies relating to prefabricated buildings development in part of provinces in China. In the second half of this report, detailed introduction to advantages and disadvantages of main prefabricated components like precast reinforced concrete composite slab which are applied for domestic constructions and combination characteristics of commonly used concrete sandwich wall. This essay may offer some references to related workers and students studying in related majors.

Determination of the Mechanical Properties of Flexible Connectors for Use in Insulated Concrete Wall Panels.

This document contains recommendations for performing a non-standard, double-shear test suitable for both continuous and discrete insulated concrete sandwich wall panels (ICSWPs). Such a standardized test does not exist, but several iterations of this and similar tests have been performed in the literature to varying degrees of success. Further, the tests in the literature are rarely-if ever-described in detail or discussed at length with respect to the testing, data analysis, or safety procedures. A test specimen configuration is recommended herein, and variations are discussed. Important mechanical properties are identified from the load versus displacement data, and their extraction is detailed. The use of test data for design, such as for determining the stiffness of the connectors, is briefly demonstrated to show how ICSWP deflection and cracking behavior may be calculated. The strength behavior of panels may be determined using the full load versus displacement curve or only the maximum connector strength. Shortcomings and unknowns are acknowledged, and significant future work is delineated.

Experimental study on seismic behavior of precast concrete sandwich shear walls under high axial compression ratio

To shed light on the seismic behavior of precast concrete sandwich shear walls (PCSSWs) in high-rise buildings, reversed cyclic loading test were conducted on eight full-scale shear wall specimens under high axial compression ratio. Totally four variables were considered in the test, i.e. type of shear wall (PCSSW, non-insulated precast concrete shear wall (PCSW), cast-in-place (CIP) shear wall), location of insulation layer (off-center or center in the section), confinement at boundary elements (with or without confined core), and details of grouted sleeve connection (double or single row of grouted sleeves). Note that in this paper the PCSSWs with off-centered insulation layer had confined cores at boundary elements while steel stirrups for additional confinement were not used in the PCSSWs with centered insulation. Test results revealed that the PCSSWs showed failure mode, hysteresis loops, loading capacities and displacement ductility similar to PCSW and CIP specimens. The loading capacities of PCSSWs and CIP specimen increased by 8.2 % ∼12.4 % because of the confined core at boundary elements. The displacement ductility of specimens with confined boundary elements varied from 2.35 to 2.65, which was higher than that of the specimens with unconfined boundary elements (1.75 ∼ 2.10). Besides, the number of rows of grouted sleeves had minor effect on hysteretic response of specimens. Based on the test results, a quadrilinear degradation restoring force model was proposed.