Steel-concrete-steel Sandwich Structure Research Articles

Pull-out strength of thin perfobond connectors and C-ties in steel-concrete-steel sandwich composite structures

Due to the remarkable mechanical property, short construction period, and labor-saving features, steel-concrete-steel (SCS) sandwich composite structures are widely used in assembled buildings, modularized immersed tunnels, and bridge cable pylons. In SCS sandwich structures, sufficient pull-out resistance in connectors is necessary to effectively prevent outward buckling of the outer steel faceplates. However, the existing connectors remain deficient in terms of load bearing capacity, ductility, and construction convenience. A novel type of connector named thin perfobond connector and C-tie (PBL-CT) was proposed to address these problems in this paper. While retaining the superior shear performance of traditional perfobond connectors (PBLs), the addition of C-ties in PBL-CTs enhances structural shear resistance. Through 18 monotonic pull-out tests, the pull-out performance of shallow-embedded thin PBL-CTs was investigated. Test results revealed that the primary failure mode of shallow-embedded thin PBLs was cracking of the surrounding concrete, with C-ties significantly improving the pull-out performance and shifting the failure mode to a combination of concrete breakout and perforated rib rupture. A nonlinear finite element (FE) model was developed and calibrated to conduct parameter analyses on concrete strength, embedment depth, and perforated rib parameters. This led to the establishment of a mixed failure model for shallow-embedded thin PBL-CTs. The ultimate pull-out bearing capacity was found to comprise two components: the pull-out resistance of the concrete cone and the shear resistance of the perforated rib. A regression-based prediction formula was derived, providing accurate and conservative predictions of the ultimate pull-out bearing capacity of shallow-embedded thin PBL-CTs.

Finite element analysis on enhanced C-channel connectors in SCS sandwich composite structures

A finite element model (FEM) was firstly developed for new enhanced C-channel connectors (ECs) in steel-concrete-steel sandwich structures (SCSSSs). This developed FEM used the continuum plasticity model (CPM) to simulate the shear fracture of C-channels and bolts used in ECs. Moreover, the FEM also considered the nonlinearities of geometry and mechanical properties of materials as well as complex interactions among different components in the ECs, e.g., channel-concrete, concrete-faceplate, and bolt-faceplate interactions. The FEM was validated by 16 push-out tests on ECs. The validations proved that the developed FEM could simulate well shear behaviours of ECs including shear-slip behaviours, failure modes, and ultimate shear resistances. With this validated FEM, a 51-case parametric study was performed to make an in-depth study on key influencing parameters on shear behaviours of ECs, which included grade and diameter of bolts, gap of bolt hole, prestressing force ratio on bolt, length of C-channel, and grade of concrete. This paper also developed analytical models to estimate the shear strength and shear-slip behaviours of ECs. The validations against test and FE simulations results confirmed the accuracies of these analytical models. Design recommendations were finally given based on these test results and FE parametric studies.

Investigation of shear strength correlations and reliability assessments of sandwich structures by kriging method

Steel-concrete-steel (SCS) sandwich composite structure with corrugated-strip connectors (CSC) is the promising structure which is applied in offshore and building structures. The behavior prediction of shear connections is of major importance in SCS structures. The present study evaluated the existing shear strength correlations of SCS sandwich structures exploiting experimental data and Finite Element Analysis (FEA). The considered system is a double steel skin sandwich structure with CSC (DSCS). Due to the limitation of the literature regarding CSC development, some new correlations were proposed and studied relying on several FEA results through the Genetic Programming method. The accuracy of the estimated shear strength predicted by the existing and proposed equations was evaluated using the FEA data and push-out test results. The FE models were verified through experimental data. Moreover, the correlations were investigated based on reliability assessment due to the high importance of the reliability analysis of such structures. Given that high accuracy in estimating the shear strength fails to necessarily lead to acceptable results in structural reliability analysis, the reliability of the existing and proposed equations was evaluated using the Kriging model by considering experimental data. This meta-model could predict accurate values with a limited number of initial training samples.

Interface monitoring of steel-concrete-steel sandwich structures using piezoelectric transducers

Abstract Steel-concrete-steel (SCS) sandwich structures have important advantages over conventional concrete structures, however, bond-slip between the steel plate and concrete may lead to a loss of composite action, resulting in a reduction of stiffness and fatigue life of SCS sandwich structures. Due to the inaccessibility and invisibility of the interface, the interfacial performance monitoring and debonding detection using traditional measurement methods, such as relative displacement between the steel plate and core concrete, have proved challenging. In this work, two methods using piezoelectric transducers are proposed to detect the bond-slip between steel plate and core concrete during the test of the beam. The first one is acoustic emission (AE) method, which can detect the dynamic process of bond-slip. AE signals can be detected when initial micro cracks form and indicate the damage severity, types and locations. The second is electromechanical impedance (EMI) method, which can be used to evaluate the damage due to bond-slip through comparing with the reference data in static state, even if the bond-slip is invisible and suspends. In this work, the experiment is implemented to demonstrate the bond-slip monitoring using above methods. Experimental results and further analysis show the validity and unique advantage of the proposed methods.

Numerical analysis on steel-concrete-steel sandwich plates by damage plasticity model: From materials to structures

Steel-concrete-steel (SCS) sandwich type of ice-resistant wall has been developed for arctic offshore structures. This paper develops a three-dimensional damage plasticity based finite element model (FEM) to simulate the ultimate strength behaviour of SCS sandwich structure under concentrated loads. The FEM offered detailed simulations on the complex geometry of hundreds of studs, complex interactions of these connectors with the concrete, and mechanical nonlinearities of the steel and concrete materials. Concrete damage plasticity model was used to simulate the post-peak softening of concrete, and continuum damage model (CDM) was developed to phenomenologically simulate the damage evolution in the steel materials. The key parameters in the CDM were calibrated by the uniaxial tensile tests on the steel coupons. The accuracy of the FE simulation was checked by nine full scale tests. The validations proved that the developed FEM simulate well the ultimate strength behaviours of the SCS sandwich plates under concentrated loads in terms of load-deflection curves, ultimate resistances, and failure modes in the steel plates, studs and concrete core. Through the FE simulations, the failure modes corresponding to different peak resistances were analysed and recognized. Finally, the FE simulation procedures on SCS sandwich plate with CDM and CDPM were recommended.

Steel-concrete-steel sandwich composite structures-recent innovations

Steel-concrete-steel (SCS) sandwich structures consisting of two steel face plates infilled with lightweight cement composite material has been developed. This paper reviews the recent innovations of SCS sandwich structures subject to blast, impact, fatigue, and static loads. Novel J-hook connectors, high strength steel plates and new lightweight cement composite materials have been considered for the development of the SCS sandwich products to improve their strength-to-weight performance. Extensive tests have been conducted to investigate the effectiveness of J-hook connectors to achieve better composite action to resist flexural, shear, impact, blast and fatigue loads. Flat and curved SCS sandwich plates under patch loading are also investigated. The experimental results are essential to understand the structural behaviour of the SCS sandwich structures and to provide data for the development of analytical models for design implementation. Design equations have been proposed to predict the shear and tensile resistances of J-hook connectors and to determine the flexural, shear, impact, blast and fatigue resistances of SCS sandwich beam. The punching shear resistance of sandwich shells and compression resistance of sandwich walls are also investigated. The accuracy of the design equations are validated by the test data and finite element analysis results.

Steel-concrete-steel sandwich composite structures subjected to extreme loads

This paper summarizes the latest research and development work on steel-concrete-steel (SCS) sandwich composite structures for the use as Arctic offshore platform, and to resist impact and blast loads. Current development of ultra-lightweight cement composite (ULCC) and a floatable structural cement composite (FSCC) to be used as infilled materials for SCS sandwich structure are presented. This paper aims to advance the application of SCS sandwich composite with the use of steel plate and lightweight concrete materials. A series of tests on lightweight SCS sandwich panels with shear connectors has been carried out. The superior performance of SCS sandwich panel is demonstrated. The results show that SCS sandwich with novel J-hook connectors is effective in preventing plate separation from concrete core, maintaining the structural integrity.

Damage plasticity based numerical analysis on steel–concrete–steel sandwich shells used in the Arctic offshore structure

This paper develops a three-dimensional damage plasticity based finite element model (FEM) to study the ultimate strength of the steel–concrete–steel (SCS) sandwich shell structure under patch loading. The FEM considers complex geometric nonlinearities of hundreds of stud connectors in the structure, complex interaction between the connectors and concrete, and material nonlinearities of steel and concrete used in the structure. In the developed FEM, the concrete core material adopts the concrete damage plasticity model to predict the post-peak softening and residual strength; the stud connectors and steel shells adopt a continuum damage model to phenomenologically describe the damage evolution in the steel material. The reasonable agreement between FE analysis and the quasi-static tests on the SCS sandwich shell structure confirms the accuracy of the FEM in predicting the ultimate shear resistance, load–deflection relationship, cracks in the concrete core, and punching shear failure of the top steel shell. A subsequence parametric study based on the validated FEM investigates the influence of the curvature on the first peak resistance of the SCS sandwich structure. Finally, the paper validates accuracy of an analytical model on the punching shear resistance of the concrete core of the SCS sandwich shell.

Numerical and parametric study of curved steel-concrete-steel sandwich composite beams under concentrated loading

The curved steel-concrete-steel (SCS) sandwich structure has been developed as the ice-resistant wall for Arctic oil and gas drilling platform. This developed curved SCS sandwich structure adopts ultra-lightweight cement composite and overlapped headed shear studs as the core material and bonding measures at the steel-concrete interface, respectively. This paper develops a three-dimensional finite element (FE) model by general commercial FE program ABAQUS to simulate the ultimate strength behaviour of the curved SCS sandwich beam. The developed FE model considers the geometric and material nonlinearities of the concrete, steel plates and connectors. The reasonable agreement between FE analysis and the quasi-static tests on nine SCS sandwich beams confirms the accuracy of the FEM in predicting the ultimate shear resistance and cracks in the concrete core of the curved SCS sandwich beam. Based on this validated FE model, a subsequence parametric study comprising 54 cases investigates the influences of the curvature, thickness of the steel face plate and core material, and horizontal movements of the supports on the shear resistance of the curved SCS sandwich beams. Finally, the paper validates accuracy of an analytical model on the shear resistance of the curved SCS sandwich beam via a comparison against a total of 41 results (32 FEA and 9 tests).

Steel–concrete–steel sandwich system in Arctic offshore structure: Materials, experiments, and design

The gravity based structure (GBS) with external Steel–Concrete–Steel (SCS) sandwich ice-resistant wall has been developed for the Arctic oil and gas drilling. This paper firstly reported the experimental studies on the mechanical properties of steel and concretes under Arctic low temperature. With the test data, design equations were developed to incorporate the influences of the low temperature on these mechanical properties. Two types of Arctic GBS structure with flower-conical SCS sandwich shell type and plate type of ice-resistant wall have been developed for the Arctic offshore structure. Besides the studies on the materials, two SCS sandwich prototype shells and plates were, respectively, prepared and tested under patch loading that simulated the localized ice-contact pressure. The structural behaviors of the SCS sandwich structure under patch loading were reported and discussions were made on the influences of different parameters on the structural behavior of the structure. Analytical models were developed to predict the punching shear resistances of the SCS sandwich structure through modifying the code provisions. The accuracies of the developed analytical models were checked through validations against 27 tests in the literature. Corresponding design procedures on resistances of SCS sandwich structure were recommended based on these discussions and validations.

Ultimate strength behavior of curved steel–concrete–steel sandwich composite beams

A concept of using curved steel–concrete–steel (SCS) sandwich structure as the ice-resistant wall has been proposed for Arctic oil and gas drilling platform. In the developed curved SCS sandwich structure, ultra-lightweight cement composite (ULCC) and overlapped headed studs were used as the core material and bonding measures at the steel-concrete interface, respectively. In this paper, quasi-static tests on ten curved SCS sandwich beams have been carried out to investigate their ultimate strength behaviors under patch loading that considers the critical local ice-contact pressure. The test results reported the failure mode and shear resistances of structures, studied the influences of thickness of the steel skin shell, curvature, spacing of the connectors, depth of the cross section, strength of core materials, and boundary conditions on the ultimate strength behavior of the curved SCS sandwich beam. Extensive discussions and analysis were also carried out to provide information for the development of the analytical models. Analytical models were developed through modifying design code provisions. These innovative modifications in the analytical models included redefining the inclination angle of shear failure surface, redefining the effective depth of the section, considering the influence of the thickness of steel skin, and developing analytical models on tensile resistance of the overlapped headed studs. The accuracy of the predictions by the analytical models was checked by the test data. All these efforts were made to provide better predictions on the shear resistance of the curved SCS sandwich beam.

Ultimate strength behavior of steel-concrete-steel sandwich beams with ultra-lightweight cement composite, Part 2: Finite element analysis

Ultra-lightweight cement composite (ULCC) with a compressive strength of 60 MPa and density of 1,450 kg/m3 has been developed and used in the steel-concrete-steel (SCS) sandwich structures. This paper investigates the structural performances of SCS sandwich composite beams with ULCC as filled material. Overlapped headed shear studs were used to provide shear and tensile bond between the face plate and the lightweight core. Three-dimensional nonlinear finite element (FE) model was developed for the ultimate strength analysis of such SCS sandwich composite beams. The accuracy of the FE analysis was established by comparing the predicted results with the quasi-static tests on the SCS sandwich beams. The FE model was also applied to the nonlinear analysis on curved SCS sandwich beam and shells and the SCS sandwich beams with J-hook connectors and different concrete core including ULCC, lightweight concrete (LWC) and normal weight concrete (NWC). Validations were also carried out to check the accuracy of the FE analysis on the SCS sandwich beams with J-hook connectors and curved SCS sandwich structure. Finally, recommended FE analysis procedures were given.

Behavior of Steel–Concrete–Steel sandwich structures with lightweight cement composite and novel shear connectors

In Steel–Concrete–Steel (SCS) sandwich structure, mechanical shear connectors are commonly used to transfer longitudinal shear forces across the steel–concrete interface. In this paper, novel shear connectors such as J-hook and cable shear connectors are proposed and their performance to achieve composite strength of SCS sandwich structures is investigated. The use of these connectors together with ultra-lightweight cement composite core reduces the overall weight of SCS sandwich system making it suitable for the construction of marine and offshore structures. Static tests were carried out on SCS sandwich beams with J-hook, cable shear connectors and headed studs. Their ultimate strengths were reported and their respective failure modes were discussed. An analytical method to predict the ultimate strength of the Steel–Concrete–Steel sandwich beams with various types of shear connectors was developed and its accuracy was ascertained by comparing with the test results. Deign recommendations are made on minimum connector spacing to prevent shear cracking of concrete core and local buckling of face plates.

Analysis and design of steel-concrete composite sandwich systems subjected to extreme loads

This paper presents the design guide based on analytical, numerical and experimental investigation of Steel-concrete-steel (SCS) sandwich structural members comprising a lightweight concrete core with density ranged from 1300 to 1445 kg/m3 subjected to static, impact and blast loads. The performance of lightweight sandwich members is also compared with similar members with normal weight concrete core and ultra high strength concrete core (fc = 180 MPa). Novel J-hook shear connectors were invented to prevent the separation of face plates from the concrete core under extreme loads and their uses are not restricted by the concrete core thickness. Flexural and punching are the primary modes of failure under static point load. Impact test results show that the SCS sandwich panels with the J-hook connectors are capable of resisting impact load with less damage in comparison than equivalent stiffened steel plate panels. Blast tests with 100 kg TNT were performed on SCS sandwich specimens to investigate the key parameters that affect the blast resistance of SCS sandwich structure. Plastic yield line method is proposed to predict the plastic capacity and post peak large deflection of the sandwich plates. Finally, an energy balanced model is developed to analyze the global behavior of SCS sandwich panels subjected to dynamic load.

Novel Steel-Concrete-Steel Sandwich Composite Plates Subject to Impact and Blast Load

This paper investigates the structural performance of steel-concrete-steel (SCS) sandwich composite system subject to impact and blast load. Novel J-hook shear connector was invented to prevent the separation of face plates from the concrete core. SCS sandwich specimens subject to 100 kg TNT blast a 5 m standoff distance were tested. The test results are reported and the factors affecting the blast resistance of SCS sandwich structures are discussed. Finite element analysis was carried out and the numerical results are verified against the blast test results. Parametric study of sandwich core strength and plate thickness is presented. Due to the superior impact performance of the proposed SCS sandwich structures, an ice caisson protective offshore structure is proposed based on the curved sandwich panel. The ultimate strength behavior of curved SCS sandwich panels is tested. The effect of arch effect is studied both experimentally and numerically.

Structural Performance of Steel-Concrete-Steel Sandwich Composite Structures

This paper investigates the structural performance of steel-concrete-steel (SCS) sandwich structures comprising a lightweight concrete core sandwiched in between two steel plates. Different types of mechanical shear connectors such as stud shear connectors and Bi-Steel bar connectors are reviewed and their uses in SCS sandwich construction are discussed. Special J-hook connectors are developed and their uses are not restricted by the concrete core thickness. Direct shear (push-out test) and tension tests have been carried out on J-hook connectors to investigate their performance in transferring shear and tension forces between steel and concrete. The structural performance of SCS sandwich beams and slabs with J-hook connectors subjected to static and dynamic loads is also investigated and test results show that SCS sandwich structures with the J-hook connectors are capable of resisting impact with less degree of damage in comparison with the sandwich structures with overlapping stud shear connectors. The plastic capacity of the sandwich beams and slabs can be predicted with reasonable accuracy using the plastic analysis described in this paper.