Steel Sandwich Research Articles

Cyclic behavior of cold-formed stainless steel sandwich tubular brace: An experimental investigation

Stainless steel shows promise for application in seismic-active regions. Previous research showed that stainless steel dampers could exhibit good energy dissipation capacity and high post-yield stiffness under cyclic loading. In light of that, a novel type of cold-formed stainless steel sandwich tubular brace (STB) is presented in this study, featuring one stainless steel square hollow section (SHS) tube as the load-carrying component and two additional stainless steel SHS tubes providing a buckling-restraining effect. Six specimens were tested under cyclic loading, varying parameters including the cross-section slenderness of the core tube, restraining ratio and loading histories. Loading protocols encompassed standardized ones following the Chinese specification (CN) and American provision (US), as well as a protocol representing the near-fault earthquakes (NF). Failure modes, hysteretic response and seismic performance indexes were obtained. Results showed that the hysteretic curves could maintain stable. Under the CN loading protocol, the specimen with a slender core cross-section exhibited uniform local buckling. The strain hardening coefficient ω stayed within the range of 1.46–1.58. The specimens exhibited a slow decay rate of tangent stiffness, highlighting their relatively high post-yield stiffness. The cumulative energy dissipation factor could reach 658, signifying good energy dissipation capacity. Additionally, under NF loading, specimens exhibited enhanced cumulative ductility compared to CN or US loading. Furthermore, an evaluation was conducted to assess the suitability of existing design methods for preventing overall buckling and local bulging in stainless steel STBs. It indicated that the current design approaches tended to be overly conservative for both overall and local stability design of stainless steel STBs, primarily due to the lack of consideration for SHS core stiffness and the interactions between flanges and webs, respectively.

Innovative design and construction of a closure joint for inland-river immersed tunnels via dry-land construction methods: A case study of the Yuliangzhou tunnel in China

Closure joints constructed to fill the spaces between immersed tunnel elements or between the tunnel elements and adjacent cut-and-cover tunnels are crucial for the longitudinal stability of immersed tunnels and affect the overall cost and duration of tunnel construction. To avoid the obstruction of navigation and reduce the difficulty of constructing closure joints, dry-land construction methods have been widely applied to construct closure joints for inland-river immersed tunnels, in particular using procedures involving axial dry docks. However, the traditional dry-land construction method has many inherent drawbacks. For example, the construction of underwater large-scale reinforced concrete antiretreat structures involves many underwater works, complicated construction processes, long operation time spans and high costs. Based on the Yuliangzhou immersed tunnel in China, a new dry-land construction method for closure joints of inland-river immersed tunnels based on tunnel–soil interface friction was developed to address the abovementioned problems. Considering the adverse influences of back-silting sediment on tunnel–soil interface friction, large-scale laboratory and onsite shear tests were carried out to derive the interface friction coefficients between the tunnel element base slabs and prelaid pebble foundation beds. A composite concrete steel sandwich (CCSS) water-retaining system was designed and assembled to separate the water in the dry dock from the river course. A simplified analysis method based on numerical simulations for the determination of the equivalent horizontal thrust P applied to element ES caused by the dewatering of the axial dry dock was proposed. Based on horizontal antisliding stability analyses of the tunnel elements during the axial dry dock dewatering stage, equations for the key design parameters of the new dry-land construction method were established. Through examination of the static equilibrium of the tunnel elements in the tunnel longitudinal direction, temporary longitudinal displacement constraint (LDC) structures at the immersion joints were designed. Furthermore, the following key construction techniques for the new dry-land construction method were systematically designed: installation of a CCSS water-retaining system at the entrance of the axial dry dock, water sealing at contact gaps, installation of finish-rolled screw-thread (FRST) steel bars as the LDC structures at the immersion joints, and construction of rigid connections between tunnel element ES and the cut-and-cover tunnel. Finally, onsite observation of the deformation states of Gina gaskets and monitoring of the tensile forces of FRST steel bars at the immersion joints verified the successful implementation of the new dry-land construction method, supporting the use of these techniques in closure joint design and construction for inland-river immersed tunnels.

ASSESSMENT OF THE MECHANICAL STRENGTH OF A STRUCTURE SUBJECT FO FIRE ATTACK AT THE WILDLAND‐URBAN INTERFACE (WUI)

AbstractFires at the Wildland‐Urban Interface (WUI) have a strong detrimental impact on the built environment. This study evaluates the effect of fire in the WUI on steel sandwich panels in a prescriptive fire field experience. The heat transfer mechanisms are obtained using a computational fluid dynamic (CFD) simulation, more specifically the adiabatic surface temperatures (AST) of the structure. The ASTs were applied in a finite element model (FEM) as boundary conditions in the thermal field in order to quantify the heat transfer processed by the FEM. In conclusion, it is identified which area of the structure is most affected due to the temperatures in the panels.

Deformation behavior of super-austenitic stainless steel sandwich panels subjected to air blast and underwater explosion

Super-austenitic stainless steel is a class of high alloy steels with enhanced toughness, outstanding strength, and corrosion resistance. In this article, the structural integrity of super-austenitic stainless steel square sandwich panels subjected to surface and underwater explosions is investigated through numerical simulations, and the results are validated with experiments. Abaqus Explicit Solver is used to predict the face deformation and core crushing failure modes of the sandwich panels. Simulations are performed for three levels of impulse load by varying the explosive quantity. The fluid-structure interaction is established by CONWEP and UNDEX algorithms for air blasts and underwater explosions respectively. The dynamic deformation behavior of the sandwich panel is modeled using the Johnson-Cook (JC) plasticity model incorporating strain rate and temperature effects. Good agreement is witnessed between the numerical predictions and experimental observations. An increment in deformation of the face sheet, cell wall buckling, and core compaction is observed with the increase in the impulse. From a series of air and underwater explosion simulations, the advantage of using sandwich structures for blast mitigation is demonstrated. In addition, the significance of numerical simulations to limit experiments and predict the deformation of the sandwich panels is presented.

Ultimate Strength Behaviour and Optimization of Laser-Welded Web-Core Sandwich Panels under In-Plane Compression

In pursuit of more efficient load-bearing solutions for ship deck panels of Very Large Crude Carriers exposed to vertical hull girder bending forces, laser-welded web-core sandwich panels are considered as an alternative to conventional stiffened panels. The primary goal is to identify a lighter steel sandwich structure capable of matching the ultimate strength of conventional counterparts. Utilizing non-linear finite element analysis, the ultimate strength of conventional decks subjected to uniaxial compression is assessed. Attention is then shifted to laser-welded sandwich panels, with a detailed examination of how various design parameters influence their performance. Specifically, four key design aspects of unidirectional vertical webs, including face thickness, web thickness, web height, and web spacing, are optimized to strike a balance between weight and strength through structural optimization techniques combined with the response surface method. Ultimately, a comparison is drawn between the ultimate strength of these innovative steel sandwich panels and their conventional, stiffened counterparts. The findings reveal that web-core sandwich panels, when employed as an alternative, result in a notable reduction in hull weight, thereby showcasing the potential for a more efficient and sustainable approach in the maritime industry.

Structural response of steel sandwich panels with PUR foam core subjected to edgewise compression: Experimental, numerical, and analytical considerations

With the objective of leading to innovative lightweight structural components in the construction sector using sandwich panels with polyurethane foam and steel face sheets, different studies were conducted on such structures, including experimental, numerical, and analytical campaigns. The experimental campaign includes the mechanical characterisation of the constituent materials and the edgewise compressive test of small-scale sandwich panels. The test protocols are detailed, and their influence on the results is assessed. Through the use of digital image correlation recordings, deformation patterns and failure mechanisms in the constituent materials and the composite structure are identified. Material constitutive models are calibrated based on the experimentally obtained results. The accuracy of such models is first evaluated against the stress–strain curves recorded during the experiments. In the second stage, the response of the sandwich panels subjected to edgewise compressive loading is simulated. A parametric analysis on the sensitivity of the numerical models to the initial geometrical imperfections is shown to be fundamental to capturing the behaviour of the sandwich panels. Furthermore, the experimental and numerical results are compared to analytical solutions of the problem of the edgewise compression of sandwich panels. Finally, a thorough discussion of the obtained experimental, numerical and analytical results is presented, along with comparisons to results available in the literature.

Prototype Tests on Screwed Steel–Aluminium Foam–Steel Sandwich Panels

Metal foams are newly developed engineered materials with attractive mechanical properties such as lightness, high resistance-to-weight ratio, and insulation capabilities. Lately, applications of these technologies have demonstrated the possibility of obtaining high-performance sandwich panels with steel skins and metal foam core, with potential applications across various fields. Within this framework, this work aims to assess the response of sandwich panels made of steel and aluminium foam to develop a new system of dry-assembled composite floors. The present study investigates a novel screwed steel–aluminium foam–steel (SSAFS) sandwich panel. This paper mainly describes and discusses the results of experimental tests devoted to evaluating the structural performance, mechanical properties, and suitability for practical applications of SSAFS. The fabrication process and the detailing of the steel skins and aluminium foam core assembly are also described. The results from the experimental tests revealed the potentialities of using SSAFS sandwich panels in terms of strength and stiffness, thus making them suitable for lightweight structural systems.

Refined and Simplified Simulations for Steel–Concrete–Steel Structures

Steel–concrete–steel (SCS) sandwich structures have gained increasing interest in new constructions. The external steel plates increase the stiffness, the sustainability, and the strength of the structures under some extreme solicitations. Moreover, the use of these plates as lost prefabricated formwork makes SCS structures modular, enabling higher construction rates. However, for a better understanding of the complex behavior of these structures up to failure, refined numerical simulations are needed to consider various local phenomena, such as concrete crushing in compression and interface interactions. Indeed, the highly non-linear steel–concrete interaction around the dowels is the key point of the composite action. In this contribution, a refined methodology is first proposed and applied on a push-out test. It is especially demonstrated that a regularization technique in compression is needed for the concrete model. Interface elements are also developed and associated with a nonlinear constitutive law between steel connectors and external plates. From this refined methodology, simplified numerical modeling is then deduced and validated. Directly applied to an SCS wall-to-wall junction, this simplified strategy enables the reproduction of the overall behavior, including the elastic phase, the degradation of the system, and the failure mode. The response of each component is particularly analyzed, and the key points of the behavior are highlighted.

Failure predictions for steel-UHPC-steel sandwich beams under three-point bending

In developing a steel-ultra-high performance concrete (UHPC) -steel sandwich structure (SUSSS) for some emerging applications, attention inevitably falls on the failure of the structure. Some typical failure modes have been summarized based on the experimental observations and numerical results. But the prediction of the failure mode is still a challenge. In the present paper, the failure of SUSSSs under three-point bending is investigated theoretically and numerically. A theoretical model is developed to predict the critical failure load of each failure mode on considering the tension–compression asymmetry of UHPC, and a failure mechanism map is constructed to predict the failure mode. The theoretical predictions are validated by the present numerical results as well as the previous experimental results. Based on the theoretical model, the effects of some geometrical and material parameters on the failure modes are discussed. It is demonstrated that the geometries of the SUSSS and the tensile strength of the UHPC core have remarkable effects on the failure modes of the structure. The present work provides a valid method to predict the failure modes of the SUSSSs.

Laser-Welded Corrugated-Core Sandwich Composition—Numerical Modelling Strategy for Structural Analysis

Laser-welding technology has recently enabled the production of corrugated-core steel sandwich panels (CCSSPs) as an innovative large-scale, lightweight structural solution in maritime and infrastructure applications. Detailed numerical analyses, specifically weld-region stress prediction in the presence of transverse patch loading and supports, are computationally challenging and time-consuming for their optimal design. This paper introduces an efficient, simplified combined sub-modelling approach for accurately predicting the detailed structural response of welded corrugated-core steel panels. The approach rests on the homogenisation of the three-dimensional (3D) panel into a two-dimensional equivalent orthotropic single layer (EOSL), where the effect of transverse compressive loads and local support conditions are captured separately via different 2D and 3D sub-modelling techniques, together with a model introduced for calculation of the weld region’s equivalent spring stiffnesses. A laser-welded corrugated-core steel sandwich panel (CCSSP), as a future generation of the steel bridge deck, was examined using different modelling approaches. It was shown that the proposed combined sub-modelling approach can accurately predict stresses and displacements in all the constituent members of the cross-section, including the welds, in a reasonable calculation time when compared with a 3D reference model, unlike the conventional homogenisation approaches.

Hysteretic performance of foam-infilled corrugated FRP-steel sandwich shear wall

A new foam-infilled corrugated carbon fiber reinforced polymer (FRP)-steel sandwich shear wall (CFSSW) is proposed for steel frame structures subjected to severe wind or seismic loadings. To reduce the excessive out-of-plane buckling deformation of conventional steel plate shear wall (SPSW), corrugated FRP laminates are fixed on both sides of the steel plate (SP). Moreover, to further improve the hysteretic behavior of the shear wall, PET foam is chosen as filler between the corrugated FRP laminates and the steel plate. Three, 1/3 scaled, single-storey shear wall specimens were built by using, as wallboard, the flat steel plate, the steel plate with corrugated FRP laminates (VCP) and the foam-infilled corrugated FRP-steel sandwich plate (VCSP). Experimental tests were carried out under low-cycle horizontal loading to study their shear performance. The results show that the CFSSW structure exhibited clear stress development pattern and stable energy dissipation capacity. Only using FRP corrugated plates as buckling-restraining components, the initial stiffness, ultimate bearing capacity and cumulative energy dissipation of conventional steel plate shear wall can be improved by 22.01%, 13.93% and 49.07%, respectively. The contribution of the infilled PET foam allowed to increase the initial stiffness, bearing capacity and energy dissipation of 28.17%, 36.39% and 105.93%, respectively. Besides, with the restraining effect of only FRP corrugated laminates or both FRP and infilled PET foam, the maximum out-of-plane displacements of the steel plate under shear force were reduced by 67.9% and 92.1%, respectively. Moreover, PET foam can help FRP laminates to effectively bear the shear forces and increased the ultimate shear capacity to 5.9% higher than nominal ultimate shear capacity of the steel plate.

Numerical and Theoretical Study on Failure Characteristics and Damage Assessment Model of Curved Steel-Concrete-Steel Sandwich Shells Subjected to Impact Load

In this study, damage assessment model of curved steel–concrete–steel (CSCS) sandwich shells subjected to impact loads was investigated. A numerical simulation method was applied to obtain failure modes of CSCS sandwich shells under impact load by changing the impact velocity as well as the mass and diameter of the hammer. From the 108 finite element (FE) models, three failure modes were found: local deformation, top steel plate fracture, and penetration. The failure mechanism for each failure mode was analyzed based on numerical simulation results, such as impact force and displacement-time histories, varying internal energy, and deformation modes of the structures. The law of failure mode distribution of the CSCS sandwich shell was also summarized. Moreover, the impact force–displacement relationship was obtained using an analytical method, and the FE results were in acceptable agreement with experiments. Finally, damage assessment model of the CSCS sandwich shells was obtained by comparing the hammer initial kinetic energy with the maximum absorbed energy of the CSCS sandwich shell. This model can be used as a quick tool to judge the failure status of the CSCS sandwich shell. The work presented in this paper is of significance and can fill the gap of the damage assessment model of CSCS sandwich shells subjected to impact loads.

Blast mitigation analysis of novel designed sandwich structures using novel approaches

Sandwich panels have excellent explosion and impact resistance capabilities. Thus, by combining square and circular honeycombs in various ways, innovative blast-proof steel sandwich panels were developed in this numerical study. A series of dynamic explicit analyses were performed at 1 to 3 kg of TNT blasts for a constant stand-off distance (SoD) of 100 mm to identify an efficiently designed sandwich panel. Further work was carried out to achieve successive improvements in the efficiently designed steel sandwich panel’s blast mitigation performance by applying different patterns of Al foam filling and fiber metal laminate (FML) facing. The ability to absorb energy, core crushing, and face deflection under blast loadings were utilized to examine the novel designed sandwich panels’ blast resistance. The Johnson-Cook (J-C) model and Hashin’s and Puck-Schurmann’s criteria were applied to accurately determine the damage behavior of steel and composite parts of the structures, respectively. The obtained results showed that the combination of square and circular honeycomb cores in a sandwich construction significantly increased blast resistance for both layered and unlayered honeycomb cases compared to the standard square honeycomb core employed in the sandwich structure (S-SS). A further enhancement in blast resistance was seen when the bottom honeycomb core of layered honeycomb was filled with foam. The further employment of the FML top face highly advanced the blast performance of the novel designed sandwich panel, and it can be applied to various parts of armor vehicles to save soldiers’ lives from air-blasts.

Shear Initiation from Low Velocity Impact

Ignition and initiation by low velocity impact are usually investigated experimentally by the so-called Steven test. In this test a heavy steel projectile is launched against a steel sandwich target containing the tested explosive. The output is monitored by blast gauges three meters from the target. The test results are in terms of the threshold impact velocity for ignition, and of the TNT equivalent of the tested explosive as a function of impact velocity beyond this threshold. To date there is no accepted model that can predict the outcome of a Steven test or any other low velocity impact event. There is a great demand for such a model for explosive safety issues. In this paper we propose a model to predict the outcome of a low velocity impact event. The model is simple to use in a hydrocode, and goes over smoothly to shock initiation and detonation phases of the impact event. We calibrate the model from Steven test data, and we then use it to predict the propagation of the deflagration wave in a Steven test.

Shear resistance and deflection prediction of steel–concrete–steel sandwich panel with headed stud connectors

Bending tests were conducted on eight specimens to investigate the mechanical behavior of steel–concrete-steel (SCS) sandwich panels with headed studs, taking into account the effects including loading mode, steel plate thickness, concrete core thickness and connectors spacing, and one sandwich panel was used as a control specimen. The failure characteristics and crack patterns of the specimens were recorded and the vertical displacement in the span was measured. The test results were used for the validation of the finite element model (FEM). Further parametric studies of the FEM yielded the effect of steel plates on the load-bearing capacity of the sandwich structure. Analytical models applicable to the initial stiffness and shear resistance of specimens with headed studs were proposed. The shear strength considered the effect of steel plate and pin action. The deflection calculation models of the sandwich panel were obtained based on the energy method and were in good agreement with the load–displacement response curves obtained by FEM results. The research results of this paper will have an impact on the large deformation and ultimate strength prediction of sandwich protective panels.

An enhanced steel sandwich foamed aluminum for strengthening RC frame structure: Experiment and numerical simulation

To improve the impact resistance performance of reinforced concrete (RC) frame structure against debris flow, an enhanced steel sandwich foamed aluminum strengthening method is proposed. A series of debris flow impact tests of the traditional reinforced concrete frame structure (TRCFS) and the strengthened reinforced concrete frame structure (SRCFS) are designed and carried out. Based on the impact test, the effectiveness of the proposed strengthening method is validated, and its energy consumption mechanism is further revealed through a comparative study. Meanwhile, the corresponding numerical simulations are carried out to validate the reasonableness and accuracy of the experimental results. The experimental results illustrate that the enhanced steel sandwich foamed aluminum strengthening method has three protection mechanisms, and this strengthening device can effectively improve the RC frame structure’s impact resistance. The SRCFS model has a more favorable force transfer mechanism, which can reasonably mobilize other members and significantly improve the normal service ultimate bearing capacity of the whole frame structure. Moreover, the numerical results match well with the experimental results, which demonstrates that the debris flow impact test can adequately reveal the impact resistance performance of the SRCFS model.

Behavior of a Composite Steel Decking and Boarding System in Fire Based on Large-Scale Experimental Testing and Numerical Modelling

This paper presents experimental and numerical results of an investigation into the thermal and structural behaviour of an innovative modular structural steel system, which includes cellular beams, that was tested in a 1-h standard fire scenario while loaded. The modular system consists of a 5.66 × 3.8 m rectangular steel frame, with a profiled steel sandwich decking (SD) system attached, which comprises of (a) profiled steel decking, (b) fibre cement, and (c) calcium silicate boards and strips. The SD system is suspended from the underside of the horizontal structural members to provide inherent fire protection to the steel beams from the bottom and acts as the load-bearing component of the flooring. The purpose of the experiment was to determine the fire resistance of the structural system, whilst under load, which is primarily based on the fire resistance of the SD system. Temperature data for the SD system was collected during the experiment and used to validate a numerical finite element analysis model. This study shows that the SD system was able to achieve a fire resistance rating of 57 min in the experiment which was governed by insulation resistance. A lower fire resistance rating is estimated based on numerical models. Structural resistance was maintained throughout the test. During preliminary testing structural collapse was observed in a separate experiment which highlights how the system is sensitive to damage to the ceiling boards. Numerical results highlight that thermal bowing and movement may result in changes in thermal interactions between adjacent elements. This paper provides novel large-scale experimental data on a loaded flooring system in fire.

Impact responses of steel–concrete–steel sandwich panels with interlocked angle connectors: Experimental and numerical studies

This study explored the impact responses of a steel–concrete–steel sandwich composite panel with novel interlocked angle connectors (SCSP-IACs). Impact tests on nine SCSP-IACs were performed via a hemispherical hammer. The failure modes of all specimens were determined as the local punching failure of the concrete core. Moreover, the impact force–time and displacement–time histories and the permanent deformation were discussed. The experiment results showed that increasing the steel faceplate thickness and concrete core height enhanced the impact performance of the SCSP-IACs. By contrast, increasing the IAC spacing weakened the impact performance. Moreover, the interlocking bolts slightly affected the impact responses of the SCSP-IACs. A finite element (FE) model was established and verified with test data. The model was used to analyze the internal forces and energy absorption of the SCSP-IACs under impact loads. The internal force diagrams of the panels at different impact stages were provided, and a significant hogging moment was observed from the bending moment distributions. The FE results also showed that the zones close to the center of the panel absorbed most of the impact energy.

Experimental and analytical study on impact response of stainless steel-aluminium foam-alloy steel sandwich panels

This paper investigates the impact response of stainless steel-aluminium foam-alloy steel sandwich panels under single and repeated impacts. Fourteen specimens were tested under single and repeated impacts, in which the dynamic response, failure pattern and energy absorption capacity of sandwich panels were investigated. Test results showed that the thickness of the front sheet, back sheet and aluminium foam had significant influences on the bearing capacity and energy absorption capacity of sandwich panels. Comparisons were also made between sandwich panels subjected to single and repeated impacts. It was found that the impact response and failure pattern of sandwich panels under repeated impacts could be significantly different from that under a single impact, mainly due to the development of arc-shaped deformations near the direct impact region. A local indentation model is proposed for sandwich panels considering the deformation of the back sheet, which can predict the first peak force, associated displacement and energy absorption with reasonably good accuracy. It also demonstrates that compared with alloy steel, the energy absorption of sandwich panels with stainless steel as the front sheet is considerably improved. This study provides an important reference for the design of stainless steel-aluminium foam-alloy steel sandwich panels under impact loadings.

Finite element analysis of steel-concrete-steel sandwich beams with novel interlocked angle connectors subjected to impact loading

The steel–concrete–steel (SCS) sandwich structures are increasingly adopted to improve the impact resistance of the buildings or infrastructures owing to their good structural performances. Recently, the SCS sandwich beams with interlocked angle connectors (SCSSB-IACs) have been developed, and their performances under impact loading have been experimentally studied. This paper presents detailed numerical analyses of the SCSSB-IACs subjected to impact loading and reveals its response mechanisms. The Finite Element (FE) models of the SCSSB-IACs were established using LS-DYNA, and the FE predictions showed a good agreement with the impact test data. The impact process as well as distribution and evolution of bending moment and shear force, stress and strain were discussed. Furthermore, the internal energy histories of the SCSSB-IACs were revealed by FE analyses. Numerical results indicated that the majority of impact energy was absorbed by the concrete and bottom faceplate, and the deformation of the SCSSB-IACs was dominated by a flexural manner. Finally, parametric studies were performed to reveal the effects of impact momentum, energy and location on the response of the SCSSB-IACs.