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The propensity of buildings for progressive collapse can be assessed using the alternative path method. Generally, there are three scenarios to be considered: internal column, side column, ...

This paper presents an experimental and numerical study on the bearing behavior of two-bolt connections arranged in the direction perpendicular to load between high-strength steel members. A series of 36 connections are fabricated from steels with nominal yield strength of 550 MPa, 690 MPa and 890 MPa and tested to failure in double shear. The effect of steel grades, end distance, edge distance and bolt spacing on the failure mode, bearing resistance and deformation capacity are investigated with the supplementary data from the validated numerical model. To explain the reduced bearing resistance compared to tearout failure, the mechanism of splitting failure in two-bolt connections is analyzed with the assistance of numerical simulation. The boundaries to identify tearout failure, splitting failure and mixed failure with the combined features of necking and tearout are derived. A formula to predict the ultimate resistance of mixed failure is proposed. To achieve an optimum use of high strength materials, an optimal range of edge distance to bolt spacing distance ratio is suggested based on the parametric analysis. Comparison with test results show that Eurocode3 method can be extended to bolted connections between high strength steel members with considerable margin of safety.

This paper provides an insight into the buckling behavior of high strength concrete encased steel (CES) columns through a comprehensive investigation including experimental, numerical and analytical analyses. Three long CES column specimens made of high strength concrete C100 and S355 H-section were tested under axial compression. The maximum test loads obtained from these tests were compared with the buckling resistance predicted by EN 1994-1-1, AISC 360-10 and ACI 318-08. Nonlinear finite element analyses were performed to predict the buckling resistance and trace the load displacement behaviour of these columns. In the finite element model, the column initial imperfections were carefully chosen to predict the maximum resistance and the load-displacement response, and compared with the equivalent imperfection values stipulated in the modern design codes. In order to examine the validity and limitation of the current design approaches in predicting the buckling resistance of CES columns made of high strength concrete, a statistical study was undertaken based on the established database covering a wider range of material strength and geometric configurations. In the statistical study, the buckling resistance and effective flexural stiffness obtained from the tests were compared with the codes' predictions from EN 1994-1-1, AISC 360-10 and ACI 318-08. Finally, the reliability of the current design methods is assessed by correlating their accuracy with respect to the variation of material strength, column slenderness ratio, load eccentricity and steel contribution ratio.

This study investigates the structural behavior and shear bond strength of composite slabs composed of profiled steel deck and ultra-lightweight cementitious composite (ULCC). ULCC topping with a density of about 1440 kg/m 3 was used to reduce the dead weight of the composite slabs. An experimental investigation was carried out to determine the shear bond characteristics between the profiled steel sheet and the ULCC. Eight composite slabs of different shear spans were tested in accordance with EN 1994-1-1:2004, in which six slabs contained ULCC and the remaining two slabs contained normal weight concrete (NWC) to serve as a benchmark for comparison. The shear bond behavior of the ULCC composite slabs was compared to that of the NWC slabs using two sets of slabs with short and long shear span lengths. The composite slabs with ULCC topping showed higher ductile behavior and load-carrying capacity than the composite slabs with NWC topping. The shear bond properties of the composite slab with ULCC were determined using the semi-empirical m−k method and the partial shear connection method (PSC) according to EN 1994-1-1:2004. For comparison purposes, the shear bond properties of NWC composite slabs were determined. ULCC was found to provide equivalent shear bond strength with profiled steel sheet compared to the conventional composite slab with NWC. Therefore, ULCC can be used effectively in composite slabs with a greater reduction in self-weight.

The use of high strength steel and concrete materials for composite column construction is partly impeded by the lack of research on their fire performance. In EN1994-1-1, the highest concrete grade allowed for designing composite columns is capped at C50. This paper investigates the behaviour of concrete encased steel (CES) composite columns made of C120 concrete and S500/690 steel section under ISO834 standard fire through a series of experimental and numerical analyses. Fire tests were carried out on five high strength CES column specimens subject to varying eccentricity of loading to study their behaviours in fire. Polypropylene fibres were added into the high strength concrete mix to prevent the explosive spalling so that explicit modelling of cover spalling phenomenon can be omitted in the numerical analysis. A unified method is proposed to determine the transient strain of high strength concrete at elevated temperatures, allowing the stress-strain curves in EN1992-1-2 to be extended to high strength concrete up to C120. A numerical model, which can capture the strain reversal of concrete caused by the flexural deformation of columns at elevated temperatures, is proposed to enable a good prediction of axial displacement responses of CES columns in comparison with the test results. Finally, based on the validated numerical model and parametric studies, a new tabulated data method is proposed for the fire resistance design of CES columns with concrete class up to C90 concrete and steel section grade up to S550.

This study is motivated by increasingly prevalent use of high strength steel and concrete materials in high-rise buildings to achieve better structural performance with less material usage. Previous studies and many modern design codes place some limits on the strength of steel and concrete for designing steel-concrete composite members, attributed to insufficient test data and design experience on their applications in construction. With this research gap being identified, an experimental program has been carried out to investigate the composite behaviour of concrete filled steel tubes (CFST) employing high tensile strength steel (HTS) and ultra-high strength concrete (UHSC). Both concentric and eccentric compression loads were applied to evaluate the overall buckling resistances and moment-axial force interaction with second-order effect considered. The yield strength of HTS under the investigation was about 800 N/mm 2 and the concrete compressive cylinder strength was up to 200 N/mm 2 . To examine the test results, the rotational stiffness of semi-rigid end supports was analytically derived and the stress-strain models of HTS and UHSC were properly calibrated to predict the composite behaviour through finite element analysis. The Eurocode 4 approach was then checked regarding its applicability to the said high- and ultra-high strength construction materials for composite design. A new database including 1160 test data was established to further study the reliability of the use of HTS and UHSC, and suggestions were made to extend the Eurocode 4 design approach.

This paper presents an experimental program investigating the behavior of high strength steel connections consisting of one bolt in double shear. A total of 24 bolted connections fabricated from three grades of high strength steel with the nominal yield strengths of 550 MPa, 690 MPa and 890 MPa were tested. The effects of end distance, edge distance and steel grade on the bolt bearing behavior were evaluated. The bolt hole elongation due to bolt bearing on high strength steel plate was measured and its implication on the plate bearing resistance was discussed. The test results were compared with Eurocode 3 and AISC 360-10 predictions and it was found that Eurocode 3 could be used conservatively to predict the bolt bearing resistance on high strength steel with nominal yield strength up to 890 MPa whereas AISC 360-10 method tends to overestimate the bearing resistance of the bolted connection. A regression analysis was performed based on the test data and those from the literature so that a more general method was proposed to predict the bolt bearing resistance on normal strength and high strength steel plate. Splitting failure was observed as a transitional failure mode between tearout failure and net cross-section failure. Splitting failure showed a lower resistance than the bolted connection with tear-out failure, therefore, a reduction factor was proposed to improve the prediction. The upper and lower boundaries of end distance to edge distance ratio for splitting failure were theoretically derived and experimentally verified.

High-strength steel is permitted in steel structures, whereas, further studies are needed to allow the use of high-strength steel in concrete-filled tubular (CFT) structures. In this study, twelve rectangular CFT columns using Q460-grade steel were tested under eccentric load and the test results were discussed. A nonlinear finite element model (FEM) was developed to predict the load-displacement and ultimate resistance behaviors of the test columns. Parametric studies were conducted using the verified FEM to investigate the influence of aspect ratios, steel strength, and width-to-thickness (h/t) ratio of steel plate. The ultimate resistance calculated by European Code (EC4), American Code (AISC 360) and Chinese Code (CECS 159) is compared with the FEM predictions to evaluate their feasibility in the use of higher aspect ratios, high-strength steel, and various h/t ratios. The results indicate that the three design codes are safe in the design of columns with higher aspect ratios. EC4 is conservative in the design of rectangular CFT columns with high-strength steel up to 690 MPa under its h/t ratio limitation. AISC 360 method can accurately predict the maximum resistance of rectangular CFT columns with steel strength 550 MPa. CECS 159 method is highly conservative and can be safely extended to the use of steel strength up to 690 MPa and plate slenderness ratio 85 235 / f y .

A steel plate shear wall system, consisting of a thin steel plate connected to the boundary frame members, is proposed as lateral load resisting system for use in the multi-storey building. To reduce the potential damage on the boundary elements caused by the tension field action in the steel plate after buckling, the steel plate is partially connected at the corner edges to the boundary frame members by bolts. Two scaled specimens were tested under cyclic loads to investigate the hysteretic behaviour of the partially connected steel plate shear wall (SPSW). Test results showed that the proposed SPSW exhibited good structural performance in terms of initial stiffness, shear resistance, ductility and energy absorption capability. An analytical method was developed to predict the shear resistance of the partially connected SPSW. The shear resistances obtained from the tests were compared with those predicted by the analytical method and a reasonable agreement was observed. In addition, a nonlinear finite element (FE) model was proposed to analyze the behaviour of the partially connected SPSW system. The accuracy of the FE models was verified by comparing the computed results with the cyclic load test results. Parametric analyses were then carried out to study the effects of plate slenderness ratio, plate aspect ratio (width/height), stiffness of the boundary frame members and initial plate imperfection on the lateral load resisting behaviour of the proposed steel plate shear wall system.

The use of high strength materials in steel-concrete composite members is expected to provide greater resistance meanwhile fulfilling the requirements of sustainable construction. Many of the modern design codes place some limits on the strength of steel and concrete in designing steel-concrete composite members due to limited test data and design experience on their applications in construction. The use of high strength materials was found to have noticeable benefits in high-rise building construction. To extend their applications, a comprehensive experimental program has been carried out to investigate the behaviour of concrete filled steel tubes (CFSTs) with high tensile steel and ultra-high strength concrete at ambient temperature. This paper presented new test results on the structural performance of CFST members subject to flexural loads. High tensile steel with yield strength up to 780 MPa and ultra-high strength concrete with compressive cylinder strength up to 180 MPa were used. The test results seek to clarify if the cross-section plastic moment resistance can be achieved if high tensile steel and ultra-high strength concrete are used in CFST members. The maximum moment resistance from tests were compared with the analytical results predicted by Eurocode 4 method. Then design recommendations were provided so that Eurocode 4 method could be safely extended to determine the flexural resistance of CFST members with high tensile steel and ultra-high strength concrete.

Concrete-filled steel tubular (CFT) columns and high-strength steel have been increasingly used in construction. However, the application of high-strength steel in CFT columns has not been permitted in many design codes. This paper reports an experimental investigation on the behavior of rectangular CFT beam-columns using high-strength steel. The influences of the in-fill concrete, eccentricity ratio and the width-to-thickness ratio on the resistance of the test columns are discussed. The contact behavior is studied using the finite element analysis. Chinese code DB 29-57 adopts the assumption that the concrete bears the axial load only, and the steel tube withstands the bending moment and part of the axial load. A new N-M interaction approach is developed based on the foresaid assumption to account for the plastic behavior of high-strength steel. The approach is verified by the experimental results and the available current design codes to be reasonably conservative, and it can be employed to design rectangular CFT beam-columns using high-strength steel.

A novel partially connected buckling-restrained steel plate shear wall as a robust and effective lateral load-resisting system is proposed in this paper. The influence of the superposition of the tension field and the high-order buckling deformation of the inner steel plate which is called “panel action” on the behavior of the new system is investigated. A modified method considering the effect of the panel action is developed to determine the minimum stiffness requirements of the vertical boundary elements so that the tension field will fairly uniformly form in the diagonal area. In addition, the nonlinear finite element method is adopted to carry out the push-over analysis to evaluate the effect of the initial imperfection on the behavior of the proposed shear wall. Meanwhile, based on the FE models validated using the available test data, an extensive parametric study is also performed to examine the effect of a change in the second moment of area of VBEs on the behavior of the novel shear wall. Finally, the FE results are compared with that predicted by the proposed method and a reasonable agreement is generally achieved between them.

Steel-Concrete-Steel (SCS) sandwich composite plate or shell structure has emerged as a viable solution for the Arctic offshore structure. Headed stud connectors are the essential structural components to enforce the composite action in the steel-concrete interface in these structures. This paper presents a parametric investigation on the shear resistance and failure mechanism in the shear connectors under low temperatures representing the Arctic conditions. The finite element (FE) approach used in the parametric study considers both material and geometric nonlinearities. Validation of the finite element procedure utilizes 54 previously reported experimental tests, with the objective to confirm the accuracy of the FE approach in predicting both the failure mechanism and the ultimate shear resistance of the stud connectors. The numerical study performs subsequently a comprehensive parametric investigation on 96 stud connectors, with the mechanical properties of the steel and concrete material measured at low ambient temperatures. To facilitate the engineering design of these connectors at low temperature conditions, this paper integrates the enhancement factors of the steel and concrete materials in a shear resistance estimation recommended in Eurocode 4. Keywords: Stud connector, Steel-concrete-steel sandwich structure, Arctic offshore structure, Steel-concrete composite, Finite element analysis, Shear resistance, Low temperature, Material properties

Ultra-high strength concrete (UHSC) and high strength steel (HSS) have been found to be attractive alternatives to normal strength materials for high-rise construction. The uses of HSS and UHSC can reduce member sizes and payload acting on foundation, which will free up more usable floor space and require less construction materials and handling works. The combination of them to form concrete-filled steel tubular (CFST) columns is more attractive compared with the columns employing either UHSC or HSS due to enhanced strength and stiffness. To better understand the structural behavior of CFST columns using UHSC and HSS, experimental and analytical studies on their fire resistance are presented in this paper. Fire tests were carried out on square S690 HSS tubes infilled with C170/185 UHSC to form the CFST columns. The fire resistance time under Standard ISO fire was recorded and checked against the conventional simple calculation model of EN1994-1-2 and the newly proposed axial force and moment interaction model. It is revealed that the column buckling curve in EN1993-1-1 can be used for fire-resistant design of CFST columns employing UHSC and HSS when the load level is less than 0.65. The use of UHSC is beneficial to improve the fire resistance of CFST columns but the use of high strength steel is not when compared with their counterparts using normal strength materials.

This paper investigates the failure mechanism and structural behavior of high strength Concrete Encased Steel (CES) composite columns subject to compression and bending. Twelve composite column specimens with C90 concrete and S500 steel section were tested under concentric compression, eccentric compression and four-point bending. All specimens had the same geometry and were reinforced with the same steel section and same amount of reinforcing bars. In some specimens, micro steel fiber was added into concrete mix with 0.5% or 1.0% dosage to delay or prevent the potential premature cover spalling. The load-carrying capacity, load-deformation response, post-peak ductility, flexural stiffness, as well as damage pattern are comprehensively analyzed. Comparison is made between the experimental results and analytical predictions using modern design codes such as EN 1994-1-1 and AISC 360–16. From the four-point bending test, the flexural stiffness obtained from the test seems to be smaller than the codes' predicted values, indicating that modification is needed to achieve better prediction of structural response of composite beams at the service load level. As for the axial force (N)-bending moment (M) strength interaction diagram, it is found AISC 360–16 gives overall more conservative prediction than EN 1994-1-1 method for high strength CES columns with C90 concrete and S500 steel. However, both methods overestimate the axial compression capacity although they can predict their flexural capacity well.

An equivalent brace model is developed to evaluate the nonlinear behavior of a novel partially connected buckling-restrained steel plate shear wall (BRSPSW) subjected to seismic loading. The high-order buckling modes of the equivalent brace under compression are taken into account meanwhile a hysteresis model is proposed to describe the stress–strain relationship of the equivalent brace. A nonlinear finite element (FE) method is employed to establish the validity of the partially connected BRSPSWs with the equivalent braces under monotonic, cyclic and seismic loads. A comparison with the FE results shows that the equivalent brace model with the proposed hysteresis properties can reasonably predict the shear resistance, hysteretic and seismic behaviors of the novel partially connected BRSPSWs. The effect of initial imperfection on the buckling responses of the restrained steel plate is also investigated. Nonlinear push-over analyses show that the increase of the initial imperfection essentially triggers the buckling mode of the restrained steel plate from high order to low order.

This paper investigates the structural behaviour of Steel-Concrete-Steel (SCS) sandwich wall which consists of two external steel plates infilled with ultra-lightweight cementitious composite material. A series of compression tests consists of a wide range of parameters have been carried out on the SCS sandwich walls of different heights forming short and slender wall. The test results show that the SCS sandwich walls with J-hook connectors exhibit comparable behaviour in compressive resistance and post-peak unloading behaviour to the ones with the overlapped headed studs. The interlocking J-hook connectors play an important role in providing composite action between the steel plates and the cementitious core, and preventing or delaying the local buckling of the external steel plates. The test results are compared against the predictions by Eurocode 4 and AISC 360 methods for composite columns. It is found that the Eurocode 4 and AISC 360 methods could over-predict the compressive resistance of sandwich wall subjected to compression. A modified method is then proposed, which takes into account the effect of interlocking J-hook connectors in providing lateral restraints to the external steel plates. The predictions show a reasonable correlation with the test results. Nonlinear finite element model has been established to predict the load-displacement curves, maximum resistance and failure modes of the sandwich walls. Both the experimental and finite element results confirm that the proposed analytical formulae are conservative for design of SCS sandwich composite walls with J-hook connectors.

A novel multi-functional water façade system with the combined function of energy saving and blast resisting is presented in this paper. The façade system utilizes water confined in a thin tank to harness the solar thermal energy and to shield the building from solar radiation. It is particularly suitable for hot climate regions near the Equator due to the constant high dense solar radiation throughout the year. The energy saving performance of the water façade in terms of harnessing the solar thermal energy and reducing space cooling load was evaluated by conducting temperature monitoring tests. As for its potential as a protective layer against blast loading, the water façade was tested under simulated blast loading through dropping projectile on an inflated high pressure airbag. The addition of water was shown to reduce the displacement of water façade and improve the blast resistant capacity through comparing the maximum displacements of the water façades with and without infilled water. An analytical model incorporating varying dynamic increase factor and coupled deflection mode shapes was developed to predict the displacement response of water façade under blast loading and the analytical predictions on maximum displacement were conservative as compared to those from finite element analyses. Keywords: Analytical model, Blast resistance, Energy saving, Finite element analysis, Water façade

This paper introduces experimental study on mechanical behaviour of an ultra-high strength concrete (UHSC) at elevated temperatures and then a simple calculation method to predict the fire resistance of tubular column infilled with the UHSC. The cylinder compressive strength of the UHSC was 166 N/mm2 at room temperature. The compressive strength and modulus of elasticity of the UHSC were measured up to 800 °C. Then the temperature-dependent mechanical properties were compared with those of normal/high strength concretes provided in Eurocode 2 and ANSI/AISC 360-10, and with those of concretes in literature. The comparisons showed that the compressive strength and elastic modulus of the UHSC were generally reduced less than those of normal/high strength concretes at the elevated temperatures. The temperature-dependent mechanical properties were proposed for evaluating fire resistance of steel tubular columns infilled with the UHSC. The UHSC investigated in this project was shown to markedly improve the fire resistance in a number of cases well documented in the literature concerning tubular columns filled with the normal- and high-strength concretes. Keywords: Ultra-high strength concrete, Elevated temperatures, Mechanical properties, Concrete filled steel tubular column, Simple calculation method, Fire resistance

This paper studied the structural behaviors of steel–concrete–steel sandwich composite plates under patch loads. Ten SCS sandwich plates, adopting an ultra-lightweight cement composite (ULCC) and overlapped headed studs as the bonding measures at the steel–concrete interface, were simply supported and subjected to patch loads till failure. The investigated parameters included spacing of the connectors, strength of the ULCC core, thickness of the steel skin, volume fraction of the fiber, and depth of the cross section. Test results estimated the size of the punching cone and showed that load-defection behaviors of the SCS sandwich plate contained five stages. The influences of the different parameters have been discussed and analyzed. Analytical models have been developed to predict the ultimate resistances of the SCS sandwich plate under patch loads through modifying the code equations. These innovations and modifications included developing models to predict the tensile resistance of the connectors, incorporating the contribution of the top steel skin on the punching shear resistance, consideration of the tensile resistance of the connectors on the second peak resistance of the structure, and adopting a proper critical perimeter. The validations of the predictions against the test results showed that the code provisions overestimated ultimate resistances of the SCS sandwich plates and the developed analytical models offered reasonably good agreements. Design recommendations were finally given based on these validations and discussions.

Novel lightweight flat slabs made of ultra-lightweight cement composite (ULCC) with density of 1329–1649 kg/m3 and strength of 52.0–87.3 MPa have been developed for buildings and offshore constructions. This paper studied the structural behaviors of the reinforced ULCC flat slabs under concentrated loading through a 14-specimen test program. The test program aimed to investigate the influences of shear span, flexural reinforcing ratio, depth of the section, and volume fraction of fibers on the failure mode, load deflection behaviors, and punching shear resistances of the ULCC flat slabs. Analytical models on predicting the tensile versus compressive strength relationships of ULCC were developed through regression analysis on 102 test data, and this developed relationship was then used to develop analytical models on punching shear resistance of ULCC flat slabs. Analytical models were developed to predict the punching shear resistance of the ULCC flat slabs through modifying the code provisions. The accuracy of these developed models was confirmed through validations against the reported test results. Keywords: Ultra-lightweight cement composite, Punching shear resistance, Fiber reinforcement, Flat concrete slab, Design models

The paper proposes a novel curved steel–concrete–steel (SCS) sandwich panel for Arctic offshore platform to resist the ice loads due to ice floes in Arctic region. The SCS sandwich panel consists of two curved steel plates infilled with a type of novel ultra-lightweight cement composite (ULCC) with a compressive strength of 60 MPa and a density less than 1400 kg/m3. Headed shear studs working in pairs with overlapped lengths are used to achieve composite action between the core material and steel face plates. This paper investigates the performance of curved SCS sandwich composite panel experimentally and analytically. Ten quasi-static tests on the curved sandwich composite panels subjected to patch loads are carried out to explore their failure modes, ultimate strength and load–defection behaviour. The main failure modes of the tests are identified as flexural failure, diagonal concrete strut crushing and shear tension failure. Based on the failure mechanism, a unified deep beam model is constructed to estimate the shear resistance of flat and curved SCS sandwich panels by considering equilibrium status, material yielding criteria and boundary conditions. The validations show that the modified model can provide close and conservative estimations on shear resistance for SCS sandwich composite panel. Keywords: Steel–concrete–steel, Steel–concrete composite, Ultra-lightweight cement composite, Ultimate strength, Shear failure, Sandwich panel

This paper presents a novel buckling-restrained steel plate shear wall with inclined slots called slotted SPSW to be used as an energy dissipation device for earthquake resistance. In the slotted SPSW, a steel plate with inclined slotted holes is sandwiched in between two external concrete panels which provide lateral restraint to achieve stable energy dissipation under cyclic reversal loading. Theoretical analysis and finite element monotonic pushover analyses are conducted to investigate the stability of slotted SPSWs. Global buckling and local buckling resistances of slotted SPSWs are determined. Some key parameters, such as the gap between steel plate and concrete panels, bolt spacing, width of steel strips, and steel panel slenderness, are investigated through numerical analyses. The shear force and lateral drift behavior of the slotted SPSW is found to be affected by the physical gap between the concrete panels and inner steel plate. The minimum concrete panel thickness for providing the effective lateral restraint to prevent buckling failure of the inner steel plate is determined based on the bolt spacing.

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. Keywords: Mild steel, High strength steel, Lightweight concrete, Curved sandwich, Sandwich plate, Punching shear

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.

This paper investigates the axial force-moment (N-M) interaction behaviour of high strength concrete encased steel (CES) composite columns. A numerical method is developed to simulate the nonlinear inelastic behaviour of CES composite beam-columns, which includes concrete cover spalling, concrete confinement effect, buckling of longitudinal reinforcing bars, and stain-hardening of the encased steel section. The numerical model is implemented in a self-developed computer program to generate the load-deflection response, moment-curvature relation, as well as the N-M strength interaction diagrams. The accuracy of the proposed analysis method is validated by comparison with the experimental results report in the companion paper and the test data available in literatures. To further understand the resistance of CES columns consisting of high strength concrete and high strength steel, parametric study is performed to evaluate the effect of concrete compressive strength, steel yield strength, load eccentricity, as well as steel area ratio. Finally, a simplified method is proposed to construct the N-M strength interaction curve of CES composite columns. The proposed method can be used to design CES beam columns for concrete grade up to C100 and steel grade up to S960.

Prefabricated Prefinished Volumetric Construction (PPVC), which is a form of modular construction, has been promoted recently for high-rise buildings to raise construction productivity. The flexibility of the inter-module connections and discontinuity of floor slabs of individual modules need to be modelled correctly in the structural analysis since they have direct effect on the building stiffness and its corresponding responses under lateral loads. In this paper, translational spring models are proposed to model the load transfer behavior of the vertical modules connections which are crucial for the structural behavior of high-rise modular buildings. The accuracy of the proposed spring models is investigated by comparing the force distribution and load displacement behavior of modular braced frames with conventional frame model established based on assumptions that the beams are either pin or rigidity connected to the columns. To enhance the productivity and work efficiency of high-rise modular construction, the feasibility of connecting the modules at the corners rather than tying the abutting beams or slabs is proposed. A more realistic approach of modelling the floor slab consisting of multiple modules inter-connected at the corners is recommended. The effectiveness of the corner connected modules in transferring the horizontal forces to the building's lateral load resisting systems is evaluated.

This paper investigates the axial load capacity of concrete encased steel composite stub columns with high strength concrete and steel materials. A total of 14 column specimens with varying material strengths and different steel section shapes were tested under concentric compression load. The test results revealed that the design methods in EN 1994-1-1 and JGJ 138-2016 overestimate the axial load capacity of high strength concrete encased steel columns. Adding a small percentage of steel fiber in the high strength concrete was found to improve the compression resistance of the composite section. A new test database consisting of 51 partially encased composite sections and 82 fully encased composite sections was established, covering a wide range of section geometric and material grades. Parametric study was then carried out to assess current design methods in predicting the axial capacity of such composite columns with respect to material strengths, steel contribution ratio, reinforcement ratio, section slenderness ratio, confined concrete area ratio, and concrete confinement efficiency. The effectiveness of concrete confinement in partially encased composite column was evaluated and a simplified method was proposed to compute the enhanced concrete strength based on regression analysis. For fully concrete encased composite columns, a concrete strength reduction factor was proposed to be used with EN 1994-1-1 to predict the compression resistance. Design recommendation was made considering the early cover spalling of high strength concrete and the material compatibility between steel and concrete in composite column design.

The structural performance of water tank under static and dynamic pressure loading was experimentally investigated in this paper. The loading was applied using hydraulic actuator/dropped projectile on an inflated high pressure airbag to assert static/dynamic pressure on the specimens. The failure modes and maximum resistance of the specimens were obtained from the test and compared to the numerical results. It was found from the static pressure test that the water tank filled with water exhibited up to 31% increase in flexural resistance under static loading as compared to the empty water tank with the same material and geometry. The improvement was attributed to the effects of water in maintaining the section modulus and delaying the local buckling of the tank. Water was also found to be useful in reducing the deformation of the tank under dynamic pressure loading. Nonlinear finite element analysis was conducted to investigate the behavior of water tank subject to static and dynamic pressure loading and the accuracy of the numerical models was verified by comparing the predicted displacement responses with those observed from the tests.

This paper investigates the robustness of steel-concrete composite building frames under column loss scenarios. Various composite building frame models, including different bracing systems, composite slab and joints are taken into account in analysing the dynamic response of the frame structure against the loss of a column due to accidental load. Robustness of ten-storey steel-concrete composite buildings with (i) diagonal braces at the corners, (ii) centre core wall, (iii) rigid moment joints are analysed for corner, perimeter and internal column loss. The analyses results show that simple braced frames are vulnerable to the progressive collapse compared with the moment resisting frames, which has higher redundancy to redistribute the loads arising from sudden column loss. Various strengthening approaches are investigated to improve the collapse resistance of the simple braced frames. Vierendeel truss was proposed at selected floor level in a building to redistribute the load due to column loss. End-plate or modified fin-plate connections were proposed for column-to-beam connections to enhance the progressive collapse resistance of simple braced frame. The resistance against progressive collapse is also investigated for building with outrigger-belt truss.

This paper investigates the progressive collapse behaviour of steel concrete composite buildings subject to ground blast explosion using nonlinear dynamic analysis and conventional alternate path approach. The alternate path approach, which is a threat independent methodology, is commonly used as a design guide for minimising the potential for progressive collapse. This method may not be always conservative in assessing the robustness of the structure, especially for building subject to heavy blast loads and thus nonlinear analysis is often needed to investigate the building response under such extreme load. In the present paper, composite slab model based on equivalent area approach and composite joint model based on Eurocode's component method are proposed for nonlinear analysis of building framework. The analysis results show that a heavy blast load may wipe out a series of columns/beams at once instead of a single one. High blast pressure may also induce large lateral drift and lead to significant damage to structural elements spreading over several storeys of the building. Generally, such extensive damage cannot be captured using the alternate path approach. The present investigation recommends that nonlinear analysis should be performed in order to capture the true behaviour of such buildings subject to extreme blast loads.

Two approaches for predicting the responses of axially restrained Steel-Concrete-Steel (SCS) sandwich panels subjected to blast loads are reported in this paper. The tensile membrane action of steel faceplates in the SCS sandwich panel is considered in these models. In the first approach, the SCS sandwich panel is idealized as a Single-Degree-of-Freedom (SDOF) system. The resistance-deflection function of the SCS sandwich panel is derived in which the resistance by concrete core is evaluated by utilizing the energy principle. Subsequently, the Lagrange Equation approach is proposed since it is allowed to define more than one deflected shape functions and therefore can capture the varying deflected shape of SCS sandwich panel during motion. The strain rate effects of steel and concrete have been accurately captured by calculating the Dynamic Increase Factor (DIF) of steel and concrete based on the varying strain rate during motion. The Finite Element (FE) analysis is carried out to verify the two proposed approaches and good agreement is observed.

This paper investigates the transverse impact performance for ultra lightweight cement composite (ULCC) filled pipe-in-pipe composite structures through drop weight impact tests and numerical simulations in LS-DYNA. Compared to steel hollow pipes, the sandwich composite pipes demonstrate superior impact performance with higher impact resistance, smaller global deformation and local indentation. The outer pipe and its thickness determine directly the impact resistance and the global bending deformation of the composite pipe. The ULCC layer restricts effectively the development of the local indentation. The presence of the inner pipe enhances the confinement to the ULCC material. The numerical simulation predicts closely the impact response for pipe-in-pipe composite specimens during the drop weight impact test.

This paper investigates the impact behavior of sandwich slabs which consist of a lightweight concrete core sandwiched in between two steel plates inter-connected by J-hook connectors. Special lightweight concretes of density 1450 kg/m3 and interlocking J-hook mechanical connectors have been developed for this purpose. Impact tests were carried out using an instrumented drop weight machine. Test data such as deflection- and impact force–time history and permanent deformation after impact were reported. Test observation showed that J-hook connectors provide an effective means to interlock the top and bottom steel face plates preventing them from separation upon impact. Steel fibers were added into the concrete core of selected test specimens to evaluate their effectiveness in reducing the brittleness of concrete due to dynamic loads. Using elastic–plastic analysis, analytical expression has been derived to predict the load–indentation relationship on the sandwich slab caused by the drop weight. It is then used in an energy balance model to predict the global response of sandwich slab subjected to impact load. The predicted results were compared with the test results so that the model can be validated for use to assess the impact performance of composite sandwich slabs.

Steel-Concrete-Steel (SCS) sandwich panel with ultra-lightweight cement composite core has been proposed to produce slim decking for bridge and building construction. One special feature of this lightweight sandwich panel is the use of J-hook connectors to improve the structural performance against combined actions of vertical shear and bending moment on the section. The proposed J-hook connectors provide effective bond between the steel and concrete, prevent local buckling and separation of the steel face plate, and enhance the transverse shear resistance to the structure. This paper investigates the tensile resistance of this new form of J-hook connectors by performing tensile tests on 79 sandwich specimens with various types of core materials including normal weight concrete, lightweight concrete, and ultra-lightweight cement composite. Their ultimate tensile resistances were obtained and corresponding failure modes were reported. The main parameters that influenced the tensile resistance of J-hook connectors were discussed and analyzed. Theoretical methods were developed to predict the tensile resistance of the J-hook connectors and their accuracy was verified against test results. Finally, recommended methods were proposed for design purposes.

This paper investigates the behaviour of hollow and concrete filled steel (CFST) mild and stainless steel columns subjected to transverse static and impact loading with a pre-compressive axial load. Transverse load was applied at the mid or quarter point of the columns. A total of three test series were carried out recently at the University of Western Sydney and the University of Wollongong to obtain the performance of mild and stainless steel hollow and CFST columns subjected to lateral static as well as impact loading with or without pre-compressive load. The test results reported in this paper are from the third test series, where both axial and lateral loads were applied to the columns. This paper also investigates the finite element (FE) modelling of hollow and CFST mild and stainless steel columns due to static and impact loads. Three-dimensional nonlinear FE models were developed using ABAQUS, where nonlinear material behaviour, enhanced strength corner properties of steel, pre-compressive loads were all included to simulate the static and impact experiments. The main objective of this paper is to compare the performance of experimental results with numerical results for mild and stainless steel hollow and CFST columns. Moreover, the behaviour of in-filled tubes under impact loading is also compared with that of hollow sections. Close agreement is achieved between the experimental and finite element results in terms of load–deflection response and ultimate strength. This paper also compares the results of hollow and CFST stainless steel columns with those of mild steel columns due to both static and impact loading. Generally, the stainless steel specimens showed higher strength and improved energy-dissipating characteristics compared with the mild steel columns.

Steel–concrete–steel (SCS) sandwich composite structure is a relative new type of system that combines the advantages of steel and reinforced concrete structure. Due to its excellent strength to cost performance, it exhibits versatile potential applications in building and offshore constructions. In order to reduce the self-weight of the structure and achieve composite action between the steel and concrete, ultra-lightweight cement composite and novel shear connectors have been developed and applied in the SCS sandwich composite structures, respectively. Meanwhile, the development of design guidelines lags behind the innovation of the structure. In this paper, experimental studies on SCS sandwich composite beams with different types of concretes and novel shear connectors are presented. This is followed by the development of analytical model to predict the ultimate strength of the SCS sandwich composite beams. Finally, the proposed analytical model is verified against the results from a series of beams tests which include Bi-steel sandwich beams, double skin beams, sandwich beams with J-hook connectors, angle connectors, and cable connectors. Through the analysis and verification, new methods to predict the ultimate strength of SCS sandwich composite beams are recommended for design purposes.

This paper investigates the blast and ballistic resistance of high strength steel XAR-450 with a tensile strength of about 1200 MPa. Compared to normal strength steel, this steel provides significant improvements in ultimate strength performance and can be designed with minimum weight, which are of increasing importance for use in the construction and defense industries. First, material properties of high strength steel are investigated to understand the protective capability and robustness of the proposed protective structures by utilizing the high strength steel plate to resist blast loading and high velocity impact. Both strain hardening and strain rate hardening of XAR-450 steel are investigated. Tensile Split Hopkinson Bar tests were performed to obtain the ultimate tensile strength at strain rates between 103s−1and 104s−1. Test results show noticeable increase of tensile strength of up to 40% with the increase of strain rate from static to 104s−1. Suitable rate-dependent constitutive models and parameters are proposed based on least-squares fitting with test data. The ductile fracture mechanics is also investigated. Thus these material parameters can be used for numerical analysis of protective structures subject to blast and impact. Finally, high velocity impact resistance of high strength steel XAR-450 against bullet and Fragment Simulating Projectile (FSP) were investigated experimentally and numerically. The blast resistance of the high strength XAR-450 steel plate is investigated by the comparison of blast field test result with the finite element analysis results.

New form of J-hook connectors and ultra-lightweight cementitious material have been developed by the authors in the previous research to produce steel–concrete–steel sandwich slim decks which have superior performance to resist blast and impact loads. This paper investigates the shear strength behavior of the J-hook connectors embedded in ultra-lightweight cement composite core and compares the behavioral differences with those in normal strength concrete. A total of 102 push-out tests were carried out on standard test specimens with varying parameters including concrete types (normal weight, lightweight and ultra-lightweight), concrete strengths, and types of J-hook connectors. Design guides are proposed to predict the shear strength and load–slip behavior of the J-hook connectors embedded in ultra-lightweight cement composite. The predicted results are compared with the test results together with those predicted by modern codes which were primarily developed for headed shear studs. Through the comparisons and verifications, it is observed that the proposed formulae offers better and more reliable predictions on shear strength as well as load–slip behaviors compared with the available methods in the literature.

Concrete-filled stainless steel tubes can be considered as a new type of composite construction technique. The characteristics of stainless steel are quite different from those of mild steel in terms of strength, ductility, corrosion resistance and maintenance costs. This paper presents the behaviour of hollow and concrete-filled stainless steel tubular columns under static and impact loading. An experimental test series has been carried out at the University of Wollongong and the University of Western Sydney to investigate the performance of stainless steel hollow and concrete-filled steel tubular (CFST) columns under static and impact loads. This paper presents the results of the first test series, where stainless steel was used and no axial load was applied. The effects of a combined axial and transverse impact loads as well as the location of the impact loading have been considered in a subsequent series. Finite element modelling was carried out to predict the behaviour of composite columns under a lateral static or impact load using ABAQUS to simulate the static and impact experiments. The comparison of the experimental results with numerical results is the main objective of this paper. Moreover, the behaviour of hollow tubes under impact loading is compared with that of the in-filled sections. This paper also compared results of hollow and CFST stainless steel columns with those of mild steel columns under both static and impact loading. Generally, the stainless steel specimens showed improved energy-dissipating characteristics compared with their mild steel counterparts, especially when concrete was used to fill the hollow tubes.

The paper is concerned with the behavior of steel–concrete composite haunch beams. Experiments were carried out to investigate the ultimate load behavior of haunch composite beams. Three continuous composite haunch beams were tested to failure. Two different proportions of slab reinforcements and two different haunch lengths were studied in order to examine the effects of these parameters on the ultimate load carrying capacity. Results obtained are presented in the form of load–deflection plots and different failure modes. It is found that through proper design and detailing optimum design of composite haunch beam can be achieved when plastic hinge occurs at haunch toes followed by a hinge at the mid-span to form a plastic collapse mechanism. Experimental results show that composite haunch beam exhibits a ductile moment–rotation behavior and is able to redistribute moment to the mid-span by loss of stiffness due to cracking of concrete slab and yielding of either steel reinforcement or cross section.

Experimental results of spalling and residual mechanical properties of ultra-high performance concrete after exposure to high temperatures are presented in this paper. The compressive strength of the ultra-high performance concrete ranged from 160 MPa~185 MPa. This study aimed to discover the effective way to prevent spalling for the ultra-high performance concrete and gauge its mechanical properties after it was subjected to fire. The effects of fiber type, fiber dosage, heating rate and curing condition were investigated. Test results showed that the compressive strength and elastic modulus of the ultra-high performance concrete declined slower than those of normal strength concrete after elevated temperatures. Polypropylene fiber rather than steel fiber was found effective to prevent spalling but affected workability. The effective fiber type and dosage were recommended to prevent spalling and ensure sufficient workability for casting and pumping of the ultra-high performance concrete.En este trabajo se presentan los resultados más relevantes del trabajo experimental realizado para valorar la laminación y las propiedades mecánicas residuales de hormigón de ultra-altas prestaciones tras su exposición a altas temperaturas. La resistencia a la compresión del hormigón de ultra-altas prestaciones osciló entre 160 MPa~185 MPa. El objetivo de este estudio fue descubrir una manera eficaz de prevenir desprendimientos y/o laminaciones en este hormigón y medir sus propiedades mecánicas después de ser sometido al fuego. Las variables estudiadas fueron la presencia y dosificación de fibras, velocidad de calentamiento y condiciones de curado. Los resultados mostraron, tras la exposición a altas temperaturas, que la resistencia a compresión y el módulo de elasticidad del hormigón de ultra-altas prestaciones disminuían más lento que las de un hormigón con resistencia normal. La fibra de polipropileno resultó más eficaz para prevenir desprendimientos que la fibra de acero pero la trabajabilidad se vio afectada. Tras el estudio realizado se recomienda el tipo de fibra más efectiva y la dosis para evitar desprendimientos y garantizar la suficiente capacidad de trabajo para la puesta en obra y bombeo del hormigón de ultra-altas prestaciones.

This paper investigates the static and fatigue strength behavior of a composite sandwich system, which consists of a lightweight concrete core sandwiched in between two steel plates and interconnected by J-hook connectors. For this purpose, fibre-reinforced lightweight concrete, of density less than 1450 kg/m3, and novel J-hook connectors that are capable of resisting tension and shear have been developed. Fatigue tests were carried out to study the fatigue behaviour of sandwich beams by varying the maximum applied load and load range. It is found that maximum applied load and load range affect fatigue performance independently. The maximum applied load has a significant effect on fatigue performance when the difference between it and the load range is large. Test evidence shows that considering only the load range, without taking into account the maximum applied load, may over-predict the fatigue life of the sandwich structural system. Finally, a three-parameter fatigue design equation, taking into account both the load range and maximum applied load, is proposed based on regression analysis of test data.

Concrete-filled tubes are often preferred for the construction of high-rise buildings because of their high strength and stiffness compared to conventional reinforced concrete or steel columns. However, prior to infilling of concrete, the steel tubes are subjected to preloads from upper floors arising from construction loads and permanent loads of the building. These preloads cause initial stresses and deformations in the steel tubes which would affect the load carrying capacity of the composite columns. In this paper, a design method based on a modified Eurocode 4 approach, incorporating the effect of preload, is proposed to evaluate the axial capacity of concrete filled composite columns. Eight full-scale composite column specimens were tested. Parameters studied included the strength of the concrete infill, slenderness of the columns and the amount of preload applied on the steel tubes. Results obtained from the proposed method are compared against test results and other published data. Comparison studies show that the test results are on average 3% higher than predicted results with a standard deviation of 0.089. Finite element analyses are also performed for systematic verification, and the results are 8% higher than predicted results. It is conclude that the proposed design method is accurate and mostly conservative and can be readily used in the context of Eurocode 4: Part 1.1 for designing composite columns.

The lesson learned from the terrorist attacks on buildings is the need to assure structures’ ability to sustain local damage without total collapse. Some of the terrorist attacks take the form of blast followed by fire which may cause catastrophic failure of the structure. This paper presents a numerical model for analyzing steel frame structures subject to localized damage caused by blast load and subsequently investigating their survivability under fire attack. The proposed numerical method adopts a mixed-element approach for modeling large-scale framework and it is proven to be sufficiently accurate for capturing the detailed behaviour of member and frame instability associated with the effects of high-strain rate and fire temperature. Design implications related to the use of various numerical models for separate assessment of blast and fire resistance of steel structures and their components are discussed. Fire–blast interaction diagrams are generated to determine the fire resistance of columns considering the initial damage caused by the blast loads. A multi-storey steel building frame is analyzed so that the complex interaction effects of blast and fire can be understood and quantified. The frame is found to be vulnerable, as it possesses little fire resistance due to the deformation of key structural elements caused by the high blast load.