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This paper presents an assessment and quantification of the environmental impacts arising from different steel-concrete composite floor systems. In particular, a demountable composite floor system using pretensioned high-strength friction grip bolts as shear connectors is compared with three conventional composite floor systems that use welded shear studs as shear connectors. The first type promotes the end-of-life scenario of disassembly and reuse of structural elements, while the conventional systems are related to the current practices of waste management for building materials, i.e. demolition and recycling. To analyse these different structural systems and relative scenarios, a comparative Life Cycle Assessment investigating two entire life cycles of the materials is developed. Based on the evaluation of several impact categories, the building with demountable composite floor system is identified as the most environmentally friendly solution among all the considered structural solutions, and the saving of emissions and resources is quantified for each impact category.

The robustness of a seismically-designed steel self-centering moment-resisting frame (SC-MRF) under a column loss scenario is numerically assessed. The prototype SC-MRF is equipped with post-tensioned bars and optimised stainless steel energy dissipation devices. The SC-MRF was modelled in full detail using solid finite elements. The numerical model was calibrated using results from previous tests on post-tensioned beam-column connections and isolated component tests on the energy dissipation devices. Quasi-static analyses were carried out to identify the failure modes of the SC-MRF under a column loss scenario. Nonlinear dynamic analyses were also performed to evaluate the dynamic response of the frame and to assess the acceptance criteria against progressive collapse according to current formalised procedures. The results show that the SC-MRF has superior robustness and it can guarantee a high level of safety under a sudden column loss scenario due to the high fracture capacity of the stainless steel energy dissipation devices and the tie force resistance provided by the post-tensioned bars.

An alternative way to decrease the peak response and provide higher robustness against the loss of post-tensioned (PT) force in self-centering structures is to provide them with stiffness degradation and pinching behaviour. In this study, an innovative PT connection using slender steel rectangles as energy-dissipating elements is proposed. Cyclic tests on five specimens considering the effect of thickness, width and number of steel rectangles, and the initial stress of the PT strands were carried out. The results demonstrate that the connections have acceptable seismic response despite stiffness degradation and pinching behaviour of the energy-dissipating steel elements. Specimens with a smaller width of steel rectangles exhibited typical three-plastic-hinge buckling. Smaller thickness of the steel segments would change the buckling behaviour to a multi-wave out-of-plane mode, which is difficult to predict and design for. The energy-dissipating capacity can be increased by increasing the number of steel rectangles while the re-centering capacity remains unaffected. In addition, a verified phenomenological hysteretic model for slender steel rectangles was developed and implemented into OpenSees as a material, which may facilitate further numerical investigations.

A demountable shear connector for use in composite floors with precast hollow-core slab units is proposed. The proposed shear connector consists of a steel square hollow tube welded on a st...

This paper presents static and dynamic tests on nominally-pinned steel joints equipped with novel structural details for progressive collapse mitigation. The proposed structural details utilise the exceptional ductility and strength of stainless steel pins to enhance both the tie force and the rotational capacity of a vulnerable steel joint. The stainless steel pins along with additional supporting elements are installed in the joint region without interfering with the design for gravity loads, and they can be used for both new designs and to retrofit existing steel buildings. A static test on a vulnerable industry-standard steel fin-plate connection is first presented followed by two static tests on the same connection retrofitted with the proposed structural details. The retrofitted connections were subsequently tested under dynamic conditions with increasing imposed loading using a test setup that simulates a sudden column loss scenario. The test results showed that nominally-pinned joints equipped with the proposed structural details can achieve the required tie force capacity while undergoing rotations larger than 0.2 rad. Analytical equations based on simple joint equilibrium are used to validate the results of the static tests. An analytical method based on the energy conservation principle is also proposed and comparison with the dynamic tests shows very good predictive capability when the assumed loss of energy is 22%.

A dual seismic-resistant steel frame, which consists of a moment-resisting frame equipped with high post-yield stiffness energy-dissipative braces, is proposed and numerically evaluated. Replaceable hourglass shape pins made of duplex stainless steel with high post-yield stiffness and large energy dissipation and fracture capacity are in series connected to conventional steel braces. Moreover, replaceable fuses are introduced in the beams at the locations where plastic hinges are expected to develop. A performance-based seismic design procedure and appropriate capacity design rules are used to design the dual frame, while its seismic performance is evaluated with advanced numerical simulations using experimentally validated shell–solid finite element models and simplified beam element models. The numerical results show that the dual frame has adequate stiffness and energy dissipation capacity to control peak storey drifts (i.e. non-structural damage), while plastic deformations (i.e. structural damage) are isolated within the replaceable pins of the braces and the beam fuses. In addition, the high post-yield stiffness of the pins, combined with the appreciable elastic deformation capacity of the moment-resisting frame, results in significant reduction of residual storey drifts, which are found to have a mean value of 0.06% under the design earthquake and a mean value of 0.12% under the maximum considered earthquake. These values indicate a superior residual storey drift performance compared to steel frames equipped with buckling restrained braces, and highlight the potential of the proposed dual frame to help steel buildings to return to service within an acceptable short time in the aftermath of a strong earthquake.

Current design standards require that beam-column joints should withstand a minimum tie force in the case of an extreme loading event resulting in the loss of one or more columns to prevent progressive collapse of a building. However, research has shown that nominally-pinned steel beam-column joints, which are commonly used in non-seismic areas and in the gravity frames of seismically-designed frames, are not capable of providing the required tie force while undergoing significant rotations imposed by a loss of column event. This paper proposes a set of novel structural details that can be added to industry-standard nominally pinned joints to increase both their tensile resistance and rotation capacity. The proposed structural details exploit the exceptional strength and ductility of duplex stainless steel pins (SSPs) under bending. SSPs are strategically placed in a way that they do not interfere with the behaviour of the joint under gravity loads. The monotonic fracture capacity of SSPs is first experimentally evaluated and the calibration of numerical models that can capture the fracture behaviour of the SSPs follows. Using the calibrated numerical models, a parametric study was carried out to identify optimal geometries of SSPs to reliably achieve the required levels of tie force and rotation in a joint. Finally, two previously tested vulnerable fin plate joints are used as design cases to demonstrate the effectiveness of the proposed structural details to increase the resistance against progressive collapse of nominally-pinned joints.

This paper presents ultralow cycle fatigue tests and the calibration of different fracture models for duplex stainless-steel devices of high seismic performance braced frames. Two different...

This paper presents progressive collapse simulations to assess the robustness of a seismic-resistant building using self-centering moment resisting frames (SC-MRFs) under a sudden column loss scenario. The first floor of the building, including the composite floor, was modelled in ABAQUS using a mixture of finite element types and simulation methods to balance computational cost and accuracy. First, key components of the numerical model, including the composite beams, the fin-plate beam-column connections, and the perimeter SC-MRFs, were validated against available experimental results to ensure a reliable simulation. The validated model was then used to study the robustness of the building under a sudden column loss event. Both nonlinear static and dynamic analyses were employed. The simulations allowed for the identification of all possible failure modes and the quantification of the contribution of the composite floor to the robustness of the frame. The results show that the building can withstand the code-prescribed load with a safety factor of 2 and that the structural limit state that triggers progressive collapse is the buckling of the gravity columns. The Dynamic Increase Factor (DIF) was also identified by comparing the static and dynamic responses.

A bstract Column bases of seismic-resistant steel frames are typically designed as full-strength to ensure that plastic hinges develop in the bottom end of the first-storey columns. Alternatively, column bases may be designed as partial-strength and dissipate energy through inelastic deformations in their main components (i.e., base plate, steel anchor rods). Both design philosophies result in difficult-to-repair damage and residual drifts. Moreover, the second design philosophy results in complex hysteretic behaviour with strength and stiffness deterioration. This paper proposes a partial-strength low-damage self-centering steel column base. The column base provides flexibility in the design as its rotational stiffness and moment resistance can be independently tuned. The paper presents an analytical model that predicts the stiffness, strength, and hysteretic behaviour of the column base. In addition, a design procedure and detailed finite element models are presented. The paper evaluates the effectiveness of the column base by carrying out nonlinear dynamic analyses on a prototype steel building designed as post-tensioned self-centering moment-resisting frame. The results demonstrate the potential of the column base to reduce the residual first-storey drifts and protect the first-storey columns from yielding.

The most common type of a steel concrete composite beam is the one using conventional welded headed studs to connect the top flange of a steel beam to the concrete slab. However, the monolithic structure between the headed studs and the concrete slab prevents the deconstruction of the beam. More sustainable solutions in construction can be achieved by developing demountable connections which allow for fully deconstruction and reuse of all structural systems. This paper presents a novel demountable shear connector for use in steel concrete composite beams in conjunction with precast hollow core slab units. The demountable connection proposed has the advantages of minimal use of in situ concrete required only in specific regions, increased ductility due to the unique shape of the shear connector and since it is not embedded in in situ concrete, it facilitates the deconstruction procedure. Ten horizontal push out tests aiming at investigating the structural performance of the demountable shear connector were carried out. The strength of the connection is predicted using simple mechanics based on plastic beam analysis. The experimental results showed that the proposed demountable shear connector can achieve increased strength depending on the geometric characteristics of the connector, a ductile slip-load curve and a very high slip capacity.

Composite steel–concrete beams are frequently used in situations where axial forces are introduced. Some examples include the use in cable-stayed bridges or inclined members in stadia and bridge approach spans. In these situations, the beam may be subjected to any combination of flexure, shear and axial loads. However, modern steel and composite construction codes currently do not address the effects of these combined actions. This study presents an analysis of composite beams subjected to combined loading. A finite element model (FEM) has been developed and the results derived from the model show excellent agreement with existing FEM and experimental results. The effect of compression and tension loads on a member subjected to flexure and shear is also explored. Design models are proposed for estimating the flexure and shear interaction of an axially loaded member.

This paper presents an experimental and numerical study on the ultimate strength of steel–concrete composite beams subjected to the combined effects of sagging (or positive) bending and axial compression. Six full-scale composite beams were tested experimentally under sagging bending and increasing levels of axial compression. A nonlinear finite element model was also developed and found to be capable of accurately predicting the nonlinear response and the combined strength of the tested composite beams. The numerical model was then used to carry out a series of parametric analyses on a range of composite sections commonly used in practice. It was found that the sagging moment resistance of a composite beam is not reduced under low-to-moderate axial compression, while it significantly deteriorates under high axial compression. Sectional rigid plastic analyses confirmed the experimental results. The moment–axial force interaction does not change significantly between full and partial shear connection. Based on the experimental and numerical results, a sagging moment–axial compression interaction law is proposed which will allow for a more efficient design of composite beams.

[EN] This paper presents the numerical assess of the robustness of a seismic-resistant steel building with self-centering moment resisting frames against progressive collapse. The numerical analyses were carried out using a 3D model developed in ABAQUS. The 3D model considers the effect of the composite slab, where composite beams and their shear connectors were modeled with a combination of shell, beam and nonlinear connector elements. All the beam-column and beam-to-beam connections were modeled using nonlinear connector elements with appropriate failure criteria, calibrated against previous experimental results. The self-centering moment resisting frame where a sudden column loss was simulated was modelled using 3D solid elements to accurately capture its local and global nonlinear behavior. Quasi-static nonlinear analyses were carried out to identify all possible failure modes and to investigate the effect of the floor slab on the overall progressive collapse resistance. Nonlinear dynamic analyses were also carried out to predict the true dynamic response and evaluate the acceptance criteria of current building design guidelines., This research was supported by a Marie Sklodowska-Curie Action Fellowship within the H2020 European Programme. Any opinions, findings, and conclusions or recommendations expressed in this paper are those of the authors and do not necessarily reflect the views of the European Commission.

A new self-centering steel post-tensioned connection has been proposed by the authors. The connection uses high-strength steel post-tensioned bars to provide self-centering behavior and steel energy dissipation elements that consist of cylindrical pins with hourglass shape to provide enhanced deformation capacity. Large-scale experimental tests showed that the connection has robust self-centering behavior by eliminating residual drifts and beam damage for drifts lower or equal to 6%. This paper presents finite element models which can be used to reliably assess the design and behavior of the connection. A simplified connection model was first developed using simple mechanics. This model can predict the connection stiffness and strength with reasonable accuracy, and enables the preliminary design of self-centering steel moment-resisting frames using the proposed connection. A detailed nonlinear finite element model was also developed. This model was calibrated against experimental results and found capable to trace the nonlinear cyclic behavior of the connection and capture all possible local failure modes. The calibrated finite element model was used to conduct a series of simulations to study the effect of different parameters on the connection behavior. The parameters studied include the adopted design procedure, beam reinforcing detailing, and the beam and column section sizes.

A new self-centering beam-to-column connection is proposed. The connection uses posttensioned high-strength steel bars to provide self-centering capability and carefully designed energy-dissipation (ED) elements that consist of steel cylindrical pins with an hourglass shape. The proposed ED elements have superior ED and fracture capacity, and are placed between the upper and the bottom flanges of the beam such that they do not interfere with the composite slab. A simplified performance-based procedure was used to design the proposed connection. The connection performance was experimentally validated under quasi-static cyclic loading. The specimens were imposed to drift levels beyond the expected design ones to identify all possible failure modes. The experimental results show that the proposed connection eliminates residual drifts and beam damage for drifts lower than or equal to 6%. A simplified analytical procedure using plastic analysis and simple mechanics was found to accurately predict the connection behavior. Repeated tests on a connection specimen were conducted, along with replacing damaged ED elements. These tests showed that the proposed ED elements can be easily replaced without welding or bolting, and hence the proposed connection can be repaired with minimal disturbance to building use or occupation in the aftermath of a major earthquake.

This paper investigates the behaviour of steel–concrete composite beams subjected to the combined effects of negative bending and axial compression. For this study, six full-scale tests were conducted on composite beams subjected to negative moment while compression was applied simultaneously. The level of the applied axial compression varied from low to high. Following the tests, a nonlinear finite element model was developed and calibrated against the experimental results. The model was found to be capable of predicting the nonlinear response and the ultimate failure modes of the tested beams. The developed finite element model was further used to carry out a series of parametric analyses on a range of composite sections commonly used in practice. It was found that, when a compressive load acts in the composite section, the negative moment capacity of a composite beam is significantly reduced and local buckling in the steel beam is more pronounced, compromising the ductility of the section. Rigid plastic analysis based on sectional equilibrium can reasonably predict the combined strength of a composite section and, thus, can be used conservatively in the design practice. Detailing with longitudinal stiffeners in the web of the steel beam in the regions of negative bending eliminate web buckling and increase the rotational capacity of the composite section. Based on the experimental outcomes and the finite element analyses a simplified design model is proposed for use in engineering practice.

Structural parts commonly comprised of composite members such as bridge approaches, inclined parking ramps and stadium beams, can be subjected to a combination of high axial loads and bending moments. Steel–concrete composite construction is a popular solution for these types of structures due to the numerous advantages that they offer. Although, current design codes (e.g. Eurocode 4, American code AISC, Australian codes AS2327 and AS5100) provide rules for the design of composite columns subjected to flexure and axial load, however the design of composite beams, which are asymmetric in nature under the combined effects of tension and bending, is not yet fully addressed. This paper investigates the ultimate strength of composite beams under the combined effects of axial tension and negative (hogging) bending moment. An experimental programme carried out in the laboratory of the University of Western Sydney comprised of a total of six specimens representing composite beams and subjected to various levels of axial tension and bending moment. Ultimate failure modes were identified and the resulting interaction diagrams were compared to the results of sectional rigid plastic analysis. Following the tests, three-dimensional finite element models were employed using the ABAQUS finite element software to further investigate the nonlinear behaviour of the composite beams and extend the experimental observations by studying the effects of parameters such as the span length and the effect of partial shear connection. Finally, simple design rules and formulae are proposed for use in engineering practice.

Steel yielding hysteretic devices provide a reliable way to increase the energy dissipation capacity of structures under seismic loading. Steel cylindrical pins with hourglass shape bending parts (called web hourglass shape pins—WHPs) have been recently used as the energy dissipation system of posttensioned connections for self-centering steel moment-resisting frames. This work evaluates the cyclic behavior of WHPs made of high-strength steel and two grades of stainless steel, i.e., austenitic grade 304 and duplex. Design rules for WHPs are established using principles of mechanics. Twenty-six tests using different cyclic loading protocols and different WHP geometries were conducted. The tests showed that the WHPs have stable hysteretic behavior and high fracture capacity. WHPs made of duplex stainless steel have the most favorable and predictable performance for seismic applications. Two micromechanics-based fracture models, i.e., the void growth model and the stress-modified critical strain model, were calibrated and their parameters are provided for high-strength steel and the two types of stainless steel. The ability of the cyclic void growth model to predict fracture in WHPs under cyclic loading is also evaluated.

Steel-concrete composite beams are currently designed against shear by neglecting the contributions of the concrete slab and composite action, while the moment-shear interaction is not addressed in current structural codes of practice. This paper presents an experimental and numerical study on the shear strength and moment-shear interaction in simply-supported steel-concrete composite beams. Fourteen composite beams and one steel beam were tested under combined bending and shear. The effects of partial shear connection and shear reinforcement in the slab were also studied. A nonlinear finite element model was developed and found capable of accurately predicting the behavior of the composite beams. Extensive parametric studies were then conducted using the validated numerical model. The results allowed for the derivation of a moment-shear interaction law for composite beams and highlighted the high degree of conservatism in current structural specifications. It is shown that both the concrete slab and the composite action contribute significantly to the shear strength of a composite section and that the main factors that influence the shear capacity of a composite beam are the slab thickness and the degree of shear connection. Based on the experimental and numerical results, a design model is proposed for a more efficient design of compact composite beams in regions where the acting shear is high.

The effect of the strength and stiffness characteristics of a previously proposed novel column base on the seismic performance and collapse capacity of steel self-centering moment-resisting frames is evaluated in this paper. This is done through three normalised parameters that represent the initial stiffness, post-yield stiffness, and strength of the column base, which can be independently adjusted. For these evaluations, a prototype steel building, which serves as a case study, is designed with sixteen different cases of a self-centering moment-resisting frame with different column base stiffness and strength characteristics (SC-MRF-CBs). A self-centering moment-resisting frame with conventional column bases and the same members and beam-column connections as those of the SC-MRF-CBs, named SC-MRF, serves as a benchmark frame. A set of 44 ground motions was used to conduct non-linear dynamic analyses and evaluate the seismic performance of the frames. Incremental dynamic analyses were also performed with the same ground motions set to evaluate the collapse capacity of the frames. Collapse capacity fragility curves and adjusted collapse margin ratios of the frames were derived and used for the comparison of the seismic risk of the frames. The results show that the new self-centering column base significantly improves the seismic performance of the SC-MRF, demonstrating the potential of the SC-MRF-CBs to be redesigned with smaller member sections. Moreover, the SC-MRF-CBs achieve significant reduction in collapse risk compared to the SC-MRF. Finally, the results show that increasing the base strength and stiffness improves the seismic performance and collapse capacity of the SC-MRF-CBs. © 2020 Elsevier Ltd