Showing papers in "Journal of Constructional Steel Research in 2013"
TL;DR: In this article, a finite element (FE) model for CFST stub columns under axial compression is presented. But the model is not suitable to be used in some cases, especially when considering the fast development and utilisation of high-strength concrete and/or thin-walled steel tubes in recent times.
Abstract: Due to the passive confinement provided by the steel jacket for the concrete core, the behaviour of the concrete in a concrete-filled steel tubular (CFST) column is always very challenging to be accurately modelled. Although considerable efforts have been made in the past to develop finite element (FE) models for CFST columns, these models may not be suitable to be used in some cases, especially when considering the fast development and utilisation of high-strength concrete and/or thin-walled steel tubes in recent times. A wide range of experimental data is collected in this paper and used to develop refined FE models to simulate CFST stub columns under axial compression. The simulation is based on the concrete damaged plasticity material model, where a new strain hardening/softening function is developed for confined concrete and new models are introduced for a few material parameters used in the concrete model. The prediction accuracy from the current model is compared with that of an existing FE model, which has been well established and widely used by many researchers. The comparison indicates that the new model is more versatile and accurate to be used in modelling CFST stub columns, even when high-strength concrete and/or thin-walled tubes are used.
TL;DR: In this paper, different alternatives for shear connectors (bolts and headed studs) are analyzed to gain better insight in failure modes of shear connector in order to improve competiveness of prefabricated composite structures.
Abstract: Prefabrication of concrete slabs reduces construction time for composite steel–concrete buildings and bridges. Different alternatives for shear connectors (bolts and headed studs) are analysed here to gain better insight in failure modes of shear connector in order to improve competiveness of prefabricated composite structures. Casting of high strength bolted shear connectors in prefabricated concrete slabs offers the higher level of prefabrication comparing to a standard method of grouting welded headed studs in envisaged pockets of concrete slabs. In addition, bolted shear connectors can easily be dismantled together with the concrete slab thus allowing the improved sustainability of the construction, simpler maintenance, and development of modular structural systems. Bolted shear connectors have been rarely used in construction, actually just for rehabilitation works, because there is a lack of design recommendation. The first step towards the design recommendation is to understand the difference between the headed shear studs and the bolted shear connectors in a push-out test. Push-out tests, according to EN1994-1-1, using 4 M16 — grade 8.8 bolts with embedded nut in the same layout and test set-up as for previously investigated headed studs were performed. Finite element models for both shear connectors were created, and good match with experimental data was obtained. Basic shear connector properties such as: shear resistance, stiffness, ductility and failure modes have been compared and discussed in detail by using experimental and FE results. Parametric FE analyses of shear connector's height are carried out and shear resistance reduction factor has been proposed for bolted shear connectors.
TL;DR: In this paper, the impact performance of concrete filled steel tubular (CFST) members was investigated and a finite element analysis (FEA) model was developed, in which the strain rate effects of steel and concrete materials, interaction between the steel tube and core concrete, as well as the confinement effect of the outer steel tube provided to the core concrete were considered.
Abstract: This paper reports an investigation into the impact performance of concrete filled steel tubular (CFST) members. A series of tests were carried out to obtain the failure modes and the time history of the impact forces for the composite components under lateral impact. The testing parameters include the axial load level on CFST specimens, constraining factor and the impact energy. A finite element analysis (FEA) model was developed, in which the strain rate effects of steel and concrete materials, interaction between the steel tube and the core concrete, as well as the confinement effect of the outer steel tube provided to the core concrete were considered. The test data were then used to verify the accuracy of the FEA model and generally a good agreement was achieved. A full-range analysis on the impact behavior of CFST member was performed by using the FEA model.
TL;DR: In this paper, a detailed concrete filled double-steel-plate (CFDSP) composite wall using high-strength concrete is proposed to improve the ductility of the core wall in super high-rise buildings subjected to high axial compressive force and seismic effect.
Abstract: In order to improve the ductility of the core wall in super high-rise buildings subjected to high axial compressive force and seismic effect, a new detailed concrete filled double-steel-plate (CFDSP) composite wall using high-strength concrete is proposed. This CFDSP composite wall is composed of concrete filled steel tubular columns at the two boundaries and concrete filled double-steel-plate wall body which is divided into several compartments by vertical stiffeners transversely connected by distributed batten plates. In order to intensively investigate the structural mechanism of this new type of CFDSP composite walls, twelve specimens are tested under large axial compressive force and reversed cyclic lateral load. No evident buckling of surface steel plates can be observed due to reasonable width-to-thickness ratios of steel plates and properly arranged batten plates, so that the surface steel plates and infill high-strength concrete can work compatibly in the whole loading process. All the specimens exhibited good energy dissipation ability and deformation capacity with full hysteretic curves and large ultimate drift ratios, thereby indicating that high-strength concrete can be used in seismic-resistant structures when the proposed new detailed walls are adopted. Based on the test results, the stiffness and strength degradations are analyzed, and the deformation characteristics of all the specimens are discussed in detail. Finally, a strength prediction approach based on the section analysis method is presented, and some detailing requirements for routine design practice are recommended.
TL;DR: In this article, the buckling performance of six pin-ended 960-MPa steel columns under axial compression was investigated and a finite element model was used to perform a large number of parametric studies, considering different cross-sectional dimensions and column slenderness.
Abstract: Investigations of the mechanical performance of high strength steel structures have become a research hotspot in civil and structural engineering, and existing experimental studies of their overall buckling behaviour have hitherto focused mainly on columns fabricated from either 460 MPa or 690 MPa steels. The present study describes an experimental programme including six pin-ended 960 MPa steel columns under axial compression. Both welded I- and box-section specimens are considered. The initial geometric imperfections and cross-sectional residual stresses are reported, with the axial loading, deformation and the strain distributions at the mid-length section being monitored during the testing. The buckling mode is clarified, and the buckling capacity is compared with design results according to current national design codes. Based on the experimental results, a finite element model is described and validated, and then used to perform a large number of parametric studies, considering different cross-sectional dimensions and column slendernesses. It is found that all specimens failed by overall flexural buckling, and the corresponding column curves in current design codes underestimate the dimensionless buckling strength of 960 MPa steel columns. Higher and more adequate column curves are suggested for such columns, and new column curves are proposed based on a non-linear fitting of the parametric results.
TL;DR: In this article, the compressive behavior of circular concrete filled steel tubes (CFSTs) when subjected to pure axial loading at a low rate of 0.6-kN/s was investigated.
Abstract: This paper presents an experimental study to investigate the compressive behavior of circular concrete filled steel tubes (CFSTs) when subjected to pure axial loading at a low rate of 0.6 kN/s. CFSTs of three different diameter-to-thickness ( D t ) ratios of 54, 32, and 20 are considered in this study filled with two concrete's compressive strengths of 44 MPa and 60 MPa. The measured compressive axial capacities are compared to their corresponding theoretical values predicted by four different international codes and standards: the American Institute of Steel Construction (AISC), the American Concrete Institute (ACI 318), the Australian Standard (AS), and Eurocode 4. Result comparisons also included some suggested equations found in the literature. It was found that the effect of ( D t ) ratio on the compressive behavior of the CFST specimens is greater than the effect of the other factors. The underestimation of the axial capacities calculated by most of these codes reduces as the D t ratio increases as verified by the experimental results. A nonlinear finite element (FE) numerical model using the commercial software package ABAQUS is also developed and verified using the presented experimental results.
TL;DR: In this article, the post-fire elastic modulus, yield strength, ultimate strength, and stress strain curves of very high strength steel S960 were evaluated. But the available research on structural and material performance of high strength steels is very limited in literature.
Abstract: For the time being, high strength steels and very high strength steels have gained employment in some significant structural components of landmark constructions, where the strength can be fully utilized. However the available research on structural and material performance of high strength steels and very high strength steels is very limited in literature, especially for very high strength steels. The potential advantage and low research level of very high strength steels call for more researches. The steel members made of very high strength steels in constructions are sometimes inevitably exposed to fire hazards, after fire whether they are reusable or not, it needs a reliable evaluation. In order to reveal post-fire material performance of very high strength steel S960, an experimental study was carried out, which serves for the evaluation of post-fire performance of structures with components made of S960. Tensile tests were undertaken on specimens made of S960 after cooling down from temperatures up to 1000 °C. Its post-fire elastic modulus, yield strength, ultimate strength, and stress–strain curves were obtained. It is found that the post-fire performance of structural steels is dependent on steel grade. Some unique predictive equations were proposed for evaluating the mechanical properties of S960 after fire.
TL;DR: In this paper, the authors describe a material test program carried out as part of an extensive study into the prediction of strength enhancements in cold-formed structural sections, covering a wide range of cross-section geometries.
Abstract: This paper describes a material test programme carried out as part of an extensive study into the prediction of strength enhancements in cold-formed structural sections. The experiments cover a wide range of cross-section geometries – twelve Square Hollow Sections (SHS), five Rectangular Hollow Sections (RHS) and one Circular Hollow Section (CHS), and materials – austenitic (EN 1.4301, 1.4571 and 1.4404), ferritic (EN 1.4509 and 1.4003), duplex (EN 1.4462) and lean duplex (EN 1.4162) stainless steel and grade S355J2H carbon steel. The experimental techniques implemented, the generated data and the analysis methods employed are fully described. The results from the current test programme were combined with existing measured stress–strain data on cold-formed sections from the literature and following a consistent analysis of the combined data set, revised values for Young's modulus E and the Ramberg–Osgood material model parameters n, n′0.2,u and n′0.2,1.0 are recommended. A comparison between the recommended values and the codified values provided in AS/NZS 4673 (2001) , SEI/ASCE-8 (2002)  and EN 1993-1-4 (2006)  is also presented. The test results are also used in a companion paper Rossi et al. (submitted for publication)  for developing suitable predictive models to determine the strength enhancements in cold-formed structural sections that arise during the manufacturing processes.
TL;DR: In this paper, the performance of hollow and concrete-filled stainless steel tubular columns under static and impact loading was investigated and the results of the first test series, where stainless steel was used and no axial load was applied.
Abstract: 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.
TL;DR: In this article, the authors proposed an innovative structural wall, named the steel tube-double steel plate-concrete composite wall, which is suited for use in high-rise buildings.
Abstract: This paper proposes an innovative structural wall, named “the steel tube–double steel plate–concrete composite wall”, which is suited for use in high-rise buildings. The composite wall consists of concrete filled steel tubular (CFST) boundary elements and a double “skin” composite wall web where two steel plates are connected by tie bolts with space between them filled with concrete. The seismic behavior of the composite walls was examined through a series of experiments in which five slender rectangular wall specimens were subjected to axial forces and lateral cyclic loading. The specimens failed in a flexural mode, characterized by local buckling of the steel tubes and plates, fracture of the steel tubes, and concrete crushing at the wall base. The extent of the CFST boundary element was found to significantly affect the deformation and energy dissipation capacities of the walls. The area ratio of steel plates had a minimal effect on the deformation capacity of the slender walls. The addition of circular steel tubes embedded in the CFST boundary elements obviously increased the lateral load-carrying capacity of the walls. When the CFST boundary element's extent was 0.2 times the wall's sectional depth and the test axial force ratio was no more than 0.25, the walls had a yield drift ratio of over 0.005 and an ultimate drift ratio of around 0.03. Simplified formulas used to evaluate the flexure strength of the composite walls were proposed. The evaluated results had good agreement with the test results, with errors no greater than 10%.
TL;DR: The structural performance of lean duplex stainless steel remains relatively unexplored to date with only a few studies having been performed as discussed by the authors, however, an experimental and analytical research program has been initiated.
Abstract: Despite growing interest in the use of stainless steel in construction and the development of a number of national and regional design codes, stainless steel is often still regarded as only suitable for specialised applications. This is partly due to the high initial material cost associated with the most commonly adopted austenitic grades. The initial material cost of stainless steel is largely controlled by the alloy content, in particular the level of nickel, which is around 8%–10% for the common austenitic grades. A recently developed grade, known as lean duplex stainless steel (EN 1.4162), has a far lower nickel content, around 1.5%, and hence lower cost. Despite the low nickel content, it possesses higher strength than the common austenitic stainless steels, along with good corrosion resistance and high temperature properties and adequate weldability and fracture toughness. The structural performance of lean duplex stainless steel remains relatively unexplored to date with only a few studies having been performed. For this reason, an experimental and analytical research programme investigating the structural characteristics of lean duplex stainless steel was initiated. The present paper summarises the laboratory tests performed on lean duplex stainless steel welded I-sections. The experiments include material testing, stub column tests and 3-point and 4-point bending tests. The experimental data were supplemented by results generated by means of a comprehensive numerical investigation including parametric studies covering a wide range of cross-sections. The obtained experimental and numerical results, together with the results of previous tests performed on lean duplex stainless steel cold-formed hollow sections are reported and used to assess the applicability of existing cross-section classification limits and the continuous strength method (CSM) to lean duplex stainless steel. Furthermore, the structural performance of lean duplex stainless steel was compared to the more commonly used stainless steel grades. Finally, based on the obtained results, design recommendations suitable for incorporation into Eurocode 3: Part 1.4 are proposed.
TL;DR: In this paper, a comparative study of existing models to predict the strength increase of cold-formed structural sections is presented, and an improved model is presented and statistically verified, which is shown to offer improved mean predictions of measured strength enhancements over existing approaches.
Abstract: Cold-formed structural sections are manufactured at ambient temperature and hence undergo plastic deformations, which result in an increase in yield stress and a reduction in ductility. This paper begins with a comparative study of existing models to predict this strength increase. Modifications to the existing models are then made, and an improved model is presented and statistically verified. Tensile coupon data from existing testing programmes have been gathered to supplement those generated in the companion paper  and used to assess the predictive models. A series of structural section types, both cold-rolled and press-braked, and a range of structural materials, including various grades of stainless steel and carbon steel, have been considered. The proposed model is shown to offer improved mean predictions of measured strength enhancements over existing approaches, is simple to use in structural calculations and is applicable to any metallic structural sections. It is envisaged that the proposed model will be incorporated in future revisions of Eurocode 3 [2,3].
TL;DR: In this article, an experiment related to a 1/3 scale progressive collapse resistance with the use of rigid composite joints was conducted, and the results of the experiment were analyzed, based on the experiment results, a FE model was developed and analyzed.
Abstract: A partial damage caused by an abnormal load could trigger progressive collapse of high rise buildings which may lead to terrible casualties. However, in the process of column failure, “catenary action” plays an important role in redistributing the internal load and preventing progressive collapses of the structure. Rigid composite joints, thanks to their high strength and good ductility, exert great influence in catenary action. Therefore, an experiment related to a 1/3 scale progressive collapse resistance with the use of rigid composite joints was conducted, and the results of the experiment were analyzed. Based on the experiment results, a FE model was developed and analyzed. This paper describes the experiment, the results analyzed, and the FE model in detail. The experiment showed that the progressive collapse mechanism of composite frame consisted of 6 stages: elastic stage, elastic–plastic stage, arch stage, plastic stage, transient stage and catenary stage. In catenary stage, catenary action evidently enhanced the resistance to the progressive collapse of the frames. The steel–concrete composite frame with rigid connections designed in accordance to current design standards showed a good resistance to progressive collapse. It is also found that horizontal restraining stiffness of the frame exerted great influence on the resistance in catenary stage.
TL;DR: In this article, the authors present the ultimate load carrying capacities and finite element analysis of optimally designed steel cellular beams under loading conditions, which are subjected to point load acting in the middle of upper flange.
Abstract: The objective of the current research is to present ultimate load carrying capacities and finite element analysis of optimally designed steel cellular beams under loading conditions. The tests have been carried out on twelve full-scale non-composite cellular beams. There are three different types of NPI_CB_240, NPI_CB_260 and NPI_CB_280 I-section beams, and four tests have been conducted for each specimen. These optimally designed beams which have beginning span lengths of 3000 mm are subjected to point load acting in the middle of upper flange. The design method for the beams is the harmony search method and the design constraints are implemented from BS 5950 provisions. The last part of the study focuses on performing a numerical study on steel cellular beams by utilizing finite element analysis. The finite element method has been used to simulate the experimental work by using finite element modeling to verify the test results and to investigate the nonlinear behavior of failure modes such as web-post buckling and Vierendeel bending of steel cellular beams.
TL;DR: In this paper, the authors present the current state of the art on the time-dependent behaviour of composite steel-concrete members, i.e. columns, slabs and beams, and how this influences both service and ultimate conditions.
Abstract: Composite steel–concrete structures represent an efficient and economical form of construction for building and bridge applications. This paper presents the current state of the art on the time-dependent behaviour of composite steel–concrete members, i.e. columns, slabs and beams, and how this influences both service and ultimate conditions. In the case of beams, only H-shaped or box steel sections with solid and composite slabs have been considered. In the initial part of the paper, a brief outline of the main aspects related to the time-dependent behaviour of the concrete is provided. This is followed by the description of the work carried out to date on the long-term response of composite columns, slabs and beams considered separately. In the case of composite columns, particular attention has been devoted to the influence of time effects on the ultimate response, role of confinement at service conditions and possible occurrence of creep buckling. Very limited work has been carried out to date on the long-term response of composite slabs. Because of this, only brief considerations are provided on this solution while still presenting recent research dealing with the development of shrinkage gradients through the slab thickness when cast on steel decks. The work outlined on composite beams has been categorised according to different design issues, which include shear-lag effects, the shear deformability of the steel beam, influence of time effects on the ultimate response, prestressing, time-dependent buckling, and sequential casting of the slab. Recommendations for possible future research work are provided in the concluding remarks.
TL;DR: In this article, the axial forces induced by the presence of axial restraints and due to nonlinear geometric effects are dealt with, and a simple analytical model is proposed on the basis of finite element model analysis results.
Abstract: Shear links are widely used in eccentric bracing of steel buildings and, recently, for seismic protection of existing bridges and buildings. Experimental tests carried out for classic eccentric bracing of steel buildings have consistently shown that peak inelastic shear forces up to 1.4–1.5 times the plastic shear strength can develop at plastic link rotations of about 0.08–0.1 rad (plastic overstrength). However, more recent tests have shown that larger forces could be developed. Three basic parameters are devised as influencing shear overstrength: (i) axial forces acting on the link, (ii) the ratio of link flange over web area and (iii) the ratio between link length and cross section depth. In this paper only tensile axial forces induced by the presence of axial restraints and due to nonlinear geometric effects are dealt with. Numerical analysis of detailed finite element models has been carried out in order to ascertain the combined influence of these factors on the plastic overstrength of short links. A simple analytical model is proposed on the basis of finite element model analysis results. The analytical predictions are compared with the results of available experimental test results, showing good agreement.
TL;DR: In this paper, the authors presented the results of experimental and numerical investigation programs assessing the stress reduction in orthotropic steel bridge decks associated with ultra high performance fiber reinforced concrete (UHPFRC) topping layer.
Abstract: This paper aims at presenting the results of experimental and numerical investigation programs assessing the stress reduction in orthotropic steel bridge decks associated with ultra high performance fiber reinforced concrete (UHPFRC) topping layer. This R&D project was aimed at evaluating the effectiveness of the UHPFRC overlay, as an alternative to conventional bituminous concrete, to reduce the stress distribution and thereby improve the fatigue resistance of the complex deck plate. Loading tests were carried out on realistic samples of orthotropic deck equipped or not with a reference bituminous concrete or a new UHPFRC topping. The deflection, and strain and stress values on the top and the bottom of the orthotropic deck plate and more particularly at the weld joint between longitudinal stiffeners (troughs) and the deck plate were measured. A 3-D shell element model has been developed using a finite element code in order to obtain the stresses in details for the most representation and critical locations. The global and local behaviors have been analyzed in order to understand and to evaluate the beneficial effects of UHPFRC topping layer under static condition. The results obtained in terms of stress reduction factor demonstrate the beneficial effects for fatigue verification.
TL;DR: In this article, the elastic shear buckling strength of trapezoidal corrugated steel webs is investigated for the design of box girder bridges with trapezoid corrugation.
Abstract: Shear strength of trapezoidal corrugated steel webs is an important issue for the design of box girder bridges with trapezoidal corrugated steel webs Eight H-shape steel girders with trapezoidal corrugated webs are firstly tested to investigate the shear behavior of webs An extensive parametric study based on the linear elastic buckling analysis is then conducted to derive the simplified formula for calculating the elastic shear buckling strength of trapezoidal corrugated steel webs considering three different shear buckling modes The proposed formula can give more satisfactory results for predicting the elastic shear buckling strength than some available formulae provided in the literature when compared with the numerical results Furthermore, the nonlinear buckling analysis is conducted to intensively investigate the shear strength associated with initial geometric imperfections, and the formulae of the shear strength are proposed Good agreements can be observed between the results calculated using the proposed prediction formula in this paper and the experimental results, and a design formula is also recommended for the routine shear design of trapezoidal corrugated steel webs
TL;DR: In this paper, a blind-bolt connection to concrete-filled square hollow sections using a modified blindbolt was proposed to address the issue of the flexibility of the blindbolt connector as well as that of the tube face.
Abstract: Moment resisting connections to hollow sections tend to utilise welding and reinforcements to achieve the stiffness required to resist moment. Blind-bolted connections to hollow sections offer a simpler, more economical and construction-friendly means of connecting to hollow sections. Such connections have been used in nominally pinned connections and in non-primary structural connections. Exploratory research work has been done by a number of researchers to improve the stiffness of such bolted connections through the use of concrete filling. Concrete filling tends to improve the stiffness of the connection. However, the improvement is not sufficient to attain significant moment resistance allowing such connections to be classified as rigid connections. This is because they address only half of the problem. That is the flexibility of the tube face. This paper reports on a blind-bolted connection to concrete-filled square hollow sections using a modified blind-bolt that addresses the issue of the flexibility of the blind-bolt connector as well as that of the tube face. The paper reports on this novel connection type and on an experimental programme aimed at measuring the resulting connection stiffness. The programme tested eight full size connections, principally varying the connection endplate type, column thickness and concrete strength. The data was cross validated with a finite element model. The paper assesses the performance of this connection using connection stiffness classification methods. It concludes that the connection is able to develop the required stiffness for it to be used as a rigid connection in braced frames.
TL;DR: In this article, the authors present two full-scale laboratory tests on steel beam-to-tubular column moment connections with outer-diaphragm, one being welded flange-welded web method and the other being welding-flange-bolted web method to connect the beam members to the outer diaphragms, under a column removal scenario.
Abstract: Removal of a column member is a typical scenario of local failure that could trigger the progressive collapse of a frame structure. Under such a situation, the behavior of the beam-to-column connection is expected to greatly influence the structural capacity in resisting progressive collapse. This paper presents two full-scale laboratory tests on steel beam-to-tubular column moment connections with outer-diaphragm, one being welded flange–welded web method and the other being welded flange–bolted web method to connect the beam members to the outer-diaphragm, under a column removal scenario. Test results demonstrate that the beam-column assemblies resisted the load applied atop the center column primarily by flexural action in the early stage of the response, and the resistance mechanism gradually shifted towards relying on the catenary action as the vertical displacement increased. Two types of flexural failure modes, namely a continuous flexural failure throughout the section (in the welded-web connection case) and an interrupted flexural failure without the fracture extending upwards (in the bolted-web connection case), were observed from the tests. The two different flexural failure modes dictated the capacity of the respective specimen in developing an effective catenary action in the subsequent phase of the response, and in this respect the bolted-web connection proved to be more redundant in terms of strength and deformability than the welded-web connection.
TL;DR: In this paper, a perforated Yielding Shear Panel Device (PYSPD) was proposed for earthquake risk mitigation of civil structures, where the diaphragm plate was welded inside a short length square hollow section.
Abstract: This paper describes an investigation into a metallic energy dissipater designed for earthquake risk mitigation of civil structures. It is called the Perforated Yielding Shear Panel Device (PYSPD). It comprises of a thin perforated diaphragm plate welded inside a short length square hollow section. The device is to be connected in the lateral load resisting system of a structure with the diaphragm plate being in the plane of the building frame. It is a displacement-based device in which energy is dissipated through plastic shear deformation of its perforated diaphragm plate. The PYSPD is a modified version of the previously tested Yielding Shear Panel Device (YSPD). Perforations on the diaphragm plate alleviate demand on supporting elements which reduces undesirable local deformations near the connections. As a result more stable force-displacement hysteresis is obtained. Three patterns of perforations are studied. Finite element models confirm that diagonal tension field develops under shearing action but stress patterns are affected by perforations. Two plate slenderness and three perforation patterns combinations were tested experimentally. Under quasi-static condition, devices with certain plate slenderness produced stable and repeatable force-displacement hysteresis, and achieved large energy dissipation capability. Compared to un-perforated specimens, perforations reduce elastic stiffness and yield strength. Under design displacement it produced a stable hysteretic behavior and endured code requirements against low-cycle fatigue.
TL;DR: In this article, the dual-pipe damper (DPD) is introduced, tested and analytically studied. But, at large displacements, a tension diagonal forms in the middle of the DPD, which adds to stiffness and strength.
Abstract: In this paper, a new passive earthquake energy dissipative device, called the dual-pipe damper (DPD), is introduced, tested and analytically studied. The device consists of two pipes welded at selected locations and loaded in shear. The inelastic cyclic deformation dissipates energy mainly through flexure of the pipe body. However, at large displacements a tension diagonal forms in the middle of the device which further adds to stiffness and strength. The strength, stiffness and energy dissipation of the DPD is more than two single pipe dampers that were previously studied. Cyclic quasi-static tests were performed on four samples of DPD. Excellent ductility, energy absorption and stable hysteresis loops were observed in all specimens. A finite element model, considering nonlinearity, large deformation, contact and material damage is developed to conduct a parametric study on different pipe sizes. Relationships that define the DPD behavioral characteristics are given for any pipe size. The DPD is very light-weight, easily fabricated and economical. It has a high deformation capacity of about 36% of its height. Possessing these features, the introduced damper is applicable as a useful device for passive control of structures.
TL;DR: In this article, a finite element method (FEM) is applied to evaluate fatigue durability of the root-deck fatigue in the trough-deck welded joints over the diaphragms.
Abstract: Orthotropic steel decks are widely used in cable-supported bridges. The fatigue cracks in trough-deck welded joints have been detected in some bridges in China. In this paper, the finite element method (FEM) is applied to evaluate fatigue durability of the root-deck fatigue in the trough-deck welded joints over the diaphragms. The reference stress is defined and the mesh size of a shell model is checked. Stress ranges under wheel loads are analyzed, and the pavement–deck interaction is discussed. The durability of the root-deck fatigue is evaluated. Results of this study show that the reference stress defined in the shell model is not sensitive to mesh size. Equivalent stress ranges of multi-axles are close to that of a single axle with multi-cycles. Traffic flow can be simplified as an axle fatigue load model with equivalent fatigue damage. Stress range regardless of the pavement–deck interaction is over estimated and the pavement–deck interaction should be considered in the stress range analysis, especially in thin decks. The predicted life of the root–deck fatigue considering the pavement–deck interaction seems to explain the fatigue cracks of bridges in China. The durability of the root–deck fatigue will be improved if steel fiber reinforced concrete (SFRC) pavement is applied.
TL;DR: In this article, the authors present the experimental results and observation of elliptical concrete filled tube (CFT) columns subjected to axial compressive load and provide a review of the current design rules for concrete filled circular hollow sections in Eurocode 4.
Abstract: This paper presents the experimental results and observation of elliptical concrete filled tube (CFT) columns subjected to axial compressive load. A total of twenty-six elliptical CFT specimens including both stub and slender composite columns are tested to failure to investigate the axial compressive behaviour. Various column lengths, sectional sizes and infill concrete strength are used to quantify the influence of member geometry and constituent material properties on the structural behaviour of elliptical CFT columns. As there is no design guidance currently available in any Code of Practice, this study provides a review of the current design rules for concrete filled circular hollow sections in Eurocode 4 (EC4). New equations based on the Eurocode 4 provisions for concrete filled circular hollow sections were proposed and used to predict the capacities of elliptical CFT columns.
TL;DR: In this paper, the authors investigated the collapse behavior of a super-tall mega-braced frame-core tube building (H = 550 m) to be built in China in the high risk seismic zone with the maximum spectral acceleration of 0.9 g (g represents the gravity acceleration).
Abstract: Research on earthquake-induced collapse simulation has a great practical significance for super-tall buildings. Although mega-braced frame-core tube buildings are one of the common high-rise structural systems in high seismic intensity regions, the failure mode and collapse mechanism of such a building under earthquake events are rarely studied. This paper thus aims to investigate the collapse behavior of a super-tall mega-braced frame-core tube building (H = 550 m) to be built in China in the high risk seismic zone with the maximum spectral acceleration of 0.9 g (g represents the gravity acceleration). A finite element (FE) model of this building is constructed based on the fiber-beam and multi-layer shell models. The dynamic characteristics of the building are analyzed and the earthquake-induced collapse simulation is performed. Finally, the failure mode and mechanism of earthquake-induced collapse are discussed in some detail. This study will serve as a reference for the collapse-resistance design of super-tall buildings of similar type.
TL;DR: In this article, the authors describe 24 tests conducted on slender circular tubular columns filled with normal, high, and ultra-high strength concrete for plain, bar reinforced and steel fiber reinforced columns.
Abstract: This paper describes 24 tests conducted on slender circular tubular columns filled with normal, high, and ultra-high strength concrete for plain, bar reinforced and steel fiber reinforced columns These were reinforced and subjected to both concentric and eccentric axial load It is a continuation of a previous research paper (Portoles et al, 2011  ), which presented test results on eccentrically loaded plain concrete columns The test parameters are nominal strength of concrete (30, 90 and 130 MPa), eccentricity e (0, 20 and 50 mm) and type of reinforcement A comparison with the corresponding empty tubular columns is performed, as the aim of the paper is to analyze the influence of each type of infill and establish the best option for practical application For the limited cases analyzed the results show that the addition of high or ultra-high strength infill is more useful for concentric loaded cases than for eccentric loaded ones, where it seems that the best design option is the utilization of bar reinforced concrete filling rather than steel fiber to reinforce CFST columns The experimental ultimate load of each test was compared with the design loads from Eurocode 4, accurate for the eccentrically loaded tests
TL;DR: In this paper, a special combination of diagonal stiffeners with a central perforation is presented, and the seismic behavior of the new system is experimentally investigated and compared to the solid infill plate models.
Abstract: One of the advantages of Steel Plate Shear Walls (SPSWs) is the easiness of openings application in infill plate. The openings are sometimes required for passing utilities, architectural purposes, and/or structural reasons. However, the recent researches on perforated steel plate shear walls have shown that the shear strength and stiffness of an un-stiffened steel shear wall decrease due to perforation of the infill plate. Hence, this paper presents a special combination of diagonal stiffeners with a central perforation. The seismic behavior of the new system is experimentally investigated and compared to the solid infill plate models. Experimental testing is performed on three ½ scaled single-story SPSW specimens under cyclic quasi-static loading. One of the specimens is un-stiffened and the two others are diagonally stiffened, which in one of them, a circular opening with the diameter of ⅓ depth of the panel is cutout from the wall center. It is observed that by means of the proposed stiffening method the shear strength of the perforated shear walls is achieved close to the un-stiffened wall with the solid panel, and the seismic behavior of the system is considerably improved. Test results show that the ductility ratio of the specially perforated specimen is about 14% greater than the un-stiffened specimen. A formula is developed and verified for the estimation of the shear strength of a perforated and diagonally stiffened SPSW. There are good agreements between the experimental outcomes and the theoretical predictions.
TL;DR: In this paper, an innovative repairable fuse device for dissipative beam-to-column connections in moment resistant steel frames with composite beams was proposed. But the proposed fuse was not suitable for the use in the case of large-scale earthquakes.
Abstract: One of the most recent trends in earthquake-resistant design of structures – damage control when these are subjected to severe earthquakes – led to the development of an innovative repairable fuse device for dissipative beam-to-column connections in moment resistant steel frames with composite beams. This fuse consists of a set of bolted steel plates, at the web and bottom flange, connecting the “I” beam profile stub to the beam element. The seismic performance of the proposed device was assessed through an extensive experimental campaign comprising twenty-four cyclic and two monotonic tests. Those tests were conducted on a set of three beam-to-column sub-assemblies with different fuse devices for each test. The tested devices varied in terms of selected geometric and mechanical parameters, such as the resistance capacity ratio and the geometric slenderness. The tests showed that the proposed devices were able to concentrate plasticity and to dissipate large amounts of energy through non-linear behaviour. Subsequently, two distinct design models are proposed to allow the computation of the resistance and stiffness of the fuses. The results of these design models were favourably compared with those from the experimental tests.
TL;DR: In this paper, an efficient and accurate finite element model of ABAQUS was established subjected to cyclic loadings, and connections with different connection methods were established to investigate the effect of connection methods on behaviors of connections, including fully welded connection, extended end-plate connection and flush endplate connection.
Abstract: In order to study the seismic behaviors of steel frame end-plate connections, an efficient and accurate finite element model of ABAQUS was established subjected to cyclic loadings. Element types, material cyclic constitutive models and contact models for bolts, end plate and members were described. Geometry and material nonlinearity were adequately considered. The simulated results of numerical models were verified by typical quasi-static tests of end-plate connections, including both hysteretic curves and failure modes. It provided a strong tool for investigating the performances of this kind of connection. Based on the verified models, connections with different connection methods were established to investigate the effect of connection methods on behaviors of connections, including fully welded connection, extended end-plate connection and flush end-plate connection. The carrying capacity, initial stiffness, hysteretic behaviors, degraded characteristics, fracture tendency index, failure modes and energy dissipation capacity were compared and discussed in depth. The results showed that: If the beam and column are reliably connected, the extended end-plate connection can obtain the same ultimate carrying capacity and initial stiffness (monotonic behaviors) as the welded connection, however, their hysteretic curves, degradation developing curves, and fracture tendency were quite different. It indicated that the connection methods could significantly affect the cyclic behaviors. The stiffeners of end-plate connection could be treated as the first defense of connection, effectively changing the failure mode and avoiding brittle fracture. Therefore, in the high seismic zones, hysteretic behaviors, failure modes and seismic ductility should be taken into account comprehensively to choose the appropriate connection methods.
TL;DR: In this paper, the bending behavior of flange-plate connections under pure bending was investigated and a practical design model was put forward to put forward a relatively clear yield line mechanism and definite pressure center.
Abstract: This paper focuses on the bending behavior of flange-plate connections under pure-bending and aims for putting forward a practical design model. Four basic types of bolted flange-plate connections are tested and related finite element analysis is implemented. The finite element model is verified by experimental results and proved to be precise and reliable. Based on the finite element analysis, the distribution of von-Mises strain and contact pressure at end plates of the connections is revealed. The valuable information can be directly used in the theoretical model to present a relatively clear yield line mechanism and definite pressure center. The bending capacity determined by flange-plates is derived with the virtual work principle. It is proved that the theoretical model can give a good prediction for the yield bending capacity of the connections. Meanwhile, traditional T-stub analogy is introduced to obtain the bending capacity determined by bolts. Combining with the two different design models and assuming that the end plates should fail before high strength bolts, a practical design procedure is put forward. The connections designed according to this procedure will meet the demand of safety and economy. Furthermore, the design model herein can provide useful reference for practical design of other kinds of bolted flange-plate connections.