Concrete-filled Steel Tubular Frame Research Articles

Seismic evaluation of stiffened CFST column to RC beam frames

A stiffened concrete-filled steel tubular (CFST) member offers improved composite action over the unstiffened counterpart in terms of delaying local buckling of the square steel tube and enhancing confinement to the infilled concrete. The diagonal ribs, made of steel plates with circular openings and welded to the steel tube, were found particularly effective among various stiffening forms in improving the structural performance of thin-walled square CFST members. To better accommodate this new type of composite columns into engineering practice, the corresponding joints with reinforced concrete (RC) beams were proposed and were found to possess good axial and cyclic behavior. Consequently, composite frames composed of diagonal rib stiffened CFST columns and RC beams are expected to have superior performance and to be widely used in practice. However, the previous research mainly focused on structural members, and no study at the system-level was conducted. In addition, the guidance on seismic design of the stiffened CFST frames in mainstream design codes is lacking. To fill this research gap, this work investigated the seismic behavior of diagonal rib stiffened CFST column to RC beam frames numerically, and fiber-based finite element (FE) models were developed in software OpenSees and were validated extensively by the experimental results. The research parameters included the column-to-beam strength ratio, bond-slip of beam reinforcing bars (rebars) within the joint zone, and shear deformation in ultra-short columns. Besides, unstiffened CFST column to RC beam frames were also designed for comparison. The pushover analysis was then carried out to investigate the effect of different parameters on the strength, deformation mode, and yielding mechanism. In addition, the incremental dynamic analysis (IDA) was also conducted to study the behavior in the elastic stage, elastic-plastic stage and collapse stage. Finally, the design considerations for stiffened CFST frames were proposed. These results will facilitate the use of this efficient form of composite structures.

Seismic behavior of prefabricated frame with special‐shaped concrete‐filled steel tubular columns and H‐shaped steel beams

AbstractTo realize the prefabricated structure of special‐shaped concrete‐filled steel tubular (CFST) column frame and enhance the level of indoor room utilization, this paper proposed a novel prefabricated frame with special‐shaped CFST columns and H‐shape steel beams connection with side plate. To investigate seismic behavior of this prefabricated frame structure, a 2‐story and 2‐bay CFST frame specimen was fabricated and tested under reversed cyclic loading. The failure mode, hysteresis behavior, degradation of lateral stiffness and bearing capacity, ductility and energy dissipation were analyzed. Experiment results indicated that failure mode presented strong columns and weak beams. Hysteresis curve of frame showed fully shuttle‐shaped. The mean story drift angle was 1/36 at ultimate stage. Equivalent viscous damping coefficient was 0.038–0.464. The bearing capacity degradation was relatively gentle, but the overall stiffness degradation was more obvious. It suggested that the frame had proper seismic and energy dissipation property. After the test, the seismic property of test frame was further investigated through the numerical simulation approach. The failure mode and skeleton curve obtained from the simulation were nearly consistent with test results, indicating that numerical analysis results were precise and with high reference meaning.

Experimental and numerical study on seismic performance of L-shaped multi-cellular CFST frames

Steel-concrete composite frames have been widely used in high-rise buildings. To improve the utilization efficiency of the indoor area, irregular-shaped concrete-filled steel tubular (CFST) columns were proposed for an alternative of the traditional rectangular CFST columns. In this paper, the L-shaped multi-cellular CFST (LM-CFST) frame was proposed, consisting of LM-CFST columns and H-shaped steel beams. Firstly, four LM-CFST frames were tested under combined axial compression and cyclic lateral loads. The local buckling was observed at both the top and bottom ends of the column, and fracture of steel occurred when the drift ratio was large. The hysteresis curves were spindle-shaped with the ductility indexes of 2.61–3.24. Then, a refined finite element model was established and validated against the test results. A parametric analysis was conducted to study the effect of axial compression ratio, web cell length, concrete strength and steel tube thickness on the seismic performance of LM-CFST frames. It was found that the axial compression ratio could affect the seismic performance of LM-CFST frames significantly, while the concrete strength had little effect. Finally, the compression-bending capacities obtained from the sectional analysis method specified in EC4 were compared with those obtained from tests. It was found that this method could predict the compression-bending capacity of the LM-CFST frame under combined axial compression and cyclic lateral loads with reasonable discrepancies.

Anti-collapse mechanism and reinforcement methods of composite frame with CFST columns and infill walls

Masonry infill walls serve as building partitions and are generally considered non-structural components. Their weights are considered in progressive collapse analysis, but the resistance of the infill walls is normally ignored in design standards. Based on the reasonable selection of constitutive models, a refined finite element (FE) model for the collapse resistance of concrete-filled steel tubular (CFST) composite frame with infill walls was established by ABAQUS/Explicit. Cohesive elements were inserted between different masonry blocks to simulate the mortar joints. The collapse resistance contribution and reinforcement methods analysis of the CFST frame with infill walls were carried out based on the validated FE models. Results show that the infill walls significantly contribute to resisting vertical load in the initial loading stage, with a maximum contribution of 55.3%. The infill walls, which are treated as the equivalent compressive struts, change the load-resisting path and effectively improve the load redistribution ability of the frame. The V-type oblique arrangement of tie rebars has better tie effect and collapse resistance of the frame than other arrangements. After pasting the CFRP sheet and spraying the ECC material to reinforce infill walls, the peak load can be increased by 25.1% and 22.9% respectively, and the ultimate load can be increased by 96.2% and 74.5% respectively. X-type pasting the CFRP sheet reinforcement has a better collapse resistance than others. Furthermore, based on the simplification of the infill walls as the diagonal struts, the simplified calculation formulas of anti-collapse capacity of CFST frame with infill walls were studied.

On Factors behind the Reasonable Failure Mode of Concrete-Filled Circular Steel Tubular Composite Frame

As the most basic structure, the concrete-filled steel tubular (CFST) frame has been widely used in various structures and systems. Compared with conventional reinforced concrete structures and steel structures, CFST structures in strong earthquake showcase more complicated strength and deformation behavior because there are many factors underlying the failure mode. Furthermore, according to the specifications at home and abroad, the corresponding design method to achieve reasonable failure modes for CFST structures has not been clarified. Based on a destructive test on steel beam-CFST plane frames under constant axial load and lateral load, the fiber mode method and solid element model method are adopted to simulate the failure process of the test frames. Based on finite element model simulations and tests, the fiber model method is proposed to carry out the pushover analysis on the CFST frame structures. The factors behind the reasonable failure mode of steel beam-concrete-filled circular steel tubular (CFCST) frame structures are analyzed. Furthermore, the law and influencing factors behind the ratio of flexural capacity of column to beam, the ratio of line stiffness of beam to column, and the ratio of axial compression on the deformation, bearing capacity, and failure modes of the structure are discussed. Some suggestions on the design of reasonable failure mode of steel beam-concrete-filled circular steel tubular (CFCST) frame structures are proposed.

Progressive collapse resistance of composite frame with concrete-filled steel tubular column under a penultimate column removal scenario

In this study, static tests of six two-story three-span composite frames with concrete-filled steel tubular (CFST) column under a penultimate column removal scenario were carried out. The experimental phenomena, vertical resistance, strain and axial force of steel beams were presented. The internal force transmission path of composite frame under a penultimate column removal scenario was investigated. The effects of reinforced concrete (RC) slab and weld-bolted connection on the progressive collapse resistance of composite frame were analyzed and discussed. Consequently, the dynamic response prediction and dynamic amplification factor (DAF) were analytically studied by energy balanced method (EBM). Further, the numerical models of composite frames were calibrated by the test results in ABAQUS/Explicit. The results showed that serious torsion of steel beam at directly affected region (DAR) reduced the resistance for the CFST frames with bare steel beam. However, for the CFST frames with composite beam (i.e., with steel beam and RC slab), the RC slab improved the initial stiffness and peak resistance of composite frame and thus mitigated and even prevented the torsion of beam. The composite frames presented an asymmetric failure mode and internal force transmission path under a penultimate column removal scenario, which was different from that under a middle column removal scenario. The composite frames with weld-bolted connection presented a lower resistance than the composite frames with welded connection due to the premature fracture of welded flanges but possessed multi-protection measures to resist progressive collapse due to the intermittent failure modes.

Research on seismic performance of prefabricated concrete-filled steel tubular frame joints

PurposeConcrete-filled steel tube structures are widely used for their high bearing capacity, good plasticity, good fire resistance and optimal seismic performance. In order to give full play to the advantages of concrete-filled steel tube, this paper proposes a prefabricated concrete-filled steel tube frame joint.Design/methodology/approachThe concrete-filled steel tube column and beam are connected by high-strength bolted end-plate, and the steel bars in the concrete beam are welded vertically with the end-plates through the enlarged pier head. In addition, the finite element software ABAQUS is used numerically to study the seismic performance of the structure.FindingsThe ductility coefficient of the joint is in 1.72–6.82, and greater than 2.26 as a whole. The equivalent viscous damping coefficient of the joint is 0.13–3.03, indicating that the structure has good energy dissipation capacity.Originality/valueThe structure is convenient for construction and overcomes the shortcomings of the previous on-site welding and on-site concrete pouring. The high-strength bolted end-plate connection can effectively transfer the load, and each component can give play to its material characteristics.

Shaking table tests on concrete-filled steel tubular-framed building assembled with microcrystalline foam boards

In recent years, prefabricated structures have been widely constructed to reduce construction costs and time. In this study, a new type of prefabricated structure, lightweight concrete-filled steel tubular (CFST)-framed building assembled with microcrystalline foam boards (MFBs), was developed. The MFBs exhibited high strength, heat insulation, soundproof, light weight, fireproof, and ecofriendly characteristics. The MFBs were combined with light steel keels and connected to the CFST frame with flexible and rigid connections. Shaking table tests on a full-scale, two-story, single-span lightweight CFST-framed building assembled with MFBs as exterior wallboards were performed to assess its dynamic properties and seismic response under the earthquake. The input waves used for the shaking table tests were the El-Centro, Taft, and Zhangjiakou artificial waves with seismic ground motion intensities of 8°–9°. The results indicated that the CFST-framed building exhibited satisfactory seismic performance. The main damage behavior was the cracking and spalling of the MFBs, however, the MFBs used as exterior wallboards were easy to repair and replace. No wallboard collapse occurred, and the lightweight CFST frame was in the elastic deformation stage. The flexible connections absorbed a large amount of energy, resulting in a reduction in the displacement of the structure and little damage to the wallboards under the earthquake. Finally, a nonlinear distribution model of acceleration amplification factors for calculating the seismic force on MFBs was established.

Collapse Behaviour of a Concrete-Filled Steel Tubular Column Steel Beam Frame under Impact Loading

The progressive collapse of a concrete-filled steel tubular (CFST) frame structure is studied subjected to impact loading of vehicle by the finite-element software ABAQUS, in the direct simulation method (DS) and alternate path method (AP), respectively. Firstly, a total of 14 reference specimens including 8 hollow steel tubes and 6 CFST specimens were numerically simulated under transverse impact loading for verification of finite-element models, which were compared with the existing test results, confirming the overall similarity between them. Secondly, a finite-element analysis (FEA) model is established to predict the impact behaviour of a five-storey and three-span composite frame which was composed of CFST columns and steel beams under impact vehicle loading. The failure mode, internal force-time curve, displacement-time curve, and mechanical performance of the CFST frame were obtained through analyzing. Finally, it is concluded that the result by the DS method is closer to the actual condition and the collapse process of the structure under impact load can be relatively accurately described; however, the AP method is not.

Dynamic Time Analysis of the Composite Shear Wall on the Grid-tube-type Double Steel Plate Wall with Infilled Concrete

In this paper, based on a 30-story building with frame-core tube structure system, three comparative schemes are established of reinforced concrete core tube construction, steel-reinforced concrete core tube construction and the combined shear wall core tube structure with the grid-tube-type double steel plate wall with infilled concrete are established, and the dynamic elastoplastic time history is analyzed. Research shows that under the influence of a severe earthquake, the lateral strength degradation and stiffness degradation are slow on the Joint structural system of concrete filled steel tubular frame and composite shear wall core tube structure with the grid-tube-type double steel plate wall with infilled concrete, so interlayer shear force and bottom shear force increase, structural lateral stiffness increased significantly, interlayer displacement angle reduces significantly, and it improves the seismic performance of tall building.

Fully nonlinear inelastic analysis of rectangular CFST frames with semi-rigid connections

In this study, an effective numerical method is introduced for nonlinear inelastic analyses of rectangular concrete-filled steel tubular (CFST) frames for the first time. A steel-concrete composite fiber beam-column element model is developed that considers material, and geometric nonlinearities, and residual stresses. This is achieved by using stability functions combined with integration points along the element length to capture the spread of plasticity over the composite cross-section along the element length. Additionally, a multi-spring element with a zero-length is employed to model the nonlinear semi-rigid beam-to-column connections in CFST frame models. To solve the nonlinear equilibrium equations, the generalized displacement control algorithm is adopted. The accuracy of the proposed method is firstly verified by a large number of experiments of CFST members subjected to various loading conditions. Subsequently, the proposed method is applied to investigate the nonlinear inelastic behavior of rectangular CFST frames with fully rigid, semi-rigid, and hinged connections. The accuracy of the predicted results and the efficiency pertaining to the computation time of the proposed method are demonstrated in comparison with the ABAQUS software. The proposed numerical method may be efficiently utilized in practical designs for advanced analysis of the rectangular CFST structures.

The structural design of Kunshan Xintiandi super high-rise office building

The Kunshan urban investment project includes 1 office tower, 4 high-rise residential buildings and 1 high-rise commercial building. Each monomer shares a large basement chassis, a total of three basement floors. This design is the second phase (5# super high-rise and corresponding basement).The height of the structure is more than 140 meters, which is a concrete-filled steel tubular frame + core tube system. The selection and structure of the structural system are analyzed, and the mechanical performance of the structure is verified through calculation and analysis.

Fragility Analysis of Concrete-Filled Steel Tubular Frame Structures with BRBs under Multiple Earthquakes Considering Strain Rate Effects

The fragility of concrete-filled steel tubular (CFST) frame structures with buckling-restrained braces (BRBs) subjected to multiple earthquakes is studied in this paper. First, a fiber beam element model with rate-dependent concrete and steel material properties is developed for CFST members and, then, the effect of the strain rate on the seismic response of the CFST frame structure is investigated numerically. The influence of BRBs on the seismic response of the CFST frame structure is then comparatively analyzed. The seismic responses of the CFST frame structure with BRBs under single mainshocks and earthquake sequences are investigated, and the fragility curves are generated using probabilistic seismic demand analysis. The obtained roof displacement and inter-story drift ratio (ISDR) of the structure decreased by 10.2% and 6.9%, respectively, when obtained while considering the strain rate effect, compared with those obtained without consideration of the strain rate effect. BRBs can effectively improve the seismic performance of the CFST frame structure in that the maximum roof displacement and ISDR can be reduced by 45.1% and 43.9%, respectively. Compared with those under single mainshocks, the maximum roof displacement and ISDR of the structure with BRBs under earthquake sequences significantly increase. The fragility of the BRB structure under earthquake sequences is more severe than that under single mainshocks. Therefore, the influences of the strain rate effect and earthquake sequence should be considered to realistically evaluate the seismic fragility of CFST structures.

Seismic Response Investigation and Analyses of End Plate Moment-Resisting CFST Frames Under Pseudo-Dynamic Loads

This paper reported an innovative semi-rigid composite frame comprised of concrete-filled steel tubular (CFST) columns and H-shaped steel beams assembled using flush or extended end plates with blind fasteners. Two specimens of two-story single-bay end plate moment-resisting square or circular CFST frames were investigated by a series of pseudo-dynamic tests. To analyze dynamic response of this type of structure under the earthquake action, time history response and story drift were investigated. The influence of the column section type and the end plate type on seismic performance of semi-rigid moment-resisting CFST frames under different earthquake loading levels were also discussed according to hysteretic behavior, rigidity degradation and energy dissipation capacity. The experimental and analytical results indicated that at the same section width and steel ratio of the column, the rigidity of end plate moment-resisting square CFST frame was greater than that of circular CFST frame, while the story drift of square CFST frame was smaller than that of circular CFST frame. The type of end plate moment-resisting CFST frames with blind fasteners, which can provide good seismic behavior and energy dissipation ability, can be well used in a seismic region.

Finite Element Analysis of the Joint Surface of Concrete Filled Steel Tubular Frame Column and Precast Shear Wall

In order to study the connection performance of a new type of shear key to concrete filled steel tubular (CFST) frame column and precast shear wall, a numerical model is established by using the finite element software Abaqus, the mechanical properties of the combined shear wall are studied by the strength of post-poured concrete, the yield strength of the shear key steel and the spacing between the shearing bonds. The results show that the failure modes of specimens are mainly related to the strength of post-poured concrete and the yield strength of shear keys. When the specimens are damaged by shear bonds, the bearing capacity and ductility of the specimens increase obviously with the increase of the yield strength of the shear key steel and the shortening of the spacing between the shear keys. The change of strength of post-poured concrete has little effect on the working performance of specimens. When the specimens are damaged by post-poured concrete, the stiffness of the specimens is larger and the ductility is worse.

Seismic tests and numerical investigation of blind-bolted moment CFST frames infilled with thin-walled SPSWs

This paper aims to investigate the seismic response of blind-bolted moment concrete-filled steel tubular (CFST) frames infilled with thin-walled steel plate shear walls (SPSWs). Tests of two-storey blind-bolted circular or square CFST frames with thin-walled SPSWs subjected to horizontal low-cyclic loading were performed. Macroscopic finite element (FE) models of the specimens were primarily established by fibre beam-column elements, zero-length springs, and truss elements. The numerical simulation results were verified by the experimental data. A parametric analysis was conducted to analyse the influence of the axial load level, material strength, and height-thickness ratio of the steel plate etc. on the hysteresis behaviour and energy dissipation of blind-bolted moment CFST frames with thin-walled SPSWs. In addition, the mechanics of the semi-rigid frame with SPSWs were compared with the pinned and rigid frames with SPSWs using mechanical analysis model and FE model. The experimental and analytical results show that the blind-bolted moment CFST frames with SPSWs connected to the beams only exhibit preferable hysteretic response, ductility and energy dissipation. The peak strength, initial stiffness and energy dissipation of blind-bolted moment CFST frames infilled with thin-walled SPSWs can be significantly affected by the axial load level as well as the steel plates' yield strength, height-thickness ratio, aspect ratio, and connection type.

Experimental study on seismic behaviour of shear wall with reinforcement of column form,concrete-filled steel tubular frames and diagonal bars

In order to reasearch and develop more efficient anti-seismic system of high-rise building structures, a new shear wall with reinforcement of column form, concrete-filled steel tubular frames and diagonal bars was put forward in this paper. Three shear wall specimens with different structural form were designed and made, and then tested by the low-cycle loading experiment. According to the test results, anti-seismic behaviour indexes such as failure characteristics, bearing capacity, ductility, and stiffness degradation of three specimens were analized. The ABAQUS model of new shear walls was established. The experimental results show that, compared with other specimens, the anti-seismic energy dissipation capacity and bearing capacity of the shear wall specimen with reinforcement of column form, concrete-filled steel tubular frames and diagonal bars is enhanced significantly, and the process of stiffness degradation is more slow. The column-form reinforcement can improve ductility, and the concrete-filled steel tubular frames can guarantee the lateral stiffness.

Experimental and Numerical Investigations of Bolted CFST Beams–CFST Columns Connections

The effectiveness of concrete-filled steel tubular (CFST) sections as compression and flexural members has been investigated by many authors. The combined utilization of CFST columns and steel beams has increased in composite building construction in recent years, but combined use of CFST columns and CFST beams is still unexplored. To explore their potential as part of CFST frame structures, two types of connections using extended end plate and seat angle are proposed for exterior joints of CFST beams and CFST columns. The performance of the proposed bolted connections subjected to static loads has been investigated by executing an experimental program involving eight specimens of exterior beam-to-column joints subjected to monotonically increasing load applied at the free end of the beam. The performance is appraised in terms of load deformation behaviour and failure modes of joints with varying test parameters like the beam section type, length and diameter of bolts. Finite element analysis for the applied load has been performed using ATENA-3D software, and the behaviour of the connections is investigated. The FE simulation results are compared with experimental test data to verify the FE model.

Experimental study on the seismic behavior of a shear wall with concrete‐filled steel tubular frames and a corrugated steel plate

SummaryShear walls and core tubes in shear walls constitute the core anti‐earthquake vertical systems of high‐rise buildings. This paper proposes a new type of composite shear wall with concrete‐filled steel tubular frames and corrugated steel plates. The seismic behavior of the new shear wall is studied using a cyclic loading test and damage analysis. The failure mode, load‐carrying capacity, ductility, stiffness degradation, hysteresis behavior, and energy dissipating capacity exhibited in the test are studied. The test results show that when the proposed wall is broken, the tension side of concrete‐filled steel tubes is torn. The concrete at the bottom of the wall is detached and peels off along the through cracks. The energy dissipation capacity of concrete walls is more fully utilized. The proposed wall exhibits excellent deformability, energy dissipation capacity, and the stiffness degradation was slower than that of other walls. The use of corrugated steel plate significantly improved the seismic performance while simultaneously increasing the ductility and reducing the damage. In addition, this paper modified the energy dissipation factor in the Park & Ang model based on the situation of the specimen and experiment. It can be used to evaluate the damage degree of this new type of shear wall.

EXPERIMENTAL STUDY ON THE SEISMIC BEHAVIOR OF A SHEAR WALL WITH CONCRETE-FILLED STEEL TUBULAR FRAMES AND SLITS

This paper proposes a new type of composite shear wall with concrete-filled steel tubular frames and artificial vertical slits. The seismic behaviour of this new shear wall is studied by using a cyclic loading test. The failure mode, load-carrying capacity, ductility, stiffness degradation, hysteresis behaviour and energy dissipating capacity shown in the course of the test are studied. And this paper proposes the calculation formula of normal section bearing capacity. The main research results are as follows. Firstly, the failure mode of this new shear wall is the flexural failure. Secondly, compared with the ordinary reinforced concrete shear wall with slits, the new shear walls with concrete-filled steel tubular frames and slits show a better performance in load-carrying capacity, ductility, stiffness degradation and energy dissipating capacity.