Article

# Seismic performance of a non-through-core concrete between concrete-filled steel tubular columns and reinforced concrete beams

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## Abstract

This paper aims to investigate the seismic behavior of a new type of non-through-core connection between a concrete-filled steel tubular (CFST) column and steel reinforced concrete (SRC) beams. In this original connection, the U-shaped steel corbels are welded to the CFST column. A strengthening ring beam is used to enhance the stiffness of the connection. Cyclic loading tests were conducted on two beam-column connection specimens. A finite element (FE) model was then developed and validated by a comparison with the experimental results. The results of the FE analysis are in good agreement with the experimental results, which demonstrated the rationality of the proposed formula for concrete damage variable based on the elastic modulus in the FE analysis. Based on the test and numerical results, the hysteretic response, the skeleton curves, the strain, ductility, stiffness degradation and energy dissipation are discussed. It is shown that the proposed connection has a favorable seismic performance. The effect of the axial compression ratio (n) on the seismic behavior of the connection is also discussed through parametric studies.

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... The displacement ductility ratio (μ = Δ u /Δ y ) [27] was calculated to evaluate the ductility performance of specimens. The general yield Table 3. From Table 3 it can be seen that the displacement ductility ratio μ ranged from 3.52 to 4.88, indicating the excellent ductility of these composite frame structural systems in comparison to the L-shaped CFST column to steel beam frame, with maximum displacement ductility ratios μ max lower than 3.31. ...
... Surface-to-surface contact interaction with a finite sliding approach available in ABAQUS was applied at the interfaces of steel tube and concrete column by specifying a hard contact property in the direction normal to interface plane. The friction coefficient used in the penalty frictional formulation was assumed to be 0.50 for the tangential behavior, in accordance with the empirical value from Ding et al. [27]. ...
... Further, the recovery factors of compressive and tensile stiffness, w c of 0.8 and w t of 0.2 respectively, were used as the ABAQUS default values in the calculations. The tensile damage variable (d t ) and compressive damage variable (d c ) of concrete were also calculated according to Ding et al. [27]. ...
... Li et al. [3] developed a rebar-penetrated connection to GCFST column and conducted experimental test and finite element analysis to examine the connection seismic performance. Ding et al. [11] performed experimental and numerical investigations on earthquake-resistance behavior of a non-throughcore connection between RC beams and CFST column in terms of strain, ductility, and stiffness degradation. Limited studies have been published that investigated the cyclic-loaded response of the connection to GCFST column. ...
... The difference of the peak value between the numerical simulation and experimental tests was approximately 10%. As indicated in relevant research studies [11,23,24], the difference between simulated and tested results up to 20% was acceptable for a complex FE model. This difference was attributed to the deficiency of concrete constitutive model and the Tie model selected to represent welding for each steel component. ...
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As a promising composite structure, gangue concrete filled steel tubular (GCFST) column exhibites favarable characteristics including high strength and economic efficiency. This paper conducted numerical investiagations on structural behavior of a ring-beam connection to GCFST column with concrete beam under cyclic loading. Furthermore, finite element models of column-beam connections were developed using ABAQUS and validated against full-scale experimental tests to identify accuracy of selected modeling approaches. Using these validated models, stress distribution of each component was examined to study the force-transferring mechanism among the components and failure modes of the ring-beam connection. Research study indicated that the ring-beam connection showed a reasonable force-transferring mechanism under cyclic loading and the remarkable earthquake-resistant performance with high capacity and acceptable ductility. Finally, parametric studies were performed to assess the influences of beam-to-column stiffness ratio,steel ratio, axial load level, and concrete compressive strength on connection cyclic behaviors. Parametric studies provided some suggestions and references for the application of the ring-beam connection in various engineering projects.
... Surface-to-surface contact is used to model interaction between the interfaces of the steel tube and concrete. A coefficient of friction of 0.35 was used between the steel tube and concrete based on previous research [17,[22][23][24]. An embedded constraint is used to connect the steel reinforcing in the foundation/cap beam to the concrete. ...
Article
Concrete filled steel tubes (CFST) are composite structural elements which provide an economical and efficient alternative to conventional reinforced concrete and structural steel construction. Under seismic loading, CFSTs undergo reversed cyclic loading, and robust connections capable of sustaining cyclic lateral load demands, while minimizing damage and degradation, are required. Previous research has utilized numerical and experimental methods to demonstrate the performance of an embedded ring (ER) CFST column-to-cap beam/foundation connection in which an annular ring is welded to the end of the steel tube, and embedded in the cap beam/foundation concrete. However, due to the complexities associated with modeling the non-linear cyclic behavior of the ER connection (including the cyclic behavior of the concrete fill and the composite interaction of the materials), prior numerical efforts have focused primarily on monotonic behavior and failure envelopes rather than cyclic behavior. This deficiency is addressed here. A detailed continuum model capable of capturing the non-linear cyclic behavior of the ER connection is introduced and validated using experimental data. The proposed model is shown to predict damage and behavior of the ER connection subjected to reversed-cyclic loading with a reasonable accuracy; failure modes, hysteretic curves, resistance at target drifts, and drifts and steel strains at the initiation of steel tearing compare well with experimental observations.
... A finite element model is also developed and validated by a comparison with the experimental results. Ding et al. [17] conducted a cyclic loading test on a group of nonthrough-core connection, established the finite element model for calculation and analysis, discussed its strain curve, ductility curve, stiffness degradation curve, and energy dissipation curve, and concluded that SRCFCST joints had better seismic performance than ordinary reinforced concrete beam-column joints. Liao et al. [18] established seven composite joint models, including four concrete-encased CFST columns to RC beam joints and three concrete-encased CFSTcolumns to steel beam joints, and then models were tested and compared under constant axial load on the top of the column and cyclic load at the end of the beam. ...
Article
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In this paper, in order to investigate the shear mechanism and shear capacity of framework joints of steel-reinforced concrete-filled circular steel tube (SRCFCST), a numerical finite element model reflecting the mechanical behavior of framework joints of SRCFCST column-reinforced concrete beam is established through simulating concrete by the damage plastic constitutive model and simulating steel by the ideal elastic-plastic material, and its effectiveness is verified by experimental data. On account of uniform distribution of circular steel reinforced around the section and without definite flange and web, the shear mechanism of the framework joints of SRCFCST is analyzed on the basis of equivalent circular steel tube (CST) to the rectangular steel tube. The method for calculating the superposed shear bearing capacities of the joint core area is proposed, which is composed of four parts, i.e., concrete inside tube, concrete outside tube, hooping and steel-reinforced web; and the corresponding formulas for calculating shear bearing capacity are established. The comparative analysis of joints’ shear bearing capacity indicates that the results of numerical simulation and shear bearing capacity formulas coincide well with the experimental values, which can provide reference for the nonlinear analysis and engineering design of similar joints.
... Different detailing schemes have been proposed and studied for these joints. This includes the ring beam connections [4], the U-shaped concrete-filled tubular (CFT) beams [5], extended end plate connections [6], the corbel-type beam-column connection [7], the I-shaped stiffening connections [8], and the non-through-core connections [9]. Yan et al. [10] developed a hysteretic model for the highstrength SRC beam-column joints under cyclic loading. ...
Article
Strong column-weak beam behavior of a concrete structure with reinforced concrete (RC) beams and steel reinforced concrete (SRC) columns can only be ensured during a seismic event if the premature failure of beamcolumn joints could be avoided. The RC beam-SRC column joints, however, require special design and reinforcement detailing due to the presence of structural steel sections in the columns. Two different detailing schemes have been explored in this study for the exterior RC beam-SRC column joints. The key parameters varied in these detailing schemes are the anchorage length of beam longitudinal bars and the provision of transverse stiffeners in the structural steel sections. Three large-scale test joint specimens have been tested under the combined axial load and the varying lateral cyclic displacements. The crack propagation patterns, hysteresis behavior, moment-rotation characteristics, lateral stiffnesses, and joint shear-distortion behaviors of the composite specimens have been compared with the RC specimen to verify the suitability of the studied configurations. The experimental moment-rotation behavior of the test specimens has been compared with the theoretical moment-rotation curves derived using the current code provisions. Finally, the recommendations for the suitable configuration of the composite connection between the SRC column and RC beam have been proposed.
... concrete proposed in Refs. [35,36] was used in the model. The elastic-plastic combined hardening constitutive model was applied for the steel [37]. ...
Article
This study investigates a novel prefabricated concrete frame beam with an innovative assembly pattern that is cost-effective, reliable, practical, and has a good fault-tolerance. Quasi-static cyclic experiments were carried out on a cast-in-place (CIP) beam and three precast concrete (PC) beams with different lengths or widths of protruding beam stumps. The cracking propagation mode, load-bearing capacity, beam ductility, beam stiffness, and plastic energy dissipation ability were comparatively analysed. It is concluded that the hysteretic behaviour of the PC beams with the innovative assembly pattern suggested in this study was similar to that of the CIP. Moreover, PC beams with a wider protruding beam stump displayed better seismic performance. In particular, development curves of crack width with cyclic load were obtained, which showed that the cracks widened gradually as the number of load cycles increased, and the main crack width increased significantly around the peak load. A finite element model (ABAQUS) was established to further reveal the working mechanisms and conduct a parametric investigation of the PC beams. Parametric simulations indicated that a reasonable and relatively larger thickness of the U-shaped beam shell and higher post-pouring concrete strength are recommended for practical applications of the proposed novel prefabricated concrete frame beams.
... Stiffness degradation reflects an accumulation of damage. The ring stiffness can be used to study stiffness degradation of the PPSRC beam-column joint, which is expressed as follows [40]. ...
Article
Full-text available
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... A concrete-filled steel tubular (CFST) frame is composed of CFST columns and steel or reinforced concrete beams [1,2]. Nowadays, this CFST frame structure has been widely used in practical construction projects, due to remarkable features, such as high bearing capacity [3][4][5][6], large stiffness [7][8][9], and superior anti-seismic performance [10][11][12][13][14]. Additionally, some special shaped concrete-filled steel tubular components, such as L-shaped columns, can be utilized to enhance the internal space and thus beneficial for the placement of furniture by avoiding undesired configuration of the edges and corners in structures [15][16][17][18][19][20][21]. ...
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... The CDP model proposed by (Han et al., 2007;Tao et al., 2013) was used to model the concrete. The damaged parameter was calculated by the proposed model of (Ding et al., 2017). The steel rebars and stirrups were both modeled as isotropic elasto-plastic material satisfying the von Mises yield criterion (T. ...
Conference Paper
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This paper focuses on the development of plastic hinge length expression for Fiber Reinforced Polymer (FRP) strengthened concrete bridge pier under combined axial and reverse cyclic loading using finite element modeling approach. In a high seismic event, a bridge pier might experience in elastic deformations which in turn could lead to developing plastic hinge regions. Bridge piers are designed in such a way so that this kind of scenario occurs away from the superstructure. The severity of this phenomenon depends on the characteristics of the seismic event and the structural details of the pier as well. Data observed from past seismic events indicate that these ground motions contain a huge surge of energy which can make considerable damage to our existing bridge structures. In order to minimize this damaging of the structures and to save the human lives, the bridge piers might require proper strengthening to withstand such a huge amount of energy exerted by the ground motions. FRP can be considered for strengthening purposes due to its relatively easy and quick installation feature. In this paper, combined axial and reverse cyclic loading have been performed to predict the nonlinear behavior of FRP strengthened concrete bridge piers and expression for calculating the plastic hinge length has been developed. Different configurations of FRP strengthened concrete bridge piers have been tested using finite element analysis and damage propagation and strain distribution have been analyzed to calculate plastic hinge length using an analytically developed equation.
... The damage plasticity concrete model and the William-Warnke five-parameter failure criteria in ABAQUS were used for concrete material in the models. Parameters of the constitutive model, including the elastic modulus (E c ), dilation angle, eccentricity ratio, and viscosity coefficient, were all determined according to previous researches by Ding et al. (2011Ding et al. ( , 2017. While for the steel parts, the combined hardening constitutive model with Von Mises yielding criteria was applied. ...
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... In the existing engineering, the connection mode of quadrilateral welding is widely used [5], which leads to problems such as excessive welding quantity, difficult to guarantee the quality of welding seam, high cost of the structure, and long time limit. e bolted steel plate shear wall is mainly used in the structural test [6][7][8][9][10], and its purpose is to facilitate the connection of the test device and the repeated use of some components, but in the finite element numerical analysis, welding is still used to simulate the connection between the wallboard and the frame. e existing bolted joints are densely arranged and require highprocessing accuracy, which not only makes the practical difficulty of the bolted joints increase greatly, but also does not meet the energy-saving and high-efficiency characteristics of the assembly structure. ...
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Through assuming reasonable constitutive relation of materials, finite element analysis (FEA) models of joints consisting of prestressed concrete-encased steel beams and concrete-encased concrete filled steel tube (CFST) columns were established by soft ABAQUS, and the simulated results were compared with tested ones. On this basis, the nonlinear analysis on the total loading process was conducted, and the stress variation of concrete, profile steel skeleton, steel bar skeleton, and prestressing tendons were observed at yield, peak, and ultimate loads; the influence of axial compressive ratio, steel tube ratio, stirrup ratio, and prestressing level on lateral load-displacement curves at column top and shear force-shear angle in joint core were investigated, and the shear capacity formulae of joint core were developed. It could be concluded that, the lateral peak loads and shear capacity could be improved with the increase of axial compressive ratio, steel tube ratio, stirrup ratio, and prestressing levels in varying degrees, and the ductility of joints will reduce with the increase of axial compressive ratio. Additionally, the shear capacity calculated by proposed practical formula was a little lower than FEA results, which could keep the joints safety and could be used in engineering design.
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In this study, three concrete-filled steel tubular (CFST) column-steel beam bolted joints with external reinforcing diaphragm were tested under cyclic loading using 1/2 scaled specimens, and the influence law of steel beam size and tie plate of high-strength bolts on the failure modes were discussed. The ABAQUS program was used to establish the three-dimensional solid finite element models of the joints, and the joint models were then verified by the test data. Taking the welded rigid joint with external reinforcing diaphragm as the benchmark, a connection detailing of bolted rigid joint and a method for classifying the joint were proposed. The stiffness, bearing capacity and plastic energy dissipation of the bolted joints with different structural detailing and reinforcing measures were compared and analyzed. The obtained results show that the bolted joints with external reinforcing diaphragm can be classified as semi-rigid joint. The stiffness and bearing capacity of the bolted joint can almost be equivalent with the welded rigid joint counterparts, when the external reinforcing diaphragm with stiffeners was connected to the steel beam using four rows of bolts and simultaneously setting web stiffeners at the beam ends. With the above configuration, the total plastic energy dissipation of the bolted joint is over 80% of that of the welded rigid joint counterpart, and the steel beam is found to be the main component contributing the plastic energy dissipation.
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The through-diaphragm connection detail has been identified as a good choice for attaching HSS beams to concrete-filled rectangular tube columns in engineering applications. In this research program an analytical study was conducted to comprehend the behavior of this detail and develop the accompanying design guidelines. The experimental results are presented elsewhere. In this paper two analytical models were established to predict the shear stiffness and yield shear strength of the HSS beam and panel zone, respectively. Theoretical results based on the proposed model well agreed with the experimental data. Finally, design provisions were introduced to check the strength in the connections.
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This paper experimentally investigated the behavior of specially shaped columns composed of concrete-filled steel tube frames (SCFST frames) subjected to constant axial load and cyclically varying flexural load. Three specimens with two storeys and a single span were tested. The effects of axial compression ratio and the beam-to-column stiffness ratios on the behavior (i.e., stiffness, strength, ductility, and energy dissipation) of SCFST frames were studied. The failure modes of the frames were studied. The hysteretic curve shapes of these three specimens were smooth and full, and the skeleton curves both have gently descending stages, which represent suitable ductility and energy dissipation ability. The load carrying capacity and stiffness decreased with the decrease in axial compression ratio, but the energy dissipation ability and ductility increased and the stiffness degeneration decreased. The load carrying capacity and stiffness decreased with the increase in beam-to-column stiffness ratio, but the energy dissipation and deformation abilities increased. Furthermore, a finite element analysis was conducted to simulate the behavior of SCFST frames. Test results agreed with the results of the finite element analysis.
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Three specimens of steel reinforced ring-beam connections of concrete filled steel columns and reinforced concrete (RC) beams were experimentally studied on the hysteretic behavior. Stress distributions and Load-displacement curves of these specimens were recorded. According to the tests, the mechanism, the ultimate failure mode and the stress patterns were also analyzed. The results show that a good behavior can be obtained by using the joints. And studies also show that a plastic hinge starts from the beam. A finite element analysis model is developed using ABAQUS. The transfer mechanism and internal force distribution of these specimens are analyzed, which may provide a good base both on theory and practice.
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In this paper, four full-scale specimens of existing and proposed through-diaphragm connections to concrete-filled rectangular steel tubular columns were tested under cyclic lateral load. The variables in the experiments include the geometry of the through-diaphragm, the configuration of the weld access hole, horizontal stiffeners, and the methods of connecting beam webs to columns. Three failure modes were observed in the test. The strength, stiffness, ductility and energy dissipation capacity were evaluated at different load cycles. It is found that the moment-rotation hysteresis curves are all stable and plentiful and exhibit no obvious strength deterioration or stiffness degradation. The energy dissipation capacity of the proposed through-diaphragm connections are significantly improved when compared to the existing one. Although fabricated in poor condition with an extremely low temperature, the proposed connections could obtain more than 0.1 rad of the inelastic rotation capacity. This indicates that the proposed through-diaphragm connections show good seismic behavior and could be applied to composite ordinary moment frames.
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The effects of cyclic local buckling on the behavior of concrete-filled steel tubular (CFST) slender beam-columns under cyclic loading were approximately considered in existing analytical methods by modifying the stress–strain curve for the steel tube in compression. These methods, however, cannot simulate the progressive cyclic local buckling of the steel tubes. This paper presents a new efficient numerical model for predicting the cyclic performance of high strength rectangular CFST slender beam-columns accounting for the effects of progressive cyclic local buckling of steel tube walls under stress gradients. Uniaxial cyclic constitutive laws for the concrete core and steel tubes are incorporated in the fiber element formulation. The effects of initial geometric imperfections, high strength materials and second order are also included in the nonlinear analysis of CFST slender beam-columns under constant axial load and cyclically varying lateral loading. The Müller's method is adopted to solve nonlinear equilibrium equations. The accuracy of the numerical model is examined by comparisons of computer solutions with experimental results available in the published literature. A parametric study is conducted to investigate the effects of cyclic local buckling, column slenderness ratio, depth-to-thickness ratio, concrete compressive strength and steel yield strength on the cyclic responses of CFST slender beam-columns. It is shown that the numerical model developed predicts well the experimentally observed cyclic lateral load–deflection characteristics of CFST slender beam-columns. The numerical results presented reflect the cyclic local and global buckling behavior of thin-walled high strength rectangular CFST slender beam-columns, which have not been reported in the literature.
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Concrete filled steel tube (CFST) columns are currently being widely used in the construction of modern buildings and bridges. In practice, the torsion effect will be often created in CFST columns when the horizontal earthquake happened. Based on geometrical, material constitutive and equilibrium equations, a theoretical model called laminated tubes model for analyzing the mechanical behavior of CFST columns under axial force-torsion combined action was proposed. The confined effect provided by the steel tube and the compression softening effect of the concrete could be considered in the proposed concrete material model. Based on the theoretical model, the non-linear analysis program was developed for obtaining the entire loading history of CFST columns under axial force-torsion combined action. The predicted results have good agreement with test results. The torsion behavior of CFST columns was detailed discussed based on the theoretical model, and the simplified formulae for practical design are also proposed based on regression methods.
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A new form of composite column, steel reinforced-concrete filled-steel tubular column (SRCFST) has been proposed to undertake higher loads. This contribution presents a numerical study of cyclically loaded SRCFST columns based on the ABAQUS standard solver. The feasibility and accuracy of the numerical method was verified by comparing the calculated results with the experimental observations. The lateral displacement–load curves and sectional stress distributions were analyzed. The results indicate that the SRCFST columns have higher specimen stiffness, peak lateral load and deformability than common concrete filled steel tubular (CFST) columns due to the presence of the section steel. A parametric study, including influence of axial load levels, ratio of section steel, yield strength of section steel, concrete strength and thickness of steel tube on peak lateral load was also carried out.
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A concrete-filled stainless steel–carbon steel tubular (CFSCT) column is introduced as a new form of composite member in this paper, which is believed to achieve higher corrosion resistance, higher bearing capacity and lower cost by combination the advantages of stainless steel and concrete filled steel tube (CFST) structure. A series of compression test was carried out on this newly proposed composite column. A modified stress–strain model for concrete core was proposed and then three-dimensional nonlinear finite-element (FE) models were established and verified with the experimental results. Close agreement was achieved between the test and numerical results in terms of load–deformation responses. A parametric study, including tube thickness, diameter and yield strength of carbon steel tube was also conducted to give a clear insight on the performance such composite columns.
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This paper presents an experimental study on seismic behavior of a composite structural frame system consisting of concrete filled steel tube columns and steel beams with bolted endplate connections. Based on current seismic provisions and previous research, a ten-story prototype building was designed. Analytical models were developed to predict the elasto-plastic behavior of the prototype frame under a series of ground motion records. A four-seventh scale sub-structure model consisting of two stories and one and half span was constructed and subjected to simulated seismic excitations using pseudo-dynamic hybrid testing method. Results from the tests indicate that the model behavior under the simulated seismic loading was consistent with the expected performances analyzed for different earthquake hazard levels. Finally, quasi-static test and pushover test were also conducted to identify the ultimate failure mode of the testing model. The study shows that the proposed system can offer appropriate strength and adequate ductility required for seismic design.
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This paper investigates the seismic behaviour of extended end plate connections to circular or square concrete-filled steel tubular (CFST) columns using blind bolts. Both the end plate type and the column section type are considered. Results of an experimental study involving four bolted moment-resisting connections subjected to cyclic loading are presented. The failure modes, hysteretic performance, strength and stiffness degradation, rigidity classification, and energy dissipation of the blind bolted extended end plate connections to CFST columns were estimated in detail to investigate the seismic behaviour. The anchorage action of reinforcing rebar welded to the bolt with concrete-filled steel tubes was also explored. The experimental results indicated the blind bolted extended end plate connections with circular or square CFST columns exhibited large hysteretic loops, good ductility, and excellent energy dissipation capacity. Failure modes for test specimens under cyclic loading were similar to those under monotonic loading, and their rotation capacities satisfied the ductility design requirements for earthquake-resistance in most seismic regions. These experimental studies enable improvement in the practical design of blind bolted moment connections.
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The concept of confined concrete has been widely accepted throughout the structural engineering field, such as the spiral, steel tube, or carbon fiber composite shell confined concrete, etc. In the present study, this concept has not only been used in the structural columns, but also in joints. In this connection system, the steel tube is interrupted at the floor, the concrete in the connection zone is confined by a stiffening ring with multiple lateral hoops, and the reinforced concrete beams are continuously arranged through the joint. The structural behavior of this new connection system in axial compression tests and reversed cyclic loading tests is presented in a companion paper. In the present study, the bearing strength of composite columns and the joint in axial compression is obtained based on the stress and strain analyses. The critical volume fraction of transverse stirrups of the composite column and the effective confining radius in the stiffening ring are proposed based on the thick cylinder model with the assumption of plane stress state. By using these solutions, it is favorable to obtain the stress distribution in confining concrete and the bearing strength of the confined concrete. For the reversed cyclic loading tests, the Clough hysteresis model is used to simulate the hysteresis loops of the specimens without considering the stiffness degradation in the unloading process. The results of the theoretical modeling are generally in good agreement with the experimental observations.
Article
A new connection system for a concrete filled steel tube composite column and reinforced concrete beams is proposed. In this connection, the steel tube is interrupted while the reinforced concrete beams are continuous in the joint zone. Multiple lateral hoops that constitute the stiffening ring are used to confine the core concrete in the connection zone. The transfer of moment at the beam ends can be ensured by continuous rebars; the weakening of the axial load bearing capacity due to the interruption of the steel tube can be compensated by the confinement of the stiffening ring. Using these configurations, concrete casting and tube lifting can be made more convenient since welding and hole drilling in situ can be avoided. Axial compression experiments on six specimens and reversed cyclic loading tests on three interior column specimens and three corner column specimens were conducted to evaluate this new beam-column system; load-deflection performance, typical failure modes, stress and strain distributions, and the energy dissipation capacity were obtained. The experimental results showed that the effective confinement can be achieved by the stiffening ring, and an excellent axial bearing capacity can be obtained, as well as a superior ductility and energy dissipation capacity. As a new connection system for the concrete filled steel tube composite column with reinforced concrete beams, it can also be applied to other types of confined concrete columns.
Structural Design and Construction of Steel-Concrete Composite Structure
• Q J Zhou
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Specificating of Testing Methods for Earthquake Resistant Building
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