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Steel Construction Published the List of Highly Influential Articles of 2020
2024 Vol. 39, No. 1
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2024, 39(1): 1-28.
doi: 10.13206/j.gjgS23071102
Abstract
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Abstract:
Concrete-filled steel tubular (CFST) columns have high strength, favorable seismic performance, reasonable cost, and are widely used as the main structural types in high-rise buildings and heavily-loaded structures. In comparison to circular CFST columns, square CFST columns have the advantages of relatively wide section, large flexural stiffness, high flexural capacity, simple joint details, convenient manufacturing and construction, convenient layout of building space, and easy decoration, and thus are widely used in practical engineering. However, the previous research indicated that the composite action between a rectangular steel tube and the in-filled concrete is relatively weak and can be improved by setting stiffening schemes. Meanwhile, shear connectors are usually welded to the steel tube to improve the interfacial longitudinal shear transfer capacity. The existing stiffening forms are summarized as point-open, point-closed and line-open confinement. The diagonal stiffener, welded on two adjacent sides of a steel tube is referred to as the diagonal rib; it is a new efficient stiffener developed recently and can also be used as the shear connector. This paper systematically summarizes the mechanical behavior and design methods of members, joints, and frames of concrete-filled steel tube stiffened by diagonal ribs. At the level of members, the concentric compression, eccentric compression and seismic behavior of columns were analyzed; the details of diagonal ribs, width-to-thickness ratio limits, thickness matching relationship between the diagonal rib and steel tube, and axial load ratio limits were recommended; the modified plastic stress distribution method was proposed to calculate the strength of columns under combined compression and bending; the shear mechanism of ultra-short columns was figured out, and the shear model and shear force versus shear deformation relationships were proposed. At the level of joint, the axial compression and seismic behavior of CFST column to RC beam joints were studied; the axial compression and shear mechanism were analyzed, and the rational details of the joint zone were suggested to satisfy the requirement of strong-joint/weak-component; the modified equations, which considered the effect of axial load and compression zone height of the column, were proposed to more accurately predict the bond performance of beam reinforcements in the joint zone. At the level of frame system, the pushover analyses, IDA analyses and seismic fragility analyses of CFST column stiffened by diagonal ribs to RC beam frame were conducted, and the yielding mechanism and collapse mechanism were analyzed. The results showed that the diagonal ribs combine the advantages of existing stiffeners, efficiently transferring the interfacial shear force, constraining the concrete and avoiding or postponing the local buckling of steel tube, significantly improve the load capacity, deformation capacity, and seismic performance of square concrete-filled steel tubular columns, and have great application prospect in practical engineering. Finally, the engineering application scenarios for diagonal-rib stiffened CFST structures are listed; the development direction and problems which need further investigation of the structure are outlined.
Concrete-filled steel tubular (CFST) columns have high strength, favorable seismic performance, reasonable cost, and are widely used as the main structural types in high-rise buildings and heavily-loaded structures. In comparison to circular CFST columns, square CFST columns have the advantages of relatively wide section, large flexural stiffness, high flexural capacity, simple joint details, convenient manufacturing and construction, convenient layout of building space, and easy decoration, and thus are widely used in practical engineering. However, the previous research indicated that the composite action between a rectangular steel tube and the in-filled concrete is relatively weak and can be improved by setting stiffening schemes. Meanwhile, shear connectors are usually welded to the steel tube to improve the interfacial longitudinal shear transfer capacity. The existing stiffening forms are summarized as point-open, point-closed and line-open confinement. The diagonal stiffener, welded on two adjacent sides of a steel tube is referred to as the diagonal rib; it is a new efficient stiffener developed recently and can also be used as the shear connector. This paper systematically summarizes the mechanical behavior and design methods of members, joints, and frames of concrete-filled steel tube stiffened by diagonal ribs. At the level of members, the concentric compression, eccentric compression and seismic behavior of columns were analyzed; the details of diagonal ribs, width-to-thickness ratio limits, thickness matching relationship between the diagonal rib and steel tube, and axial load ratio limits were recommended; the modified plastic stress distribution method was proposed to calculate the strength of columns under combined compression and bending; the shear mechanism of ultra-short columns was figured out, and the shear model and shear force versus shear deformation relationships were proposed. At the level of joint, the axial compression and seismic behavior of CFST column to RC beam joints were studied; the axial compression and shear mechanism were analyzed, and the rational details of the joint zone were suggested to satisfy the requirement of strong-joint/weak-component; the modified equations, which considered the effect of axial load and compression zone height of the column, were proposed to more accurately predict the bond performance of beam reinforcements in the joint zone. At the level of frame system, the pushover analyses, IDA analyses and seismic fragility analyses of CFST column stiffened by diagonal ribs to RC beam frame were conducted, and the yielding mechanism and collapse mechanism were analyzed. The results showed that the diagonal ribs combine the advantages of existing stiffeners, efficiently transferring the interfacial shear force, constraining the concrete and avoiding or postponing the local buckling of steel tube, significantly improve the load capacity, deformation capacity, and seismic performance of square concrete-filled steel tubular columns, and have great application prospect in practical engineering. Finally, the engineering application scenarios for diagonal-rib stiffened CFST structures are listed; the development direction and problems which need further investigation of the structure are outlined.
2024, 39(1): 29-40.
doi: 10.13206/j.gjgS23072801
Abstract:
Concrete-filled steel tubular column to composite beam joint with stiffening ring is widely used in super high-rise buildings due to its excellent performance. This paper conducted finite element research on the seismic performance of concrete-filled square steel tubular column to composite beam joint with stiffening ring under high axial pressure. On the basis of the triaxial plastic damage model of concrete and the mixed strengthening model of steel, a ductile damage model of steel was further applied, and solid fine finite element models based on test specimens were established. By comparing with experimental results, it is proven that the finite element model can accurately simulate the seismic performance and failure modes of joints, as well as the decline of ultimate capacity in the later stage of loading, with ultimate capacity errors within 8%. Finite element parametric analysis was conducted, considering the construction of “strong beams” with increased steel beam height and “strong columns” with column stirrup. The effects of different parameters on hysteresis curves, skeleton curves, failure modes, and plastic energy distribution and failure mechanisms of joints were analyzed. The analysis results indicate that under high axial compression ratio, after increasing the steel beam height and using the construction of stirrup at the column end, the bending capacity and energy dissipation capacity of the joints are significantly improved, and the composite joints still maintain the beam end failure mode at high axial compression ratio. When the ratio of bending capacity of beam to column is between 1.39 and 2.11, the joint with stiffening ring takes a transition from beam energy consumption to column energy consumption; According to the Code for Seismic Design of Buildings (GB 50011—2010), it is considered as a strong -column weak-beam when the value of the ratio of bending capacity of beam to column is less than 1. This is relatively conservative for the definition of strong-column weak-beam for joints with stiffening ring. It is recommended that the ratio of bending capacity of beam to column for joints with stiffening ring corresponding to strong-column weak-beam can be enlarged to less than 1.3.
Concrete-filled steel tubular column to composite beam joint with stiffening ring is widely used in super high-rise buildings due to its excellent performance. This paper conducted finite element research on the seismic performance of concrete-filled square steel tubular column to composite beam joint with stiffening ring under high axial pressure. On the basis of the triaxial plastic damage model of concrete and the mixed strengthening model of steel, a ductile damage model of steel was further applied, and solid fine finite element models based on test specimens were established. By comparing with experimental results, it is proven that the finite element model can accurately simulate the seismic performance and failure modes of joints, as well as the decline of ultimate capacity in the later stage of loading, with ultimate capacity errors within 8%. Finite element parametric analysis was conducted, considering the construction of “strong beams” with increased steel beam height and “strong columns” with column stirrup. The effects of different parameters on hysteresis curves, skeleton curves, failure modes, and plastic energy distribution and failure mechanisms of joints were analyzed. The analysis results indicate that under high axial compression ratio, after increasing the steel beam height and using the construction of stirrup at the column end, the bending capacity and energy dissipation capacity of the joints are significantly improved, and the composite joints still maintain the beam end failure mode at high axial compression ratio. When the ratio of bending capacity of beam to column is between 1.39 and 2.11, the joint with stiffening ring takes a transition from beam energy consumption to column energy consumption; According to the Code for Seismic Design of Buildings (GB 50011—2010), it is considered as a strong -column weak-beam when the value of the ratio of bending capacity of beam to column is less than 1. This is relatively conservative for the definition of strong-column weak-beam for joints with stiffening ring. It is recommended that the ratio of bending capacity of beam to column for joints with stiffening ring corresponding to strong-column weak-beam can be enlarged to less than 1.3.
2024, 39(1): 41-52.
doi: 10.13206/j.gjgS23083101
Abstract:
Normal concrete filled steel tube columns (CFST) exhibit poor potency under high axial compression ratio in seismic action. In contrast to other inner constraint measures of CFST, the transverse stirrups effectively prompt the constraint confinement efficiency and seismic performance of CFST columns under high axial compression ratio. Based on the test and the research of circular and square CFST columns’ seismic performance under high axial compression ratio, the three-dimension solid finite element model was established and the test results were verified, The mechanical properties parameter analysis of stirrup-confined circular CFST columns under monotonic loading and hysteretic loading was carried out. The influence of stirrups on the interface sliding behaviour, stress level and seismic performance was probed. The research results elucidate: 1) The interface sliding behaviour exists between steel tube and concrete under compression-bending loading, which leads to the inconsistent changes in the neutral axis height of steel tube and concrete during the loading progress. Under the hysteretic loading, the tensile area of concrete lessens conspicuously and the difference between the neutral axis of concrete and steel tube augments, resulting in greater interface sliding. Finally, the full section of concrete is compressed while the steel tube resists bending. 2) When the steel tube consumption remains unchanged, the difference between the neutral axis of concrete and steel tube reduces after the stirrups were set to the end of the columns. The diminishing of the interface sliding gives rise 10% of the bending stiffness. The stirrups directly constrain the concrete and resist the buckling of the steel tube, which increased the tensile stress level of the steel tube and the compression stress level of the concrete and the stress level is more uniform. The tensile area of steel tube increases while the compressive area of concrete decreases, which leads to the 20%-50% increase of the ultimate capacity. 3) Stirrups effectively improve the seismic performance of the CFST columns under hysteretic loading. When the steel consumption of CFST column remains unchanged, the stiffness of high axial compression ratio CFST columns remains unchanged. The bearing capacity increases by 10%-20%, and the energy dissipation of the CFST columns is increases by 2 times. The energy dissipation of the concrete increases by 1 time due to the confinement effect of the steel tube and the stirrups. The compression region height of the CFST column is reduced, which leads to the greater rotational capacity of the member. The plastic energy dissipation of the steel tube can be effectively elicited by a factor of 3.
Normal concrete filled steel tube columns (CFST) exhibit poor potency under high axial compression ratio in seismic action. In contrast to other inner constraint measures of CFST, the transverse stirrups effectively prompt the constraint confinement efficiency and seismic performance of CFST columns under high axial compression ratio. Based on the test and the research of circular and square CFST columns’ seismic performance under high axial compression ratio, the three-dimension solid finite element model was established and the test results were verified, The mechanical properties parameter analysis of stirrup-confined circular CFST columns under monotonic loading and hysteretic loading was carried out. The influence of stirrups on the interface sliding behaviour, stress level and seismic performance was probed. The research results elucidate: 1) The interface sliding behaviour exists between steel tube and concrete under compression-bending loading, which leads to the inconsistent changes in the neutral axis height of steel tube and concrete during the loading progress. Under the hysteretic loading, the tensile area of concrete lessens conspicuously and the difference between the neutral axis of concrete and steel tube augments, resulting in greater interface sliding. Finally, the full section of concrete is compressed while the steel tube resists bending. 2) When the steel tube consumption remains unchanged, the difference between the neutral axis of concrete and steel tube reduces after the stirrups were set to the end of the columns. The diminishing of the interface sliding gives rise 10% of the bending stiffness. The stirrups directly constrain the concrete and resist the buckling of the steel tube, which increased the tensile stress level of the steel tube and the compression stress level of the concrete and the stress level is more uniform. The tensile area of steel tube increases while the compressive area of concrete decreases, which leads to the 20%-50% increase of the ultimate capacity. 3) Stirrups effectively improve the seismic performance of the CFST columns under hysteretic loading. When the steel consumption of CFST column remains unchanged, the stiffness of high axial compression ratio CFST columns remains unchanged. The bearing capacity increases by 10%-20%, and the energy dissipation of the CFST columns is increases by 2 times. The energy dissipation of the concrete increases by 1 time due to the confinement effect of the steel tube and the stirrups. The compression region height of the CFST column is reduced, which leads to the greater rotational capacity of the member. The plastic energy dissipation of the steel tube can be effectively elicited by a factor of 3.
2024, 39(1): 53-67.
doi: 10.13206/j.gjgS23063003
Abstract:
The seismic performance of the traditional reinforced concrete pier is insufficient under strong earthquakes, but the concrete filled steel tube (CFST) pier has better seismic performance. CFST pier has broad application prospects in highway, expressway, urban expressway and high-speed railway, and has been gradually popularized in bridge structure in recent years. In order to improve the seismic toughness of bridge piers, the ultimate seismic capacity of square section reinforced concrete piers, partially filled CFST piers, CFST piers and stirrup-confined CFST piers are compared and studied. Seismic elastoplastic and plastic large deformation time history analysis of full-size finite element models of square section reinforced concrete pier, partially filled CFST pier, CFST pier and stirrup-confined CFST pier were carried out, and the seismic limit performance and application range of different types of pier were discussed. In the analysis, the finite element software ABAQUS is used to establish a refined finite element model of solid shell. In the model, a parametric deterministic concrete triaxial plastic-damage model is adopted for the concrete stress-strain relationship, and crack insertion technology is introduced. The combined hardening-ductile damage model of steel stress-strain relationship was adopted, and the finite element model was verified by the existing experimental results of the seismic performance of reinforced concrete pier, partially filled CFST pier, CFST pier and and stirrup-confined CFST pier under unidirectional pseudo-static, unidirectional pseudo-dynamic, bidirectional pseudo-dynamic, and shake table loading test. Finally, three evaluation indexes: displacement response, cumulative energy dissipation and stiffness damage, are used to evaluate the seismic toughness of various piers under different ground motion intensity at the same cost. The analysis results show that: 1) the elastic-plastic and large deformation seismic calculation methods of the refined solid-shell FE model of CFST pier can reasonably reflect the “pinch” effect of hysteretic curve under cyclic load, the degradation of bearing capacity during large plastic deformation and the displacement response under dynamic load. 2) When the bridge fortification requirement is 6-7 degrees, it is recommended to choose reinforced concrete pier; when the bridge fortification requirement is 8 degrees, it is recommended to choose CFST pier. When the bridge fortification requirement is 9 degrees or above, it is recommended to choose the stirrup-confined CFST pier.
The seismic performance of the traditional reinforced concrete pier is insufficient under strong earthquakes, but the concrete filled steel tube (CFST) pier has better seismic performance. CFST pier has broad application prospects in highway, expressway, urban expressway and high-speed railway, and has been gradually popularized in bridge structure in recent years. In order to improve the seismic toughness of bridge piers, the ultimate seismic capacity of square section reinforced concrete piers, partially filled CFST piers, CFST piers and stirrup-confined CFST piers are compared and studied. Seismic elastoplastic and plastic large deformation time history analysis of full-size finite element models of square section reinforced concrete pier, partially filled CFST pier, CFST pier and stirrup-confined CFST pier were carried out, and the seismic limit performance and application range of different types of pier were discussed. In the analysis, the finite element software ABAQUS is used to establish a refined finite element model of solid shell. In the model, a parametric deterministic concrete triaxial plastic-damage model is adopted for the concrete stress-strain relationship, and crack insertion technology is introduced. The combined hardening-ductile damage model of steel stress-strain relationship was adopted, and the finite element model was verified by the existing experimental results of the seismic performance of reinforced concrete pier, partially filled CFST pier, CFST pier and and stirrup-confined CFST pier under unidirectional pseudo-static, unidirectional pseudo-dynamic, bidirectional pseudo-dynamic, and shake table loading test. Finally, three evaluation indexes: displacement response, cumulative energy dissipation and stiffness damage, are used to evaluate the seismic toughness of various piers under different ground motion intensity at the same cost. The analysis results show that: 1) the elastic-plastic and large deformation seismic calculation methods of the refined solid-shell FE model of CFST pier can reasonably reflect the “pinch” effect of hysteretic curve under cyclic load, the degradation of bearing capacity during large plastic deformation and the displacement response under dynamic load. 2) When the bridge fortification requirement is 6-7 degrees, it is recommended to choose reinforced concrete pier; when the bridge fortification requirement is 8 degrees, it is recommended to choose CFST pier. When the bridge fortification requirement is 9 degrees or above, it is recommended to choose the stirrup-confined CFST pier.
2024, 39(1): 68-70.
doi: 10.3724/j.gjgS23082020
Abstract:
The distribution of confining stresses and bending moments along 4 side-plates in concrete filled tube as a compression member are introduced. The plastic hinge lines formed in side-plates in the ultimate states are assumed and the average confining pressure is computed. By requiring the same confining pressure is achieved in concrete filled circular pipe in its ultimate state, the corresponding radius-thickness ratio of the pipe is determined and equivalent confining coefficient is obtained. The equivalent coefficient is presented and compared to the test result, and is found to be able to predict the average strength of the test results. Finally when the full strength weld between side-plates is required is provided.
The distribution of confining stresses and bending moments along 4 side-plates in concrete filled tube as a compression member are introduced. The plastic hinge lines formed in side-plates in the ultimate states are assumed and the average confining pressure is computed. By requiring the same confining pressure is achieved in concrete filled circular pipe in its ultimate state, the corresponding radius-thickness ratio of the pipe is determined and equivalent confining coefficient is obtained. The equivalent coefficient is presented and compared to the test result, and is found to be able to predict the average strength of the test results. Finally when the full strength weld between side-plates is required is provided.
