Stiffness Degradation of Shear Wall with Frame Column and its Influence to Structural Performance

The shear wall with frame column has a wide application prospect in practical engineering for it has better ductility, bearing capacity and stiffness degradation than the shear wall with unframed column. In this paper, the finite element model of shear wall with frame column for an experiment was established in ABAQUS software firstly, Then on the base of proving the model’s precision, the axial compression ratio and the stiffness ratio of shear wall with frame column were adjusted, the influence of different axial compression ratio and stiffness ratio on the stiffness degradation coefficient was analyzed and the corresponding formulas were fitted. At last, by changing the axial compression ratio and the stiffness ratio of shear wall with frame column, The influence of stiffness degradation on the maximum displacement amplification coefficient and the bottom shear amplification coefficient were studied and the relevant formulas were fitted.

Experimental Study On Hysteretic Behavior of Concrete Filled Square CFRP Steel Tubular Beam-Column

In order to study the hysteretic behavior of concrete filled square CFRP steel tubular Beam-Column under different influence factors, 12 specimens were designed, and the failure mode, middle section lateral force-deflection(P-Δ) curve, middle section bending moment-curvature(M-φ) curve and middle section deflection-deformation(Δ−Δ') curve were studied. Axial compression ratio and longitudinal CFRP reinforcement coefficient as influencing factors, the effects of axial compression ratio and longitudinal CFRP reinforcement coefficient on P-Δ skeleton curve, M-φ skeleton curve, strength and stiffness degradation, ductility, cumulative energy consumption and other indexes were studied; the P-Δ curve and deformation mode of the specimens were simulated by ABAQUS, and the effects of axial compression ratio, slenderness ratio and other main parameters on the hysteretic performance of the members were studied. The test results show that CFRP has good lateral restraint and longitudinal reinforcement effect on CFST, and the local buckling of CFST is delayed. The P-Δ curve and M-φ curve of all specimens are full. In addition, the steel tube and CFRP have good synergy in both longitudinal and transverse directions. The change of axial compression ratio and longitudinal CFRP reinforcement coefficient has no significant effect on the strength degradation. The increase of axial compression ratio and longitudinal CFRP reinforcement coefficient can improve the flexural capacity and stiffness of the specimens, and slow down the stiffness degradation, but reduce the ductility and cumulative energy consumption of the specimens. The finite element software ABAQUS is used to simulate the P-Δ curve and deformation mode of specimens. It is found that the simulation results are in good agreement with the experimental results. Based on the model analysis of the main parameters, it is found that the increase of steel yield strength and CFRP layers can improve the bearing capacity of the specimens, and the axial compression ratio has the most significant effect on the specimens.

Numerical Analysis of Seismic Performances of Post-Fire Scoria Aggregate Concrete Beam-Column Joints

In order to analyze the post-fire seismic performances of scoria aggregate concrete (SAC) beam-column joints precisely and effectively, one finite element model (FEM) was developed to simulate the seismic behavior of SAC beam-column joints. The FEM consists of two sequential parts: firstly, the heat transfer analysis of the beam-column joints, and then the seismic analysis of the SAC joints by combining the temperature field distribution obtained from the heat transfer analysis with the mechanical properties of the SAC after fire, both of which were implemented in ABAQUS. In order to make the simulation results more accurate, spring elements were applied to simulate the bond–slip behavior with material degradation due to fire damage in the simulation of seismic analysis. Moreover, in order to validate the FEM, the seismic behavior of the natural aggregate concrete (NAC) beam-column joints after fire was simulated with the established FEM, and the simulation results were compared with the available test data. It is proved that the FEM we built was accurate and effective and provided efficient solutions for evaluating the seismic performance of post-fire beam-column joints so that the effects of various parameters, namely, fire time, longitudinal reinforcement ratio, and axial compression ratio on the seismic performance of SAC beam-column joints after fire were investigated in depth, which indicated the increase of axial compression ratio can improve the strength, initial stiffness, and energy dissipation capacity of SAC joints, while the increase of longitudinal reinforcement ratio can increase the strength and stiffness of SAC joints to a small extent, but too high reinforcement ratio will significantly weaken the energy dissipation capacity of SAC joints.

Calculation Model of Shear Capacity of Multiple Composite Core Column Joints Based on Softened Tension-Compression Bar Model

This paper aims to study the seismic performance of multiple composite core column joints. The influence of the stress mechanism, axial compression ratio, and shear span ratio on the failure mode, hysteretic performance, and shear capacity of the multiple composite core column joints was studied through the low-reversed cyclic loading tests of three specially designed and manufactured multiple composite core column joints. The angle ratio method is used to calculate the effective area of the vertical tie bar, and based on the mechanism of the softening tension-compression bar, the formula for calculating the shear capacity of the joint with multiple composite core column is established. In addition, it is also verified by the test data in this paper. The experimental results show that when the axial compression ratio increases from 0.26 to 0.45, the number and width of cracks at the beam end decrease. When the shear span ratio increases from 1.67 to 2.22, the number and width of cracks at the joint beam end increase. The average value and standard deviation of the ratio between the measured value and the calculated value of the shear capacity are 0.97 and 0.16, indicating that the proposed calculation method has a high agreement with the actual value and strong engineering application.

Numerical Simulation on Seismic Behavior of Steel Fiber Reinforced Concrete Beam—Column Joints

Steel fiber reinforced concrete (SFRC) is a novel material of concrete, which has a great potential to be used in practical engineering. Based on the finite element software Opensees, the main objective of this paper presented a numerical simulation method on investigating the seismic behavior of SFRC–beam-column joints (BCJs) through modifying the calculation method of joint shear and longitudinal reinforcement slip deformations. The feasibility and accuracy of the numerical modeling method were verified by comparing the computed results with experimental data in terms of the hysteresis curves, skeleton curves, feature points, energy dissipation, and stiffness degradation. And then, the influences of some key parameters on the seismic behavior of BCJs were investigated and discussed in detail. The parametric studies clearly illustrated that both adding the steel fiber and increasing the stirrup amount of joint core area could significantly improve the seismic behavior of BCJs. The axial compression ratio had limited influence on the seismic behavior of BCJs. Finally, based on the main factors (steel fiber volume ratio, stirrup amount, and axial compression ratio), a formula for predicting ultimate shear capacity is derived.

Experimental Study and Failure Mechanism Analysis of Rubber Fiber Concrete under the Compression-Shear Combined Action

In order to examine the compression-shear combined mechanical properties of rubber fiber concrete, an experimental study was carried out on rubber fiber concrete of three different configurations using a material compression-shear testing machine by considering different axial compression ratios. The failure modes and shear stress-strain curves of rubber fiber concrete under different loading conditions were obtained. By comparatively analyzing the mechanical parameters of rubber fiber concrete under different axial compression ratios, the following conclusions were drawn. With the increase of the axial compression ratio, the failure mode in the shear direction gradually developed from a relatively straight crack to a main crack accompanied by a certain amount of axial cracks; meanwhile, the number of concrete slags on the shear failure section was gradually increased and the friction marks were gradually deepened. The addition of rubber particles increased the randomness and discreteness of the concrete upon failure, while fibers inhibited the development of oblique micro-cracks and the dropping of concrete slags. The shear stress of the concrete specimen containing rubber particles was significantly lower than those without rubber particles. Comparatively, fibers showed little effect on the shear stress. As the axial compression ratio increased, the shear stress and shear strain of rubber fiber concrete were gradually increased, but the increasing amplitude of shear stress tended to become flattened. Under the influence of the axial compression ratio, the shear stress of C-0%-0%, C-30%-0%, and C-30%-0.6% was increased by 4.57 times, 3.26 times, and 2.69 times, respectively, suggesting a gradually decreasing trend. At the same time, based on the principal stress space and the octahedral stress space, the compression-shear combined failure criterion was proposed for the three different rubber fiber concretes. The research findings are of great significance to the engineering application and development of rubber fiber concrete.

Seismic Performance of Steel Fiber Reinforced High–Strength Concrete Beam–Column Joints

In high–strength concrete, the reinforcement concentration will cause some problems in the beam–column joints (BCJs) due to a large amount of transverse reinforcement. Hence, the main object of this paper is to prevent the reinforcement concentration and reduce the amount of transverse reinforcement in the BCJs through the ideal usage of steel fibers and reinforced high–strength concrete. Pseudo–static tests on seven specimens were carried out to investigate and evaluate the seismic performance of beam–column joints in steel fiber reinforced high–strength concrete (SFRHC). Test variables were steel fiber volume ratio, concrete strength, the stirrup ratio in the core area, and an axial compression ratio of the column end. During the test, the hysteresis curves and failure mode were recorded. The seismic indicators, such as energy dissipation, ductility, strength, and stiffness degradation, were determined. The experimental results indicated that the failure modes of SFRHC beam–column joints mainly included the core area failure and the beam end bending failure. With the increase in stirrup ratio, volume ratio of steel fiber, and axial compression ratio in the core area, both the ductility and energy consumption of beam–column joints increased, while the opposite was true for concrete strength.

Experimental Study on the Shear Performance of Steel-Truss-Reinforced Concrete Beam-Column Joints

In order to study the influence of the axial compression ratio and steel ratio on the shear-carrying capacity of steel-truss-reinforced beam-column joints, five shear failure interior joint specimens were designed. The effect of different coaxial pressure ratios (0.1, 0.2, and 0.3) and steel contents on the strain, ultimate bearing capacity, seismic performance, and failure pattern of cross-inclined ventral and chord bars in the joint core area was investigated. The experimental results show that the load-displacement hysteretic curves of all test specimens exhibit a bond-slip phenomenon. With the increase of the axial compression ratio, the ultimate bearing capacity of the joint core increases by 3.4% and 5.9%, respectively. While the ductility decreases by 10.3% and 13.1%, and the energy consumption capacity decreases by 3.2% and 5.8%, respectively. The shear capacity and ductility of the member with cross diagonal ventral steel angle in the joint core are increased by 12.9% and 13.4%, respectively. The shear capacity and ductility of the joint can be significantly improved by increasing the amount of steel in the core area. The expression of shear capacity suitable for this type of joint is obtained by fitting analysis, which can be used as a reference for engineering design.