This paper presents an experimental study on the structural behavior of low yield point steel(LYP225)under both monotonic and cyclic loading under the triaxial stress states.A total of 14 tensile tests on four types of specimens with various initial geometries were conducted to establish monotonic mechanical properties of LYP225 steel under triaxial stress states,and 10 ultra-low cyclic tests(cycles＜100)were carried out to study the ultra-low cycle fatigue of LYP225 steel under various loading systems.A combination of both isotropic and kinematic hardening characteristics can be observed from the hysteresis curves of LYP225 steel.The A-F(Armstrong-Frederick)plasticity constitutive model of LYP225 steel including the characteristics of both isotropic and kinematic hardening was calibrated based on an optimization algorithm.The influences of stress triaxiality and Lode angle on fracture ductility of LYP225 steel were investigated.A fracture criterion with combination of stress triaxiality and Lode angle was proposed.An ultra-low cyclic fracture criterion,termed as CBW was established based on the accumulation of ductile damage and the attenuation of ductile damage threshold.
A self-centering concrete-filled square steel tubular frame with slit steel plate shear walls (SC-SSPSW) adopting post-tensioned (PT) column base was proposed in this study. The slit steel plate shear walls (SSPSWs) with edge stiffeners were only connected to the beams. Cycle tests were conducted on three 1/3 scaled single-span twostory specimens to investigate their mechanical and seismic behavior, and the formulas for beam and column internal forces considering frame expansion effects were derived. Finite element (FE) models of SC-SSPSWs were established, and the FE results agreed well with the test results. The results indicate that the hysteretic curves of specimens exhibit a typical double flag shape, and the residual deformation of all specimens is approximately 0.20% when loading to 2.0% story drift. Damage is primarily concentrated in the SSPSWs while other structural members remain elastic, and favorable resilience and energy dissipation capacity are achieved. With an increase in the width-to-thickness ratio or aspect ratio of links while keeping the thickness of SSPSWs unchanged, the energy dissipation decreases, and the self-centering capacity improves. The column that expands in the same direction as the loading direction bears more lateral loads. The theoretical gap opening value, PT tendons force, as well as beam axial force agree well with the test and FE results.
The combination of polyvinyl chloride(PVC)with corrosion resistance,carbon fiber(CFRP of lightweight and high-strength)and spiral reinforcement(with strong plastic-ity)can make full use of the characteristics of the materials,in order to provide constraints for concrete and effectively improve the mechanical properties of reinforced concrete.To study the seismic performance of concrete columns with spiral reinforcement embedded in CFRP-PVC tubes,low cycle repeated loading tests were completed on 9 specimens with va-rying parameters of spiral reinforcement diameter,spiral reinforcement spacing and shear span ratio.The results show that most of the specimens fail due to compression bending of CFRP-PVC composite tube,and the spiral reinforcement provides significant restraint in the compression area after reaching the ultimate load,which may improve the seismic perform-ance of concrete columns;The failure ductility of all specimens may range from 2.76 to 4.35,and the ultimate inter-story drift ratio is greater than 1/30,which meets the require-ments of the specification;The decrease of the diameter of spiral stirrups,the increase of the spacing of spiral reinforcements and the increase of the shear span ratio all reduce the shear capacity and ductility of the specimens,but they have little effect on the stiffness deg-radation.The refined finite element model built by ABAQUS software can accurately predict the bearing capacity and internal concrete cracking behavior of CFRP-PVC spiral reinforce-ment composite confined concrete columns under constant axial force and repeated horizontal force.The parameter analysis shows that the axial compression ratio and concrete strength significantly affect the bearing capacity and deformation capacity of the specimen,and the strength and diameter of the longitudinal reinforcement have a great impact on the bearing capacity and the stiffness of the specimen after its yielding.The relationship between the con-crete strength and the limit value of the axial compression ratio is proposed.The proposed calcu-lation method of the compression bending bearing capacity of the concrete columns has good ap-plicability for the cases with low axial compression ratio and ordinary strength grade concrete.
An eccentrically braced composite frame with a low-yield-point (LYP) steel shear link is an efficient energy dissipation system that exhibits good mechanical properties. However, existing experimental studies have not fully demonstrated the superiority and applicability of the structural system. We present a structural mechanics and finite element model analysis of an eccentrically braced composite frame with a vertical shear link. The effect of the design parameters on the seismic performance of the structure is analyzed. First, a theoretical model of the mechanics of the structural system is established to provide a comprehensive description of the key parameters. Then, a finite element model is developed using the computer program ABAQUS to analyze the mechanical and energy dissipation mechanisms. Finally, the beam-to-column stiffness ratio, shear link web thickness, shear link web width and length, and diagonal brace stiffness are analyzed to determine their effects on the mechanical properties of the structural system. Furthermore, some design parameter values are suggested.
This paper presents the results of field tests performed to investigate the installation effects of pre-bored grouted planted (PGP) pile in deep clayey soil. The variation of horizontal soil displacements, excess pore water pressures and lateral soil pressures was measured in the PGP pile installation process. The test results show that the drilling and grouting process induced large horizontal soil displacements in the soil within a radial distance of 2 d ( d is pile diameter), and the maximum horizontal soil displacements induced by the drilling and grouting process were smaller than 15.9 mm when the radial distance reached 4–5 d. Moreover, the horizontal soil displacements decreased along the soil layer depth, as the superficial soil layers were of small deformation modulus and lateral soil pressure. The drilling process brought large excess pore water pressures in the soil when the radial distance was less than 3 d, and the excess pore water pressures induced by the drilling stage were all less than 55 kPa when the radial distance reached 4–6 d. The drilling process also induced some lateral soil pressure increases in the soil within a radial distance of 3 d, while the measured maximum lateral soil pressure increases were smaller than 10.9 kPa when the radial distance increased to 4 d. On the whole, the excess pore water pressures and lateral soil pressure increases induced by the installation of PGP pile were much smaller than that induced by the installation of driven PHC pile. Moreover, the horizontal soil displacements, excess pore water pressures and lateral soil pressure increases induced by the installation of PGP pile all recovered rapidly after the installation of pile, as the cemented soil in the pile hole was in liquid state after the drilling and grouting stage.
