Seismic behavior of exteriorbeam–column joints with high-performance steel rebar: Experimental and numerical investigations

Three full-scale exterior beam–column joints with anti-seismic steel reinforcement were tested under quasi-static cyclic loading and column axial compressive loading. The test variables were column axial load ratio and joint core hoop reinforcement ratio. Experimental results, including failure mode, hysteretic curve, ductility, energy dissipation, stiffness degradation, and decoupling of deformations, were presented and analyzed. The tests revealed that the anti-seismic rebar resulted in good joint seismic performance and that column axial load ratio and joint core hoop reinforcement ratio impose limited influence of joint performance when the joint failed in beam flexural failure. The calibrated finite element models developed based on OpenSees were then used to simulate the behavior of joint specimens. Parametric studies via finite element modeling were performed to study the influence of various parameters on the performance of beam–column joints.

Analytical Study on the Effective Flange Width for T-shaped Shear Walls

This study was organized to derive simplified expressions to estimate the effective flange width for T-shaped shear walls at different loading stages. For that purpose, the variation in the effective flange width was explored by introducing dimensionless effective flange width coefficient. According to the principle of minimum potential energy, the theoretical expression of the effective flange width coefficient in the elastic stage was obtained. Furthermore, a parametric study considering the axial load ratio, height-width ratio of flange and width-thickness ratio of the flange, as well as the section aspect ratio was conducted to determine the effective flange width using verified nonlinear finite-element models. In light of the parametric analysis results, a formula model was proposed depending on the axial load ratio and height-width ratio of flange. Finally, the predictions of the proposed simplified formulas were verified with the theoretical solutions or finite element (FE) results, which indicated that the proposed formulas can accurately capture the effective flange width at the elastic, yield and limit state.

Experimental Investigation on Seismic Resistance of RC Shear Walls with CFRP Bars in Boundary Elements

Experimental investigation on seismic performance of RC shear walls reinforced with CFRP bars in boundary elements to enhance the resilience was presented which is expected for stable resistance capacity and small residual deformation. Six RC shear walls reinforced with CFRP bars as longitudinal tensile materials in boundary elements were tested under reversed cyclic lateral loading while subjected to constant axial compression with different axial load ratios of 0.17, 0.26 and 0.33, respectively. Two forms of stirrups were used for each axial load ratio, which were rectangular and circular stirrups in boundary elements. A reference specimen, ordinary RC shear walls, was also introduced to certify the excellence of CFRP bars. The test results indicated that the walls utilizing CFRP bars had small residual deformations and residual crack widths. Lower crack propagation height and larger concrete crushing region, bearing capacity and equivalent viscous damping coefficient (EVDC) could be observed with the increase of axial load ratios. The effects of stirrup forms on experimental results had a relation to the axial load ratio. When the axial load ratio was small, the shear walls with circular stirrups had better energy dissipation than that with rectangular stirrups at a given drift level, while the cumulative energy dissipation (CED) were similar. With the increase of axial load ratio, the walls exhibited similar energy dissipation at the same drift level, however, the shear walls with rectangular stirrups had larger CED.

Experimental study on the cyclic behavior of ultra high performance concrete–filled steel tube beam-columns

This article experimentally investigates the cyclic behavior of ultra high performance concrete–filled steel tube beam-columns. A total of eight specimens were tested. The considered parameters were the axial load ratio and steel ratio. The results showed that all ultra high performance concrete–filled steel tube beam-columns had a very good cyclic behavior without significant pinching. Increasing the axial load ratio results in the decrease of strength and ductility, but it has no obvious influence on the initial flexural stiffness. Reducing the steel ratio results in the decrease of the strength, stiffness and ductility, and energy dissipation capacity.

Experimental behaviour of hollow reinforced concrete members with inner octagonal steel tube under lateral impact

This work investigated the impact performance of hollow reinforced concrete members with inner octagonal steel tube. Experiments on 13 specimens subjected to low-velocity drop weight impact are presented in this article, covering key parameters such as the impact height, boundary condition, axial load ratio and thickness of the inner tube. The dynamic processes, failure patterns, impact force and mid-span deflection histories, and residual mid-span deflections were obtained from the experiments. Flexure-shear was observed as the main failure pattern for all the specimens under impact. It was found that all the key parameters considered had influences on the impact performance of hollow reinforced concrete specimens with inner octagonal steel tube. Effects of these parameters on the impact performance of hollow reinforced concrete members were discussed.

Assessment of ultimate drift capacity of RC shear walls by key design parameters

The latest version of the Standard for Structural Calculation of Reinforced Concrete Structures, published by the Architectural Institute of Japan in 2010 [1], allows the design of shear walls with rectangular cross sections in addition to shear walls with boundary columns at the end regions (referred to here as “barbell shape”). In recent earthquakes, several reinforced concrete (RC) shear walls were damaged by flexural failures through concrete compression crushing accompanied with buckling of longitudinal reinforcement in the boundary areas. Damage levels have clearly been shown to be related to drift in structures; this is why drift limits are in place for structural design criteria. A crucial step in designing a structure to accommodate these drift limits is to model the ultimate drift capacity. Thus, in order to reduce damage from this failure mode, the ultimate drift capacity of RC shear walls needs to be estimated accurately. In this paper, a parametric study of the seismic behaviour of RC shear walls was conducted using a fibre-based model to investigate the influence of basic design parameters including concrete strength, volumetric ratio of transverse reinforcement in the confined area, axial load ratio and boundary column dimensions. This study focused on ultimate drift capacity for both shear walls with rectangular sections and shear walls with boundary columns. The fibre-based model was calibrated with experimental results of twenty eight tests on shear walls with confinement in the boundary regions. It was found that ultimate drift capacity is most sensitive to axial load ratio; increase of axial load deteriorated ultimate drift capacity dramatically. Two other secondary factors were: increased concrete strength slightly reduced ultimate drift capacity while increased shear reinforcement ratio and boundary column width improved ultimate drift capacity.