High-Strength Concrete Beam-Column Joints Research Articles

Analysis on the Seismic Performance of Steel Fiber-Reinforced High-Strength Concrete Beam-Column Joints.

The present research study aims to investigate numerically the behavior of steel fiber-reinforced high-strength concrete (SFRHC) beam–column joints (BCJs) under seismic action. Based on the plastic damage constitutive model of concrete and elastic–plastic mixed-strengthen constitutive model of steel material, the finite element software ABAQUS was utilized to establish the 3D finite element (FE) model of BCJs. Additionally, the feasibility and accuracy of the numerical simulation were verified by comparing the computed results and experimental observations in terms of the hysteresis curves, skeleton curves, and failure mode. Furthermore, based on the validated FE modeling approach, load vs. displacement hysteresis curves of SFRHC–BCJs during the loading process were analyzed in detail; the failure process was also investigated. Furthermore, the effect of various parameters on the seismic behavior of BCJs was analyzed comprehensively, including the concrete strength, the volume ratio of steel fiber, and the stirrup ratio in the core area. Finally, parametric studies illustrated that increasing the concrete strength helps in enhancing the ultimate load, while the ductility decreased noticeably. Both adding the steel fiber and increasing the stirrup ratio can significantly improve the seismic performance of BCJs.

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.

Analytical Investigations of Reinforced Concrete Beam–Column Joints Constructed Using High-Strength Materials

ABSTRACTAnalytical investigations were carried out on high-strength concrete beam–column joints reinforced with high-strength steel rebars. The bond performance of test specimens was evaluated and compared with building code provisions. An analytical approach was obtained to study the influence of various patterns of column axial loading on the failure mechanism of beam–column joint subassemblies. In addition, a finite-element study was conducted to investigate the seismic behavior of reinforced concrete beam–column joints designed with high-strength materials. A novel recommendation for the joint depth to beam bar diameter ratio and the comparison between the proposed equations and those suggested by codes was presented.

High-Strength Concrete Interior Beam-Column Joints with High-Yield-Strength Steel Reinforcements

This study presents the experimental and analytical investigations carried out on high-strength concrete beam-column joints with Grade 700 longitudinal bars in beams and columns. Seven full-scale interior RC beam-column joints with various reinforcement detailing were designed according to the specific seismic provisions of current building codes. Test specimen variables included concrete compressive strength, reinforcement yield strength, and axial compression loading level. The test specimens were subjected to constant column axial loading and quasi-static lateral load reversals. The performance of each test assembly was examined in terms of cracking patterns, lateral loading capacity, reinforcement strain profiles, secant stiffness, energy dissipation capacity, joint shear strength, and bond performance. All specimens displayed ductile failure mode and it is concluded that the use of high-strength concrete and applied axial compression loading can improve specimen bond conditions. Parametric studies via finite-element analysis were performed to examine the influence of various parameters on the strength, bond condition, and energy dissipation capacity of the specimens. In addition, a backbone curve model for the shear behavior of the joints is proposed. An explanation for the observed cracking pattern and further analytical investigation on the joint shear capacity of the specimens is presented.

Experimental and Numerical Investigations of the Seismic Behavior of High-Strength Concrete Beam-Column Joints with Column Axial Load

This paper presents the experimental findings of high-strength concrete (HSC) interior beam-column joints under column axial compressive loading. Eight full-scale interior beam-column joints with varying degrees of reinforcement detailing were subjected to a constant column axial compressive load and quasi-static horizontal cyclic load. The test revealed that HSC improved the bond condition of bars with a larger diameter due to the higher achievable bond stress, thereby allowing for the use of longitudinal beams of a larger diameter. Parametric studies via finite-element (FE) modeling were performed to study the influence of various parameters on the strength and bond of HSC beam-column joints. The study confirmed that reinforcement of larger diameter can be used in HSC beams with the improvement in the bond condition. The presence of axial compressive load improved the bond stress of HSC beam-column joint but a threshold limit should be applied. Last, two standards were reviewed and improvements to the design equations were proposed.

Seismic Testing and Performance of Precast High-Strength Concrete Beam-Column Joints Subjected to High Axial Tension

High-rise buildings are subjected during severe earthquakes and strong winds to intensive large axial and lateral loads, particularly at their lower stories, where the exterior columns experience varying high axial loads. Herein, the seismic performance of two precast high-strength reinforced concrete exterior beam-column joints subjected to different varying high-axial levels is investigated while premature shear failure is generally suspected. High-grade steel bars were used for reinforcement. Splice grout-sleeves and mechanical anchors were used in the columns and beams, respectively. The strength of the concrete was 70 MPa. The maximum axial tension level in columns was 90% of the yield strength of the main bars. Under high axial tension, the tested subassemblies exhibited stable response, good damping characteristics, appropriate lateral force resistance and energy absorption capacity. They performed well within the lateral story drift angle of 3% where the successive failure modes (beam/column flexural yielding followed by joint shear failure) confirmed the appropriateness of the design equations in AIJ and ACI regulations. Furthermore, the use of mechanical anchors proved to be very effective and no sign of concrete crushing (pushing toward the exterior face of the joint) was observed within the lateral story drift angle of 2%.

Strengthening of reinforced high-strength concrete beam–column joints using advanced reinforcement details

Lack of ductility in high-strength concrete members raises serious concerns for overall structural safety, especially for reinforced concrete beam–column joints. In the current study, experimental research was performed to improve the seismic strength and performance of reinforced high-strength concrete exterior beam–column joints under cyclic load reversals. A new design approach for beam–column joints was introduced using advanced reinforcement details. Specimens of reinforced high-strength concrete beam–column joints were manufactured based on the new design method developed from the concept of a moving beam plastic hinge using anchor-type intermediate bars and advanced details of doubly confined closed stirrups in the beam near the joint, and tested for comparison with specimens designed using the conventional approach. The newly developed design approach minimised damage and considerably improved the structural performance of beam–column joints under cyclic load reversals. The manufactured joints were expected to be effective in improving the weakness induced by the brittleness of high-strength concrete in reinforced high-strength concrete beam–column joints.

General Analytical Model for Nominal Shear Stress of Type 2 Normal- and High-Strength Concrete Beam-Column Joints

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Response of reinforced high-strength concrete beam–column joints under load reversals

With the increasing use of high-rise reinforced concrete structures, high-strength materials, smaller member sections and larger reinforcing bars should be employed. Therefore, the stress resistance capacity of a joint is also required to be increased over other parts of a structure. The application of high-strength concrete has progressively increased in many structures, and it has now been used in many parts of the world. Previous research1–3 has shown that the behaviour of a reinforced high-strength concrete structure subjected to monotonic or earthquake-type loading is significantly different from that of a reinforced normal-concrete structure. It tends to be brittle when overloaded to failure, and to show a more sudden appearance of microcracking. Lack of ductility in concrete members raises serious concerns for structural safety. The behaviour of reinforced high-strength concrete members and joints must be accurately assessed before high-strength concrete can be used with confidence in reinforced concrete frame structures. The objective of this experimental research was to study the behaviour of reinforced high-strength concrete beam–column joints, and to develop a new approach for the design of such joints in high-rise reinforced concrete buildings.