Strength Of Coupling Beams Research Articles

Seismic performance and shear strength of coupling beams using engineered cementitious composites with different reinforcement layouts

The coupling beam is the key component in high-rise coupled-wall and core-tube structures. To further improve the seismic performance and damage tolerance of traditional reinforced concrete coupling beams, engineered cementitious composites (ECC) becomes a prospective choice, due to the superior characteristics including tension strain-hardening and multi-cracking properties. However, there have been only limited researches on ECC coupling beams, causing the lack of comprehensive understanding of the seismic behaviour and practical design formula. In this study, eight large-scale ECC coupling beam specimens with different aspect ratios, transverse and diagonal reinforcement ratios are fabricated and cyclically tested. The seismic performance of coupling beams is thoroughly investigated in terms of the damage and failure modes, energy dissipation, stiffness deterioration, strength degradation and shear distortion. The contribution of ECC, transverse and diagonal reinforcement to the shear strength is evaluated and compared. Besides, the whole-process hysteretic curves of the axial force are reported for the first time. Finally, a shear strength equation is proposed based on the analysis of nineteen specimens collected from the literature and this study. The test results demonstrate that ECC coupling beams with a hybrid reinforcement layout exhibit superior seismic performance, which is a reasonable choice to balance both the seismic and construction performance. It is strongly recommended that axial force should be considered in the strength prediction of coupling beams, with a 10% axial force ratio suggested for design. The proposed method is verified and can give precise prediction for the bearing capacity of ECC coupling beams.

Hysteretic Behavior of Conventionally Reinforced Concrete Coupling Beams in Reinforced Concrete Coupled Shear Wall

This paper presents the experimental results of four full-scale coupling beams in which only horizontal reinforcements are placed, without diagonal reinforcements, with the aim to develop reinforcement details for coupling beams used in connecting side walls in a wall-slab structural system. Each coupling beam specimen was designed according to the deep-beam design procedure that does not use diagonal reinforcements and that is found in current standards. Two cases for basic deep-beam design specimens were investigated wherein (1) U-type reinforcement was added to prevent sliding shear failure of the joints and (2) horizontal intermediate reinforcements were placed. The coupling beam specimens were fabricated with a shear span-to-depth ratio (aspect ratio) of 1.68 and were connected to walls only by horizontal reinforcements, i.e., without diagonal reinforcement. The experimental results indicate that the strength of the beams was about 1.5 times the designed strength of a strut-and-tie model, which suggests that the model is available for predicting the strength of coupling beams with conventional reinforcement layouts such as horizontal and transverse reinforcement bars. The deformation capacity of these conventionally reinforced concrete coupling beams ranged from 1.48 to 3.47% in accordance with the reinforcement layouts of the beams. Therefore, this study found that the performance of conventionally reinforced concrete coupling beams with an aspect ratio of 1.68 can be controlled through the implementation of reinforcement details that include U-type reinforcement and the anchorage of intermediate horizontal bars.

병렬전단벽의 강도와 강성이 커플링보의 설계내력에 미치는 영향

본 연구에서는 초고층건물의 횡력저항 구조형식으로 널리 사용되는 병렬전단벽-커플링보 구조시스템에서 전단벽의 강도, 강성이 커플링보의 설계 강도에 미치는 영향을 분석하였다. 커플링보에 발생하는 설계내력은 코어벽체의 두께와 콘크리트의 강도가 변하더라도 층별 설계내력은 유사한 경향을 보이고 있으며, 벽체 콘크리트 강도와 두께에 따라 커플링보에 발생하는 외력은 다소 감소하는 경향이 있다. 커플링보의 설계내력은 6개 모델 전부 40층 건물에서, 10층에서 15층의 범위에서 가장 높게 발생하고 있음을 알 수 있다. 즉, 병렬전단벽의 휨변형 변곡점이 형성되는 건물높이의 0.25H~0.375H 위치에서 최대 부재력이 발생한다. 벽체두께가 증가 할수록 코어내부의 커플링보의 발생 외력은 점차 증가하는 것으로 확인되었다. 또한 벽체 두께가 두꺼워질수록 벽체의 콘크리트 강도 증가에 따른 커플링보의 부재력 변화는 적게 나타나는데, 이는 벽체 두께가 두꺼우므로 콘크리트 강도변화의 영향이 적게 미치는 것으로 분석된다. 병렬전단벽의 두께증가는 콘크리트의 강도증가보다 강성변화에 큰 영향을 미치고, 이에 따라 커플링보의 부재력 변화에도 더 큰 영향을 미치는 것으로 분석된다. In this research, the effects of the strength and stiffness of shear walls on the design strength of coupling beams are studied in the shear wall-coupling beam structural system widely used as the lateral-drift resistant system of high-rise buildings. The results show that the design strength of the coupling beams decreases with decreasing concrete strength and core wall thickness, but the shape remains unchanged. In all six models, the design strength of the coupling beams has the largest value at the 10~15th floors in a 40-story building. In other words, the design strength of the coupling beams has the largest value at 0.25H~0.375H where the inflection point exists. The thicker the walls, the smaller the change in the member forces. The thickness of the coupled shear walls has more influence on the design strength of the coupling beams than the concrete strength.

Experimental study of a replaceable steel coupling beam with an end-plate connection

In order to enhance the post-damage repair capability of the hybrid coupled shear wall systems, a different type of replaceable steel coupling beam with end-plate connection was investigated. Different from conventional configurations, the coupling beams were not embedded into the walls to minimize the post-event repair/replacement difficulties and expenses. To assess the seismic behavior and post-damage replaceability of the coupling beam, a two-stage experimental program was performed to test the full-scale specimens, each utilizing coupling beams with different strength and stiffness. The results of the first specimen indicated a ductile failure with a concentration of inelastic deformation at steel web and thus exhibited desirable deformation and energy absorption capacities with minimum damages to the shear wall. Again, on the minimum repaired wall-pier, the second specimen via the proposed connection, with improved characteristics such as strength and stiffness, was installed and tested. The results demonstrated excellent stiffness, strength, and ductility characteristics of subassemblages under cyclic loading, with considerable energy dissipation concentrated in the coupling beam web. Although the second specimen failed from the threaded area of the tensile bolts, due to increased coupling beam strength, the specimens were able to sustain large nonlinear displacements without significant damage in the connection to the wall pier regions; representing that this connection configuration would require little repair, if any, after a severe earthquake.

Evaluation of Coupling Beams Behavior Concrete Shear Wall with Rectangular and Octagonal Openings

Reinforced concrete coupled walls are cantilevered shear walls joined by coupling beams and are used in high-rise apartment for many years. Rectangular openings are the most common shape of openings used in shear wall in order to provide doors, windows, entrance to car park areas and elevators or staircases. Behavior of coupling beams affect the strength of coupled walls. This research suggests adding haunches to the corners of rectangular openings and form octagonal openings as a method to increase the strength of coupling beams. The experimental results of shear wall with single band of rectangular and octagonal openings are compared in terms of behavior of coupling beams under cyclic load. The results demonstrate that the coupling beams in shear wall with octagonal openings are stronger than coupling beams in shear wall with rectangular openings.

이중골조형식 고층건물 커플링보의 실용설계

In this study, practical design method of coupling beams is proposed. The member forces varies according to the location of the members and the members at 25%~40% of building height shows large member forces. The 100mm increase of wall thickness causes 3~4% variation of member forces and the 100MPa increase of concrete strength decrease approximately 3% of member forces. The required strength of coupling beams is twice the resistant strength and 80% reduction of coupling beam stiffness is necessary to fulfill the design criteria. The stiffness reduction of coupling beams is not necessary over the entire stories and the strength reduction range can be estimated considering design requirements.

The Seismic Behavior of Pseudo Strain-Hardening Cemetitious Composites Coupling Beams with Polyvinyl Alcohol Fiber

This paper addresses the seismic behavior of pseudo strain hardening cementitious composite (PSH2C) coupling beams with different failure modes in hybrid coupled shear wall. Test variables included the ratio of steel coupling beam strength to beam-wall connection strength. The results show that Specimen PSH2C-SCF exhibits a better stable behavior in comparison with Specimens PSH2C-SBVRT and PSH2C-FCF.

Seismic Behavior and Bearing Capacity Calculation of the Three-Layer-Closed-Restraining Stirrups Coupling Beam with Small Span-to-Depth

Seismic behaviors of the nine coupling beam specimens that three-layer-closed-restraining stirrups arranged in the coupling beam section depth direction were investigated experimentally. Effects of span-to-depth, amount of stirrups and longitudinal bars of coupling beam on its failure mode are studied, as well as the hysteretic behavior, stiffness degradation, and deformation capacity. Coupling beams with span-to-depth ratio of 0.75－1.5 were observed to suffer shear failure or flexural-shear failure, no matter whether longitudinal reinforcements yield or not. The existing of three-layer-closed-restraining stirrups along the section depth of coupling beam effectively improved its deformation and energy dissipation capacity. According to the experimental results, the formulae for estimating shear strength of the coupling beams were suggested considering the effect of longitudinal reinforcements. Estimated shear strength of coupling beams agreed well with the experimental data.

Seismic behaviour and design of steel coupling beams in a hybrid coupled shear wall systems

The hybrid coupled shear wall system is more efficient and economical than individual structural walls because the steel coupling beams connected shear walls significantly increase the strength, stiffness and energy dissipation capacity of the system. In this study, experimental studies on the steel coupling beam were carried out. The main test variables were the ratios of the coupling beam strength to the connection strength. In addition, the seismic design methods are presented for steel coupling beam–wall connection and shear critical and flexure critical steel coupling beams in hybrid coupled shear wall system consisting of steel coupling beams and reinforced concrete shear walls. Finally, this paper provides background for design guidelines in hybrid coupled shear walls that include steel coupling beam–wall connections and steel coupling beams.

Experimental studies on seismic behavior of steel coupling beams

Hybrid coupled shear walls in tall buildings are known as efficient structural systems to provide lateral resistance to wind and seismic loads. Multiple hybrid coupled shear walls throughout a tall building should be joined to provide additional coupling action to resist overturning moments caused by the lateral loading. This can be done using a coupling beam which connects two shear walls. In this study, experimental studies on the hybrid coupled shear wall were carried out. The main test variables were the ratios of coupling beam strength to connection strength. Finally, this paper provides background for rational design guidelines that include a design model to behave efficiently hybrid coupled shear walls.

Seismic behaviour of coupling beams in a hybrid coupled shear walls

Steel coupling beams in a hybrid coupled shear wall provide a viable alternative for concrete coupling beams coupling individual reinforced concrete wall piers. Due to the lack of information, current design methods for calculating embedment lengths are silent about cases in which hybrid coupled walls have connection details of stud bolts and horizontal ties. In this work, an analytical study was carried out to develop a model for calculating the embedment lengths of embedded steel sections. Five models for calculating embedment lengths in a hybrid coupled wall are developed as variations of the Prestressed Concrete Institute guidelines for steel brackets attached to reinforced concrete columns. In addition, experimental studies on the hybrid coupled shear wall were carried out. The main test variables were the ratios of the coupling beam strength to the connection strength. The test results indicate that it is more advantageous to design the coupling beams as shear yielding members since the shear-critical coupling beam exhibits a more desirable mode of energy dissipation than the flexure-critical coupling beam.