Low-rise Shear Walls Research Articles

Cyclic behavior of self-slitting squat composite shear walls with concrete-filled steel tubes: Experiment

To improve the deformation capacity of low-rise shear walls, an alternative approach of self-slitting squat composite shear wall with concrete-filled steel tubular columns (SSLSST) was proposed by the authors. This paper presents the experimental results of five SSLSST specimens subjected to cyclic loading, experimental parameters included steel tube thickness (ts), spacing of transverse reinforcement (S), axial compression ratio (n), and shear stud arrangement of inner steel tube. The results showed that owing to weakened effects of both horizontal anchorage to concrete and vertical shear resistance, the self-slit occurred in the SSLSST specimen with half-section shear studs of inner steel tube; SSLSST specimens maintained integrality to resist lateral force like the normal shear wall before the yielding status; with the lateral deformation increasing, the SSLSST specimens were divided into three independent column-type segments to jointly resist both lateral and compressive forces, and the seismic damage mainly concentrated within the slits, resulting in the seismic damage of the whole shear wall body was reduced. Increasing both S and ts can not only greatly improved the seismic resistance and ductility but also reduced the seismic damage and post-earthquake residual deformation (PERD). As expected, high n was not beneficial for the ductility ratio, energy dissipation, and PERD. Generally, the proposed SSLSST showed slight seismic damage, good seismic resistance capacity, ductility, and self-centering ability. Therefore, it is worthy to promote this new type of low-rise shear wall system to actual engineering.

Analysis of the Seismic Performance of a Masonry Structure with RC Frames on the First Story with Concrete-Filled Steel Tubular Dampers

The concrete shear walls of masonry structures with RC frames on the first story are low-rise shear walls with a height–width ratio of less than 1. The strength, stiffness, and ductility of these low-rise shear walls are not matched, resulting in poor seismic performance. Based on the idea of the passive control theory and multi-seismic defensive lines, the scheme of a masonry structure with RC frames on the first story with a concrete-filled steel tubular (CFST) dampers is proposed in this paper. To explore the seismic mitigation effect of CFST dampers applied to a masonry structure with RC frames on the first story, the seismic performance under low-reversed cyclic loading of the frame with the CFST dampers is first compared with that of the energy-dissipated low-rise concrete shear wall proposed by previous researchers and the ordinary low-rise concrete shear wall. Furthermore, the response of the masonry structure model with RC frames on the first story with CFST dampers and two other comparative structural models under earthquake action are discussed. The results show that a masonry structure with RC frames on the first story with CFST dampers has a fuller hysteretic loop, lighter pinching, better energy dissipation ability, and better seismic performance. Compared with the other two structures, the energy dissipation capacity of the masonry structure with RC frames on the first story with CFST dampers is significantly improved, by 1.25~1.5 times. The amplification effect of the deformation angle allows the CFST dampers to play a significant role in energy dissipation, whereas the main structure still undergoes a small deformation. The CFST dampers can dissipate more seismic energy to protect the main structure from damage and improve the seismic performance of masonry structures with RC frames on the first story.

Ciklični odgovor konstrukcij iz strižnih sten, spetih s skritimi sponami, v zgradbah z majhnim številom nadstropij

Ciklični odgovor konstrukcij iz strižnih sten, spetih s skritimi sponami, v zgradbah z majhnim številom nadstropij

EXPERIMENTAL STUDY ON SEISMIC BEHAVIOR AND SHEAR STRENGTH CALCULATION OF HIGH DUCTILE CONCRETE LOW-RISE SHEAR WALL

The usage of high ductile concrete (HDC) in low-rise shear walls was proposed to improve their seismic behavior. The effects of axial load ratio, the amount of horizontal reinforcement and steel plate on failure patterns, ductility and energy dissipation capacity of shear walls were studied by quasi-static tests of five shear walls with the shear span ratio of 1.0. The results showed that the deformability of the HDC low-rise shear walls is significantly improved compared with the high-strength concrete low-rise shear walls. The energy dissipation capacity and deformability of shear walls are improved with the increase of the axial load ratio and the decrease of the spacing of horizontal reinforcement. The collaborative work between HDC and steel plate improves the shear capacity and energy dissipation capacity of the low-rise shear walls. A formula for calculating the shear capacity of the HDC low-rise shear walls is proposed based on the softened strut-and-tie model, and the calculation values agree well with the test data.

Experimental study on seismic performance of low-rise recycled aggregate concrete shear wall with single-layer reinforcement

A total of four full-scale low-rise recycled aggregate concrete shear wall specimens were tested adopting a quasi-static loading method to analyze the seismic performance. The low-rise shear walls consisted of recycled aggregate concrete, single-layer reinforcements, concealed special-shaped columns, and expanded polystyrene thermal insulation modules. Based on the experimental results, the seismic performance and failure characteristic of the specimens were comparatively analyzed. The factors affecting the seismic performance of the low-rise shear wall were also analyzed. The shear bearing capacity calculation model and formula of the walls were proposed based on the softened strut-and-tie model. A comparison of the calculated results and the experimental results shows that they are in good agreement. The results show that the load bearing capacity and deformation capacity can be significantly improved by expanded polystyrene thermal insulation modules, and that the shear wall specimens with higher recycled aggregate concrete strength and larger reinforcement ratio of the shear wall exhibit better seismic performance.

Seismic Performance of Composite Shear Walls Constructed Using Recycled Aggregate Concrete and Different Expandable Polystyrene Configurations.

The seismic performance of recycled aggregate concrete (RAC) composite shear walls with different expandable polystyrene (EPS) configurations was investigated. Six concrete shear walls were designed and tested under cyclic loading to evaluate the effect of fine RAC in designing earthquake-resistant structures. Three of the six specimens were used to construct mid-rise walls with a shear-span ratio of 1.5, and the other three specimens were used to construct low-rise walls with a shear-span ratio of 0.8. The mid-rise and low-rise shear walls consisted of an ordinary recycled concrete shear wall, a composite wall with fine aggregate concrete (FAC) protective layer (EPS modules as the external insulation layer), and a composite wall with sandwiched EPS modules as the insulation layer. Several parameters obtained from the experimental results were compared and analyzed, including the load-bearing capacity, stiffness, ductility, energy dissipation, and failure characteristics of the specimens. The calculation formula of load-bearing capacity was obtained by considering the effect of FAC on composite shear walls as the protective layer. The damage process of the specimen was simulated using the ABAQUS Software, and the results agreed quite well with those obtained from the experiments. The results show that the seismic resistance behavior of the EPS module composite for shear walls performed better than ordinary recycled concrete for shear walls. Shear walls with sandwiched EPS modules had a better seismic performance than those with EPS modules lying outside. Although the FAC protective layer slightly improved the seismic performance of the structure, it undoubtedly slowed down the speed of crack formation and the stiffness degradation of the walls.

Shaking Table Tests of Low-Rise Shear Walls Made of Recycled Aggregate Concrete

Experimental studies on the structural reinforced-concrete shear wall members using recycled aggregate concrete (RAC) have been focusing on static loading conditions. The dynamic tests on the reinforced concrete members made of RAC are fairly few. Shaking table tests are necessary because it is difficult to predict the influence of variations in particular properties on the overall dynamic behaviour of the reinforced RAC shear walls made of various mixed materials. The aim of the research work presented in this paper was to investigate the dynamic behaviour of shear walls made of RAC, with different recycled aggregates and reinforcement arrangements, in comparison with shear walls made of natural aggregate concrete (NAC). Five low-rise shear walls were tested in this project: a shear wall made of NAC, a shear wall made of recycled coarse aggregate concrete, and three shear walls made of recycled coarse and recycled fine aggregate concrete with different reinforcement arrangements. Dynamic characteristics and responses of all specimens at different loading stages were determined experimentally, and a comparison of failure modes was presented. The earthquake response time-history analysis of each specimen was also conducted using the finite element software ABAQUS. The ABAQUS results showed good agreement with the test results. The comparison of results showed that, when the reinforcement arrangement was the same, the seismic performance of the shear wall made of recycled coarse and recycled fine aggregate concrete was weakened greatly compared with that of the shear wall made of NAC. The seismic performance of the shear wall made of recycled coarse aggregate concrete was similar to that of the shear wall made of NAC. The seismic resistance capacity of the shear wall made of RAC could be greatly improved by installing concealed bracings.

Seismic Behavior of the Low-rise Shear Wall with CFST Frame and Embedded Steel-plate

In this paper, two low-rise shear wall specimens are tested on the shaking table, one is shear wall with CFST frame and embedded steel-plate, the other one is no concrete outside the steel-plate in comparison of the first one. The reduced scale of the two specimens is 1/12. The seismic wave “Taft” is input in the shaking table test. Based on the experiment, the author conducts the time history analysis (including elastic stage and plastic stage) of the specimens. The calculated results and measured results are compared.

Simplified Method for the Seismic Design of Low-Rise, Shear Wall Base- Isolated Buildings

A simplified method for the seismic design of low-rise, base-isolated shear wall structures is proposed in MOC-2012. This simplified method is basically a hybrid method, where the design of the isolation system is a simpler version for the static method available in US guidelines for the design of base-isolated structures and the design of the superstructure essentially is an improved version of the simplified method for the seismic design of conventional low-rise shear wall structures of Mexican seismic codes. The application of this method and its effectiveness to obtain safe designs is illustrated with a practical example. It is anticipated this simple methodology would help promote the use of base isolation in low-rise shear wall structures and reduce their vulnerability when subjected to strong earthquakes.

Seismic Behavior of RC Low-Rise Shear Wall with Vertical Mild Steel-Lead Energy Dissipation Strips

A RC shear wall with vertical mild steel-lead energy dissipation strips was proposed as an improvement in seismic behavior over existing shear wall designs. In order to test and ascertain the projected increase in performance, five low-rise shear wall specimens: one normal RC shear wall, one RC shear wall with slits, two shear walls with vertical X style mild steel energy dissipation strips under different design parameters, and one shear wall with vertical X style mild steel-lead energy dissipation strips were tested under cyclic loading. Based on the experiment, the damage characteristics, hysteresis characteristics, load-carrying capacity, stiffness, ductility, and energy dissipation of the specimens were comparatively analyzed. Results show that the ductility and energy dissipation of the RC low-rise shear wall with vertical X style mild steel energy dissipation strips and the one with X style mild steel-lead energy dissipation strips offer a significant improvement in seismic performance over accepted designs. In addition, the failure behavior of the low-rise shear wall tended towards bending failure rather than shear failure.

Experimental Investigation on Seismic Behaviors of High-Performance Concrete Shear Walls of Rectangular Section

The paper explores the failure mode, failure mechanism and deformation capacity of medium-high and low-rise shear walls. The experimental results from load-tests of 5 high-performance concrete shear walls with 1.5 and 1.0 shear span ratio indicate that the shear walls deformation capacity benefits from several bar rings like a chain along boundary element in plastic hinge zone, showing that shear wall deformation capacity design is reliable to a certain extent, in that the plastic hinge zone often influences the damage level of shear walls. With the damage at different stages, the paper divides the performance of shear wall structure into three kinds: serviceability, life-safety and collapse-prevention. Accordingly, it is proposed that the performance controlling indicators for shear wall structures is composed of storey drift ratio and the rotation of plastic hinge zone, and also provides consult values for each performance level.

Pseudo-dynamic tests on low-rise shear walls and simplified model based on the structural frequency drift

Twelve low-rise shear walls, with the same aspect ratio of 0.4 but with different structural parameters including the design frequency, reinforcement ratio and normal force, have been submitted to pseudo-dynamic (PSD) tests conducted at the ELSA laboratory of the Joint Research Centre. The focus of this testing campaign was to study the engineering margin for shear walls depending on the relative position of their structural frequency with respect to the excitation peak. After presenting the parameters of the PSD tests, three methods for identifying the structural frequency drift observed as damage occurs have been used in this paper: a numerical identification from a nonlinear pushover analysis, and two methods from experimental data, a system identification method based on an error output model and a more direct identification method based on the secant stiffness of force–displacement cycles. For each shear wall, a relationship f ( X ) between the structural frequency and the maximum of the top-displacement is derived from the previous methods and the consistency between the three approaches has been checked. Finally, these f ( X ) curves have been employed in a single degree of freedom model for predicting time–history top-displacements. The predictions turn out to be quite satisfactory, in particular when f ( X ) relationship is identified by the error output model.

Nonlinear model of reinforced concrete frames retrofitted by in-filled HPFRCC walls

A number of studies have suggested that the use of high ductile and high shear materials, such as Engineered Cementitious Composites (ECC) and High Performance Fiber Reinforced Cementitious Composites (HPFRCC), significantly enhances the shear capacity of structural elements, even with/without shear reinforcements. The present study emphasizes the development of a nonlinear model of shear behaviour of a HPFRCC panel for application to the seismic retrofit of reinforced concrete buildings. To model the shear behaviour of HPFRCC panels, the original Modified Compression Field Theory (MCFT) for conventional reinforced concrete panels has been newly revised for reinforced HPFRCC panels, and is referred to here as the HPFRCC-MCFT model. A series of experiments was conducted to assess the shear behaviour of HPFRCC panels subjected to pure shear, and the proposed shear model has been verified through an experiment involving panel elements under pure shear. The proposed shear model of a HPFRCC panel has been applied to the prediction of seismic retrofitted reinforced concrete buildings with in-filled HPFRCC panels. In retrofitted structures, the in-filled HPFRCC element is regarded as a shear spring element of a low-rise shear wall ignoring the flexural response, and reinforced concrete elements for beam or beam-column member are modelled by a finite plastic hinge zone model. An experimental study of reinforced concrete frames with in-filled HPFRCC panels was also carried out and the analysis model was verified with correlation studies of experimental results.

철근의 배근 위치가 다른 철근콘크리트 부재의 거동 분석

When the shear force governs the response of an RC element, as in the case of a low-rise shear wall, the effect of shear on the element`s response is thought to be responsible for the `pinching effect` in the hysteretic loops. However, it was recently shown that this undesirable pinching effect can be eliminated in the hysteretic load-deformation curves of a shear-dominant element if the steel grid orientation is properly aligned in the direction of the applied principal stresses. In this paper, the presence and absence of the pinching mechanism in the hysteretic loops of the shear stress-strain curves of RC elements was explained rationally using a compatibility aided truss model. The analytical results indicate that the pinching effect of the RC elements is strongly related to the direction of the steel arrangement. The area of the energy dissertation does not increase proportionally to the difference between the direction of the principal compressive stress and the direction of the steel arrangement.

Strength and deflection prediction of double-curvature reinforced concrete squat walls

This study presents a model to better understand the shear behavior of reinforced concrete walls subjected to lateral load. The scope of the study is limited to squat walls with height to length ratios not exceeding two, deformed in a double-curvature shape. This study is based on limited knowledge of the shear behavior of low-rise shear walls subjected to double-curvature bending. In this study, the wall ultimate strength is defined as the smaller of flexural and shear strengths. The flexural strength is calculated using a strength-of-material analysis, and the shear strength is predicted according to the softened strut-and-tie model. The corresponding lateral deflection of the walls is estimated by superposition of its flexibility sources of bending, shear and slip. The calculated results of the proposed procedure correlate reasonably well with previously reported experimental results.

Inherent Ductility of Non-seismically Designed and Detailed Reinforced Concrete Shear Walls

Large-scale reinforced concrete low-rise shear walls designed without seismic considerations, as practised in low probability of seismic occurrence regions, are tested under reversed cyclic loading. The seismic behaviour and available displacement ductility of the shear walls are investigated, and emphasis of the study is placed on the inherent ductility of the walls with different steel details and aspect ratios. Experimental results show that the inherent displacement ductility factors of 2.5 to 3 are commonly achieved with the current non-seismic design practice. By correlating the available ductility with the required ductility demands, it is concluded that an ordinary low-rise shear wall with non-seismic design and detailing may not possess the ductility to adequately respond to an unexpected moderate earthquake.

ARTIFICIAL ACCELEROGRAMS REPRESENTATIVE OF THE DAMAGE DISTRIBUTION ON A LOW-RISE SHEAR WALL

This study attempts to reproduce in an artificial way, at a given magnitude-distance couple, the statistical characteristics of damage caused by real accelerograms. The structure adopted is a low-rise shear wall, modelled as a nonlinear, one degree of freedom system with a degrading frequency as a function of a non-cumulative damage variable. Strong-motion records, contained in a large database, are characterised in terms of seismological and seismic parameters. Artificial accelerograms are generated from response spectra representative of real accelerograms belonging to different magnitude-distance zones. Although the mean damage is consistent, the low dispersion of damage caused by the artificial accelerograms with respect to that caused by the real accelerograms is highlighted. In order to reproduce the damage dispersion in addition to the mean damage, a generation method of representative artificial accelerograms is proposed. This method introduces the standard deviation drawn from attenuation relationships into a dispersion pre-process with respect to the regressed spectrum at a given magnitude-distance point. The method turns out to be capable of reproducing the statistical features of damage produced by real strong-motion records.

Stiffness, Ductility, and Energy Dissipation of RC Elements under Cyclic Shear

A new Cyclic Softened Membrane Model (CSMM) was recently developed to predict the stiffness, ductility, and energy dissipation of reinforced concrete (RC) elements subjected to reversed cyclic shear. Using the nonlinear finite element analysis, we can integrate these responses of elements to predict the behavior of a whole structure, such as a low-rise shear wall, subjected to earthquake action. This study of CSMM summarizes systematically the effects of the two primary variables: the steel bar angle with respect to the direction of the applied principal stresses and the steel percentage. The results clearly show that RC structures under cyclic shear stresses could be designed to be very ductile, have large stiffness, and possess high energy-dissipation capacities (just like flexural-dominated elements), if the steel bars are properly oriented in the directions of principal stresses and if the steel percentages are kept within certain limits.

Nonlinear Analysis of R/C Low-Rise Shear Walls

An analysis method for predicting the response of low-rise shear walls under both monotonic and cyclic loading is presented in this paper. The proposed analysis method is based on the softened truss model theory but utilizes newly proposed cyclic constitutive relationships for concrete and steel bars obtained from cyclic shear testing. The successfulness of the analysis method, when combined with new materials constitutive relationships, is checked against the test results of 33 low-rise shear walls reported in the technical literature. The theoretical predictions are compared with the reported test results and are found to be applicable throughout the loading history. The effects of loading types (monotonic versus cyclic) as well as the effects of the boundary elements on the predicted results are also addressed.

Damaging potential of low-magnitude near-field earthquakes on low-rise shear walls

The purpose of this study is to show that small earthquakes close to the site cause less damage in reinforced concrete structure than what is implied by their peak or spectral acceleration, used often as indicators of the destructive potential of earthquake shaking. For this purpose, an important step is to set up a simplified model of a representative reinforced concrete structure, capable of reproducing the global damage. A non-linear single degree of freedom model of a low-rise shear wall, proposed in a previous paper, has been adopted [Eng Struct 25 (2003) 1]. In this paper, the validity of the simplified approach is confirmed by comparing numerical damage predictions engendered by 501 strong motion records with those provided by a finite element approach using local models. Thanks to the drastic reduction of the computation time, the interdependency between the seismic acceleration parameters proposed in the literature and the damage is explored. A spectral intensity, taking into account the degradation of the fundamental frequency, is proposed. The spectral intensity turns out to be much more independent of the distance and magnitude of the causative earthquakes than the PGA and the spectral acceleration at the initial frequency corresponding to the undamaged state.