Nonlinear Behavior of Reinforced Concrete Slit Shear Walls under Seismic Actions *

A reinforced concrete slit shear wall is a new breed of earthquake resistant structure recently proposed by the authors. In this paper, the seismic responses of the slit shear walls under the shake of earthquake excitation have been dealt with. Based on a simplified structural model, which is shown to have a sufficient accuracy for the real slit shear wall structure, the analysis focuses on the influence of nonlinear behavior of the connecting beams between the slits on the dynamic performance of the whole slit shear wall structure. It has been found that the yielding of connecting beams in a slit shear wall can provide significant improvement in reducing the structural responses, and by choosing an appropriate strength value for the connecting beams, it is possible to optimize the seismic response of the slit shear wall.

Post-fire cyclic behavior of reinforced concrete shear walls

The effects of fire exposure,reinforcement ratio and the presence of axial load under fire on the seismic behavior of reinforced concrete(RC) shear walls were investigated.Five RC shear walls were tested under low cyclic loading.Prior to the cyclic test,three specimens were exposed to fire and two of them were also subjected to a constant axial load.Test results indicate that the ultimate load of the specimen with lower reinforcement ratio is reduced by 15.8%after exposure to elevated temperatures.While the reductions in the energy dissipation and initial stiffness are 59.2%and 51.8%,respectively,which are much higher than those in the ultimate load.However,this deterioration can be slowed down by properly increasing reinforcement due to the strength and stiffness recovery of steel bars after cooling.In addition,the combined action of elevated temperatures and axial load results in more energy dissipation than the action of fire exposure alone.

Nonlinear Finite Element Analysis of Mechanical Performance of Reinforced Concrete Short-Limb Shear Wall

On the basis of test, nonlinear finite element analysis of reinforcedconcrete (R. C) short-limb shear walls under monotonic horizontal load are carried out by ANSYSprogram in order to understand the evolution of cracking, deformation and failure course of thespecimens. At the same time, the results of numerical calculation are compared with the results oftest. The results indicate that, under monotonic horizontal load the failures of the specimens withflange wall and without flange wall all occur at the intersections of lintel bottom and limb ofwall, the failures also occur at the bottom of limb; the load-displacement curve of wall withoutflange is steeper than that of wall with flange, and the ductility is worse than that of wall withflange; the results, such as cracking, deformation, yield load and so on of finite element analysisagree well with the results of test. These results provide theoretical basis of study andapplication of R. C short-limb shear wall.

Performance index limits of high reinforced concrete shear wall components

The deformation performance index limits of high reinforced concrete （RC） shear wall components based on Chinese codes were discussed by the nonlinear finite element method. Two typical RC shear wall specimens in the previous work were first used to verify the correctness of the nonlinear finite element method. Then, the nonlinear finite element method was applied to study the deformability of a set of high RC shear wall components designed according to current Chinese codes and with shear span ratio λ≥2.0. Parametric studies were made on the influence of shear span ratio, axial compression ratio, ratio of flexural capacity to shear capacity and main flexural reinforcement ratio of confined botmdary members. Finally, the deformation performance index and its limits of high RC shear wall components under severe earthquakes were proposed by the finite element model results, which offers a reference in determining the performance status of RC shear wall components designed based on Chinese codes.

Experimental studies on behavior of fully grouted reinforced-concrete masonry shear walls

An experimental study is conducted on fully grouted reinforced masonry shear walls (RMSWs) made from concrete blocks with a new configuration. Ten RMSWs are tested under reversed cyclic lateral load to investigate the influence of different reinforcements and applied axial stress values on their seismic behavior. The results show that flexural strength increases with the applied axial stress, and shear strength dominated by diagonal cracking increases with both the amount of horizontal reinforcement and applied axial stress. Yield displacement, ductility, and energy dissipation capability can be improved substantially by increasing the amount of horizontal reinforcement. The critical parameters for the walls are derived from the experiment: displacement ductility values corresponding to 15% strength degradation of the walls reach up to 2.6 and 4.5 in the shear and flexure failure modes, respectively; stiffness values of flexure- and shear-dominated walls rapidly degrade to 17%–19% and 48%–57% of initial stiffness at 0.50 Dmax (displacement at peak load). The experiment suggests that RMSWs could be assigned a higher damping ratio (～14%) for collapse prevention design and a lower damping value (～7%) for a fully operational limit state or serviceability limit state.

Shear strengthening of pre-damaged reinforced concrete beams with carbon fiber reinforced polymer sheet strips

This paper presents the results of an experimental investigation on the response of pre-damaged reinforced concrete （RC） beam strengthened in shear using applied-epoxy unidirectional carbon fiber reinforced polymer （CFRP） sheet. The reasearch included four test rectangular simply supported RC beams in shear capacity. One is the control beam, two RC beams are damaged to a predetermined degree from ultimate shear capacity of the control beam, and the last beam is left without pre-damaged and then strengthened with using externally bonded carbon fiber reinforced polymer to upgrade their shear capacity. We focused on the damage degree to beams during strengthening, therefore, only the beams with sidebonded CFRPs strips and horizontal anchored strips were used. The results show the feasibility of using CFRPs to restore or increase the load-carrying capacity in the shear of damaged RC beams. The failure mode of all the CFRP-strengthened beams is debonding of CFRP vertical strips. Two prediction available models in AC1-440 and fib European code were compared with the experimental results.

The Influence of Steel and Basalt Fibers on the Shear and Flexural Capacity of Reinforced Concrete Beams

To improve the shear and flexural capacity of flexural members, the steel and basalt fibers were used in model beams tested under flexure. Three series of single span free supported model beams were prepared from SFRC （steel fiber reinforced concrete） with longitudinal steel reinforcement （steel ratio of 1.2 %） and varied spacing of steel stirrups and they were tested till failure. Another three series of BFRC （basalt fiber reinforced concrete） double-span model beams with a span of 2 mm~ 1,000 mm and cross section 180 mm ~ 80 mm were tested. During the tests till to the failure the beam reactions, vertical deflections and horizontal strains in concrete were registered, to clarify the range of redistribution of bending moments and shear forces over the span of the beams. Almost all the tested model beams failed in shear, showing visible influence of steel and basalt fibers on the shear capacity of the tested beams. The tests results confirmed that steel and basalt fibers in reinforced concrete beams can partially replace （in certain cases） the traditional steel stirrups calculated for shear.

Analysis on Construction Quality Control Technology of Reinforced Concrete Shear Wall Structure

In the process of continuous development of construction enterprises, new requirements have been put forward for construction projects. By strengthening the construction quality control of reinforced concrete shear wall structure, the construction level of reinforced concrete can be continuously improved, the construction quality can be guaranteed, and the construction project can be successfully completed, which is worthy of extensive application and promotion in construction enterprises, thus providing a broader development space for construction enterprises.

Modified imperialist competitive algorithm-based neural network to determine shear strength of concrete beams reinforced with FRP

Fiber reinforced polymers (FRPs), unlike steel, are corrosion-resistant and therefore are of interest;however, their use is hindered because their brittle shear is formulated in most specifications using limited data available at the time. We aimed to predict the shear strength of concrete beams reinforced with FRP bars and without stirrups by compiling a relatively large database of 198 previously published test results (available in appendix). To model shear strength, an artificial neural network was trained by an ensemble of Levenberg-Marquardt and imperialist competitive algorithms. The results suggested superior accuracy of model compared to equations available in specifications and literature.

Progressive collapse resisting capacity of reinforced concrete load bearing wall structures

Reinforced concrete(RC) load bearing wall is widely used in high-rise and mid-rise buildings. Due to the number of walls in plan and reduction in lateral force portion, this system is not only stronger against earthquakes, but also more economical. The effect of progressive collapse caused by removal of load bearing elements, in various positions in plan and stories of the RC load bearing wall system was evaluated by nonlinear dynamic and static analyses. For this purpose, three-dimensional model of 10-story structure was selected. The analysis results indicated stability, strength and stiffness of the RC load-bearing wall system against progressive collapse. It was observed that the most critical condition for removal of load bearing walls was the instantaneous removal of the surrounding walls located at the corners of the building where the sections of the load bearing elements were changed. In this case, the maximum vertical displacement was limited to 6.3 mm and the structure failed after applying the load of 10 times the axial load bored by removed elements. Comparison between the results of the nonlinear dynamic and static analyses demonstrated that the "load factor" parameter was a reasonable criterion to evaluate the progressive collapse potential of the structure.

Shear capacity of reinforced concrete columns strengthened with CFRP sheet

This paper discusses the results of tests on the shear capacity of reinforced concrete columns strengthened with carbon fiber reinforced plastic (CFRP) sheet. The shear transfer mechanism of the specimens reinforced with CFRP sheet was studied. The factors affecting the shear capacity of reinforced concrete columns strengthened with CFRP sheet were analyzed. Several sug-gestions such as the number of layers, width and tensile strength of the CFRP sheet are proposed for this new strengthening technique. Finally, a simple and practical design method is presented in the paper. The calculated results of the suggested method are shown to be in good agreement with the test results. The suggested design method can be used in evaluating the shear capacity of reinforced concrete columns strengthened with CFRP sheet.

Elasto-plastic Analysis of High-strength Concrete Shear Wall with Boundary Columns Using Fiber Model

In this study,an experimental study and numerical calculations using fiber model were conducted for four high-strength concrete shear walls with boundary columns under low cyclic load.The boundary column and shear wall were divided into fiber elements,and PERFORM-3D finite element analysis software was used to carry out push-over analysis on the test specimens.The results show that the finite element analysis results were in good agreement with the experimental results.The proposed analysis method could perform elasto-plastic analysis on the high-strength concrete shear wall with boundary columns without distinguishing the categories of frame column and shear wall.The seismic performance of high-strength concrete shear wall with boundary columns was analyzed using the following parameters:axis compression ratio,height to width ratio,ratio of vertical reinforcement,and ratio of longitudinal reinforcement in the boundary column.The results show that the increase in the axial compression ratio causes the bearing capacity of the shear wall to increase at first and then to decrease and causes the ductility to decrease.The increase in the height to width ratio causes the bearing capacity of the shear wall to decrease and its ductility to increase.The ratio of vertical reinforcement was found to have little effect on the bearing capacity and ductility.The increase in the ratio of longitudinal reinforcement in boundary column resulted in a significant increase in the bearing capacity and caused the ductility to decrease at first and then to slowly increase.

Mechanical Properties of Polypropylene Fiber Reinforced Concrete under Elevated Temperature

Apart from many advantages,High Strength Concrete(HSC)has disadvantages in terms of brittleness and poor resistance to fire.Various studies suggest that when polypropylene(PP)fibers are uniformly distributed within concrete,they play an active role in improving spalling resistance of concrete when exposed to elevated temperature while having no adverse effect on its mechanical properties.Therefore,there is a necessity to quantify the effect of the addition of polypropylene fibers in terms of the fiber dosage,the strength of the concrete,and the residual mechanical properties of fiber-reinforced concrete under exposure to high temperature from fire.The study was carried out on three water/cement(w/c)ratios(0.47,0.36&0.20)using granite aggregate for determining short term mechanical properties of Polypropylene fiber reinforced concrete in comparison to control mix.The experimental program includes 100×200 mm&150 x 300 mm cylinders with fiber volume of 0.5%,that were subjected to temperatures exposures of 400°C and 600°C for durations of 1 hour.From the results,it was observed that no significant enhancement in mechanical properties such as modulus of elasticity,Poisson’s ratio,split tensile strength,flexural strength,and compressive strength was observed at room temperature and at elevated temperatures.

Experimental and analytical study on seismic behavior of steel-concrete multienergy dissipation composite shear walls

In this paper, a steel-concrete multi-energy dissipation composite shear wall, comprised of steel-reinforced concrete （SRC） columns, steel plate （SP） deep beams, a concrete wall and energy dissipation strips, is proposed. In order to study the multi-energy dissipation behavior and restorability after an earthquake, two stages of low cyclic loading tests were carded out on ten test specimens. In the first stage, test on five specimens with different number of SP deep beams was carried out, and the test lasted until the displacement drift reached 2%. In the second stage, thin SPs were welded to both sides of the five specimens tested in the first stage, and the same test was carried out on the repaired specimens （designated as new specimens）. The load-bearing capacity, stiffness, ductility, hysteretic behavior and failure characteristics were analyzed for both stages and the results are discussed herein. Extrapolating from these results, strength calculation models and formulas are proposed herein and simulations using ABAQUS carried out, they show good agreement with the test results. The study demonstrates that SRC columns, SP deep beams, concrete wall and energy dissipation strips cooperate well and play an important role in energy dissipation. In addition, this study shows that the shear wall has good recoverability after an earthquake, and that the welding of thin SP＇s to repair a deformed wall is a practicable technique.

Punching shear behavior of steel fiber reinforced recycled coarse aggregate concrete two-way slab without shear reinforcement

In this paper,the punching shear performance of 8 steel fiber reinforced recycled coarse aggregate concrete(SFRCAC)two-way slabs with a size of 1800 mm×1800 mm×150 mm was studied under local concentric load.The effects of RCA replacement ratio(rg)and SF volume fraction(Vf)on the punching shear performance of SFRCAC two-way slabs were investigated.Digital Image Correlation(DIC)measurement and Acoustic Emission(AE)technique were introduced to collect pictures and relevant data during the punching shear test.The test results show that the SFRCAC two-way slab mainly exhibits punching shear failure and flexure failure under local concentric load.The punching shear failure space area of SFRCAC two-way slab has no obvious change with increasing rg,however,show a gradual increase trend with increasing Vf.Both of the punching shear ultimate bearing capacity(Pu)and its deflection of SFRCAC two-way slab decrease with increasing rg and increase with increasing Vf,respectively.Finally,through the regression analysis of the results from this study and the data collected from related literature,the influence of rg and Vf on the Pu of two-way slabs were obtained,and the equations in GB 50010-2010,ACI 318-19,and Eurocode 2 Codes were amended,respectively.Furthermore,the amended equations were all applicable to predicted the ultimate bearing capacity of the ordinary concrete two-way slab,RCAC two-way slab,SFRC two-way slab,and SFRCAC two-way slab.

High-Rise Residential Reinforced Concrete Building Optimisation

In the last few decades structure optimisation has become a main task in a civil engineering project. As a matter of fact, due to the complexity and particularity of every structure, the great amount of variables and design criteria to considerate and many other factors, a general optimisation’s method is not simple to formulate. As a result, this paper focuses on how to provide a successful optimisation method for a particular building type, high-rise reinforced concrete buildings. The optimization method is based on decomposition of the main structure into substructures: floor system, vertical load resisting system, lateral load resisting system and foundation system;then each of the subsystems using the design criteria established at the building codes is improved. Due to the effect of the superstructure optimisation on the foundation system, vertical and lateral load resisting system is the last to be considered after the improvement of floor. Finally, as a case example, using the method explained in the paper, a 30-story-high high-rise residential building complex is analysed and optimised, achieving good results in terms of structural behaviour and diminishing the overall cost of the structure.

Effect of fiber angle on LYP steel shear walls behavior

Steel shear wall(SSW) was properly determined using numerical and experimental approaches.The properties of SSW and LYP(low yield point) steel shear wall(LSSW) were measured.It is revealed that LSSW exhibits higher properties compared to SSW in both elastic and inelastic zones.It is also concluded that the addition of CFRP(carbon fiber reinforced polymers) enhances the seismic parameters of LSSW(stiffness,energy absorption,shear capacity,over strength values).Also,stress values applied to boundary frames are lower due to post buckling forces.The effect of fiber angle was also studied and presented as a mathematical equation.

Seismic behavior of large-scale FRP–recycled aggregate concrete–steel columns with shear connectors

The application of fi ber-reinforced polymer (FRP) composites for the development of high-performance composite structural systems has received signifi cant recent research attention. A composite of FRP–recycled aggregate concrete (RAC)–steel column (FRSC), consisting of an outer FRP tube, an inner steel tube and annular RAC fi lled between two tubes, is proposed herein to facilitate green disposal of demolished concrete and to improve the ductility of concrete columns for earthquake resistance. To better understand the seismic behavior of FRSCs, quasi-static tests of large-scale basalt FRSCs with shear connectors were conducted. The infl uence of the recycled coarse aggregate (RCA) replacement percentage, shear connectors and axial loading method on the lateral load and deformation capacity, energy dissipation and cumulative damage were analyzed to evaluate the seismic behavior of FRSCs. The test results show that FRSCs have good seismic behavior, which was evidenced by high lateral loads, excellent ductility and energy dissipation capacity, indicating RAC is applicable in FRSCs. Shear connectors can signifi cantly postpone the steel buckling and increase the lateral loads of FRSCs, but weaken the deformation capacity and energy dissipation performance.

Experimental testing of RC shear wall seismic retrofit using selective weakening,self-centering and Ultra High performance concrete

Traditional retrofit methods often focus on increasing the structure’s strength,stiffness,or both.This may in-crease seismic demand on the structure and could lead to irreparable damage during a seismic event.This paper presents a retrofit method,integrating concepts of selective weakening and self-centering(rocking)to achieve low seismic damage for non-code compliant reinforced concrete shear walls.The proposed method involves con-verting traditional cast-in-place concrete shear walls into rocking walls,which helps to lower the shear demand,while allowing re-centering.Two large-scale lateral load tests were performed to validate the retrofit concept on a concrete shear wall designed according to pre-1970s standards.The design parameters investigated were amount of energy dissipating reinforcements and confinement enhancement.Two different methods using Ultra High Performance Concrete(UHPC)were investigated to provide additional confinement to boundary elements of older shear walls.Observations from the tests showed minimized damage and enhanced recentering in the retrofitted wall specimens.Use of UHPC in the boundary elements of the retrofitted walls provided additional confinement and reduced damage in the rocking corners.

Collapse Patterns and Their Discrimination of Reinforced Concrete Shear Wall Under Combined Stresses of Compression and Shear due to Strong Earthquake

The collapse patterns of reinforced concrete(RC)shear walls under seismic load are proposed.The crack distribution and propagation of shear walls are specifically based on the failure criterions of Mohr-Coulomb with tension cutoff.Three zones and five different corresponding failure modes of RC shear walls are determined according to the transfer path of shear stress in shear wall.These failure modes of shear walls under seismic load are verified by many experimental results and can be utilized in collapsing analysis for frame-shear wall structure.