Reinforced Concrete Wall Specimens Research Articles

Assessment of critical parameters affecting the behaviour of bearing reinforced concrete walls under fire exposure

PurposeThis research paper aims to investigate reinforced concrete (RC) walls' behaviour under fire and identify the thermal and mechanical factors that affect their performance.Design/methodology/approachA three-dimensional (3D) finite element (FE) model is developed to predict the response of RC walls under fire and is validated through experimental tests on RC wall specimens subjected to fire conditions. The numerical model incorporates temperature-dependent properties of the constituent materials. Moreover, the validated model was used in a parametric study to inspect the effect of the fire scenario, reinforcement concrete cover, reinforcement ratio and configuration, and wall thickness on the thermal and structural behaviour of the walls subjected to fire.FindingsThe developed 3D FE model successfully predicted the response of experimentally tested RC walls under fire conditions. Results showed that the fire resistance of the walls was highly compromised under hydrocarbon fire. In addition, the minimum wall thickness specified by EC2 may not be sufficient to achieve the desired fire resistance under considered fire scenarios.Originality/valueThere is limited research on the performance of RC walls exposed to fire scenarios. The study contributed to the current state-of-the-art research on the behaviour of RC walls of different concrete types exposed to fire loading, and it also identified the factors affecting the fire resistance of RC walls. This guides the consideration and optimisation of design parameters to improve RC walls performance in the event of a fire.

Experimental study on the seismic behavior of corroded reinforced concrete walls in an artificial climate corrosion environment

Previous research shows that corrosion of reinforcement caused by chloride penetration is the key factor that weakens the seismic performance of reinforced concrete (RC) structures. Both environmental erosion and squat walls have so far been underexplored, which makes it difficult to evaluate the seismic performance of RC shear wall structures subjected to chloride salt erosion. Accordingly, in this paper, eight squat RC wall specimens with an aspect ratio of 1.0 are subjected to accelerated corrosion tests in an artificial climate environment and pseudostatic tests, and the effects of corrosion degree, axial compression ratio and horizontal distribution of rebar spacing on the seismic performance of corroded squat RC wall specimens are investigated. The results show that the corrosion morphology of rebar in an artificial climate environment is similar to that in a natural environment. With an increasing corrosion level, the bearing capacity, deformation capacity and energy dissipation capacity of the specimen degrade gradually, but the deformation capacity degrades to a greater degree. At the same time, the average shear deformation and the proportion of shear deformation in the total deformation of the specimen under different load conditions increase gradually, which manifests in a transformation of the failure mode of the corroded specimen from flexural-shear failure to shear-dominated failure. Additionally, the increase in density of horizontally distributed rebar has a more significant influence on the deformation capacity and energy dissipation capacity of the corroded specimens than on the bearing capacity. Finally, the existing equation is revised based on the test data, and the calculation equation for the characteristic point parameters of the corroded squat wall skeleton curve, including the corrosion degree, the axial compression ratio and the horizontal distributed reinforcement ratio, is established.

Experimental investigation into the seismic behavior of squat reinforced concrete walls subjected to acid rain erosion

Acid rain erosion will continuously deteriorate the physical and mechanical properties of materials and finally degrade the seismic performance of reinforced concrete (RC) structures. Nevertheless, the effect of acid deposition on squat RC walls, an important part of lateral force-resisting systems, has not been reported in existing research. Thus, in this paper, an artificial climate simulation method was used to accelerate the acidic attack process on four squat RC wall specimens with an aspect ratio of 1.0. Then quasi-static loading tests were conducted to observe their cyclic behavior under different acid rain spraying cycles (ARSCs). The results show that as ARSCs increase, the degree of degradation of concrete strength and the corrosion weight loss of steel bars have a rising trend, and the bearing capacity and deformation capacity of the squat RC walls deteriorate gradually. Simultaneously, the ratio of shear displacement to total lateral displacement increases, indicating a more noticeable shear failure characteristic with the addition of ARSCs. Moreover, the failure mode shifts from the mixed flexure and diagonal compression mode to the diagonal tension mode with a significant decrease in ductility and energy-dissipation capacity. It is also found that the degradation rate of the shear strength of squat walls under acid rain erosion is larger than that of the flexural strength, which may lead to the transition of failure mode.

Damage and sensitivity analysis of a reinforced concrete wall building during the 2010, Chile earthquake

Buildings with Reinforced Concrete (RC) walls are commonly used to resist lateral forces in seismic countries because they provide high lateral stiffness and strength. In recent earthquakes, shear wall buildings have shown good behavior in general; however, a small percentage underwent severe damage localized typically in lower stories. Several numerical models have been developed and proposed to simulate the failure mechanism and behavior of RC walls. From the existing models, only those denoted as micro-models can accurately simulate the stress and strain distributions. The aim of this research is double: (i) to validate a nonlinear finite element wall model and the associated material stress-strain constitutive relationship using the behavior of a real building during the 2010 Chile earthquake; and (ii) to analyze the uncertainty of the response of the building due to changes in model parameters. To validate the response of the wall model, four experimental benchmark RC wall specimens were studied, and model accuracy was evaluated using five parameters: initial stiffness, peak base-shear, ultimate base-shear, maximum displacement, and dissipated energy. A sensitivity analysis was carried out to study the influence of material parameters in the wall response and its damage. The case-study is a 18-story building with 1 basement, which suffered severe damage during the 2010 Chile earthquake, which has been studied by non-linear response-history analysis. Uncertainty in the building response due to three important modeling assumptions was considered: Rayleigh’s damping model parameters; effective elastic bending stiffness of the structural elements; and effect of the vertical ground motion component. Results showed that the proposed model can predict the seismic response of the building with reasonable accuracy by identifying correctly the damage location. This case-study enabled us to assess also the effect of damping in non-ductile structures, the important influence of the slab stiffness in the response, and the effect of the vertical ground motion component in the sequence of damaged walls.

Vision-based measurements of deformations and cracks for RC structure tests

This paper develops vision-based measurement methods for experimental tests of reinforced concrete (RC) structures. The methods can measure deformations and characterize cracks from images of RC specimens. The coordinates of objects of interest (OOIs) in the specimen are measured using a target tracking approach, and then deformation components (e.g., flexural, shear and sliding deformations) of the specimen are computed from the coordinates of OOIs through geometry analysis. The cracks are (i) identified using binary images converted from color images, (ii) and then quantified using the filter-based algorithm. The morphological operations, separation algorithm and connected component labeling algorithm are used in the image processing for crack measurements. The developed vision-based measurement methods were applied to cyclic tests of RC wall specimens. The accuracy of the vision-based measurements was validated by comparison with the results of traditional measurement techniques using the displacement transducers and crack scales. The proposed vision-based measurement methods demonstrate much higher efficiency and provide more useful information than the traditional measurement techniques. The paper also discusses a few application issues such as the specimen surface requirements and resolution of the vision-based measurements.

A study on the resistance of SC walls subjected to missile impact using large-scale impact tests

Nuclear power plants (NPP) should resist local impact loads such as aircraft engine impact as well as internal and external missile impacts based on the international regulations for NPP structures. Although a wide variety of studies on the local responses of conventional reinforced concrete (RC) walls under impact loading have been performed and the design methods for preventing local failure are previously established, no appropriate design methodology is available for steel-plate concrete (SC) walls except for that recently cited in AISC N690 specifications.In this paper, the local resistance and behavior of SC walls subjected to missile impact were investigated experimentally. A total of ten large-scale impact tests for SC and RC walls were performed. The SC wall specimens were designed using various parameters including wall thickness and steel-plate thickness (reinforcement ratio). A set of RC wall specimens were designed for comparison. Initial and residual velocities of projectile, strain and acceleration of the rear plate, local failure mode and deformation, etc. were measured utilizing high speed cameras and various instrumentation devices. From this study, the actual local impact behaviors of SC walls were investigated and the quantitative impact resistance was evaluated. Overall, the current AISC N690 design method was somewhat conservative and needs to be improved for beyond-design-basis events such as aircraft engine impact.

Experimental and Numerical Seismic Evaluation of RC Walls Under Axial Compression

Recent studies show that code-based equations usually do not provide an accurate estimate for the shear strength of short reinforced concrete (RC) walls due to the negligence of many important factors including the beneficial effect of axial compression. In the current study, quasi-static reversed cyclic testing is conducted for two RC wall specimens, one under axial load and one without axial load to assess the effect of the axial compression on the shear strength of RC walls in high-rise buildings. The results of the experimental study show that the axial compression load significantly improves the shear strength of RC walls. Results are also compared with the performance-based seismic evaluation code practices. Based on the experimental findings, recommendations are made for improvements in the existing codes. The experimental results are further compared with different numerical models to explore the suitable computer modeling options for non-linear response prediction of RC walls.

Effect of construction joints on the seismic performance of RC structural walls

A survey of earthquake damage in reinforced concrete (RC) structural walls after the 2008 Wenchuan Earthquake in China showed unexpected phenomena at the location of a construction joint at the base of the wall, suggesting that the construction joint has an impact on the seismic performance. In this study, the test of six medium-scale RC wall specimens (height-to-length aspect ratio 2.1) with and without construction joints at the footing-wall interface were implemented under the pseudo-static reversed cyclic lateral loading, and the failure process, hysteretic response, and energy dissipation capacity were investigated. It showed that wall specimens without a construction joint exhibited better seismic performance than comparable specimens with a construction joint, mainly reflected by a higher lateral load capacity, better energy dissipation capacity, and longer plastic hinge length. A numerical model was developed using the multiple-vertical-line-element-model (MVLEM) to simulate the response of RC walls with construction joints, and walls with different axial load ratios and boundary element reinforcement ratios were studied. Results indicated that the presence of a construction joint reduces the lateral load capacity of RC wall. The influence of construction joint on the lateral load capacity is more obvious when the boundary element reinforcement ratio and axial load ratio are both low. These results show that the presence of construction joints should be considered to accurately predict the response of RC walls subjected to seismic loading conditions.

Shear–flexure-interaction models for planar and flanged reinforced concrete walls

This paper presents information on development, calibration, and validation of three companion macroscopic modeling approaches for nonlinear analysis of reinforced concrete (RC) structural walls, including: (1) the baseline two-dimensional two-node formulation of the Shear–Flexure-Interaction Multiple-Vertical-Line-Element-Model (SFI-MVLEM), (2) extension of the baseline SFI-MVLEM for modeling of squat walls (SFI-MVLEM-SQ), and (3) extension of the baseline SFI-MVLEM to a three-dimensional four-node element for simulation of non-planar RC walls under multi-directional loading (SFI-MVLEM-3D). The models are implemented in the computational platform OpenSees. Models presented are calibrated and validated against experimental results obtained from tests on RC wall specimens that cover a wide range of physical and behavioral characteristics, including: (1) one slender, two moderately-slender and one medium-rise planar RC walls tested under in-plane loading used for validation of the baseline SFI-MVLEM, (2) three squat planar RC wall specimens tested under in-plane loading used for validation of the SFI-MVLEM-SQ, and (3) one T-shaped and one U-shaped RC wall specimen tested under unidirectional and multi-directional loading, respectively, used for validation of SFI-MVLEM-3D. The comprehensive comparisons between analytically-obtained and experimentally-measured wall responses suggest that the analytical models proposed can accurately simulate both global and local wall responses, within their range of applicability. The models capture load–displacement response features of the walls, including lateral load capacity, lateral stiffness, cyclic stiffness degradation, and pinching characteristics, as well as nonlinear shear deformations and their coupling with flexural deformations during cyclic loading. Comparisons between experimental and analytical results at local response levels suggest that the models can also replicate distributions and magnitudes of wall vertical strains and curvatures at various locations. Overall, the analytical models presented provide robust and reliable tools for nonlinear analysis of RC walls, with a wide range of applicability.

State-of-the-art in nonlinear finite element modeling of isolated planar reinforced concrete walls

A number of finite element modeling approaches for reinforced concrete (RC) structural walls have recently become available for both research purposes and design applications. Five conceptually-different state-of-the-art finite element models for RC walls are described and evaluated in this paper, including models based on either a fixed-crack or a rotating-crack approach for simulating the biaxial behavior of concrete under plane-stress state, models characterized with either a single- or a multi-layered representation of the wall cross-section, and models with or without consideration of various individual failure mechanisms (e.g., buckling of reinforcement, out-of-plane instability). Modeling approaches were validated against experimental data obtained for five benchmark RC wall specimens, all with rectangular cross-sections, yet are differentiated by a range of salient response characteristics (e.g., aspect ratio, axial load, failure mechanism), in order to assess the capabilities of the models in representing the response of isolated planar walls under uni-directional lateral loading, as well as to identify future research directions. Results presented suggest that the models considered in this study can all capture the lateral load at yield and the peak lateral load capacity of the wall specimens with ±10% accuracy, while the initial stiffness and yield stiffness can be overestimated as much as 3.0 and 1.8 times, respectively. All models can capture nonlinear shear deformations and interaction between flexural and shear responses under cyclic loading, where the analytically-predicted flexural and shear deformations are within ±30% of the experimentally-measured values. Moderate differences between the predicted crack orientations and distributions are noted between the models, and the model results for the magnitudes of principal compressive stresses in concrete and the extent of stress localization are comparable. All models can capture the nonlinear distribution of vertical strains measured along the base of the walls, where the magnitudes of the predicted tensile and compressive strains are within ±50% of experimentally-measured strains for most models. Although some of the model formulations proved to be successful in capturing the experimentally-observed strength loss mechanisms for individual wall specimens, none of the models were capable of comprehensively simulating all of the strength degradation mechanisms observed during the tests.

Coupled axial tension-flexure behavior of slender reinforced concrete walls

Reinforced concrete (RC) walls in high-rise buildings, in particular wall piers that form part of a coupled or core wall system, may experience coupled axial tension-flexure loading when subjected to lateral demands. The seismic behavior of RC walls with various axial tensile forces was investigated by quasi-static tests on four RC slender walls subjected to the combined tension and flexure loading. The failure modes, strength and deformation capacity, effective flexural stiffness, and design equations are presented. The failure modes included flexural-sliding failure and flexural failure. The effective flexural stiffness and lateral strength of the walls significantly decreased as the axial tensile forces were increased. The ACI 318-14 and ASCE/SEI 41-13 code provisions overestimated the effective flexural stiffness of RC walls subjected to axial tension. Although equations proposed by Paulay & Priestley and Adebar et al. consider the influence of axial forces, they were not able to accurately predict the effective flexural stiffness of the RC wall specimens subjected to tensile forces. Both sectional analysis using XTRACT and JGJ 3-2010 (China) code equations provided accurate estimation of the flexural yield strength of walls. Finally, both a refined model and simplified equation were proposed to estimate the axial elongation for RC slender walls subjected to axial tensile force and cyclic lateral loading.

Coupled axial tension-shear behavior of reinforced concrete walls

Reinforced concrete (RC) shear walls in high-rise buildings may experience coupled axial tension-shear loading when subjected to strong ground motions. To understand how the tensile force influences shear strength and stiffness of RC walls, a series of quasi-static tests are conducted on six wall specimens with low aspect ratios. The failure modes of the specimens vary with different degrees of axial tension forces, which include diagonal tension failure (without tensile force), shear-sliding failure (under low to moderate tensile force) and sliding failure (under high tensile force). Increase of axial tensile force leads to linear decrease of the shear strength capacity of RC walls, with a factor of approximately 0.35. Sliding shear strength of specimens subjected to high axial tension is only 24%–33% of the shear strength capacity of the specimen not subjected to axial tension. High axial tensile force also results in a significant decrease in lateral stiffness of the walls. In addition, the axial tensile behavior of RC wall specimens is also presented to validate various tension-stiffening models of cracked concrete. Finally, design formulae of shear stiffness and strength of RC walls under axial tension are estimated, using the data from this experimental program and past tests. The strut-and-tie model provides a reasonable estimate of effective lateral stiffness of low-aspect-ratio RC walls under low to moderate tensile forces. The design formulae specified in ACI 318–14 (U.S.) code provide a conservative estimate of the shear strength capacity of the RC walls subjected to tensile forces. The average experimental-to-calculated ratio is 1.68. However, the JGJ 3–2010 formulae (China) tend to overestimate the shear strength capacity of RC walls under moderate axial tensile forces, with an average experimental-to-calculated ratio of 0.93.

New opensees models for simulating nonlinear flexural and coupled shear-flexural behavior of RC walls and columns

This paper describes new model elements and material constitutive relationships implemented by the authors into the widely-used open-source computational platform OpenSees (Open System for Earthquake Engineering Simulation), aimed to enhance current nonlinear analysis and response assessment capabilities for reinforced concrete (RC) walls and columns. Classes added to the existing OpenSees library include: (1) the Multiple-Vertical-Line-Element-Model (MVLEM) element with uncoupled axial/flexural and shear responses, (2) the Shear-Flexure-Interaction-Multiple-Vertical-Line-Element-Model (SFI-MVLEM) element with coupled axial/flexural and shear responses, (3) the Fixed-Strut-Angle-Model (FSAM), which is a two-dimensional constitutive model for RC panel elements, (4) an improved uniaxial constitutive model for concrete, and (5) an improved uniaxial constitutive model for reinforcing steel. Representative validation studies are also presented, where the analytical model predictions are compared with results of quasi-static lateral load tests on selected RC column and wall specimens. Response comparisons reveal that the implemented models capture, with reasonable accuracy, the experimentally-observed behavior of the test specimens investigated. Based on the comparisons presented, model capabilities are assessed and potential model improvements are identified.

Seismic retrofitting of RC walls externally strengthened by flax–FRP strips

Abstract Several studies available in the literature have demonstrated that natural fibres can be employed in externally bonded (EB) fibre-reinforced polymer (FRP) strips used to strengthen existing reinforced concrete (RC) members. The study aims to demonstrate the feasibility of retrofitting RC walls using flax–FRP (FFRP). The study consists of an experimental campaign and analytical evaluations, the latter aimed at determining the evolution of relevant damage indices during cyclic loading processes. The behaviour observed in the tests of RC walls strengthened by FFRP is compared with that of both a reference wall and that of similar specimens strengthened with more conventional composite materials (i.e., carbon-FRP or CFRP). The test results show that FFRP has the potential to be used for seismic retrofitting as a viable alternative to more common FRP materials and other traditional techniques. Indeed, RC wall specimens strengthened with FFRP demonstrated strength increases of up to 150% and ductility gains equal to about 30%. Moreover, the tests show that walls strengthened by FFRP generally dissipate more energy than those strengthened with CFRP: this is an important property for the seismic strengthening and retrofitting of existing RC structures.

Seismic behavior of composite walls with encased steel truss

This paper studies the seismic behavior of reinforced concrete (RC) walls with encased cold-formed and thin-walled (CFTW) steel truss, which can be used as an alternative to the conventional RC walls or steel reinforced concrete (SRC) composite walls for high-rise buildings in high seismic regions. Seven one-fourth scaled RC wall specimens with encased CFTW steel truss were designed, manufactured and tested to failure under reversed cyclic lateral load and constant axial load. The test parameters were the axial load ratio, configuration and volumetric steel ratio of encased web brace. The behaviors of the test specimens, including damage formation, failure mode, hysteretic curves, stiffness degradation, ductility and energy dissipation, were examined. Test results indicate that the encased web braces can effectively improve the ductility and energy dissipation capacity of RC walls. The steel angles are more suitable to be used as the web brace than the latticed batten plates in enhancing the ductility and energy dissipation. Higher axial load ratio is beneficial to lateral load capacity, but can result in reduced ductility and energy dissipation capacity. A volumetric ratio about 0.25% of encased web brace is believed cost-effective in ensuring satisfactory seismic performance of RC walls. The axial load ratio should not exceed the maximum level, about 0.20 for the nominal value or about 0.50 for the design value. Numerical analyses were performed to predict the backbone curves of the specimens and calculation formula from the Chinese Code for Design of Composite Structures was used to predict the maximum lateral load capacity. The comparison shows good agreement between the test and predicted results.

Experimental Study on Failure Mechanism of RC Walls with Different Boundary Elements under Vertical and Lateral Loads

Reinforced concrete (RC) shear walls have been widely applied in high-rise buildings. DBSD (Displacement-Based Seismic Design) of shear wall structures requires more accurate deformation evaluation theories and methods. Boundary elements of RC walls have been found to have a significant impact on the seismic behaviours, but the strain-stress development details including plane section assumption and linear curvature distribution are seldom investigated by specialized experiments. To investigate the failure mechanism of shear walls and the influence of the boundary element, 6 RC wall specimens with different boundary elements are studied in this paper. Strain development data of the shear wall section and along wall height were collected during the loading procedure. The failure mechanism of the RC walls with different boundary elements is studied by discussing the development of the strain. Study emphasis is laid on the adaption of plane-section assumption during the whole service procedure, the curvature development along the wall height during the whole service procedure, the influence of boundary element to moment-curvature relationship. Test results indicate that boundary element can restrain the growth of the strain, enhance the horizontal bearing capacity, and improve the seismic resistant capacity. The study also re-evaluates the plane section assumption and linear curvature distribution currently used based on the results of the deformation of the shear walls by the experimental investigation of the shear walls with different boundary element.

Strain gradient effect in RC elements subjected to torsion

The strain gradient effect of two-dimensional (2D) constitutive models of softened concrete used in three-dimensional (3D) torsion problems has never been addressed. The latest 2D theoretical model for reinforced concrete (RC) membrane elements in shear, the softened membrane model (SMM), was recently applied to analyse the torsion of RC members to create a new theory called the softened membrane model for torsion (SMMT). The SMMT framework makes it possible to identify and quantify the strain gradient effect of concrete in RC torsional beams for the first time. Two amplification factors, λ and μ, for the pre-cracking stiffness and the strain at peak stress of the tensile stress–stress relationship of concrete, and a reduction factor R for Poisson's ratio (Hsu/Zhu ratio) v12 are proposed and used in the SMMT. This paper describes the quantification of the two amplification factors and the reduction factor, and discusses and interprets the physical meanings behind the amplification and reduction. This paper also uses the SMMT originally quantified for RC torsional beams to analyse an experiment on RC wall specimens under torsion, and compares the SMMT analytical results with experimental data to demonstrate the physical significance of the SMMT in detail.