Transverse Reinforcement Ratio Research Articles

Maximum Drift Demands of Earthquake Damaged Reinforced Concrete Columns Based on Residual Flexure Cracks

AbstractAssessment of existing reinforced concrete (RC) structures after an earthquake is a challenging task that must somehow relate qualitative and quantitative observations in the plastic hinge regions and the associated residual deformation capacity of damaged structures. Having an estimate available for the remaining drift capacity will result in more economical and informed decisions regarding demolition or strengthening options. This study aims to develop a practical methodology to estimate the maximum drift demand of an RC column based on the residual crack width. For this purpose, fiber-based frame elements are used to model the RC column considering appropriately concrete behavior in compression and tension stiffening effects. Afterwards, the accuracy and reliability of the proposed methodology are demonstrated by validating the computational approach with two cyclic experimental results from literature and new test data for a one-bay one-story RC frame conducted within the course of this study. A comprehensive parametric study is performed for RC columns with different axial loads, longitudinal and transverse reinforcement ratios, and ground motions to exhibit the stochastic behavior. The study identifies the axial load ratio as the predominant parameter. Key findings include strong correlations between maximum drift ratios and total residual crack widths, as well as maximum compressive strains, with regression analysis yielding equations for accurate drift ratio estimation. Simple predictive models are proposed to estimate the maximum deformation demands based on observed residual crack widths. Residual cracking exceeding 5 mm poses significant risk for the columns with axial load ratios above 0.4, with 90% probability of exceedance 2% drift ratio.

Shear friction capacity of monolithic construction joints reinforced with self-prestressing reinforcing steel bars

This study examined the shear friction capacity of a monolithic concrete interface reinforced with newly developed self-prestressed reinforcing steel bars (SPRBs). Twelve push-off specimens with SPRBs were prepared according to the different compressive strengths of concrete (f′c) by applying compressive stresses (σx) on a monolithic concrete interface. To compare the shear friction capacities of monolithic concrete interfaces reinforced with conventional reinforcing bars, four companion specimens were prepared. The test results showed that the shear cracking and shear friction capacities were high for specimens with high f′c and σx values, resulting in the highest values for specimens with f′c = 40 MPa and σx = 0.5fy, where fy is the yield strength of the reinforcing steel bar. The test results confirmed that at a similar (ρvffy+σx)/f′c, a σx of more than 0.35fy is required for the SPRBs to achieve a λn value comparable to that of the specimens reinforced with conventional reinforcing bars, where ρvf is the transverse reinforcement ratio and λn is the shear friction capacity. The prediction models ACI 318-19 and AASHTO significantly underestimated the shear friction capacity with low accuracies. In particular, the difference between the experimental and underpredicted values became large as the (ρvffy+σx)/f′c value increased. However, the Mattock's model well-estimated the measured shear friction capacities of all the specimens tested in this study, irrespective of ρvffy and σx. Thus, the mean and standard deviation values of the measured-to-predicted shear friction capacity ratio were 1.07 and 0.13, respectively.

Axial compressive behavior of predamaged RC columns retrofitted with precast steel-reinforced grout jackets

Steel jacketing and concrete jacketing are popular retrofitting techniques to strengthen the axial compressive behavior of reinforced concrete (RC) columns. However, these retrofitting methods lack efficiency in practical application due to intensive labor and time-consuming installation. In order to improve the retrofit efficiency of damaged RC columns, this study proposed a novel precast steel-reinforced grout jacket (PSRGJ) consisting of early-strength cementitious grout and a steel frame. Ten columns were tested to investigate the axial compressive behavior of predamaged RC columns retrofitted with PSRGJ. The tested parameters were the stirrup reinforcement ratio, the transverse reinforcement ratio of PSRGJ, and the predamage level. The results indicated that the columns’ peak load and ductility index I10 were significantly improved by PSRGJ retrofitting and increased with the increase of transverse reinforcement ratio of PSRGJ. Besides, the peak load and the initial stiffness of PSRGJ-retrofitted RC columns decreased with the predamage level, while the ductility index I10 increased. In addition to the confinement effect, PSRGJ carried 11%−17% of the peak load through the interfacial bonding effect. Based on the test results, the actual confinement pressure model and interfacial bonding strength model were proposed. Further, peak load models considering the size effect were developed for PSRGJ-retrofitted intact and predamaged RC columns. The predictions of the proposed models agreed well with the test results from this study and the literature.

A Machine-Learning-Based Failure Mode Classification Model for Reinforced Concrete Columns Using Simple Structural Information

The seismically deficient column details in existing reinforced concrete buildings affect the overall behavior of the building depending on the failure type of the column. The purpose of this study is to develop and validate a machine-learning-based prediction model for the column failure modes (shear, flexure–shear, and flexure failure modes). For this purpose, artificial neural network (ANN), K-nearest neighbor (KNN), decision tree (DT), and random forest (RF) models were used considering previously collected experimental data. Using four machine learning methodologies, we developed a classification learning model that can predict the column failure modes in terms of the input variables using the concrete compressive strength, steel yield strength, axial load ratio, height-to-dept aspect ratio, longitudinal reinforcement ratio, and transverse reinforcement ratio. The performance of each machine learning model was compared and verified by calculating the accuracy, precision, recall, F1-Score, and ROC. Based on the performance measurements of the classification model, the RF model has the highest average value for the classification model performance measurements among the considered learning methods and can conservatively predict the shear failure mode. Thus, the RF model can rapidly predict the column failure modes with the simple column details. Additionally, it was demonstrated that the predicted failure modes from the selected model were exactly same as the failure mode determined from a code-defined equation (traditional method).

Structural behavior of RPC beams subjected to flexural and torsional effects

This research is concerned with the behavior of reactive powder concrete beams (RPC) under the combined effects of bending and torsion moments, with three main parameters: torsional to bending moments ratio (T/M), longitudinal reinforcement ratio ( ), and transverse reinforcement ratio ( ). 12 rectangular reinforced RPC beams with dimensions of (1500 200 150) mm were tested. The outcome demonstrated that increasing the longitudinal reinforcement ratio from =0.009 to =0.016 improved the ultimate capacity significantly by 34.16%, and 35.54% in cases of (T/M) =0, and 0.5 respectively, also it significantly improved moment-deflection response in the case of (T/M) = 1, and well improved torque-rotation response in cases of (T/M)=0.5, and 1. Increasing the transverse reinforcement ratio from = 0.0042 to =0.0075 improved the ultimate capacity significantly by 49.22% in case of pure torsion and slightly improved it in other cases. Also it significantly improved moment- deflection response in case of (T/M) = 1 and improved torque -rotation response in cases of (T/M)=1and ꝏ.

Structural behavior of RPC beams subjected to flexural and torsional effects

This research is concerned with the behavior of reactive powder concrete beams (RPC) under the combined effects of bending and torsion moments, with three main parameters: torsional to bending moments ratio (T/M), longitudinal reinforcement ratio ( ), and transverse reinforcement ratio ( ). 12 rectangular reinforced RPC beams with dimensions of (1500 200 150) mm were tested. The outcome demonstrated that increasing the longitudinal reinforcement ratio from =0.009 to =0.016 improved the ultimate capacity significantly by 34.16%, and 35.54% in cases of (T/M) =0, and 0.5 respectively, also it significantly improved moment-deflection response in the case of (T/M) = 1, and well improved torque-rotation response in cases of (T/M)=0.5, and 1. Increasing the transverse reinforcement ratio from = 0.0042 to =0.0075 improved the ultimate capacity significantly by 49.22% in case of pure torsion and slightly improved it in other cases. Also it significantly improved moment- deflection response in case of (T/M) = 1 and improved torque -rotation response in cases of (T/M)=1and ꝏ.

Prediction model and sensitivity analysis of ultimate drift ratio for rectangular reinforced concrete columns failed in flexural-shear based on BP-Garson algorithm

Considering that the deformation capacity of reinforced concrete (RC) columns is crucial in performance-based seismic design, the ultimate drift ratio of RC columns failed in flexural-shear are studied using BP neural network and Garson (BP-Garson) algorithm. Firstly, this study employed data onto tests conducted on 35 rectangular RC columns with flexural-shear failure. Nine influencing factors including axial load ratio, shear span ratio, longitudinal reinforcement configuration, transverse reinforcement configuration, and material strength were selected as variables, a BP neural network was used to establish the relationship between the ultimate drift ratio and these variables. Accordingly, a predictive model for the ultimate drift ratio of RC rectangular columns failed in flexural-shear was constructed. Then, the Garson algorithm for local sensitivity analysis was applied to determine the sensitivity of each influence of the ultimate drift ratio of RC rectangular columns failed in flexural-shear. The results showed that the BP neural network could accurately predict the ultimate drift ratio of RC rectangular columns with flexural-shear failure, of which the primary influencing factors are shear span ratio, axial load ratio, volume transverse reinforcement ratio and longitudinal reinforcement ratio. The BP-Garson algorithm integrates model development with influence analysis, which could improve computational efficiency and serves as a reference for evaluating the sensitivity of seismic performance and its influencing factors in other structural components.

Shear Capacity of Geopolymer Concrete Deep Beams with Variation of Transverse Reinforcement Ratio

Shear Capacity of Geopolymer Concrete Deep Beams with Variation of Transverse Reinforcement Ratio

Experimental and Numerical Study of Torsional Solid and Hollow Section of Polyolefin Fiber-Reinforced Concrete Beams

An experimental and theoretical program was undertaken to enhance comprehension regarding how variations in fiber ratio impact the structural performance of both solid and hollow reinforced concrete beams when subjected to pure torsion. Polyolefin fiber was utilized in this study. To achieve this objective, a total of sixteen specimens of fiber-reinforced concrete beams were manufactured. Among these, eight were solid beams, while the remaining eight were hollow beams, all featuring rectangular cross-sections. These specimens were constructed employing polyolefin fiber. The findings indicated that incorporating polyolefin fiber into the concrete mixture led to improved mechanical properties in the cured concrete. The most significant enhancements were observed in the splitting tensile strength and flexural strength tests conducted on the specimens. Both solid and hollow beams exhibited notable enhancements in their torsional performance. These enhancements occurred as the polyolefin fiber percentage increased from zero to 1.5%, while the transverse and longitudinal reinforcement ratios remained constant. Furthermore, the reduction ratio of torsional strength becomes more noticeable when comparing solid and hollow sections in high-strength beams, as opposed to normal-strength beams.

Research on the Estimation Model of Energy Consumption Capacity for Reinforced Concrete Components with Axial Force

The research group utilized the estimation model of energy consumption capacity for reinforced concrete components without axial force to assess the energy consumption capacity of 92-reinforced concrete components from the PEER database, which were subjected to axial force and bending. The study also examined the impact of design parameters, including longitudinal reinforcement ratio, transverse reinforcement ratio, axial compression ratio, and shear-span ratio, on the estimation results. The research findings revealed that when applying the estimation model of energy consumption capacity for reinforced concrete components without axial force to calculate the energy consumption capacity of reinforced concrete components with axial force, there was a significant deviation rate in the estimation of cumulative energy consumption. The relationship between the deviation rate of cumulative energy consumption and longitudinal reinforcement ratio, axial compression ratio, and shear-span ratio remained unclear. However, a more apparent linear relationship was observed with the transverse reinforcement ratio. By conducting a quantitative analysis of the transverse reinforcement ratio, the researchers proposed an modified estimation model of energy consumption capacity for reinforced concrete components with axial force. Nonetheless, the accuracy of the modified estimation model was found to be high within the range of 0–250,000 kN mm of cumulative energy consumption. For cumulative energy consumption exceeding 250,000 kN mm, further experimental and theoretical research is still required to enhance the reliability of the modified estimation model.

The influence of longitudinal rebar type and stirrup ratio on the bond performance of reinforced concrete with corrosion

This study investigated the bond-slip mechanism of eccentrically pulled out rebar under different corrosion level. The variation patterns of the bonding performance between two types of steel rebars (i.e., plain round rebar and ribbed rebar) and concrete with different stirrup ratios were obtained with respect to the amount of steel rebar corrosion. The differences in bonding performance between plain round rebars and ribbed rebars with concrete were compared, and the bond-slip mechanisms of plain round rebars and ribbed rebars with concrete were elucidated. The influence of longitudinal bar type and stirrup ratio on the ultimate bond strength and bond-slip constitutive curve was analyzed. It has been determined that in the case of uncorroded specimens featuring ribbed bars, the ultimate bond strength exhibits an approximately linear increase in relation to the stirrup ratio. Conversely, the stirrup ratio does not have a significant impact on the ultimate bond strength of uncorroded specimens with plain round bars. Transverse reinforcement plays a crucial role in mitigating the effects of cracked concrete by delaying the reduction in bond stress caused by the corrosion rate of longitudinal reinforcement. This phenomenon becomes increasingly prominent when higher stirrup ratios are utilized in the case of plain round reinforcement. Transverse reinforcement serves to suppress the occurrence of the brittle failure stage that follows the peak bond stress in specimens exhibiting a low corrosion rate. The magnitude of this effect becomes more pronounced as higher transverse reinforcement ratios are employed.

Probabilistic Seismic drift-based capacity model of unbonded prestressed reinforced concrete columns: Prediction model and dispersion

Structures designed with high ductility often have significant residual displacement. As a self-centered structure, unbonded prestressed reinforced concrete (UBPRC) columns can effectively reduce residual displacement. However, the quantitative analysis of their structural capacity is still insufficient, and further research is needed to quantitatively analyze the effects of various design parameters. In this study, predictive expressions for the drift limit states of UBPRC columns were derived based on a well-calibrated nonlinear finite element model. The effects of the design parameters, including the aspect, reinforcement, axial load, and prestressing force ratios, and the strengths of the reinforcement and concrete, on the drift limit state of UBPRC columns were studied. The results indicate that the aspect ratio, axial load ratio, yield strength of the longitudinal reinforcement, and transverse reinforcement ratio are the primary parameters affecting the drift capacity of UBPRC columns. In addition, these parameters have a logarithmically linear relationship with the drift ratios under different limit states. Accordingly, 58 (390,625) models were established in OpenSees, and simple and reliable predictive expressions for estimating the drift capacity were obtained through multivariate regression analysis. Moreover, after considering the uncertainties in the materials, it was observed that the capacity of the UBPRC columns exhibited a lognormal distribution. Based on the proposed predictive expression and uncertainty of the materials, the dispersion of the capacity of each limit state was obtained, which can be used in practical applications.

Torsional behavior of FRP-strengthened reinforced concrete members considering various wrapping configurations: Theoretical analysis and modeling

Reinforced concrete (RC) structural members such as spandrel, flanged and curved beams, slab beams, and bridge girders may be subjected to significant torsional loading. Despite extensive research on the strengthening of RC members, very little is known about the torsional behavior of RC members strengthened with fiber-reinforced polymer (FRP) sheets. Therefore, very limited guidelines apply to the design of externally bonded FRP systems for torsional strengthening, and no design provisions exist for the U-wrapped and 2-sided strengthening systems in torsion. This study aims to contribute to this growing area of research by developing a new analytical model to predict the full torsional response of strengthened RC members with many conventional configurations such as spiral, transverse and longitudinal FRP, continuous and intermittent strips along the beam length, side bonded, and full-wrapped systems. Moreover, this study provided an analytical model accurately predicting the contribution, efficiency, and failure mode of side-bonded strengthening systems. Additionally, the influence of various parameters such as FRP stiffness and transverse steel reinforcement ratio is taken into account in the constitutive law of concrete and internal reinforcement for the first time. The good agreement between the test results of 32 collected FRP-strengthened RC beams from the literature and the theoretical ones, which were predicted through programming proves the validity and accuracy of the presented theory.

Shear and Bending Performances of Reinforced Concrete Beams with Different Sizes of Circular Openings

The present study pertains to the effects of transverse opening diameters and shear reinforcement ratios on the shear and flexural behavior of RC beams with two web openings across different spans, i.e., a single opening in each half-span. Within the scope of the study, a total of 12 RC beams with five different opening diameter-to-beam depth ratios (0, 0.20, 0.27, 0.33, 0.40, and 0.47) and two shear reinforcement ratios were tested to failure under four-point bending. The load capacities, ductilities, rigidities and energy dissipation capacities in the elastic and plastic ranges of beam behavior were compared. Furthermore, the load capacities of the beams were compared to the existing analytical shear strength formulations in the literature. The test results indicated that whether an RC beam with openings has adequate or inadequate amounts of shear reinforcement, the frame-type shear failure becomes much more pronounced with increasing opening diameter. The reductions in the load capacity and modulus of toughness with increasing opening diameter are more considerable in the presence of inadequate amounts of shear reinforcement, while the beam ductility is less affected in shear-deficient RC beams with openings as compared to the ones with adequate shear reinforcement.

Compressive stress-strain behavior and model for geometrical-similar BFRP RC square columns

This paper presents experimental, numerical and analytical investigations to evaluate the compressive behavior and size effect of square concrete columns internally reinforced with basalt fiber-reinforced polymer (BFRP) bars and ties. Nine BFRP reinforced concrete (RC) square columns were tested under axial compression. The main parameters included cross-sectional heights, transverse reinforcement ratios, and configuration of transverse BFRP ties. The compressive behaviors of BFRP RC columns were discussed in terms of axial load-strain response, confined strength, and ductility index. The results revealed that there was significant size effect on the confined efficiency and ductility. With the increasing cross-sectional height, the maximum decreases of confined efficiency and ductility index were 16.0% and 18.9% respectively. Moreover, a meso-scale numerical model considering the heterogeneity of concrete was developed and verified using the test results. A parametric analysis was then performed to evaluate the effects of cross-sectional height and transverse reinforcement ratio on the compressive performance of BFRP tie-confined concrete. Finally, a design-oriented stress-strain model was proposed considering the effect of cross-sectional height and transverse reinforcement ratio. The proposed model was validated using the test results in the present study and literature.

Nonlinear Behavior of the Concrete Core of the Diagonally Reinforced Coupling Beams

Coupled shear walls with coupling beams are constructed because of openings such as doors, windows, or other installations that are left behind due to functional reasons in shear walls. In coupling beams having a ratio of span-to-depth less than two, shear fracture occurs rather than flexural fracture. In order to meet the shear force and the bending moment formed by the coupling beams, diagonal bundles are used in the coupling beams. Diagonal reinforced coupling beams are generally preferred because diagonal reinforced coupling beams exhibit better behaviour than conventional reinforced coupling beams. The diagonal reinforcement bundles have to be confined by transverse reinforcements prescribed in the codes. Confined concrete in the diagonal reinforcement bundles has stress-strain characteristics that are distinctly different from those of plain concrete. The effects of longitudinal and transverse reinforcement ratios on the stress-strain behaviour of confined concrete inside the diagonal reinforcement bundles were investigated. Fifty-four reinforced concrete coupling beams with different confining parameters of the diagonal reinforcement bundles and different variables were analysed using the program. It was demonstrated that the strength and the maximum strain of the concrete inside the diagonal reinforcement bundles increase with the reinforcement ratio of the confinement reinforcement. The increase in the diameter of the transverse reinforcement and the decrease in the spacing of the transverse reinforcement diagonal bundles, increase the confining effect, strength, and ductility in the concrete sections. The increase in the ratio of transverse and diagonal reinforcement significantly affects the seismic behaviour of the coupling beams.

Analysis of the shear behavior of reinforced recycled aggregate concrete beams based on shear transfer mechanisms

This study aims to contribute to a more rational understanding of the shear behavior of reinforced recycled (concrete) aggregate concrete beams. Twelve reinforced concrete beams - six with natural aggregate concrete (NAC) and six with 100% coarse recycled concrete aggregates (RAC) - with same concrete compressive strength (38 MPa) and proportions of cement and aggregates per volume, varying the longitudinal (1.15%, 1.75%, and 2.50%) and transverse (0%, 0.086%, and 0.114%) reinforcement ratios, were tested under a 4-point bending setup with a full-field displacement monitoring. A thorough examination of the failure span along the tests, associating critical crack shape and kinematics with an investigation of the shear transfer mechanisms provided by mechanical models from the literature was conducted. Direct shear tests on push-off specimens followed by analyses of their failure surface evaluated the characteristics of shear crack surfaces and a proper modeling of the aggregate interlock contribution. The results showed a 28% average reduction in the shear strength of RAC beams with no stirrups in comparison with their reference beams (NAC), whereas beams with stirrups of same characteristics showed a similar shear strength, regardless of the type of coarse aggregate. The evaluation of the shear transfer mechanisms enabled an understanding of the reasons for those behaviors. Experimental results were also compared with those predicted in design codes. They were conservative for beams with stirrups, and, in general, less accurate than those obtained by the shear transfer mechanisms.

Size effect on the compressive behavior of BFRP RC circular columns: Experiments and a size-dependent stress-strain model

To investigate the size effect on compressive performance of circular concrete columns reinforced with basalt fiber-reinforced polymer (BFRP) bars and spirals, nine geometrically similar columns were fabricated and tested under concentric compression. The variables tested were cross-sectional diameters (200, 400, and 600 mm) and transverse reinforcement ratios (1.2%, 2.2%, and 3.3%). The results evidently indicated the size effect on the confined strength, corresponding strain and deterioration rate (in the post-peak branch) of concrete core confined by BFRP spirals. Specifically, with the cross-sectional diameter changing from 200 mm to 600 mm, the maximum decreases in the confined strength and corresponding strain were 14.1% and 31.9%, respectively, while the maximum increase in the deterioration rate was 318%. In addition, the size effect on confined strength could be weakened with the increase of transverse reinforcement ratio. Increasing the transverse reinforcement ratio could enhance the load-carrying capacity as well as effectively increase the confinement strength and ductility. Finally, a size-dependent stress–strain model, which considers the size effect of confined strength, corresponding strain and deterioration rate, was developed for evaluating the confined behavior of FRP RC columns.

Shear strength behavior of high-strength fly ash concrete beams with low-bond reinforcement

This study aims to investigate the shear behavior of high-strength fly ash (HSFA) concrete beams with low-bond reinforcement (LBR). With this purpose, twenty-three HSFA concrete beam specimens were constructed and tested. The experimental results showed that owing to the high-strength property of LBR, the tested beams easily failed in shear. The shear strength of the HSFA beams was mainly controlled by the shear span to depth ratio (a/d) and transverse reinforcement ratio. The shear strength Vs carried by the transverse reinforcement started to increase when the shear strength Vc carried by the concrete started reducing or growing at a lower rate. Formulas in design provisions, except for strut-and-tie model (STM) and those in the “AIJ standard for structural calculation of reinforced concrete structures” proposed by Architectural Institute of Japan (AIJ), could not accurately assess the shear strength of HSFA concrete beams because they do not reasonably consider the effect of a/d on the Vc. Generally, the current design models underestimate the Vs. Based on the test results, a new model that can reasonably consider the effect of a/d on Vc was proposed to accurately evaluate the shear strength of HSFA concrete beams reinforced by LBRs. This study deepens the understanding of researchers and engineers of the shear behavior of HSFA concrete beams with LBRs.

Failure time of reinforced concrete column under blast load

To explore the damage and the failure time of the reinforced concrete column in an adjacent physical field of explosion, a comprehensive finite element model of TNT-air-column in the software LS-DYNA is set up in consideration of the advanced numerical simulation technologies (i.e., element birth and death technology, large deformation technology, contact technology, etc) and the strain rate effects of the concrete and steel materials. First of all, an explosion test is conducted on two scale models of the reinforced concrete column, and the finite element model is validated by comparing the numerical simulation results with the experimental data. The failure process, failure mode, and failure criterion of the reinforced concrete column under blast load are further investigated. Thereafter, a series of parameter studies are conducted to investigate the damage and the failure time of the reinforced concrete column. Finally, a new method is proposed to estimate the failure time of the reinforced concrete column and the corresponding basic steps are given in this study. Through the researches and analyses of the typical cases, the results show that the failure modes change from punching failure to compression-flexure failure via compression-shear failure with the increase in the scaled distance. The medium damage and the high damage occur mostly on the reinforced concrete column in an adjacent physical field of explosion. The damage index of the reinforced concrete column varies significantly with the compressive strength of concrete, column height, column depth, longitudinal reinforcement ratio, transverse reinforcement ratio, and axial compression ratio, especially the column depth and the axial compression ratio; however it has little relation with the column width. The failure time of the reinforced concrete column is up to tens of milliseconds or even more than one hundred milliseconds. The calculation formulas used in the proposed method are based on previous research and simulation results. The proposed method is rigorous and thorough and the predicted results are highly accurate and effective. Besides, this method can provide a good prediction of the failure time of the reinforced concrete columns with different axial compression ratios.