Yield Strength Of Longitudinal Reinforcement Research Articles

Probabilistic curvature-and-drift limit states predictive models of high-strength bridge columns

This study presents the derivation of closed-form component limit state expressions for high-strength concrete columns reinforced with high-strength steel bars (HSC-HSSB) from an extensive database through the moment–curvature analysis approach. Initially, sensitivity analysis was conducted to investigate the regularity of the parameters (section size, axial-load ratio, longitudinal reinforcement ratio, stirrup reinforcement ratio, concrete compressive strength, and yield strength of longitudinal reinforcement) on the curvature limit state. The approach being convenient, massive samples were obtained in a short time, therefore, 6^7(279936) levels were generated to derive the predictive expressions of curvature and moment limit states by using the logarithm linearity model. Subsequently, based on the cross-section expressions, the drift displacement and shear force limit states predictive expressions were derived and verified by experimental studies, and these limit states were predicted with high precision. Moreover, after considering the uncertainty of material and section size, the curvature and drift displacement of the HSC-HSSB column exhibited a lognormal distribution, and the useful suggested standard deviations (βc) in different limit states were proposed for practical application of fragility curves to assess the vulnerability of bridge columns to earthquakes.

Seismic performance of RC columns under combined cyclic flexural and constant axial loadings

In this study, an experimental test procedure is conducted to investigate seismic performance of reinforced concrete columns under earthquake loading. Earthquake loading is simulated by combination of constant axial load and reversing cyclic load. The main variables of the experimental program are selected to be dimensionless axial load level and the ratio of shear span to effective column depth. Test results are compared with the current suggestions and approximations used for performance-based design and/or evaluation of reinforced concrete (RC) columns under seismic loads. It is observed that section curvature plays an important role to express failure damage limit state under cyclic loading as well as to sudden decrease in load carrying capacity. Besides, two new simple suggestions are made for performance-based design and/or evaluation process of RC columns. As a first step of this suggestions, a relation between damage limit states and curvature ductility ratios of RC columns is defined. This relation is validated with the experimental results of test columns through damage index model based on section curvature. The proposed damage limit states vary according to damage level definition and based on buckling parameter in terms of diameter, buckling length and yield strength of longitudinal reinforcement. The second suggestion is made to relate damage limit state to decrease in shear resistance of columns. To this purpose, a model to express concrete contribution to shear strength due to the proposed damage limits is used. With these two new proposed equations, it is both aimed to obtain a damage limit state in terms of curvature ductility ratio and to control ductile failure mode in a simple yet effective way.

Torsional capacity evaluation of RC beams using an improved bird swarm algorithm optimised 2D convolutional neural network

This study presents the application of deep learning technology in torsional capacity evaluation of reinforced concrete (RC) beams. A data-driven model based on 2D convolutional neural network (CNN) is established, where model inputs contain the beam width, beam height, stirrup width, stirrup height, concrete compressive strength, steel ratio of longitudinal reinforcement, yield strength of longitudinal reinforcement, steel ratio of transverse reinforcement, yield strength of transverse reinforcement and stirrup spacing. To enhance the prediction accuracy of the proposed model, an improved bird swarm algorithm (IBSA) is leveraged to optimise the hyperparameters of CNN in the training phase. A comprehensive dataset, comprising 268 groups of laboratory tests of RC beams collected from published articles, is used for model development and validation. The results show that the proposed 2D CNN with hyperparameter optimisation exhibits high performance in predicting torsional strength of RC beams, which outperforms other machine learning models, building codes and empirical formula in terms of a series of evaluation metrics.

Study on the Time-dependent Reliability of Corroded Reinforced Concrete Bridge Structures due to Ship Impact

The cumulative damage caused by chloride ion erosion to coastal bridge structures reduces the ship impact resistance of channel bridge structures and leads to changes in reliability of bridge structures on ship impact. It is of great theoretical and practical significance to study the performance degradation change law of corroded bridge structures and to evaluate the ship impact time-dependent reliability of in-service corrosion-damaged bridge structures. Based on the durability decay model of reinforced concrete structures in a chloride ion erosion environment, the time-dependent resistance analysis of bridge structures is carried out considering the reduction of yield strength of longitudinal reinforcement and hoop reinforcement in pile sections and the decay of compressive strength of protective layer concrete. Based on the study of the probabilistic model and parameters of random variables affecting the time-dependent reliability of ship-bridge collision, the typical damage modes of bridge structures under ship impact are analyzed, the time-dependent reliability analysis model of bridge structures under ship impact is established based on the structural damage criterion, the ship-bridge crash limit state functional function is given, and the time-dependent reliability analysis of ship-bridge collision is carried out based on the response surface method.

Neural network prediction of joint shear strength of exterior beam-column joint

Beam-Column joints are the critical locations in the reinforced concrete structures as they experience a massive amount of deformations under earthquake. The shear failure of the beam column joint should be avoided for the safety of the structure. In the present study, prediction of joint shear capacity of exterior Beam-column joint is proposed using artificial neural network (ANN). Experimental investigations performed by different authors have been examined and used to prepare the data sets for training, testing and validating the neural network. Parameters responsible for the shear strength of the exterior Beam-Column Joints are identified and the artificial neural network model is proposed to predict the joint shear strength. Input parameters for the ANN model are width and depth of the joint, concrete compressive strength, length of beam, top and bottom longitudinal reinforcement in the beam, yield strength of longitudinal reinforcement in beam, ratio of beam to column depth, joint Shear reinforcement index, beam bar index and column load index. The performance of the neural network model is evaluated by the statistical relations like Coefficient of correlation, Root mean square error and Scatter index. The proposed model is compared with an empirical formula and different equations suggested by the design codes. The results show that the proposed neural network model can effectively predict the joint shear strength of the Exterior Beam-Column joint.

Experimental and numerical investigations on seismic performance of RC bridge piers considering buckling and low-cycle fatigue of high-strength steel bars

In order to promote the application of high-strength steel bars (HSSB) in reinforced concrete (RC) bridge structures, the mechanical properties of HSSB as well as seismic performance of high-strength RC piers were investigated by experimental study and numerical analysis. First, monotonic and low cycle fatigue tests of HRB400E and HTRB600 steel with different slenderness ratios (L/D) were conducted to comparatively study their mechanical properties. Then, quasi-static cyclic tests of seven rectangular RC piers were conducted to study the effects of concrete cover, longitudinal reinforcement yield strength, concrete strength and axial load ratio on seismic behavior of RC piers. Finally, a fiber-based beam-column element was used to simulate the mechanical behavior of steel material and nonlinear response of RC piers. Material tests indicate that HTRB600 steel has lower uniform and fracture elongations, as well as inferior low-cycle fatigue performance than HRB400E steel. Increase of the slenderness ratio (L/D) severely weakens low-cycle fatigue life of steel bars, and the low-cycle fatigue parameters of steel can be fitted for each slenderness ratio, respectively. Even though HTRB600 steel has relatively lower ductility and inferior low-cycle fatigue performance, the RC piers with HTRB600 steel still have higher or at least comparable deformation capacity than that with HRB400E steel. This results from the reduction of strain demands of longitudinal bars by the utilization of HSSB in RC piers. Removing the concrete cover neighboring the longitudinal bars in the plastic hinge region has trivial impact on bar buckling and ultimate displacement of RC piers, which confirms that the concrete cover has already spalled off prior to the initiation of longitudinal reinforcement buckling. With identical steel strength and tie configuration, the ultimate displacement of RC pier with C80 concrete is significantly lower than that with C40 and C60 concrete, while the latter two have similar deformation capacity. Increase of axial load ratio (from 0.06 to 0.18) obviously reduces ultimate displacement of RC piers, since the concrete in the compression zone endures greater compressive stress under higher axial load and thus compressive failure occurs earlier. The ReinforcingSteel material model in OpenSees is calibrated by experimental data to accurately simulate the buckling and low-cycle fatigue properties of HRB400E and HTRB600 steel. The fiber-based finite element model (FEM) can predict the strain development of longitudinal bars of RC piers under cyclic loading, and the resulting low-cycle fatigue damage of steel material as well as strength degradation of RC piers. Combined with experimental study and FEM, this paper reveals the influence mechanisms of different factors on the seismic performance of RC piers in detail.

Effect of reinforced concrete beam confinement under cyclic loading on ultimate drift ratio

The purpose of this paper is to evaluate the effect confinement on ultimate drift ratio of reinforced concrete beam specimens using normal concrete. All beam specimens were tested under cyclic loading. The measured compressive strength of the concrete is in the range of 25 – 41.8 MPa, longitudinal reinforcement yield strength is in the range 350 – 570 MPa and transverse reinforcement yield strength is in the range 275 –570 MPa. Test parameters include s/db ratio, ρt , and Vs,a/Mn ratio. The results showed that Vs,a/Mn ratio have a significant effect on the ultimate drift ratio. Increase the nominal shear strength by confinement leads to an increase of ultimate drift ratio. In other hands, spacing of transverse reinforcement not exceeding 8db can achieve minimum 3.00% ultimate drift ratio.

Mechanical Behavior of Slender Composite Columns under Axial Compression Load

In the present experimental investigation, polyvinyl chloride (PVC) plastic pour-in form (PPF) was used in three low-cost composite systems for concrete construction. It included concrete-filled tubular plastic forms (CPPF), steel-reinforced concrete-filled tubular plastic (CPPF-SC and CPPF-Re), and welded wire fabric reinforced concrete-filled tubular plastic (CPPF-WM). The core was laboratory mixed concrete with an average 28-day compressive strength of 31.3 MPa. The performance of the three systems was compared with the corresponding pure concrete (PC), and reinforced concrete (RC) specimens, by testing 16 slender specimens with unequal end restraint-conditions. The analyzed parameters were the tube thickness and diameter, the amount and yield strength of longitudinal reinforcement, slenderness ratio and the rotation of the upper loading steel platen. The test results show that using PPF a hinge was formed and the mode of failure changed from brittle shear for RC specimens to ductile beam failure mode for CPPF with compression softening. The extent of enhancement in strength and ductility depends on the type of composite specimen.

Ultimate bearing capacity correlation of steel tube confined RC column under combined compression-bending-torsion load

Based on the completed experimental study, the structural response of steel tube confined RC (STRC) columns under pure torsion, bending-torsion and compression-bending-torsion load were investigated through the finite element method (FEM). Experimental results were used to verify the proposed finite element model and the verification results revealed that the assessment capability of the developed models was efficacious. The model considered the 3D equilibrium, compatibility, and constitutive laws of materials at the section and structural level. In addition, a parametric study was performed to visualize the influence of steel tube, section size, concrete, longitudinal reinforcement, stirrup, and axial force on the ultimate bearing capacity and the ultimate bearing capacity correlation of STRC columns. To this aim, a total of 72 STRC columns were modeled. It was noticed that the thickness of steel tube, the yield strength of longitudinal reinforcement, the diameter of longitudinal reinforcement (longitudinal reinforcement ratio) and axial force were the most crucial parameter, influencing the ultimate bearing capacity of STRC columns significantly. As well, it was overtly beheld from the study that the correlation curves of flexural and torsional capacity were similar under the influence of different parameters, and relevant equations of flexural and torsional capacity were proposed through curve fitting.

Analysis of deformation characteristics of high-strength reinforced concrete beams under explosion load

The dynamic response and failure characteristics of reinforced concrete beams under explosion loads are affected by various factors. To study the effect of reinforcement strength on the deformation properties of RC beams and to analyze the deformation differences of high-strength RC beams under different explosion loads, comparative explosion tests on two kinds of simply supported RC beams with longitudinal reinforcement yield strength of 400 MPa and 700 MPa were carried out respectively in this paper. The test results show that the deformation of the mid-span section concrete of the high-strength RC beam is basically the same as that of the ordinary RC beam when the peak overpressure value is small, and the strength advantage of the high-strength reinforcement has not been fully exerted. With the increase of explosion load, the maximum tensile strain and compressive strain of concrete at the mid-span section of high-strength RC beams are 46.6% and 43.5% of ordinary RC beams respectively. Under the action of high overpressure explosion load, the deformation of RC beams can be significantly reduced by high-strength reinforcement, which limits the development of cracks.

Research on Concrete Columns Reinforced with New Developed High-Strength Steel under Eccentric Loading.

The use of new developed high-strength steel in concrete members can reduce steel bar congestion and construction costs. This research aims to study the behavior of concrete columns reinforced with new developed high-strength steel under eccentric loading. Ten reinforced concrete columns were fabricated and tested. The test variables were the transverse reinforcement amount and yield strength, eccentricity, and longitudinal reinforcement yield strength. The failure patterns were compression and tensile failure for columns subjected to small eccentricity and large eccentricity, respectively. The same level of post-peak deformability and ductility could only be obtained with a lower amount of transverse reinforcement when high-strength transverse reinforcements were used in columns subjected to small eccentricity. The high-strength longitudinal reinforcement improved the bearing capacity and post-peak deformability of the concrete columns. Furthermore, three different equivalent rectangular stress block (ERSB) parameters for predicting the bearing capacity of columns with high-strength steel are discussed based on test and simulated results. It is concluded that the China Code GB 50010-2010 overestimates the bearing capacity of columns with high-strength steel, whereas the bearing capacities computed using the America Code ACI 318-14 and Canada Code CSA A23.3-04 agree well with the test results.

Ultimate torsional capacity of steel tube confined reinforced concrete columns

Based on two quasi-static experiments of steel tube confined reinforced concrete columns (STRC) under pure torsion load, detailed finite element (FE) simulation and theoretical derivation of the corresponding calculation methods were conducted in this paper. FE models of STRC specimens under pure torsion were established using the finite element software ABAQUS, the feasibility of which was then validated against the testing results in terms of both ultimate torsional capacity and failure modes. Comprehensive parametric analysis was presented, including the yield strength of steel tube, the thickness of steel tube, the dimension of cross-section, the strength of concrete, the yield strength of longitudinal reinforcement, the ratio of longitudinal reinforcement, the yield strength and the ratio of stirrup, to investigate the influence on the torsional capacity of STRC columns with important structural factors. It can be found from the parametric analysis results that, the thickness of steel tube, the dimension of cross-section and the ratio of longitudinal reinforcement are the most important parameters for the torsional capacity of STRC. Based on the results parametric analysis, an accurate and simplified calculation method for the ultimate torsional capacity of STRC columns under pure torsion was proposed.

Estimation of in-plane shear capacity of confined masonry walls with and without openings using strut-and-tie analysis

Strut-and-tie analysis is popularly used for the design of shear critical structures and can be applicable for the analysis of confined masonry (CM) walls, which often behave as shear walls. Properties of ties in a strut-and-tie model of CM wall can be simply computed from the yield strength of longitudinal reinforcement whereas that of masonry compression strut may depend on various parameters such as its aspect ratio, the strength of masonry and concrete. A non-linear parametric analysis was performed on more than 200 finite element models to understand the behaviour of masonry strut and a stepwise methodology for the formulation of the strut-and-tie model was proposed for CM walls. The proposed strut-and-tie method was validated by various experimental studies available in the literature. The developed strut-and-tie models consistently provided good predictions for the in-plane capacity of CM walls with and without openings when compared to the experimental results.

Parametric study of RC beams under a wide range of loading rates

Over the years, numerical investigation has been presented as a viable alternative to experimental studies, as testing of structural members to assess the effect of several parameters at a time is not only cumbersome but also expensive. Thus, after validating the results from a finite-element analysis with experimental outcomes, a numerical parametric study was conducted to investigate the effects of various parameters on the dynamic increase factor (DIF) of the maximum resistance and the failure mode of reinforced-concrete beams under a wide range of loading rates. From the results, it can be concluded that the DIF of maximum resistance for beams with a small amount of longitudinal reinforcement is greater than that for beams with a large amount of longitudinal reinforcement. A change in the failure mode can be observed (mainly at high rates, 2 m/s) when the longitudinal reinforcement ratio is increased (approaching the balanced-reinforcement ratio) in an under-reinforced beam. For beams with a large amount of transverse reinforcement, the DIF would be lower than for beam with a small amount of transverse reinforcement. Furthermore, it was found that the yield strength of longitudinal reinforcement is the key parameter affecting the failure mode change from flexure at static loading to shear at high loading rates.

Parametric study of RC beams under a wide range of loading rates

Over the years, numerical investigation has been presented as a viable alternative to experimental studies, as testing of structural members to assess the effect of several parameters at a time is not only cumbersome but also expensive. Thus, after validating the results from a finite-element analysis with experimental outcomes, a numerical parametric study was conducted to investigate the effects of various parameters on the dynamic increase factor (DIF) of the maximum resistance and the failure mode of reinforced-concrete beams under a wide range of loading rates. From the results, it can be concluded that the DIF of maximum resistance for beams with a small amount of longitudinal reinforcement is greater than that for beams with a large amount of longitudinal reinforcement. A change in the failure mode can be observed (mainly at high rates, 2 m/s) when the longitudinal reinforcement ratio is increased (approaching the balanced-reinforcement ratio) in an under-reinforced beam. For beams with a large amount of transverse reinforcement, the DIF would be lower than for beam with a small amount of transverse reinforcement. Furthermore, it was found that the yield strength of longitudinal reinforcement is the key parameter affecting the failure mode change from flexure at static loading to shear at high loading rates.

Behavior of reinforced concrete short columns exposed to fire

Fire could dramatically reduce strength of reinforced concrete columns. The objective of this work is to study columns exposed to fire under axial load and to evaluate reduction in column compressive capacity after fire. The first part of this research is experimental investigation of fifteen-column specimens (15×15×100)cm exposed except one specimen to (600°C) fire. The second part is a theoretical analysis performed using three-dimensional nonlinear finite element program. The main studied parameters were concrete strength, fire duration, level of applied loads, longitudinal reinforcement yield strength, percentage of longitudinal reinforcement, and bar diameters.Comparison between experimental results and theoretical analysis indicated that for columns not exposed to fire, the first crack appeared at 80% of column failure load while the first crack occurred at 50% of column failure load for columns exposed to fire. Columns with the same reinforcement percentage but with smaller bar diameters gained less lateral strain and smaller vertical displacement than columns with bigger bar diameters. Using high-grade steel as main reinforcement showed failure load higher by 55% than that of column reinforced by mild steel. Cooling column by jet water resulted in 17% reduction in failure load than columns cooling gradually in room temperature.

Behavior of concentrically loaded high performance concrete tied columns

The paper presents an experimental study of behavior of high performance concrete (HPC) columns under monotonic concentric loading. The test variables include strength of concrete, amount and spacing of transverse reinforcement, configuration of ties and amount and yield strength of longitudinal reinforcement. Concentrically loaded columns of HPC are characterized by early cover spalling due to the plain of separation formed between the cover and core. The equation in codes and literature to predict the axial load capacity of columns were based on tests of normal strength concrete (NSC). Hence, use of existing code equation leads to overestimation of concentric load capacities. The failure pattern is sequenced by the buckling of longitudinal bars, yielding of lateral ties and rupture of ties. The test results indicate decrease in the spacing of lateral ties and increase in volumetric ratio of transverse steel, increases marginally the strength but largely the ductility. Also an equation is proposed such that the prediction of axial load capacity is neither overestimated nor too conservative.

Behavior of Reinforced Concrete Columns with ‘T’-Shaped Cross Section after Exposure to Fire

The residual strength of reinforced concrete (RC) columns with ‘T’-shaped cross section after fire are decreased more quickly than those of RC columns with rectangular cross section for the former have thinner sectional thickness and larger surface area. The influence of several main parameters, such as exposure times, effective lengths, sectional dimensions, load eccentricity ratios, reinforcement ratios, load angles and longitudinal reinforcement yield strength on the residual strength of RC columns with ‘T’-shaped cross section after exposure to fire was investigated. A self-developed finite element program CAFIRE was applied in this study. 24300 hypothetical cases of columns after subjected to fire on all sides were selected for residual strength analysis. Different fire exposure times, effective lengths, cross section dimensions, load eccentricity ratios, reinforcement ratios, load angles and longitudinal reinforcement yield strength were considered in the analyses. Based on the simulation results, a practical method was proposed for calculating the residual strength of columns with ‘T’-shaped cross section after subjected to fire on all sides. The simulation results indicate that: (a) the residual strength of columns with ‘T’-shaped cross section decreases linearly with the increase of effective length, but it increases linearly with sectional width, ratio of sectional height to sectional width, and yield strength of longitudinal reinforcement strength; (b) the residual strength of ‘T’-shaped columns decreases markedly for a load eccentricity ratio in the range of 0.0 to 1.0, whereas it varies slightly for a load eccentricity ratio between 1.0 and 3.0.

Genetic-programming-based modeling of RC beam torsional strength

This study investigates the use of Genetic Programming (GP) to model Reinforced Concrete (RC) beam torsional strength. Experimental data of 76 rectangular RC beams from an existing database were used to develop the GP model. The following input parameters, which affect torsional strength, were selected: beam cross-sectional area, closed stirrup dimensions, stirrup spacing, closed stirrup cross-sectional area of one leg, stirrup and longitudinal reinforcement yield strength, stirrup steel ratio, longitudinal reinforcement steel ratio and concrete compressive strength. Moreover, a short review of well-known building codes in relation to the design of RC beams under pure torsion is presented. The accuracy of the codes in predicting the RC beam torsional strength was also compared with the proposed GP model using the same test data. The study concludes that the proposed GP model predicts RC beam torsional strength more accurately than building codes

Modeling ultimate deformation capacity of RC columns using artificial neural networks

This paper aims to explore the feasibility of the potential use of artificial neural networks (ANN) in deformation estimates of RC columns whose behaviour is dominated by flexural failure. Experimental data of 237 rectangular columns from an existing database were used to develop an ANN model. The input parameters were selected based on past studies such as aspect ratio, longitudinal reinforcement ratio, yield strength of longitudinal reinforcement, uniaxial (cylindrical) concrete strength, yield strength of transverse reinforcement, transverse steel spacing, ratio of transverse steel parallel to the direction of loading, axial load ratio, and confinement effectiveness factor. Ultimate displacement estimates of reinforced concrete columns by the ANN model were compared to the existing semi-empirical and empirical models. The ANN model was found to perform well. The promising results have shown the feasibility of using ANN models for deformation estimates of RC columns.