Yield Strength Of Transverse Reinforcement Research Articles

CURVATURE DUCTILITYOF REINFORCED CONCRETE BEAM SECTIONS STIFFENED WITH STEEL PLATES

This paper presents theoretical parametric study of the curvature ductility capacity for reinforced concrete beam sections stiffened with steel plates. The study considers the behavior of concrete and reinforcing steel under different strain rates. A computer program has been written to compute the curvature ductility taking into account the spalling in concrete cover. Strain rate sensitive constitutive models of steel and concrete were used for predicting the moment-curvature relationship of reinforced concrete beams at different rate of straining. The study parameters are the yield strength of main reinforcement, yield strength of transverse reinforcement, compressive strength of concrete, spacing of stirrups and steel plate thickness. The results indicated that higher strain rates improve both the curvature ductility and the moment capacity of reinforced concrete beam sections. Moreover the section curvature ductility increases as the thickness of the stiffening plates decreases.

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.

Effect of Configuration and Yield Strength of Transverse Reinforcement on Lateral Confinement of RC Columns

In general, the lateral confinement capacity of RC columns is influenced by the strength and configuration of transverse reinforcement. In this study, performed antisymmetric flexural moment experiments that simulated seismic loads, with the configuration and yield strength of the transverse reinforcement of RC square columns as main variables. The eight specimens were square cross-sections measuring 250 × 250 mm, and the lateral confinement effect in relation to main variables was examined by inducing flexural failure in the plastic hinge zone under a shear span-to-depth ratio (a/D) of 3.0. Transverse reinforcements comprised a square and octagonal S-series and tie-based H-series. The yield strengths of the transverse reinforcements were 453 MPa and 1053 MPa, respectively. Compared to the H-series, the S-series, whose configuration of transverse reinforcement is closer to a circular form, exhibited more prominent ductile behavior after flexural yield with increasing yield strength of transverse reinforcement, which indicates greater lateral confinement.

Theoretical and practical models for shear strength of corroded reinforced concrete columns

In order to predict the shear strength of corroded reinforced concrete column (CRCC) accurately and efficiently, both theoretical and practical models for shear strength of the CRCC were established through theoretical derivation and experimental validation. The deterioration mechanism for shear strength of the CRCC due to the steel reinforcement corrosion was explored first based on the shear mechanism analysis of the truss-arch model. Then a theoretical model for shear strength of the CRCC was developed by taking into account the influences of steel reinforcement corrosion on the effective yield strength of transverse reinforcement, the effective cross-sectional area of both corroded transverse and longitudinal reinforcements as well as the effective concrete shear area. Meanwhile, three practical models to evaluate the shear strength of the CRCC were proposed based on 54 sets of experimental data by determining the approximate values of three important parameters, including the contribution coefficient of shear strength for concrete, the ratio of shear stiffness between the truss model and the arch model, as well as the tangent value of the critical crack angle. Finally, the accuracy and applicability of both theoretical and practical models for shear strength of the CRCC were validated by comparing with five existing empirical shear strength models.

Behavior of Plastic-steel Fiber Reinforced Lightweight Aggregate Concrete Columns Subjected to Concentric Axial Loading

This paper presents the findings of an experimental study on the behavior of plastic-steel fiber (PSF) reinforced lightweight aggregate concrete (LWC) columns under axial compression loading. The experimental variables were concrete compressive strength, main reinforcement percentage, and PSF volumetric ratio. The behavior of the PSF reinforced LWC columns was evaluated in terms of the failure mode, load-bearing capacity, steel reinforcement strain, and ductility. The results showed that the addition of PSFs not only prevented premature spalling of the concrete cover but also strengthened the bond between the LWC and the steel bar. Compared with that of the control specimen, the ductility of the fiber-reinforced columns improved significantly. In addition to the experimental program, a numerical investigation based on nonlinear finite element (FE) analysis was performed using ANSYS 10.0. The experimental and numerical results were compared and found to be in satisfactory agreement. Furthermore, an analytical model developed in a previous study was used to predict the load-bearing capacities of the PSF reinforced LWC columns. The compressive strength of concrete, the spacing, and yield strength of transverse reinforcement were considered in the analytical models, and the analytical predictions were in agreement with the experimental results.

Structural behaviour of prestressed concrete beams with high-strength stirrups

Many studies related to high-strength concrete material have been conducted, but relatively few studies have considered high-strength steel reinforcement. Four current design codes – ACI 318-14, Eurocode 2, CSA A23.3-04, and JSCE-07 – limit the yield strength of transverse reinforcement to control diagonal crack width, and to ensure yielding of transverse reinforcement prior to brittle failure mode. ACI, Eurocode 2 and CSA A23.3-04 limit the yield strength of transverse reinforcement to 420, 600, and 500 MPa, respectively; while JSCE-07 limits the yield strength to 800 MPa, when the compressive strength of concrete is higher than 60 MPa. The implementation of high-strength transverse reinforcement in prestressed concrete (PSC) and reinforced concrete (RC) beams has been determined in this study. A total of 16 beams were strengthened using higher yield strength stirrups than the code limitations, and were monotonically loaded to failure. All the beams were designed to experience shear failure prior to flexural failure. Most of the test results showed yielding of the stirrups, and narrower crack width than the code limitations even though the specimens were strengthened with higher than 420 MPa stirrups. The test results imply the feasibility of using high-strength stirrups for PSC beams with regard to serviceability.

ДЕФОРМИРОВАНИЕ ЦЕНТРАЛЬНО СЖАТЫХ ЖЕЛЕЗОБЕТОННЫХ КОЛОНН ИЗ БЕТОНА С ДОБАВЛЕНИЕМ КРУПНОГО ЗАПОЛНИТЕЛЯ ИЗ БЕТОННОГО ЩЕБНЯ

The article presents results of experimental studies of centrally compressed reinforced concrete columns with the addition of concrete rubble as coarse aggregate. Previous studies shows that recycled concrete in the form of crushed concrete rubble obtained from construction waste is an environmentally friendly alternative to traditional coarse aggregate for the manufacture of load-bearing structures. Currently, the scientific literature has a limited amount of information about the calculation methods to be used for the design of reinforced concrete columns with the addition of concrete rubble as coarse aggregate. In this paper, the experimental data on the physicomechanical properties of concrete available in the foreign and domestic literature are summarized. In addition, the deformation features of reinforced concrete columns are highlighted to substantiate the initial premises, hypotheses and possible limitations when developing methods for calculating centrally and eccentrically compressed elements from the specified concrete. Researches are analyzed related to the effect of different content of recycled concrete aggregate in the concrete, the number of longitudinal steel reinforcement in the cross section of the element and its yield strength, pitch and yield strength of transverse reinforcement on the deformability and bearing capacity of concrete columns with the addition of coarse aggregate from concrete rubble. The use of such concrete for the manufacture of centrally and eccentrically compressed concrete columns leads to an insignificant decrease in their bearing capacity. This indicates the possibility of recycling a significant amount of concrete rubble resulting from the processing of reinforced concrete structures destroyed during the demolition of buildings; it allows to attribute this technology to “green building”.

New empirical formulations for indirect estimation of peak-confined compressive strength and strain of circular RC columns using LGP method

Reinforced concrete (RC) columns have been basically designed to withstand compressive loads by means of strain and ductility of the longitudinal and transverse reinforcing materials. The objective of this paper is to propose new predictive models of confined compressive strength and strain at confined peak stress of circular-reinforced concrete columns using a powerful evolutionary-based computational technique, namely, linear genetic programming (LGP). For this aim, a collection of data is utilized to develop new models. The models obtained in this study characterize peak-confined compressive strength and corresponding strain factors in terms of the compressive strength of unconfined concrete cylinder specimens, core diameter of circular column, yield strength of transverse reinforcement, ratio of volume of lateral reinforcement to volume of confined concrete core, spacing of lateral reinforcement or spiral pitch, and ratio of longitudinal steel to area of core of section in addition to the column height. These factors have also been considered as the most significant input variables in several models proposed by scholars in the existing literature for approximation of the peak-confined compressive strength and corresponding strain of RC columns. To evaluate the validity of the obtained models, several analyses are conducted and the results are compared with those provided by other researchers to validate and verify the capability of the proposed models. Consequently, the results explicitly approve that the proposed models are of a notably better performance than the traditional models in the literature.

An empirical model for confined concrete after exposure to high temperature

SummaryIn this study, constitutive relationships have been developed for confined concrete subjected to elevated temperature to specify the fire‐performance criteria for concrete structures after exposé to fire. This study extends over a total of 63 circular hoop confined concrete specimens that were casted and tested under concentric compression loading after exposure to high temperature. The test variables studied are the yield strength of transverse reinforcement, spacing of the hoop, and exposure to temperatures from ambient to 800°C. It is shown that all of these variables have significant influence on concrete behavior at different temperatures and further an improvement in the thermal resistance of concrete when confined using transverse steel reinforcement. On the basis of experimental results, a model for confined concrete after exposed to high temperature is proposed to predict the results of residual behavior after thermal cycles. The proposed empirical stress‐strain equations are suitable to predict the postfire behavior of confined normal strength concrete in compression. The predictions were found to be in good agreement and well fit with experimental results.

Enhancing the confinement of ultra-high-strength concrete columns using headed crossties

This study investigates the influence of headed crossties on the confinement of 200MPa ultra-high-strength concrete (UHSC) columns. A Total of six UHSC columns confined by headed crossties (deformed reinforcing bars with heads welded on both ends) and seismic crossties, detailed with 90° bend anchorages alternated end to end, were constructed and tested under pure axial load. The amount and yield strength of transverse reinforcement were varied to determine the efficiency of headed crossties on the confinement of the UHSC columns. The columns with seismic crossties exhibited some loss in confinement due to the loss of anchorage of the 90° hooks that opened up before significant yielding of the crossties could occur. The relatively small heads used are capable of developing the yield force of high-strength transverse reinforcement in the UHSC columns. The use of high-strength headed crossties resulted in improved confinement compared to columns with high-strength seismic crossties resulting in improved post-peak performance of UHSC columns. A prediction model that accounts for the additional confinement pressure due to the bearing of the heads, brittle cover spalling and the stress-strain relationship of UHSC was used to predict the axial load-strain behavior of the UHSC columns.

Behavior of a Novel Circular HSC Column with Double High Strength Spirals

During the last decades, great progress has been made in the research and application of high strength concrete (HSC). Due to its high strength, low dilation and brittle nature, substantial more transverse reinforcement is needed for HSC columns to obtain ductile behavior, especially for columns with large axial load ratio and/or located in seismic zones. In this paper, a novel HSC concrete column with double high-strength stirrups is proposed, which features two concentric transverse stirrups. The concrete in the cross section are divided into three parts under different confinement level, namely unconfined concrete, singly and doubly confined concrete. This structural form possesses many advantages over traditional HSC with single stirrup and steel-concrete composite columns, including enhanced strength and ductility, easy to construction and easy to connection with RC beams. Three demonstrative circular HSC columns with double spirals were prepared and tested under concentric axial compression. A current stress-strain model for steel confined HSC was modified and found suitable to predict the behavior of present HSC column with double spirals. A parametric study was then conducted to investigate the influence of several key parameters on load-strain response of HSC column with double spirals, including concrete strength, transverse reinforcement ratio, yield strength of transverse reinforcement and center to center diameter of inner spiral.

Structural Behavior of RC Cylinders Confined with High Strength Transverse Reinforcement

The number of high-rise reinforced concrete (RC) buildings is steadily increasing since 1980’s. The use of high strength concrete is indispensible for high-rise RC construction to ensure sufficient strength of the structure. The effect of high strength concrete can be significantly improved by the use of high strength and large size reinforcing bars. The yield strength of transverse reinforcement is limited in the current design codes to prevent possible sudden concrete failure due to over reinforcement. This paper presents the effects of the yield strength of transverse reinforcement and compressive strength of concrete on the structural behavior of reinforced concrete cylinders. Two parameters were considered in this investigation: compressive strength of concrete and the yield strength of transverse reinforcement (472MPa, 880MPa, and 1,430 MPa). Analytical and experimental results indicated that the structural behavior of RC cylinders confined with high strength transverse reinforcement is strongly influenced by compressive strength of concrete.

철근콘크리트 교각의 소요연성도에 따른 심부구속철근량 산정식 수정

Structural Team, Seoyeong Engineering Co., Ltd., Seoul 135-240, KoreaABSTRACT An equation for calculating confining reinforcement amount of RC bridge columns, specified in the current bridge designcodes, has been made to provide additional load-carrying strength for concentrically loaded columns. The additional load-carrying strengthwill be equal to or slightly greater than the resistant strength of a column against axial load, which is lost because the cover concrete spallsoff. The equation considers concrete compressive strength, yield strength of transverse reinforcement, and the section area ratio as majorvariables. Among those variables, the section area ratio between the gross section and the core section, varying by cover thickness, is avariable which considers the strength in the compression-controlled region. Therefore, the cross section ratio does not have a large effectin the aspect of ductile behavior of the tension-controlled region, which is governed by bending moment rather than axial force. However,the equation of the design codes for calculating confining reinforcement amount does not directly consider ductile behavior, which is animportant factor for the seismic behavior of bridge columns. Consequently, if the size of section is relatively small or if the section arearatio becomes excessively large due to the cover thickness increased for durability, too large an amount of confining reinforcement willbe required possibly deteriorating the constructability and economy. Against this backdrop, in this study, comparison and analysis were per-formed to understand how the cover thickness influences the equation for calculating the amount of confining reinforcement. An equationfor calculating the amount of confining reinforcement was also modified for reasonable seismic design and the safety. In addition, appro-priateness of the modified equation was examined based on the results of various test results performed at home and abroad.Keywords : bridge columns, confining reinforcement, section area ratio, cover thickness, safety

Finite Element Simulation and Parametric Studies of Perfobond Rib Connector

Simulating the push-out test and conducting parametric study using finite element model are conducted using perfobond connectors. The finite element model was verified through comparing with push-out test results. The verified finite element model was then used to conduct parametric study aiming to investigate the effect of several parameters, such as height and thickness of connector, cross sectional area and yield strength of transverse reinforcement, concrete compressive strength and rib holes, on resistance capacity. The results of the parametric study are treated statistically to produce a mathematical model suggested to estimate the resistance capacity of the perfobond connector.

CURVATURE DUCTILITYOF REINFORCED CONCRETE BEAM SECTIONS STIFFENED WITH STEEL PLATES

This paper presents theoretical parametric study of the curvature ductility capacity forreinforced concrete beam sections stiffened with steel plates. The study considers the behavior ofconcrete and reinforcing steel under different strain rates. A computer program has been written tocompute the curvature ductility taking into account the spalling in concrete cover. Strain ratesensitive constitutive models of steel and concrete were used for predicting the moment-curvaturerelationship of reinforced concrete beams at different rate of straining. The study parameters are theyield strength of main reinforcement, yield strength of transverse reinforcement, compressivestrength of concrete, spacing of stirrups and steel plate thickness. The results indicated that higherstrain rates improve both the curvature ductility and the moment capacity of reinforced concretebeam sections. Moreover the section curvature ductility increases as the thickness of the stiffeningplates decreases.

Characteristic Behavior of High-Strength Concrete Columns under Simulated Seismic Loading

The main objective of this research is to examine the behavior of high-strength concrete(HSC) columns. Eight test columns in one-third scale were tested under the conditions of cyclic lateral force and a constant axial load equal to 30% of the column axial load capacity. The <TEX>$200{\times}200mm$</TEX> square columns were reinforced with eight DB bars constituting a longitudinal steel ratio of 2.54% of the column cross-sectional area. The main experimental parameters were volumetric ratio of transverse reinforcement(<TEX>${\rho}_s$</TEX>=1.58, 2.25 percent), tie configuration(Type H, Type C, Type D) and tie yield strength(<TEX>$f_{yh}$</TEX>=548.8 and 779.1 MPa). It was found that the hysteretic behaviour and ultimate deformability of HSC columns were influenced by the amount and details of transverse reinforcement in the potential plastic hinge regions. Columns of transverse reinforcement in the amount 42 percent higher than that required by seismic provisions of ACI 318-02 showed ductile behavior. At 30% of the axial load capacity, it is recommended that the yield strength of transverse reinforcement be held equal to or below 548.8 MPa. Correlations between the calculated damage index and the damage progress are proposed.

Curvature Ductility of Reinforced Concrete Column Sections Under Different strain Rates

This paper presents theoretical parametric study of the curvature ductility capacity for reinforced concrete column sections. The study considers the behavior of concrete and reinforcing steel under different strain rates. A computer program has been written to compute the curvature ductility taking into account the spalling in concrete cover. Strain rate sensitive constitutive models of steel and concrete were used for predicting the moment-curvature relationship of reinforced concrete columns at different rate of straining. The study parameters are the yield strength of main reinforcement, yield strength of transverse reinforcement, compressive strength of concrete, spacing of ties and the axial load. The results indicated that higher strain rates improve both the curvature ductility and the moment capacity of reinforced concrete column sections.

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.

Seismic performance of high-strength concrete columns

This experimental investigation was conducted to examine the behaviour of eight one-third scale columns made of high-strength concrete. The columns were subjected to a constant axial load corresponding to 30% of the column axial load capacity and a cyclic horizontal load-inducing reversed bending moment. The variables studied in this research are the volumetric ratio of transverse reinforcement (ρs = 1·58, 2·25%), tie configuration (Type H, Type C, Type D) and tie yield strength (fyh = 548·8 and 779·1 MPa). Test results show that the flexural strength of all the columns exceeds calculated flexural capacities based on the equivalent concrete stress block used in the current design code. Columns with 42% higher amounts of transverse reinforcement than that required by seismic provisions of ACI 318-02 showed ductile behaviour. With an axial load of 3% of the axial load capacity, it is recommended that the yield strength of transverse reinforcement be held equal to or below 548·8 MPa. Relationships between the calculated damage index and the observed damage such as initial crack, spalling of concrete, buckling of longitudinal bar, and crushing of concrete are proposed.

Behavior of Confined High Strength Concrete Columns under Axial Compression

An experimental study was carried out to investigate the behavior of high strength concrete short columns confined by circular spirals and square ties under monotonically increasing concentric compression. The test variables included volumetric ratio, spacing and yield strength of transverse reinforcement, longitudinal reinforcement ratio, lateral steel configuration, shape of cross section and concrete compressive strength. The effects of these variables on the uniaxial behavior of high strength concrete columns are presented and discussed The results indicate that more confinement is required in columns of high strength concrete than in columns of low strength concrete to achieve the desired post-peak deformability. The behavior of high strength concrete columns is characterized by the sudden spalling of concrete cover, leading to a loss of axial capacity. A comparative study of existing confinement models of high strength concrete columns was also conducted to assess their capabilities of predicting the actual test behavior. To this end, the stress-strain curves of the specimens tested in the present study were compared with the ones predicted by the various models. It is shown that Legeron & Paultre (2003) model estimates the actual experimental curves more closely as compared to the other models employed in the study.