Lateral Reinforcement Ratio Research Articles

Numerical evaluation of axial compressive behavior of hollow concrete columns reinforced with GFRP bars and spirals

AbstractWith the advancement in the concrete technology, the application of precast concrete elements in the buildings and road infrastructures is increasing very rapidly. One of such applications is the use of precast hollow concrete elements in the bridge construction. As the conventional steel reinforcement is highly susceptible to corrosion, the use of non‐corrosive reinforcement in precast hollow concrete piers and piles of bridges could be a good option for the durability of bridge structures., In this regard, hollow concrete columns reinforced with fiber‐reinforced polymer (FRP) have been considered as a potential solution to overcome the structural deterioration due to corrosion. In the past, limited studies have been carried out on hollow concrete columns reinforced with FRP, consequently, the behavior of such columns is not fully understood. Therefore, to comprehensively evaluate the behavior of hollow concrete columns for various design parameters, a finite element model (FEM) was developed in this study using the commercial tool “Abaqus”. The model was developed and verified based on the experimental results of studies conducted by two independent research groups on circular concrete columns. The proposed model well predicted the peak loads with an error less than 10% and the failure modes of the tested columns. The verified constitutive relation and establishing method were further employed to conduct parametric evaluations to observe the influence of different parameters, such as inner‐to‐outer diameter ratio, longitudinal reinforcement ratio, lateral reinforcement ratio, and concrete strength, on the behavior of hollow concrete columns. Parametric analyses show that reduced inner‐to‐outer diameter ratio and larger longitudinal or lateral reinforcement may lead to higher peak load and confined concrete strength. Finally, based on the experimental and FEM evaluations, the strength prediction equations were developed for the analysis and design of hollow concrete columns reinforced with GFRP bars.

A Case Study On Concrete Column Strength Improvement with Different steel fibers and polypropylene fibers

High presentation concrete is chiefly cast-off in multistory constructions where it expressively lessening the measurements of columns, which styles it a more economical excellent for building than normal strength concrete. In seismic area, high enactment concrete posses more complications, since it has less ductility in comparison with normal concrete. The purpose of this research is to detect the combined consequence of fibers and ties on the conduct of reinforced columns and to advance their ductility. This study presents an investigational valuation of strength and ductility of ordinary and high presentation concrete short columns limited by tie with and without steel fibers and polypropylene fibers. Five square concrete columns (100×100×1000) mm were established. The variables considered were, concrete strength, volume percentage of longitudinal reinforcement (4.52%), volumetric ratio of lateral reinforcement (spacing between ties) (5.58%) volume fraction of fibers (0.5% and 0.75%), form of fibers (hooked steel fiber and polypropylene) and phase ratio of steel fibers (100) (length 50mm and diameter 0.5mm) and (60) (length 30mm and diameter 0.5mm). The column specimens were tested under axial load. The values presented that the adding of steel fibers (volume friction 0.75% and aspect ratio 100) for high presentation concrete improves the compressive strength, splitting tensile strength, flexural strength, and static modulus of elasticity. Commonly, the effects also exhibited that the adding of fibers to usual and high act concrete upsurges the strength and advances their performance.

Longitudinal axial strain in plastic hinge regions of reinforced-concrete columns

Energy dissipation of columns in the post-yielding range of deformation plays a significant role in preventing the total collapse of reinforced-concrete (RC) structures. However, such plastic deformations cause elongation in plastic hinge regions of RC columns if the axial force ratio is low. This study investigated the elongation behaviour of RC columns by testing five groups of 20 specimens subjected to three different loading patterns. Experimental results showed that the longitudinal axial strain of RC columns was quite different from that of RC beams because of the presence of axial force. The longitudinal axial strain of RC columns reduced with increasing axial force. Axial strain was also a function of loading pattern and lateral reinforcement ratio. Based on these observations, an analytical model was developed to predict the axial strain behaviour of RC columns. The proposed model includes four path types: a loading region, an unloading region, a slip region and a repeated loading region. The model was verified against 32 test results, including specimens tested in this study and reported in the literature. The longitudinal axial strain predicted using the proposed model agreed reasonably well with the experimental axial strains results.

Simulation study on the shear transfer behavior of recycled aggregate concrete

In this paper, a three‐dimensional finite element method (FEM) model of push‐off tests for specimens made with recycled aggregate concrete (RAC) was presented. The FEM model used ABAQUS/Standard module software. The model considered the plasticity of concrete and the concrete‐to‐concrete contact properties, and was found to agree with experimental data from shear transfer tests. The verified model was then used for a parametric study that investigated lateral reinforcement, concrete strength, and recycled coarse aggregate (RCA) replacement ratio. The parametric study shows that the ultimate shear strength increases by 23.1% when the lateral reinforcement ratio increases from 0.56% to 1.12%; the ultimate shear stress increases almost linearly when the concrete strength increases from 30 MPa to 60 MPa; the ultimate shear stress is reduced by 13.8% when the RCA replacement ratio increases from 0% to 100%.

鉄筋軸方向に圧縮力を受けるコンクリートの付着割裂強度に関する実験的研究

The influence of the stress in a direction perpendicular to the bar on bond strength has already been studied a lot in association with lateral reinforcement, however, the influence of the axial stress has not been clear yet. In this study, a brush type loading equipment was used in order to reduce the friction and pull-out tests were conducted with the concrete under axial compression. The parameters were concrete cover thickness, lateral reinforcement ratio, and axial force ratio. The results show that bond strength decreases with the increase in the axial force ratio in the case of no lateral reinforcement, and the load with which the first crack occur decreases with the increase in the axial force ratio regardless of the exist of lateral reinforcement.

Inelastic Displacement Spectra for Displacement-Based Seismic Design of High-Speed Railway Bridge Pier

The inelastic displacement spectra is established based on the elastic displacement spectra and the strength reduction factor, the calculation process of Displacement-Based Seismic Design is presented in this paper, the seismic design of high-speed railway bridge piers is conducted to verified the method. The calculation results show that, at the same performance target, the pier height is taller, the cross-section is bigger; at the same pier height, the performance target is higher, the cross-section of pier is bigger; the reinforcement ratio with the different pier height and performance target are the lower limit of calculation value, it mean that the lateral reinforcement ratio of piers can just meet the detailing requirements.

BOND SPLITTING TEST OF REINFORCED STRAIN-HARDENING CEMENTITIOUS COMPOSITE BEAMS

Recently, RC buildings with core wall structures have been constructed. The coupling beams connecting core walls are possible to be failed by bond splitting during an earthquake. Short span beams using SHCC (Strain Hardening Cementitious Composites) with PVA fibers have been developed to improve brittle behavior. In this study, cantilever-shaped specimens were subjected to bond splitting tests to investigate bond characteristics of SHCC beams. The experimental bond strength shows higher value than calculated strength by conventional formulas for RC beams. The effect of SHCC can be expressed by modifying the term of lateral reinforcement ratio in these formulas.

Stress–strain curve for concrete in circular columns based on elastoplastic analysis

This paper presents a stress–strain curve that describes the axial behavior of concrete in circular columns with lateral reinforcement. As opposed to most studies on this subject, which used semiempirical methods, the proposed stress–strain relations are based on a theoretical derivation. They have been derived from analysis of the problem’s full range according to the theories of elasticity and plasticity. Based on these theories, the current study analytically examines the influence of the main variables, such as the volumetric lateral reinforcement ratio and the material properties, on the behavior of circular confined concrete columns and proposes theoretical expressions that describe their stress–strain relations. Application of the proposed curve shows good agreement with published test results. Since these expressions were derived from a theoretical analysis, they can be considered as an analytical verification of existing empirical curves, yet they are also simple enough for practical applications.

Displacement Ductility of Helically Confined HSC Beams

This paper presents an experimental investigation of the effect of helix pitch and helix diameter on beam be- haviour through testing 10 helically confined beams. Two groups of beams had exactly the same geometry and reinforce- ment; with the only differences being the helices diameter and pitch. 8 mm helix was used in the first group of beams and 12 mm bars in the second group. The helix pitches varied between 25 mm and 160 mm. Beams' cross section was 200  300 mm, with a length of 4 m subjected to four point loading. The main results indicate that the helical effectiveness is neglected when the helical pitch is 160 mm (helix diameter) and the displacement ductility index increases as the helical pitch decreases. Finally, there is a considerable release of strain energy responsible for spalling off the cover. efficiency of tie confinement is 50% of the helical confine- ment for the same lateral reinforcement ratio. The same ef- fectiveness of confinement is applicable in columns and beams. Helix confines the concrete more effectively than rectangular ties as the helix applies a uniform radial stress on the concrete along the concrete member, whereas a rectangu- lar tie tends to confine the concrete mainly at the corners. Thus the effective concrete area at the cross section is re- duced because the concrete pressure will tend to bend the tie sides outward due to their low stiffness compared to the four corners (3). As such a significant portion of the concrete in the cross section is considered as unconfined. On the other hand the arching of the concrete between the ties reduces the effective confined concrete at the cross section of the mem- ber. Thus using helical confinement in the compression zone of rectangular beams is more effective than using rectangular ties. Nevertheless, to prove experimentally that the helix is more effective than the rectangular ties, there is a need to compare beams helically confined with beams confined us- ing rectangular ties. A study by Whitehead and Ibell (4) proved that the use of helical confinement is more effective than rectangular ties in beams.

Seismic Behavior of 200 MPa Ultra-High-Strength Steel-Fiber Reinforced Concrete Columns under Varying Axial Load

Cyclic loading tests were carried out on ultra-high strength RC columns under high axial load conditions. Effective concrete strength of 200 MPa with high-strength steel fibers (SF) was used. The investigated parameters were: 1) volumetric ratio of steel fiber, 2) lateral reinforcement ratio, and 3) axial loading type. The main characteristics of the tested columns (maximum strength, deformation capacity and equivalent viscous damping factor) are presented and the influence of various parameters is discussed. The test results revealed the advantage of using SF in terms of strength and damage control. The maximum strength of the tested columns using SF, assessed using a number of different formulas, proved to be on the safe side. On the other hand, in the case of columns in which SF was not used, the estimated maximum strength was found to be larger than the tested value, except when using NZS3101 equation. This difference is probably due to early spalling off of the cover concrete.

Development of a confined model for rectangular ordinary reinforced concrete columns

In order to estimate the flexural behaviour of reinforced concrete members, the stress–strain behaviour of the constituent materials must be well established. The behaviour of confined concrete is important to the designer in order to determine the quantity of the confining steel required in reinforced concrete column sections to achieve the ultimate curvatures required in seismic design for ductility. The objective of this study is to develop an analytical model for the confinement mechanism in rectangular reinforced concrete columns. The proposed model was established on the basis of the observations derived from several experimental studies conducted in past years and encompasses some features of already established models. The main variables examined in the model include the volumetric ratio of lateral reinforcement, the characteristics of steel and concrete and the effectiveness confinement coefficient. The comparison with other existing models illustrates the validity of the proposed equations.

An analytical model for stress–strain behavior of confined concrete

It is well known that the strength and ductility of concrete are highly dependent on the level of confinement provided by the lateral reinforcement. The stiffness and the constitutive behavior of the confining reinforcement (elastic, elastoplastic, etc.) are the important factors affecting the behavior of concrete. In this study, a new simple confined concrete model is developed for describing the axial and lateral deformation characteristics of concrete under triaxial compression. The stress–strain relationship of confined concrete in the axial direction is defined with an elastic region followed by a nonlinear curve. The descending region of the stress–strain curve is defined using a constant failure energy criterion. The elastic limit, ultimate strength, and residual capacity of confined concrete are determined using the Leon–Pramono criterion. The lateral deformation of confined concrete is described using a function that provides a smooth transition from elastic to inelastic behavior and satisfies the zero volumetric strain condition at ultimate strength. The model estimations are compared with the results of triaxial concrete compression tests, and fiber reinforced polymer (FRP) and steel confined concrete tests reported in the literature. A good agreement was observed in terms of ultimate strength, residual strength, and axial and lateral deformation behavior. It was observed that the model can be successfully applied for FRP and steel confined concrete, removing the need to adjust parameters for different lateral reinforcement types. Finally, a parametric study was conducted to investigate the effect of the lateral reinforcement ratio, concrete strength, and compressive failure energy on the behavior of steel and FRP confined concrete.

Neural Network Modeling of Confined Compressive Strength and Strain of Circular Concrete Columns

The application of artificial neural networks (ANN) to predict the confined compressive strength and corresponding strain of circular concrete columns is explored. Using available data from past experiments, an ANN model with input parameters consisting of the unconfined compressive strength, core diameter, column height, yield strength of lateral reinforcement, volumetric ratio of lateral reinforcement, tie spacing, and longitudinal steel ratio was found to be acceptable in predicting the confined compressive strength and corresponding strain of circular concrete columns subject to limitations in the training data. The study shows the importance of validating the ANN models in simulating physical processes especially when data are limited. The ANN model was also compared to some analytical models and was found to perform well.

An experimental study of the behaviour of high-strength reinforced concrete columns subjected to reversed cyclic shear under constant axial compression

An experimental study was conducted to examine the behaviour of high-strength reinforced concrete (R/C) columns subjected to a reversed cyclic load and axial compression, and to find the relationship between the amount of lateral reinforcement and the axial load ratio. Twenty column specimens were tested. The test parameters of the column specimens were the compressive strength of concrete (f′c = 25, 52 and 70 MPa), the axial load ratio (0·3 and 0·5 f′cAg) and the volumetric ratio of lateral reinforcement (ρs = 1·05, 2·1 and 3·15%). The test results indicated that the axial load ratio and the shape of the lateral reinforcement could significantly affect and alter the behaviour of high-strength R/C columns under inelastic cyclic loading.

A model for stress—strain relationship of spirally confined normal and high-strength concrete columns

An analytical model is developed to predict the complete stress–strain relationship of normal and high-strength concrete subject to uniaxial compressive loading and confined by transverse reinforcement. The confinement pressure is assumed to be uniform within the core of the column. The internal force equilibrium, the properties of the materials, and the geometry of the section are used to evaluate the pressure. The model utilizes a single fractional equation which satisfies realistic behaviour of the ascending portion, the peak point, and the post-peak descending portion of the stress–strain relationship. The predictions of the model and the available experimental results are compared over a range of concrete strengths. The model shows good predictive capability and is applicable for a wide range of variables such as the diameter of the circular section, the pitch, diameter and yield stress of the spiral, and the volumetric ratio of lateral reinforcement.

Analytical Study for Concrete Confinement in Tied Columns

The finite element method is used to study the confinement of concrete by rectangular ties in reinforced‐concrete tied columns. Eight columns are analyzed under monotonically increasing axial cumpression until failure. A general approach for nonlinear analysis of reinforced‐concrete columns based on the finite element is developed. The effects of the volumetric ratio of lateral reinforcement and the distribution of the longitudinal steel and the resulting tie configuration on the confinement action are studied. The results indicate that both the strength and ductility of tied columns increase as the volumetric ratio of the lateral ties increases. The study demonstrates that the relationship between gain in strength of the confined concrete and the volumetric ratio of the lateral steel is approximately linear. It is found that lateral confinement had no effect on the behavior of tied columns at loads less than 70% of the ultimate load. The finite element approach favorably predicted the results obtained experimentally by other investigators.

Analytical Model for Concrete Confinement in Tied Columns

An analytical model for the confinement mechanisms in tied columns has been developed. The model is based on the test results reported previously. A complete stress-strain curve for confined concrete is proposed. The strength of the confined concrete is calculated by using the concept of the effectively confined concrete area within the nominal concrete core. The area of the effectively confined concrete is determined by the tie spacing, the distribution of longitudinal steel around the core perimeter and the resulting tie configuration. According to the model, better distribution of longitudinal steel and smaller tie spacing result in higher strength and ductility of concrete. Other variables examined include the volumetric ratio of lateral reinforcement and the characteristics of steel. The results from the model agree well with the test results. Practical examples demonstrating the application of the model have been presented. Building code requirements for confinement are examined and it has been concluded that in certain circumstances the Codes provisions may be unsafe, while in others they may be unnecessarily conservative.

Anchorage Behavior Of 90-degree Hooked BeamBars In Reinforced Concrete Knee Joints

Beam bars of reinforced concrete structures are usually anchored with 90-degree hooks in exterior beam-column joints. However, there have been far fewer studies on the anchorage behavior of 90-degree hooked-bar than on straight-bar anchorage. In our previous paper, we divided the anchorage failure of 90-degree hooked bars in exterior beam-column joints in a middle storey in a building into three modes: side split failure; local compression failure; and raking-out failure, in which a concrete block, approximating the inside dimensions of the hooked bar in size, is raked out toward the beam side of the column due to the presence of many beam bars and/or to short development length within the joint. The purpose of this paper was to clarify the anchorage performances on the raking-out failure mode of beam top-bars with 90-degree hooks arranged in an exterior beam-column joint in the roof story of a building. Fifteen specimens of knee joints with various arrangements of L-shaped beam bar anchorage and various material properties, were subjected to pull-out loading on the beam top-bars. From the experimental results, we were able to conclude that: (1) the anchorage mechanism depends on stress transmission from the tail portion of the beam bar hooks to the adjacent column bars in a joint and that the anchorage mechanism in a knee joint was quite different from that in a exterior beam-column joint in a middle story; (2) the main factors in influencing anchorage strength are tail length, horizontal distance between tail and column bars and between tail bars and the beam end, lateral reinforcement ratio within the joint and concrete strength; and (3) accurate estimation of anchorage strength can be obtained by taking into account the influence of the above mentioned factors.