Volumetric Ratio Of Transverse Reinforcement Research Articles

Seismic performance of circular hollow concrete columns

AbstractFour circular hollow reinforced concrete columns were tested under quasi‐static reversed lateral loading to investigate their seismic performance. The effects of the wall thickness ratio and confinement configuration on their seismic performance were studied, and the applicability of seismic ductility design requirements on circular hollow concrete columns was examined. The test results showed that circular hollow concrete columns with a single layer of transverse reinforcement presented limited ductility, and their displacement ductility improved as the wall thickness ratio increased. Two layers of transverse reinforcement with crossties allowed circular hollow concrete columns to present excellent seismic performance. However, the column designed with a smaller amount of inner transverse reinforcement presented a better response than the as‐built column with equal amounts of inner and outer transverse reinforcement. In addition, the widely used seismic design requirements on the volumetric ratio of transverse reinforcement seem to be conservative for the ductile design of circular hollow concrete columns.

Effect of Uncertainties in Material and Structural Detailing on the Seismic Vulnerability of RC Frames Considering Construction Quality Defects

This paper evaluates the effect of construction quality defects on the seismic vulnerability of reinforced concrete (RC) frames. The variability in the construction quality of material properties and structural detailing is considered to assess the effect on the seismic behavior of RC frames. Concrete strength and yield strength of the reinforcement are selected as uncertain variables for the material properties, while the variabilities in the longitudinal reinforcement ratio and the volumetric ratio of transverse reinforcement are employed for structural detailing. Taking into account the selected construction quality uncertainties, the sensitivity analysis of the seismic vulnerability of the RC frames is performed and the impact of significant parameters is assessed at the global and local levels. This extensive analytical study reveals that the seismic vulnerability of the selected RC frame is particularly sensitive to concrete strength and the volumetric ratio of transverse reinforcement.

Research on uniaxial compressive behavior of high‐strength spiral stirrups confined circular ultra‐high performance concrete columns

AbstractTo study the uniaxial compressive behavior and constitutive relationship of high‐strength spiral stirrups confined circular ultra‐high performance concrete (UHPC) columns, an experimental investigation was presented. In this research, 14 confined UHPC columns and seven unconfined UHPC columns were tested to investigate the effects of the stirrup spacing, stirrup yield strength, and steel fibers volume content on the compressive behavior of the UHPC columns. The test results indicated that transverse reinforcement can effectively improve the deformation capacity of the UHPC columns, and all the confined UHPC columns showed ductile failure. The results also demonstrated that the high‐strength stirrup was more effective than normal‐strength stirrup for improving the post‐peak behavior of the confined UHPC. Compared with the stirrup strength, the volumetric ratio of transverse reinforcement had a more significant effect on the post‐peak ductility and toughness of the confined UHPC columns. Transverse reinforcement and steel fibers had a combined effect on improving the post‐peak behavior. Reducing the stirrup spacing or increasing the steel fibers volume content can better improve the axial compressive behavior of columns. A new constitutive model for confined UHPC was proposed. Compared with four existing models, this new model was in good agreement with the experimental curves.

A unified approach to evaluate axial force-moment interaction curves of concrete encased steel composite columns

This paper presents a unified approach to evaluate the axial force and moment interaction strength curve of Concrete Encased Steel (CES) composite columns made of different steel and concrete grades. A database was established by collecting the test results of CES composite columns in the literature covering concrete compressive strength ranging from 20 to 104 MPa and steel yield strength from 280 to 913 MPa. A sensitivity study was then carried out to investigate the effect of different design parameters on the accuracy of the current design method EN 1994-1-1 in predicting the ultimate strength of CES composite columns. These design parameters include characteristic strength of materials, steel contribution ratio, concrete cover thickness ratio, longitudinal reinforcement ratio, and volumetric ratio of transverse reinforcement. Analytical study was performed through a self-compiled computer program which was developed based on materials strain compatibility principle. The comparison between the analytical results and test results confirms the validity of the proposed method to provide reasonable prediction of cross-sectional axial-moment interaction curves for CES columns for a wide range of steel and concrete grades. The existing EC4 method, which is based on plastic design principle, was found to be un-conservative in predicting the cross section resistance of CES composite columns with high strength concrete and high strength steel. Further enhancement was made to the proposed method to include both the strain gradient effect and concrete confinement effect to achieve a better agreement with the test results reported in literature. Finally, a simplified method was proposed to construct the axial-moment interaction curves of CES columns, which can be used as a unified approach to design such columns with normal and high strength steel and concrete materials.

Stress-strain model for C-shape confined concrete masonry boundary elements of RM shear walls

Reinforced masonry (RM) shear walls with boundary elements have been recently presented as a more ductile alternative to RM rectangular shear walls. Evaluating the complete (i.e. including the post-peak branch) compression stress-strain behavior of the confined and unconfined masonry is essential for predicting the seismic response of the RM walls with boundary elements. Recently, the authors investigated the effect of various volumetric ratios of transverse reinforcement, vertical reinforcement ratios, and grout strength on the axial stress-strain behavior of reinforced masonry boundary elements (RMBEs). However, all the specimens had a specific height to thickness ratio (i.e., AR = 5). This study presents the observed stress-strain relationship of seventeen half-scale fully grouted unreinforced and RMBE specimens, built using C-shape blocks, tested under concentric compression loading up to failure. Thus, quantifying the effect of various aspect (height to thickness) and confinement ratios on the RMBEs peak stress, strain corresponding to peak, and post-peak behavior. The results indicate that, as the hoop spacings and/or aspect ratio decreases, the peak stress and post-peak strains increase. Moreover, this study presents a stress-strain empirical model capable of predicting the RMBE stress-strain response by computing the confined and unconfined masonry stress-strain behavior. The model is calibrated using the experimental data of thirty-three RMBE specimens, tested in this study and literature. The proposed model presents an efficient tool that can be implemented in different analytical/numerical packages.

Assessment of ultimate drift capacity of RC shear walls by key design parameters

The latest version of the Standard for Structural Calculation of Reinforced Concrete Structures, published by the Architectural Institute of Japan in 2010 [1], allows the design of shear walls with rectangular cross sections in addition to shear walls with boundary columns at the end regions (referred to here as “barbell shape”). In recent earthquakes, several reinforced concrete (RC) shear walls were damaged by flexural failures through concrete compression crushing accompanied with buckling of longitudinal reinforcement in the boundary areas. Damage levels have clearly been shown to be related to drift in structures; this is why drift limits are in place for structural design criteria. A crucial step in designing a structure to accommodate these drift limits is to model the ultimate drift capacity. Thus, in order to reduce damage from this failure mode, the ultimate drift capacity of RC shear walls needs to be estimated accurately. In this paper, a parametric study of the seismic behaviour of RC shear walls was conducted using a fibre-based model to investigate the influence of basic design parameters including concrete strength, volumetric ratio of transverse reinforcement in the confined area, axial load ratio and boundary column dimensions. This study focused on ultimate drift capacity for both shear walls with rectangular sections and shear walls with boundary columns. The fibre-based model was calibrated with experimental results of twenty eight tests on shear walls with confinement in the boundary regions. It was found that ultimate drift capacity is most sensitive to axial load ratio; increase of axial load deteriorated ultimate drift capacity dramatically. Two other secondary factors were: increased concrete strength slightly reduced ultimate drift capacity while increased shear reinforcement ratio and boundary column width improved ultimate drift capacity.

Experimental study on the cyclic behavior of steel fiber reinforced high strength concrete columns and evaluation of shear strength

In this paper, the effectiveness of steel fiber inclusion on the structural performance of steel fiber reinforced high strength concrete columns was investigated with test of 7-high strength concrete specimens with and without steel fiber. All test specimens were subjected to axial load and reversed cyclic lateral loads. It was shown that test steel fiber inclusion significantly increase the structural performance. Steel fiber inclusion was remarkably effective than the transverse reinforcement about structural performance such as strength and energy dissipation capacity. Steel fiber reinforcement was more effective with high volumetric ratio of transverse reinforcement. Compressive strength of matrix affect to the strength and ductility. High strength matrix column specimens showed better performance than normal strength matrix column specimens. In order to verify the safety of existing strength estimation equations, test results were compared with estimated values. Most of the estimation equations were over estimated the shear strength of concrete. Therefore, in this study, for the safe design of steel fiber reinforced high strength concrete columns, newly developed estimation equation was suggested.

Critical factors in displacement ductility assessment of high-strength concrete columns

Ductility of high-strength concrete (HSC) columns with rectangular sections was assessed in this study by reviewing experimental data from the available literature. Up to 112 normal weights concrete columns with strength in the range of 50–130 MPa were considered and presented as a database. The data included the results of column testes under axial and reversed lateral loading. Displacement ductility of HSC columns was evaluated in terms of their concrete and reinforcement strengths, bar arrangement, volumetric ratio of transverse reinforcement, and axial loading. The results indicated that the confinement requirements and displacement ductility in HSC columns are more sensitive than those in normal strength concrete columns. Moreover, ductility is descended by increasing concrete strength. However, it was possible to obtain ductile behavior in HSC columns through proper confinement. Furthermore, this study casts doubt about capability of P/Agfc′ ratio that being inversely proportional to displacement ductility of HSC columns.

Size effect of confined concrete subjected to axial compression

In order to investigate the size effect and other effects on the stress-strain relationship of confined concrete, 42 specimens with different sizes and section shapes were placed under axial compression loading. Effects of key parameters such as size of specimens, tie configuration, transverse reinforcement ratio, and concrete cover were studied. The results show that for specimens with the same configuration and the same volumetric ratio of the transverse reinforcement, along with the increasing specimen size, the peak stress, peak strain and deformation of the post-peak show a down trend, however, the volumetric ratio of the transverse reinforcement is lowered, the decreasing of the peak stress is accelerated, but the decreasing of the deformation is slow down. For specimens with the same volumetric ratio but different configurations of transverse reinforcement, though the transverse reinforcement configuration becomes more complicated, the peak stress of the large size specimen does not improve more than that of the small size. However, the deformation occurs before the stress declines to 85% of peak stress, and the improvement with the grid pattern tie configuration is much greater due to size effect.

Seismic shear strength and deformation of RC columns failed in flexural shear

This paper investigates the seismic shear strength and deformation capacity of flexural shear critical columns in the post-yield range of longitudinal reinforcement. In total, 24 reinforced concrete (RC) column specimens with span-to-depth ratios ranging from 1·63 to 6·16 and volumetric ratios of transverse reinforcement of 0·77% and 1·54% were tested under constant axial load ratios of 0·2 and 0·5 and cyclically reversed horizontal load. Of these 24 RC column specimens, seven failed in flexure, two failed in shear and 15 failed in flexural shear. Based on the test results, simple models are proposed to predict the shear strength and displacement capacity of columns failed in flexural shear mode. The proposed shear model includes the effects of span-to-depth ratio, axial load ratio, transverse reinforcement and displacement ductility. Analytical results from the proposed model were compared with test data and consistent agreement was achieved.

SEISMIC ENHANCEMENT OF REINFORCED-CONCRETE COLUMNS BY REBAR-RESTRAINING COLLARS

When reinforced-concrete columns are subjected to lateral cyclic loading, columns usually suffer failures at plastic hinges. If the buckling of longitudinal reinforcements at plastic hinges can be prevented or delayed, columns are expected to carry gravity loads at a higher ductility level. In this study, the rebar-restraining collar (RRC) was developed to improve the post-buckling behavior of longitudinal reinforcements. The behavior was investigated under monotonic loading tests of reinforcing bars with the RRCs and the cyclic loading tests of two reinforced-concrete bridge columns with and without RRCs. From the monotonic loading test, it was found that the RRCs significantly improved the post-yielding behavior of longitudinal reinforcing bars. The ductility and energy dissipation of longitudinal reinforcing bars with RRCs was significantly higher than that of the bare bar. Then, cyclic loading tests of two reinforced-concrete bridge columns were conducted. The cross section of columns was 0.4 m × 0.4 m, and the effective height was 2.15 m. The ratio of longitudinal reinforcing bars was 0.0123, and the volumetric ratio of transverse reinforcement was 0.00424. The column with RRCs did not have buckling of longitudinal reinforcements and had the ductility enhancement of about 17%, comparing to the column without RRCs. One evident benefit of using the RRCs is to control damage at plastic hinges of columns. Hence, the repair cost of columns after an earthquake can be reduced.

Seismic Performance of High Titanium Heavy Slag High Strength Concrete Columns

For expedite the development of high titanium heavy slag concrete, eight high titanium heavy slag high strength reinforced concrete (HTHS-HSRC) scale model column are studied. The eight HTHS-HSRC model columns are tested under reversed horizontal force. Primary experimental parameters include axial load ratio varying from 0.3 to 0.5, volumetric ratios of transverse reinforcement ranging from 1.38% to 1.56%, strength of high titanium heavy slag high strength concrete varying from 55.9 to 61.6 N/mm2 and configurations of transverse reinforcement. It is found from the test result that HTHS-HSRC model columns provides comparable seismic performance to those usually used reinforced concrete column in terms of member ductility, hysteretic and energy dissipation capacity. Primary Factors of Displacement Ductility of Model Columns are also discussed.

Cyclic Constitutive Model for High-Strength Concrete Confined by Ultra-High-Strength and Normal-Strength Transverse Reinforcements

In this paper, a cyclic constitutive model is developed for high-strength concrete (HSC) confined by ultra-high-strength and normal-strength transverse reinforcements (UHSTR and NSTR), with the intention of providing efficient modeling for the member and structural behaviour of HSC in seismic regions. The model for HSC subjected to monotonic and cyclic loading, comprises four components; an envelope curve (for monotonic and cyclic loading), an unloading curve, a reloading curve, and a tensile unloading curve. It explicitly accounts for the effects of concrete compressive strength, Volumetric ratio of transverse reinforcement, yield strength of ties, tie spacing, and tie pattern. Comparisons with test results showed that the proposed model provides a good fit to a wide range of experimental results.

Transverse Reinforcement of RC Columns Considering Effective Lateral Confining Reduction Factor

An experimental investigation was conducted to examine the hysteretic behavior of ultrahigh-strength concrete tied columns under stress to determine the effect of the volumetric ratio of transverse reinforcements on column deformability. Eight 1/3-scale columns were fabricated to simulate a half-story of actual structural members, and their axial load ratio, transverse reinforcement configuration, and transverse reinforcement volumetric ratio were changed during the simulation. The column deformability was found to be affected by the configurations and volumetric ratios of the transverse reinforcement. The column behavior was particularly affected by the axial load ratio as compared to the amount and configuration of the transverse reinforcement. To improve the ductility behavior of an RC column using ultrahigh-strength concrete in a seismic region, a volumetric ratio of transverse reinforcement was suggested for all data satisfying the required displacement ductility ratio of over 4. The results indicate that the effective lateral confining reduction factor λc, calculated by considering the configuration and spacing of transverse reinforcement and the axial load ratio, is reflected in the volumetric ratio of transverse reinforcements.

유효횡구속압력 감소계수를 사용한 RC 기둥의 횡보강근량 평가

본 연구는 고축력과 반복횡력을 받는 초고강도 RC 띠철근 기둥의 실험적 연구를 수행하였다. 콘크리트 압축강도 100 MPa 초고강도 RC 띠철근 기둥의 횡보강근의 양을 제안하는 것이다. 철근콘크리트 구조물의 실제 보를 스터브로 이상화한 1/2개 층의 기둥 실험체를 계획하여 1/3 크기의 19개 실험체를 제작하였다. 주요 변수는 축력비, 횡보강근의 형상 및 체적비로 하였다. 실험 결과, 띠철근 기둥의 강도와 연성은 횡보강근의 형상과 체적비의 영향을 받는 것으로 나타났으나, 무엇보다 축력비에 가장 큰 영향을 받는 것으로 나타나 초고강도 콘크리트 기둥의 횡보강근량 설계를 위해서는 축력비에 따른 적절한 횡보강근의 형상으로 보다 합리적인 설계가 이루어져야 할 것으로 판단된다. 또한, 초고강도 철근콘크리트 기둥의 충분한 연성확보를 위하여 최소한의 변위연성능력 4이상을 확보할 수 있도록 설계식을 제안하였다. 따라서 이는 축력비와 함께 횡보강근의 형상, 간격 및 주근의 개수 등을 고려한 유효횡구속감소계수(λc)를 적용한 것이므로 횡보강근량 산정시 보다 합리적일 것으로 판단된다.

FLEXURAL BEHAVIOR OF OVER REINFORCED HSC BEAMS CONFINED BY RECTANGULAR TIES

This paper presents an experimental and analytical investigation on the flexural behavior of over reinforced concrete beam confined by rectangular ties. The experimental investigation was conducted through testing four full-scale beams with normal strength concrete (NSC). Three out of these four beams were confined using rectangular ties located on the compression region of the beams. The variables studied in these specimens were the volumetric ratio of transverse reinforcement, and the volumetric ratio of the main rebars. A finite element model was established with both material and geometrical non-linearity by using ANSYS software package. Accuracy of the model was assessed by applying it to the three tested beams. Comparison of analytical results with the available experimental results for ultimate load values and load– deflection relationships show a good agreement between the finite element and experimental results. After validating the accuracy of the proposed model, parametric study was undertaken to gain additional insight into the overall behaviour, failure modes, and deformation capacity for the concrete beams using high class concrete strength. The parameters studied were, the concrete compressive strength, the number and diameter of longitudinal rebars, and diameter of rectangular ties. The obtained results show that, the strength and ductility of high strength concrete (HSC) beams are enhanced through the application of rectangular tie reinforcement located in the compression region of the beams. The concrete compressive strength, the longitudinal bars number and diameter, and the diameter of rectangular ties are important parameters controlling the level of strength and ductility enhancement of overreinforced HSC beams.

Analytical Stress–Strain Model for High-Strength Concrete Members under Cyclic Loading

A new proposal for describing the hysteretic stress–strain behavior of high-strength concrete (HSC) under reversed cyclic loading is presented. The envelope curve is derived from the results of uniaxial, monotonic, compression loading tests of 108 large-scale specimens. It explicitly accounts for the effects of concrete compressive strength, volumetric ratio of transverse reinforcement, yield strength of ties, tie spacing, and tie pattern. The proposed model is implemented in the finite element program ADAPTIC, with a view to analyzing HSC members under reversed cyclic loading. This analysis accounts for energy dissipation through hysteretic behavior, stiffness degradation as damage progresses, and degree of confinement. Comparisons with test results showed that the proposed model provides a good fit to a wide range of experimentally established hysteresis loops. This model also keeps the computing costs of nonlinear analysis within acceptable limits.

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.

100 MPa 초고강도 콘크리트 띠철근 기둥의 이력거동에 관한 실험적 연구

An experimental investigation was conducted to examine the hysteretic behaviors of ultra-high strength concrete tied columns. The purpose of this study is to investigate the safety of ultra-high strength concrete columns with 100 MPa compressive strength for the requirement of ACI provisions. Eight 1/3 scaled columns were fabricated to simulate an 1/2 story of actual structural members with the cross section and the aspect ratio 4. The main variables are axial load ratio, configurations and volumetric ratios of transverse reinforcement. The results show that the deformability of columns are affected by the configurations and volumetric ratios of transverse reinforcement. Especially, it has been found that the behavior of columns are affected by axial load ratio rather than the amounts and the configurations of transverse reinforcement. Consequently, to secure the ductile behavior of 100 MPa ultra-high strength concrete columns, ACI provisions for the requirement of transverse steel may considered axial load level and the details of transverse reinforcement.

고강도 철근콘크리트 교각의 내진 거동

This experimental investigation was conducted to examine the seismic performance of reinforced concrete bridge columns. The columns were subjected to a constant axial load and a cyclic horizontal load-inducing reversed bending moment. The variables studied in this research were the volumetric ratios of transverse reinforcement (ps=0.96, 1.44 percent) and axial load ratios (P/Po=0.05, 0.1, 0.2) and concrete strengths (35, 60MPa). Test results showed that bridge columns with higher amounts of transverse reinforcement than that required by seismic provisions of ACI 318-02 showed ductile behavior. For bridge columns with axial load ratio(P/Po) less than 0.2, the ratio of , nominal moment capacity predicted by ACI 318-02 provisions, was consistently greater than 1 with approximately a margin of safety.