Reinforced Concrete Short Columns Research Articles

Bond Behavior of Embedded Reinforcing Steel Bars for Varying Levels of Transversal Pressure

Because of columns loads, reinforced concrete (RC) continuous beams in skeleton structures are subjected to transverse compressive stress at support locations. Such lateral pressure can enhance the bond between the main top reinforcing bars and the surrounding concrete because of the confinement effect. Thus, the development length can be reasonably decreased compared to the case of no lateral pressure. However, different codes of practice, such as the Egyptian code standard ECP 203-2007 and the American Concrete Institute (ACI) code standard ACI 318-11, stipulate increasing the reinforcement location factor for upper reinforcement implemented in the calculation of the development length of such bars. On the other hand, the Comite Euro-International du Beton (CEB-FIP) model code standard CEB-FIP 2010 considers this enhancement in bond stress calculations as being due to transverse compression stress. To assess such effects, pull-out tests were performed on reinforcing bars embedded in short RC columns subjected to different levels of axial pressure. The experimental findings showed the same trend as manifested in the CEB-FIP 2010 results, where increasing the lateral pressure on the reinforcing bar resulted in decreasing the development length for both smooth and deformed steel bars. In contrast, the results of development length calculations based on both ECP 203-2007 and ACI 408R-03 were constant regardless of the level of lateral pressure on the reinforcing bar. This highlights the need for both ECP 203-2007 and ACI 408R-03 to consider the effect of transverse lateral pressure on development length calculations due to varying lateral pressure on the reinforcing bar.

Strengthening of Heat Damaged Reinforced Concrete Short Columns

The purpose of this study was to investigate the effectiveness of different strengthening schemes in strengthening heat damaged reinforced concrete short columns. A series of 63 heat damaged specimens were tested under concentric compression after jacketing externally with High Strength Fiber Reinforced Concrete (HSFRC), Ferrocement (FC) and Glass Fiber Reinforced Polymer (GFRP) jackets. The specimens were subjected to various heating and cooling regimes. The overall response of strengthened specimens was investigated with reference to un-strengthened specimens in terms of axial compressive strength, ductility, lateral stress-strain, and axial stress-strain behaviour. It was observed that while the GFRP jacketing is quite effective in improving compressive strength and energy dissipation, it is not capable of improving stiffness. On the contrary FC and HSFRC jacketing were mainly effective in improving stiffness property. Overall GFRP jacketing was found to be the most effective method of strengthening fire or heat damaged concrete columns.

Seismic Response of Reinforced Concrete Short Columns Failed in Shear

First Name is required invalid characters Last Name is required invalid characters Email Address is required Invalid Email Address Invalid Email Address

Research of Compression Bearing Capacity of Steel Reinforced Concrete Short Column Replaced by C-BAR

t is essential to study the performance of reinforced concrete short column. In this paper, the main reinforcements and hoopings in short columns were replaced by C-BAR reinforcements, the regularity of reinforcing bar replaced by C-BAR reinforcements was summarized. The results show that the axial compression bearing capacity of concrete short column is increased.

Axial Bearing Capacity of Steel Reinforced Concrete Short Column with Double Circular Steel Tubes

Based on the twin shear unified strength theory, analyzing the condition of load for the steel tube and the core-concrete under tri-axial compression, the formula of axial bearing capacity of steel reinforced concrete short column with double circular steel tubes was established and the influencing factors on it were discussed. By the comparison between the results calculated by the formula and the test results, it shows good agreement. Meanwhile, applying the formula to an engineering example, good agreement can be found in the comparison between the calculation in this paper and finite element analysis result in relevant literature. The conclusions can provide a reference for the engineering design.

Splitting Failure of Reinforced Concrete Columns

Many earthquake reconnaissance studies have revealed a unique splitting failure mode of reinforced concrete (RC) columns that has yet to be fully elucidated. Most available shear strength models in the current codes are established based on the concept of a diagonal shear plane through which shear force must be transferred; this concept might not be as applicable to RC columns that failed by vertical cracks, or via splitting failure from an earthquake. In this study, an alternative load-transferring path is proposed that not only explains the failure mechanism, but also allows the estimation of shear strength of the test specimens. Experimental observations from 17 RC columns that underwent splitting failure were used to validate the proposed model. To enhance the applicability of the model, it was corroborated further with 89 short columns screened from existing literature. The validations showed that, while simple to apply, the proposed model can give better predictions of shear strength for RC short columns than other shear strength models available in the literature.

Performance of CFRP Wrapped Square Reinforced Concrete Columns Subjected to Eccentric Loading

Abstract Strengthening concrete columns with fibre-reinforced polymers (FRP) has been studied extensively, but the majority of published studies have focused on circular columns. Most concrete columns in the field have square or rectangular cross sections and resist eccentric loading as well. The objective of this study is to investigate the performance of square reinforced concrete (RC) columns wrapped with carbon FRP subjected to eccentric loading. The influence of two parameters was studied including the number of FRP layers and the magnitude of eccentricity. Compression testing was conducted on twelve short square RC columns wrapped with CFRP composites. The columns had a dimension of 200 mm x 200 mm x 800 mm and a round corner with a radius of 34 mm. The results of the study demonstrated that wrapping the square RC columns under eccentric loading with CFRP enhanced their performance by providing higher load carrying capacity and ductility compared to unwrapped RC columns.

Seismic Behaviour on Composite Strengthening for Existing Reinforced Concrete Short Columns

In order to develop an effective seismic shear strengthening method for improving the earthquake behavior of existing R/C short columns, experimental studies are conducted by using four beam-column sub assemblage specimens with a short column. Three short columns of these specimens are strengthening by steel plates and concrete, while other one is without any steel plate strengthening. All the specimens are tested under a constant gravity load and alternately repeated lateral forces. Test results demonstrate that, if the short column is strengthened by a welded square tube and concrete, then brittle shear failure does not occur and the column can develop its ultimate flexural moment capacity. It is also shown by tests that the proposed strengthening method using steel plates and concrete is applicable to repair and rehabilitate the damaged short columns failed in the brittle shear mode.

Seismic behavior and shear strength of tubed RC short columns

Abstract Reinforced concrete (RC) short columns are vulnerable to brittle shear failure during an earthquake. The objective of this research is to evaluate the performance enhancement of RC short columns tubed with circular or square tubes. Eight short columns were tested under combined constant axial load and cyclic lateral load. The tested specimens included three circular tubed RC (CTRC) columns and three square tubed RC (STRC) columns. Two common RC short columns including one circular RC column and one square RC column were also tested as control specimens. The test results indicated that common RC short columns suffered brittle shear failure with little ductility, while the ductility of tubed RC short columns was excellent due to the effective confinement of the outer thin tube to the core concrete. The lateral load strength of CTRC short columns increases with the increasing of axial load ratio, while the axial load ratio has little effect on the plastic deformation capacity of CTRC short columns. The shear strength increases with increasing of axial load ratio, while the plastic deformation capacity decreases with increasing of axial load ratio for STRC short columns. A circular tube prevents the core concrete from shear failure more effectively than a square tube for the tubed RC short columns. A modified ACI design method is adopted to calculate the nominal shear strength of STRC columns as well as CTRC columns based on the test and analysis results.

An improved design formula for a biaxially loaded slender RC column

Nonlinear analyses are conducted to evaluate the ultimate resisting capacity of slender reinforced concrete (RC) columns subjected to an axial load with biaxial bending moments. Consideration is given to the geometric nonlinearities caused by the P – Δ effect and the long-term behavior of concrete and to the material nonlinearities caused by the cracking of concrete and the yielding of steel. In addition, the biaxial stress state in an RC section is simulated on the basis of a fiber model. Because of the complexity of Bresler’s load contour method, which was introduced in the ACI 318 code, this paper introduces a new design approach to the construction of the failure surface of a slender RC column subjected to biaxial bending. Through a parametric study of slender RC columns, where consideration is given to the P – Δ effect and the time-dependent deformation of concrete, two regression formulas are proposed on the basis of the slenderness ratio and the creep deformation of concrete. Furthermore, the direct multiplication of the proposed formulas on the P – M interaction diagram for a short RC column subjected to axial force and a uniaxial bending moment enables a P – M interaction diagram to be generated for a slender RC column subjected to long-term axial force and biaxial bending moments. Correlation studies between analytical and experimental results are conducted with the objective of establishing the validity of the introduced numerical model. In addition, the ultimate resisting capacities calculated from the regression formula are compared with those obtained from rigorous nonlinear analyses and from the ACI formula, with the objective of establishing the relative efficiency of the proposed regression formula.

Mechanical Properties and Applications of CFRP in Retrofitting and Repairing Reinforced Concrete Short Columns

The mechanical properties of CFRP without epoxy resin were tested by the monotonic load method, and the corresponding stress-strain relationship curve was established. The probability model and the parameter fitting based on Weibull distribution theory were applied, and the characteristic strength parameter and the shape parameter of CFRP were obtained. Three large scale RC short columns were constructed, the specimen not retrofitted, specimen strengthen retrofitted by CFRP and specimen repaired by CFRP which has been damaged by earthquake were simulated respectively. Quasi-static testing was carried out. The hysteretic-loop curve and average framework curve were obtained, furthermore, the performance of ductility and strength were analyzed and compared. The calculational results approximately agree with the experimental results, which prove the validity of OpenSees. The short columns retrofitted by CFRP have superior ductility so as to enhance the seismic performances effectively. The residual seismic behavior of short columns can also meet the requirement of seismic code. The research provides reference to seismic analysis and engineering design of retrofitted reinforcement concrete structures.

Experimental Study on Mechanical Property of Steel Reinforced Concrete Short Columns of T-Shaped

The horizontal press performance of column is deteriorated because of special-shaped section. Moreover, because the antiseismic performance of columns is worse, it is only used in regions where seismic intensity is lower. So the main problem is to enhance the ductility. This test study on mechanical performance has been carried out through fourteen SRCTSSC and RCTSSC. The study focuses on the impact of test axial pressure ratio(nt), hooped reinforcement ratio(ρv), shear span ratio(λ) and steel ratio(ρss) to the shear strength and the antiseismic performance of SRCTSSC. It can be concluded that the shear strength of SRCTSSC is increasing with the increasing of nt and ρss , but the degree of increasing is small when nt is a certainty value, and that the shear strength of SRCTSSC is decreasing with increasing of λ; The shear resistance formula of T-shaped column is derived through tests, the calculated results are in correspondence with those of the tests. It also can be concluded that the hysteretic loops of the SRCTSSC are full and the hysteretic behaviors are improved and that the displacement ductility is increasing with increasing of ρv and ρss , but decreasing with the increasing of nt and the degree of variety in high axial pressure ratio is larger than in low axial pressure ratio. If steel bars are added, the shear strength and displacement ductility of SRCTSSC is increased in a large degree, and the capacity of energy dissipation is also enhanced. This test, for applying the special-shape column to higher intensity region, has the certain instructive significance.

Behavior and Ductility of Reinforced Concrete Short Columns using Global Truss Model in Concrete Beams

First Name is required invalid characters Last Name is required invalid characters Email Address is required Invalid Email Address Invalid Email Address

Assessment of time-dependent reliability of reinforced concrete columns with uncertain load eccentricity

An approach for the time-dependent reliability analysis of reinforced concrete (RC) columns considering the correlation between the axial load and the bending moment or the uncertainty in the load eccentricity is presented. The approach recursively uses the efficient first-order reliability method for the time-dependent reliability analysis. The proposed approach is more efficient than the ones used in the literature for the reliability analysis of RC columns. The proposed approach is used to carry out sensitivity analyses of the reliability of short RC columns to the time-dependent live load effects and to the correlation between the axial load and the bending moment. Results of the analyses suggest that the reliability of RC columns can be sensitive to the correlation between the axial load and the bending moment due to live load. The differences between the reliability indices obtained by considering the live load modeled as a pulse process and as an extreme variate can be large.Key words: reliability, load, time-dependent, time-independent, uncertainty, correlation, concrete, reinforcement, column.

Modeling Error of Strength of Short Reinforced Concrete Columns

This study conducted probabilistic analyses of the modeling errors of several selected strength prediction models for short reinforced concrete (RC) columns. The selected strength models included the rectangular stress block model and the stress-strain relation-based theoretical model. A relatively large amount of test data on RC columns was collected from the literature, and the test results were compared with the predicted ones obtained from different strength models. Both normal- and high-strength concrete columns were studied. The dependency of the modeling errors on concrete compressive strength and the load eccentricity was investigated. Probabilistic analyses of the modeling errors were carried out by using the pseudolikelihood estimation method. Sets of probabilistic models of the modeling errors by considering different analysis approaches are suggested for short RC columns.

Biaxial Interaction Diagrams for Short RC Columns of Any Cross Section

A general method that determines the biaxial interaction diagrams for any orientation of the neutral axis of a reinforced concrete (RC) short column of any cross section under axial load and bending about two axes is presented. Closed form expressions for MnX, MnY, and Pn are derived that evaluate the theoretical ultimate strength of RC short columns using (1) Gauss' integral method for equilibrium; (2) a nonlinear stress-strain relationship for the concrete; and (3) a multilinear elastoplastic relationship for the reinforcement. These equations and the proposed method can be reproduced by another user with minimal calculations (as opposed to other methods), allowing the designer to investigate the biaxial bending behavior and failure mode of short RC columns under compression or tension. The proposed method can also be utilized in the study of the effects of creep and confinement of the concrete on the strength and failure mode of RC short columns of any cross section under biaxial bending and axial load...

せん断伝達理論に基づく鉄筋コンクリート短柱のせん断耐力に関する研究 : 第 2 報 : せん断繰り返し荷重による崩壊条件

せん断伝達理論に基づく鉄筋コンクリート短柱のせん断耐力に関する研究 : 第 2 報 : せん断繰り返し荷重による崩壊条件

Sustained Load Strength of Eccentrically Loaded Short Reinforced Concrete Columns

Sustained Load Strength of Eccentrically Loaded Short Reinforced Concrete Columns

Inelastic Behavior in Tests of Eccentrically Loaded Short Reinforced Concrete Columns

Inelastic Behavior in Tests of Eccentrically Loaded Short Reinforced Concrete Columns