Behavior Of Circular Concrete Columns Research Articles

Design-oriented stress-strain model for short concrete columns wrapped with FRP sheets

Previous studies have presented models aimed at predicting the axial stress-strain behavior of circular concrete columns wrapped with carbon fiber reinforced polymer (CFRP). The majority of these models were developed based on normal strength concrete (NSC) with strengths below 50 MPa. Moreover, several of these models relied on a limited experimental database. In this study, a large collection of experimental data was gathered, including 310 concrete columns confined with CFRP wraps. This database comprised test results for unconfined concrete with a compressive strength ranging from 19.7 to 169.7 MPa, and a height-to-diameter (H/D) ratio of two. From these data, two new expressions were developed to estimate the ultimate compressive strength and the corresponding strain. To model the stress-strain behavior, new relationship was suggested. A comparison between the proposed model and the experimental results revealed good agreement, outperforming several existing models. Additionally, the expressions for ultimate strength and corresponding strain are simple and accurate, making them easy to apply in design. Furthermore, the proposed model demonstrates superior performance compared to other existing models.

Seismic Behavior of Concrete Columns Reinforced with Weakly Bonded Ultra-High Strength Rebars and Confined by Steel Tubes.

The usage of weakly bonded ultra-high strength (WBUHS) rebars has emerged as a promising approach to enhance the resilience of concrete components due to their remarkable mechanical properties. To promote the application of WBUHS rebars, this paper presented an investigation on the seismic behavior of circular concrete columns reinforced with squarely arranged WBUHS rebars and externally confined by bolted steel tubes. Eight columns, including two reinforced with normal strength (NS) rebars and six reinforced with WBUHS rebars, were fabricated and tested under reversed cyclic lateral loading. Experimental results showed that the columns reinforced with WBUHS rebars exhibited remarkable drift-hardening capacity up to the drift of at least 5% as well as significantly reduced residual deformation even when subjected to relatively high axial compression with an axial load ratio of 0.33 in comparison to the traditional ductile columns reinforced with NS rebars. Notably, the precast columns reinforced with WBUHS rebars, with an embedment length of 20 times their diameter, behaved nearly identically in terms of resilience as cast-in-place columns. Additionally, a numerical analysis was performed to assess the hysteretic performance, and the analytical results, with consideration for the slippage of WBUHS rebars, were capable of capturing the hysteretic performance of test columns.

Seismic Behavior of Circular Concrete Columns Reinforced by Low Bond Ultrahigh Strength Rebars

Seismic Behavior of Circular Concrete Columns Reinforced by Low Bond Ultrahigh Strength Rebars

Uniaxial compressive behavior of circular concrete columns actively confined with Fe-SMA strips

An increased interest in the strengthening and rehabilitation of deficient or deteriorated structures took place in the past few decades to maintain the sustainability and integrity of existing structures. Different strengthening techniques have been recently studied and used to retrofit or strengthen concrete elements. One of these techniques is the use of Shape Memory Alloys (SMA), taking advantage of its shape memory effect property. This property allows the application of an initial confining pressure, called active confinement, when the material is restrained. Such pressure is developed when the material undergoes phase transformations upon heating to a certain temperature. As a result of their unique properties, different types of SMA for different structural engineering applications have been studied. In this paper, an experimental program was conducted to evaluate the behavior of concrete columns confined with iron-based SMA (Fe-SMA) strips under uniaxial compressive loading. A total of 25 circular columns were tested, and the results were analyzed to identify the influences of selected parameters: 1) presence of internal reinforcement, 2) initial confining pressure, and 3) ratio of external SMA confinement. The test results indicated great improvement in the overall behavior of the confined columns, especially their axial deformation capabilities. In addition, an analytical approach was proposed to model the axial load-deformation behavior of the actively confined columns. The proposed expressions showed to adequately capture the axial behavior of the columns, and the obtained results were in good agreement with the experimental test results of columns confined with Fe-SMA strips.

Data-oriented analysis of axial capacity of externally CFRP-confined concrete columns transversely reinforced with steel hoops or spirals

Limited research is available in the literature for exploring the axial compressive behavior of circular concrete columns confined by both external CFRP wraps and internal transverse steel reinforcement (SCC columns). The main objective of the present work is to develop an empirical model and an analytical model for predicting the axial compressive strength of SCC columns by considering the interaction between the CFRP composite and steel reinforcement confinement action. An extensive experimental database of 76 SCC columns has been developed from the literature work. A general regression analysis method and curve-fitting techniques on the experimental test results of SCC columns are used for developing the new empirical model. The confinement mechanics-based analytical model has also been suggested by considering the influence of CFRP and transverse steel confinement. The comparative study solidly substantiated the superiority of the proposed empirical model over the proposed analytical model and the previous models with =0.892, =12.83, and =9.78. A parametric study is also performed using the proposed empirical strength model to examine the effect of different parameters of SCC columns confined by both CFRP and transverse steel.

Behavior of axially loaded low strength concrete columns reinforced with GFRP bars and spirals

This paper investigates the behavior of circular concrete columns reinforced with glass fiber reinforced polymer (GFRP) bars and spirals under axial load. Nine circular low strength concrete columns of 230 mm diameter and 1500 mm height were constructed and tested. The test parameters included reinforcement type (GFRP and steel), longitudinal reinforcement ratio, and spacing of spirals. Most tested columns showed two peak loads. Test results revealed that the GFRP-RC columns behaved similarly to the steel-RC counterparts. However, the GFRP-RC columns gave a slightly lower first peak load compared to their counterparts reinforced with steel. Increasing the GFRP reinforcement ratio slightly enhanced the capacity of the columns. Highly confined columns showed better ductile failure and significantly increased the second peak load of the columns. Design equations that predict the capacity of FRP-RC columns were evaluated using the experimental data of this study. The results showed that the Canadian Standard Association equation was conservative especially for columns with high reinforcement ratios. In addition, three different confinement models were used to predict the maximum confined concrete strength and they gave reasonable predictions compared to the experimental ones. Furthermore, an existing analytical model was used to predict the load-axial displacement of the tested columns and it showed reasonable correlation with the experimental ones up to the first peak loads. However, significant deviations were observed at the post-peak stages.

Behavior of circular concrete columns reinforced with hollow composite sections and GFRP bars

Hollow concrete columns (HCCs) constitute a structurally efficient construction system for marine and offshore structures, including bridge piers and piles. Conventionally, HCCs reinforced with steel bars are vulnerable to corrosion and can lose functionality as a result, especially in harsh environments. Moreover, HCCs are subjected to brittle failure behavior by concrete crushing due to the absence of the concrete core. Therefore, this study investigated the use of glass fiber-reinforced polymer (GFRP) bars as a solution for corrosion and the use of hollow composite-reinforced sections (HCRSs) to confine the inner concrete wall in HCCs. Furthermore, this study conducted an in-depth assessment of the effect of the reinforcement configuration and reinforcement ratio on the axial performance of HCCs. Eight HCCs with the same lateral-reinforcement configuration were prepared and tested under monotonic loading until failure. The column design included a column without any longitudinal reinforcement, one reinforced longitudinally with an HCRS, one reinforced longitudinally with GFRP bars, three reinforced with HCRSs and different amounts of GFRP bars (4, 6, and 8 bars), and three reinforced with HCRSs and different diameters of GFRP bars (13, 16, 19 mm). The test results show that longitudinal reinforcement—whether GFRP bars or HCRSs—significantly enhanced the strength and displacement capacities of the HCCs. Increasing the amount of GFRP bars was more effective than increasing the bar diameter in increasing the confined strength and the displacement capacity. The axial-load capacity of the GFRP/HCRS-reinforced HCCs could be accurately estimated by calculating the load contribution of the longitudinal reinforcement, considering the axial strain at the concrete peak strength. A new confinement model considering the combined effect of the longitudinal and transverse reinforcement in the lateral confinement process was also developed.

Compressive behavior of FRP ring-confined concrete in circular columns: Effects of specimen size and a new design-oriented stress-strain model

This paper presents the results of an experimental program aiming to investigate the effect of the specimen size on the axial compressive behavior of circular concrete columns wrapped with spaced FRP rings. A database consisting of the up-to-date test results on FRP ring-confined concrete in the literature is established, and it is used for proposing a new design-oriented stress-strain model for FRP ring-confined concrete. The accuracy and reliability of the new model are validated by comparing the test results presented in this paper with the predictions by the new model. The comparisons show that the new model provides close predictions with test results.

Stress-strain behavior of concrete in circular concrete columns partially wrapped with FRP strips

Fiber-reinforced polymer (FRP) wrapping has become an attractive strengthening technique for concrete columns. Within this strengthening technique, FRP jackets are wrapped around the concrete column with the fibers in the jacket being oriented in the hoop direction. In practice, the FRP jackets can be either continuous or discontinuous along the column height and thus the resulting column is referred to as FRP fully or partially wrapped concrete columns. Existing research has demonstrated that the FRP partial wrapping strengthening technique by discrete FRP strips (rings) is a promising and economic alternative to the FRP full wrapping strengthening technique. Although a number of experimental investigations have been conducted on FRP partially wrapped concrete columns, the stress-strain behavior of FRP-confined concrete in partially wrapped concrete columns is not yet completely understood. This paper presents an experimental program to investigate the axial compressive behavior of circular concrete columns partially wrapped with FRP strips. The test results are presented and compared with five existing representative stress-strain models to examine the reliability and accuracy of each model. It has been demonstrated that the Teng et al.’s (2007) model is superior to the other four representative models and it provides reasonably accurate predictions of the ultimate axial stress of FRP partially wrapped concrete while it usually underestimates the ultimate axial strain.

Compressive Behavior of Circular Concrete Columns Confined by Basalt Fiber Reinforced Polymer (BFRP)

This paper presents an experimental study on the compressive behavior of circular concrete columns confined by a new class of composite materials originated from basalt rock, Basalt Fiber Reinforced Polymer (BFRP). The primary objective of this study is to observe the compressive behavior of BFRP-confined cylindrical concrete column specimens under the effect of different number of layers of basalt fiber as a study parameter (3, 6, and 9 layers). For this purpose, 8 small scale circular concrete specimens with no internal steel reinforcement were tested under monotonic axial compression to failure. The results of BFRP-confined concrete specimens of this study showed a bilinear stress-strain response with two ascending branches. Consequently, the performance of confined columns was improved as the number of BFRP layer was increased, in which all the specimens exhibited ductile behavior before failure with significant strength enhancement. The experimental results indicate the well-performing of basalt fiber in improving the concrete compression behavior with an increase in number of FRP layers.

Development and validation of a FRP-wrapped spiral corrugated tube for seismic performance of circular concrete columns

This paper presents the cyclic behavior of circular concrete columns confined with a proposed FRP-wrapped spiral corrugated tube (FWSCT) that serves as a permanent ribbed surface between FRP and concrete. Five FWSCT column specimens with GFRP layers and axial load ratios as design parameters were tested for the flexural and shear performances. The FWSCT specimens that did not use transverse steel hoops in the entire column used longitudinal reinforcement for the flexural capacity and FWSCT for the shear capacity. Specimen FWSCT-0 was confined with only a spiral corrugated steel tube without GFRP wraps; Specimens FWSCT-1, FWSCT-3, FWSCT-5 and FWSCT-8 were confined with a spiral corrugated steel tube and additional 1, 3, 5 and 8 GFRP layers, respectively. Test results showed that Specimen FWSCT-0 experienced shear failure at about 1% drift; Specimen FWSCT-1 experienced flexural shear failure at about 4% drift, while Specimens FWSCT-3, FWSCT-5 and FWSCT-8 exhibited rupture of longitudinal reinforcement at drift ratios of 7% to 8%, without shear failure. A plastic hinge was developed in un-wrapped column ends, further extending into the footing. An analytical method that used the residual shear model and a proposed plastic hinge length reasonably predicts the flexural and shear capacities of FWSCT columns.

Combined effect of CFRP-TSR confinement on circular reinforced concrete columns

The use of external carbon-fiber-reinforced polymer (CFRP) wraps is one of the most effective techniques existing for the confinement of the circular concrete columns. Currently, several researches have been made to develop models for predicting the behavior of this type of confinement. The disadvantage of the most models, is to not take into account the contribution of the transverse steel reinforcements (TSR) effect, However, very limited models have been recently developed that considers this combined effect and gives less accurate results. This paper presents the development of a new model for the axial behavior of circular concrete columns confined by combining external CFRP warps-and-internal TSR (hoops or spirals) based on the existing experimental data. The comparison between the proposed model and the experimental results showed good agreement comparing to the several existing models. Moreover, the expressions of estimating the ultimate strength and the corresponding strain are simple and precise, which make it easy to use in the design applications.

Strength and Axial Behavior of Circular Concrete Columns Reinforced with CFRP Bars and Spirals

AbstractThe behavior of concrete members reinforced with fiber-reinforced polymer (FRP) bars has been the focus of many studies in recent years. However, limited research work has been conducted to examine the axial behavior of concrete columns reinforced with FRP bars. In this paper, the behavior and compression strength of 11 full-scale circular concrete columns reinforced with carbon fiber–reinforced polymer (CFRP) bars and spirals were investigated. The test variables included reinforcement type (CFRP versus steel); longitudinal CFRP reinforcement ratio; and the volumetric ratio, size, and spacing of CFRP spirals. The test results indicated that the CFRP and steel reinforced concrete (RC) columns behaved in a similar manner up to their peak loads. The CFRP bars were effective in resisting compression until after crushing of concrete, and contributed on average 12% of column capacity. The design equation is modified to accurately predict the ultimate load capacities of CFRP RC columns. A new factor (αc...

Behavior of Circular Concrete Columns Repaired with Steel Bars and Wire Mesh-Mortar

In order to increase the strengthening efficiency of steel bar mat-mortar (BM) jacket and wire mesh-mortar (WM) jacket around existed circular concrete columns, an attempt to strengthen the columns with hybrid bar mat-wire mesh-mortar (HBWM) jacket was proposed. A comparatively experimental study on axial compression behaviors of concrete columns wrapped with three different strengthening systems, namely BM, HWBM and carbon fiber reinforced polymer (CFRP) was performed. The experiment results showed that much more cracks appeared in HWBM columns compared with those in BM columns. As a result, on the premise that the concrete compressive strength of the HWBM columns increased 90% compared with that of the BM columns, the ductility of the HWBM columns reached about twice as that of the BM columns. The increase of the concrete compressive strength of CFRP strengthened columns was higher than those of HWBM and BM strengthened columns. The ductility of CFRP strengthened columns, however, was obviously lower than that of HWBW columns.

Analytical Model for FRP-Confined Circular Reinforced Concrete Columns

One disadvantage of most available stress–strain models for concrete confined with fiber-reinforced polymer (FRP) composites is that they do not take into consideration the interaction between the internal lateral steel reinforcement and the external FRP sheets. According to most structural concrete design codes, concrete columns must contain minimum amounts of longitudinal and transverse reinforcement. Therefore, concrete columns that have to be retrofitted (and therefore confined) with FRP sheets usually contain lateral steel. Hence, the retrofitted concrete column is under two actions of confinement: the action due to the FRP and that due to the steel ties. This paper presents a new designed-oriented confinement model for the axial and lateral behavior of circular concrete columns confined with steel ties, FRP composites, and both steel ties and FRP composites. Comparison with experimental results of confined concrete stress–strain curves shows good agreement between the test and predicted results.

Experimental behavior of circular concrete columns under reversed cyclic loading

This paper experimentally investigates the cyclic behavior of reinforced concrete circular columns confined using a new confinement technique. The new confinement technique uses two opposing spirals (cross spirals) to confine circular columns in order to enhance their strength and ductility or to increase the spiral spacing to facilitate the flow of concrete during construction. Twelve cantilever circular columns with two different lengths and several spiral spacing and patterns were tested. The columns were subjected to constant axial load and reversed cyclic lateral displacement to study the influence of the new confinement technique on the lateral strength and ductility of circular columns compared to columns confined with conventional single spiral. Six of the columns (1000mm high and 200mm diameter) were designed to study the flexural behavior, and the other six columns (500mm high and 200mm diameter) were designed to study the shear behavior.

Investigation of the behavior of circular concrete columns reinforced with carbon fiber reinforced polymer (CFRP) jackets

Recent advancements in the fields of fiber reinforced polymers (FRPs) have resulted in the development of new materials with great potential for applications in civil engineering structures, and due to extensive research over recent years, FRPs are now being considered for the design of new structures. This study describes how carbon fiber reinforced polymer jackets can be used to reinforce circular concrete columns. Fibers aligned in the circumferential direction provide axial and shear strength to the concrete, while fibers aligned in the longitudinal direction provide flexural reinforcement. Prefabricated FRP jackets or tubes would also provide the formwork for the columns, resulting in a decrease in labor and materials required for construction. Also, the enhanced behavior of FRP jacketed concrete columns could allow the use of smaller sections than would be required for conventionally reinforced concrete columns. Furthermore, FRP jacket reinforced concrete columns would be more durable than conventionally reinforced concrete columns and therefore would require less maintenance and have longer service life.Key words: bridge, carbon, column, concrete, confinement, fiber reinforced polymer, jacket, retrofitting, seismic, strengthening.

Investigation of the behavior of circular concrete columns reinforced with carbon fiber reinforced polymer (CFRP) jackets

Investigation of the behavior of circular concrete columns reinforced with carbon fiber reinforced polymer (CFRP) jackets