Circular Reinforced Concrete Columns Research Articles

Loss assessment of rigid-frame bridges under horizontal and vertical ground motions

Previous investigations have attributed some reinforced concrete (RC) bridge piers suffered significant damages during large earthquakes due to vertical ground motion effects. This has motivated this study to investigate the use of concrete-filled steel tube (CFST) columns as a more resilient and sustainable alternative to resist combined horizontal and vertical ground motions. The classic performance-based earthquake engineering (PBEE) framework is used to examine the seismic performance of a rigid-frame bridge with construction options of circular RC, circular CFST, and square CFST columns. The hysteretic response of each column is calibrated to the results of hybrid testing of columns under combined horizontal and vertical ground motions. The incremental dynamic analysis (IDA) is conducted using a suite of 50 near-fault records. The results are used to compare the observed damage states and quantify the repair sustainability metrics including repair cost (economic), repair downtime (social), and repair carbon emissions (environmental), as well as the loss of resilience. The losses are integrated with the hazard curves to compute the expected annual losses, all defined as a set of decision variables in the PBEE framework. The results confirm the outstanding seismic performance of CFST columns and highlight their benefits in improving the resilience and sustainability of critical and post-disaster bridges that are prone to strong multi-directional ground motions.

Enhancement of circular RC columns using steel mesh as internal or external confinement under the influence of axial compression loading

Reinforced concrete (RC) columns cannot get supreme confinement by using the customary steel stirrups reinforcement because of the requirements for the spacing distances between the stirrups in addition to concrete continuance trouble. For this, Steel Mesh (SM) externally wrapped around the outer perimeter of the column as contributory confinement are being widely used due to its features. Limited tests focused on using SM for the internal confinement around the reinforcing cage of RC columns. Moreover, no experimental comparison was presented between RC columns internally and externally confined using SM. This paper investigates experimentally the behavior of circular RC columns confined internally or externally by SM. Six short RC columns have been subjected to axial loading until failure. The main studied parameters were SM schemes, number of SM wraps, SM position (internally or externally), and the steel stirrups existence. Results demonstrated that SM could decrease the crack opening, diminish the concrete spalling, increase the maximum failure load, and enhance the ductility, energy absorption, and column stiffness. Furthermore, the partially internal confinement using two wraps of SM around the steel ties presented the maximum capacity with reasonable ductility. In general, internally confined columns showed better behavior than the externally confined one.

Analytical Review on Eccentric Axial Compression Behavior of Short and Slender Circular RC Columns Strengthened Using CFRP.

Although reinforced concrete (RC) columns subjected to combined axial compression and flexural loads (i.e., eccentric load) are the most common structural members used in practice, research on FRP-confined circular RC columns subjected to eccentric axial compression has been very limited. More specifically, the available eccentric-loading models were mainly based on existing concentric stress–strain models of FRP-confined unreinforced concrete columns of small scale. The strength and ductility of FRP-strengthened slender circular RC columns predicted using these models showed significant errors. In light of such demand to date, this paper presents a stress–strain model for FRP-confined circular reinforced concrete (RC) columns under eccentric axial compression. The model is mainly based on observations of tests and results reported in the technical literature, in which 207 results of FRP-confined circular unreinforced and reinforced concrete columns were carefully studied and analyzed. A model for the axial-flexural interaction of FRP-confined concrete is also provided. Based on a full parametric analysis, a simple formula of the slenderness limit for FRP-strengthened RC columns is further provided. The proposed model considers the effects of key parameters such as longitudinal and hoop steel reinforcement, level of FRP hoop confinement, slenderness ratio, presence of longitudinal FRP wraps, and varying eccentricity ratio. The accuracy of the proposed model is finally validated through comparisons made between the predictions and the compiled test results.

Predictive model for slenderness limit of circular RC columns confined with FRP wraps

AbstractApplication of fiber‐reinforced polymer (FRP) for retrofitting and rehabilitation of concrete structures is a common method. The main role of FRP confinement for reinforced concrete (RC) columns is to increase the ultimate strength and strain of confined concrete core and therefore improve in the load carrying capacity of the columns. However, it is possible that a previously short column fails due to buckling after the application of FRP confinement. In other words, the enhanced compressive strength of a retrofitted column may go beyond its buckling load. Therefore, a design criterion to predict this condition is necessary for the designers in the preliminary and final stages of the design. In this paper, a predictive model is proposed to determine the slenderness limit of FRP‐confined circular RC columns. The suggested relation was derived using one of the accurate design‐oriented strength models for FRP‐confined concrete columns as well as analytically derived buckling equations. The effect of hybrid FRP confinement is also incorporated in the suggested slenderness limit. Moreover, a parametric study was performed on the suggested model to specify most influential parameters. The accuracy of the proposed relation was evaluated using a database of experimental results collected from previous studies. The results of the evaluations demonstrated acceptable accuracy of the proposed relation in predicting behavior and failure mode of FRP‐confined RC columns.

The effect of CFRP-shear strengthening on existing circular RC columns under impact loads

In recent decades, accidents involving derailed train collisions have increased, owing to the rapid development of railway construction worldwide. Reinforced concrete (RC) columns in train stations are likely to be subjected to derailed train collisions, resulting in a brittle shear failure of the columns and catastrophic damage to the entire structure. In view of these problems, this study investigated the effectiveness of carbon fiber-reinforced polymer (CFRP) shear strengthening in improving the failure modes of circular RC columns. A drop hammer impact test was performed on a plain circular RC specimen and a CFRP-shear-strengthened circular RC specimen with fixed supports. The tested specimens were scaled from a regular train station column in China, and the impact height was selected as 2/9 of the effective span length, in accordance with the dimensions of a high-speed train locomotive. The test results revealed that wrapping a layer of CFRP sheets can effectively mitigate the shear damage of the concrete, and transform the failure mode of the column specimen from brittle-shear to ductile-flexural. In addition, finite element (FE) models were developed and verified based on the experimental results. Using the verified FE models, the structural design-related parameters (e.g., the longitudinal reinforcement ratio, transverse reinforcement ratio, impact location, concrete compressive strength, and axial load ratio) were extensively analyzed, aiming to further investigate the effectiveness of CFRP strengthening on RC columns. The results demonstrated that wrapping existing RC columns with CFRP can achieve a consistent good strengthening effect, despite variations in these basic design parameters.

Axial capacity and stiffness of post-heated circular and square columns strengthened with carbon fiber reinforced polymer jackets

The exposure of reinforced concrete (RC) columns to elevated temperatures is detrimental to its axial capacity and stiffness. Selecting the proper strengthening technique to repair heat-damaged RC columns is critical to ensure that the axial capacity and stiffness are restored. This paper examines the performance of different strengthening schemes using carbon fiber reinforced polymer (CFRP) jackets and near-surface mounted (NSM) steel bars in repairing circular and square RC columns damaged due to the exposure to high elevated temperature. The tested columns were divided into three categories, un-heated and un-strengthened columns, post-heated and un-strengthened columns, and post-heated and strengthened columns. The heated columns were exposed to 600 °C for 3 h. Two strengthening schemes were evaluated. The first strengthening scheme consisted of unidirectional CFRP strips in combination with NSM steel bars. The second scheme consisted of strengthening with unidirectional CFRP strips only. All the columns were tested under axial compression until failure. The test results showed that exposure to elevated temperatures caused a reduction in the load-carrying capacity of 38% in circular columns and 29% in square columns. Both strengthening schemes were effective in restoring and exceeding (by approximately 16%) the initial load-carrying capacity of heat-damaged RC columns. The use of CFRP strips in combination with NSM steel bars was more effective in restoring the initial stiffness of the post-heated columns compared to using CFRP strips alone. The initial stiffness recovery was more pronounced in circular columns compared to square columns. Circular columns exhibited 15% higher initial stiffness when compared to the control columns before heat-exposure. For square columns, the initial stiffness was equivalent to the initial stiffness of the control RC columns before heat-exposure.

Modelling strategy impact on structural assessment of deteriorated concrete bridge columns

Different methodologies have been suggested in the literature to simulate the adverse impact of reinforcement corrosion on the non-linear structural behaviour of deteriorated reinforced concrete (RC) structures. The modelling methodology used, however, can significantly bias the predicted time-dependent structural behaviour of deteriorated structures. Considering the critical importance of numerical modelling in bridge maintenance scheduling and effective decision making, the influence of different modelling strategies on the anticipated time-variant structural performance of corroded concrete bridge columns is investigated. To this end, various simple and advanced modelling methodologies are evaluated. The effect of the considered modelling scenarios on the estimation of damage limit states, the sequence of multiple failure modes, structural capacity (both ductility and strength) and energy dissipation capacity of a benchmark circular RC column is evaluated over its service life. The results show that the modelling strategy significantly affects the predicted time-variant structural performance of the deteriorated structure.

Carbon fibre-reinforced polymer confinement of corroded circular concrete columns

Corrosion is a major cause of deterioration and cracking in reinforced concrete (RC) members and leads to a significant reduction in their structural capacity and service life. The rehabilitation of damaged RC members using carbon fibre-reinforced polymer (CFRP) is a viable and cost-effective method. This study evaluates the effectiveness of CFRP wrapping of corroded circular RC columns. Four sets of scaled columns were fabricated and subjected to different levels of accelerated corrosion to simulate no, mild, moderate, and severe corrosion. A total of 14 CFRP-confined columns and 10 unconfined columns were axially tested. The load–strain capacity, stress–strain relationship, and failure modes were analysed. The results showed that CFRP wrapping of corroded columns improved their stiffness properties as well as the ductility and deformation behaviour at their ultimate capacities. Ruptures due to failure were largely located in the upper half of the columns, which suggests that the region near the supports must be strengthened to prevent extreme stress concentration. Furthermore, the compressive performance of the tested columns demonstrated their sensitivity to the severity of corrosion. Hence, at higher corrosion levels, CFRP confinement with more layers is recommended.

Experimental Study on Slender CFRP-Confined Circular RC Columns under Axial Compression

The test results on the performance of carbon fiber-reinforced polymer (CFRP)-confined reinforced concrete (RC) columns under axial compression load are presented in this study. Twelve slender CFRP-confined circular RC columns with a diameter of 200 mm were divided into two groups. Six specimens with different slenderness ratios of 12, 20, 32, 40, 48, and 56 were contained in each group. The experimental results demonstrated the circumferential CFRP wrap was effective in enhancing the ultimate axial load of slender CFRP-confined circular RC columns compared with unwrapped RC columns. The experimental investigation also showed that the slenderness of the specimens had important influences on the axial compressive behavior, and the axial bearing capacity of slender CFRP-confined circular RC columns decreased as the slenderness ratio increased. In order to predict the load-carrying capacities of slender CFRP-confined circular RC columns, a formula was proposed and the prediction agreed with the experiments. The slenderness of slender CFRP-confined circular RC columns was recommended to be less than 26.5 in practical engineering.

Nonlinear structural performance and seismic fragility of corroded reinforced concrete structures: modelling guidelines

The current paper provides modelling guidelines for nonlinear analysis and fragility assessment of corrosion-damaged reinforced concrete (RC) structures. A systematic guideline is proposed to model the adverse impact of corrosion on mechanical properties of steel and concrete materials including the negative impact of corrosion on inelastic buckling and low-cycle fatigue (LCF) degradation of reinforcing bars. The proposed fibre-based modelling technique is capable of simulating the spatial variability of localised corrosion and the influence of corrosion on damage states (DS). Corrosion-dependent pushover and cyclic analyses, incremental dynamic analyses (IDAs) and fragility analyses are carried out on three different case studies: (i) a cantilever square RC column, (ii) a cantilever circular RC column and (iii) a RC frame. The analyses results indicate that corrosion significantly affects the DS, sequence of failure mode, flexural capacity and energy dissipation capacity of RC structures. Moreover, alongside the corrosion, the geometry of RC components also affects their failure sequence, cyclic behaviour and energy dissipation capacity. It is shown that increasing degree of corrosion penetration results in the concentration of damage mainly in confined concrete.

Confinement Properties of GFRP-Reinforced Concrete Circular Columns under Simulated Seismic Loading

Abstract Columns in earthquake-resistant reinforced concrete (RC) structures need to be adequately confined to provide satisfactory levels of stability and deformability. In circular RC columns, co...

Equivalent stress block to characterise force–displacement behaviour of circular RC column considering steel bond slip

The compressive zone of concrete with a circular cross-section is simplified to an equivalent rectangular stress block with a width, height and thickness of the peak concrete strength considering the confinement ratio. The shape factors of the equivalent stress block at any concrete strain level are modelled through selected equations of the ratios of the axial load and moment sustained by compressive concrete. The proposed equivalent stress block is used to predict the force–displacement behaviour of a circular, reinforced-concrete (RC) column considering steel bond slip. A comparison with the test results of column specimens indicates that the proposed equivalent stress block can predict the lateral responses with good accuracy; moreover, the variation in the strain of longitudinal rebar and the deformation ratios of flexure and steel bond slip can also be reasonably predicted. The proposed equivalent stress block can be applied widely to other concrete models; furthermore, the capacity curve of the circular RC column can be reasonably predicted by the proposed simplified piecewise model based on the equivalent stress block.

Axial compressive behavior of damaged steel and GFRP bars reinforced concrete columns retrofitted with CFRP laminates

In reinforced concrete (RC) structures, Glass Fiber Reinforced Polymer (GFRP) bars have gained wide acceptance as an alternative to steel bars in coastal and corrosive environments. The majority of studies focused on the axial compressive behavior of undamaged GFRP bars RC columns, comprehensive research on the axial compressive behavior of retrofitted GFRP bars RC has not been conducted because of the limitations of available design codes. This study investigates the axial compressive behavior of damaged GFRP reinforced columns confined with the carbon-FRP (CFRP) sheet. A total of 14 short circular RC columns were fabricated. Seven columns were reinforced with GFRP bars and the remaining seven columns were reinforced with steel bars. Firstly, all the columns were tested under different axial compression conditions until a 35% drop in the peak strength and then these columns were retrofitted with CFRP fabric. The test parameters comprise of testing retrofitted columns under concentric and eccentric loadings. The influence of these parameters on the mode of failure and the ultimate load and displacement conditions of the retrofitted specimens were carefully analyzed. The results revealed that the externally bonded CFRP technique can significantly improve the ultimate axial strength and displacement capacities of damaged GFRP reinforced columns.

Data-Driven Models for Predicting the Shear Strength of Rectangular and Circular Reinforced Concrete Columns

AbstractPredicting the shear strength of structural elements subjected to gravity loads and ground motions is an important component of seismic design. Among all primary structural components, the ...

Behavior of corroded circular RC columns strengthened by C-FRCM under cyclic loading

This study presents an experimental investigation on the seismic behavior of corroded reinforced concrete (RC) columns strengthened by carbon-fabric reinforced cementitious matrix (C-FRCM). To this end, cyclic loading tests were conducted on seven circular RC columns, six of which were suffered from corrosion with duration of 360 days. Four of the corroded specimens were afterwards strengthened by C-FRCM composites. Among these, two specimens were externally bounded with two layers of C-FRCM, the other two specimens were externally bounded with three layers of C-FRCM. After the corrosion process, cyclic loading tests were conducted on the specimens, wherein various axial compression (AC) ratios were considered. The test results show that the secant stiffness, strength, ductility and energy dissipation capacity of corroded specimens were significantly reduced compared with those of the uncorroded counterparts. This phenomenon is severer with larger AC ratio. The C-FRCM can effectively enhance the stiffness, strength, ductility and energy dissipation capacity of the corroded RC columns, wherein two layers of C-FRCM is considered to be desirable for the C-FRCM strengthening approach.

Influence of bond property of longitudinal bars on seismic behaviour of reinforced-concrete columns

Four circular fly-ash concrete columns reinforced by steel rebars with different bond levels were tested to investigate the influence of bond strength of longitudinal steel rebar on the seismic behaviours of reinforced-concrete (RC) members. Furthermore, a fibre-element method considering steel bond slip was used to investigate the influence of bond properties of steel rebar on seismic responses of circular RC columns, with the test results used to validate reasonability. The comparison of results shows that the anchorage of the steel rebar has a significant influence on, and the plastic hinge length no effect on, the seismic behaviours of the columns. The analytical and test results show that low bond strength delays the yielding process of steel rebars adjacent to the beam–column interface, which can improve the deformability of RC columns, but does not obviously influence the moment resistance. However, the stiffness of the cross-section is reduced from a certain drift level. Six equations are proposed to predict with very good accuracy the reduced ratio of the stiffness of the cross-section, the enhanced ratios of the drift at the ultimate moment and the drift at the maximum lateral load of the column models reinforced by bonded or unbonded steel rebars.

A Simplified Method to Predict Damage of Axially-Loaded Circular RC Columns Under Lateral Impact Loading

Detailed finite element (FE) models are often employed to predict the impact responses of reinforced concrete (RC) columns. However, they always require substantial investments of time and effort in modeling and analysis so that they are not widely used in practice, particularly in preliminary designs. Moreover, although some simplified models have been established for beams and slabs under impact loading, few attempts have been made on modeling RC columns. For these reasons, this paper proposes a simplified modeling method to accurately capture the impact-induced response and damage of circular RC columns. In the proposed method, a two-degree-of-freedom (DOF) system was used to describe the interaction between the impactor and the impacted column. The formulas, and procedure to estimate the force–deformation relationship with strain-rate effects were presented according to the section-based analysis. The influence of the unloading stiffness on the residual deformation was addressed, and the method to determine the unloading stiffness of circular columns was proposed. Furthermore, a fiber-based beam-column element modeling method was developed to estimate the force–deformation relationship of the columns with strain-rate effects. The proposed simplified method was demonstrated by the drop-hammer impact tests to be capable of predicting the impact response of RC columns well. Its accuracy in the residual deformation is superior to that of the detailed FE simulation. Parametric studies were performed to investigate the damage characteristics of axially-loaded circular RC columns under various impact scenarios.

Comparative Nonlinear Behavior of Corroded Circular and Square RC Columns

This paper discusses performance of the reinforced concrete structures deteriorated by corrosion on basis of numerical simulation analysis. The purpose is to preliminarily investigate the idea of performance comparison of circular and square reinforced concrete columns under corroded conditions. Previous research carried out by the authors shows that equivalent area reinforced concrete (RC) columns exhibit similar load-displacement behavior under flexural and shear controlled conditions. The two types of columns deviate from this similarity after the corrosion of steel reinforcement present in the concrete. The change in the load-displacement behavior is highly dependent upon factors including the corrosion ratio, axial load, presence of web reinforcement etc., The experimentally verified 3D finite element modelling (FEM) program (COM3D) was used to investigate the seismic performance of the circular shaped and its equivalent area square shaped RC columns. The results show that the effect of mild corrosion (around 2% corrosion) on the load-displacement behavior of square RC columns is more significant as compared to circular RC columns at without axial load and at lesser main reinforcement ratio while a similar behavior or reverse trend is observed at higher main reinforcement ratios and for cases with 10% axial load. The effect of corrosion on the web reinforcement present in square columns is more pronounced as compared to circular columns at low main reinforcement ratios.

Effect of pre-damage on compressive properties of circular RC columns repaired with BFRP composites: Testing and modeling

In reinforced concrete (RC) structures, structural members with damage should be repaired before reuse. Unlike existing studies that focus on strengthening of undamaged RC columns, the present study focused on the compressive properties of pre-damaged RC columns repaired with basalt fiber reinforcement polymer (BFRP) composites. Twenty-two circular columns with a relatively large size were tested. The influence of pre-damage levels, number of BFRP layers, and steel rebars on the compressive properties of the repaired RC columns were investigated. The test results showed that repairing with BFRP increased the strength and ultimate strain of the pre-damaged RC columns by 26–142% and 574–1147%, respectively, compared to the plain concrete counterparts. However, the axial stiffness and compressive strength of the repaired pre-damaged RC columns decreased as the pre-damage level increased. Addressing the adverse effect of pre-damage and the contribution of steel rebars, a strength model, ultimate strain model, and stress–strain relationship model were proposed to predict the compressive responses of the BFRP-repaired RC columns. The proposed models predicted well the test results. This study demonstrates that BFRP repairing is effective in enhancing the compressive strength and deformation capacity of damaged RC columns, even though the pre-damage level is severe.

Repairing of Circular Reinforced Concrete Columns Damaged By Heat Using Carbon Fiber Reinforced Polymers (CFRP) (Rope) Technique

This study investigated the behavior of repaired circular reinforced concrete RC columns exposed to temperature considering effect of spacing between CFRP ropes, number of layers of carbon fiber reinforced polimers CFRP and degree of temperature. Six circular RC specimens divided into two groups with diameter of 185 mm and length of 800 mm were tested. First and second groups consisted of three RC columns exposed to temperature degree of 400°C and 600°C, respectively. In each group, the first column used as control specimen, the second and third RC columns were repaired using one layer and two layers of CFRP ropes, respectively. The results showed that the repaired RC columns damaged by heated up to (400°C and 600°C) with one layer of spacing 100 mm and two layers of spacing 200 mm exhibited load capacity about (140% and 188%) and (123% and 164%), respectively as control specimen. Hence, one layer of CFRP rope at spacing of 100 mm was more effective than two layers at spacing of 200 mm. In addition, as the exposure temperature of fire increases, the regained capacity of the repaired column increase.