Strengthening Of Reinforced Concrete Columns Research Articles

Cracking and failure mode behavior of hybrid FRP strengthened RC column members under flexural loading

AbstractStrengthening of reinforced concrete (RC) members in bridges and buildings is often required to improve flexural performance. Strengthening using fiber‐reinforced polymer (FRP) composites has become popular as FRPs offer multiple advantages compared with conventional strengthening practices like steel jacketing and concrete enlargement. External bonding (EB) using carbon FRP (CFRP) laminates/fabric has become a common strengthening practice. The effectiveness of the EB strengthened system is reduced due to possible debonding of FRP from concrete substrate. The near‐surface mounting (NSM) of FRP laminates is efficient in reducing the debonding failure, but it is not effective under dominant compression loading. Hybrid FRP (HYB) strengthening combines the advantages of both the NSM and EB techniques. HYB strengthening can enhance the performance of RC members under all loading combinations. The main objective of this study is to understand the flexural crack opening behavior of control and hybrid FRP strengthened RC column members under pure bending. The digital image correlation (DIC) analysis shows that the crack width and its propagation are significantly reduced due to hybrid FRP strengthening. The crack widths measured using the DIC are compared with the analytical predictions based on Eurocode 2 and fib bulletin 90. HYB FRP strengthening increased the strength and post‐cracking stiffness of RC elements under flexure without compromising the ductility. In addition, the HYB strengthening distributed the damage under flexural loading, unlike localized damage observed in control RC elements.

IMPACT EFFECT ON THE EXISTING AND STRENGTHENED REINFORCED CONCRETE COLUMNS

Reinforced concrete (RC) columns are the main vertical elements in the buildings. Superstructure loads are transferred to the foundation by the columns whose design involves sufficient section sizes with longitudinal and transverse reinforcements. However, RC columns are required to be strengthened when low concrete quality and lack of reinforcement is stated. The most common strengthening technique for the RC columns is jacketing. In this method, strength of the existing column is improved by concreting and installing jacketing reinforcements. Although columns are designed according to several vertical and lateral load combinations, impact loads whose effects may reach very high values at short notice are not regarded. In the scope of this study, impact behavior of the existing and strengthened RC columns is numerically investigated. For this purpose, non-linear incremental dynamic analysis is carried out by Abaqus software that is widely utilized by engineers for such solutions. Acceleration, displacement and impact load values as well as crack patterns are obtained after numerical analysis. The results are comparatively presented for the existing and the strengthened columns. Analysis outputs reveal that proposed finite element models give an opinion about the impact responses of the RC columns. Consequently, it is evaluated that this study may make contribution to the researchers generating non-linear analysis without having to perform impact experiments that require high costs and heavy workloads in the laboratory conditions.

Finite element analysis and retrofit of the existing reinforced concrete columns in Iraqi schools by using CFRP as confining technique

Abstract There are many studies about the use of carbon fiber-reinforced polymer (CFRP) to strengthen concrete members such as columns, beams, and slabs. The effectiveness of these strengthening techniques has been proved by enhancing the mechanical properties of concrete structures. So, CFRP has been used to strengthen and repair existing concrete structures in Iraq. For example, in Al-Mosul city, the strengthening and repairing system is done for concrete members such as beams, columns, and slabs using the Near Surface Mounted or confinement technique. Therefore, the research aim is to use CFRP for maintenance as an alternative material to strengthen and repair concrete members in Iraqi schools. This article employs methods to enhance and repairing of some of concrete columns at Al-Abeer school in Najaf city by using modern materials as an alternative method of maintenance. In addition, finite element analysis was carried out using Abaqus software to verify the effectiveness of strengthening. The reinforced concrete (RC) column strengthened by using fiber-reinforced polymer as a confining technique increased compressive strength by about 91% compared to the control column. In addition, the value of strains increased to nearly 100% in the longitudinal direction with the stability of the value of the lateral strains, despite the occurrence of a significant increase in the compressive strength capacity. So, the values of vertical displacement at stress 4 MPa were 22.3 mm for the strengthened RC column and 5 mm for the control RC column. Thus, the strengthened RC column increases the values of compressive strength with a decrease in displacement to approximately 22%. Four years ago, the strength of the school building was assessed, thus the success of the strengthening.

Enhancement of the Lateral Performance of RC Columns Using Steel Jacketing: A Numerical Approach

Steel jacketing has become an attractive strengthening technique for reinforced concrete (RC) columns due to ease of construction and less space requirement. The steel cage consists of angle sections placed at corners and held together by battens at intervals along the RC column height. A numerical investigation of the effective use of steel jackets as a strengthening technique in RC columns is presented in this paper. First, the finite element models of the strengthened column were developed and validated using past experimental data. Then, with the validated model, six sets of steel jacket sections with modified cross-sections such as batten spacing, batten thickness, batten width, end batten width, L angle thickness and steel jacket height were tested under constant axial and lateral loading to understand the effectiveness of steel jackets as the strengthening technique. AnunstrengthenRC column were also analysed to compare the performance of a similar column strengthened by steel jackets with modified parameters. It was shown that strengthening RC columns with steel jackets was effective in enhancing the lateral performance of the columns and resulted in a more stable load-displacement curve with lower strength degradations as compared with the un-strengthened ones. Additionally, it was found that the most effective method to increase the lateral strength and ductility is increasing the L angle thickness. On the other hand, increasing the steel jacket height also increases the lateral performance, however, it was identified that increasing the jacket height is effective only up to 1/3rd of the RC column height. Finally, the obtained results for each parameter were compared to study the behaviour of each component of the steel jacket towards lateral strength and ductility improvements.

Behavior of large-scale columns strengthened with basalt fiber-reinforced polymers sheets or bars and hybrid FRPs

Basalt fiber-reinforced polymers (BFRP) have recently become a widely used material for increasing the ultimate load capacity of reinforced concrete (RC) columns and improving their behavior throughout their entire life. So, an experimental program consisting of 19 large-scale RC columns of low strength has been prepared to examine the behavior of strengthened RC columns at all stages of loading. In this program, the columns were divided into two groups. The main parameters include the strengthening materials (BFRP wrap, BFRP bars, and carbon fiber reinforced polymers (CFRP) wrap), the strengthening techniques (fully or partially wrapping, the number and direction of layers), the cross-sectional shapes (square, rectangular, and circular), and the loading types (eccentric and concentric). The confinement of BFRP wraps significantly improved the service load and the ultimate failure load. The hybrid systems achieved an adequate level of confinement of the strengthened columns, increased the maximum load by 43.61 %, and absorbed energy by 477.2 % compared to the control column. BFRP bars used as a near-surface mounted material improved the behavior of the columns by up to 60 % and 411 % in maximum load and absorbed energy, respectively. The ACI and ECP codes predicted good estimates for the stress of columns strengthened with a single layer but underestimated for columns strengthened with a single layer and BFRP bars. Based upon the existing test data, BFRP-RC is recommended. Furthermore, this research can support using BFRPs as strengthening materials.

Analysis of eccentrically loaded FRP partially wrapped reinforced concrete columns subjected to combined environmental erosion

The behavior of eccentrically loaded fiber reinforced polymer (FRP) partially wrapped reinforced concrete (RC) columns under combined environmental erosion was investigated in this paper. Circular RC columns were firstly subjected to chloride erosion where the target corrosion degree (0, 10 %, and 20 %) is obtained with externally applied current. This was then followed by partially strengthening with 2-ply of glass fiber reinforced polymer (GFRP) strips as well as 50 freeze–thaw cycles. Series of eccentric compression tests were conducted with ranging eccentricities of 0, 5 mm, 10 mm, and 15 mm. For comparison, the carbon fiber reinforced polymer (CFRP) partially strengthened columns with the corrosion degree of 10 % and subjected to 50 freeze–thaw cycles were also eccentrically loaded with an eccentricity of 10 mm. Results showed that with increasing corrosion degree, the bearing capacity of GFRP strengthened column showed a 2-stage behavior (firstly increased and then decreased), which may be caused by the confinement reduction of FRP on columns due to severe environmental erosion. Under small eccentric loading, The CFRP strengthened RC columns showed better compressive behavior than that of GFRP strengthened RC columns. Based on the stress–strain relationship of constituent materials, a simplified analytical model considered the effects of chloride and freeze–thaw erosion was put forward to predict the bearing capacity of FRP partially wrapped RC column under eccentric loading.

Flexural strengthening of RC columns with EB-CFRP sheets and NSM-CFRP rods and ropes

Externally bonded (EB) and near-surface-mounted (NSM) systems have been investigated in the literature to be used in flexural strengthening of reinforced concrete (RC) columns. Research has shown that NSM-FRP systems are preferred in most cases over the use of EB-FRP systems especially in flexural strengthening RC columns against lateral loads. However, limited studies have been conducted to accurately compare the behavior of columns strengthened with EB-FRP or NSM-FRP systems. In this study, six specimens were fabricated and tested. To add to the novelty of this investigation, CFRP ropes were used for the first time in flexural strengthening of RC columns against cyclic lateral loads. Two of the columns were strengthened with NSM-CFRP ropes, one with NSM-CFRP rods, one with EB-CFRP sheet, and one with CFRP lateral confinement only. The results showed that both EB-CFRP and NSM-CFRP techniques can improve the flexural resistance of RC columns. The percentage of enhancement in lateral resistance ranged from 35% to 60%. Limited slippage of NSM-CFRP rods was an advantage and led to a more ductile response. Finally, theoretical analyses were performed to predict the lateral response of strengthened RC columns. The predicted load–displacement relationships had good agreement with the experimental results.

Anti-collision performance of RC columns strengthened with a composite of FRP grid and UHPC

To improve the anti-collision performance of existing reinforced concrete (RC) columns subjected to vehicle impact loading, this paper proposes a composite strengthening method involving the use of fiber-reinforced plastic (FRP) grid and reinforced ultra-high performance concrete (UHPC). An RC column strengthened with the composite of FRP grid and UHPC and an ordinary RC column were prepared to investigate their anti-collision performance under impact loading. Using the methods of numerical analysis and tests, the effects of the vehicle impact velocity, reinforcement layer thickness, and material strength on the anti-collision performance were discussed. The test results showed that the lateral displacement of the RC column significantly decreased after strengthening with the composite. This indicated that the anti-collision performance of RC columns strengthened with the composite of FRP grid and UHPC can be effectively improved. The numerical results showed that the lateral displacement of the strengthened columns was increased by 37.8 % with an increase in the impact velocity from 3.69 m/s to 4.3 m/s; however, the impact velocity had no evident effect on the impact force acting on the surface of the RC columns. In addition, the anti-collision properties of the strengthened RC columns were significantly enhanced with the increase in the FRP grid–UHPC composite thickness and material strength. The lateral displacement of the strengthened RC columns reduced by 7.5 %–13.5 %, and its peak impact force increased by 14.9 %–33.2 % with an increase in the composite thickness from 20 mm to 40 mm. Moreover, the lateral displacement of the strengthened RC columns reduced by 14.5 %–36.1 %, and its peak impact force increased by 10.9 %–46.4 % with the increase in the compressive strength of concrete from 45 MPa to 210 MPa.

Vehicular Impact Resistance of FRP-Strengthened RC Bridge Pier

As-built bridge piers are likely to be subjected to vehicular collisions, causing severe damage to the bridge substructure and even resulting in the collapse of the entire bridge. This study aimed to evaluate the effectiveness of fiber-reinforced polymer (FRP) strengthening in enhancing the vehicular impact resistance of as-built bridge piers. A typical local, refined finite-element (FE) model of a simply supported two-span, double-column, reinforced-concrete (RC) bridge was established. The adopted material constitutive models and the FE analytical approaches were then validated through reduced vehicle model lateral impact tests on bare and carbon fiber–reinforced polymer (CFRP)-strengthened RC columns. The effective schemes for FRP strengthening of bridge piers against vehicle impact are discussed from the aspects of fiber orientation, number of layers, and strengthened height as well as by FRP type. Based on the FRP strengthening scheme, 48 vehicle–bridge collision scenarios were designed to evaluate the collapse of bridges with/without FRP-strengthened piers. It was found that (1) external FRP wrapping can effectively enhance vehicular impact-resistance of as-built bridge piers (e.g., reducing the degree of damage and deformation of the impacted pier); (2) for typical bridge piers, the effective strengthening scheme comprised a fiber orientation of 0° in reference to the circumferential direction, a 3-m strengthened height, and four-layer CFRP wrapping; (3) compared with bare bridge piers, FRP-strengthened piers could improve the vehicular impact-resistant safety redundancy of as-built bridges and, to some extent, avoid bridge collapses under truck collisions at high speed. Furthermore, through introducing the dynamic increase factors of concrete strength, reinforcement rebars, and FRP, and considering the nonuniform distributions of the strain rate of FRP-strengthened bridge piers caused by vehicular collision, the dynamic shear capacity of strengthened bridge pier was formulated.

Compressive behavior of GFRP partially strengthened corroded RC columns subjected to freeze-thaw erosion

The compression test of glass fiber-reinforced polymer (GFRP) partially strengthened corroded reinforced concrete (RC) columns subjected to freeze-thaw cycling was conducted in this study. A total of 45 small-scale RC columns were prepared. The columns were firstly subjected to accelerated corrosion conditioning to obtain the target level of steel loss, and then partially strengthened with 2-ply GFRP strips; finally, the strengthened RC columns were subjected to different freeze-thaw cycles. The main parameters in this experiment were reinforcement corrosion degree (0, 10%, and 20%) and number of freeze-thaw cycles (0, 25, 50, and 75). The compressive behaviors of columns were evaluated in terms of failure mode, load capacity, load-displacement response, stiffness, and ductility. Results showed that GFRP partially strengthening could significantly improve the load capacity, stiffness, and ductility of corrosion-damaged RC columns, while the ultimate load capacity and stiffness of strengthened columns decreased with the increase of freeze-thaw cycles. Moreover, a design-oriented calculation method for the ultimate load capacity of GFRP partially strengthened corroded RC columns subjected to freeze-thaw cycles was proposed and validated by the experimental results.

Seismic Behavior of Strengthened RC Columns under Combined Loadings

Twenty-five reinforced concrete (RC) columns of section size 250 × 250 mm were designed and tested to study the seismic response considering the effect of loading case, strengthening method, and the predamage level, containing 21 columns reinforced with high-performance ferrocement laminate (HPFL)-bonded steel plates (BSPs), i.e., the intact strengthened columns (ISCs), earthquake-damaged strengthened columns (EDSCs), corrosion-damaged strengthened columns (CSCs) and coupled-predamaged strengthened columns (CPSCs). The bearing capacity of the specimens under the four different types of loading methods is ranked as follows: uniaxial compression–bending–shear (CBS) members, biaxial CBS members, biaxial CBS-torsion (CBST) members, and uniaxial CBST members. Compared with nonstrengthened specimens, the cracks of the strengthened RC columns are more fully developed, and the failure modes have been changed after strengthening. The failure modes and load–deformation curves had little significant difference for the strengthened RC columns with different damage under combined loading levels. The bearing capacity of strengthened RC columns with the applied loading of 400 kN improved, which increased to 60.1%–114.7%, 29.9%–103%, 65.2%–127%, and 49.2%–104.5% for ISCs, EDSCs, CSCs, and CPSCs, respectively. Moreover, the bearing capacity of specimens decreased due to the existence of horizontal eccentricity. Finally, based on the degraded trilinear restoring force model, the strengthened influence coefficient for loading α and displacement β and the torsion influence coefficient for loading γ and displacement ξ were introduced. A modified restoring force model of RC columns was presented, reflecting the loading method, predamage level, and strengthening method. The theoretical calculation values align with the test load–deformation curves, and the mean absolute error is almost less than 15%.

Experimental investigation on short concrete columns laterally strengthened with ferrocement and CFRP

The use of ferrocement in strengthening reinforced concrete (RC) structures has increased recently. Ferrocement has mostly been used to provide extra confinement for RC columns. However, its performance, especially in combination with CFRP confinement has not yet been fully understood. In this study, a total of fifteen columns were experimentally tested to investigate the effects of using ferrocement confinement in strengthening square RC columns. The combination between CFRP and ferrocement in strengthening RC columns has also been investigated. In addition to providing extra confinement, ferrocement is used to modify the shape of square columns to curvilinear shape, which is more effective for confinement. The parameters were (1) the materials used for confinement (ferrocement, CFRP, or both), (2) cross-sectional shape (square, curvilinear, or circular), and (3) the amount of confinement (full vs. partial confinement). The results show that ferrocement is very effective if combined with CFRP. The curvilinear shape provided by ferrocement helps to distribute the lateral stresses and ultimately reduces stress concentration which is usually the cause of failure for columns strengthened with CFRP confinement. The results are analyzed and discussed, and a number of conclusions are presented.

Dynamic Behavior of RC Columns Confined with Micro-Expansive Concrete-Filled Steel Tubes Subjected to Lateral Low-Velocity Impact: Experimental and Numerical Study

In order to improve the anti-collision capacity of existing reinforced concrete (RC) columns under vehicle impact load, an experimental study on the anti-collision performance of RC columns strengthened with micro-expansive concrete filled steel tube was carried out. By combining an experiment and finite element calculation, the influence of steel tube strength, micro-expansive concrete strength and steel tube wall thickness on the anti-collision performance of strengthened RC columns were studied. The results showed that the peak displacement of an SM-RC column is 25.9% lower than that of an RC column, due to the increased stiffness, the peak impact force increased by 138.2%. The micro-expansive concrete filled steel tube reinforcement method can significantly improve the anti-collision performance of RC columns and reduce the lateral deformation. Increasing the strength grade of steel tube and thickness of steel tube can greatly improve the impact resistance of strengthened RC columns and reduce the lateral deflection deformation of short columns, compared with steel tube strength Q235, the displacement of Q690 is reduced 47.4%. the displacement of the 8-mm thick steel tube is reduced by 48.1% compared with the 4-mm one. while the strength grade of micro-expansive concrete has little effect on the impact resistance and lateral deflection deformation of strengthened RC columns.

Experimental study on the eccentric performances of high predamaged rectangular reinforced concrete columns strengthened with carbon fiber reinforced polymer

The mechanical behaviors of 12 high predamaged reinforced concrete (RC) rectangular columns strengthened with carbon fiber reinforced polymer (CFRP) under eccentric compression were experimentally investigated. The effects of the predamaged degree ( δ), CFRP strips spacing ( s f ) and eccentricity ( e) on failure mode, bearing capacity, strain behaviors of CFRP strengthened predamaged columns were examined systematically. Test results demonstrated that the strengthened RC columns with small-eccentricity were destroyed by the yielding of compressive longitudinal steel bars and the crushing of compression concrete while the transverse CFRP strips were not ruptured. The failure mode of the strengthened RC columns with large-eccentricity was distinguished by the yielding of tensile and compressive longitudinal steel bars, the rupturing of longitudinal CFRP sheet, and the crushing of compressive concrete. With the increase of predamaged degree or eccentricity, the maximum bearing capacity of specimens decreased. In contrast, CFRP strips spacing had little effect on bearing capacity. Considering the effect of predamaged degree and eccentricity, a modified model for conveniently predicting the stress–strain relationship of CFRP strengthened predamaged RC columns under eccentric compression was proposed. On the basis of experimental study, the influence coefficients of predamaged degree and eccentricity and a strain distribution coefficient of CFRP strips were introduced, a calculation formula for predicting bearing capacity of high predamaged rectangular RC columns strengthened with CFRP under eccentric compression was proposed and validated test data with good agreement.

Evaluation of square slender RC columns subjected to eccentric loading strengthened with longitudinal FRP sheets based on PIV analysis

In this study, the behavior of square slender reinforced concrete (RC) columns strengthened with carbon fiber-reinforced polymer (CFRP) sheets was investigated. The externally bonded reinforcement on grooves (EBROG) method as a new technique was employed to strengthen the specimens compared to the externally bonded reinforcement (EBR) method as the conventional strengthening technique. Twelve small-scale slender square RC columns (i.e., 125 × 125 × 900 mm) with a slenderness ratio of 25 were loaded under eccentricity-to-cross-section ratios (e/h) of 0, 0.24, 0.48, and 0.72. The results showed the EBROG's superiority over EBR in load-carrying capacity enhancement of the strengthened RC column specimens in various eccentricities; i.e., the loading enhancements were 10.6 to 99.3% for the EBROG specimens and 1.2 to 41.7% for the EBR specimens at varying eccentricities of 0 to 90 mm, compared to those of un-strengthened specimens. Furthermore, the moment capacity enhancement of the EBROG specimens was higher than that of the EBR columns; i.e., it was 100.0% for the EBROG specimens and 42.2% for EBR specimens in the eccentricity of 90 mm, compared with the un-strengthened specimen. Using particle image velocimetry (PIV) analyses, the results of flexural stiffness, strain distribution, ductility, and energy absorption were presented and discussed. Results revealed that by increasing the eccentricity, flexural stiffness decreases; this reduction was more intense for EBR specimens (42%) than the EBROG specimen (36%). An analytical procedure was conducted to compare the experimental and theoretical results. The analysis demonstrated good agreement between the results and the superiority of the EBROG method over the EBR.

Models for Predicting Strength of RC Columns Strengthened with NSM-CFRP Strips and CFRP-Fabric Wraps

A comprehensive experimental investigation was carried out on reinforced concrete (RC) columns strengthened with near surface mounted (NSM) Carbon fiber reinforced polymer (CFRP) strips with CFRP fabric wraps as confinement. The number of NSM-CFRP strips and the number of CFRP-Fabric wraps were varied. The RC columns were subjected to concentric and eccentric loads with different eccentricities that resulted in uniaxial bending. Significant improvements in strength and ductility were observed in the strengthened columns compared to that of the control specimen. In this investigation four empirical models, based on the experimental results, were developed to predict the un-strengthened and the NSM-CFRP strengthened RC columns using different parameters. The capacities of the columns predicted by the developed empirical models were validated using the obtained experimental results. It is observed that the developed empirical models have exponential decay and a near-perfect fit to the experimental results, with R2 averaging more than 99% and an average mean absolute percent error (MAPE) of 6.6%. It is concluded that the developed models can be used as useful tools for predicting capacity of columns with NSM-CFRP strips and CFRP wraps under axial loading and uniaxial bending.

Experimental analysis of RC rectangular and square columns confined using carbon fiber composites

Most of the places around the world are associated with the deterioration of major components such as columns in the reinforced concrete buildings or structures. The inventive strengthening and rehabilitation techniques for reinforced concrete structures and components, specifically with fiber composites, have occupied a huge part of the investigation work in the arena of restoration and repair of structural components. The technique of strengthening RC columns by means of carbon fiber composite is widely used due to its excellent properties compared to other FRP sheets. Many research works were directed in the field of strengthening reinforced concrete circular columns. However, other cross-section shapes like rectangular or square columns did not take the same attention which is mostly preferred in actual constructions. The main focus of this present work is to study the comparative axial behavior of square and rectangular columns after strengthening with carbon fiber composite through experimental investigations. The experimental analysis comprised twelve reinforced concrete (RC) columns consisted of unwrapped and carbon fiber composite wrapped. The axial response of rectangular and square was recognized through the evaluation of outcomes in the form of axial strengths, ductility and failure patterns. The experimental outcomes exhibited that the effect of confinement on square columns significantly improves the strength-ductility behavior compare with confined rectangular columns. The comparative study exposes the variations in cracking patterns at failure loads on rectangular and square RC columns confined with carbon fiber composite. It is also observed that the axial behaviors of unwrapped and wrapped RC columns are significantly affected by the change in shape.

RETRACTED: Effect of EBR- and EBROG-GFRP laminate on the structural performance of corroded reinforced concrete columns subjected to a hysteresis load

The reinforced concrete (RC) columns infiltrated by chloride ions in the marine environment are much vulnerable under seismic loading and corrosion can severely reduce their load-bearing capacity. To improve the load-bearing capacity of RC columns subjected to different load conditions and hazardous environments using glass fibre reinforced polymers (GFRP) have been gained a great deal of attention. Therefore, this paper investigated the seismic behaviour of RC columns strengthened by GFRP laminate exposed to the different rebars corrosion levels. A total of 15 square RC columns were fabricated and tested under the lateral seismic load. A novel wrapping method was employed to perform different longitudinal rebar corrosion at levels of 0%, 5%, 10%, 15% and 20%. To introduce GFRP laminate on the specimens’ surfaces, two strengthening techniques were applied: Externally Bonded Reinforcement (EBR) and Externally Bonded Reinforcement on Grooves (EBROG), and the effect of these strengthening techniques on the hysteresis behaviour, energy dissipation, stiffness, ductility, load-bearing capacity, and deformation of specimens were studied. Additionally, new models were developed to predict the ductility, stiffness, and energy absorption of EBR- and EBROG-GFRP strengthened RC columns with various rebar corrosion levels. Results showed that using GFRP laminate improved the maximum load-bearing capacity, stiffness, ductility and energy absorption of corroded RC columns, and these properties were further improved using the EBROG technique. However, the difference between the improvement effect of EBR and EBROG techniques was declined with increasing the longitudinal rebars corrosion level. Additionally, the proposed models with high accuracy could be utilized as an efficient tool to anticipate the ductility, stiffness and energy absorption of EBR- and EBROG-GFRP strengthened RC columns exposed to different rebar corrosion levels.

Strengthening of axially and eccentrically compression loaded RC columns with UHPC jacketing system: Experimental investigation and finite element modeling

The paper presents an experimental and numerical evaluation of reinforced concrete (RC) columns strengthened with ultra-high-performance concrete (UHPC). Fifteen columns were tested under static eccentric loading. The variables considered in the experimental program are the thickness of UHPC and the loading eccentricity. A three-dimensional (3D) numerical model was developed using ABAQUS software and validated with the experimental results. The validated numerical model was utilized to develop additional results of the strengthened RC column considering UHPC strength as a variable. Finally, an analytical model was proposed to predict the failure load and moment for rectangular RC columns strengthened with UHPC. The results confirmed the effectiveness of UHPC jacketing to strengthen RC columns under eccentric loading. The degree of enhancement is proportional to UHPC jacket thickness and inversely proportional to the nominal eccentricity. The proposed analytical model accurately predicted the failure load and moment for rectangular RC columns strengthened with UHPC.

Reliability-based optimization of external wrapping of CFRP on reinforced concrete columns considering decayed diffusion

A cost-efficient maintenance plan is crucial to ensure the reliability of decayed reinforced concrete (RC) structures. A reliability-based optimization strategy is proposed that considers a time-variant deterioration model for planning the optimal time and degree of carbon-based fiber reinforcement polymer (CFRP) strengthening of RC columns. A genetic algorithm (GA) has been used as an optimization tool, and the particle swarm optimization algorithm was used to validate the outcomes. A deteriorating RC column exposed to chloride attack was modeled to compare the time-dependent failure probabilities calculated by a recently-developed closed-form equation and the correspondent reliability indexes as lifetime performance indicators. The influence of CFRP wraps on the decayed diffusion rate, and corrosion current density has been modeled using existing formulations. The results of the decaying diffusion model also have been compared to the extreme cases of “no influence” and “complete corrosion stop”. It was found that a GA can successfully determine the optimum solution in terms of the number of required CFRP layers and strengthening time to yield the minimum life-cycle costs. The findings can assist engineers and asset owners in providing optimized maintenance and repair strategies for decayed structures. It also highlights the significance of proper modeling of the corrosion process in CFRP-strengthened RC columns.