Retrofitting Reinforced Concrete Research Articles

Earthquake response of reinforced concrete frames with infill and active external confinement: Tests and dataset

One option to retrofit reinforced concrete (RC) frames is the construction of infill walls. Infill increases lateral strength and stiffness but tends to reduce drift capacity relative to bare frames. Few studies have quantified the reductions in drift demand attributable to infills prior to failure. This report summarizes data from experiments designed to compare drift demands of frames with and without infill. Included data come from two experimental programs completed at Purdue University which focused on the in-plane dynamic response of reduced-scale, non-ductile RC frames to uniaxial simulated earthquake ground motions. 254 dynamic tests were conducted on bare frames, frames with masonry infill walls, and frames with timber infill walls. In 11 of 14 test series, active confinement was applied to columns using external post-tensioned reinforcement. The complete dataset is open-access online on Zenodo, DOI: 10.5281/zenodo.6954967.

Seismic performance of underground structures improved by using PET FRP retrofitting central columns

The seismic failure mechanism of underground structures presents that the insufficient lateral deformation capacity of central columns will result in the collapse of the overall structure. Therefore, this study proposed applying Polyethylene Terephthalate Fiber-reinforced Polymer (PET FRP) to enhance the lateral deformation capacity of the central columns of underground structures and then improve the seismic capacity of the overall structures. The numerical models of PET FRP retrofitting reinforced concrete (RC) columns subjected to high axial loads and increasing cyclic deformations were verified by experimental results. With the calibrated models, the inter-story deformation capacity of the underground structures with and without PET FRP retrofitting was contrastively analyzed, and the seismic response of the two underground structures subjected to both horizontal and vertical ground motions was simulated and discussed. It was found that the PET FRP retrofitting structure experienced smaller earthquake threats due to the larger lateral deformation capacity. Furthermore, the repairability of the PET FRP retrofitting underground structures after earthquakes was also investigated. Numerical results presented that applying PET FRP retrofitting central columns of underground structures could improve the seismic performance of overall underground structures.

Hysteretic model for corroded reinforced concrete columns retrofitted with FRP

A hysteresis model was developed for fiber reinforced polymer (FRP)-retrofitted reinforced concrete (RC) columns with corroded reinforcing bars. The test data of 49 FRP-retrofitted corroded columns and 19 intact columns (with no corrosion or FRP wraps) under repeat-cyclic loading were collected to establish a database. A polygonal model was adopted to simulate the hysteretic behavior of FRP-retrofitted corroded columns. This was determined using backbone and cyclic parameters. For the backbone parameters, a hybrid influence factor (HIF) was introduced to incorporate the coupling effects of corrosion and FRP retrofitting. A suite of empirical equations was developed using multivariate linear regression analysis to predict the HIFs of each backbone parameter in association with the corrosion rate and important column design parameters. Moreover, an empirical relationship was developed to determine the cyclic parameters of the hysteretic model using a regression analysis. The predicted hysteretic curves were compared with the experimental results, demonstrating sufficient accuracy for both intra- and extra-database tests. Finally, the developed hysteretic model was used to establish a macro-type structural model for the FRP-retrofitted corroded RC frames. This benefitted the analysis of structural collapse under earthquakes, and the effects of the corrosion rate and FRP retrofitting schemes on the seismic collapse capacity of RC frames were examined.

Cyclic Behavior of Interfaces for Seismically Retrofitted RC Buildings

In seismically retrofitted reinforced concrete (RC) structures, new members are connected to existing members using interfaces with roughened surfaces and post-installed dowel bars. During an earthquake, the interfaces are subjected to cyclic shear and normal stresses. Therefore, the structural design of interfaces is essential. In a previous study, normal and shear loads were applied to interface specimens. Moreover, a shear strength estimation method was proposed; however, the cyclic behavior was not discussed. This paper presents a cyclic model of the roughened surface in retrofitted RC structures. First, an envelope model was constructed using the previous shear strength estimation method and Saenz model, a constitutive law of concrete. Subsequently, the cyclic rules were modeled. Moreover, a previous dowel model was incorporated into the proposed cyclic model to estimate the test results. Finally, the proposed model provided reasonably estimated test results; the average ratio of the test results to the model results was 1.04. In addition, as δ increased, the effect of the dowel bar intensified in terms of shear.

Energy-dissipation in Seismic Retrofit RC Building with Friction Dampers

Reinforced concrete (RC) buildings have suffered severe damage in the past due to inadequate lateral force resistance or energy dissipation capability. There is a need to improve the seismic performance of existing, vulnerable RC structures, particularly those that were either not initially intended for seismic effects or were planned to an obsolete seismic standard. Friction dampers are a revolutionary technique for improving lateral force resistance and energy dissipation capacity in the seismic retrofit of RC buildings. In this study, energy dissipation in seismically retrofitted RC buildings using friction dampers is investigated. An investigation of the nonlinear response history was performed after friction dampers were applied to the RC building. The analysis results indicate that the peak story drift ratios are reduced and constant throughout the height of the building, which may be a sign that the structure has not suffered soft story damage. In addition, the total friction damper’s energy-dissipation is half of the total input energy.

Experimental study on the seismic behavior of RC columns with high axial compression ratios retrofitted by large rupture strain fiber-reinforced polymer

Fiber-reinforced polymer (FRP) composites being utilized to retrofit reinforced concrete (RC) columns has been well documented. However, the axial compression load of the FRP retrofitting RC columns was relatively limited. Aiming to analyze the applicability of FRP retrofitting RC columns with higher axial compression loads, this paper presents an experimental study on the seismic performance of RC columns retrofitted by the Polyethylene Terephthalate (PET) FRP composites. A total of twelve 1/3 scale RC columns were fabricated, including four control specimens and eight PET FRP retrofitting columns with two retrofit schemes. All the columns were tested under combined high axial compression load and cyclic lateral displacement excursions, and the maximum axial compression ratio reaches 1.1. The seismic performance of RC columns retrofitted by PET FRP was analyzed detailedly from the failure mode, shear force and deformation capacity, energy dissipation and ductility. The test results showed that PET FRP retrofitting changed the failure mode of RC columns from brittle to more ductile. The post-peak strength degradation of the columns was more rapid with the increase of axial compression ratio, but the strength degradation of the PET FRP retrofitting columns was more gradual. PET FRP retrofitting significantly improved the ductility and lateral deformation capacity of the columns even under the high axial compression ratio. PET FRP retrofitting can be applied for the RC columns with serous demand of deformation capacity due to the lighter change of shear-loading capacity and stiffness. Contrastively, the improvement of the seismic capacity of the RC columns retrofitted by the laterally wrapped scheme is higher than that of the striped wrapped scheme. Conclusions from this study provide useful references for the seismic retrofitting of RC structures.

Structural Behavior of FRP-Retrofitted RC Beams under Combined Torsion and Bending.

Fiber-reinforced polymers (FRPs) retrofit reinforced concrete (RC) structures. ABAQUS finite element software was used to perform numerical parametric analysis on a group of RC beams in this research. All specimens were retrofitted by FRP strips as an external retrofitting and experimentally tested up to previous researchers’ failure points. The range of subjects examined in these RC beams included cracking torque, ultimate torque, angle of twist, and the effect of using FRP on these subjects. We applied artificial neural networks (ANNs) to predict the structural behavior of RC beams under combined torsion and bending to develop the research accuracy. After testing, the ANN results were compared with the ABAQUS results. Consequently, a reasonable examination of the determined mathematical and trial results confirmed this study’s logical accuracy in predicting retrofitted RC beams’ structural behavior under combined loading.

Experimental and Numerical Investigation of Different Types of Jacketing Effect on Retrofitting RC Short Columns Using ECC Concrete

Given the deterioration of civil infrastructure throughout the world, developing more efficient repair and strengthening is essential. Jacketing is one of the most common methods for retrofitting reinforced concrete (RC) columns. Notably, using engineered cementitious composite (ECC) within the jacketing area increases the bearing capacity and significantly enhances the ductility of the columns. The recent development of ECC concrete with suitable compressive strength and higher ductility of about 5 % can significantly enhance the performance of reinforced concrete structures. The behavior of retrofitted RC columns depends heavily on the cohesion between the jacket and the original column as well as the mechanical properties of the jacketing materials. This study investigates jacketed square and circular RC columns using ECC and conventional/normal concrete (NC) using different casing techniques to retrofit RC columns, namely galvanized mesh, U and L-shape joints, removing the cover, core drilling, and integrated models. All specimens were subjected to a compression test. The results indicate that in both square and circular specimens, the use of ECC as a super ductile material and vertical U-shaped elements to connect the longitudinal rebars of the casing and the core leads to much higher ductility and bearing capacity than in NC specimens. These elements also showed suitable ductility because of using ECC as a super ductile material. In order to optimize these methods, finite element analysis (FEA) was conducted using Abaqus software to verify experimental models, as well as a parametric study to achieve an optimum design of the jacketing.

Flexural behaviour of circular reinforced concrete columns strengthened by glass fibre reinforced polymer wrapping system

The use of prefabricated glass fibre reinforced polymer (GFRP) wrapping systems in retrofitting reinforced concrete (RC) columns has emerged to enhance the overall axial performance. However, the effect of these systems on columns subjected to bending is still limited although the flexural loading on columns in real life is inevitable. This paper presents experimental, numerical, and theoretical investigations on the flexural behaviour of circular RC columns strengthened by a GFRP wrapping system. A total of eight columns were prepared and tested under three point bending to determine the contribution of the GFRP wrapping system to the overall flexural performance. The annulus between the RC columns and the GFRP wraps was filled with epoxy or cementitious grout to ensure transfer and distribution of stresses. The load-midspan deflection responses and failure modes were presented and evaluated. Furthermore, a nonlinear finite element modelling (FEM) was conducted using ABAQUS software to simulate the performance of unwrapped and GFRP-wrapped columns under flexural loading. A theoretical analysis was also developed using the basic beam theory to obtain the flexural capacity of the tested columns and compare it with experimental and FEM results. A parametric analysis was carried out to assess the effect of varying the thickness of GFRP and infill, as well as the loading mode, on the flexural behaviour of RC columns. The results of experimental tests demonstrated that GFRP-wrapped columns with epoxy infills significantly enhanced the flexural load capacity whereas columns with grout infills showed a prominent enhancement in ductility and energy absorption. The results of FEM and theoretical analyses were in good agreement with experimental results. The results of the developed theoretical model were found to have a good correlation with the results of the parametric investigation. Overall, the GFRP wrapping system implemented in this study is an effective repair technique for structural RC columns subjected to flexural loading. The proposed theoretical model can be used by the practising engineers to design a composite repair system for deteriorated reinforced concrete columns.

Progressive collapse performance of shear strengthened RC frames by nano CFRP

Abstract To investigate the effect of nano carbon-fiber-reinforced polymer (nano CFRP) on retrofitting reinforced concrete (RC) structures, this article presented the progressive collapse performance of two half-scale four-bay RC frames including one control specimen S1 and specimen S2 with nano CFRP retrofitting beam ends. The progressive collapse performance was discussed by comparing crack patterns, failure mode, load–displacement curves, horizontal displacement, strains, and rotational and energy dissipation capacity. The test results demonstrated that nano CFRP did not change the ductile beam-hinge failure mode, but improved the load-bearing capacity and ductility efficiently, and postpone shear failure of the joint core region obviously. Due to the insufficient development of plastic hinges limited by nano CFRP, S2 failed to enter catenary action, which revealed its own defects in anti-progressive collapse. It was shown that the retrofitting strategy using nano CFRP can substantially improve the mechanical characteristics and implement the strong column-weak beam failure mode.

The Effect of Strengthening Methods on the Performance of Reinforced Concrete Columns against Vehicle Impact

Columns at the ground floor and parking garages that could be hit by a car pose a significant risk to the structural stability of the building superstructures. Generally, these columns are not built to sustain the lateral impact force generated by car–column collision. In this study, the performance of axially loaded retrofitted reinforced concrete (RC) columns against car impact is evaluated using finite element (FE) simulation. The FE model of the RC column with axial load was validated with experimental results. For the car-crushing simulations, two SUV car models with a mass of about 2250 kg, which had been experimentally validated, were used to simulate the car–column collision. The results of the FE analysis revealed that once the impact speed exceeds 30 km/h, the horizontal impact force has a significant effect on the column joint at the foundation. The impact force increases linearly as the impact velocity of the car increases up to 20 km/h. When car impact velocities are more than 20 km/h, the generated impact force increases in power to the car-crashing velocity. Both types of cars have almost the same effect on the generation of impact force and the lateral displacement of the column. It is found that the generated impact forces are higher than the recommended design values of Eurocode 1. To protect the column from car impact damage, two types of column-strengthening systems were investigated. One form of strengthening system involves retrofitting the lower half of the column with an aramid fiber-reinforced polymer (AFRP) warp, while the other involves putting a reinforced concrete jacket of up to 1.3 m in the height of the column. Based on the comparative study, design recommendations are suggested to protect the RC column from accidental car-crashing damage.

Analysis of Reinforcement Overlapping on Retrofit Reinforced Concrete Beams of Bending Behavior

The length of reinforced concrete blocks varies widely, while in general the reinforcement produced in Indonesia is 12 m. Therefore, the use of reinforcement in a long stretch is done to be connected. The through connection is the most economical connection [2]. Lap splice can be made by overlapping the reinforcement which is touching or separate [3]. Splicing reinforcement can cause the strength of reinforced concrete beams to be reduced or even damaged so that rehabilitation measures are needed which can be in the form of retrofit (repair). Retrofitting with wiremesh and self compacting concrete (SCC) is considered to improve building structures. Reinforcement overlapping on reinforced concrete beams retrofit with wiremesh and self compacting concrete can be analyzed by numerical methods to determine their effect on bending behavior. Now, to analyze a structural behavior, it can be done using finite element method based program. The application of the finite element method is used in several programs, including ABAQUS, ADINA, Atena, ANSYS, etc. This study aims to analyze the overlapping of reinforcement in retrofit reinforced concrete beams against the flexural behavior, overlapping is made at one-third and one-third of the beam span using finite element method based analysis software.

Evaluation of Effective Polymer Fiber Length on Energy Absorption Capacity of Reinforced Beams by EBR and NSM Methods

This study presents a comparison of two methods used for retrofitting Reinforced Concrete (RC) beams, namely, the Externally Bonded Reinforcement (EBR) and the Near-Surface Mounting (NSM) methods. A parametric analysis was carried out using variables such as the retrofitted, the retrofitting method (EBR and NSM), and the thickness of the Carbon Fiber-Reinforced Polymer (CFRP) sheets. To achieve this goal, the finite element method and ABAQUS software were employed. An un-retrofitted beam was also simulated as the control specimen for comparison. Beam responses were compared through load–displacement and energy absorption capacity diagrams. Results show that the higher energy absorption capacity in all CFRP-retrofitted RC beams, which was 1.69–5.54 times higher than in un-retrofitted beams. In the case where half of the beam was reinforced using CFRP sheets, the entire beam assembly and the CFRP sheet contributed to load-bearing, thus delaying crack nucleation in the beam and increasing its energy absorption capacity. As a result, the energy absorption capacity of the beam, in this case, was less than that obtained in the previous one where half the span of the beam was retrofitted.

Experimental and numerical investigations on a novel plate anchorage system to solve FRP debonding problem in the strengthened RC beams

Method of externally bonded reinforcement (EBR) is one of the most prominent systems for retrofitting reinforced concrete (RC) beams containing fiber-reinforced polymers (FRP). Many studies conducted in this field confirm the fact that the majority of the beams strengthened in this way experience failure due to the sudden detachment of FRP sheets from the concrete substrate. In this regard, an innovative plate anchorage technique was presented to solve the FRP debonding problem. In this method (EBR by Welded Steel Plates), two plates are placed near the beam supports, which are connected by welding to a longitudinal tension reinforcement through the angles. FRP sheets are placed on seat plates at both ends and fixed in their position by another plate placed over them. Ten RC beams with 150 × 200 × 2000 mm were prepared from concrete in 21 and 35 MPa strength classes. All specimens were subjected to a quasi-static four-point bending test. A comparative study was also done using an analytical method and comparing experimental results in the literature. This research results revealed that the better and more practical performance of the suggested plate anchorage system resulted in postponing or completely solving the FRP surface debonding problem.

Machine learning prediction of structural response for FRP retrofitted RC slabs subjected to blast loading

Explosive and impact events, which in recent years have inflicted colossal human and economic losses, are dire warnings that civil infrastructure is not immune to blast and explosion scenarios. Thus, designing resilient new civil infrastructure and retrofitting the existing one to enhance its blast resistance is paramount. Retrofitting reinforced concrete (RC) slabs using external fiber-reinforced polymer (FRP) is known to enhance blast resistance, mitigate displacements and cracking, and contain debris. However, existing approaches to simulate the structural response to blast loading require competent knowledge, substantial modeling efforts, and high computational cost. Therefore, this study investigates the practicality of deploying machine learning to predict the maximum displacement of FRP strengthened RC slabs under blast loading as a novel approach to achieve simplified and accurate predictions. A Gaussian process regression algorithm was implemented for model development considering several influential features of the application. Due to the limited pertinent data in the open literature, a novel approach based on Tabular Generative Adversarial Network (TGAN) was used to generate 200 additional synthetic data used for model training. A design parameter prediction model was also proposed to predict the cross-section of FRP retrofitting considering blast parameters and the displacement specified by the design code. Statistical performance metrics including MAE, MAPE, and R2 indicate that the developed model achieved predictions with superior accuracy. Feature importance analyses were also conducted and corroborated by existing experimental and numerical studies. Based on the proposed model and its validation and feature importance analyses, the implementation of ML was proven to be a viable approach for structural response predictions under blast loading. Thus, the proposed model can potentially provide designers with accurate results for FRP retrofitting of RC slabs against blast loading through a highly simplified approach at low computational cost.

Optimal design of reinforced concrete columns strengthened with square steel tubes and sandwiched concrete

The effectiveness of retrofitting reinforced concrete (RC) columns with steel tubes and sandwiched concrete has been confirmed through numerous studies. However, it is necessary to establish a strengthening design method that focuses on cost minimization to ensure the widespread application of the strengthening technology. Therefore, this paper presents an optimisation design study on circular RC column strengthened with square steel tubes and sandwiched concrete (SSTSC) jackets. Experimental investigations were firstly conducted to determine the constraints needed in the optimisation design model, including the width-to-thickness ratio, minimum width of the steel tube, confinement ratio and slenderness ratio. A formula was then proposed to predict the ultimate capacities of the strengthened specimens. Finally, based on optimisation theory of the complex-shape method, an optimal design program was developed in MATLAB. The cost of the rehabilitation scheme was taken as the objective function, while the load-bearing capacity and other related requirements served as the constraint functions. The cost of the optimised specimens was reduced by 17.72% on average, verifying the effectiveness of the model. This investigation focused primarily the cost-efficiency of schemes for retrofitting circular RC columns with SSTSC jackets. The results of this study indicate that the cost of the strengthening process can be reduced, and is expected to promote the widespread application of the strengthening technology. Furthermore, the basic principle and the development process of the model can be used as a reference for the optimal design of other types of strengthening methods.

An empirical FRP-concrete bond-slip model for externally-bonded reinforcement on grooves

The externally-bonded reinforcement on grooves (EBROG) has been recently developed as a substitute for the conventional externally-bonded reinforcement (EBR) technique used to retrofit reinforced concrete (RC) structural members with fiber-reinforced polymer (FRP) composites. While the presently available bond-slip models predict the bond-slip behavior of FRP composites adhered to the concrete surface via the conventional EBR method, there is a lack of reports in the literature on rigorous bond-slip model for FRP composites attached to concrete surfaces via the EBROG technique. Using a nonlinear regression on experimental data, the current research attempts to introduce an empirical model for such bond-slips. For this purpose, FRP composite strips were bonded to 68 concrete prism specimens retrofitted through the EBR and EBROG technique, before subjecting them to the single lap-shear experiment (108 tests in all). The test parameters included compressive strength of concrete, grooves dimensions (width and depth), composite strip width, and composite stiffness. A bilinear bond-slip model was proposed. Maximum shear stress, fracture energy, and associated slip were determined by analyzing on-groove and out-of-groove stresses and strains via the image processing method of particle image velocimetry (PIV). Finally, analysis of variance and different statistical tools were employed to validate the results obtained from the bond-slip model developed.

Susceptibility of strain-hardening cementitious composite to curing conditions as a retrofitting material for RC beams

Strain-hardening cement-based composites (SHCC) have recently been developed as repair materials for the improvement of crack control and strength of flexural members. This work focuses on strengthening and flexural enhancement using SHCC layer in tensile regions of flexural members under three different curing conditions. The curing conditions simulate the effect of different environmental conditions prevailing in the central and coastal regions of the Arabian Peninsula on the properties of SHCC as a retrofitting material. In this investigation, beams with SHCC layer were compared to control beams. The beams with SHCC layer of 50-mm thickness were cast. The results revealed that the flexural behavior and the load-carrying capacity of the normal concrete beam specimens under hot and dry environmental conditions were significantly reduced, lowering the ductility of the section. However, compressive strength is comparatively unaffected. Similarly, the hot curing conditions have also led to a notable reduction in the loading capacity of the beam with SHCC layer with a slight effect on its stiffness. On the other hand, steam-curing conditions have shown improvement in load-carrying capacity and a reduction in section ductility of the beam with SHCC layer. It was found that the structural unit retrofitted with SHCC layer was a curing-regime dependent as the tensile and strain-hardening properties of SHCC are highly sensitive to the alteration in the cement hydration process. A normal curing regime was found effective and satisfying the practical, cost, and performance requirements. Accordingly, a normal curing regime could be implemented to retrofit reinforced concrete (RC) beams with SHCC layers as recommended in the study.

Retrofitting of the corroded reinforced concrete columns with CFRP and GFRP fabrics under different corrosion levels

This study aims to evaluate the seismic performance of retrofitted reinforced concrete (RC) columns with glass fibre reinforced polymers (GFRP), and carbon fibre reinforced polymers (CFRP) fabric with different rebar corrosion levels. For this purpose, a total of fifteen square cross-section RC columns with different rebars corrosion ratios were fabricated and tested under the lateral hysteresis and a constant vertical load. A new wrapping technique is employed in order to apply the corrosion, and five different corrosion level of 0%, 5%, 10%, 15% and 20% were obtained. Therefore, the hysteresis performance, energy dissipation, cyclic stiffness, ductility, the maximum bearing capacity and deformation of the specimen were examined. Some models were also developed to predict the ductility and energy absorption of corroded rebars RC columns. The obtained results indicated that the influence of polymer fibre fabrics on the maximum deformation is higher than those with no polymer fabric at low corrosion level (less than 15%) while by raising the corrosion level of rebars, the influence of polymer fibres on the lateral displacement was dropped.

Flexural strengthening of reinforced concrete beam using a natural fibre reinforced polymer laminate: an experimental and numerical study

Synthetic fibres like carbon and glass fibres are commonly used as reinforcing material in polymer composites used by the construction industry to retrofit reinforced concrete (RC) structures. Natural fibres can be developed as a more sustainable alternative to these synthetic fibres in polymer composites. In this study, a kenaf fibre reinforced polymer (KFRP) laminate was designed and fabricated to strengthen an RC beam in flexure. Four-point bending test was carried out on a full-scale control and KFRP-strengthened beam. The beams were also modelled numerically with the ANSYS finite element software. The kenaf fibre laminate increased the ultimate load of the RC beam by 77.9% and reduced beam deflections at similar loads with the control beam. The results from the numerical analysis in terms of the beams load–deflection response, ultimate load and crack plots compared well with the experimental investigation. This study provided further insight into the design and use of a more sustainable material for strengthening RC beams and shows how numerical analysis can enhance the development of emerging materials.