Reinforced Concrete Jacketing Research Articles

Numerical Investigation of Reinforced Concrete (RC) Columns Strengthened with Ultra-High-Performance Fiber-Reinforced Concrete (UHPFRC) Jackets.

The strengthening of existing columns using additional reinforced concrete (RC) jackets is one of the most popular techniques for the enhancement of a column's stiffness, load-bearing capacity and ductility. Important parameters affecting the effectiveness of this method are the strength of the additional concrete, concrete shrinkage and the connection between the old and the new concrete. In this study, the application of Ultra-High-Performance Fiber-Reinforced Concrete (UHPFRC) jackets for the structural upgrade of RC columns has been examined. Extensive numerical studies have been conducted to evaluate the effect of parameters such as the thickness of the jacket, concrete shrinkage and the addition of steel bars, and comparisons have been made with conventional RC jackets. The results of this study indicate that the use of UHPFRC can considerably improve the strength and the stiffness of existing reinforced concrete columns. The combination of UHPFRC and steel bars in the jacket leads to the most effective strengthening technique as a significant enhancement in the stiffness and the ultimate load capacity has been achieved.

Hybrid strengthening scheme for reinforced concrete beams: Flexural behaviour and large-scale testing

Revision of design standards, new regulations, and planned/unplanned increases in loadings potentially make buildings vulnerable to changes in capacity demands. This may result in some structural components of an existing structure requiring strength or stiffness improvement. Strengthening of capacity deficit members is widely recognised as the preferred and sustainable choice in terms of conserving resources and minimising the carbon footprint. Strengthening techniques such as Reinforced Concrete (RC) jacketing, steel jacketing and Fibre Reinforced Polymer (FRP) wrapping have been explored and widely used. However, when adopted solely, each scheme has its drawbacks. RC jacketing results in a considerable rise in the dead load, influencing the loading on the foundation and restricting the functional space available post-jacketing. Steel jacketing often lacks flexibility as a significant effort is required for installation. FRP improves the flexural strength response but produces low stiffness enhancement and lesser ductility. A hybrid strengthening option, i.e. a combination of the above strengthening methods, presents a viable option to address the limitations cost-effectively. This paper presents a pioneering attempt focused on improving the flexural performance of RC beams using a hybrid strengthening scheme comprising of RC jacketing and FRP. Four large-scale RC beams were prepared, and three of them were strengthened. The first was strengthened by RC jacketing, the second by a combination of RC jacketing and flexural FRP, and the last by the combination of RC jacketing, flexural FRP and FRP ‘U wrap’ in the shear zones. The specimens were tested using the four-point bending test. The flexural behaviour was assessed in terms of the peak moment capacity, flexural stiffness, load-displacement response, crack pattern and failure modes. The test results confirmed that hybrid strengthening leads to strength gain and stiffness gains of 105% and 90% respectively, as compared with the unstrengthened beam. The efficacy of the theoretically predicted strengths against the test strengths is assessed.

Seismic performance evaluation and strengthening of RC beam-column joints adopted in Nepal

Beam-column joints are a crucial component of the reinforced concrete (RC) moment-resisting frame (MRF) as the behavior of the joints significantly influences the strength and ductility of the overall framing system. This study is performed to explore the seismic behavior of interior and exterior beam-column joints designed based on NBC 205:1994 (NBC1), NBC 205:2012 (NBC2), and the revised seismic design standard NBC 105:2020, defined as a well-designed joint (NBC3) which are the building standards used for designing low-rise RC buildings in Nepal and compares the results from the numerical simulations quantitatively. Three possible retrofit options (CFRP, steel and RC jacketing) were explored. Finally, retrofitting options were suggested for the joint of NBC1 and NBC2 with consideration of a well-designed joint (NBC3) as the currently required capacity of the joint based on the demand of revised seismic design standard NBC 105:2020.

Non Linear Analysis of Reinforced Concrete Column Strengthened by Reinforced Concrete Jacketing with High Strength Steel

The strengthening column structure elements with reinforced concrete jacketing were chosen in this study because it is the most common and easy to apply practically to existing column structures. Modeling data using test specimens from Ersoy et. al by adhering to constitutive models of concrete materials from Attard and Stunge and Bilinear steel. The purpose is to perform non-linear analysis modeling through the behavior of the section of the RC column reinforced with RC jacket by taking into account the influence of interface slip and initial strain by using a two-dimensional sectional analysis approach with a fiber-based method made using MATLAB. Non-linear analysis was performed to obtain the moment-curvature relationship and validate the modeling results with the experimental model then make modeling variations based on the variations high strength steel reinforcement and evaluate the results in curvature ductility and index ductility. The prediction results showed a fairly good fit with the experimental results and modeling variations showed that the greater value of interface slip coefficient, the higher the curvature ductility and index ductility, the variation modeling using high-strength steel in longitudinal reinforcement can increase flexural, axial and lateral capacity, but it is lower in ductility, while using normal strength steel for longitudinal reinforcement and high strength steel for lateral reinforcement with tighter spacing provides higher ductility.

Retrofitting of Shear Compression Failure-Critic Short Columns with a New Technique

One of the reasons that cause the collapse of buildings is deficient short columns, which need to be retrofitted to prevent the collapse of the building in a potential earthquake. External reinforced concrete (RC), steel plates, and fiber-reinforced polymer (FRP) jacketing are standard retrofitting methods to retrofit columns to increase their shear capacity. However, in compression shear failure, the effectiveness of steel and FRP jacketing is quite limited due to the premature buckling of the FRP and steel material. On the other hand, RC jacketing is not practical because it requires more labor and covers more architectural places. Thus, the main motivation of this study is to present the effectiveness of a new method to retrofit short columns, including those with dominated shear compression failure. For this purpose, HSPRCC (high-performance steel plate-reinforced cementitious composite) was adapted to retrofit such short columns. This method is a combination of high-performance concrete and perforated steel plates. Short-column specimens representing existing RC buildings were retrofitted using the HSPRCC and tested. Perforated steel plates anchored to the specimen by steel bolts and repair mortar are used as a matrix. The retrofitted specimens were found to exhibit much better performance both in terms of shear strength and deformation capacity. It was also observed that the retrofitting method is effective in contributing to increasing the compression shear capacity.

Seismic retrofitting of a deteriorated RC building

Numerous existing reinforced concrete (RC) buildings don’t fulfill current seismic code provisions as they haven’t been designed to satisfy these provisions. Also, due to many environmental factors, structural members such as columns, beams, and slabs are exposed to severe deterioration leading to high-risk levels. In this research, the performance of an existing seven-floor reinforced concrete building in Zagazig city, Egypt, constructed about 50 years ago, without considering the seismic requirements prescribed in the current Egyptian code (ECP-2012) is studied. The studied building suffers severe deterioration in its main structural elements, especially the basement floor slab. SAP2000 software is utilized to evaluate the structural behavior of the building under vertical loads (dead and live loads). The model failed to fulfill the ECP-2012 requirements under the applied loads. After building investigation, a retrofitting technique was proposed through providing the building with new grid beams at the basement floor level as well as replacing the existing basement floor slab with a new one. Moreover, RC jackets were provided to all basement floor columns. Through response spectrum analysis (RSA), the performance of the building with the newly proposed technique was assessed considering a peak ground acceleration equals 0.15 g (seismic zone 3). The model showed a significant enhancement in its response that fulfilled the ECP requirements concerning both strength and serviceability. Utilizing SeismoStruct software, the horizontal capacity of the model was inspected through the pushover analysis to check the efficiency of the proposed retrofitting technique. The model showed acceptable capacity in its two main directions.

Earthquake Retrofitting of “Soft-Story” RC Frame Structures with RC Infills

Multi-story, old reinforced concrete (RC) structures with a “soft-story” on the ground floor, sustain considerable damage to the soft story during earthquakes due to the presence of masonry infills in the upper stories. Aspects of such masonry infill–RC frame interaction are briefly discussed and a particular retrofitting scheme for the soft story is studied. It consists of RC infills, added within the bays of the ground floor frames and combined with RC jacketing of the surrounding frame, aiming to avert such soft-story deficiency. The impact of such a retrofit is studied through the measured response of 1/3 scaled single-story, one-bay frames subjected to cyclic seismic-type horizontal loads. It is shown that this retrofit results in a considerable beneficial increase in stiffness, strength, and plastic energy consumption. The importance of the presence of effective steel ties connecting this RC infill with the surrounding frame is also demonstrated. In order to achieve these desired beneficial effects to such vulnerable buildings, additional design objectives are established with the aim of avoiding premature failure of the RC infill panel and/or fracture of the steel ties and to protect the surrounding RC frame from undesired local damage. A numerical methodology, which is validated by using the obtained experimental results, is shown to be capable of predicting reasonably well these important response mechanisms and can therefore be utilized for design purposes.

Investigation on the performance of reinforced concrete columns jacketed by conventional concrete and geopolymer concrete

The objective of this investigation is to experimentally study the behaviour of reinforced concrete (RC) columns strengthened using RC and geopolymer concrete (GPC) jacketing by subjecting them to axial loading. The experimental results were analytically validated by the finite element model (FEM). For this investigation, six columns of M25-grade conventional concrete were subjected to more than 75% of the ultimate load. Then three columns were jacketed by using M40-grade RC and another three columns were jacketed by using M40-grade GPC. The interfacial behaviour of the conventional RC column and jacketed GPC columns was studied and compared. The 3D linear and FEM was employed to measure the effect of conventional RC and GPC-jacketed columns under increasing load by considering the concrete damage plasticity (CDP) and elastoplastic models with isotropic hardening. The validation against the experimental results confirmed 90% accuracy of the analytical model.

Residual strength and strengthening capacity of reinforced concrete columns subjected to fire exposure by numerical analysis

AbstractThis study is a numerical investigation of the performance of reinforced concrete (RC) columns after fire exposure. This study aims to investigate the effect of introducing lateral ties and using the RC jacket on improving post-fire behavior of these columns, the effect of the duration of the fire on ultimate load of columns. The analysis was performed through ABAQUS, a 3D – non-linear finite element program. 4 m tall lengthening square RC column with a cross- section of 0.4 m × 0.4 m was used as a test specimen. The RC column was reinforced by 4Ø28 mm longitudinal bars bonded by steel tie bars of Ø10 mm spaced at 400 mm. The firing temperature was increased to 600°C for 60 min. The results indicated that as the fire load duration increases, the load’s capacity diminishes. The effect of increasing the steel ratio of the RC column resulted in a decrease in the percentage of load reduction following combustion. It was concluded that strengthening columns by RC jackets is efficient and that the axial load capacity of reinforced columns was enhanced.

Optimized Strengthening Based on Concrete Jacketing for Minimum Eccentricity

The coupled lateral-torsional response is observed in building structures subjected to dynamic excitation due to lack of symmetry in terms of mass/stiffness in any of the stories’ plan views; such structural systems are called eccentric. Much damage and even collapse are concerned with building structures with asymmetric plan views. Combined torsional-translational vibration of their structural system results in higher ductility demands, especially to vertical structural elements located at the perimeter of the plan view. This study examines the minimization problem of the torsional response of an eccentric, multi-story reinforced concrete (RC) building by strengthening its vertical structural elements with RC jackets. The problem of minimizing the eccentricity between mass and rigidity centers for all story layouts and the corresponding minimization problem of the eccentricity between mass and strength centers for all stories are considered two separate formulations for the reduction of the torsional response optimization problem. Based on recent studies, the center of strength is preferable for assessing the torsional response of buildings in case of inelastic response. The imperialist competitive algorithm (ICA), a member of the family of evolutionary search algorithms, is used to solve the two optimization problems. The optimization problems are formulated for the case study building considered after assessing its structural behavior and capacity through nonlinear static analyses before and after strengthening. The later process was implemented to meet code requirements and examine the improvements achieved through optimization.

A fragility-oriented approach for seismic retrofit design

This study proposes a practical fragility-oriented approach for the seismic retrofit design of case-study structures. This approach relies on mapping the increase of the global displacement-based ratio of capacity to life-safety demand ( CDRLS) to the building-level fragility reduction. Specifically, the increase of CDRLS due to retrofitting is correlated with the corresponding shift in the fragility median values of multiple structure-specific damage states, observing that a pseudo-linear trend is appropriate under certain conditions. Accordingly, a practical approach is proposed to fit such a (structure-specific) linear trend and then use it by first specifying the desired fragility median and subsequently finding the corresponding target value of CDRLS that must be achieved through retrofit design. The validity of the proposed approach is illustrated for an archetype reinforced concrete (RC) structure not conforming to modern seismic design requirements, which has been retrofitted using various techniques, namely, fiber-reinforced polymers wrapping of columns and joints, RC jacketing, and steel jacketing.

Retrofitting of Reinforced Concrete Beams using Lightweight RC Jacket Containing Silica Nano Particles and Glass Fiber

The concrete jacket method is a common method used in retrofitting buildings. Although this method has many advantages, engineers criticize it due to an increase in the structure's weight. In the present study, lightweight concretes containing silica nanoparticles (SNPs) and glass fibers (GF) have been used in concrete jackets to strengthen concrete beams. Several reinforced concrete (RC) beams were constructed and retrofitted using the proposed lightweight concrete jackets and their response to four-point loading was evaluated. The SNPs amount in the lightweight concrete jackets was 0, 2, 4, and 6% by weight of cement and the amount of GF was 1.5% by volume of concrete. Load-deflection curves were extracted and the response of the beams was examined by parameters such as crack load, yield load, maximum load, energy absorption capacity, and ductility. The proposed lightweight concrete jacket containing 1.5% of GFs in which 0, 2, 4, and 6% of SNPs were used, increased the energy absorption capacity by 33%, 54%, 61%, and 62%, respectively. The presence of SNPs in lightweight concrete reinforced by GFs leads to the filling of small cavities in the concrete. Also, the bearing capacity of the retrofitted RC beams increased with an increase in SNPs in the concrete jacket. A portion of this increase can be attributed to an increase in tensile and compressive strength of the proposed concrete, and the other part can be attributed to the effect of SNPs on the surrounding surfaces of the main beam and jacket.

A Comparative Analysis on the Methods of Strengthening Isolated Reinforced Concrete Columns

In the construction industry, there are several methods which have been used to improve the capacity and effectiveness of structural concrete structures. Engineers can extend the life of the structures by implementing strengthening techniques. One of the techniques to strengthen columns and beams is the use of jacketing. The strength of the structural members is enhanced through the surface structural bonding of materials such as Carbon-Fibre Reinforced Polymer (CFRP), Glass-Fibre Reinforced Polymer (GFRP), ferrocement, steel angles, steel plates, wire mesh and so on. In this study, 18 reinforced concrete short columns of cross-sectional size 60 mm × 60 mm and 500 mm height were cast using concrete grade 30 MPa. The columns were subjected to compressive axial loads till failure. Moreover, the damaged columns were strengthened using three structural strengthening techniques namely, Reinforced Concrete Jacketing (RCJ), Reinforced Concrete Wire Mesh Jacketing (RCWJ) and, Steel Jacketing (SJ). The columns strengthened using RCJ and RCWJ had a cross section of 120 mm × 120 mm while SJ had a cross section of 66 mm × 66 mm. Six different configurations were used for each technique. The experimental investigations showed a minimum increase of 48.0%, 48.7% and 35.2% in the axial compressive strength when strengthened using RCJ, RCWJ and SJ respectively. Among the three strengthening techniques, SJ was determined to be the effective technique on considering structural design, time production and costs.

Reinforced Concrete Beams Retrofitted with External CFRP Strips towards Enhancing the Shear Capacity

The practical difficulties in upgrading the structural performance of existing reinforced concrete (RC) structures is discussed, when retrofitting structural members by conventional RC jacketing. The use of retrofitting schemes employing externally applied fiber reinforcing polymer (FRP) strips attracted considerable research attention as a preferable alternative. Such retrofitting FRP schemes aiming to upgrade the shear capacity of existing RC beams have been examined in many published works employing such externally applied FRP shear reinforcing schemes without confronting the practical difficulties arising from the presence of the RC slab. Anchoring external CFRP strips aiming to shear upgrade, which is the focus here, overrides this difficulty. It is shown that effective anchoring, using either mechanical anchors such as the ones devised by the authors or CFRP anchor ropes produced by the industry, can effectively upgrade the shear capacity of an RC T-beam under-designed in shear to the desired level. A novel laboratory test set-up, devised by the authors, can be utilized to quantify the tensile capacity of CFRP stirrups with or without anchors, that can be of practical use. The predicted, according to design guidelines, upgraded shear capacity of the tested prototype RC T-beam, employing the used shear retrofitting schemes, under-estimates the measured shear capacity by 58%. This conservatism can counter-balance uncertainties arising from in situ conditions in constructing the various parts of such a shear retrofitting scheme.

Slag-Based Geopolymer Concrete as Reinforced Concrete Jacketing Agent

The acceptance of geopolymeric systems in construction industry as an alternative to portland cement has paved the way for using it in the strengthening of reinforced concrete structures. In this regard, a study was carried out to develop a novel method of strengthening reinforced concrete beams by jacketing using ultrafine blast-furnace slag-based geopolymer. The reinforced concrete beams were in a fully damaged, partially damaged, or undamaged state prior to jacketing. Geopolymer concrete (GPC) exhibited appreciable performance as a jacketing agent. The results of GPC-jacketed beams in terms of strength, ductility, and stiffness degradation were superior compared to portland cement concrete (PCC). GPC-jacketed beams exhibited appreciable performance even at the early age of three days. The levels of damage also influenced the behavior of the jacketed beams.

Experimental study of jacket height and reinforcement effects on seismic retrofitting of concrete columns

This study evaluates the jacket height and reinforcement effects on reinforced concrete (RC) square columns retrofitted with normal concrete. Five one-third scale columns with non-ductile reinforcement were tested. Four columns were retrofitted with RC jackets with quarter height (h/4) and half height (h/2) where h is the column height. Subjected to cyclic loading, the failure pattern, lateral load capacity, stiffness, ductility, and energy dissipation of the column were investigated. Results show that increasing the jacket height significantly affected the failure pattern and lateral load capacity. Increasing the jacket height from h/4 to h/2 showed a pronounced shear failure and steeper diagonal cracks. Columns jacketed with h/2 jacket almost doubled the original lateral load capacity. The difference in the lateral load capacity of columns with h/2 jackets and h/4 jackets was above 23%. The jacket reinforcement confinement reduced the level of jacket damage and increased the damage and concrete crush in the column above the jacket. However, the unreinforced jacket increased the jacket damage and reduced the damage above the jacket. The jacket reinforcement increased the lateral load capacity by the shear transfer mechanism while the jacket height enhanced the energy dissipation of the jacketed columns by arch (strut) action. In addition, the jacket height and reinforcement increased the column’s stiffness and consequently, the stiffness irregularity produced short column shear failure above the jacket. From the results, a simplified analytical model was developed to predict the structural capacities of the jacketed column.

Eccentrically Loaded Slender Columns Strengthened by High-Strength Fiber Reinforced Concrete Jackets.(Dept.C)

The behavior of eccentrically loaded cracked slender High-Strength Concrete (HSC) columns strengthened by HSC jackets contain steel fibers and have cube compressive strength equal to 89.3 MPa has been studied experimentally. The results of these tests have been used to examine the applicability of the design requirements of slender columns of the Eurocode 2 (EC-2), the Egyptian code (ECCS-2001) and ACI 318-99 building eode, when applied to the strengthened columns. The testing p rogram included 11 columns with slenderness ratios before strengthening ranged between 17.3 and 69.3. The main variables considered in this study were the slenderness ratio of the strengthened columns, the type of the steel fibers, the end eccentricity of the applied axial load and the transverse reinforcement ratio of the HSC jackets. The results showed that, eccentrically loaded slender and short cracked columns strengthened by HSC jackets contain 1% steel fibers (by volume) can be treated as new integral columns. Using a steel fibers into the HSC mix of the jackets reduces to a great extent the early cover spalling of the tested columns and increases the ultimate loads comparing with the same columns strengthened with HSC jackets without steel fibers. The three different methods for design of slender columns required by the ECCS-2001, EC-2 and ACI 318-99 building code can be safely used for design of slender columns strengthened by HSC jackets contain steel fibers.

Retrofitting of RC Beams using Reinforced Self-compacting Concrete Jackets Containing Aluminum Oxide Nanoparticles

The purpose of this study was to introduce a proposed method to retrofit RC beams. For this purpose self-compacting concrete containing aluminium oxide nanoparticles (ANPs) and silica fume (SF) was used in RC jackets. The laboratory experiment and numerical simulation were used to investigate the behavior of the beams. The experimental variables were included the amount of ANPs used in the jackets (0 and 2.5% by weight of cement) and the surface interaction between beam and jacket (75% and 100% of the side and bottom surfaces of the beam). Five RC beams with a length of 1.4 m and the same dimensions were made and subjected to four-point loading. After completing the laboratory steps, RC beams were simulated according to laboratory conditions using the finite element method and ABAQUS software. After verifying the used method, parametric analysis was performed and parameters such as beam span length (1.5, 3, 4.5 m), concrete jacket thickness (4, 8, and 12 cm), and the diameter of the bars used in the jacket (8, 10 and 12 mm) were examined. The results showed that the use of RC jackets containing ANPs, depending on the jacket thickness, the diameter of the bars used in the jacket, and the length of the beam span increased the beams flexural strength by 155 to 447%. It was observed that the crushing of concrete without nanoparticles compared to concrete contain nanoparticles is more severe because nanoparticles affected the concrete matrix and reduced its crushing in RC jackets.

Review on Strengthening Reinforced Concrete Columns Using Reinforced Concrete Jackets

This paper highlights the review of the effects of concrete surface treatment and loading on the structural behavior of reinforced concrete (RC) columns retrofitted with RC jackets. The concrete surface treatment aspect is assessed based on the surface roughness, use of dowel bars, use of shear connectors, and applying bonding agent between the column core and the jacket. However, the loading aspect is evaluated based on preloading history and the applied loading pattern. The latest researches and recommendations for concrete jacketing are presented. It is found that sand-blasting with the use of dowel bars or shear connectors helps the retrofitted column to behave monolithically. Preloading does not have a significant effect on the retrofitted column. However, it is recommended to apply the load on the full retrofitted cross-section.

Use of fiber-section beam elements for modelling the monotonic flexural response of RC jacketed columns

The use of reinforced concrete (RC) jacketing is a common technique for retrofitting existing RC columns with poor structural performances. Literature studies highlighted that the relative slip occurring at the interface between the new and the old concrete can affect substantially the flexibility and the strength of the retrofitted member. For this reason, several interface treatments are usually applied, aiming to induce a monolithic behaviour to the column. However, despite the commonness of RC jacketing, a limited number of studies investigated numerical modelling strategies for including these phenomena, especially with reference to the development of numerical models for design-oriented applications.This paper presents the results of a finite element modelling (FEM) approach for evaluating the flexural behaviour of members reinforced with RC jackets. The proposed method takes advantage of fiber-section beam elements connected through a non-linear interface. Monotonic static non-linear analyses are performed and results highlights the differences with the usual assumption of monolithic behaviour. The comparisons with experimental results confirm the reliability of the approach, which allows to obtain accurate results with a substantial reduction of the computational cost with respect to brick-based FEM.