Concrete Jacketing Research Articles

Behaviour of CFST slender columns strengthened with steel tube and sandwiched concrete jackets under axial loading

A strengthening method for slender concrete-filled steel tube (CFST) columns using a steel tube and sandwiched concrete jackets was investigated. The strengthening decreases the member slenderness owing to the enlarged cross section, which is beneficial for avoiding instability problems. The effect of the variation in slenderness ratio on the different strengthening parameters was evaluated, and the optimal strengthening strategies for stub, slender and long columns were suggested. The experimental parameters included the length-to-diameter ratio, diameter-to-thickness ratio, and sandwiched concrete strength. All specimens tested in this study were intermediate-length columns. The results indicate that the limiting value of the length-to-diameter ratio between intermediate-length and long columns is slightly larger than 10.0. For intermediate-length columns, thicker outer steel tubes are more effective than high-grade sandwiched concrete. A finite-element model was then developed using ABAQUS, considering both intermediate-length and long retrofitted columns. The differences between the two types of columns were analysed based on the loads on each component. Additionally, a parametric analysis was conducted to determine the effects of the strengthening parameters, including the outer steel tube strength, and damages to the inner column on the capacity after strengthening. The relationship between the reduction factor related to the length and confinement index was then presented. Finally, a model for calculating the load-bearing capacity of slender strengthened columns was proposed.

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.

Experimental investigation of offshore crane load during installation of a wind turbine jacket substructure in regular waves

Installation of offshore structures for harvesting energy or oil and gas industries is still burdensome because of the rough sea state. Unless a calm water condition prevailing, installing any substructure or floating structure at offshore sites is very difficult. Hence, there has been great potential for research to investigate offshore structures’ installation for normal and more energetic wave conditions. To understand and develop the methodology for the installation, the hydrodynamic response of the structure and impact received by the offshore crane is vital. In this context, the present study focuses on installing a heavy concrete jacket foundation sub-structure (Equivalent steel jacket) of an offshore wind energy structure. Due to the heavyweight and the temporary buoyancy tanks, the structure’s response during installation is different from the tubular steel structures predominantly used for jacket structures. In this work, the structure’s response in regular waves at different positions of upending is analysed. Also, the peak force received by the crane at different sea states is measured for different positions of upending. Finally, the forces to be expected while upending the jacket in waves is quantified, and a suitable weather window is suggested. Furthermore, the critical positions in upending are established.

A computational framework for selecting the optimal combination of seismic retrofit and insurance coverage

AbstractEconomic earthquake losses can be mitigated through either building retrofit strategies and/or, to some extent, risk‐transfer to the (re)insurance market. This paper proposes a computational framework to select the optimal combination of seismic retrofit and insurance policy parameters for buildings. First, a designer selects a suitable retrofit strategy. This is implemented incrementally to define interventions with increasing retrofit performance levels. The cost of each intervention is calculated, along with the cost of property rental while the retrofit is implemented. Alternative insurance options are considered. For each retrofit‐insurance combination, the insured and uninsured economic losses within a given time horizon are estimated. The optimal retrofit and insurance combination minimizes the tail value at risk of the life cycle cost. The selected confidence level for this metric depends on the homeowner's risk aversion. The proposed framework is illustrated for a case‐study archetype Italian reinforced concrete frame building retrofitted with concrete jacketing, also considering the Italian retrofit tax incentives/rebates called “Sismabonus.”

Analytical Model for the Design of HSFC and UHSFC Jackets with Various Steel Fiber Volume Fraction Ratios for the Retrofitting of RC Beam-Column Joints

High-strength steel fiber-reinforced concrete (HSFC) and ultra-high strength steel fiber-reinforced concrete (UHSFC) jackets have been proved experimentally to be much more effective with respect to other strengthening schemes in improving the hysteresis performance of existing substandard reinforced concrete (RC) structural members. In this paper, an existing analytical model for the prediction of the shear capacity of RC beam-column joints strengthened with a HSFC or UHSFC jacket is extended to provide design formulation of these innovative HSFC and UHSFC jackets. An authoritative validation of the proposed formulation is also achieved by comparisons of experimental results of 50 beam-column joint specimens with the analytical predictions of the model. Test data used for verification have been collected from the literature based on experimental studies of the authors and other researchers. The merits of the HSFC and UHSFC jacketing technique are also highlighted in the state of practice. Design and application of the proposed fiber-reinforced concrete jackets in deficient existing RC beam-column joints provides a sustainable strengthening technique by contributing to the reduction in the cost and to labor-intensive procedures of common jackets by completely replacing the installation of reinforcement.

Seismic Upgrading of Reinforced Concrete School Buildings

This paper evaluates the seismic behavior of four methods for retrofitting typical reinforced concrete school building. The original school (SO) suffers from limited ductility and lateral resistance. The four seismic upgrading methods are using carbon fiber reinforced polymers (SUFRP), steel jacket (SUSJ), bracing (SUBR), or concrete jacket (SUCJ). Nonlinear pushover and time history analyses are made for the five schools. Three code-scaled natural earthquakes are utilized for the inelastic response history analysis. The pushover analysis revealed that providing the school with bracing (SUBR) results in reducing the lateral displacements. However, the three other types of seismic retrofit (SUFRP, SUSJ, and SUCJ) develop larger lateral displacements when compared to the original school (SO). The translation ductility and energy dissipation for school SUBR is poor while they are good for schools SUFRP, SUSJ, and SUCJ. The base shear is increased for the four upgrading methods (SUFRP, SUSJ, SUBR, and SUCJ) compared to school SO. From the nonlinear time-history analysis, the maximum interstorey drift was approximately similar for schools SO, SUFRP, and SUCJ. Lesser values for the maximum interstorey drift are obtained for schools SUSJ and SUBR. The nonlinear time-history analysis also gives similar base shear for all the upgrading methods compared to school SO with the exception of school SUCJ which showed increase in the base shear.

Seismic Strengthening of Concrete Columns by Ultrahigh-Performance Fiber-Reinforced Concrete Jacketing

This paper presents the structural performance of jacketed concrete columns subjected to cyclic lateral loading using ultrahigh-performance fiber-reinforced concrete (UHPFRC) with various advantages as construction materials of high strength and durability with self-compacting. The UHPFRC jacketing with/without textile reinforcement for concrete columns for the seismic retrofitting demonstrates its strengthening efficiency and reduction of jacket thickness through the experimental program in this study. Especially, textile-reinforced UHPFRC (TR-UHPFRC) jacketing has enhanced ductility compared with that of UHPFRC jacketing by changing critical failure crack patterns in jackets. The satisfactory interface shear strength between UHPFRC jackets and substrate concrete of columns was confirmed by a series of slant shear test programs provided that required roughness on substrate with moisture were prepared according to current design guidelines. This study also investigates the effects of discontinuity of tension forces in jackets at the floor level of columns on shear load paths, which are intended to alleviate jacketing construction for columns in existing buildings as a member intervention technique. Shears and axial forces induced in jacketed columns under lateral loading are mainly resisted by compression forces in diagonal struts through the jacket with substrate concrete columns and are explained by arch actions for enhancement of shear strength after jacketing.

FLEXURAL BEHAVIOR OF STRENGTHENED AND RPIARED SUSTAINABLE R.C. BEAMS USING REACTIVE POWDER CONCRETE JACKET

Thin fiber reinforcement and rehabilitation of reinforced concrete beams Concrete jackets have several benefits, including increased ultimate load and improved serviceability limit condition. The current paper was carried out to investigate the effect of the strengthening and repairing by using reactive powder concrete(RPC) jacket for reinforced concrete beams that’s casted with recycled coarse aggregate (RCA) in enhancement the mechanical properties such as load capacity and deflection . Nine reinforced concrete beams mm were casted by using RCA with constant details and jacketed with RPC with variable of steel fiber content and jacket thickness to estimate the optimum details. The result showed the effectiveness of the proposed technique in both deflection and ultimate load.

EXPERIMENTAL STUDY ON SHEAR BEHAVIOR AND CAPACITY PREDICTION OF RC BEAMS STRENGTHENED WITH HIGH DUCTILE CONCRETE

In order to study the shear response of reinforced concrete (RC) beams strengthened with high ductile concrete (HDC) jacketing layer, 7 HDC jacketed RC beams and 4 non-strengthened RC beams were designed. The failure modes, load-deflection curves, shear capacities and cracks of the beams with different shear span ratios, stirrup ratios, thickness of HDC jacket and stirrups in HDC jacket were studied by static tests. The test results show that the HDC jacket can significantly improve the shear capacity of the beams. The HDC jacket can share partially shear loads which were taken by stirrups, and improve the shear failure pattern. After the ultimate displacements were reached, beams strengthened with HDC jacket exhibit good integrity and high residual bearing capacity. A formula based on the truss-arch model for calculating the shear capacity of beams strengthened with HDC jacket is proposed, and the calculated results are in good agreement with the test results.

Shear Behavior of Concrete Walls Retrofitted with Ultra-High-Performance Fiber-Reinforced Concrete Jackets

Shear Behavior of Concrete Walls Retrofitted with Ultra-High-Performance Fiber-Reinforced Concrete Jackets

Axial behaviour of square stub CFST columns strengthened with square steel tube and HPC jacket

This study examines the performance of 26 concrete-filled steel tube square stub columns strengthened with square steel tube and concrete jacket, 21 steel tubes were infilled with high-performance concrete (HPC) jackets and 5 were infilled with ordinary concrete (OC). The test results of the failure modes, load–axial shortening curves, ductility index, and strain analysis revealed that no evident effect was observed on the load-bearing capacity when steel fibre-reinforced concrete (SFC) or self-stressing concrete (SSC) alone was used; however, an enhancement was achieved with the combination, i.e., steel fibre-reinforced self-stressing concrete (SFSSC). The results also indicated that SFC demonstrated a positive effect on ductility, whereas SSC decreased the deformation capacity. A finite element model was established for further analysis of retrofitted columns and comparison of the failure modes and load-shortening curves with the experimental results. The model was used to analyse the confinement of the concrete jacket and inner concrete. The curves of the load on the components indicated that the contribution of the concrete jacket to the peak load was lower than that of the outer tube owing to the uneven confinement effect, and the different types of concrete jackets only affected the load they bore. Based on the numerical database, equations for predicting the ultimate strengths of retrofitted columns with OC were proposed. A coefficient related to SSC was considered in the equations for predicting the capacities of columns with HPC. The calculated results showed good agreement between the experimental and numerical results.

Retrofitting of an RC frame building damaged in “April 2015 Gorkha earthquake” in Kathmandu valley

The effect of “April 2015 Gorkha Earthquake” was devastating in terms of loss of life, heritage, buildings and emotions. A residence located at Purano Naikap-13, Kathmandu, built in 2006 was also severely damaged amongst many buildings. The building was a three and half story non-engineered reinforced concrete (RC) building. The main objective of this paper is to show the step-by-step process of retrofitting adopted in this building. After the initial survey and structural analysis in ETABS software, a suitable repairing and restoring of the stability of the structure was done which was followed by an appropriate retrofitting techniques. Concrete jacketing and steel jacketing with epoxy chemical grouts in columns were the two main interventions implemented. Pushover analysis was done to assess performance of the retrofitted building. The building was deemed acceptable; the Life Safety level was not exceeded under design basis earthquakes.

Strengthening of RC Beams Using SCC Jacket Consisting of Glass Fiber and Fiber-Silica Fume Composite Gel

In this paper, strengthening of RC beams with self-consolodating concrete (SCC) jacket containing glass fiber (GF) and fiber-silica fume composite gel (FSCG) were investigated. FSCG can use as a substitute for a part of the cement that contains silica fume powder, polypropylene fibers, superplasticizer, concrete waterproof, and some other admixtures. In order to evaluate the performance of the proposed jacket, twelve beams were strengthened and a control beam was made. The variables included the amount of glass fibers consumed in the jacket (0, 0.25, 0.5, 0.75, 1 and 1.25% by volume) and the amount of FSCG gel (0 and 7.5%), respectively. Fresh and hardened concrete properties and flexural capacity of RC beams were investigated. The use of FSCG in RC jackets can compensate well for the deficiency in strength due to the GF entry into the concrete matrix. High affinity of these materials improve the cohesion between cement and GFs. RC jackets containing GF and FSCG increased the beams' energy absorption capacity by about 89 to 463%, depending on the percentages of GFs. RC jacket containing GF and FSCG delays the growth of the primary crack and it can significantly increase the maximum load. Also, GFRP sheets have poorer performance compared to the proposed method due to separation from the surface of the strengthened beams, and their load-bearing capacity and energy absorption are lower.

Retrofitting of Column by Concrete Jacketing

This study has been conducted through basic experimental research in order to analyze retrofitting of the structure is better alternative instead of total replacement of structure. It may even be economical to use Concrete Jacketing for damaged column While Replacing Coarse Aggregate With Broken Glass in Concrete Jacketing. It improves axial and shear strength of column and major strengthening of foundation may avoided. So to study Retrofitting Of RC Square Column By Concrete Jacket Made By Replacing Aggregate With Broken Glass which helps to increase the seismic resistance of a building in both orthogonal directions of a structure and advantages ventilation and natural light.

RC columns strengthened by steel caging: Cyclic loading tests on beam-column joints with non-ductile details

Beam-column joints suffer intense damage from seismic events and are the cause of many buildings collapsing. These zones present complex behaviour under cyclic loads, including tensile-compression cycles, which make reinforcement adherence worse and cause severe cracking in concrete. Although columns can be strengthened by various methods (e.g. concrete jacketing, fibre-reinforced polymers and steel jacketing-caging), beam column joints require complex systems being applied, but are not always effective. In Europe, fitting steel caging around columns is one of the most frequently used techniques, although its effectiveness against seismic events requires further study. The aim of this work is to analyse the behaviour of beam-column joints strengthened by steel caging subjected to cyclic loading, for which an ambitious experimental campaign was carried out on seven full-scale steel-caged specimens with a variety of strengthening solutions at joints. The results provide insight into the complex behaviour of joints with columns strengthened in this way, used as the basis for practical recommendations for engineers and architects who have to routinely retrofit structures against seismic events.

Strengthening of Edge and Corner Columns using Concrete Jackets

Strengthening of columns using concrete jackets depends on friction at the interface between them. So strengthening of edge and corner columns in only one story needs a large cross section area due to the shortage of friction length which leads to architectural issues. This research aims to study strengthening the edge and corner columns using a concrete Jacket in more than one story which increases the friction area between the Jacket and the original column. As a result, the load transferred from original column to the jacket will be increased. Thirteen models were done using ANSYS program to study the effect of various factors on the Jacket capacity such as the number of strengthened floors, the Jacket type (two sides or three sides), and whether there were shear connectors or not. The results showed that in the case of the edge and corner columns, it is preferable to strengthen the column by making a concrete Jacket on at least two or three floors to increase the surface area, which leads to increase the friction and thus increases the capacity of the strengthened column by an acceptable percentage. The results of ANSYS models were compared with the Indian code IS 15988 (2013) and the results were shown differently because the code equations depend on the presence of a full bond between the concrete column and the Jacket, which does not occur, but rather the load is transferred by friction between the Jacket and the original column. Doi: 10.28991/cej-2021-03091716 Full Text: PDF

COMPARATIVE SEISMIC PERFORMANCE ASSESSMENT OF UHPC JACKETING AND SCED BRACING TECHNIQUES

Observed damage to existing pre-seismic code buildings in previous earthquakes has raised interest among the engineering community for improving the performance of these structures using different seismic retrofit measures. This paper throws light on contemporary techniques for the seismic retrofit of RC buildings, namely ultra-high-performance concrete (UHPC) jacketing and self-centering energy dissipative (SCED) braces. Detailed fiber-based numerical modeling of a benchmark structure is undertaken to evaluate the effectiveness of the selected retrofit measures. The case study structure is a two-story pre-seismic code residential building designed for gravity and wind loads, exhibiting poor seismic performance. Along with the two retrofit strategies investigated, several parameters are also considered. Inelastic static pushover and incremental dynamic analyses are conducted to select the retrofit measures and assess their effects on seismic performance. Using a collection of far-field earthquake records and a set of performance criteria, fragility functions are constructed to assess the vulnerability of the benchmark structure with and without the retrofit solutions. The study shows that the adopted index that links cost to the seismic performance obtained from the fragility functions can provide a rational ranking of the selected retrofit approaches relative to the existing building and support selecting the most effective and economical alternative.

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.

Elastic Restraint Effect of Concrete Circular Columns with Ultrahigh-Performance Concrete Jackets: An Analytical and Experimental Study.

Concrete circular columns are among the most common vertical load-bearing members in structural engineering. Because of the change of service loads or environmental factors, the strengthening of deteriorated members is often demanded to restore and maintain their performance. In view of the limitations of the traditional strengthening methods and the superior mechanical properties of the new material, ultra-high-performance concrete (UHPC), this study analyzed the stress–strain state of concrete circular columns confined by UHPC jackets under axial compression in the elastic stage. Since elastic analysis is the basis for the service limit state design, the elastic stress solution was derived through the theory of elasticity, and experimental verification of the effectiveness of the UHPC jackets in circular concrete columns was performed. Theoretical bases and references for practical strengthening works are provided.

Experimental Study on Shear Strengthening of Reinforced Concrete Beams Using Different Techniques of Concrete Jacketing

A large number of RC structures or at least some of their members need strengthening or rehabilitation. Among the typical failure modes, the shear failure is more dangerous and less predictable, because of usually brittle behavior and sudden collapse. Therefore, there are necessities for upgrading the shear capacity and the local ductility of reinforced concrete beams. In this study, four different techniques of concrete jacketing were used to improve the behaviors of the shear deficiencies beams. The four techniques used in this study to enhance the behavior of the beams were by using a Self-Compacted Fiber Reinforced Concrete jacket without stirrups (S.-J. + Steel Fiber), a concrete jacket of Self Compacted Concrete with stirrups (S.-J. + Stirrups), a concrete jacket of ferrocement jacket (S.-J. + Ferrocement), and a concrete jacket of ferrocement jacket with external steel reinforcing bars (S.-J. + Ferrocement + R). These techniques contributed to enhancing the load-carrying capacity and delaying the appearance of the first crack in tested beams compared with the control beam by a percentage of (35, 59, 30, 6) % and (18, 35, 81, 80) %, respectively. The specimen (S.-J. + Stirrups) showed the best performance in comparison with the other used strengthening techniques used in this study in terms of stiffness and the ultimate load-carrying capacity. The ferrocement jacket (S.-J. + Ferrocement) was found to be the most suitable jacketing system used to enhance the shear capacity in terms of cracking load.