Shear Retrofit Research Articles

Shear Retrofitting Effect of Self-prestressed Iron-based Shape Memory Alloy for Reinforced Concrete Beams

Shear Retrofitting Effect of Self-prestressed Iron-based Shape Memory Alloy for Reinforced Concrete Beams

Fragility curves for reinforced concrete frames with retrofitted masonry infills

Seismic retrofit of existing reinforced concrete framed buildings often involves both structural members and infill walls. The strengthening of infill walls is mainly aimed at preventing out-of-plane mechanisms and, in some cases, also increases in-plane capacity. On the other hand, the enhancement of the infill's strength might modify the failure mode of the frame, as stated by recent studies. In the case of gravity load-designed buildings, the presence of strong infill walls can lead to brittle failure of columns due to local interaction. This study investigates the effects of the in-plane shear retrofit of infills on the seismic behaviour of reinforced concrete buildings through non-linear dynamic analyses on a three-dimensional infilled frame. The seismic response of the structure is analysed in case of un-reinforced masonry wall and retrofitted wall, considering two types of retrofit. The analysis results are used to calibrate a simplified model aimed at computing fragility curves of reinforced concrete infilled frames and updating existing formulations, in order to account for the properties and the type of the infill. The proposed parameter can be applied in vulnerability assessment studies and for the design of new buildings.

Hysteresis behavior of 3D RC exterior beam-column joints strengthened with CFRP sheets and spike anchors

Full-scale 3D exterior beam-column joints lacking shear reinforcement but externally shear-strengthened with carbon fiber reinforced polymer (CFRP) sheets were investigated with respect to their behavior under both gravity and lateral cyclic loadings. For this purpose, three such joints including one control and two experimental ones (strengthened either with CFRP sheets or with both CFRP sheets and spike anchors) were subjected to relevant tests. Prior to CFRP installation, all the externally strengthened specimens were subjected to surface preparation and grooving in order to prevent possible CFRP debonding. The flexural capacity of both the non-strengthened and strengthened joints were estimated using a specially-developed analytical method. Comparisons of the lateral load–displacement hysteresis curves and in the test results revealed that, compared to the control, the externally strengthened joints showed enhancements of 30, 222, and 200% in lateral load-bearing capacity, energy dissipation, and secant stiffness, respectively. It was further found that despite the efficacy of the shear retrofit design proposed for 3D exterior connections, those strengthened with the combined CFRP sheets and spike anchors outperformed the ones solely strengthened with CFRP sheets. The sectional analysis results also revealed that the simple method proposed in this study is well capable of estimating bearing capacity in both the control and strengthened connections with reasonable accuracy.

One-sided shear retrofit of reinforced concrete beams in existing high-rise buildings

This paper presents the evaluation of one-sided shear retrofit schemes for reinforced concrete (RC) coupling beams in existing buildings. Three full-scale beam Specimens CB1, CB2 and CB3 are planned for cyclic tests. Specimen CB1 represents a RC coupling beam in existing 24-story RC buildings, completed in Taiwan, 2017. Specimens CB2 and CB3 are retrofitted by added stirrups in the increased beam cross section and a bolted a steel plate from only one side of the RC beam, respectively. Test results showed that the shear strengths of the two retrofitted specimens exceeded the force of the RC coupling beam expected at the maximum considered earthquake (MCE) level. Specimen CB1 exhibited flexural-shear failure during the cycle of 5% drift. Specimens CB2 and CB3 exhibited shear failure during the cycle of 4% drift, and then concrete crushing associated with longitudinal bar buckling in the plastic hinge region. The peak shear forces of the added stirrups in Specimen CB2 and of the added steel plate in Specimen CB3 were 34 and 22% of the total shear forces, respectively, at large drifts. The added stirrups in the increased beam cross section provided larger shear force than the bolted steel plate. Both schemes were used to retrofit RC beams in the existing high-rise buildings in New Taipei City.

Efficient shear retrofitting of reinforced concrete beams using prestressed deep embedded bars

The Deep Embedment (DE) technique is a promising reinforced concrete (RC) shear strengthening scheme. When compared with the other retrofitting systems, the DE approach is impressive in many ways. Particularly, since the DE element is installed to the beam core, the truss mechanism is enhanced and that enables achieving high shear enhancements. Due to the internal application of the DE reinforcement, steel can also be utilized as the retrofitting material without reservations on corrosion. It is however identified that the tensile capacity of the DE bar is partially utilized. In this context, the potential of using prestress in the DE system as an improvement was explored through a non-linear numerical study and an experimental study. Two DE reinforcement types of normal steel and high-tensile steel were considered and the prestress level was set to 40%. Both approaches showed that the use of prestress in the DE system was capable of enhancing the beam shear capacity significantly, where the extra strength gain in one case was almost 26%. The serviceability performance of the beams was also improved due to the prestress application. Meanwhile, the numerical predictions showed good correlations with the global and local behaviours of the experimental beams.

Structural shear retrofitting of reinforced concrete beam: multilayer ferrocement technique

Most of the existing buildings in developing countries lack proper reinforcement and are in danger of collapse under seismic and extreme events. Therefore, a sustainable and feasible retrofitting technique is necessary to ensure the safety of the infrastructure and its occupants. This paper describes a broad experimental programme, in which a total of 20 reinforced concrete beams with shear deficiency were constructed, 4 of them considered as control beam, while the rest of the beams were retrofitted with ferrocement in four different techniques after loading up to initial crack. All the specimens were tested up to the failure, and beam deflection at different points along with the load versus displacement response was recorded for each case. It allowed the determination of elastic stiffness, peak strength and associated displacement capacity of the retrofitted beam, compared with control beams. From the observed results, a plausible technique of retrofitting using ferrocement is suggested. A preliminary finite element model is developed for future study, which compared the experimental and FE results.

Evaluation of design concepts for post-installed punching shear retrofitting

Punching shear is a brittle and sudden mode of failure observed in reinforced concrete slabs structures. This type of failure typically occurs around the slab-column connections, due to transverse forces being highly concentrated in these areas, thereby causing the column to punch through the slab. Several methods have been proposed for retrofitting and strengthening existing flat slabs against punching shear failure using different reinforcement-types. One of these methods relies on post-installed shear reinforcement for existing flat slab systems. The estimation of the punching shear resistance depends on several variables (geometry, mechanical, material properties, etc.) with some level of uncertainty. This study aims to assess the safety and economic performance of different methods for the design of post-installed reinforcement in an existing flat slab structure endangered by punching shear, using probabilistic analysis. The methods considered include the design procedure according to the American Concrete Institute (ACI) design code, the Canadian Standards Association (CSA) design code, the European Eurocode 2 (EC2) design code and analytical method based on the Critical Shear Crack Theory (CSCT). The probabilistic analysis was conducted based on the Monte Carlo simulation technique implemented using a MATLAB code developed in this study. The reliability index obtained for EC2 design procedure was found to be close to the EN 1990 target reliability level. CSCT and CSA, on the other hand, have a low-reliability index for most of the cases investigated.

Pre-Test Analysis on Reinforced Concrete Beams with Shear Strengthening using GFRP by Finite Element Method

Research on the developments of new materials as well as the methods and techniques of retrofitting structures showed that the Fiber Reinforced Polymer (FRP) is a promising material for use in strengthening reinforced concrete structures. This research aims to model reinforced concrete beams with shear strengthening using GFRP based finite element method. By using computer program Finite Element Analysis (FEA) the modelling was carried out by 2-dimension models on 3 testing material variations namely: the test normal concrete beams without the shear retrofitting (BGN), beams with shear retro fitting using GFRP are continuous on the shear span (BGPF), beams with retrofiting using 3 strips (BGP3S). The research result indicated that generally, the programused can show the behavior closed to the theoretical design result. The ultimate load of results normal concrete beams without the shear retrofiting (BGN) is 76,393 kN, beams with shear retrofitting using GFRP are continuous on the shear span (BGPF) is 77,798 kN, and beams with retrofiting using 3 strips (BGP3S). The results showed that the percentage increase of normal ultimate load of beam with shear reinforcement using GFRP was 1.4%, 11.01%, for reinforced using 3 strips (BGP3S). This indicated that the material behavior response produced from simulation study can well be described by the program.

Seismic mobile shaker testing of full-scale RC building frames with high-strength NSM-FRP hybrid retrofit system

Past seismic events have led to the premature failure of many existing seismically-vulnerable reinforced concrete building frames due to their inadequate column details. To ensure the ductile behavior of the non-ductile building frames, a hybrid retrofit system combining high-strength near surface mounted bars (flexural retrofit) with carbon fiber reinforced polymer sheets (shear retrofit) can be installed to the seismically-vulnerable columns. This study presents the experimental dynamic assessment of the non-ductile building frames retrofitted with the hybrid system. To prevent the column shear failure due to the flexural strengthening, a two-stage design procedure for the hybrid retrofit system was proposed. The full-scale dynamic testing was performed on the retrofitted test frame to realistically measure dynamic responses and quantify the retrofit effects. The hybrid retrofit system reduced the peak inter-story drift of the first-story columns by about 25% and their hinge rotation by approximately 76%. Additionally, the retrofit system can uniformly distribute the damage or drift over the entire structure, i.e. mitigation of soft-story mechanism.

Shear Retrofitting of Corner 3D-Reinforced Concrete Beam-Column Joints Using Externally Bonded CFRP Reinforcement on Grooves

AbstractBeam-column joints are fundamental structural components to provide stability to a concrete frame. Compared to other types of joint, corner joints are more susceptible to failure due to the...

Retrofitting of RC Beams using Glass Fiber Reinforced Polymer Sheets: An Experimental Study

Objective: An experimental investigation to check flexure and shear behavior of Reinforced concrete (RC) beams retrofitted with glass fiber reinforced polymer composites. Methods/Analysis: Two point symmetric loading. In this study two set of beams were cast out of those first set was weak in flexure (A) and second was weak in shear (B). In all beams same grade of concrete was used but with different structural detailing. In set a three beams (weak in flexure) were cast out of which one was control beam and other two were retrofitted using Glass Fiber Reinforced Polymer Sheets (GFRP) sheets in soffit of beam and till neutral axis including soffit. In set B three beams (weak in shear) were cast out of which one was control beam and other two were retrofitted by using GFRP sheets on sides and U-jacking at corners respectively. Hand wet lay-up method was used for application of GFRP sheets on beam. The retrofitting of beams was done with different amount and configuration of GRFP sheets. Retrofitted RC beams with epoxy-bonded glass fiber reinforced sheets were tested till failure using a symmetric two point loading system. Load, deflection, failure modes and crack pattern of each beam was recorded for a particular GFRP orientation. Experimental investigation concluded that there was increase in load at initial crack and also at ultimate failure for retrofitted beams as compare to control beams. Failure in case of set a retrofitted beams was flexural shear failure. It was also recommended that flexural retrofitting should be performed along with shear retrofitting. In case of set B beams failure was shifted to flexural failure which was initially shear failure. So retrofitting in shear zones was observed most effective. Finding: Retrofitting in shear zones was observed most effective in case of ultimate, flexural failure and shear failure.

Assessing a Retrofitting Method for Existing RC Buildings with Low Seismic Capacity in Turkey

AbstractIn this research, external retrofit of reinforced concrete (RC) buildings, especially the ones located in Turkey, was studied. Most of Turkey’s population live in an active seismic zone where frequent earthquakes are experienced. Turkey’s existing residential building stock consists mainly of reinforced concrete buildings that are prone to earthquake damage because of a lack of lateral strength. Therefore, a fast and feasible shear retrofit method for these buildings is crucial. In this study, three six-story prototype RC buildings were created to study the effectiveness of external shear retrofit with and without the inclusion of window openings, constructed at building corners. As always desired, this retrofit method was shown to be fast to apply and its construction requires minor damage on the building. The three-dimensional (3D) finite-element model of the building was analyzed nonlinearly by a commercially available software package. The modeling of concrete material as well as embedded stee...

Experimental and Numerical Investigation on Shear Retrofitting of RC Beams by Prefabricated UHPFRC Sheets

Different methods are used for retrofitting RC members. One of the new methods in this field is using externally bonded fiber-reinforced Concrete (FRC) sheets in order to increase RC member’s shear and flexural strength. In this study, applicability of ultra-high performance fiber-reinforced concrete sheets in shear and flexural retrofitting of RC beams was investigated. In total, eight RC beams (dimensions 10×20×150 cm) with two different bending capacity and lack of shear strength were used and were tested in 3-points bending test. Of these, four were control beams and four were retrofitted with laterally bonded UHPFRC sheets. Dimensions of the sheets used for retrofitting were (3×15×126 cm). Also FEM analysis was used to model the effect of The method. the results show that this method can be well used for retrofitting RC beams. In this method the way of connecting sheets to beam’s surfaces has a fundamental role in behavior of retrofitted beams.

Development of Hybrid Jute Fibre Composite Plates for Potential Application in Shear Retrofitting of RC Structure

Development of Hybrid Jute Fibre Composite Plates for Potential Application in Shear Retrofitting of RC Structure

Cyclic performance of reinforced concrete T-beams strengthened in shear with fiber-reinforced polymer composites: Sheets versus laminates

Much existing reinforced concrete (RC) civil infrastructure worldwide is in need of shear strengthening and rehabilitation. The use of externally bonded (EB) carbon fiber-reinforced polymer (CFRP) sheets and laminates to strengthen deficient RC beams in shear is now an acceptable and cost-effective practice, particularly under static loads. However, due to its complexity, the cyclic (fatigue) behavior and performance of shear-strengthened beams is not fully documented. Recently, use of CFRP continuous sheets wrapped over the shear length for fatigue upgrade has been studied. This technique may present drawbacks related to surface preparation and FRP debonding. Therefore, when possible, prefabricated CFRP L-shaped laminates can be a cost-effective alternative because they require less surface preparation and do not peel off easily. The objective of this paper was to present the results of an experimental investigation that compared cyclic (fatigue) and static (post-fatigue) behavior of two EB CFRP techniques (sheets vs. laminates) for shear retrofit of RC T-beams. In total, six laboratory tests on full-size 4520-mm-long beams were conducted. The specimens were subjected to fatigue loading of up to 6 million load cycles at a rate of 3 Hz. Specimens that sustained 6 million cycles were then tested monotonically up to failure. The variables examined in the paper were: (1) the EB CFRP strengthening scheme, and (2) the presence and ratio (spacing) of internal shear reinforcement. The test results confirmed the effectiveness of using EB CFRP shear-strengthening methods under cyclic loading. They also revealed that the fatigue performance of RC T-beams strengthened with L-shaped laminates is significantly superior in extending fatigue life compared to corresponding T-beams strengthened with U-wrapped sheets. This was quantified in terms of deflection response (47% increase due to fatigue loading for specimens with L-shaped laminates compared to 90% for specimens with U-wrapped sheets), and the level of increase in steel-stirrups strain range (9–42% vs. 62–114%) and in EB CFRP (36–97% vs. 58–163%).

Development of Hybrid Jute Fibre Composite Plates for Potential Application in Shear Retrofitting of RC Structure

Application of natural fibre based composite plate in retrofitting of structure is the current interest of construction industry. This paper presents the finding of an experimental study on jute rope fibre hybrid composite plates for potential application in shear strengthening of RC beam. In the experimental programme, hybrid composite plates had been fabricated using jute rope and carbon fibres with five different mixes i.e. 45% jute rope with 0% carbon; 43% jute rope with 2.5% carbon; 41% jute rope with 5% carbon; 41% jute rope with 7.5% carbon and 39% jute rope with 10% carbon.The physical and mechanical properties of the fabricated hybrid composite plates were thenexperimentally investigated. Results showed thatcarbon contents had an influence to enhance the tensile strength of the plates. Hybrid composite plate with 10% carbon content had shown 170% higher tensile strength as compared to that of plate without carbon fibre. The carbon content also had enhanced the modulus of elasticity of plates. Higher percentage of carbon had shown higher tensile strength and modulus of elasticity of hybrid composite plates.All fabricated plates had linear elastic properties under tension. The density of plates increased with the increasing of carbon content in composite plates. The research findings indicated that the developed hybrid composite jute rope could be used for shearstrengthening of reinforced concrete beam.

Optimisation of shear strengthened reinforced concrete beams

External prestressed carbon fibre reinforced polymer straps can be used to strengthen shear-deficient reinforced concrete structures. For an efficient shear retrofitting system, the optimum combinations of parameters such as the number of straps, strap locations, strap stiffness and initial strap prestress need to be identified. The modified compression field theory and the shear friction theory have previously been applied to carbon fibre reinforced polymer strap strengthened beams. As implemented, both of these methods are iterative. Particle swarm optimisation and genetic algorithm stochastic optimisation methods were used to reduce the computational cost associated with the shear strength evaluation and also to search the design space for carbon fibre reinforced polymer strap strengthened beams. An initial comparison across several test functions showed that the preferred optimisation algorithm depended on the characteristics of the design space. When applied to a reinforced concrete case study, the genetic algorithm was better for searching the shear friction theory shear strength design space that was characterised by several peaks. However, for the smoother modified compression field theory shear strength evaluation space, and for the design space for the carbon fibre reinforced polymer strengthened beams calculated using either the modified compression field theory or the shear friction theory, the particle swarm optimisation converged more quickly and accurately. The optimised solutions reflect the assumptions within the underlying evaluation methods.

Shear retrofitting of reinforced concrete beams with steel fiber reinforced concrete

With the objective of evaluating the performance of steel fiber reinforced concrete (SFRC) as a retrofitting material for reinforced concrete beams the experimental study of reinforced concrete beams repaired and strengthened with a SFRC jacketing and tested under shear is presented in this paper.The reinforced concrete beams were designed with high amount of longitudinal steel and minimum transverse reinforcement so that they present shear failure. Some of the beams were strengthened with very fluid high strength SFRC jacketing and some of them were first tested under shear to produce some damage and then they were repaired with the same technique. Plain concrete and SFRC with two different fiber dosages, 30kg/m3 and 60kg/m3, were used for the reinforcement.The experimental program showed the possibility of performing the retrofitting at work place. The repaired beams showed excellent strength and deformation capacity restitution. The strengthened beams exhibited increase of load bearing capacity. The addition of fibers to the concrete played an important role in the prevention of the jacketing debonding from the beams.

Design Considerations for Shear Bolts in Punching Shear Retrofit of Reinforced Concrete Slabs

This study addresses design aspects for the punching shear bolt retrofitting system for reinforced concrete flat slabs supported on columns. Shear bolts are an external type of reinforcement installed in existing slabs by first drilling small holes through the slab thickness, installing the bolts into them, and tightening the bolt nuts. Previous experimental research at the University of Waterloo showed the effectiveness of this system in increasing strength and ductility of existing slabs, with little changes in the slab’s appearance. The procedures for the design of the shear bolts and their installation in slabs are proposed in the paper. Recommendations are provided regarding the stem diameter, the head area and thickness, and the spacing and the layout of the bolts in a plane of a slab.

Retrofit of RC hollow piers with CFRP sheets

Hollow bridge piers, particularly those built before the seventies, often have insufficient shear capacity due to inadequate transverse reinforcement details. Therefore, special attention must be given to this very important aspect when reinforced concrete (RC) piers with hollow sections are analysed and retrofitted. This paper covers the experimental analysis of retrofit solutions using CFRP sheets along the piers’ entire height to prevent shear failure. Experimental cyclic tests were carried out to evaluate the shear retrofit strategy efficiency on a set of RC piers with square hollow sections. This work also covers the study of design procedures for CFRP shear retrofitting and the evaluation of the associated ductility capacity improvement. The various transverse reinforcement detailing scenarios were assessed to determine their shear-failure prevention efficiency. The corresponding cyclic response behavior was also evaluated. The most relevant experimental information is presented in the paper, such as the evolution of the outer damage pattern. Finally, shear retrofit solutions, with a 40% increase over the maximum flexural force, show that this strategy is adequate to allow satisfactory ductility behavior.