Retrofitted RC Beams Research Articles

Shear strengthening of continuous RC T-beams with deep embedded CFRP and steel bars: A numerical study

This paper presents a non-linear finite element parametric study of continuous RC T-beams shear retrofitted with deep embedded (DE) carbon fibre reinforced polymer (CFRP) bars and steel bars. Two-dimensional nonlinear finite element (NLFE) models for these shear-retrofitted beams have been developed and validated with the published literature based on the ultimate shear strength, load versus displacement behaviour, failure mode and strain developed in the longitudinal steel at mid-span. NLFE models of five RC T-beams are developed, out of which one model is for the un-strengthened beam, two are for the shear retrofitted beams with vertical DE bars and the leftover two are for the shear retrofitted with inclined 45° DE bars. Parametric investigations have been conducted to evaluate the impacts of shear span to depth ratio (a/d), compressive strength of concrete, effective beam depth and DE bar reinforcement to the existing shear links ratio on the shear strength, load versus deflection behaviour and strain developed in the shear links of these continuous beams. It is found that the above considered parameters of the continuous RC-T beams influence the shear capacity, load–displacement behaviour and strain in the shear link significantly. Moreover, the present work will provide sufficient knowledge to the designers for designing the shear retrofitted RC beams with DE bars.

Behaviour of carbon fiber reinforced polymer strengthened and retrofitted RC beams

This paper deals with an experimental investigation on self-compacting concrete (SCC) reinforced concrete beams of size 150x150x700mm with externally bonded carbon fiber reinforced polymer (CFRP) composites for flexural and shear strengthening. In general, strengthening techniques aims to improve load carrying capacity. Mix proportion for M30 grade concrete was arrived by Nan Su method. The strengthening techniques included are of four types such as Beam strengthened at tension face (BST), Beam strengthened at tension face extending to half depth on two sides of the beam (BSHU), Beam strengthened with four numbers of U-strips (BSUS) and Beam strengthened with two number of U-strips with CFRP inserted in hole (BSUR). Further the failed control beams were retrofitted by similar application as adopted for strengthening and were tested for load–deflection behaviour. The results indicate that among the four configurations, the beam strengthened at tension face (BST) has better flexural response compared with beam strengthened at tension face and extended to half depth at two sides of beams. Beam strengthened with 50 mm wide U-strips with CFRP inserted in a hole exhibited significant increase in toughness. Correlation equations have been developed by using regression analysis and coefficient of correlation obtained are in the range of 0.98 to 0.99 for various applications.

Flexure Behavior of Carbon Fiber Reinforced Polymers Retrofitted RC Beams

Flexure Behavior of Carbon Fiber Reinforced Polymers Retrofitted RC Beams

Retrofitting of reinforced concrete beams using CFRP with various adhesive

In the past few years, FRP (fiber reinforced polymer) has been high in retrofitting reinforced concrete beams due to their properties over strength and durability. Carbon fiber reinforced polymer (CFRP) is broadly used as external bonding material over the RC beams for retrofitting and strengthening purposes. CFRP has several benefits as well as some demerits. The shortfall of ductility is one of its significant flaws. This experiment examines the strengthening behaviors of reinforced concrete beams with single-layer CFRP laminates bonded externally with different adhesives such as epoxy, orthophthalic resin(GP) and ISO resin. The beam specimens were subjected to a two-point loading test until the beams failed. The single-layer CFRP strengthened beams (B4 and B5)with GP and epoxy adhesive exhibited high ultimate load capacity and deflection than control and ISO resin beams (CB1 and B3). Failure of retrofitted RC beams (B4 and B6) was recorded as mid-span debonding and B5 as both compression failure and mid-span debonding. The findings of this study are intended to be used in real-world retrofitting techniques for existing beams.

Static and fatigue responses of retrofitted RC beams with GGBS based UHPC strips

The strengthening techniques are primarily studied and well documented for the monotonic responses of RC structures. Perhaps, the knowledge concerned about fatigue or cyclic responses of RC structures is limited in the literature. Hence, the static and fatigue responses of retrofitted RC beams with GGBS based ultra-high performance concrete strips (5, 10 and 15 mm thick) have been investigated in this study. The results illustrated that even a thin UHPC strip (5 mm) can significantly increase the static and fatigue performance of RC members. A finite element model has been developed to predict the numerical response of retrofitted RC beams subjected to static and fatigue loads. Numerical studies incorporated with crucial parameters such as concrete damage model, failure criteria, stress-crack relation and fracture properties are performed. The predicated numerical model correlates with the corresponding experiments with a little deviation of less than 12%. These deviations could be mainly attributed to the porosity of concrete, rebar slip, and experimental errors in testing the massive specimen under fatigue loading.

Torsional Strength Determination of Ferrocement U-Wraps RC Beams with using Different Methods

Retrofitting of distressed structures is a major concern worldwide for researchers particularly against torsion. Determination of torsional strength of retrofitted RC beams “U” wraps is again a difficult task. The experimental program is taken up with 30 rectangular beams tested under pure torsion. Torque of such a “U” wrapped RC beam with other dimension and material cannot be derived from these experimental results. To compute the same; analytical method based on softened truss model of Hsu is employed with modification on material properties. Both experimental and analytical methods are unable to provide a single equation to quantify the torsional strength. To overcome the same, soft computing method MARS and WASPAS method is employed in the present investigation. The methods are easy and time saving.

Retrofitting of Shear-Deficient RC Beams Using UHP-FRC

The shear-deficient structural elements affect the designed serviceability of structures. The early decay in serviceability reduces the functionality of the structures and leads to global failure of the structure. The retrofitting offers a greater flexibility to restore the serviceability by restrengthening the distressed structural elements. The concrete, ferrocement and fiber-reinforced polymers (FRPs) jacketing are some of the retrofitting techniques tried in the past. But all these techniques have their associated advantages and disadvantages; for example, one of the disadvantages of FRP jacketing is a brittle failure due to debonding of FRP. These failures restrained the serviceability of retrofitted structure elements. In the current study, the newly developed material, i.e., ultra-high-performance fiber-reinforced concrete (UHP-FRC), is being used to retrofit the shear-deficient reinforced concrete beam. The high compressive strength (above 110 MPa), high tensile strength due to the addition of fibers, high flexural strength, very low permeability and high workability of UHP-FRC are expected to improve the performance of retrofitted RC members. Hence, the performance of UHP-FRC as a retrofit material for beams deficient in shear is explored in the present experimental study. The beams designed deficient in shear are initially stressed to 60% of the ultimate failure load and then retrofitted by UHP-FRC. The U-type retrofitting and external side face jacketing are used to retrofit the initially stressed beams. The results show that the behavior of retrofitted RC beams improved in terms of ultimate load carrying capacity, ductility and energy absorption. Further, it is observed that the U-type retrofitting is better than side face jacketing retrofitting.

Effect of Length of External Bar at Soffit on the Performance of Retrofitted RC Beams – a Finite Element Study

This paper presents the results of the finite element study on the effect of length of the external bar at soffit on the flexural behavior of retrofitted RC beams. A reference beam specimen and five retrofitted beam specimens with external bar length as variable were analysed using ANSYS 12.0 software and the results are presented. Initial cracking, performance at yielding of internal bar and at ultimate stage, ductility behavior, formation and propagation of cracks were studied and reported in this paper.

Fundamental Mechanics Governing FRP-Retrofitted RC Beams with Anchored and Prestressed FRP Plates

AbstractIt is often found that a major limitation to retrofitting RC beams by adhesive bonding fiber-reinforced polymer (FRP) plates is premature debonding, which restricts the FRP strains to well below that at fracture. Tests have shown that the FRP peak strains can be increased by anchoring the plate ends of adhesively bonded plates and also by prestressing the anchored plates before adhesive bonding, both of which make the system much more efficient. In this paper, a mechanics-based numerical approach is developed that quantifies the stiffness, strength, and ductility of FRP retrofitted RC beams, in which the FRP plates are anchored, prestressed, and adhesively bonded. The approach can cope with any degree of anchorage and prestress and whether adhesively bonded or not. The approach is generic as it can be applied to any type of RC beam, anchor, and FRP plate and any distribution of load. Furthermore, it allows for discrete flexural cracks and for the formation of softening hinges should these occur. W...

Interfacial stress assessment at the cracked zones in CFRP retrofitted RC beams

In this work, an experimental examination was carried out to study interfacial stresses developed at the junction zones between carbon fiber reinforced plastic (CFRP) fabrics (~1 mm thickness) and tensile concrete portion in CFRP retrofitted RC beams. In this respect, initially six similar RC beams of 150 x 150 x 1000 mm dimensions were prepared. Three of which were strengthened with CFRP fabrics at the tensile side of the beams. Furthermore, a notch was cut at the center of the bottom surface for all of the studied beams. The notch was 15 mm deep and ran across the full width of tension side of the beams. The mentioned interfacial stresses could be calculated from strains measured using strain gauges mounted on the interface zone of the tensile concrete and the CFRP sheet. Based on the results obtained, it is shown that interfacial stresses developed between CFRP fabrics and RC beam had a noticeable effect on debonding failure mode of the latter. The load carrying capacity of CFRP strengthened RC specimens increased ~75% compared to that of the control RC beams. This was attributed to the enhancement of flexural mode of the former. Finally, finite element analysis was also utilized to verify the measured experimental results.

Experimental and Computational Investigation of Hybrid FRP Bonded-Reinforced Concrete Beams under Cyclic Loading

Although several experimental and numerical studies have been carried out on the shear capacity of RC beams retrofitted by carbon or glass fibre-reinforced polymers, there has been little work on hybrid FRP sheet applications, particularly under cyclic loading. In the present research, five RC beams were constructed, and four of which were retrofitted using various schemes of FRP sheets. All beams were subjected to quasi-static cyclic loading in an attempt to represent the effect repetitive loading. The ultimate load, and deflection response at mid-span of the beams were measured and compared with predictions of a computational model based on finite element analysis. Experimental results demonstrated that hybrid applications of FRP sheets can improve the shear performance of retrofitted RC beams and increase the ultimate strain of the FRP sheets at failure. The results of the computational model were in reasonable agreement with the corresponding experimental results.

The effect of CFRP and CFRP/concrete interface models when modelling retrofitted RC beams with FEM

Concrete structures retrofitted with fibre reinforced plastic (FRP) applications have become widespread in the last decade due to the economic benefit from it. This paper presents a finite element analysis which is validated against laboratory tests of eight beams. All beams had the same rectangular cross-section geometry and were loaded under four point bending, but differed in the length of the carbon fibre reinforced plastic (CFRP) plate. The commercial numerical analysis tool Abaqus was used, and different material models were evaluated with respect to their ability to describe the behaviour of the beams. Linear elastic isotropic and orthotropic models were used for the CFRP and a perfect bond model and a cohesive bond model was used for the concrete-CFRP interface. A plastic damage model was used for the concrete. The analyses results show good agreement with the experimental data regarding load-displacement response, crack pattern and debonding failure mode when the cohesive bond model is used. The perfect bond model failed to capture the softening behaviour of the beams. There is no significant difference between the elastic isotropic and orthotropic models for the CFRP. (C) 2009 Elsevier Ltd. All rights reserved. (Less)

Numerical analysis of multilayered CFRP retrofitted RC beams with partial interaction

This paper presents a theoretical model to simulate the behaviour of RC beams strengthened with multilayered CFRP matrix allowing for inter-layer slip. An element of the composite beam is assumed to be subjected to a system of forces that satisfy equilibrium and compatibility of deformations. The inter-layer slip is allowed for by relating the differential strain at the interfaces between the CFRP layers and the concrete to the longitudinal shear flow at the corresponding interface through the shear stiffness of the adhesive layer. The basic differential equations are derived in terms of displacement variables and solved numerically using finite differences. The results of the numerical simulation included slip values along the interfaces, maximum slip values, stresses and strains and deflections. The results compare reasonably well with experimental findings.

Assessment of available prediction models for the strength of FRP retrofitted RC beams

A reinforced concrete beam retrofitted with fibre reinforced polymer composites (FRP) to enhance its flexural capacity can experience several failure modes, namely flexural failure, end debond and midspan debond. The mechanism of those failures and available prediction models are first identified in this paper. The models are then assessed with an up to date database of beams reported in literature together with beams tested by the authors. The study verifies that beam theory can predict flexural failure well. The credibility of several methods to predict end debond and mid-span debond is also proved.

Rehabilitation of Cracked and Corroded Reinforced Concrete Beams with Fiber-Reinforced Plastic Patches

The behavior under static loading of fiber-reinforced plastic (FRP) retrofitted reinforced concrete beams, possessing a high chloride content and rebar corrosion, was studied both experimentally and analytically. The test beams were characterized as falling into three different groups according to the state of their corrosion damage: (1) natural corrosion, (2) cathodic protection, and (3) accelerated corrosion. The load carrying capacities of the beams, with or without FRP patching, were tested in the laboratory. The experimental results show that the state of corrosion of the steel, the water/cement ratio of the concrete material, and the arrangement and the number of FRP patches all affect the strength as well as the failure mechanisms of retrofitted RC beams. Some simple analytical models and a design concept for retrofitting cracked and corroded RC beams with FRP sheets are also presented and discussed.