Strengthening

Monotonic axial behavior and modelling of RC circular columns confined with CFRP, Chastre, Carlos, and Silva Manuel A. G. , Engineering Structures, Aug, Volume 32, Number 8, p.2268-2277, (2010) AbstractWebsite

The retrofit of reinforced concrete columns with FRP jackets has received considerable attention in recent years. The advantages of this technique compared to other similar techniques include the high strength-weight and stiffness-weight ratios of FRP (Fibre Reinforced Plastics), the strength and ductility increase of RC columns confined with FRP jackets as well as the fact that FRP external shells prevent or mitigate environmental degradation of the concrete and consequent corrosion of the steel reinforcement. Furthermore, this method also reduces the column transversal deformation and prevents the buckling of longitudinal reinforcement. Twenty five experimental tests were carried out on reinforced concrete columns confined with CFRP composites, and subjected to axial monotonic compression. In order to evaluate the influence of several parameters on the mechanical behavior of the columns, the height of the columns was maintained, while changing other parameters: the diameter of the columns, the type of material (plain or reinforced concrete), the steel hoop spacing of the RC columns and the number of CFRP layers. Predictive equations, based on the experimental analysis, are proposed to estimate the compressive strength of the confined concrete, the maximum axial load and the axial or the lateral failure strain of circular RC columns jacketed with CFRP. A stress-strain model for CFRP confined concrete in compression, which considers the effect of the CFRP and the transversal reinforcement on the confined compressive strength of the column is also proposed. The curves, axial load versus axial or lateral strain of the RC column, are simulated based on the stress-strain model and include the longitudinal reinforcement effect. The results demonstrate that the model and the predictive equations represent very well the axial compression behavior of RC circular columns confined with CFRP. The applicability of this model to a large spectrum of RC column dimensions is its main advantage.

Flexural Behaviour of RC T-Beams Strengthened with Different FRP Materials, Carvalho, Tiago, Chastre Carlos, Biscaia Hugo, and Paula Raquel , The Third International fib Congress and Exhibition "Think Globally, Build Locally", , Washington DC, (2010) Abstract

The strengthening of reinforced concrete structures with FRP materials has received a
considerable increment in recent years due to the high strength-weight and stiffness-weight
ratios of FRP compared to other materials.
An experimental programme was conducted in order to analyse the behaviour of different
structural solutions to strengthen reinforced concrete beams with FRP composites (EBR
GFRP, EBR CFRP, NSRM-CFRP) and is described. The RC T beams had a 3m span by 0.3m
height and were tested until rupture in a 4-point bending test system.
The NSMR technique has proved to be the most effective of the three alternatives tested, as it
obtained high strength, combined with high ductility. Nevertheless, all the systems show
great strength increment in relation to the non retrofitted T-beams, proving to be effective
approaches to the flexural strengthening of RC beams.

UFRG – Unidirectional fibre reinforced grout as strengthening material for reinforced concrete structures, Gião, R., Lúcio V., Chastre C., and Bras A. , BEFIB2012 – Fibre reinforced concrete, Guimarães, (2012) Abstractgiao2012vlchbr.pdf

The present study is part of an extensive research project, where the main objective is to evaluate a strengthening solution for reinforced concrete structures using a small thickness jacketing in the compression side of the RC element with unidirectional fiber reinforced grout - UFRG.
For this purpose a high performance cementitious grout reinforced with continuous and unidirectional non woven fibermat has been developed. It was expected that the use of these type of fibers allowed an optimization of its percentage and orientation. It was expected that the use of these type of fibers allowed an optimization of its percentage and orientation. Besides, for continuous fibers (with an aspect ratio, defined as the length-to-diameter ratio, l/d=∞), the composite should attain higher tensile strength since the fiber embedment length is enough to prevent fiber pullout.
The experimental campaign included a set of preliminary tests that allowed the design of the fiber reinforced grout, sustained with rheological parameters [7] and mechanical characterization tests of the materials.
Finally, an experimental campaign was carried out in order to proceed to the mechanical characterization of the unidirectional fiber reinforced grout. Compressive tests were conducted in small thickness tubular specimens that enable the determination of the compressive strength and the static modulus of elasticity of the material. The tensile strength of the material was obtained using splitting tests of cubic specimens (according the standard DIN 1048-5). The experimental results are presented and analyzed.