Strengthening of Low-Strength Concrete Columns with Fibre Reinforced Polymers. Full-Scale Tests

Sonia Martínez,Ana De Diego,Rafael P Soldado,Gabriel Rentero,Francisco J Barroso,Luis Echevarría,José Pedro Gutiérrez,Viviana J Castro

doi:10.3390/infrastructures5110091

Sonia Martínez, Ana De Diego + Show 6 more

Open Access

https://doi.org/10.3390/infrastructures5110091

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Abstract

Confinement of columns with externally bonded fibre reinforced polymers (FRP) sheets is an easy and effective way of enhancing the load carrying and strain capacity of reinforced concrete (RC) columns. Many experimental studies have been conducted on cylindrical small-scale un-reinforced concrete specimens externally confined with FRP. It is widely accepted that confinement of square or rectangular columns is less efficient than the confinement of circular columns. The theoretical models for rectangular sections are mostly based on approaches for circular columns modified by a shape factor, but the different models do not give similar results. This paper presents an experimental program on large-scale square and rectangular RC columns externally strengthened with carbon FRP sheets and subjected to axial load. The main variables were the side-aspect ratio of the cross-section, the radius of curvature of the corners and the amount of FRP reinforcement. The results show that the FRP confinement can increase the strength and strain capacity of rectangular concrete columns with low strength concrete. The FRP hoop ultimate strain was much lower than the material ultimate tensile strain obtained from flat coupon tests and the strain efficiency factor achieved in the tests was less than the value usually recommended by design guides.

Highlights

The use of fibre reinforced polymer (FRP) jackets for the strengthening of reinforced concrete (RC) structures has proven to be a very effective technique to improve the resistance and the concrete strain capacity of members subjected to compression [1,2]
There have been many more studies on square and rectangular columns reinforced with CFRP carried out testing small-scale specimens [15,16,17,18,19] compared with those that include large-scale tests
Another study carried out by Zeng, J.J. [22] in 2018 includes tests of eight columns reinforced with CFRP proved that the stress–strain curves of FRP confined concrete in large-scale FRP confined rectangular RC columns, generally have a typical bilinear shape

Summary

Introduction

The use of fibre reinforced polymer (FRP) jackets for the strengthening of reinforced concrete (RC) structures has proven to be a very effective technique to improve the resistance and the concrete strain capacity of members subjected to compression [1,2]. [22] in 2018 includes tests of eight columns (height 1300 mm) reinforced with CFRP proved that the stress–strain curves of FRP confined concrete in large-scale FRP confined rectangular RC columns, generally have a typical bilinear shape. Other stress–strain models propose exponential equations for the ultimate axial stress and the ultimate axial strain, such as Wei and Wu’s model [29] This model is not directly related to the corresponding equations for circular columns but is based on small-scale tests. This project aims to contribute to the research on the behaviour of large scale FRP confined reinforced concrete columns with square and rectangular cross sections [31]

Main Parameters of Experimental Program

FRP Jacket Strains Obtained by Testing

Findings

Conclusions