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

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.

The Effects of Bond–Slip Laws on the Debonding Failure and Behavior of Flexural Strengthened RC Slabs in Hybrid FRP Retrofit Systems

“…Strengthening structures with external bonded materials has become one of the popular choices for rehabilitation and upgrading existing reinforced concrete (RC) structures [ 1 , 2 ]. Researchers and engineers are particularly interested in restoring and strengthening partially damaged RC structures to minimize the impact on environmental deterioration and cost savings [ 3 , 4 , 5 ].…”

A Design Method to Induce Ductile Failure of Flexural Strengthened One-Way RC Slabs

“…The demand for strengthening and rehabilitation of infrastructures becomes more urgent in modern society [1][2][3]. Apart from the aging, corrosion, unexpected excessive loads, and accidental damage, the rectify of initial design and construction faults or upgrading the load capacity of reinforced concrete (RC) structures are also of interest to structural engineers and researchers [4][5][6].…”

Confinement of FRP concrete columns: Review of design guidelines and comparison with experimental results

“…Glass fibre has higher ultimate strain compared to carbon fibre and, applying a maximum effective strain value, the results are well below the outcomes obtained by applying the efficiency factor. Martínez et al (33) pointed out that the FRP hoop ultimate strain was much lower than the material's ultimate tensile strain obtained from flat coupon tests and the strain efficiency factor obtained in the tests was less than the value usually recommended by the design guidelines.…”

“…Most experimental and theoretical studies in the literature focus on FRP concrete confinement for circular sections (29,30) However, it is also common to design columns with a rectangular or square cross-section (31). It is well accepted that FRP confinement is less effective for rectangular columns than for circular columns (16,32,33); in circular sections, the FRP jacket uniformly confines the concrete whilst in rectangular sections it is non-uniformly confined as FRP confinement is mainly concentrated at the column corners. Only some of the concrete column core is effectively confined and, as a result, confinement effectiveness is reduced (34).…”