A study on sprayed fiber reinforced polymer composites for strengthening of reinforced concrete members

A study on sprayed fiber reinforced polymer composites for strengthening of reinforced concrete members

Name: Hussain, Qudeer

keyword: Strengthening

; SFRP

; Strength models

; Delamination failure

; Shear strengthening

; RC deep beams

; Openings

; Anchors

; Finite element analysis

Abstract: Extensive research is currently being conducted concerning the use of uni-directional fiber reinforced plastic (FRP) wraps or laminates in the strengthening and rehabilitation of reinforced concrete (RC) members. These unidirectional FRP(s) include carbon, glass, aramid, polyethylene terephthalate (PET) and polyethylene naphthalates (PEN). As strengthening materials, they offer some advantages over conventional steel and concrete jacketing such as low weight, high strength and excellent resistance to corrosion. Over the last few decades, a new method of strengthening reinforced concrete members by Sprayed Fibre Reinforced Polymer (shortly as SFRP) composites has been introduced. This method further simplifies the application procedure to apply fiber using a spraying process. The salient features of SFRP are quick and easy application as well as the uniform tensile properties in all directions. This thesis reports extensive usage of sprayed fiber reinforced plastic (SFRP) strengthening system on RC members using glass and carbon fibers embedded in a polyester matrix. In the first step, small scale circular and square columns strengthened with different thicknesses of SFRP were tested under uniaxial compression to investigate the increase in the ultimate strength and ductility. It was found that substantial increases in ultimate load carrying capacity, member stiffness and ductility can be achieved with SFRP confinement for both circular and square sections. The efficiency of SFRP for providing the external confinement and the resulting increase in strength and ductility is greater in circular columns than in square columns. The obtained experimental results were used to access the performance of existing strength models developed for unidirectional FRP. It was found that almost all existing models are conservative to predict the experimental compressive strength of SFRP-confined concrete. New strength models are proposed based on the obtained experimental data for both circular and square SFRP-confined columns and a good correlation was found between experimental and analytical values. The second phase aims to investigate the effectiveness of externally bonded SFRP in shear strengthening of RC deep beams under quasi-static loading. Given that bond between SFRP and concrete surface is the critical link, different anchoring systems i.e. Through Bolts (TB), Mechanical Expansion Bolts (MB), and Epoxy Chemical Bolts (EB) were proposed and used to enhance the bond between concrete surface and SFRP. The proposed anchoring systems are found to be effective to prevent the de-lamination of SFRP. Test results indicated that SFRP was capable of enhancing the ultimate load and deflection of RC deep beams provided that adequate anchoring system is installed. The performance of SFRP strengthening depends on several key variables such as SFRP material, thickness, strengthening configuration, strength of concrete, type of anchoring system and length of the anchor bolt. The third step aims to evaluate a possible use of the SFRP technique to elevate the shear strength of RC deep beams with web openings. Towards this goal, an extensive experimental program has been conducted. Both circular and square openings of different sizes were investigated. Two types of concrete (i.e., low and high strength) were used to cast the specimens. The deep beams with openings were strengthened with a variety of SFRP thicknesses and strengthening configurations. The externally bonded SFRP was remarkably effective to increase the ultimate load of the RC deep beams with both the square and circular openings and both low- and high-strength concrete beams. Also, SFRP applied on 3 sides (U-shaped) was more effective than 2-sided SFRP in shear strengthening. The efficiency of the SGFRP strengthening and MB anchoring system was lower for the high-strength concrete specimens as compared with the low-strength specimens. Then, in a fourth step, the research work was primarily focused on the development of two-dimensional nonlinear finite element analysis for RC deep beams (with and without openings) strengthened with SFRP. In the finite element analysis, realistic material constitutive laws were utilized which were capable of accounting for the non-linear behavior of materials. The finite element analysis was performed using computer software WCOMD. The calculated finite element results are found to be in good agreement with the experimental results and to capture the structural response of both un-strengthened and SFRP strengthened RC deep beams. A comparison between the finite element results and experimental data proved the validity of the finite element models. Further, the finite element models were utilized to investigate the behavior of RC deep beams strengthened with different directions of SFRP strips and web openings located at different locations. The finite element results showed that there is considerable de-crease in the ultimate load carrying capacity when openings are induced in shear span. The SFRP strengthening is found effective to enhance load carrying capacity of RC deep beams with openings irrespective of openings locations and shape. The vertical SFRP strips are found to be more effective than horizontal ones. At the end of this study, an experimental program was conducted to investigate the behavior of large scale non-ductile RC columns (representing reinforcement detailing of those structures which were designed against gravity loads only or constructed prior to the development of modern seismic codes) strengthened using SFRP. Three types of RC columns (i.e. shear, flexure-shear and flexure dominated) were strengthened using SFRP jackets and tested under lateral cyclic loading. A constant axial load was also applied along with lateral cyclic loading. In SFRP, two types of fiber materials (i.e. glass and carbon) were used for strengthening of RC columns. The results of SFRP strengthened RC columns were compared with control or un-strengthened RC columns. SFRP strengthening is found effective for all types of investigated columns (i.e. shear, flexure-shear and flexure dominated) to increase strength and ductility. Both types of SFRP (i.e., glass and carbon) jackets greatly improved the behavior of strengthened RC columns in terms of strength and ductility

Thammasat University. Thammasat University Library

Address: BANGKOK

Email: preserv@tu.ac.th

Name: Amorn Pimanmas

Role: advisor

Name: Winyu Rattanapitikon

Role: co-advisor

Created: 2015

Modified: 2021-09-09

Issued: 2021-09-09

วิทยานิพนธ์/Thesis

application/pdf

DOI: 10.14457/TU.the.2015.8

eng

DegreeName: Doctor of Philosophy

Level: Doctoral Degree

Descipline: Engineering

Grantor: Thammasat University

©copyrights Thammasat University

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