Bond characteristics of CFRP plated concrete members under elevated temperatures

doi:10.1016/j.compstruct.2006.04.068

Composite Structures

Volume 75, Issues 1–4, September 2006, Pages 199-205

https://doi.org/10.1016/j.compstruct.2006.04.068 Get rights and content

Abstract

Fire related structural degradation is a challenge to the safe design of structural members. Carbon fibre reinforced polymer (CFRP) strengthened concrete members show degradation of bond properties with temperature. Therefore, a detailed investigation of heat effects on composites is required before further application of this system can be effective. This paper focuses on a 3D model developed to predict the behaviour of CFRP–concrete composites under fire. Heat transfer analysis was employed to predict the temperature within the adhesive layer of epoxy, which is the most critical part of the member at high temperature. The model showed that the epoxy reached the failure point within a short time under standard fire. The model was also used to predict the required insulation thickness requirement for two-hour and three-hour fire resistance levels. The effects of rate of temperature increase on bond strength of composite structures are demonstrated through numerical analysis. The model results were validated with experimental data.

Introduction

The intensity and duration of fire, and the level of performance needed are important when designing structural members for fire-critical applications especially for high-rise buildings. The main aspects of fire behaviour that must be considered include: fire resistance, smoke evolution and toxicity, heat generation characteristics, and flame spread. Many of these factors should be further investigated in the application of CFRP composites as external reinforcements for strengthening of concrete and steel structures. Fire resistance can be defined as the ability of an element of construction, component or structure to fulfil for a stated period of time the required structural adequacy, integrity, thermal insulation or other expected duty specified, during exposure to a fire test specified in the Standard (AS1530.4). Fire tests are frequently conducted, to ensure that materials and designs fulfil the necessary fire performance requirements under exposure to the standard fire. However, full scale fire tests are very difficult to conduct in some situations and are very expensive. Therefore, it may be necessary to develop an accurate numerical model as a routine tool in the development of composite systems. This paper presents the details and the results of the numerical model developed to predict the heat transfer behaviour of CFRP strengthened concrete members. Also, the experimental program and the test results are briefly discussed.

Section snippets

Overview

Two series of single shear tests were conducted on the CFRP strengthened concrete blocks. The first series consists of eleven specimens made of non-insulated CFRP strengthened concrete blocks. The objective of these tests was to verify the critical temperatures, the temperature distributions and the factors affecting the performance of composite members at elevated temperature. Two insulated specimens were tested under the second series to determine the effects of insulation on the heat

Numerical studies

The strand7 finite element analysis program (version 2.2.5), developed by G+D Computing, was used to develop the numerical model for heat transfer analysis. The program employs the finite element method, and its theory is based on Fourier’s law for heat conduction. Two models were developed to predict the heat transfer behaviour of insulated and non-insulated CFRP strengthened concrete members. The models consist of mainly three materials including concrete block, epoxy and CFRP plate. The

Model results and comparison

Validation of the numerical model was carried out using experimental results for both non-insulated and insulated specimens.

Conclusions

•
Epoxy adhesive being used in the construction industry is very sensitive to temperature variations. Both experimental and finite element results show that the epoxy temperature should not exceed 70 °C in order to maintain the integrity between the CFRP and concrete at high temperature.
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The bond strength at elevated temperature does not depend on the CFRP bond length.
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The CFRP–concrete composites reach the failure point within 5.5–6 min under exposure to the standard fire. This indicates the need

References (6)

AS1530.4. Methods for fire tests on building materials, components and structures. Part 4: Fire-resistance tests of...
Gamage JCPH, Wong MB, Al-Mahaidi R. Bond performance of CFRP plated concrete members at elevated temperatures. In:...
Gamage JCPH, Al-Mahaidi R, Wong MB. Effect of insulation on the bond behaviour of CFRP-pated concrete elements. In:...

There are more references available in the full text version of this article.

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