A new design model for adhesive joints used to bond FRP laminates to steel beams: Part B: Experimental verification

doi:10.1016/j.conbuildmat.2011.12.005

Construction and Building Materials

Volume 30, May 2012, Pages 686-694

https://doi.org/10.1016/j.conbuildmat.2011.12.005 Get rights and content

Abstract

A new design model for adhesive joints used to bond fiber reinforced polymer, FRP, laminates to steel beams was presented in part A of this paper. Quasi-static tests were performed on representative and full-scale beam specimens to evaluate some of the most important failure criteria discussed in part A and the new design model proposed in this study. Three strengthening systems, from two manufacturers (Sika® and STO®), were used to prepare the specimens. It was observed that, in all cases, the failure took place at the steel–adhesive interface. It was found that, failure criteria based on material strength, considered in this study, fail to provide reasonable predictions of the strength of joints. The new design model presented in part A of this paper was found to be accurate in terms of predicting the ultimate load and failure mode of the joints.

Highlights

► Failure of the joints used in this study was governed by debonding at steel–adhesive interface. ► Design models, with assumption of adhesive failure, do not provide accurate failure load predictions. ► The proposed design model in this study does not need stress analysis of the joints to be designed. ► The proposed design model predicts the failure load and mode of failure with a good accuracy.

Introduction

In part A of the paper, a review of the most common failure criteria used to predict the strength of adhesive joints was presented. The drawbacks of each criterion were discussed and a new design model for adhesive joints used to bond FRP laminates to flexural steel members was proposed. The new design model is based on comparison of the axial force in the laminate at the anchorage length in a beam bonded with FRP laminate with a critical value obtained from a representative specimen. The new model aims to overcome the shortcomings involved in existing design models. In this part of the paper, some of the most important failure criteria mentioned in part A are evaluated and the accuracy of the proposed new model is investigated.

Section snippets

Specimens

Two types of tests were conducted. In the first type, double-sided strengthened steel plates, referred to as representative specimens, were prepared and tested. In the second type, full-scale steel beams, strengthened on the tension flange, were tested. Three series of representative specimens made of three different strengthening systems and in each series 10 specimens were prepared in order to obtain reliable results. Three series of beam specimens, including six specimens, made of the same

Representative specimens

Table 4 presents the strength of the representative specimens in terms of ultimate load, P_u and corresponding maximum shear, τ_max, and maximum peeling stress, τ_max, in the adhesive layer calculated from the analytical solution proposed by Bocciarelli et al. [2]. It is worth mentioning that, in most of the specimens, failure took place in two phases. In the first phase, a crack was formed on one side of the specimen at the end of the laminate (these initial cracks could be heard, but they were

Strength prediction and discussion

In this section, an attempt is made to evaluate some of the stress-based and fracture mechanics-based failure criteria mentioned in part A of this paper and to predict the strength of the tested specimens using the new proposed model.

Conclusions

An experimental study was carried out to study the strength of adhesive joints used to bond CFRP laminates to tensile and flexural steel members in order to evaluate the existing design methods and the new design model proposed in part A of this paper. In the light of the results obtained from this experimental work, the following conclusions can be drawn:

(1)
Failure hypotheses based on material strength, i.e. adhesive, were found not to be suitable for the design of adhesive joints in this study.

References (6)

A. Andre et al.
Application of fracture mechanics to predict the failure load of adhesive joints used to bond CFRP laminates to steel members
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M. Bocciarelli et al.
Prediction of debonding strength of tensile steel/CFRP joints using fracture mechanics and stress based criteria
Eng Fract Mech
(2009)
L. Goglio et al.
Design of adhesive joints based on peak elastic stresses
Int J Adhes Adhes
(2008)

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

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