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The behaviour of CFRP strengthened steel joints


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Phan, HB 2016 , 'The behaviour of CFRP strengthened steel joints', Research Master thesis, University of Tasmania.

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In recent years, carbon fibre reinforced polymers (CFRP) have been growing in popularity for
external strengthening and repairing of deteriorated steel structures. On one hand, compared
to traditional strengthening methods such as welding and bolting, CFRP has shown
significant advantages such as light weight, high strength, and corrosion resistance.
Furthermore, the application process for CFRP is very simple, quick and requires minimal
labour. On the other hand, due to the high strength properties of steel and CFRP, failure is
most likely to occur at the bond interface. Therefore, it is vital to study the bond behaviour
and the failure mechanism of CFRP strengthened steel structures as well as the factors that
play crucial roles in the bond quality. These factors including the material properties, the
surface treatment prior bonding or the bond length must be studied before applying in a real
The current research program studied the bond behaviour of double strap joints which were
formed by using CFRP to connect two steel plates. Experiment was conducted to investigate
the effect of various material properties, bond lengths and surface roughness levels on the
bond quality and the failure modes. It was found that there existed an effective bond length
for CFRP-to-steel structures; once it was exceeded no improvement in the load carrying
capacity could be obtained. This effective bond length varied with material properties,
especially the steel grade. It was also found that variations of surface roughness level
between 0.73μm and 7.75μm had no significant effect on the ultimate loading capacity of the
specimens. However, the CFRP and the adhesive types played very important roles in the
bond strength and the failure modes.
Experiments were also conducted to study the fatigue behaviour of double strap joints. These
joints were prepared by using strand CFRP with and without primer resin. After the curing
process the joints were subject to fatigue tensile loading until failure. The fatigue lives and failure modes were recorded. Results showed that the fatigue lives of the double strap joints
prepared with strand CFRP were comparable to those of specimens strengthened with CFRP
plates and other high modulus CFRP sheets. However, a reduction in fatigue life was
observed for the samples with primer resin.
A cohesion zone finite element model was established to simulate the bond behaviour and to
investigate some factors that could affect the load carrying capacity of the joints such as the
steel grade. The results obtained from the model were compared with the experimental data
in order to verify the cohesion zone model. The results showed an agreement between the
experiments and numerical analysis. The cohesion zone was proved to be suitable for
predicting the ultimate load of the joints as well as the stress transfer from CFRP-to-steel. It
was found that the steel grade had a significant effect on the bond capacity and the effective
bond length.

Item Type: Thesis - Research Master
Authors/Creators:Phan, HB
Keywords: CFRP, steel, strengthening, double strap joints, fatigue
Copyright Information:

Copyright 2015 the Author

Additional Information:

Chapter 3 has been published as: Taylor, C., Jiao, H., Phan, H. B. & Zhao, X.-L. (2014). Bond strength of steel plates connected using strand CFRP sheets and selected epoxy resins. Proceedings of the 7th International Conference on FRP Composites in Civil Engineering, International Institute for FRP in Construction, 2014 Vancouver, Canada. It has been removed for copyright reasons.

Chapter 4 appears to be the equivalent of a post-print version of an article published as: Jiao, H., Phan, H. B., Zhao, X.-L., 2014. Fatigue behaviour of steel elements strengthened with strand CFRP sheets, Advances in structural engineering, 17(12), 1719-1727

Chapter 5 appears to be the equivalent of an Accepted Manuscript of an article published by Taylor & Francis Group in Australian journal of structural engineering on 16/11/2015, available online:

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