Behaviour and design of adhesive joints in flexural steel members bonded with FRP laminates

Doktorsavhandling, 2010

The use of bonded CFRP laminates to strengthen and upgrade existing structures has attracted a great deal of attention during the past two decades. The superior mechanical properties of CFRP laminates, such as high strength and stiffness, excellent fatigue properties and good durability characteristics, have made them a suitable alternative to steel plates used in traditional strengthening and repair methods. Advantages suggested by the adhesive bonding technique, such as ease of application and improved fatigue behaviour, have also made this technique a suitable alternative to traditional joining methods such as welding and bolting. FRP bonding has been widely researched and practised in the strengthening of concrete members. However, when it comes to steel structures, it is somewhat limited in terms of field applications. One of the most important obstacles to the widespread use of FRP bonding in steel structures is the lack of design codes. This is mainly due to the lack of design models for adhesive joints used to bond FRP laminates to steel substrates. Issues such as the lack of knowledge about the behaviour of adhesive joints, the lack of suitable material models for structural adhesives and difficulty analysing adhesive joints are contributing to the difficulty associated with establishing design models. The work presented in this thesis is mainly concerned with a detailed study of adhesive joints used to bond FRP laminates to steel substrates in order to develop a design model. Comprehensive analytical, numerical and experimental work has been carried out to obtain a good understanding of the behaviour of these adhesive joints. The work focuses on failure initiation and propagation, failure modes and the influence of material properties on the strength of joints. The effect of geometrical modifications on the behaviour of joints is another subject which has been investigated in this thesis. Recommendations about using geometrical modification as a tool to enhance joint strength have been proposed. Finally, a new design model has been proposed for steel beams bonded with FRP laminates. The advantages offered by the new design model include ease of application, the opportunity to treat different loads and geometries of joints and accuracy of predictions.