Repair of cracked steel structures by FRP patching

Composite fiber patching techniques are being considered as alternatives to traditional methods of strengthening and fatigue crack repair in structures due to the growing use of fiber reinforced polymer (FRP) composite materials to different engineering structures. In the past few decades, most of the research studies focused mainly on the application of FRP on the repair of aluminum or titanium alloys, which are the common materials used in aircraft engineering, and also in strengthening and repair of reinforced concrete structures. However, there are relatively fewer studies of the application of FRP patching on the repair of steel structures. Therefore, an investigation of the application of FRP patching on repairing steel structures was carried out. The investigation includes three main parts: (1) a study of the tensile load transfer behaviour of FRP/steel double lap joints, (2) a study of the fracture behaviour of cracked steel plates repaired by FRP patching and (3) a study of the fatigue behaviour of cracked steel plates repaired by FRP patching.;An experimental and a numerical study of the static tensile strength of carbon fiber reinforced polymer (CFRP)/steel double lap joints were carried out and the results showed that loading could be transferred successfully from the parent steel plate to the CFRP plate. Finite element models were developed for predicting the stress intensity factor (SIF) of cracked steel plates with CFRP patching and the model was calibrated by the experimental results of Kennedy and Cheng (1998). The finite element results showed that for cracked steel plate with single-side CFRP patching, the SIF was reduced significantly on the patched side and increased slightly on the unpatched side. In addition, the SIFs varied non-linearly across the thickness of the crack tip and as a result, different crack grow rate was expected through the thickness of the crack tip. To account for the variation of the SIFs through the thickness of the crack tip, a new set of finite element models was developed for the cracked plate with single-side FRP patching. Based on the finite element results, a set of equations was proposed for predicting the fatigue life of welded steel plates with cracks in the welded region repaired by Boron FRP patching. The analytical results compared well with the fatigue test results of welded steel plates with edge crack and single-side FRP patching (Roach and Rackow 2005). In addition, finite element parametric study of the SIF and prediction of fatigue life of cracked steel plates with FRP patching with different adherent stiffness ratio and different forms of crack and patching were carried out. It is shown that a higher efficiency of FRP patching was observed for the plates with edge crack than that of the central crack plate. It is also found that the increase in fatigue life was more pronounced for cracked plates with double-side patching. Lastly, based on the finite element model of the cracked plates with FRP patching, cracked steel circular tube structures with FRP patching were studied and the corresponding extension of the fatigue life was investigated.