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Description
The research presented in this paper refers to the reinforcing method of thin-walled cold-formed steel (TWCFS) elements using Carbon Fibre (CF) composites joined by bonded connection. The proposed reinforcing method is a good response to TWCFS steel structures designers' needs which strive to achieve solutions which are fast easy and simultaneously safe. The originality of the proposed strengthening method lies in the fact that the mats are bonded across the cross-section to form a segmental closed cross-section. It should be noted that thin-walled cold-formed steel elements (TWCFS) are widely used in civil engineering practice due to it beneficial relation describing bearing capacity versus material consumption. Unfortunately the increased use of such structures, in the event of damage or over-loading, may require reinforcement. Due to very small thickness of the wall of its cross-section, traditional methods using welded connections or mechanical fasteners are not recommended because they can lead to the weakening of the cross-section of TWCFS elements. The main results of the presented investigation were the identification of failure mechanisms of CFS “sigma” beams restrained with CFRP textiles. It was observed very complex failure mechanisms including deboning of the adhesive layer, local plastic deformation, and local, global, and distortional buckling deformation. It was also found that proposed restraining methods of CFS “sigma” types beams using CFRP wraps are the most effective in case of distortional buckling deformation. To investigate this phenomenon the numerical model was made in ABAQUS software, using the Finite Element method (FEM). In this model, TWCFS sigma beams were modelled with C3D8R hexahedral elements were used. The supports, stiffeners and plates were modelled with shell discrete rigid elements with linear shape function of the R3D4 type. Ultimately, the CFRP mat was modelled with M3D4 tetrahedral membrane elements were used. The verification consisted of comparing the force-displacement relationship for the numerical model and results from full-scale laboratory tests. Based on conducted analysis three forms of joint damage were observed, namely at the steel-adhesive interface, fibre rupture and mixed damage behaviour. A combination of adhesive failure and fabric rupture, suggests complex interactions between the materials. It was also noted that the proposed method can be very beneficial due to its simplicity and non-destructive nature simultaneously providing high bearing capacity of the reinforced element.
