CFRP strengthened butt-welded very high strength (VHS) circular steel tubes

This paper investigates the behavior of carbon fibre reinforced plastics (CFRP) strengthened butt-welded very high strength (VHS) circular steel tubes. The VHS steel has a yield stress of 1350 MPa and an ultimate strength of 1500 MPa. Three types of epoxy resins with different lap shear strength were used. Tests were conducted to determine the lap shear strength between CFRP and VHS steel tubes. A total of 21 butt-welded VHS tubes strengthened with CFRP were tested in axial tension. Three kinds of failure modes, i.e. adhesive failure, fiber tear and mixed failure were observed. The suitable epoxy adhesive for strengthening VHS tubes was recommended. A significant strength increase was achieved using CFRP–epoxy strengthening technique. A theoretical model was developed to estimate the load carrying capacity of butt-welded VHS tubes strengthened using CFRP.