Plastic collapse analysis of CFRP strengthened and rehabilitated degraded steel welded RHS beams subjected to combined bending and bearing

• CFRP strengthened as-received and rehabilitated corroded box girders were subjected to 3-point bending.
• Three phases of deformation were observed, namely, denting, bending and denting, and structural collapse.
• Two theories were presented, namely, the energy and the equilibrium theories.
• The energy theory suffered from few simplifications.
• The equilibrium theory well predicted the collapse curves particularly for the rehabilitation series.

Innovative techniques using the lightweight, high strength and corrosion resistance of carbon fibres reinforced polymers (CFRP) composites have been proposed in a recent paper by the author. The present paper presents plastic mechanism analyses of CFRP strengthened and rehabilitated rectangular hollow sections (RHS) under quasi-static large deformation 3-point bending. The strengthening series was for un-degraded RHS beams from the manufacturer reinforced using externally wrapped CFRP sheets. The rehabilitation series was for artificially degraded RHS beams repaired using externally wrapped sheets or bonded plates. The main parameters examined in this paper were the section type, section and member slenderness and the type and number of the CFRP sheets. Three different phases of plastic deformation were observed during the test, namely, denting, denting and bending, and structural collapse. Two methods were used to model the large plastic deformation measured during plastic collapse of the composite RHS beams, namely, equilibrium and energy methods of analysis. It was found that the predicted collapse curves using the equilibrium approach were in good agreement with the measured curves for the bare and composite specimens examined in the strengthening and rehabilitation series, particularly for the latter series. This may be caused by a number of factors such as the specimens in the rehabilitations series were comparatively longer and had larger bearing width. The energy theory was found to have deficiencies represented in the simplified linear polygon shape adopted for the mechanism geometry, and adopting the plastic 1/2-wave length used for I-sections, as well as the use of a simplified formulae to describe the relationship between the local denting displacement and global bending rotation angle for the three phases of deformation observed during the test.