Failure mechanism and mechanical properties of CFRP strengthened super-servicing reinforced concrete poles

Super-servicing reinforced concrete poles (RCP) whichcome from a road section in a power grid, including six pole shafts and six specimens with a mid-span steel joint, were selected as samples to conduct a flexural strength test, in which three shafts and three poles with steel joint in the middle span were strengthened by CFRP in the longitudinal direction. The mechanical behavior and failure mechanism under different CFRP layers pasted werecomparatively studied. Based on the measured test data, the calculation methods of strength and stiffness were investigated, and the mathematical expression of stiffness degradation mechanism was proposed. The result shows that the final failure mode of CFRP strengthened poles is the local bond failure between CFRP material and the external concrete, and the longitudinal CFRP is snapped. The process of damage is rapid and brittleness. The mean strain of cross-section is in accord with the assumption of plane cross-section. The strength degradation of shaft specimens without strengthened is throughly serious. As for the strengthened poles, the bearing capacity and stiffness under each forcing stage are improved with different levels. The damage of strengthened specimens develops faster and more intensive than that of none-strengthened ones. When multi-aspects are synthetically considered, there is a suggestion that double layers of CFRP should be pasted along the longitudinal in the joint of the site within a certain distance, and the single layer of CFRP should be adopted in the shaft.