Experimental study concerning the material behavior of CFRP confined plain and reinforced concrete

It is well known that confinement introduced by CFRP (Carbon Fiber Reinforced Polymer) jackets highly increases the ultimate compressive strength and ductility of concrete. Various experimental research programs have been proposed to express the increase in strength and strain by the use of CFRP jackets, but, in the majority of cases, the additional effects of reinforcing elements, like ties or spirals, have not been analyzed very well. This paper provides the investigations on wrapped short concrete columns with and without ties and spirals. In an extensive research program the volumetric ratio of the CFRP jacket and the ratio of transverse reinforcement were varied. Thereby, columns with different geometrical shape, different CFRP thickness, and with different transverse reinforcement elements were produced. Executed deflection controlled compression tests provided investigations concerning the structural behavior of the test specimens. The main results of these tests will be explained. A solution is proposed to take the confinement action of the external CFRP material and of the internal transverse reinforcement into account.