Experimental investigation on the compressive behavior of short-term preloaded carbon fiber reinforced polymer-confined concrete columns

Strengthening of concrete columns with fiber reinforced polymer sheets provides a good improvement to the existing structural members in terms of load and strain capacity due to the properties of the composite jacket. A proper knowledge of the load–strain response of the composite members is necessary to design retrofitting intervention of existing structures; however, so far the available design methods do not allow to take into account the effect of the possible presence of service loads on the compressive behavior of the reinforced columns. An experimental investigation on the compressive behavior of preloaded circular concrete columns reinforced with carbon fiber reinforced polymer was carried out to determine the load and deformational capacity of confined concrete subjected to short-terms loads. Nineteen compression tests were performed to underline the difference respect to the standard compressive stress–strain response of the confined specimens. The results indicate that the compressive behavior seems to be not particularly influenced by the preloading. As the preloading level increases, ultimate axial load and axial strain do not have significant change respect to the test performed without preloading; however, the load–strain response of the confined concrete is affected by a reduction of the secant stiffness.