The stability and strength of concrete columns confined by tangential CFRP wrapping and longitudinal external CFRP sheet is studied. Plain and confined columns of slenderness l = 40 are tested. Two batches of concrete with different ultimate compressive strengths 25 and 50 MPa are investigated. The total number of specimens is 24 (sixteen 300 mm high cylinders for material properties and eight 1500 mm high columns, all specimens with diameter 150 mm). Unconfined and with one and two CFRP sheet layers confined concrete columns are tested. Further longitudinal CFRP sheet in one and two layers are added on the confined columns. The theoretical prediction of ultimate strength and stability of columns coincides rather well with experimental results. It is concluded that additional external strengthening of CFRP confined concrete columns by attaching longitudinal CFRP sheets is efficient. The two methods applied lead to similar results, that the additional longitudinal reinforcement is efficient for improving stability of confined columns in region of moderate slenderness 3
