BEHAVIOUR OF FRP RETROFITTED REINFORCED CONCRETE COLUMNS UNDER AXIAL COMPRESSION AND CYCLIC HORIZONTAL LOADS C. Chastre Rodrigues, Universidade Nova de Lisboa, UNIC, Portugal Manuel A. G. Silva, Universidade Nova de Lisboa, UNIC, Portugal Abstract starts minimum 100mm from top of paper, 12 points centre justified) Abstract The seismic retrofit of reinforced concrete columns with FRP materials jackets has received a considerable increment in recent years due the high strength- weight and stiffness-weight ratios of FRP compared to other materials. The FRP outer shell also contributes to prevent or delay environmental degradation of the concrete and corrosion of the steel reinforcement. An experimental program conducted in order to analyze the behavior of reinforced concrete columns jacketed with FRP composites or repaired with polymeric concrete and subjected to axial compression and cyclic horizontal loads is described. The dimensions of the cylindrical columns were 1500 mm height by 250 mm diameter. The influence of various parameters on the response, including the type of confining material and the number of FRP layers, is reported. The results of the tests are shown and interpreted and some recommendations on more adequate design procedures are advanced. Keywords: Retrofitting, FRP Composites, Reinforced Concrete Columns, GFRP, CFRP 1. Introduction There is an increasing need to repair and strengthen concrete structures. Among the reasons of this kind of intervention are design and construction faults and structural degradation or damage due to environmental actions such as earthquakes, accidents, fires or structural deterioration due to lack of conservation. Besides, if the structure is used for purposes other than the original ones, retrofitting may be a necessity to compensate the increase of the live load or the elimination of structural elements. The eligible structural reinforcement depends on technical and economical factors, namely the efficiency of the retrofit intervention, the conditions and cost of the work and the local availability of specialized workers, materials and equipment. It is also important to evaluate whether the structure needs to be used during the works and estimate its behavior against the aggressions of the environment during and after strengthening. Among the options to retrofit a given reinforced concrete structure the following are to be referred: reinforced concrete; shotcrete; structural steel; external post-tension; bonded steel plates with epoxy resins and retrofitting using FRP composites.