Mechanical properties of fiber reinforced polymers (GFRP) laminates change with water sorption, solar rays or cycles of low-high humidity and their degradation is studied under accelerated aging. The results showed that (i) the Young's modulus of plates suffers only minor changes; (ii) moisture exposure by immersion in water causes only minor degradation; (iii) thermal cycles of small amplitude, around room temperature, increased the ultimate strain; (iv) salt fog spray cycles were most severe: (v) selected dry-wet cycles caused higher degradation than the thermal cycles; (vi) cycles of uv radiation and flooding led to continuous decay of tensile strength. The degradation in properties of the laminated plates due to environmental conditions differs from that of the same composite when wrapped or bonded to a structural member. The validity of straight transfer of ultimate strength measured in flat coupons to the design of structural members is addressed herein. The actual effects of aging were smaller on confined columns than on the laminates.