1. Lecturer, Dept. of Civil Engineering, Laboratory of Reinforced Concrete and Masonry Structures, Aristotle Univ. of Thessaloniki, Thessaloniki 54124, Greece (corresponding author).
2. Professor, Dept. of Civil Engineering, Laboratory of Reinforced Concrete, Demokritus Univ. of Thrace, Vas. Sofias 12, Xanthi 67100, Greece.