1. Postdoctoral Researcher, Dept. of Civil Engineering, School of Engineering, Section of Mathematics and Management, Democritus Univ. of Thrace, Vasilissis Sofias 12, Xanthi 67100, Greece (corresponding author).
2. Professor, Dept. of Civil Engineering, School of Engineering, Section of Mathematics and Management, Democritus Univ. of Thrace, Vasilissis Sofias 12, Xanthi 67100, Greece.