1. Graduate Student, Dept. of Civil Engineering, Aristotle Univ. of Thessaloniki, 54124 Thessaloniki, Greece.
2. Researcher, Institute of Engineering, Seismology and Earthquake Engineering (ITSAK), 55102 Thessaloniki, Greece.
3. Professor, Dept. of Civil Engineering, Aristotle Univ. of Thessaloniki, 54124 Thessaloniki, Greece.