1. Discipline of Civil Engineering, School of Engineering, Univ. of KwaZulu-Natal, 4041 Durban, South Africa (corresponding author).
2. Institute for Particle Technology, Technical Univ. of Braunschweig, Volkmaroder Str. 5, 38104 Braunschweig, Germany.
3. Faculty of Architecture, Applied Mechanics Laboratory, Technical Univ. of Crete, GR-73100 Chania, Crete, Greece.
4. School of Production Engineering and Management, Institute of Computational Mechanics and Optimization, Technical Univ. of Crete, GR-73100 Chania, Crete, Greece.