1. Associate Professor, Dept. of Civil Engineering Science, Univ. of Johannesburg, Auckland Park Kingsway Campus, P.O. Box 524, Auckland Park, 2006 Johannesburg, South Africa (corresponding author).
2. Research Assistant, Dept. of Civil Engineering Science, Univ. of Johannesburg, Auckland Park Kingsway Campus, P.O. Box 524, Auckland Park, 2006 Johannesburg, South Africa.