1. Dept. of Civil and Environmental Engineering, Univ. of Auckland, 20 Symonds St., Auckland 1142, New Zealand (corresponding author).
2. Professor, Dept. of Civil Engineering, Univ. Putra Malaysia, 43400 UPM-Serdang, Malaysia.
3. Senior Lecturer, Dept. of Civil and Environmental Engineering, Univ. of Auckland, 20 Symonds St., Auckland 1142, New Zealand.