1. School of Engineering & Electronics, University of Edinburgh, King's Buildings, Edinburgh, EH9 3JL, UK
2. Infram, PO Box 16, 8316, ZG Marknesse, The Netherlands
3. Dept Civil Engineering, University of Roma Tre, v. Volterra 62, 00145 Rome, Italy
4. School of Engineering, University of Warwick, Coventry, CV4 7AL, UK