1. Research Assistant, Dept. of Civil, Chemical, Environmental, and Materials Engineering (DICAM), Univ. of Bologna, Viale Risorgimento 2, 40136 Bologna, Italy (corresponding author).
2. Professor, Dept. of Civil, Chemical, Environmental, and Materials Engineering (DICAM), Univ. of Bologna, Viale Risorgimento 2, 40136 Bologna, Italy.
3. Professor, Dept. of Engineering, Univ. of Cambridge, Cambridge CB2 1PZ, U.K.