1. Ph.D., Univ. of Maribor, Faculty of Civil Engineering, Smetanova 17, 2000 Maribor, SI (Corresponding author), e-mail: primoz.jelusic@um.si
2. Professor, Univ. of Maribor, Faculty of Civil Engineering, Smetanova 17, 2000 Maribor, SI, e-mail: bojan.zlender@um.si