1. Pedagogical Univ. of Cracow, ul. Podchorążych 2, 30-084 Kraków, Poland. E-mail: kkuzniar@ap.krakow.pl
2. Professor, Institute of Computer Methods in Civil Engineering, Cracow Univ. of Technology, ul. Warszawska 24, 31-155 Kraków, Poland (corresponding author). E-mail: zenwa@twins.pk.edu.pl