In this paper base isolate structures from earthquake atack by means of spring dashpot system are presented. A mathematical model to predict the nonlinear behaviour of five story steel frame from earthquake attack by means of springdashpot system is also given. The paper has developed two stages: the development of the form of the mathematical model, and the establishment of the parameter functions appearing in the model both using optimization and experimental data. The experimental work was carried out using the shaking table of the Institut of Earthquake Engeenering, University of Skoplje, Yugoslavia. The base isolate system is consisted of helical springs and dashpots were manufactured in German company GERB. The experiments involved horizontal earthquake excitations.