mehran tiv - International Institute of Earthquake Engr. and Seismology P.O.Box ۱۹۳۹۵/۳۹۱۳, Tehran, Islamic Republic of Iran
mohsen ghafory ashtiany - International Institute of Earthquake Engr. and Seismology P.O.Box ۱۹۳۹۵/۳۹۱۳, Tehran, Islamic Republic of Iran
hosen tehranizadeh - International Institute of Earthquake Engr. and Seismology P.O.Box ۱۹۳۹۵/۳۹۱۳, Tehran, Islamic Republic of Iran

A ۱/۲ scaled model of a common four-story steel structur Iran has been designed, constructed, and tested by a pair of harmonic force vibration exciters. The model is one that resembles most of the low to medium rise Iranian steel structures which include semi-rigid beam-to-column connections of the so called "Khorjinee" type, and masonry jack-arch flooring system. In this paper, steps taken in designing the model and the preliminary results of a forced vibration test, in the form of frequency spectrum of floor acceleration response, are presented and compared with those of a mathematical model with rigid connections. An obvious shift of natural frequencies implies a more flexible frame than that of the mathematical model.