Abstract: The structural damage that happens during earthquakes explains the necessity for seismic evaluation, which is used to forecast the potential of structural damage. This paper compares the vulnerability of steel buildings with and without supplemental damping system. Fragility curves are used to describe the degree of vulnerability. Supplemental damping system is a new design and retrofit idea that deals with a well-designed damping system. It is an additional cable damping system that can considerably reduce the risk of damage.