The equivalent damping ratio is a key factor in determining equivalent period for displacement based seismic design.The equivalent damping ratio models of different researchers are compared.Influences of hysteretic models

ductility factor and equivalent period on equivalent damping ratio are discussed. It is concluded that tendency of equivalent damping ratio in different models is basically identical. The hysteretic models have important influence on equivalent damping ratio.The equivalent damping ratio of Rambcrg-Osgood model is 2.56 times that of Flag shaped model.The equivalent damping ratio becomes large with the increasing of ductility factor

especially whenμis within[2

4].The equivalent damping ratio within short vibration periods is 2 times that of moderate or long vibration periods.So when effective period is shorter than 1 second

the influence of effective period on equivalent damping ratio must be taken into account.