Abstract
Many seismic codes in the world adopt a factor that is to reduce seismic design forces considering an energy absorbing capacity of a structure. The concept of the factor appeared in the SEAOC code as K factor. Now similar factors are included in many codes, e.g. R in U.S. and Ds in Japan. Though the concept of the factor is well recognized, the value varies much between countries. This is one of the largest differences between the seismic codes in the world. For example, for the most ductile structures, U.S. code reduces the design forces by the factor of 1/8=0.125, whereas Japanese code reduces the forces by the factor of 1/4=0.25. This paper discusses the background of the factor and to what extent the seismic forces can be reduced due to energy absorbing capacity.
