Abstract: This paper deals with the dynamiccharacteristics of the structures containing infinitely stiff members,for which the vibration equations ofthe systems are usually inertially coupled.Combined with the element consistent mass matrix in finite elementdynamic analysis, the concept of hiddeninfinitely stiff and relative inertial coupling is presented. The paperdiscusses some problems in setting up the computational models fordynamic response analyses of tall buildings, using a branched modal andtaking pile-soil-superstructure interaction into account.