Hossein Abdollahi Parsa - Graduate Student, Faculty of Civil Engineering, Kharazmi University, Tehran, Iran
Peyman Homami - Assistant Professor, Faculty of Civil Engineering, Kharazmi University, Tehran, Iran

During previous years, several studies have been done on vulnerability of structures against earth-quakes. In seismic analyses of these studies only horizontal components of earthquake were consid-ered and little attention was paid to vertical acceleration especially in near fields. Investigation of rec-ords shows that vertical peak ground acceleration (PGA) can approach horizontal (PGA) to a great ex-tent or even go beyond it in some cases. In the present paper, the influence of vertical acceleration on structure responses has been investigated by comparing behaviors of different members of three mo-ment resisting R/C frames first by considering horizontal component alone and then by considering vertical and horizontal components simultaneously under three near field records. Results show that vertical component has much influence on axial force of the columns as well as on vertical displace-ment of mid-points of the beams in different stories; however it has little influence on lateral dis-placement of the stories

Vertical Component; Near Field; Non-linear time history analysis