Mohsen Tehranizadeh - Professor, Department of civil engineering, Amirkabir University of Technology, Tehran, Iran
Arsam Taslimi - Graduate Student of Earthquake Engineering, Amirkabir University of Technology, Tehran, Iran
Mohammad Reza Shamlu - Graduate Student of Earthquake Engineering, Amirkabir University of Technology, Tehran, Iran

The occurrence of recent earthquakes with a considerable vertical component has drawn both engineers and researchers attention to the effect of vertical excitations more than the past. Regarding the high vertical to horizontal acceleration ratio of earthquakes which sometimes exceed the unit, the simultaneous effects of these two componentscannot be ignored. In addition, the susceptibility of beams’ length to vertical ground motions has been evident, yet studies on how the collapse risk of the buildings with various beam length can be affected by vertical excitations are a handful. Thus, in this paper, four 10 and 30-story RC frame-Core wall buildings with 6 and 12-meter beam span are designed, and the nonlinear models of them are developed in the platform of Open sees. Incremental Dynamic Analysis (IDA) in two states, once only under horizontal acceleration (H) and the other under both vertical and horizontal accelerations (H+V) are conducted using a suite of near-field ground motion records. Then, the IDA and the fragility curves are derived, and the collapse probability of the buildings in 1 year and 50 years has been calculated through the integration of seismic hazard and fragility curves in which the derivative of fragility curve is combined with hazard curve using the risk integral. The results indicated that the collapse risk of the buildings with longer beam spans under simultaneous horizontal and vertical excitations are noticeably greater than that of the buildings with 6-meter spans, and the sensitivity of tall buildingsto vertical excitations is generally less than mid-rise buildings.

Span length, Collapse risk, IDA, Fragility, Vertical excitation