3D analyses of buildings under vertical component of earthquakes

This study first investigates how to perform the 3D dynamic analysis of buildings under the vertical component of earthquakes. The analysis results indicate that (1) dividing a main girder into two elements is required to perform the vertical earthquake analysis; (2) including secondary beams for the building analysis is similar to refine modeling of the building (at this time, one building member, such as a secondary beam or a portion of the main girder, modeled by a two-node beam element can also produce an accurate result); (3) neglecting the floor stiffness in the vertical direction is suitable, if the floor thickness is not too thick; and (4) the required vertical effective mass ratio is suggested to be 80%. In the second part of this paper, 1,080 time-history analyses and 180 static analyses of reinforced concrete buildings were performed in order to investigate the relationships of extreme column axial forces and beam moments between vertical earthquake and dead loads. The analysis results indicate that these relationships are linearly proportional to the maximum acceleration obtained from the response-spectrum figure using the first vertical frequency.