PEAK VERTICAL FLOOR ACCELERATIONS OF TALL STEEL STRUCTURES

To meet modern day challenges structural engineers must properly design not only the primary structural elements of buildings but increasingly the secondary elements too. Damage or failure of nonstructural components (NSCs) and their attachments can present large economic losses, impaired building services and functionality, as well as life safety and emergency egress concerns. To properly design these components, it is important to accurately estimate their maximum acceleration demands including horizontal and vertical components of acceleration. In an effort to better understand vertical acceleration demands of rigid NSCs in multistory buildings and assess the building code provisions a 20-story office building, that is representative of a typical structure, is designed. Vertical acceleration demands are characterized through the use of floor acceleration spectra which are obtained for various points on the plan floor by running elastic modal time histories using 106 recorded ground motions. The main findings of this study are that peak vertical floor acceleration (PVFA) demands vary in plan due to the out of plane flexibility of the floor. Points in the mid portions of the floor slab experience much higher accelerations than points at column locations. The vertical seismic force design provisions of ASCE 7-10 underestimates the PVFA in a majority of the points found in the floor plan at least 50% of the time. A comparison and discussion between these results and the findings of a recent study out of the University of Reno is provided