Quantification and parametric analysis of large overhang RC planar frames subjected to horizontal and combined horizontal–vertical earthquake loading

Eurocode 8 (Part 1) and Indian Standard IS 1893 (Part 1) recommend accounting for the impact of vertical earthquakes on structures with large overhangs, but they do not provide specific guidance for modeling large overhang reinforced concrete (RC) planar frames, particularly regarding the representation of vertical masses during vertical seismic events. This paper quantifies the modeling of vertical masses in large overhang RC planar frames subjected to Vertical Ground Motion (VGM) using eight near-fault seismic excitations in SAP2000 software. At first, a modal analysis was performed to determine the horizontal and vertical time periods of the large overhang RC planar frames. The nonlinear time-history analysis utilized both the horizontal earthquake component and the combined horizontal and vertical components. In accordance with ASCE 7-05 and ATC-63 standards, eight near-fault earthquake records were selected from the PEER NGA database, comprising four pulse-type and four non-pulse-type seismic excitations. The response of the large overhang RC planar frames was evaluated using parameters such as vertical displacement, column axial force, base shear, and base moments. Furthermore, a methodology has been proposed for the identification of critical parameters for large overhang RC planar frames subjected to vertical ground motion (VGM). Additionally, a parametric study has been conducted on single-story to four-story large overhang RC planar frames using twelve non-pulse near-fault vertical earthquake events. The critical earthquake-related parameters selected include the vertical peak ground acceleration, the horizontal peak ground acceleration, the vertical-to-horizontal peak ground acceleration ratio, the predominant spectral time period for vertical ground acceleration, and the predominant spectral time period for horizontal ground acceleration. The structure-related critical parameters considered are vertical displacement at top joints, axial force, base shear, and base moments. This study demonstrates that the critical parameters related to a large overhang RC planar frame and the vertical ground motion should be considered in modern seismic design codes.