The Nature of the Vertical Distribution of Seismic Responses in Multi-Story Structures

Abstract

This Ph.D. research investigates the vertical distribution of seismic responses and controlling seismic response patterns in multi-story reinforced concrete and steel structures. Seismic responses of buildings designed by conventional force-based or displacement-based approaches result in significant force demands compared to nominal design as observed in both experimental studies and earthquake simulations. Furthermore, force patterns suggest that the floor forces are predominantly controlled by higher modes especially when modal properties of buildings alter due to inelastic deformations. Therefore, actual force patterns experienced by buildings may not comply with the design code assumptions such as equivalent lateral force or response spectrum analysis. The main assumption in those methods, that the response of a building is dominated by the first mode excitation, may not be valid under strong earthquakes when inelastic deformations contribute significantly to the total response. Design code assumptions imply inelasticity to have same effects in all modes of response, though it may have significant effects on the demands associated with the first mode, higher modes may not be affected the same way. Further the distribution of seismic responses may differ for different types of lateral force resisting systems since each system possesses different response mechanisms such as formation of inelastic deformations. To better understand the distribution of seismic demands, response intensity measures obtained through nonlinear time history analysis are examined closely in terms of magnitude and shape along the height of buildings for different types of lateral force resisting systems in this study. This dissertation examines various types of buildings to address and shade light on those issues and observations mentioned above.