Pushover analysis of 2D frames with stiffness irregularity in vertical direction

Abstract

There is an important relationship between the architectural design of a building and its safety. When collapsed or severely damaged buildings are investigated, it is seen that the causes of damage are directly or indirectly related to the irregularities developed during the architectural design. Irregularities mean discontinuity in plan and section (Horizontal and vertical direction). Various analysis methods, both elastic and inelastic, are available for new and existing concrete buildings containing these kinds of irregularities. Elastic and Inelastic procedures are available for analysis. An elastic analysis procedure gives a good indication of the elastic capacity of structures and indicates where first yielding will occur, it cannot predict failure mechanisms and account for redistribution of forces during progressive yielding. Inelastic analyses procedures help to demonstrate how building will really behave by identifying modes of failure and potential for progressive collapse. Inelastic procedure such as Pushover analysis which is a Nonlinear Static Procedure (NSP) of analysis where a model directly incorporating inelastic material response is displaced to a target displacement, and resulting internal deformations and forces are determined. A parametric study has been performed for a 20 structure with vertical stiffness irregularities under earthquake loading with specific aims and possible outcomes. Several types of vertical irregularity have been considered as Strong column and weak beam, Strong beam and weak column, set back and soft story. Increasing column section and reinforcement (strong column and weak beam) has definite impact on the structure both in stiffness and strength but decreasing column section (Strong beam and weak column) has lesser effect on strength of the whole structure. Soft story at lower stories is critical for the whole structure but after 4th story it's not much harmful for strength point of view. And setback has negative impact at ground and 1st floor level of the structure by decreasing both stiffness and strength. But it stiffens and strengthens the structure while it occurs at the upper stories.