A Proposed Lateral Load Pattern Using Seismic Energy Distribution along the Height of Buildings

Abstract eng:
In this paper, a new pattern for lateral load used in equivalent static method for seismic designing the structures, is proposed and effect of this pattern on distribution of earthquake energy absorption and damage along the height of the buildings is studied. Proposed pattern for lateral load is a triangular-rectangular pattern based on current triangular distribution in Iranian Seismic Code. A dual step absorbing energy system for steel frame connections is the other suggestion for improving the inelastic behavior of the steel frames against the severe earthquakes. The current triangular lateral load pattern in seismic codes provides the strength and stiffness more than seismic demand in upper stories and it affects the capacity-demand ratio variable along the height of buildings. Earthquake reports show that damage concentration usually happens in one or some of the lower stories of a building. Also inelastic dynamic analysis shows the plastic hinges occurring and their developing in lower stories, which causes the story mechanism and collapse of the structure. Permanent deformation of structural elements and soft story mechanism are one of the main reasons for buildings damage and their failure in major earthquakes. In order to investigate on effect of proposed lateral load pattern on energy absorption and damage distribution along the height of the buildings, two steel moment resisting frames, 4 and 9 story, with four analytical models by different lateral load pattern and connection behavior, were considered and subjected to a series of inelastic dynamic analysis due to the numerous records. The results of the inelastic time history analysis confirmed that using the triangular-rectangular lateral load pattern caused the better uniform earthquake energy distribution along the height of buildings and prevented damage localization in lower stories. The proposed lateral load pattern did not change the earthquake input energy in comparison to the current lateral load distribution and it was more effective for mid-height frame model.

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