|M.Sc Student||Nsieri Emad|
|Subject||Seismic Behavior of Ductile Structural Walls: Shear Forces|
|Department||Department of Civil and Environmental Engineering||Supervisors||Professor Emeritus Avigdor Rutenberg|
|Professor Robert Levy|
study the seismic base shear demand on multistory structures comprising ductile
cantilever walls is reexamined. Two effects are studied: (1) shear force
amplification due to higher vibration modes before and after the formation of
plastic hinge at the wall base; (2) shear redistribution among walls through
load transfer from yielded walls to those still elastic, including the in-plane
floor forces involved.
The shear force amplification due to higher vibration modes at the wall base is studied parametrically using a suite of 20 historic accelerograms.
It is shown that the amplification of base shear depends strongly on both the flexural strength at the base of the wall and the fundamental natural period. The shear amplification factor is found to be much larger than specified by seismic codes, and a simple design formula is proposed as function of the fundamental natural period and force reduction factor. It is also shown that non-simultaneous yielding at the wall bases has a significant effect on the base shear distribution among the walls. It is demonstrated that the shear demand on the flexible walls (shorter ones) is likely to be much larger than is commensurate with their relative stiffnesses, or even relative to their flexural strengths.
The effects of shear deformation in the walls, in-plane flexibility of the floor diaphragms, foundation rotational stiffness, and distributed plasticity over the building height on the dynamic base shears are also investigated. It is shown that these effects mitigate to some extent the shear forces redistribution among walls due to the successive formation of plastic hinges.