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Thank you for your reply. Dynamic stiffness refers to the ratio of dynamic force and dynamic displacement. I look at the dynamic characteristics only when a structure needs to be constructed in severe seismic zone. Looking at the overall global behavior of the structure (without any split), it has two sides, flexible (short side in this case) and stiff (long side in this case). Even a uni-directional excitation in longitudinal direction yields around 15% absolute maximum and 20% absolute minimum displacement in transverse direction mainly because of stiffness and mass eccentricities. Considering first 3 modes with 3rd mode being dominant in torsion has developed height wise variation in the deflection response of the structure in this particular case. Before the architectural planning, I reminded the architect about one expansion joint in order to have a reasonable aspect ratio of the structure considering the seismicity of the region. But the architect himself planned the structure with 3 portions. Anyways, you are right and I agree to your point on this. Regarding the thrust on foundation, I'm not sure that's why I have asked it here. Found this statement in the geotechnical report.

As it is a reinforced concrete structure, the sliding should not be a concern due to the self-weight of the structure; same goes for overturning moment. The consideration of the frost penetration will govern the depth, if applicable. IF there is SOG, it can also govern the minimum possible depth of the footing. Why would you ask that? How can a retaining wall transfer any thrust to the foundation? There is no need to split the structure of this size in three portions. What is dynamic stiffness? I have not come across this term before in relation to the structural design of a building.

The structure is located in the lawn of the Red fort in Muzaffarabad. Probably, the seismic event caused the collapse. Inadequate stiffness, lack of flexural strength and confinement in the area of plastic hinge are reasons for the collapse.

According to the section 10.10.6.5 and its commentary (of ACI 318-08), we do not need to use minimum eccentricity if there are negligible second order effects.