Can any Body Explain the phenomenon of Soft Story in Building Structures?

Soft story is the weak story, when you have difference of stiffness in one or more floor of the building in case of an earthquake there could be the probability that the building collapse in the floor that have less stiffness(Pancake effect). Typically, when you have large opening in the lower floor or pilotis floor. The experience in earthquake engineering have demonstrated that non structural element play an important role in the structural response.

We term a storey as "soft story" when that particular story has considerable differences in stiffness compared to adjacent stories. This is confirmed if the story has less than 70% of the stiffness of the story just above it or if the story stiffness is less than 80% of the average stiffness of three stories above it.

Such stories are typically due to vast open floors with sudden changes in the number of columns/shear walls compared to that in higher/lower stories (e.g. at car parking floor, convention hall etc.). It is better to avoid such stories since they are susceptible to seismic collapse, and if not, special consideration should be taken while designing these floors (e.g. providing sufficient external shear walls to increase stiffness).

no should be expert only

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the Ratio of differential stiffness between a floor level and level above or below specified by the code

this story may has an excessive sway and hinge formation and generally lead to non ductile failure pattern

thanks for invition ,,,,,,,,,,

i am wating for experts answers

if you have large openings on some floors than other floors or say no wall on building frame for some purpose, example: in parking, commercial shutter, the stiffness of that floor will be less than other floors, less than 70% as stiff as the floor immediately above it, such floors tends to collapse in earthquake. Such building with less stiffer floor is called soft-storied building.

Personally speaking may be if you provide shear wall that will act very better.