The seismic response of existing un-reinforced masonry (URM) buildings is strongly dependent on the characteristics of floors/diaphragm. For this type of building, commonly used floor system is wooden floors with mud/clay overlay where floor thickness varies widely. Is there any specific procedure/ research to determine engineering properties of this type of flooring system?
Dear Chandani:
I have not seen any procedures for determining the properties of this floor system that can be used for seismic analysis of URM buildings that feature it. It is a complicated problem because the floor system features many elements. From what I saw in Kathmandu following the Gorkha earthquake, the wood floors comprised wood sheathing over wood joists, and a soft flooring material is placed on top of the clay/mud fill.
The floor can be treated as a composite system which includes: wood joists, wood sheathing, nails between the joists and sheathing, clay/mud fill, and a frictional interface between the fill and sheathing. The soft flooring can be disregarded given its limited ability to resist stress. The essential questions concern 1) the amount of stress that the fill can resist, and 2) the amount of stress that the frictional interface can deliver to the fill. I believe that these stresses are very small relative to that which the wood joists and sheathing can resist.
Therefore, in lieu of a complicated analysis, I suggest that you assume that only the joists and sheathing provide resistance to loading, and that the fill only adds to the weight of the floor diaphragm. For additional guidance on the resistance and deformability of wood floor diaphragms, I refer you to the American Wood Council's "Special Design Provisions for Wind and Seismic"
https://www.awc.org/codes-standards/publications/sdpws-2015
I hope that this information helps you.
Sincerely,
Arturo
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