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# Civil Engineering/Expansion joint in G+4 rcc building

Question

Thanks for helping all with your guidance.
I have G+4 building of L type with size 77x16 m and 30x17 m, so I provide an exp.joint at the intersection so the size is now 61x16m and 45x17m with thermal consideration for 61x6m building.
Now when I want to calculate the size for exp.joint considering static seismic with uncracked section(i.e divided by 0.7)I am getting the width around 125mm using the formula Dm=Sq(dm1^2+dm2^2).
My question is do this size is correct or not for this type of building and if I need to reduce it how can I do it.

Regards,

Musherib

Hi Musherib,

Yes, depending on the R factor used for seismic loading and the slenderness of the building, one can end up with quite a wide seismic gap to avoid pounding. This gap should be bridged using crushable filler with low modulus and for pedestrian traffic you can detail a steel plate fixed to one building and sliding at the other side.

Ways of reducing this gap is to reduce ductility demand on the frame and design just using stiff (bearing) shear walls, so that your seismic sways are reduced. Of course you can also reduce the gap as you go down the building- the maximum gap width being at roof level.
Questioner's Rating
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Civil Engineering

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