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What are the Ponding Considerations In Buildings?

Those flat roof which face a problem of water accumulation require stability analysis under ponding conditions. For checking the stability we need to see the following equations, if both of these are fulfilled

Cp+0.9Cs<= 0.25

C p= 32 Ls L4p/107Ip
Lp= Length of primarymember or girder in ft (m)
Ls= Length of secondary member or purlin ft (m)
S= Spacing of secondary members ft (m)
Ip= Moment of inertia of primary member in in4 mm4
Is= Moment of inertia of secondary member in in4 mm4
I d= Moment of inertia of steel deck supported on secondary members, in4/ft (mm4/m)


It should be noted that Is should be decreased by 15% for trusses and other open-web members. Also the value of the total bending stress due to ponding , dead loads and live loads should not exceed 0.80Fy(the minimum specified yield stress for the steel)

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Kanwarjot Singh

Kanwarjot Singh is the founder of Civil Engineering Portal, a leading civil engineering website which has been awarded as the best online publication by CIDC. He did his BE civil from Thapar University, Patiala and has been working on this website with his team of Civil Engineers.

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