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

C_p+0.9C_s<= 0.25
I_d>=25S⁴/10⁶
Where
C _p= 32 L_s L⁴_p/10⁷I_p
C_s=32L_s⁴/10⁷I_s
L_p= Length of primarymember or girder in ft (m)
L_s= Length of secondary member or purlin ft (m)
S= Spacing of secondary members ft (m)
I_p= Moment of inertia of primary member in in⁴ mm⁴
I_s= 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 I_s 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 0.80F_y(the minimum specified yield stress for the steel)