WORLD FOR CIVIL

PONDING CONSIDERATIONS IN BUILDINGS

Flat roofs on which water may accumulate may require analysis to ensure that they are stable under ponding conditions. A flat roof may be considered stable and an analysis does not need to be made if both of the following two equations are satisfied:

C _p + 0.9 C _s £ 0.25

I _d ³ 25S ⁴ / 10 ⁶

Where C _p = 32 L _s L ⁴ _p / 10 ⁷ I _p

C _s = 32 SL ⁴ _s / 10 ⁷ _s

_{L p = length, ft (m), of primary member or girder}

_{L s = length, ft (m), of secondary member or purlin}

_{S = spacing, ft (m), of secondary members}

_{I p = moment of inertia of primary member, in ⁴}

_{(mm ⁴ )}

_{I s = moment of inertia of secondary member, in ⁴}

_{(mm ⁴ )}

_{I d = moment of inertia of steel deck supported on secondary members, in ⁴ /ft (mm ⁴ /m)}

_{For trusses and other open-web members, I s should be decreased 15 percent. The total bending stress due to dead loads, gravity live loads, and ponding should not exceed 0.80F y , where F y is the minimum specified yield stress for the steel.}