Question

How are ponding loads on each individual joist calculated?

I know ponding is currently 5 in (26 psf)

The gable roof has slopes of .25 in and 3/8 in (per foot).

Answer 1

Ponding load can be determined by the following ways:

1. Graph giving the deformation or deformed shape of the structure depending on the volumes of water available.

2. Graph giving the internal moments in the structure keeping in mind the volume of water.

3. Graph giving the relation between the water level on the roof and the amount or volume of water stored on the roof.

With slopes of .25 in and 3/8 in/foot according to the AISC the procedure required is:

1. Load the initial joist with water and no drainage

2. The joist will deflect downwards

3. Re-calculate water depth based on new joist deflection

4. Re-calculate joist deflection based on the new calculated depth

5. Repeat the steps until it completely converges.