Curb Angle Sizing

[Leinster]

I would like some help in sizing a curb angle due to the tension caused by the rafters.

I have the attached as a sample which is a rafter roof for a 9m Dia tank using an IPE 160 as the rafters with a 1:5 slope.

1) I would initially like to ask a seemingly simple question as to how the horizontal load of the rafters is 19,720N?

2) I would also like some clarification on how the moment and thrust were calculated?

I had asked a similar question a while ago and was told to consult "Roarks Formula for Stress and Strain" which I assume is where the attached calculations were derived from however am not sure where exactly to find these calculations in the book.

3) Is the maximum tension in the attached calculation also taken from "Roarks Formula for Stress and Strain"?

Any assistance would be greatly appreciated.

 

[JStephen]

It looks to me like the calculation shown is incomplete. The horizontal load should be the total load divided by number of rafters divided by the slope. The total load would be the framing weight plus weight of roof plate and snow/live loads, and the latter loads are not shown on that page, just the framing weight.

The calculation for tension and bending in the ring should be from the formulas in Roark for N radial loads on a circular ring.

That is not necessarily a standardized calculation, so don't take my comments to indicate that is how it SHOULD be done, just trying to guess at what was done.

 

[yosamitysamm]

This design method comes from the Structural Engineering Handbook by Gaylord, Gaylord and Stallmeyer. They give formulas for the maximum thrust, moment and the expected stress in the ring beam.