load combination used when checking the deflection of purlins.

[malikasal]

can anyone clarify the load combinations that should be used when checking the deflection of purlins ?

Should the wind load be included in the vertical deflection of the purlins???



ôIf you don't build your dream someone will hire you to help build theirs.ö

Tony A. Gaskins Jr.

 

[jayrod12]

Depends on the direction of wind load. If it's a flat roof that is always seeing uplift then I would be checking the gravity loads (snow, live) in one case, and the win load in a separate case. Typically it is the gravity loads that govern deflection, and the wind loads that govern strength since in uplift, the compression flange in unbraced.

 

[malikasal]

What if the wind load is causing pressure on the purlin.
Is it ok to check the wind load separately without combinig it with other loads ?



ôIf you don't build your dream someone will hire you to help build theirs.ö

Tony A. Gaskins Jr.

 

[jayrod12]

No. You must use the appropriate load combinations that consider all of the loads. Where I practice you'd need to account for wind as the primary and live/snow as companion loads and vice versa where live/snow is the primary loading and the wind would be companion loading.

Most other codes have the same requirement.

Wind doesn't know whether the roof is already loaded with live or snow loads.

 

[MotorCity]

Agree w/ jayrod.

However, I think you will find that most engineers only consider wind uplift even though technically wind can produce a downward force on the roof as well.