Posted by: JDB
Stiffening ribs modelling procedure? - 06/10/04 02:04 AM
I was just wondering what would be the best method for modelling stiffening ribs on GRP (glass reinforced plastic) ducting. The ducting diameter is 1600mm and the spacing between ribs is approximately 1500mm.
My concern is that the wall thickness of the ducting was probably calculated according to BS7159:1989, which would allow for a lesser wall thickness due to the presence of stiffening ribs. If I divide the Caesar II model into sections, the one consisting of the typical ducting wall thickness and the other representing the thickness of the stiffening ribs, will Caesar II not calculate a stress in the duct wall away from the rib which is higher than that allowed for by the code? As a result would it be correct to reduce the stress induced due to vacuum (or external pressure) by a certain factor (or possibly reduce the applied vacuum)?
If not, how should one approach modelling pipes / ducts which have stiffening ribs?
Thank you for your time
Jason
My concern is that the wall thickness of the ducting was probably calculated according to BS7159:1989, which would allow for a lesser wall thickness due to the presence of stiffening ribs. If I divide the Caesar II model into sections, the one consisting of the typical ducting wall thickness and the other representing the thickness of the stiffening ribs, will Caesar II not calculate a stress in the duct wall away from the rib which is higher than that allowed for by the code? As a result would it be correct to reduce the stress induced due to vacuum (or external pressure) by a certain factor (or possibly reduce the applied vacuum)?
If not, how should one approach modelling pipes / ducts which have stiffening ribs?
Thank you for your time
Jason