RAM Parapet Wind Load - Incorrectly applied GCpn

[rharting]

I started looking into how RAM calculates the wind load and for a building approximately 16.5' tall with a 2.5' parapet. Based on the building characteristics, the qz at the top of the parapet is around 18psf and with the GCp =1.5 for windward parapet and -1 for the leeward parapet (per section 6.5.12.2.3), the combined pressure is 45.211 psf. After doing some digging through the applied loads, it appears as though RAM is applying this 45.211 psf to both the leeward and windward parapet.

This is in essence, doubling what many to believe a very conservative wind load (especially for taller parapets). I think it's pretty clear the term GCpn is the combined positive and negative pressures on each parapet. So why is RAM applying this load twice.

Anyone else notice this?

 

[WillisV]

It was correct at one time, what version of RAM are you using? Ask Bentley tech support - post back here.

 

[rharting]

While developing my rational, i found an error in my spreadsheet i was using to check their loads. It's a one story building, so for the load into the diaphragm you divide the height by 2. I was doing the same thing for the parapet load. Do you know if there is a way to remove this post, as i don't want people thinking there is an issue with RAM that is not valid.

 

[WillisV]

Your response here lets people know it was not valid and why you thought it might have been an issue - this could help someone out in the future so I would let the post stand.

 

[SethGuthrie]

Plus it highlights one thing we don't do that is worth mentioning.
For a one story structure with a parapet the force to the top level diaphragm should actually be more than the full parapet pressure plus the pressure on the top half of the story below due to cantilever or prying action. We don't do that in RAM Frame.
The Report - Exposure boundaries is helpful for visualizing the areas exposed to wind as the program sees it.
Our wind load wiki has a few more useful tips:

http://communities.bentley.com/Prod...is_and_Design__Wiki/ramss-wind-loads-faq.aspx