Wind Load - Canopie roof 3

[sconst]

Hello Everybody.

In EC 1991-1-4 for canopie (7.3 chapter) we have coefficients Cpnett and over force coefficients Cf moreover we have 4 pictures with roof and forces.

I do not know when i Should use Cpnett and when Cf.

(As chapter 5.3 says -> Fw=CsCd*q_p(ze)*Cf*Areff)
So here we use Cf but i dont see this force on construction... I have purlins,griders and roof - where i should use cpnett, and where Cf.

Maybe as 1st i must calculation Cpnettm after that use Cf and total wind force use to calculation griders?

Have no idea, maybe someone can give me some links to wokred example - canopie roof.

Thanks for your help


Thanks for your help.

 

[Ron]

I suggest you delete this post and re-post in the structural engineering forum...you're more likely to get an answer...I'm not familiar with the EuroCode document, but looks similar to ASCE 7, used in the US.

 

[sconst]

Ron Could and explain me how u do it in ASCE 7 -> i mean how you calculate canopie roof?? I would be really greatfull . Thanks.

 

[bimr]

Open buildings with flat roofs should use parapet wind pressures on the fascia for MWFRS calculations. ASCE 7-05 section 6.5.13.2.

http://www.ce.udel.edu/courses/CIEG407/CIEG_407_Protected/Chapter 6 Wind Loads.pdf

http://www.bgstructuralengineering.com/BGASCE7/BGASCE7007/Wind_Provisions.ppt

 

[Ron]

I do a lot of canopy design and treat them as open structures. Depending on configuration, the structural frame can either be MWFRS or components and cladding. If it is free standing, I use MWFRS...if attached to the primary building, I use components and cladding.

 

[msquared48]

A canopy behaves like an air foil. That's the reason that Architects design them with no support. With all that uplift, who needs a foundation?

Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask

 

[Ron]

Mike...exactly right! And even more so here in Florida with high wind loads! I get all excited when I get a canopy design with snow loads, where finally something points down!

 

[sconst]

It's quite familiar to EC - I think it's going to be use at the same rules -> some diffrents as everywhere.

Just the only one problem now is that: should i use cpnett only to cladding and steel construction calculate by using Force - and Cf coefficient.

But as i see it depends on you want to precisely calculate or not .

Thanks all of you for help.

 

[Ron]

Even when I use Cf and develop the point load, I check it as a distributed load.

 

[sconst]

I have decided to use on my project only Cpnett, because calculation with Cf gives me lower loads -> so its not wrong to make construction on bigger loads :> Maybe its not so economical, but if i had to calculate wih Forces method(and here use coefficient Cf) it would take so much time.


Thank you Ron for your interest my thread.

(Thanks to all of you who answered)

 

[Ron]

In later versions of ASCE 7, monoslope roofs over open structures are designed using Cn rather than Cf applied as a single force.

 

[sconst]

I have found AISC 7. But in EC we have only Cpnett coefficients and Overall Force Coefficients cf.
Moreover :
For a monopitch canopy the center of pressure should be taken at d/4 from the windward edge : d = alongwind dimension,

Where Fw=CsCd * qz * Cf * Aref

And what Aref should be ( area of beams? rafters etc? or surface where we have cladding (much bigger than area of beams) - in some books i have seen Aref as a whole surface where we use claddings -> when we have repating frames where exactly put the Force ( in d/4)

(in AISC 7 is : F= qZ G Cf Af (N))

The overall force coefficient represents the resulting force. The net pressure coefficient represents the maximum local pressure for all wind directions. It should be used in the design of roofing elements and fixings.


So if i calculate whole construction using Cpnett -> it's save choice .( using Fw force it's better choice, beacuse we have smaller loads on cinstruction = Cf coeff is smaller than Cpnet)

Sum Up:
Cpnet for cladding -> and if i have a lot of money (joke) i can use those coefficients to calculate frame and rest of construction.

But the best choice is :

Cladding calculate -> use Cpnet

Frame Construction -> Use Fw (with Cf coeff) and Aref is then surface bettwen two repeating frames.