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structural analysis of steel canopy roofs with two codes of ASCE 05-07 and PrEn 1991-1-4:2004

structural analysis of steel canopy roofs with two codes of ASCE 05-07 and PrEn 1991-1-4:2004

structural analysis of steel canopy roofs with two codes of ASCE 05-07 and PrEn 1991-1-4:2004

(OP)
Hello there! I have some questions on canopy/open buildings that I have faced while referring two codes, PrEN1991-1-4:2004 and ASCE -7:05, I will try to explain them below;
1. when we refer to PrEN1991-1-4:2004, it states that the location of the wind pressure to is to be at d/4 distance from windward direction, and when we refer to the figure 7.16 it says that the wind force not the wind pressure, so is it the wind pressure or the wind force to be loaded at the predetermined distance?
2. whenever there is a double skin membrane roof system, PrEN1991-1-4:2004 recommends some rules on loading system in section 10, for our case the eternal skin is the most rigid/ air impermeable membrane so that it has to be loaded with the value of Cpnet = Cext-Cint, and the internal membrane is the air permeable membrane with uniformly distributed openings so Cint/3. the thing is that we do not have the value of Cext and Cintexplicitely when referring to canopy roof recommendations of exposure factors instead we do only have Cpne and Cf values, so how can I determine the values in this two membranes?
3. in referring PrEN1991-1-4:2004 for canopy roofs we do only have wind directions of 0 degree and 180 degree, how can we determine the wind load in 90 degree?
4. I get nothing on double skin membranes while I refer to the code ASCE 7:05, is there anything you could suggest me?
5. I am living in Ethiopia that the basic wind pressure is measured on 10 minute gust wind at 10 meter height so if I ever wanted to refer ASCE code which the basic wind speed is 3 second gust wind at 10 meter height how can I change the 10 minute gust wind into 3 second gust wind?
Thank you so much for your cooperation in advance.

RE: structural analysis of steel canopy roofs with two codes of ASCE 05-07 and PrEn 1991-1-4:2004

1.wind force
2. Not sure, if you post a sketch,could answer.
3. You could use pressure coeff for roof angle of 0 deg

Wind load codes seem to leave alot to engineering judgement (cant cover all cases)

RE: structural analysis of steel canopy roofs with two codes of ASCE 05-07 and PrEn 1991-1-4:2004

it is difficult to use a Wind Code which is made for Europe in Africa
or would you use snow loads for Alaska in Ethiopia ?

I am sure wind speeds and especially wind directions are different in your country
You can use European or american codes as a 'guideline' but when it come to specific numbers ( like wind speed ) you have to use the local values
If wind loads are important for your project you need to ask a wind specialist around you


best regards
Klaus

RE: structural analysis of steel canopy roofs with two codes of ASCE 05-07 and PrEn 1991-1-4:2004

(OP)
thank you Guys for your response (Klitor and Klaus), the points that i rais before are the gups that i have found on this two codes, and ethipia uses the european code together with local context, of coarse the wind speed is going to be taken with the local condition. let me attach you some snipped pics and reccommendations from the eurocode and check them out.


Regards, Naol

RE: structural analysis of steel canopy roofs with two codes of ASCE 05-07 and PrEn 1991-1-4:2004

Try posting a sketch of your structure. Maybe you dont have a classic canopy structure according to eurocode.
The snip you posted is more applicable to closed structure.

RE: structural analysis of steel canopy roofs with two codes of ASCE 05-07 and PrEn 1991-1-4:2004

Why are you using two codes? You should use your locally governing code.

RE: structural analysis of steel canopy roofs with two codes of ASCE 05-07 and PrEn 1991-1-4:2004

(OP)
hello klitor hear i attached you the pic of the canopy sheltering on of the worlds wonder monumentalchurch found here in Ethiopia, it is 30 meter with 45 meter having an average height of 13 meter. the roof is meant to be a a double skinned monopitch canaopy roof, which basically comply with both codes.
And Motorcity, as i said before our country does use European building code with some modifications on it to make the code contextual with our countries condition, as of the code says to refer the national annexs whenver nedded.

RE: structural analysis of steel canopy roofs with two codes of ASCE 05-07 and PrEn 1991-1-4:2004

I would dostribute wind according to 'Degree of blocking (phi)' factor.
Design main elements for cca phi=0.7 (looks realistic when looking at picture).
Design upper cover for pressure when phi=0, and put rest of the pressure on the bottom cover.

I would definitely look at covering as solid, and dont forget to load the sides

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