Glazing Roof

[nisha1980]

I am designing a Glazing Roof . Model Snap shot attached. it is a crossing roof which has only 4 supports. Length of the cantilever portion is 3.2m. After loaded up the model with dead , live and wind loads, there are local deflection in end members around 100mm .

Can any one help me to come up with an idea to make this roof to work without adding additional supports. ?
Thanks

http://files.engineering.com/getfil...-1a94-4d91-a36f-4cacc8fe49c0&file=Capture.JPG

 

[MotorCity]

Instead of adding supports, can you use larger roof members or reinforce the roof members if its existing?

 

[dhengr]

Nisha1980:
Several things that I see might improve your roof structure, and improve its cantilever end deflections. You might do well to make ridge heights higher. This would deepen each roof plane/surface and make them stiffer, sorta as folded plates or frames. You show some sort of a saw toothed structural system from each column and cantilevering out toward the free end, under the eaves. This would be better if it were stiffer, deeper, heavier members, HSS members good in vert. and lateral cantilever bending from the column. Structurally, these eave edge frames should go from max. depth at the col. to zero depth at the end of the canti. roof. They should not go to zero out at the second roof A-frames. Run the ridge members continuous through the center of the roof system so they can react the canti. end deflection. Right now, they lose their tension strength at the center cupola opening in the roof, or you need one heck of a stiff tension ring as the cupola opening. Use a prestressing system (tension rod) up at the ridge elevation, in each direction and running through the cupola opening, to pull the canti. tips up and counteract the canti. deflection. A few tension ties from eave to eave out at the canti. ends would help. The four frames which span btwn. the columns should probably be a little huskier than all the other roof frames. These might frame the roof over the columns and inward. Then, the 8 roof planes which canti. are each about 11' square in their own plane. Fab. each of these in a stl. shop, as Vierendeel trusses, with some in-plane strength and stiffness, and ready for glazing. These get bolted (welded?) to the frames over the columns, and to ridge members with the tensioning rods in them, and a tie rod is applied btwn. the eaves out at the canti. ends.

 

[Ron]

My thoughts are similar to dhengr....make ridge members continuous and tie valley struts all at center.

 

[nisha1980]

Thanks a lot for all your replies. it helped me to improve the roof frame.

Dhengr can you please clarify this again for me ?at
what do you mean by

[highlight #000000]"Structurally, these eave edge frames should go from max. depth at the col. to zero depth at the end of the canti. roof.
They should not go to zero out at the second roof A-frames."[/highlight]

Thanks

 

[nisha1980]

Sorry In previous reply the wordings shown in highlighted.

Below is what i need to get clarify

"Structurally, these eave edge frames should go from max. depth at the col. to zero depth at the end of the canti. roof.
They should not go to zero out at the second roof A-frames. "

Thanks

 

[dhengr]

Nisha1980:
You have 4- 3.2m long canti. gable/A-frame roof elements, the sub-systems in your whole roof system. There are 5 A-frames, with .8m spacing btwn. them in each canti. roof element sub-system. In your sketch, you show, with heavy lines, some saw toothed structure which appears to be the following: a truss like structure, its top chord might be the eave board of the A-frames; this eave truss appears to have a max. depth ‘d’ at A-frame #1 (at the columns), then its depth starts reducing as it moves out on the canti. and is ‘d/2’ at A-frame #2, and is zero at A-frame #3, and is ‘d’ at A-frame #4, and is zero again at A-frame #5, the end of the canti. sub-system.

My comment was intended to say, that that canti. eave truss is not particularly effective structurally. It would be better if it was deeper at the columns, and wasn’t saw toothed, but rather tapered up to zero uniformly on its way out to the end of the canti. sub-system. I don’t know what you intend this to be, or how it works. It does not appear to be a very helpful supporting structure in your whole roof system.

You could actually build the 4- 3.2m long canti. gable/A-frame roof elements, the sub-systems in your whole roof system, that is, A-frames #1-5 for each roof element and other parts, on the ground, and them lift them up onto their columns. Then, temp. support them out at their outer corners, out at the canti. ends and then, tie them together at the col. tops, and install some sort of ridge beam cross shaped frame with tensioning ability, valleys, etc. for the center roof. Finally, tension the two ridge lines so that the canti. ends are slightly above level.

 

[nisha1980]

Thanks dhengr for your descriptive explanation.
this roof will be fabricated and bring into site as four pieces . so we can not make ridge members continuous. my below sketch shows arrangement for eave truss. this arrangement helped to counteract with deflection . but not much.

if managed to get additional support deflection problem can be solved as below sketch.

But i want to try many options without adding extra supports. i am not sure how we can add extra tension rods in eave to eave out . also in cupola opening a heck of tension rods in each directions. appreciated if u can further explain this . then i could try applying those to my model and see the new deflections.
thanks