150 feet span roof
150 feet span roof
(OP)
I have to design a circular roof 150 feet diameter. Shall I use two way steel truss. by the way what is space frame, is it two way truss? (the roof is flat so nothing parabolic)
When was the last time you drove down the highway without seeing a commercial truck hauling goods?
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RE: 150 feet span roof
Dik
RE: 150 feet span roof
Mike McCann
MMC Engineering
RE: 150 feet span roof
RE: 150 feet span roof
Dik
RE: 150 feet span roof
Dik
RE: 150 feet span roof
RE: 150 feet span roof
Mike McCann
MMC Engineering
RE: 150 feet span roof
What do you or your architect intend as the roofing material? The selection of a structural system would depend to a degree on how the roof slopes, the amount of secondary members required, etc.
RE: 150 feet span roof
Mike McCann
MMC Engineering
RE: 150 feet span roof
I followed this whole post and don't really want a piece of that design. Maybe if you guys were all in my office.
RE: 150 feet span roof
RE: 150 feet span roof
RE: 150 feet span roof
Have done things like this using three or four "main" trusses running parallel to a diameter. Cuts down on the total "central" truss load. Obviously they are different lengths.
RE: 150 feet span roof
RE: 150 feet span roof
Radial trusses from a central ring is generally an elegant solution. The only drawback with this concept is that it depends solely on the integrity of the central ring and it's conn to the radial trusses. If you are confident of quality fabrication/erection and effective maintenance, then it would be a viable option. Unfortunately, in these low-tech projects, one or all of these requiements may be lacking.
With that in mind, I believe I would tend to go with the parallel trusses as it results in a more redundant and robust structure and less sensitive to the potential shortcommings mentioned above.
RE: 150 feet span roof
Dik
RE: 150 feet span roof
RE: 150 feet span roof
Dik
RE: 150 feet span roof
RE: 150 feet span roof
You are proposing a basic system. Anybody can design that. I wanted two way system to cut down the 96" deep truss which you proposed. I wanted 5 feet maximum depth of trusses. That's why I floated my question to get an idea. Any ideas of designing this roof to cut down depth is appreciated. and of course I will keep at least 2% slope.
and thanks for some discouraging remarks. All I can say that I can bet anyhting that there was a day when you also knew nothing. If you can learn, I can too and that's what I am trying. This forum is for this purpose.
RE: 150 feet span roof
The roof can slope... with the main truss or transverse to it. It can also slope using the main truss as a ridge to the perimeter or as the main truss as a valley... You can also shape the main truss to achieve any number of ways... even to have a huge downspout in the middle of the circle (if you really wanted).
The framing has the advantage of the roof deck spanning one direction only. I arbitrarily picked 3" deck because it minimised the number of smaller trusses. The main truss can be deeper to improve the efficiency. The depth of the shorter span trusses can remain the same or can be varied to be more optimum.
Connections are simple and common to nearly all steel framing. No wierd and wonderful space frame connections. A space frame connection cost would be fatal unless you want to pay for the added elegance. It's boring, but cheap.
If the money is available, then radial trusses will do, but you have an interesting connection detail at the centre and the direction of deck span will have to change with each 'pie' shape, more difficult for lateral load analysis.
Columns can be located on the circumference as required with beams framing between them, picking up the steel deck and/or shorter span trusses.
Dik
RE: 150 feet span roof
I wasn't suggesting that your scheme doesn't allow the roof to slope...was just pointing out that "flat roof" doesn't mean flat.
RE: 150 feet span roof
http://www.deltastructures.com/
RE: 150 feet span roof
You are right, this is a good place to come to learn, and for the most part, all are welcome. Furthermore, all of us did start in this engineering business with considerably less knowledge and understanding of the subject matter than we had after 20 years of experience. But, you must also admit that intelligent questions beget more meaningful answers. And, you don't get a very high grade for your OP, IMHO. If you had combined your several posts in your OP, you would have better indicated some of your knowledge of the subject and elicited much better answers. If you ask a dumb, incomplete question, as you did in your OP, you can expect to get some hassle about you qualifications and some fairly simple reminders about things like flat roofs shouldn't be flat, etc. If you know how to come here, try Googling 'space frame' or look in a few general Structural Engineering text books, so you come here well prepared with some basic understanding of your problem. You must admit that some of us will be a bit leery about engineering qualifications when an OP'er. says they are charged with designing a 150' dia. space frame, what should I do, and their first follow up question is 'what's a space frame?'
There should be no shame in asking an intelligent question, and if you give us an indication of your background and level of experience we will even adjust the definition of 'intelligent question' to fit your background. But, don't pull our legs by pretending to be someone you are not, or by pretending to be doing a design you have no business tackling for lack of engineering knowledge or experience, and/or without some real serious local supervision. It's a little like asking a butcher to do open heart surgery because he's used a sharp knife before.
RE: 150 feet span roof
May not meet the 5' max dept of a truss, though.
Using full length parallel trusses would spread the fdn loads out more evenly and by fiddling with the spacing of the trusses one might get a truss with max depth of 5' to work.
A space frame, in my opinion, could be quite costly. If cost is not an issue and esthetics is of more importance, then by all means, look into a space frame.
RE: 150 feet span roof
Dik, I think you are from canada.Is that right. which city are you in?
RE: 150 feet span roof
As noted earlier... the solution isn't elegant and if to be exposed, a space frame looks a lot prettier...
Dik
RE: 150 feet span roof
RE: 150 feet span roof
A conical shape may be something to consider using radial members, a compression ring in the middle and a tension ring on the perimeter.
BA
RE: 150 feet span roof
RE: 150 feet span roof
RE: 150 feet span roof
BA
RE: 150 feet span roof
RE: 150 feet span roof
RE: 150 feet span roof
Where did you grow up? I grew up 20mi. north of Spooner and about 25mi. west of Hayward in the little berg of Minong. I think you are pulling my leg a bit about 5' snow drifts, at least as a common event, unless you grew up in Hurley. Although they will stand with a vert. face when you cut them with a snow shovel, so they couldn't have induced much lateral loading. In fact, they would melt away from a heated building in a few days if you didn't remove them. I do remember going out the back door a few times to get at a snow drift which had blocked the out swinging storm/screen door which we usually used.
Sorry for highjacking this thread for a moment.
RE: 150 feet span roof
a2mfk hasn't grown up yet. He's a Seminole.
RE: 150 feet span roof
But I just wanted to know some technical guidelines if available.
RE: 150 feet span roof
BA
RE: 150 feet span roof
Here is the La Villita Assembly Hall in San Antonio, Texas (see attached photo).
This was a circular, cable roof assembly (not flat - a natural ponding concern!!) that was constructed of an outside compression ring and an inside tension ring, radial cables were pre-tensioned by pulling down on the interior tension ring, stretching the cables. Then concrete precast planks were placed on the cables. The tension ring was released, placing the concrete in compression, which held the concave shape you see in the photo.
This was "imagineering" at its best. But I tell you, if you are in the position to design something like this based on a Google search, please tell me where this building will be constructed (I like to avoid pitfalls).
RE: 150 feet span roof
this roof has a downward slope so good candidate for ponding in my opinion. so I will avoid this approach. And do not worry, the design of this roof will be ok.If I do not feel comfortable, I will hire someone.
RE: 150 feet span roof
htt
RE: 150 feet span roof
RE: 150 feet span roof
BA
RE: 150 feet span roof
Dgkhan.... Wake up, this is serious business, not likely learned from an internet link or a twitter from a twit you don't even know or who may have no more experience than you do on the matter. You have gotten some good advice and suggestions, now get a life, get some experience on this kind of structure under the guidance of someone who knows what he/she is doing, because you obviously don't. Right now you and your thinking are dangerous, wherever you are.
RE: 150 feet span roof
If you are still considering designing a spaceframe on your own, I suggest you read up on the collapse of the Hartford Civic Center in 1978. Better to know what not to do before you start learning what to do. But for a 150' circular roof, a proprietary system would be my choice. It's just a commodity item. By the way, the Hartford Center is discussed in Levy and Salvadori's book "Why Buildings Fall Down". You will find several of the other systems suggested above there as well.
RE: 150 feet span roof
my decade old teachers at Princeton, NJ if they are still there.
To all of you who have spend time in writing mocking comments, you can clearly read in my post that I will hire someone for help if I could not do it. Anybody interested and confident that she/he can do it multiply it's salary x 2 and I can hire.As a head of my company I also like to learn as mush as I can which created so much ado.
RE: 150 feet span roof
And read this article, you may have a serious case of the Dunning-Kruger effect going on right now.
RE: 150 feet span roof
What is sad and scary is that the OP is probably some offshore engineer doing outsourced work for North American projects.
dhengr – I just promoted you to a 5-star general and a2mfk to a 4-star.
RE: 150 feet span roof
Not right. Just because some person is named "khan", you should not assume that he is an offshore engineer doing outsourced work.
RE: 150 feet span roof
Not right. You're the one on the wrong here for assuming I did.
I'm not that stupid to base my hunch on an online handle.
I was curious that someone didn't know what a space frame is and yet is attempting to design a 150 ft. diameter roof. So I actually looked at some of his previous posts that led me to believe that he is one of those engineers.
RE: 150 feet span roof
There are competent engineers in all parts of the world. I do understand what you are trying to imply by "sad and scary" when it comes to work being outsourced. A lot can get lost in translation. Let's hope its not one of those cases.
RE: 150 feet span roof
BA