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Old 11-12-2012, 10:45 AM
fourtheboys96 fourtheboys96 is offline
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Default Size of angle bar for roof trusses


I am planning a project to install a roof DIY in a small area in my mother's house.
The area is quite small (around 15'x15') and serves as a garage/driveway.

A mono truss is the best and the simplest IMO. The truss would be installed along a wall on one end and supported by two existing concrete columns (part of the gate and fence structure).

From a safety point of view, what size of angle bars should I use?
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Old 11-12-2012, 03:27 PM
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Default Re: Size of angle bar for roof trusses

HI fourtheboys96,

Is this related to the other thread that you were asking regarding the concrete slabs, just curious here. Anyway 15' is quite long for an angle bar to be used as your roofing trusses, probably a 3" X 3" X 1/4 inch thick, but hope you attach or weld some support to each other so that it will not sag. Another option for your trusses will be the use of 2" X 4" tubular with 1.5mm thickness, for sure this till be more sturdy provided they are all secured on both ends then use 2" X 2" X 1/4 inch thick as your purlins across to receive the galvanized roofing. Then you can secure your galvanized roof with Hex screws to the angle bars.




HOPE this HELPS !!!
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Old 11-13-2012, 07:28 AM
fourtheboys96 fourtheboys96 is offline
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Default Re: Size of angle bar for roof trusses

Quote:
Originally Posted by rosy View Post
HI fourtheboys96,

Is this related to the other thread that you were asking regarding the concrete slabs, just curious here. Anyway 15' is quite long for an angle bar to be used as your roofing trusses, probably a 3" X 3" X 1/4 inch thick, but hope you attach or weld some support to each other so that it will not sag. Another option for your trusses will be the use of 2" X 4" tubular with 1.5mm thickness, for sure this till be more sturdy provided they are all secured on both ends then use 2" X 2" X 1/4 inch thick as your purlins across to receive the galvanized roofing. Then you can secure your galvanized roof with Hex screws to the angle bars.


HOPE this HELPS !!!
hahaha. It is indirectly related. The concrete slabs will be installed near the apartment where my wife and I live.
This roof project is for my mother's (our ancestral) house. But both projects were as a result of an additional vehicle from my side. I will be lending our old car to my mother and I said it should have at least a roof.

Maybe an angle bar is not sufficient to support the load.
What do you call the steel bar that looks like two angle bars welded together (shaped like a T)?
Maybe I can use this instead of a tubular steel.
Anyway the truss will not support a load except for the weight of a few GI roof and the material itself.
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Old 11-13-2012, 10:59 AM
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Default Re: Size of angle bar for roof trusses

Hey bro fourtheboys96,

That bar you are asking about is called a T-bar and usually used for the fabrication of steel casement windows. May I suggest that you don't use that for your trusses, not strong or sturdy enough, lulundo rin yan. It seems for your plan you are trying to minimize expenses as much as possible in materials.

I will not stop you from doing so, that's your project but bear in mind I am giving you already proper tips on material to use. If you do not like using the rectangular tubings, there is another option to that, you can buy several pieces of GI pipes, 1/2" X 20' and fabricate your own trusses, it will be more fun too. Just cut pieces of pipes of about 6" or 8" in length then weld them to two parallel GI pipes in a diagonal positions. I guess this will be strong enough to carry the total weight of the angle bar purlins and the corrugated galvanized roofing.

-----------------------------------------------------

ANOTHER OPTION HERE:
Bili ka na lang ng 2 piraso ng kawayan, then cut it to your required length size for your trusses, napaka mura lang ng kawayan, Php140 to Php180 per whole piece.

Last edited by rosy; 11-13-2012 at 11:13 AM.
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Old 11-13-2012, 02:42 PM
fourtheboys96 fourtheboys96 is offline
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Default Re: Size of angle bar for roof trusses

Yeah I'm trying to minimize cost but my main priority is safety of the structure without overdoing it.
I'm not doubting your suggestion. It's just that a lot of metal trusses I've seen including the one in our current parking area didn't use tubular steel, only T-bar or angle bars.

Anyway, maybe we have a bit of misunderstanding.
I plan to make a mono truss which has a bottom chord and top chord (looks like a right triangle) and a webbing in the middle. So the its design itself makes it sturdy.

Maybe if I'm just going to hang the long metal materials as is, then I'll go for the tubular type material.
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Old 11-13-2012, 05:28 PM
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Default Re: Size of angle bar for roof trusses

hehehe, some misundestanding ?, may be yes, may be no, I don not know! but for sure I do understand you in trying as much as possible to minimize unwanted expenses on the future plan/project. Siguro bro di lang tayo nag kakasalubong ng iniisip na plano ng magiging construction. If you have seen in other private parking spaces using angle bars as its trusses on its roofing and you find it sturdy enough, then just go ahead with your plan, follow that, at least may pattern ka na na masusundan.
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Old 11-14-2012, 04:52 AM
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horge horge is offline
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Default Re: Size of angle bar for roof trusses

15' x 15' is not 'quite small', in that it implicates a considerable 4.6m span.
You furthermore seem to be talking about just a single truss to support the
roof purlins @ midspan, the purlin-ends supported by CHB wall, and it's not
clear to me that your preexisting concrete columns are strong enough to
support your truss.

Quote:
Anyway the truss will not support a load except for the weight of a few GI roof and the material itself.
It will also support the additional dead load of purlins, plus occasional live loads
(someone has to go up and install/paint/repair the roof, lol), and wind loads...
and if you start hanging crap from it, like a ceiling and its joists, electricals and
(God forbid) a chain hoist ... it starts to add up substantially.

Anyway: assuming a typical pitch of 25-ish degrees, you might get away with
50x50x6mm MS for your chords. 75x75x6mm might be a better choice, and
any more might cross the line into overdesign-heaviness. Webbing section size
will depend on what web configuration you choose. So will sizing your gusset
plates: the fewer the webs, the lighter the truss, but the more-critical your
weld connections. The broader your gussets, the longer the welds and the
stronger your truss connections will be. Weld-quality is pretty important.

What is also often overlooked is how critical your bearing points will be.
Again, assuming your collumns are fit to support the truss, the best case is
to use horizontally-oriented MS bearing plates, positioned flat on top of the
aforementioned RC columns, and secured conventionally with rod or bolt
anchors. Far less desirable is the use of steel dowels embedded along a
vertical surface: those dowels will have to resist the shear load of the entire
weight of the roof, purlins, truss, plus the aforementioned crap to be hung
from it AND any wind loads.

You may want to crossbrace the truss at midspan with 10mm threaded rod
and turnbuckles, anchored to the walls on either side of the truss: I am just
playing safe here, as I have zero idea what the wind/seismic conditions are
where you're building this thing.

tl;dr:

Get a CE/SE graduate to design your truss for you.
I know several licensed CE's (and one SE) who've given me more complex
designs, for as little as a beer and a cheese sammich. Then again, they get
a lot of paid work from me.

Last edited by horge; 11-14-2012 at 05:10 AM.
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Old 11-14-2012, 11:12 AM
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Default Re: Size of angle bar for roof trusses

@ fourtheboys96,

hahaha, consider this advice from one of our reliable architects here in the forum !!!!!

Thanks bro horge, very well explained.
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Old 11-15-2012, 06:54 PM
fourtheboys96 fourtheboys96 is offline
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Default Re: Size of angle bar for roof trusses

Thanks a lot for your suggestion. although some of the terminologies not familiar to me, I can get a clearer picture now.

I'll try post some pics with actual measurements to get an accurate suggestion.

I'll see if I can ask some CE here in the university where I work.
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Old 11-22-2012, 07:41 PM
fourtheboys96 fourtheboys96 is offline
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Default Re: Size of angle bar for roof trusses

Hi! I did not have a chance to ask some engineers but I did have time to google.

But first, the exact dimension of the driveway I plan to have a roof is 4.10m x 3.20m (13.5'x10.5'). The span of the mono truss I am thinking of building is 4.10m.

This is the truss I am planning to make

http://www.nzdl.org/gsdlmod?e=d-0000...d3f516df.7.8.6

The shortest span of the truss in this book which uses angle bars is 6m which longer than what I am planning to make. Now I am a bit confident that angle bars can be used as a material for roof truss as long as there is enough webbing to support the compression and the tension load.

I am just figuring out the appropriate size of the angle bar.
I read in a blog of someone building a house somewhere in Panay (I know not the most scientifically source of info), angle bar of size 2"x2" 5mm thick was used for top and bottom chord and 2"x2" 3mm thick for webbing.
(He used a 2"x6" C purlins)

I assume I will use a smaller size angle bar than this.

I am considering only the dead load, wind load, and occasional rain.
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