Trusses

Page 1 of 2  
question on trusses. contractor is building a stand-alone garage 24'x30'. 2nd floor is for storage. he's using 2x8 lumber for the floor joists, mated in the middle with a gusset plate.
is this sufficient for bearing weight on the 2nd floor for storage? some reason I thought wood-composite i-beams were better. he said the gusset-type should be fine.
yes? no? opinions?
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On 17 May 2007 18:18:17 -0700, snipped-for-privacy@gmail.com wrote:

They would be ok, but I would go with the TGI beams.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
I think you have a reason to be concerned. Search the internet using google. I think you will find many stories of gusset plate failures when used in floors. Ok for roofs but I would never have a floor built that way. One story I read a while back was a condo that they had to rip out ceilings and sister every truss with a solid beam. It is going back a few years but if I remember correctly the original manufacturer who had invented the system had misrepresented strength and engineers had been relying on those numbers when designing floors.

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

is the 2x8 part of an attic truss? if so, then they would be engineered and will be fine. I joists might support more load, but I assume the project has some budget---I joists would require second floor framing or perhaps a hand framed roof, all more expensive.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Hopefully, because it is a truss, there are some support members such as vertical framing to form walls that would add strength to 24 feet of 2 x 8s with a joint in the middle. Otherwise I would be concerned with its usability for storage.

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
snipped-for-privacy@gmail.com wrote:

A couple of things don't seem quite right here: there are commercial trusses stacked up in the yards at all the box stores and lumber yards and I have (so far) never seen any up to 30' or so with a bottom chord bigger than a 2 x 4. Seems to me that a 2 x 8 is a huge overkill. You're not going to be storing a dozen or so Chevy 350 crate engines up there, are you? Truss chord mambers are often (maybe usually) mated with 'nailing plates' at junctions with other truss bracing elements. If your contractor is building his own trusses, better back off and order the proper engineered and factory built types. If he doesn't have a properly architect-designed system it may not pass your local building inspector. HTH
Joe
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Joe wrote:

Standard roof trusses are designed to carry weight on the *roof*, not on the bottom truss members.
Unless specifically engineered for it, the bottom truss members will only be designed to handle the weight of the ceiling and insulation, with enough extra to let people walk around up in the attic safely.
Chris
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
snipped-for-privacy@gmail.com ( snipped-for-privacy@gmail.com) says...

As long as there is a bearing wall or heavy beam under the joists where they meet in the middle, it will be fine. Otherwise, forget it.
Let me guess: either you live in some backwoods community with no building codes, or you are trying to bootleg a building in without a permit. What you are describing would never pass a structural plan check or inspection.
Do a quick structural calc. Suppose you want to load just the center 12' of the upstairs with something fairly heavy, say 100 psf. If the joists are 16" on center, that means each joist has to support 1560 lbs, plus the weight of the lumber and decking. Divide by 2 (two joists) times 12' of lever arm, divided by 2/3 of a foot (8 inch joist) gives 14,040 lbs. of tension on the bottom edge of that gusset plate. Now how do you think it's going to work?
--
For email, replace firstnamelastinitial
with my first name and last initial.
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Joists or trusses? Your confusion alone is worrisome.
You want engineered floor trusses for that span and load. Not joists assembled by the contractor.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
| question on trusses. contractor is building a stand-alone garage | 24'x30'. 2nd floor is for storage. he's using 2x8 lumber for the floor | joists, mated in the middle with a gusset plate. | | is this sufficient for bearing weight on the 2nd floor for storage? | some reason I thought wood-composite i-beams were better. he said the | gusset-type should be fine. | | yes? no? opinions? |
rip it out and do it the right way. floors can NOT have splices or nailers in them. 24 ft span...........2x8......................under sized for storage. TJI's would work best......................1 piece.............no joints.
or add a strong back to the top of the spliced joists.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

With a perfect splice, S = bd^2/6 = 1.5x7.25^2/6 = 13.1 in^3 and M = fS = 13100 in-lb and W = 8M/L = 8x13100/(12x24) = 365 pounds of total load, ie 15.2 pounds per linear foot or 11.4 psf on 16" centers, if I did that right.
So maybe we need more than a perfect splice, eg a kingpost or a truss or a wall under the middle.
Nick
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On 17 May 2007 18:18:17 -0700, snipped-for-privacy@gmail.com wrote:

I'm a bit confused. You say question about trusses but I don't think you are describing trusses? To me, you are describing a 24' long 2x8 spliced in the center of the span, right? Also, are you building a 2 story garage so there is a floor at the 2nd story or is it just a normal garage where the ceiling chords are going to be used for storage above?
Assuming a 2 story garage with a long 2x8 with a splice in the middle of the span and NO support in the middle (like a column or beam) you do NOT want this. Not only will it not support a FLOOR load but it will also DEFLECT too much. And if these members are only ceiling chords as in a normal garage, I'd still want no splices and at least 2x10 members.
Please do yourself a favor and hire an engineer or architect for adequate member sizes. It sounds to me like the contractor is not good or is trying to keep the cost very low by building a subquality garage. Over the years you will be sorry about this garage.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On May 18, 6:22 am, under construction <> wrote:

There are a lot of people posting on this thread that have never seen a set of attic trusses. If your contractor is using attic roof trusses, they commonly come with spliced 2x8's for bottom chords. These will be engineered and gauranteed for a certain load. They do come with some caveats--usually the specs call for no holes and of course no alterations. I have installed many sets of these. Again, they do have splice plates. I have used them in houses as well as garage storage areas. Trusses usually come with a packet that will spell out the assumed loads--your contractor should have that. It does not mean that your contractor is not good. Floor joist can have splices. You do not have to rip it out and do it the right way. What you are doing would indeed pass inspection.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Here is a drawing of an attic truss. Note the splice plate in the bottom chord. http://service.govdelivery.com/docs/STPAUL/STPAUL_DeptLIEP/STPAUL_249/STPAUL_249_20051014_en.pdf
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

First of all, your diagram (other post) is NOT a "floor joist" but rather a chord member for a truss. That said, floor joists should not have splices especially in the middle (in commercial structures they use drop in beams). The reason your chord member (in your diagram) has a splice in the middle is that it is a tension member. If you are going to help at least give correct advice.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On May 18, 9:24 am, under construction <> wrote:

Here is a link for the engineering of an attic truss. Note the splice in the bottom chord. Note the bottom chord loading of 40 psf. http://www.wsitruss.com/Prod_Frame.asp?Truss 48. Why would you use an attic truss if you couldn't use the space created for a room?
The OP used the term "floor joist", but I suspect that he is looking at the bottom chord of an attic truss. He needs to clarify this. Since most attic trusses will have a spliced bottom chord, I suspect that is what he has, and his contractor hasn't given him a very good answer.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Just to clarify, I agree that bottom chords can have bending between panel points if engineered accordingly but generally they are tension members. Notice tho even as in floor joists, the splice is not in the middle to avoid maximum stresses.
I agree w/ your 2nd paragraph.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
under construction wrote:
> Notice tho even as in floor joists, the splice is not in > the middle to avoid maximum stresses.
Actually, take a look at truss A288 at the same site. The splice is dead-center.
Chris
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Fri, 18 May 2007 10:21:54 -0600, Chris Friesen

I'll take your word on that but generally it's not good practice to do that but that doesn't mean it can't be done. It generally means heavy plates and more nails to carry the additional stresses.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Fri, 18 May 2007 11:54:13 -0500, under construction <> wrote:

I meant to say not heavy plates but "thicker" plates. My bad.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Related Threads

    HomeOwnersHub.com is a website for homeowners and building and maintenance pros. It is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.