I'm getting ready to break ground on a 40 x 60 stick built garage. I would like to put a mezzanine along the 40 foot span. Along this wall will be several rooms roughly eight foot deep and I plan to use this as a load-bearing wall for the mezzanine. I would like to come out an additional 8 ft and somewhat of a modified cantilever setup. Basically I would like to build a 16 by 40 mezzanine with a load-bearing wall 8-foot out I don't want to have any post in my for so my idea is the ad extra trusses and supports in the wall and then runs Port cables up to the upper runs of the trusses not the lower cross sections I need help with the math of how wait the extra trusses can bear so I can determine how many I need right now I'm thinking too so at the end of my 16 foot span my 40 foot truss there will be three trusses total sandwich together with support cables running up to to them
Suspended mezzanine
- Thread starter Jking24
- Start date
firebirdparts
Well-known member
That is relatively simple to do. For example you might design based on 40 pounds per square foot. If it was me, I would use 16 foot long joists, so that the "real" load is actually balanced on the wall (walls are strong). But the conservative design for the overhead would be to ignore that, and design the 8 foot span to just hold itself. So the weight on the truss would be perfectly distributed and you'd have just 4 feet x 40 pounds on each foot of truss (160 pounds on each foot of truss). The total weight as you can see is 160 x 40 = 6400 pounds. that's not huge.
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rburke65
Well-known member
You could also stop at your local truss mfg......not so much at Lowe's or HD......a truss mfg.
Sorry I'm on my phone auto correct really botched that. I am planning on running extra studs up the wall to support extra trusses and either sandwiching three trusses together or reinforcing two with a 2x8 or somthing along those lines to crest a stronger truss in this area at the end of the cantilevered section of the mezzanine. Then running support cables to the upper runs of the truss so the weight is distributed down the truss to the wall. So not really cantilevered at all but supported from above verses say three post along the span to the floor. The use for this space will be storage and recreational use(man cave ) of sorts
cvairwerks
Well-known member
Time for consulting a structural engineer. Truss design takes this all into account. Just adding a suspension cable with an extra board simply moves the static and dynamic loading and has a high possibility of inducing failure. Doubling or tripling up on trusses is a sure way to spend lots of extra money without knowing if the structure is capable of handing the load or not.
Depending on where you are located, you will most likely need stamped plans anyway, so it will have to go through a structures guy to get the stamp.
Depending on where you are located, you will most likely need stamped plans anyway, so it will have to go through a structures guy to get the stamp.
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This is beyond hammer mechanics. Call your truss mfg and give them the loads. If you have not broke ground yet, hopefully they have not built your truss. If they have, they can reinforce them as required. Why **** this up from the get go when you have not even built anything yet??
matt_i
Well-known member
Just to add what the others are saying, the truss isn't designed for concentrated loads, its designed for distributed loads. Running a steel cable is going to cause a concentrated point or line loading.
If you sized an I beam for the point loads, the I-beam would sit atop the walls with sized columns columns and a design for shear in the direction of the wall plane plus the plane thru the columns and the beam, you'd be all set to start running the cables.........as soon as you design the connections to the I-beam.
A couple of posts, while unideal for the layout below, is far easier and cheaper in the long-run...
If you sized an I beam for the point loads, the I-beam would sit atop the walls with sized columns columns and a design for shear in the direction of the wall plane plus the plane thru the columns and the beam, you'd be all set to start running the cables.........as soon as you design the connections to the I-beam.
A couple of posts, while unideal for the layout below, is far easier and cheaper in the long-run...
James-W
Well-known member
I agree 100 percent. The time to get this whole thing taken care of is now before the project starts.
ThankYou to those of you who gave constructive and informative responses. Clearly i haven't "fucked" up anything yet because they generally don't build your trusses until you tell them how many you want. That is not what i came here for. I haven't chosen who will supply the lumber package yet so i don't have direct contact with the truss manufacture at this time. The plans for the base building habe already been approved. This was left out because in my area any space that could be considered "liveable" sends you down a whole other rabbit hole. I don't know any structural engineers witch is why i came here with the idea. Trusses are cheap in comparison to a 40ft steel beam. I thought this might be a feasible plan considering i Am not trying to add to much I regards to overall length than what is normally considered acceptable to cantilever. From what i have been told in the past if you had a 8 ft span you cantilever 4ft. Safley. And if i made the load bearing wall at 10ft i could nearly cantilever the whole thing. I understand that the trusses original design was not designed with this in mind. But their is a concentrated load that a given truss could handle and if that number were to fit my needs i would happily pay a few hundred dollars vs a few thousand dollars for a beam
mike93lx
ALLIANCE MEMBER
So you came here for advice, but won't listen to it...
This is easy. Call an engineer. No one here can design your building based on a couple posts online.
This is easy. Call an engineer. No one here can design your building based on a couple posts online.
sberry
Banned
bczygan
Well-known member
Do you want the mezzanine to be open to the main floor (Except for the cables)?
The easiest way to do this is a 40' beam supporting the end of the mezzanine.
I haven't done the calcs or checked the tables, but in an LVL, it could end up a fairly deep section with a number of plys. If you could stand one column in the middle, it would reduce that. Steel for the beam would also reduce the depth.
If you don't mind blocking off some of the mezzanine opening to the main floor, a girder truss extending down to the floor of the mezzanine might be the cheapest answer. Run the numbers on each option.
Commercial lumber yards should be able to size the LVL's and price a girder truss for you. Steel suppliers for the steel beam.
Bill (Designer)
BTW, the rule of thumb is cantilever 1/3 of span.
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uncletater
Well-known member
Simple answer is no you cannot go out 8 feet without it having bounce cables or not.
normally the rule for cantilever is one out 3 in. 8 8'out would be 24 in. Think back to elementary school your load bearing wall is your fulcrum.
Just get an engineer involved pay the simple money and do it right. the inspector will thank you for it.
And don't get your ******* in a wad if people on here don't give you the answer you want.
normally the rule for cantilever is one out 3 in. 8 8'out would be 24 in. Think back to elementary school your load bearing wall is your fulcrum.
Just get an engineer involved pay the simple money and do it right. the inspector will thank you for it.
And don't get your ******* in a wad if people on here don't give you the answer you want.
Thankyou bill
I misunderstood when the cantilever rule was explained to me. The mezzanine does not have to be open to the main floor at all. I've looked into lvl's but as you stated it would have to be very tall and my overall height is a issue so that option is out. The idea for the mezzanine came after the plans for the garage were submitted and approved. For this reason and as i mentioned before any space deemed liveable in my area becomes a nightmare to get approved. Basically in my county they don't want any living spaces above garages period. The mezzanine will not be built until after the final is done. This is where adding or reinforcing trusses came into mind. The steel beam is not out of the question. With my lbw set at 8ft what size beam would i need to support the additional 8ft?
What you described is pretty much what i had in mind. Just figuring the most cost effective way to support that 6400lbs
The girder truss is also a good option i am not familiar with them though. I'm not quite sure i understand how your suggesting to install it could you elaborate?
Whats the justification for 4 trusses sistered? How do you distribute the load to all 4 trusses without a local failure (pull out, shear failure) at the connection point?
Buying 4 trusses is "spending money", without any proof it will work. Buying engineering is proof it will work, and could save money in the build. I can guarantee when he goes to sell, a competent home inspector will raise a red flag when structure is supported by cables to a truss. hence having the paper work from an engineer in said file cabinet.
Its all risk vs reward. Thats all engineering is, mitigating risk, and economizing construction.
I assume half of the 8 foot span of the mezzanine is supported by the wall, leaving to other half to be hung from the trusses. This is true if we run a saw through the joists right along the wall, which is not the case, so I have a little headroom here. I further assume the trusses holding up the roof are designed to do what they do, so not asking for any more load. My next assumption is to make the floor in the mezzanine as strong as the roof - 40 psf or whatever. So, how many trusses hold up 8 feet of roof? Three? Plus the one thats already there; four. The OP can make his own assumptions, but that my thought process.
Come to think of it, I wouldn't use cables for this. 16D or 20D nail pattern, glue, and some nice plywood sheer panels to hold the sistered trusses on plane.
Cmcgarage you make valid points but your other remarks are unnecessary. Nobody said anything about buying trusses and guessing weather or not they will hold. As far as distributing the shear load. I have virtually unlimited access to metal within reason from my work and i was thinking i could plate the trusses redistribute the load as needed where the cables mount. I understand the trusses are not originally designed for this use but with some cheap modifications i feel like they may be up to the task. If their not i won't do it. But it's gonna take more than telling me to just hire a engineer to do this. I can not afford to hire a engineer for a idea. I'm not be being stubborn here. I value all information and opinions but i dont need to be bashed for asking a few questions. Feel free to explain why this could never ever possibly work I'm all ears . My trusses are roughly 160$ each not allot of cosy to add if it will work
I'd be interested in your assessment. Please understand I appreciate what structural engineers do, with wind loads, earthquakes, soil strengths and dynamic behavior, etc. I would never take on a clean sheet design of a large retaining wall or an entire structure....But, once it's there I think I can enlarge a window, move a wall, hang a hoist...I probably have an above average understanding of beams, columns, load paths, shear walls and so forth. Dunno, I might have wrong thoughts, but at least they're orderly.
In your very first post..." so my idea is the ad extra trusses and supports"
Im not sure how you are not guessing they will hold if you dont do a design. If you feel they might be up to it, then lets hope they are too.
You are asking what we think, and we have told you.
I have given my reason why I think its a bad Idea, you are putting a concentrated load onto a member that is not designed for it. Plain and simple.
Designing a building isnt just guess work. Most buildings fail at connections, not at main members.
Lets hope it all works out and nothing ever happens. Just dont sign up onto here and expect everyone to do everything for you.
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If it was a simple check of a point load on a known member, we could bless it and move on. He wants to point load a truss, usually a indeterminate structure that are usually designed for the load and not much more. Adding a couple more trusses probably will be fine, but also the connections are issues. Most building failures are due to connection issues.
Most time I gloss over stuff folks do on here. What I see him wanting to do has a bigger chance of a failure.
dfiler2
Well-known member
You mentioned you didn't want to lose headroom in the shop area with an over sized LVL, that beam would not need to hang down, it would work as well to put the extra up and use joist hangers for the floor joists.
ard
Well-known member
My thought as well- basically the top of the LVL could be 'inside' a pony wall that defines the end of the mezzanine.
But I lost interest in helping this OP.....
It would be a huge LVL, due to deflection. but could stick it up as the edge of the mezz. Need a small forklift too to install!
Point loading a truss is likely to be a challenge. Sistering several trusses and adding shear panels might be a better solution, which is what I suggested. I would use Simpson joist changers for the floor joists. They make several hangers with long tails for crawling up a shear panel.
Why do we always devolve into "this is so complicated you can't do it" instead of helping a guy? It's not that complicated. I know, you're going to say it IS that complicated...
Point loading a truss is likely to be a challenge. Sistering several trusses and adding shear panels might be a better solution, which is what I suggested. I would use Simpson joist changers for the floor joists. They make several hangers with long tails for crawling up a shear panel.
Why do we always devolve into "this is so complicated you can't do it" instead of helping a guy? It's not that complicated. I know, you're going to say it IS that complicated...
Im not here to do designs for folks. We (engineers) will sometimes check what folks are doing, and make suggestions. The OP didnt want any of that because he wants to get around the Building department and build this mezzanine illegally.
The OP even admits that there is some concentrated load the truss will handle, Just ask them what it is, or give them the loads you are going to put on the truss.
I suggested giving the truss designer the load, let them design the truss for the load, or give a modification for the truss. OP doesnt want any part of that.
Others have suggested a beam, or girder truss. All good options.
You suggested a few more trusses, the math seems to work, but again, trusses are not set items that numbers can easily be put to. How many connections do you need? How many shear panels do you need, what thickness of shear panels, what connections do you need for the shear panels?
You could have 20 trusses there, but if the connection fails, then those 20 trusses do you no good. OP suggested he has plenty of steel, again, great but we are not going to design it for you.
When if comes to engineering, you dont know what you dont know.
If he is buying 30+ trusses, for one or two to be beefed up is easy, just tell them the loads. they will engineer it for him.
I dont know why its out of the question to do this?
I ran some truss designs, for cables @ 10' o.c. you would need 1/4" thick plate 2/3 of the height of the truss. The connections would need to be 3/8" dia, min of 12" spacing.
What size metal can you get from work? 1/4" thick available?
EDIT - I based my design on a double howe truss type. if your supplier does it different, the fix might change.
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lakeroadster
Well-known member
If you refuse to get the mezzanine addition engineered and stamped by a P.E. you need to abandon your idea of supporting it from the trusses and handle all loads from the walls below.
Even if you talk to the truss manufacturer, you'll need to tell them that this isn't a typical engineered truss with a floor attached to the lower chord. You are talking about point loads on the lower chord, a drastically different design than a load spread across the entire lower chord.
You have already begun with the permitted build, when you go to sell your place sometime down the road and the drawings on file are pulled they will see the trusses weren't designed for the application they are being used for, and you'll be in the middle of a huge mess.
Folks that tell you otherwise aren't looking out for your best interest.
Even if you talk to the truss manufacturer, you'll need to tell them that this isn't a typical engineered truss with a floor attached to the lower chord. You are talking about point loads on the lower chord, a drastically different design than a load spread across the entire lower chord.
You have already begun with the permitted build, when you go to sell your place sometime down the road and the drawings on file are pulled they will see the trusses weren't designed for the application they are being used for, and you'll be in the middle of a huge mess.
Folks that tell you otherwise aren't looking out for your best interest.
See above, suggested all this, but wants no part of it. Now just trying to get him to do something safe.
LX-Markham
Well-known member
This is at the heart of the problem.
This is not an engineering difficulty. The truss simply needs to be designed for the loads it is going to carry. Simple. We have designed tons of roof supported floor structures.
Building an illegal mezzanine and broadcasting it on the internet.... not so simple.
lakeroadster
Well-known member
Yeah.. I know. I was backing your play, well, part of it anyway.
Since you don't know his location, environmentals loading, roof pitch, roof type, mezzanine weight and design, etc. I'm not sure why you would walk out on a limb and start recommending plate thicknesses, cable sizes and spacing, etc.
Watch your six.
I have seen the 40psf number thrown out there a bit, and the OP didn't say that was wrong. Either way, my design is pretty conservative. I didn't recommend a cable size, or a connection to the trusses. Hopefully the OP has that squared away.
Also assumed a truss type, so pretty moot point, it could be totally different when he orders them.
I doubt 1/4 plate across a 40' truss will be any cheaper than giving the load to the truss guy and having them beef it up.
But, we are here to help, not just tell them to get it engineered.
sberry
Banned
I agree putting a concentrated load on the truss is a bad idea, not that it couldn't be done but it gets expensive. Personally would likely sister the bottom chord to get the thickness, cantilever the bottom to a simple beam on the end and then sheet it from there to the chord over a stud wall.
Essentially this.
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Yes 1/4" plate is available. Alot of words seem to be getting put in my mouth i never once said or gave any indication that I had no interest in speaking with the truss manufacturer I said I have not chosen who I'm purchasing my lumber package from yet as a result I don't have a truss manufacturer to speak to yet. I said from the beginning I was looking for information on how to calculate what a trust could handle I am not looking for anybody to design anything for me I asked for help with math. I understand Point loads and the design of the truss I clearly don't do this everyday. But I'm continually getting blasted on here for asking a question and not accepting because you just can't as an answer. Just because it's not getting designed and stamped by an engineer doesn't mean that it can't be designed and built correctly. I have my reasons why it's not going to get an inspection and they are not going to change. I apologize for the delayed replies I have a very hectic work schedule and sometimes forget to check back on things for a day or two or more at a time you said from the beginning to contact my truss manufacturer and give them my point loads those loads are in fact what I was trying to get help with calculating. This is basically a feasibility study to figure what the necessary modifications and the amount of trusses to do my idea versus the cost of the modified truss from the manufacturer which is to be determined.
Start with getting your truss purchased. If they wont design it for you, come back with the standard design and we can check it out.
Or make sure they provide a double howe truss and steel plate it both sides as suggested.
Thankyou cmc and you are correct about the snow loads.i am right on the line where they move from 25 psf to 35 psf in my area but i am technically below the line. Despite the many criticisms here about my idea. I let that 40 psf ride because a. I figured it allowed for a greater safety margin witch many have stated i clearly don't care about . B. i don't claim to be a very educated person but I'm smart enough to figure out how somebody came to a given number. I will be deciding on the vendor for my lumber this weekend so after that i will be able to speak with the truss company. From the looks of your calcs those numbers are for running 3 cables across the span and using just one reinforced truss ? I only asked to get a better understanding because 1/4" plate 3" tall is pretty hefty .