# Structural Engineering



## GLENNpm (Dec 15, 2018)

I recently built a lumber storage rack in my garage that I can back my truck up under - at least that's the goal. I just finished it and loaded it up and now I'm really scared it won't hold up. I did some calculations before I started and thought I over-engineered it, but now I'm afraid not. it looks like there is just the slightest bow on the x-axis. So, I need some structural engineering advice. I've included pics, but this is what I have:

- material: pine from Home Depot
- 4 10 ft 2×6's and 7 10 ft 2×4's in the x-axis
- 7 10 ft 2×6's in the z-axis
- each side has 2 2×6's screwed together laying directly on top of 4×4 posts that are anchored into the slab floor.
- the 2×6's along each wall are also screwed into the studs on that wall.
- every joint is half-lapped and supported by joist hangers on both sides.
- 1/2" grooves along the top of each board to increase airflow and minimize surface contact area to help with sticker stain.
- The current load is around 5300 lbs. And as you can see, there's room to add more.

Any advice to make sure it's super stable would be greatly appreciated. I really don't want it crashing down on me or my truck/tools one day. I'm starting to stress out about it.

I think the biggest issue is the 10 ft gap along the front side of the x-axis. I don't want a post there, though, because that defeats the purpose of being able to pull my truck under it.

My current idea is to buy 2 more 4×4 posts to support 2 2×12's screwed into the front face of the x-axis The only think I don't like about that is the current height is the minimum to allow me to walk under it without ducking. The 2×12's would lower that part 6 inches and require ducking and, likely, head bonking. But I'd rather that than for it to all crash down.


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## GLENNpm (Dec 15, 2018)

Update:

I got too nervous, ran home on my lunch break, and wedged these 2×4'x under it for a temporary fix until I can get a permanent solution. It was definitely sagging. the 2×4's are cut to the same length as the 4×4's and it took quite a bit of hammering to get them wedged up under there. It looks straighter now too. Please forgive the mess in the pics. This is part of my organizational process to fix the mess. 










Also, I'm not so sure about my permanent solution idea of putting up extra 4×4 posts and nailing in 2×12's now, though. Because this is a really tight fit for my truck to back in I think if I add those extra 4 inches to the front of the rack will keep the truck from fitting. So, I'm thinking about putting up a steel bar or I-beam. I just have to figure out what size.


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## MrUnix (May 18, 2012)

Skinning the top with plywood would probably solve the problem.

Cheers,
Brad


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## ceabrm (Dec 29, 2016)

maybe consider sistering up some of those 2×6s? that's a pretty long unsupported span for that kind of dead weight i think. your joists are 16" oc?
there are engineering tables you can use to determine unsupported span, wood species & moisture content, etc.
have you thought about using the ceiling joists above for additional support?
also, there are engineered wood ibeams or glulams that could work great in a span that wide.
looks like you really do need a structural engineer… GL! 
really cool wood storage unit


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## CaptainKlutz (Apr 23, 2014)

Not enough information to check design.

+1 Sheet the top with plywood; minimum 5/8, preferably 3/4 CDX.

Can find online timber load capacity tables from American Wood Council based on lumber center line (OC), span, lumber type/grade, and sheeting. If the deck is 10×20, you need minimum of 30PSF load capability to support 6000lbs over your truck comfortably.

Best Luck.


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## GLENNpm (Dec 15, 2018)

> maybe consider sistering up some of those 2×6s? that s a pretty long unsupported span for that kind of dead weight i think. your joists are 16" oc?
> there are engineering tables you can use to determine unsupported span, wood species & moisture content, etc.
> have you thought about using the ceiling joists above for additional support?
> also, there are engineered wood ibeams or glulams that could work great in a span that wide.
> ...


All the 2×6's around the perimeter are doubled up. I looked up and calculated all of that before I started. I must have calculated incorrectly. A coworker is telling me that I reduced the overall strength by using half-lap joints. But I thought those joints were stronger?

I was originally considering using the ceiling joists but was told they weren't meant for that and I might damage my home. I didn't want to risk it, so I put it on posts.

I'm looking at steel I-beams or at least plates that I can sandwich between 2×6's, but hadn't thought about the engineered wood beams. Thanks!


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## OnhillWW (Jan 10, 2015)

First - I would have used fir instead of pine. But since the cake is baked - empty the top. Purchase quality luan (adds minimally to the thickness) and attach to top AND bottom of your decking via construction adhesive and screws every 8-10" creating a torsion box. Let cure. If possible, in a few places mid span, tie into ceiling above with threaded rod type pipe hangers.
Good luck


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## Knockonit (Nov 5, 2017)

framed wrong, imo. and way too much weight for how designed,. joists always go short distance, and setting on a beam is much better than hanging, 12'' on center would have sufficed with some total width assumption,s, then block it, decking such as osb would work to shear panel it and then load

my mezzanine is 9 ft x 22 ft. 2×6's at 16'' oc , with half inch osb, presently is loaded two feet high by about 8 ft plus in length, with a tad of room for more, which i seem to be adding as i'm a wood hoarder. 
might imo rethink how to frame it, best to do it once right than try to put band aides on to fix. jmo
best of luck
rj in az


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## PCDub (Sep 24, 2017)

half-laps weakened the joists-if they were 2×6, they are now effectively 2×3

plywood torsion box (re)construction sounds like the best bet (per OnHillWW)


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## splintergroup (Jan 20, 2015)

The underside of the platform is where you experience tension side to side, the top is under compression.

Some 3/4 plywood on the underside (glued/screwed to insanity) would be the first place I'd address.

You could also add some steel strategically to gain strength with minimal loss of clearance.

Any joist defects on the edges (knots, etc. need to be away from the bottom edge, that is where the joist will crack first


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## CommonJoe (May 8, 2021)

Beef it up, Add to the bottom of what you have there. Also add plywood to the top.


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## EdWeber (Jun 17, 2021)

IMO, this is not framed correctly
You would have been better off simply framing it just like a standard floor. You have far too many metal joist hangers than needed for this space.
Laying out standard 16" or 24" on center joists, with some stringing or blocking would work out better IMO.
I do agree with others with sheathing the top. This will add some strength, but not do much of anything for the sagging.


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## BurlyBob (Mar 13, 2012)

If you can't or don't want to rebuild it. Consider adding a piece of iron to that 2×6,. A piece of 1/4" should work.


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## controlfreak (Jun 29, 2019)

Not an engineer here but here is my take. I would have put something akin to a laminated beam or at least a double 2×12 down the right side. Lag bolt a band around the back and left side. Steel pole at the floating corner. Span the short width with a appropriate sized joist for the load with on center spacing once based on load. Ply on top to stiffen against racking and to spread load. One other thing, if you back into that corner pole you will know it.


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## gdaveg (Aug 1, 2020)

Draw picture of a plan view. Show all dimensions and member sizes. Take a picture or scan your sketch and post it here.

*Added questions at 10:22 am pacific time.*

Are you saying the 2×6 singles spanning 10 feet are half lapped into the double 2×6's on the perimeter?
If so this is dangerous.

You might find a structural engineer to come to your house and give you some direction.

Also looks as if the double 2×6 in photo one does not sit on the post but only held up by the sheet metal brackets.
Also iffy.


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## Notw (Aug 7, 2013)

What are the 2x's against the wall accomplishing? Unless I am looking at the picture wrong there doesn't seem to be anything they are supporting?


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## HokieKen (Apr 14, 2015)

I think that span is too long for 2×6 beams. Should have probably been double 2×10s for a 12' span. However, if I had what you already have, I'd probably try bracing up at the corners with some 2×6s as close to the center of the beams as you can while still being able to get your truck between them. And skin the top with plywood. Adding another 4×4 post on each side would be a better solution but that would prevent you from being able to get your truck under it.


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## prazbotta (May 20, 2020)

I know plenty about framing to give an opinion. I know what I know from professionals and reading material professionals follow. I am not a professional. You should have one come into your space and confirm what I am about to suggest.

Rebuild it. Don't use less than 2×8, 16"OC for the span, and run them the short(est) way. I would run them left to right as your first picture is oriented. If you go with 2×6, I would put them 12"OC. The joists should connect to a doubled 2×8 header (with 1/2" plywood between) spanning between the 4×4 posts on both sides. The 'front' and 'back' do not need to be doubled, but maybe double the front for piece of mind.

Here is a LINK to a span chart.

You can bridge the joists, but you don't need to. I would probably run two or three rows of bridging. I would also use the same dimension lumber for the bridging, unless you go with the 'X' style straps.

Sheet the top. I don't care with what, just sheet it. Your truck will thank you. If you are worried about getting the lumber up off the sheeting for whatever reason, then put a sticker on top of each joist.

The good news is you can reuse most of the lumber you have there for any number of projects. Hope this helps, but I have a feeling it is not what you want to hear. Good luck!


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## Knockonit (Nov 5, 2017)

You can use 2×6's you just have to cantilever about 18 inches over a new beam.

give a size and i'll share how you should frame it, pretty simple, you started pretty good, but with a little more info you can make a nice mezzanine for storage, and not worry bout failure.

need width and length, and height, we can re design to maximize your room
you can message me pm here and i'll give you a email address with some dwgs.
good luck, but 'd not go with what you have 
rj in az


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## squazo (Nov 23, 2013)

As a rough guide here is a neat formula an engineer showed me.

The multiple of a beam depth squared is how much stiffer the new beam is. I know terribly stated. Have an example.

A 2×6 (not nominal to make the math easy) vs a 2×12. The 2×12 is 2 times deeper so 2 squared is 4. Therefore a 2×12 is 4 times as stiff as a 2×6. A 2×18 (i know its just an example) is 3 times deeper 3 squared is 9 so it is 9 times stiffer. You can do the same with support span. A 3 ft span is going to be 4 times stiffer than a 6 ft span (with the same beam spanning both)


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## ibewjon (Oct 2, 2010)

Get the load off asap. Then tear it all down and start over with properly sized material.


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## 1thumb (Jun 30, 2012)

add some unistrut and threaded rod


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## rwe2156 (May 7, 2014)

+3 on tear it down and start over.

2×8 SYP. SYP is a lot stronger than spruce.


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## ibewjon (Oct 2, 2010)

Most trusses are designed for top load, not any real load hanging from the bottom chord. So I would not attach to the bottom of the trusses to strengthen the deck. Unless the rod goes through the roof and the strut is on top of the shingles.


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## GLENNpm (Dec 15, 2018)

I grossly miscalculated the load. I thought I had a lot more boards than I did. I haven't counted them in a while. But I did that today after removing as many as I could before work and found that the full load was actually only around 1800 lbs. So, that's good. But obviously still not strong enough since it bowed so quickly.

Thanks for all the advice. I'm in contact with an engineer to be sure it's more than strong enough for anything I put up there. I'll update once I figure it out.


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## robscastle (May 13, 2012)

Glen Glen !

*Priority 1 De load it.*

Then maybe consider
a. extending the joists to canter lever the load.
b. replace with I beams.
c. Build something nice quick smart with all the timber.
d. Build a wall mounted Floor to ceiling Rack, a lot safer, easier to access, and manage.
Finally: And of utmost importance …If that fell on my motorbike I would be pissed!


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## GLENNpm (Dec 15, 2018)

> Glen Glen !
> 
> *Priority 1 De load it.*
> 
> ...


haha. Thanks! I'm already on it. I really messed up my calculations. Fortunately, the load isn't as heavy as I first thought. But I'm unloading it anyway. I think I'm going to go with option B. Even if I have to rebuild it, I'll do it at the ceiling again. I understand the benefits to the wall-mounted rack, but I really need as much wall space as I can get. I'm quite limited on space and unable to create anymore - other than getting creative like this. As for the motorbike, I'm seriously about to pull it into my den until I get time to fix it up.. the beauty of being a bachelor. lol.


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## DS (Oct 10, 2011)

Sorry that I have no advice on how to frame it in wood.

What I do know is that our STEEL cantilever style lumber rack has 6" tall tapered steel rails to support about half that many boards per tier.

Not sure if that helps at all.

Good luck


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## Lazyman (Aug 8, 2014)

Oh, that is a motorcycle. I thought it is a lumber rack.


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## GLENNpm (Dec 15, 2018)

> Oh, that is a motorcycle. I thought it is a lumber rack.
> 
> 
> 
> ...


Only temporarily. lol


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## HokieKen (Apr 14, 2015)

If I were a bachelor, I'd put the lumber rack in the den. ;-)


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## bigblockyeti (Sep 9, 2013)

Well, I am an engineer and I would probably rebuild part of it, this would require a bit more evaluation and some deflection measurements with known mass to see exactly what needs to be done. Under no circumstances would I consider tying into the house structure, there's a slim chance you'd be fine, there's a great chance something could go wrong. Cutting into the bottom of any span beam (joists in this case) is always a no-no.

Over engineering is a bit of a misnomer, in industry it just means poorly appropriated resources resulting in wasted $$, not the same as over building which would be under engineered.


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## JCamp (Nov 22, 2016)

If you'll put some braces from the sides up to the top at a angle it should mostly fix the issues or at least help. If you'll get a 2×12 a put along the top. Mounting the top, sides and braces to it and that should keep it stable. I'm not a engineer just a *********************************** so take this with a grain of salt. If it was me and that's the issue I faced that's what I'd do.


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## GLENNpm (Dec 15, 2018)

> If I were a bachelor, I d put the lumber rack in the den. ;-)
> 
> - HokieKen


That's exactly where it's been up to now! haha


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## GLENNpm (Dec 15, 2018)

> Well, I am an engineer and I would probably rebuild part of it, this would require a bit more evaluation and some deflection measurements with known mass to see exactly what needs to be done. Under no circumstances would I consider tying into the house structure, there s a slim chance you d be fine, there s a great chance something could go wrong. Cutting into the bottom of any span beam (joists in this case) is always a no-no.
> 
> Over engineering is a bit of a misnomer, in industry it just means poorly appropriated resources resulting in wasted $$, not the same as over building which would be under engineered.
> 
> - bigblockyeti


I really appreciate your input. Obviously, I don't know what I'm doing at all. I can send you drawings and as much detail on the setup as I can if that would help.


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## GLENNpm (Dec 15, 2018)

> If you'll put some braces from the sides up to the top at a angle it should mostly fix the issues or at least help. If you'll get a 2×12 a put along the top. Mounting the top, sides and braces to it and that should keep it stable. I'm not a engineer just a *********************************** so take this with a grain of salt. If it was me and that's the issue I faced that's what I'd do.
> 
> - JCamp


That was my original idea. I was going to sandwich a quarter-inch metal plate.. and I still might. But I think I'll need more. I'm learning the half-lap idea was a bad one in this application. Unfortunately, I only know how to learn things the hard way, apparently. I thought about the angled supports as well, but I can't make them too aggressive without defeating the purpose of this whole thing. My truck bed barely fits under it as is.


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## controlfreak (Jun 29, 2019)

I don't think there is a fix for the half lap other than a do over.


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## HokieKen (Apr 14, 2015)

> I really appreciate your input. Obviously, I don t know what I m doing at all. I can send you drawings and as much detail on the setup as I can if that would help.
> 
> - Glenn


I'm an engineer but I'm mechanical, not civil so I don't offer engineering advice outside my field. But, if you have drawings and could host them online somewhere and post a link, I imagine there's a few who would review them and give you feedback of a professional nature.

If it were me, I'd probably look at requirements for building a deck to determine maximum spans and beam sizes, joist size and spacing etc. As others have suggested, the half laps are a bad idea and I imagine just having properly sized beams and joists would be sufficient. I'd also echo what Yeti said about tying into the house structure. If I were going to do that, I'd definitely get some professional advice on-site.


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## bigblockyeti (Sep 9, 2013)

I'm in the same boat as Kenny, I'm mechanical not civil but what we have here is a pretty simple statics problem with very little live load if you design it as such it will be fully loaded all the time. Given the home gamer aspect of this project, cost will be of much greater concern than if it were part of a large industrial project and there's several way to do this right, some of which look less appealing given a certain BOM required to construct it.

Hosting drawings of your idea could allow input from several folks from different fields. Better pictures of the span members and where they have been cut would aid in determining what if any can be salvaged.


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## GLENNpm (Dec 15, 2018)

@hokieken @bigblockyeti Thanks for the offer. I'm not sure if this is what you mean, but here's a link to a Google Photo album with pics and a drawing:

https://photos.app.goo.gl/Ys6w2b84HVeXMsPd9

Here's some additional info if you need it:

- Material = yellow pine
- Sides 1 and 2 are screwed into walls with studs every 16". 
- Every joint is half-lapped to create a flat top. The "A" boards are 2×4s that form the top of the joint (with the bottom cut out). The "B" boards are 2×6s that form the bottom of the joint (with the top cut out).
- Each joint is also supported with a joist hanger on 2 sides.
- 4×4 posts are anchored into the concrete slab floor.
- Current load is around 1800 lbs
- Max load should be no more than 3500 lbs (based on current load)

If possible, I don't want to change the footprint of the design. If anything is added to side 4, I won't be able to fit my truck in the garage. If the underside is any lower, I'll hit my head. It's currently maximized in those directions.

I'm wondering if I can just replace the peripheral beams with metal, cut out all the 2×4s, sister new 2×6s up to the old ones (and possibly add more if needed), then properly block between them. I'm not sure how to keep it from racking without tying it into the garage walls, though. I'd rather not sheath the top not only will it reduce airflow, but it will be impossible to access as it's already a tight fit between the deck top and the ceiling. I need to squeeze up through the joists from below to load/unload. I'd also rather not put up X braces around the sides for various reasons.

Obviously, this is all new to me. I'm learning and trying to be self-sufficient. Thanks so much to everyone for all the assistance so far!


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## AMZ (Jan 27, 2020)

Hard to tell from the pictures what is bearing on what. An earlier post mentioned half laps-where are they? I've been following this since the first post, with my firth thought being glue down 3/4" T&G plywood, but something seems off. What is and how much bearing on support beams?


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## controlfreak (Jun 29, 2019)

I feel the half laps must go. I would entertain an appropriate sized band around the perimeter with some ply sandwiched in between he two boards making up the band. Support the four corners to the ground and maybe anchor to the wall for lateral support. Make the load joists span from front to back and use blocking in between and top with ply. Just more *********************************** advise.


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## Sark (May 31, 2017)

The framing rule of thumb is 1" depth (or height) for each foot of span. So 10' wide structure should be framed with 2×10's. That means 2×10's every 16" on center, and from your picture, that's from left to right.

Blocking between the joists helps to distribute the load by tying adjacent joists together. But the blocking is not load supporting (per se). Prazbotto, above, recommends the same thing. No joist hangers are required. The blocking just gets nailed in.

Now conventional house-floor framing is designed for minimal sag (1/360 of the length). But some sag is OK in the garage, so I agree with previous comment that a 2×8" would probably be fine. But that's continuous 2×8, not cut into with half laps. That seriously weakens the structure.

Can your current structured be saved? Probably, but it might not be worth the trouble. What are your basic dimensions? 10×12? Couldn't tell from your pictures and description.


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## robscastle (May 13, 2012)

I would have my motorbike in there too


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