Our old buddy Linn Westcott tells us that a 1x3 is acceptable up to a span of 54" and a 1x3 L can go to 114". What would you expect out of a pair of 1x3's laminated together?
I need to go 105". I'm leaning toward laminated 1x3's with a 1-1/2" x 1/16" piece of steel sandwiched between them, but thinking the steel may be overkill.
Any structural engineers out there?
I have the right to remain silent. By posting here I have given up that right and accept that anything I say can and will be used as evidence to critique me.
I'm not a structural engineer, but I work in construction.
I am going to presume that this "girder" is going to support a train. It was not mentioned in the original post.
If Linn said that a 1 x 3 laid flat will span 54" and support an HO train, I will disagree. I think there will be some pretty nasty deflection. The proposed span for the girder is over 8'!
I would consider laminating that piece of steel vertically between two CLEAR 1 x 2's (or strips of 3/4 ply). I would use several through bolts and also, most likely, epoxy. And then I would lay the 1 x 3 flat on top.
It also wouldn't be the end of the world to go with 1/8 x 1 1/2 (twice as strong). And a 1/8 x 2 would be even better. Another layer of twice-as-strong. And steel is awfully cheap.
Overbuilding is ALWAYS better than underbuilding. Except maybe sometimes in airplanes.
Ed
from my study of aircraft spar design, you would be better with a taller piece of wood, such a 1x4 or why not a 1x6.
if you have steel strips the length you need, capping the 1x3 with them, creating an I shaped beam would probably be stronger than you can imagine.
in general, you need more material at the top and bottom and/or further from one apart. On top helps compression and bottom helps tension. Reinforcing the center is the least optimal.
greg - Philadelphia & Reading / Reading
The critical dimension for girders is the span to depth ratio. Therefore laminating two 1x3s together has little advantage. For steel spans ratios up to 30:1 are often used. For wood the ratio is much lower in the range of 15:1 to 20:1. With the light loads of our models we can stretch the upper limit a bit.
Using these rules of thumb a 1x3 (actually 0.75 x 1.5) laid flat shouldn't be used for a span over 16 inches. Laid vertical the 1x3 "L" girder would have depth of 2.25 inches and could span 48 inches - a tripleing of the flat span with only twice the lumber.
This doesn't help you with your 105 inch span. You need a member with a depth of about 5 inches. A 1x6 vertical will work, but could be subject to lateral buckling, and will be heavy. If you have access to a table saw, make a beam out of two 1x2s with a web of 0.25 inch plywood. Cut a 0.25 inch deep slot in the flat face on one side of each 1x2. Cut a 4 inch strip of plywood and glue into the slots. You'll end up with a lightweight beam 1.5 inch wide by 5 inches deep. That should span your 105 gap without lateral bracing. No need for the steel.
Ray
7j43kOverbuilding is ALWAYS better than underbuilding. Except maybe sometimes in airplanes. Ed
Amen to that.
Ray's ciphering sounds about right, but I've gotten away with a little less building the catwalks for the feline members of the household to stalk around above our heads.
This one is around 12' long and is composed using a 1x4 vertical web. The plate on top is 1x6. The oldest cat is no lightweight and heavier than most trains until you get to O scale and there is no deflection when she strolls across.
I used New Zealand Select pine I got from Menards for this. The stuff basically has no knots, amazingly fine wood, not too expensive, either.
Mike Lehman
Urbana, IL
I guess it's clear I should have been more specific about what I am trying to accomplish.
I called this a girder, perhaps inaccurately, because that's what Linn Westcott called a horizontal piece of lumber on edge used to support a layout. I assumed this usage of the term would be familiar to model railroaders.
This "girder" is going to be the front edge of a 26" deep grid that will support a section of the upper deck of my layout. The back will be attached to the wall with 3-1/2" #10 screws into the studs. Cross members are every 16". My desire is that it be as small as possible so that it doesn't intrude on the lower deck.
Ah, that's a little more clear, you want to laminate two 1x3s together. The issue will likely be finding any 1x3 longer than 96" as they are usually sold as lathing. Obviously, you could cut a 1x4 (which are commonly available in longer lengths) down if you need a little extra clearance below.
FWIW, I used 1x4 fashioned into L-girders to support Silverton here over a 128" span. It's freestanding (used two L-girders), but width is about what you need so should work attached to the wall on one side like you intend.
1X6 is grossly oversized for the job you need this structural member to support.
You say 105"? Get two 10' lengths of quality 1X4 and rip one of them down it's length into two equal halves. Place the remaining 1X4 on edge, glue the top edge, and apply one of the two ripped halves along that edge. If you wish, and don't have clamps, use wood screws to drive the two together for a good glued fit, say a screw every 8". When the glue sets, you can remove them if you wish...I left them in place.
That beam, or what we call an L-girder, will support a lot of weight across the 105" span.
carl425My desire is that it be as small as possible so that it doesn't intrude on the lower deck.
Tony Koester talks about keeping the decking thin in his book on multi-deck layouts. I thought he ended up using utility shelf brackets.
An h section (hope I got the teminoligy right) fence post would work if you can find one long enough or weld two together, would end up being less than 2" in height.
Are you sure you really really want to involve a structural engineer? Just kidding . . . I’m a civil engineer, but I took a statics class about forty years ago, and I don’t want to have to go dig out some musty old textbook.
Most of the responses are correct, even helpful. They correctly indicate that a vertical orientation of structural members is stronger than a horizontal one. The technical term involves section modulus, and in the mathematical formulas the vertical dimensions are squared (or, actually, cubed). But the thing about long-span thin-web structures is lateral support. The whole cabobble would tend to twist or warp or buckle. If your ‘girder’ is attached to the plywood decking, then the decking will act as a membrane and provide that lateral support. Otherwise, as in the L or T arrangements suggested, the horizontal member would provide it. Buckling is more pronounced in the compression area of the beam (top) than in the tension area (bottom). So, I’d suggest that you glue two 1x3s to form an L-girder or a T-girder with the horizontal member at the top.
Lynn Westcott seemed to indicate that a 1x3 L-girder should work up to 114” and I have no reason to doubt that, and Mike Lehman’s T-beam catwalk seems to prove it.
Good luck.
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carl425 Our old buddy Linn Westcott tells us that a 1x3 is acceptable up to a span of 54" and a 1x3 L can go to 114". What would you expect out of a pair of 1x3's laminated together? I need to go 105". I'm leaning toward laminated 1x3's with a 1-1/2" x 1/16" piece of steel sandwiched between them, but thinking the steel may be overkill. Any structural engineers out there?
You should be OK. When looking at the chart of support spreads and overhangs on page 18 of Linn's book How To Build Model Railroad Benchwork, you need to note not just the support spread length but the amount of allowable overhang and thus the total length of benchwork that can be supported.
When he says 1x3, the chart shows the lumber on edge with no flange (that is, not an "L" girder) with braced 2x2 legs. He has a support spread max of 4'6" (I assume that is where you get your 54" from) with an overhang max of 18" so a four leg bench maximum length of 7'6." There should be minimal deflection when the 1x3s are on edge.
He does say that 1x3s in an L girder can go to 9'6" in support spread and 38 inches overhang for a max bench length of 14'. And L girders using 1x4 (with the flange being 1x2) can go even longer: support spread of 13' (156") and overhang of 4'4" for a total bench length of 21'8" with just four legs (2x2s with supports, note).
Rather than laminate, if you want greater strength go with 1x4 L girder.
What he says on page 6 is that 1x3s are good for joists but 1x4 is best for the actual girder webs for large layouts. His goal was framework which in his words "is easier to assemble, easier to revise, and easier to move into another home. Cost is saved by using wood only where it is needed and because smaller lumber can provide the needed strength."
Dave Nelson
Check your local area for a supplier of heavy-duty building supplies (not Lowes or HD) and see if you can get a heavyweight 120 inch 2x4 equivalent steel stud. Physically it's 3.5 inches tall - and plenty strong enough to support the outer ends of the joists supporting your layout.
I have two serving as main girders under my peninsula - a wedding cake of steel framing and trackwork five layers high. They haven't deviated a micrometer (0.0001 millimeter) since I erected them 12 years ago, and I have used them as handholds to lift my considerable body weight. Granted they aren't the usual answer, but a good hacksaw and a couple of sharp drill bits are all that's needed for assembly.
From my point of view, the best feature is that steel is dimensionally stable. It sneers at humidity problems that are nightmares for forest products.
Chuck (Modeling Central Japan in September, 1964 - on steel stud benchwork)
a limited amount of bending is usually assumed in bridges, airplaine wings and flatbed trucks.
since i assume you want the shelf to be reasonably flat, some overkill is needed.
have you consider 1" angle iron? My hardware store has aluminum angle and u beam.
Something like this in mind you have?
All are 1x4s. The back is attached to the wall but the weight is transfered by tose "leg" in the back to the floor. Brackets are 16" long beyound the legs, and a total of 12" long on the top of the structure. The fronting is also 1x4. All of the lumber somes from buildings that we have torn down, none was purchased new.
ROAR
The Route of the Broadway Lion The Largest Subway Layout in North Dakota.
Here there be cats. LIONS with CAMERAS
I may be misunderstanding, but it would seem to me that a thick girder at the front would only be adding weight, not strength or resistance to deflection (sag) -- in fact, it would make sag worse. I've seen many layouts built with benchwork that tapers in thickness toward the aisle.
This helps with sight lines and makes the benchwork lighter.
I'd probably try individual joists from the wall rather than a grid -- and I would make them from tapered L-girders extending commercial shelf supports. Then maybe just some cross-bracing to tie them together and to prevent "racking" -- and a thin fascia at the aisle edge.
As Westcott (I think) said: "build bridges, not tables".
Edit: Folks also use square steel tubes with welded flanges, as pictured in Layout Design Journal # 58, published by the Layout Design SIG. Steel angles, as others noted, might work as well.
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Robert and Byron's comments reminded me of how I did the end of the Cascade Extension at Snowden.
The steel bracket is 15" wide. Wider brakets are available and the wood parts could be extended beyond the end of the steel 6" to 8" easily. The 3/4" plywood makes it very stiff. Total depth could be as little as 2", but I ended up deeper because I need the vertical space on the fascia for various things.
The way I interpret the problem is that the front edge of carl425’s upper deck is to be supported by a simple beam with vertical legs spaced 105” (8’-9”) apart. If the 26” deep grid is to be cantilevered from the wall, then that would be a different situation altogether and would require moment connections to the wall to prevent the entire deck from tilting down. (In Mike’s photo the moment is resisted by steel angle brackets at what looks like about 36” spacing.) If this is the case, then carl425’s girder along the front edge serves only to stiffen the deck and does not support anything.
Lance Mindheim had an article in the October MRR regarding lightweight benchwork cantilevered from the wall, but his deck was only 16” deep and very lightweight. Ten additional inches doesn’t sound like much, but it makes a world of difference.
Robert,
You're real close on the bracket spacing, it's 38" with an overall length of 6'. If I was going to do 26" wide, I'd go with 20" wide brackets and extend the 1x2" x-members. To go the span that Carl needs, I'd use 4 or 5 brackets, withe the spacing not too critical as long as it's fairly well spread.
The x-member ends are tucked close on mine (only about 1" longer) because I needed the aisle space. So long as you don't space them too far apart, a 6" overhang past the end of the bracket sounds OK to me, but I tend to be a by-the-eye engineer.
I'd probably also make the back brackets that the other end of the x-member ties into deeper (1x3), perhaps with cleats to help tie the x-members into them, for the span that Carl needs.
Robert has it right. It will be a 26" by 105" grid attached to walls on 3 sides. (it's actually 114", but the right end sits on top of the grid on that wall which is 9" deep) There is a lower deck below it. I can't use shelf brackets like Mike's because they would interfere with the view of the lower level.
I am also avoiding the track type brackets because my space is severely limited and I don't want to move the backdrop away from the wall. It may not seem like much, but moving the backdrop forward to hide shelf tracks would cost me about 4.5% of the best real estate on the layout.
Ian't it interesting how someone that's been obsessing over a problem for weeks tends to assume that others understand it without a complete explanation? Sorry about that, but I do appreciate the brain power the community is willing to invest on my behalf.
Carl,
Understand the misgivings on the brackets sticking down. The ones in the pic are 10" deep. I never see them myself, because the deck height is 66" and there's nothing but storage down there to look at but I don't. But if there was another deck down there, I wouldn't see the brackets unless I either sat down or stepped well back from the edge of the fascia. Your deck will be wider, so will tend to hide the brackets more than the 16" wide one here.
It may be worth mocking up the two decks to see what the relationship will be between everything conceals the brackets somewhat more than you think right now, but only if the girder thing doesn't work.
A bracket or two can be hidden, with a little thinking. Below the fascia, the top of a tall building (grain elevator, feed mill, plastic fabricator's pellet silo...) or a low cloud (fluffed cotton or white fiberglass) will do it. Or invert the bracket, then put a building, hill or grove of trees on/over it. You could even run a track through the bracket, hidden from view of course.
Whatever method or combination of methods you adopt, make sure the result is solid, buildable benchwork. You can't build anything, in any scale, without a solid foundation.
Chuck (Modeling Central Japan in September, 1964)
Thanks all for the comments and ideas. I've decided to go with plan-A. Metal Supermarket is cutting me a piece of 1/8" x 1-1/2" steel and drilling the bolt holes for me. My lumber yard is cutting two pieces of 1 x 3 and milling out a 1/16" x 1-1/2" channel down the middle of one side. This leaves me 1/2" above and below the steel to glue the 1 x 3's together. I figure having the glue and the bolts should make a pretty good beam.
Did I mention that I am lucky enough to have a great lumber yard? You can't pick up a 9' plus 1 x 3 with a 1/16 x 1-1/2 channel just anywhere.
carl425Did I mention that I am lucky enough to have a great lumber yard? You can't pick up a 9' plus 1 x 3 with a 1/16 x 1-1/2 channel just anywhere.
carl425 Thanks all for the comments and ideas. I've decided to go with plan-A. Metal Supermarket is cutting me a piece of 1/8" x 1-1/2" steel and drilling the bolt holes for me. My lumber yard is cutting two pieces of 1 x 3 and milling out a 1/16" x 1-1/2" channel down the middle of one side. This leaves me 1/2" above and below the steel to glue the 1 x 3's together. I figure having the glue and the bolts should make a pretty good beam. Did I mention that I am lucky enough to have a great lumber yard? You can't pick up a 9' plus 1 x 3 with a 1/16 x 1-1/2 channel just anywhere.
rrebellBut I can imagine what it cost you.
The whole thing (steel, lumber, drilling & milling) will end up just a little over $100. Certainly not cheap, but not outrageous.
I have limited hobby time available to me so when I have the opportunity to outsource a job that I consider "work" I tend to go for it. I rationalize my railroad spending by comparing it to what friends spend on their hobbies. Outsourcing the drilling and milling will cost me less than a round of golf and save me about the same amount of time - which I get to spend on the parts of the hobby I enjoy. That makes it a good deal for me. Your mileage may vary.
carl425....This "girder" is going to be the front edge of a 26" deep grid that will support a section of the upper deck of my layout. The back will be attached to the wall with 3-1/2" #10 screws into the studs. Cross members are every 16". My desire is that it be as small as possible so that it doesn't intrude on the lower deck.
While the photo below shows the 1/8" fascia in place, the front members are 1"x4"s, mainly to allow drilling-out holes large enough to accommodate switches to control track power without weakening their strength. The cross members are 1"x2"s, except at the ends of the two grid sections (necessitated by the steel post holding up the house which keeps the rain and snow off the layout). The wood used to "hide" the post does perform duty as a support.
The spans are about 5.5' and 7', and the grid about 21" deep. The rear member of the grid is 1"x2", screwed to the wall studs.
The grid used here on the upper level is of similar construction and in multiple sections to facilitate handling during installation.
Total span is about 16', with additional support provided by custom-welded brackets lag-bolted to the wall studs. Individual 1"x2" crossmembers of the grid sit atop each bracket.
The deep fascia hides the fluorescent fixtures used to light the lower level, and also controls the view for operators (the lower level is meant to be operated from rolling office-type chairs).
The brackets, four on the 16' section, effectively cut the span requirements to 4'. The top on all areas shown is 5/8 t&g plywood, which also contributes to the overall strength. It was applied in a manner that places the joints not directly over the joints in the grid-type framework. Layout depth here is about 32".
The area across the end of the aisle was built in a similar fashion, but with the end 1"x4" crossmembers attached to the wall studs where they meet the adjacent walls. The rear 1"x2" member of the grid is also screwed to the wall studs and rests on a 2"x4" bolted in place when the room was constructed. (My original plan was to use it to support engineered floor trusses for the front of the 16' section shown previously, and a similar one on the other side of the aisle, but that would have put the total length at almost 20', requiring a much deeper construction and a post at the opposite end.)
The layout here is 38" deep and uses no support backets, so the span of the front 1"x4" is 104". The plywood top, screwed in place, effectively turns the 1"x4" into a 104" long angle member (albeit a lopsided one). This portion of the upper level will support my full weight (under 200lbs.) a fact which I discovered when I found it impossible to paint the back side of the rails, even when standing on a step ladder.
So, to finally answer your question about that 105" span, a 1"x4" front member will definitely be strong enough if the ends of it are fully supported: either by end-crossmembers firmly attached to abutting walls or solidly supported by shelf brackets, posts, or blocking. The cross members (and plywood top, if applied) will add lateral strength.
Wayne
doctorwayne So, to finally answer your question about that 105" span, a 1"x4" front member will definitely be strong enough if the ends of it are fully supported: either by end-crossmembers firmly attached to abutting walls or solidly supported by shelf brackets, posts, or blocking. The cross members (and plywood top, if applied) will add lateral strength. Wayne
Well put Wayne. My thoughts exactly. If the front "girder" is well supported at each end, and the "cross joists" are well anchored at the wall then I would suggest there is no need for any special construction for the front girder.
Bill