Subscriber & Member Login

Login, or register today to interact in our online community, comment on articles, receive our newsletter, manage your account online and more!

Cantilever Question

1443 views
18 replies
1 rating 2 rating 3 rating 4 rating 5 rating
  • Member since
    December 2019
  • From: San Juan Capistrano, CA
  • 60 posts
Cantilever Question
Posted by CapnCrunch on Friday, April 17, 2020 4:25 PM

Background:

I am designing a shelf layout along one wall of the garage.  The overall layout length is 20 feet. There will be a 42"X42" square at each end for reverse loops and a 30" deep section between them.  The squares at each end will be supported by legs but the center section must be supported by the wall to accomodate equipment storage below.  The layout deck framing will be 1X4 3/4" plywood on edge and the surface will be 1/4" plywood.  I am thinking of using 16X18" closet shelf brackets (the kind with diagonal bracing) to support the 30" deep center section.  The brackets will be attached to studs in the plywood-covered wall with suitable deck screws.  The manufacturer specification claims that a pair of the brackets will support 1,200 lbs.

Questions:

1.  Given the weight of the deck materiels and the framing being proposed, how far can the deck reasonably project beyond the shelf brackets?

(I'm hoping that with 16-18" of support from the bracket depending on its orientation, a projection of 12-14" would be acceptable.)

2.  Would it be better to attach the 16" side or the 18" side to the wall?

Thanks in advance for your thoughts and recommendations.  The project is already underway and I will be posting a separate build thread with photos soon.  I have many, many questions from track layout to reverse loops to DCC wiring to......Confused

Tim 

  • Member since
    February 2005
  • From: Vancouver Island, BC
  • 22,105 posts
Posted by selector on Friday, April 17, 2020 4:38 PM

If I understand you, you are using 1/4" plywood atop stringers of 3/4" ply that will be about 4" high...is this correct?  Are the stringers going to lie flat, or are they going to be vertical?  Will the tips of the brackets be fully supported by a gusset or a brace, or will there be a tongue with a hole for a screw projecting beyond the brace?

These questions are all relevant, but.....with 1/4" plywood, I wouldn't be worried so much about the braces and the weight.  I would be more worried, quite a bit actually, about you grabbing crepe paper plywood in a desperate bid to keep yourself righted and find you cracking it for several feet, and all those nice items cascading onto the floor.  For that reason, I would want top grade ply and a projection of maybe 4" beyond the eyelet-with-screw-hole.  Having such thin plywood projected much more than that is inviting great regret in the future. 

Now, if you could see your way to upping the ply to even 1/2", that would bring you out to the 12" you desire.  Then the problem would also include the anchoring closer to the wall to ensure you don't horse the whole shelf off of the braces and have it all come down.

  • Member since
    November 2015
  • 703 posts
Posted by UNCLEBUTCH on Friday, April 17, 2020 4:48 PM

 Just  thinking outloud

 I question that 1200lb rating,  You might be better off to build your own bracket. Use a longer leg against the wall and brace from the floor, or near it, to at least the center of the shelf.

 lets say you screw a 2x4 to wall stud. run your 1x4 on both sides, then a 2x4 brace from near the floor to at least the center of the 1x4s. Then your only having 15in hanging over. but supporting the entire 30in.  

 On 30in you need to factor in the ''lean on '' aspect, besides the weight

MHO

  • Member since
    September 2004
  • From: Dearborn Station
  • 19,310 posts
Posted by richhotrain on Friday, April 17, 2020 4:59 PM

This reminds me of a thread that Randy Rinker started a while back. Lots of good ideas back and forth in the thread.

http://cs.trains.com/mrr/f/11/t/280870.aspx

Rich

Alton Junction

  • Member since
    September 2004
  • From: Dearborn Station
  • 19,310 posts
Posted by richhotrain on Friday, April 17, 2020 5:15 PM

This reminds me of a thread that Randy Rinker started a while back. Lots of good ideas back and forth in the thread.

http://cs.trains.com/mrr/f/11/t/280870.aspx

Rich

Alton Junction

  • Member since
    December 2019
  • From: San Juan Capistrano, CA
  • 60 posts
Posted by CapnCrunch on Friday, April 17, 2020 5:36 PM

Thanks everyone for the quick response.  I should have been more clear.  The plywood deck will be completely supported around its entire perimeter by vertical 1x4s on edges with 1x4 cross bracing minimum 16" o.c.  The framing for the deck will be reinforced with interior 45 degree gussets.  The plywood deck will be glued and screwed to the framing.  The shelf brackets will have flat 1X4s bolted across the top bracket and that 1X4 projection will extend to the outer edge of the layout to provide support of the cantilevered portion.  (I knew I should have drawn a detail for clarity but I haven't quite mastered posting a jpg yet...Embarrassed.

  • Member since
    December 2019
  • From: San Juan Capistrano, CA
  • 60 posts
Posted by CapnCrunch on Friday, April 17, 2020 5:41 PM

Rich,

Thanks for the suggestion.  I did go through the rrinker thread and didn't seem to find what I was looking for.  Plus, I didn't want to poach someone else's thread. Angel

Tim

  • Member since
    February 2002
  • From: Reading, PA
  • 28,183 posts
Posted by rrinker on Friday, April 17, 2020 6:28 PM

 Personally, I think of you build 1x4 frames for the 30" wide sectiosn and just screw them into the wall studs, and every third stuf put a diagonal brace down from the front edge to the floor, it will be plenty strong. Every other if you are paranoid.  This is more or less what Jason Schron from Rapido did for his layout

                    --Randy


Modeling the Reading Railroad in the 1950's

 

Visit my web site at www.readingeastpenn.com for construction updates, DCC Info, and more.

  • Member since
    September 2004
  • From: Dearborn Station
  • 19,310 posts
Posted by richhotrain on Friday, April 17, 2020 6:38 PM

rrinker

 Personally, I think of you build 1x4 frames for the 30" wide sectiosn and just screw them into the wall studs, and every third stud put a diagonal brace down from the front edge to the floor, it will be plenty strong.  

Plenty strong, for sure. The key here is stability, and it seems that you have that factor covered. Simple shelf brackets would not have provided the necessary stability.

Rich

Alton Junction

  • Member since
    July 2006
  • From: Central Vermont
  • 4,268 posts
Posted by cowman on Friday, April 17, 2020 7:06 PM

Think I'd scrap the 1/4" plywood and go with 2"foam, very little weight.  A friend of mine did 1/4" in his non-climate controlled building and before he got track down, it was already warping.  Not even a particularly changeable season.  

I asked my local hardware store about bracket loads, it depeds on spacing, but 16" should give you good weight bearing.  I am thinking of putting a 1x4" flat on  top of each  bracket, that will come all the way to the front.  They should be wide enouth to give a sufficient support surface at the joints too.

You might want to consider small (but long) lag bolts to hold whatever you use for brackets the wall.

Good luck,

Richard

  • Member since
    February 2002
  • From: Reading, PA
  • 28,183 posts
Posted by rrinker on Friday, April 17, 2020 8:32 PM

 If you want plywood subroaded - use 3/4". With a cross brace every 16" it won't sag. Foam is fine too, I've built two layouts with foam tops. Still needs support every so often, I used 2' centers with 2" foam with no issues, 16" would be even better, and since you need to attach to each stud anyway...

                                --Randy

 


Modeling the Reading Railroad in the 1950's

 

Visit my web site at www.readingeastpenn.com for construction updates, DCC Info, and more.

jjo
  • Member since
    March 2020
  • 142 posts
Posted by jjo on Friday, April 17, 2020 9:30 PM

In  woodworking and construction, the rule of thumb for a cantilever is  that a max (no more than)of 1/3 of the beam can extend beyond the support....Just a general guideline

  • Member since
    August 2005
  • From: Austin, TX
  • 1,752 posts
Posted by Don Z on Friday, April 17, 2020 10:10 PM

This section of benchwork protruded from the wall 22". I had no legs touching the floor and the benchwork was strong enough for me to sit on it. Shot the vertical flat to the stud, then pocket holed the angle brace to the wall piece and then the frame of the layout.

  • Member since
    December 2019
  • From: San Juan Capistrano, CA
  • 60 posts
Posted by CapnCrunch on Saturday, April 18, 2020 12:17 PM

Unclebut  I think you're right about the weight capacity.  More like 120 lbs instead of 1200.

DonJ  Thanks for the pic.  Your example would be ideal but may not work with my equipment storage limitations.

Richard and Randy  Foam may be an option.  I'll bring ithat up again in the build thread.

jjo  Your one-third rule of thumb is what I recall (thanks!).  As I understand it, the beam can support it's full load capacity out to a cantilever of one third of its length.  After that, under maximum load, the beam will begin to deflect.  The total weight of the road deck and framing I plan to build is well under the rated capacity of the brackets so I'm hoping that the portion that extends beyond the one-third cantilever will not sag.

 

  • Member since
    December 2001
  • From: Northern CA Bay Area
  • 4,246 posts
Posted by cuyama on Saturday, April 18, 2020 1:05 PM

Note that when you place a long extension on a pre-fab shelf bracket, you are creating a long mechanical lever that will increase the force on the bracket and whatever is holding it to the wall – perhaps well beyond the design parameters if someone leans on the edge of the benchwork. As others have noted, diagonal braces to the wall from near the edge are an excellent idea.

  • Member since
    February 2001
  • From: Wyoming, where men are men, and sheep are nervous!
  • 2,408 posts
Posted by Pruitt on Saturday, April 18, 2020 3:10 PM

In the first post, the OP said a pair of shelf brackets will hold 1200 pounds. That sounds right. But that's a dead load, distributed evenly across the horizontal leg of the brackets, so 600 pounds per bracket. The weight of the benchwork, scenery, trackwork, etc. would be a deal load.

The other consideration is live loads. These are the transients, like someone leaning on the benchwork. In structural design, live loads are generally allowed to be 10-25% of the dead load capability of the structure, so the 600 lbs per bracket becomes 60-125 lbs of live load concentrated at a single spot. And at 30" from the wall, nearly twice the length of the 16" bracket leg, the live load rating at that point will be roughly 32-67 lbs. Someone leaning heavily on the benchwork might easily exceed those numbers. I doubt the brackets or the benchwork would collapse, but the deflection from the load may be more than what would be considered acceptable.

  • Member since
    September 2002
  • 6,871 posts
Posted by ndbprr on Saturday, May 30, 2020 7:31 AM

 

I  would simplify the entire support system.  Mount 1x4s on the wall. Mount a horizontal 1x4 at the edge of the layout and cut 1x4 braces to fit betweeen the two.  You shouldn't even need to trim the ends of the braces but if you did it would look a little neaterbut either way it should hold an elephant

  • Member since
    October 2007
  • From: Fullerton, California
  • 1,009 posts
Posted by hornblower on Monday, June 1, 2020 2:38 PM

Tim 

Your benchwork design sounds quite familiar to what I did on my own double-deck 18' by 19' HO scale layout.  I used 1/2" cabinet grade plywood (plenty strong) to construct open grid benchwork that I cantilevered off the perimeter walls of my garage.  I supplemented the strength of the cantilever design by adding a "structural" fascia member spanning the space between two other well supported structures (similar to your 42" by 42" squares at each end).  The idea is kind of like laying the ends of a ladder across two sawhorses and screwing one leg of the ladder to the adjacent wall.  The result is benchwork spans over 13 feet long without any legs or supports beyond screwing the benchwork spans to the walls and adding the structural fascia.  I achieved the longer than 8' spans by doubling the structural fascia and using long angled lap joints to achieve the lengths I needed (you could also order 12' long plywood sheets).  Remember to glue the cantilever/span benchwork section together as it will be significantly stronger than just nailing/screwing together (I would glue the square end sections together, too).  A 2x2 cut into short "glue" blocks can be used to reinforce the plywood frame corner joints.  You don't have to glue the cantilever/span section to the square end structures.  I have not seen any sag at all in my cantilever/span sections in over 10 years and the entire layout is rock solid, including the double-deck double-cantilevered central peninsula.  Add to that the fact that the layout has survived two large earthquakes since it was built (Yeah, I'm in Southern California) and it still hasn't budged!

Hornblower

  • Member since
    December 2019
  • From: San Juan Capistrano, CA
  • 60 posts
Posted by CapnCrunch on Monday, June 15, 2020 10:22 AM

Hi Hornblower,

Sorry for my tardy reply but I just came across your post.  Your recommendations of how to design the grid benchwork framing in such a way as to increase the span between supports is exactly where I'm headed.  I'm sending you a PM about it.

Belated thanks to everyone who offered advice on the original cantilever question, I went with a design that uses a brace and gussets to transfer the load back down to the wall footing.  Here is a photo of the support brackets I posted a couple of weeks ago in WPF.  

https://flic.kr/p/2j4QoxS

Tim

Subscriber & Member Login

Login, or register today to interact in our online community, comment on articles, receive our newsletter, manage your account online and more!

Users Online

Search the Community

ADVERTISEMENT
ADVERTISEMENT
ADVERTISEMENT
Model Railroader Newsletter See all
Sign up for our FREE e-newsletter and get model railroad news in your inbox!