Brain exercise for the day - strength of stiles in panel

[Brian Tymchak]

I'm designing a stackable bookcase where I will stack 5 cases up on a base. Cases will be made of white oak with the end panels of each case a frame and panel construction. I'm thinking that 1.5" stiles/rails will look good, and .75" thick. I think stiles of this dimension will be sufficient to carry the load of fully loaded cases, but I'm not completely sure. Not being a mechanical engineer, I'm guessing it's ok, but I'd like to be sure.

All the weight of the cases + contents will come down on the 4 stiles of the end panels of the bottom case. I haven't calculated what the actual load might be yet but the question to the engineers here on the Creek is this:

If I divide the estimated load by the cross sectional area of the 4 stiles to get load psi, is the design sufficient if that result is less than the compression strength of white oak? Or am I completely off track with this logic?

I'm assuming I can find the compressive strength of white oak in some table somewhere although my first googles came up dry.

Edit: found this page of wood strengths with a little more googling.

Actually the stiles will effectively be .75" x 1.25" taking into account the groove for the panel.

Thanks for your help on this!

[Lee Schierer]

One stile calculates out to 7430 pounds of load bearing. That is about two cars worth. Build your cabinets.

[Bruce King]

Don’t forget to fasten the modules together and fasten near the top to the wall.

[Brian Tymchak]

One stile calculates out to 7430 pounds of load bearing. That is about two cars worth. Build your cabinets.

Lee, did you calculate this using my logic or do you have a different formula?

After finding that table of compressive strengths, I question the data or my formula. I've read that a 2x4 stud can carry about a 3000 lbs of load. With the data in this table, a white pine stud should handle ~25,000 lbs. Being that far off what I've read causes me to question my formula.

Thanks, Brian

[Brian Tymchak]

Don’t forget to fasten the modules together and fasten near the top to the wall.

Yep, definitely in the design.

thanks!

[Lee Schierer]

Lee, did you calculate this using my logic or do you have a different formula?

After finding that table of compressive strengths, I question the data or my formula. I've read that a 2x4 stud can carry about a 3000 lbs of load. With the data in this table, a white pine stud should handle ~25,000 lbs. Being that far off what I've read causes me to question my formula.

Thanks, Brian

I found compression strength of white oak is 6,060 psi. You have .9375 square inches of surface in a stile. Therefore .9375 x 6060 = 5, 681 pounds of load per stile. Bear in mind this is ideal loading as measured in a lab on a compression machine. I don't believe you can get that many books in your cabinets. Your bigger concern should be the bending of the supporting shelf.

[Brian Tymchak]

I found compression strength of white oak is 6,060 psi. You have .9375 square inches of surface in a stile. Therefore .9375 x 6060 = 5, 681 pounds of load per stile. Bear in mind this is ideal loading as measured in a lab on a compression machine. I don't believe you can get that many books in your cabinets. Your bigger concern should be the bending of the supporting shelf.

Thanks Lee. You are confirming my logic. Although you have found a different value for compressive strength of white oak. What is your source?

Still, hard for me to grasp that those 4 little stiles could hold up 3 pickup trucks with some room to spare.

[Bruce King]

It won’t hold that much weight because the load will never be exactly centered over the piece. In reality you should not put more than 150 lbs on each stile. That number goes up when you have the stile attached or braced but never as high as a lab test.

[Brian Tymchak]

It won’t hold that much weight because the load will never be exactly centered over the piece. In reality you should not put more than 150 lbs on each stile. That number goes up when you have the stile attached or braced but never as high as a lab test.

Bruce, where are you getting the 150 lb recommendation? That number would cause me concern about my design as this stack of cases will be holding a good amount of magazines. (My FWW collection).

Thanks.

[Kevin Jenness]

No need to obsess about the compressive strength of the stiles. Just make sure the end panels are strongly joined together and to the shelves, the shelves are thick enough for the load and the modules are securely registered to one another with splines, dowels or similar.

[Bruce King]

Just an educated guess because those are small pieces. Are you going to have panels connecting everything together or is this an open design. Remember that wood bends before breaking. Your shelves need to be thicker than you think for books and magazines too.

[Doug Garson]

Couple of points to consider. It's highly unlikely the stiles would fail in compression, more likely a joint would fail due to racking. Securing the book case to the wall would likely prevent this from happening. Typically a factor of safety is included in any design, not sure if the compressive strength given included a factor of safety. One third point, not all mechanical engineers are structural engineers and not all structural engineers are mechanical engineers. (Retired mechanical but not structural engineer)

[Alan Rutherford]

I have some shelves supported on boxes made from mahogany 1x4's and 1/4" mahogany veneer plywood. Think college-dorm-style planks resting on concrete blocks. The 1x4's are vertical in the front and back and the plywood forms the sides, so the boxes are about 4" thick, the height of the shelves and slightly less than the depth. The shelves are 5/4 pine and 6 feet long, narrower toward the top. There are 2 boxes per shelf and they are about 52 inches on center. All the loads are in compression.

I have never hesitated to load these up (in fact they are more stable with a good load on them) and they have served well for several decades, including a couple of earthquakes. It might have been fastened to the wall when we lived in earthquake country - it's been a while. If I understand your design, it's significantly stronger than mine. I wouldn't worry about it as long as the load is on the wood and not on the joints.