Bingo, or as I often call them, squash blocks.
I’m not sure whether I will add in some additional parameters for these or just leave it up the user to either model in their own squash blocks. Thoughts?
Version 1.7.7b - 12.28.2020
- Enabled anchor bolts within the shearwall module.
- Enabled sole plate fasteners within the shearwall module.
- Enabled top plate clips within the shearwall module.
All that is left is the specialized blocking for shearwalls.
I lay awake last night pondering your question. My conclusion is that some structures are going to be built precisely as illustrated. If squash blocks are shown, they will be included. If not, not. Maybe there are technical issues with what is shown (I didn’t do much light wood construction while I was active, so I don’t have a good feel for what could go wrong. I can imagine, though, that the vertical stress could exceed the bearing capacity of the sill plate or subflooring. Is that a realistic concern? I don’t know.) but those issues are not going to bring the building down whereas no squash blocks at all might.
So, yes, the default should be to illustrate squash blocks. Perhaps you could give the user the option of not doing so.
One problem is going to arise if there is a joist under the end of the shear wall. It would be the cat’s meow if your program would detect that and make allowances, but that’s asking an awful lot; so if I were in your shoes, I think I would ask the user to define any such joists and where they are located laterally in respect to the end of the panel.
For what they are worth, there are my thoughts.
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You bring up two very valid concerns:
1.) Yes, the compressive load applied by the shearwall post to the sole plate (and sill plate) below might exceed its compressive strength. In many cases the lumber used for either plate is often HF (and pressure treated). You will notice on the second page of my shearwall spreadsheet there is a check of the “bearing” on the wall plates:
2.) Having a joist land directly under a shearwall post can and does happen. It is not the preferred situation but in my mind it is not the end of the world. The easiest way to handle this is to position squash blocks on both sides of the joist. The squash blocks should fit nice and snug so the compressive load is distributed primarily to them and not to the joist.
Unfortunately, a lot of attention is often given to shearwalls and their construction and then the squash blocks are forgotten or inadequate. Inspectors need to realize that the humble squash block is also an integral part of the equation, without them the shear wall is pretty much useless in my opinion. It’s all about load path and making sure it is continuous throughout the structure.
I remember a few years back I had a client who was building his own home. We had an interior shearwall positioned within his rather large home. It extended two stories up into the expansive structure, however he had failed to connect it properly to the roof diaphragm in any meaningful way. I inspected the project in person after the framing was completed and quickly detected the lack of a load path between the roof and the shearwall (and we corrected it). The rest of the shearwall and its construction was almost perfect in craftmanship and design but without the connection to the roof it would have proved completely worthless regardless of the care and attention to detail in its construction.
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Good points. How about the LSL rim joist compression? Or a need for additional blocks over the plate? Are these a concern?
My friend, a contractor, bought a two-story house for himself where squash blocks were left out in bearing locations. The floor was pushed way down. You could imagine all the work and swearing he had to do to wrestle the framing back up again and shore it properly. ( He also had to pull in walls that were 2" out of plumb. I hope he got a deal on the place because he made it beautiful in the end!)
If squash blocks are properly inserted then there should only be negligible load on the rim joist. I’m not sure I fully understand your second question.
Sounds like your friend’s house was a disaster (initially) due to shearwalls being improperly constructed. I’ve seen all kinds of similar cases with shear walls and other structural deficiencies. It’s much easier to get it right the first time.
I’ve seen both ways of handling stacked shearwall panels, however the strap method would make more sense from an economic standpoint:
The main point here is that you have either option at your disposal with the new shearwall module.
Notice the inclusion of the top plate clips on the lower shearwall and the 16d Common fasteners in the sole plate of the upper shearwall. Both of these items are optional however if that degree of detail is required or desired it is also readily available to the designer or engineer.
See model here:
P.S.
Some of you may be scratching your head looking at all of this hardware that goes into a wall especially at a shear panel… I know, Simpson Strong-Tie isn’t a multi-million dollar company for nothing. A lot of old time contractors really dislike us engineers.
Bottom line, when the wind blows really hard or you just happen to be lucky enough to be in a major earthquake, these construction methods will prevent your house from toppling over and potentially killing you.
Engineers like myself are entrusted with making sure the built environment around you is safe and secure.
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I take it this is all segmented shear wall panels employing the Wood Frame Construction Manual approach as apposed to the IRC methods behind the Simpson online calculator?
Have you looked much at Simpson’s framing screws? They seem to make good arguments for them. One of the problems with straps and solid sawn lumber, at least, is the lumber shrinks and the straps go slack. The screws seem to avoid that issue, IIRC.
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I looked over your shearwall calculator example. Very cool!
It appears that you are calculating the vertical loads at the extreme fiber of the chords. I’ve always used the middle of the chord, myself; but, then, it was almost impossible to make things too strong for the clients for whom I did most of my work.
The general notes say to reduce the allowable load if unblocked studs at 16" are used. Can I assume that blocked studs at 16" are your standard? What about studs at 24"? Aren’t a lot of house builders using 2x6s at 24" to make more room for insulation?
Suppose that the axial force exceeds the bearing capacity of the plate. I can see three ways of contending with that issue: (1) make the chord members bigger, (2) cut the plate to allow the chord to go right on through, (3) distribute the load with a properly-sized steel plate. I guess I’d use #3 for the shear panels and #1 for squash blocks, but what do you typically do?
On a shearwall-related note, the code calls for the designer to analyze a bunch of different wind zone conditions. Perhaps that is feasible on big projects, but it’s just not in the budget for a residence. Toward the end of my career, I just used the previous code requirements. How do you handle the situation?
Finally, let us not lose sight of my main recommendation, which is that you show some sort of squash block (or, maybe a note to the designer right on the drawing.) If you do not show something, you can bet that some people are going to assume that nothing is needed.
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I created my shearwall calculator for my own use specifically and then as an after thought I pushed it out to my website and offered it to other engineers who might find it useful. At the time I never considered 24" o/c studs since I never actually encountered those in my practice.
I get the whole advanced framing mindset but I personally don’t like 24" o/c studs, I don’t think one should sacrifice structural integrity for environmental concerns. If you need more insulation then apply a layer of foam to the outside of the sheathing or make the walls deeper.
I agree leaving the squash block question completely up to the user might create the impression that they are not needed. I’m am thinking about this and considering how best to address this.
I’m also wondering whether a shearwall schedule would be useful (drawn within the model). This is not the same as drawing the table in Layout. However there is currently no way to program (real time) tools within Layout so it would be created in the model. I’m trying to figure out if this would be useful and would users want it. Any feedback at all in this regard would be very much appreciated.
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I’ve got a couple stories, too.
One of my clients cut notch from the edge all the way to the web out of both flanges of a fairly tall steel column (W8x31, if I remember correctly) to install a conduit. After years of me telling them that was not acceptable, they moved the conduit and welded patches on. The thing is, though, that for all those years the column just stood there, doing its job. Goes to show how strong steel really is.
A contractor I worked with built a for-sale house. A few months after it was sold, the buyer called to complain. The floor was sagging, and there were cracks big enough to put a hand in all over the house. The contractor went to look, and sure enough, it was bad. He went to the basement and soon asked the owner, “What happened to the 6x6 post that was here?” “It was in my way, so I took it out.”
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Don’t know about the strength concern, but around here every framer knows how to do 2x4 at 16", but they are befuddled by 2x6 at 24, so the latter costs more.
I agree with putting insulation outside the sheathing. Indeed, I am beginning to think that all the insulation should be outside the sheathing.
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This seems an unfair assessment of OVE / Advanced Framing: done properly (as part of an engineered wall assembly) there is no sacrifice to structural integrity in pursuit of reducing thermal bridging and increasing realized (vs nominal) R-values. (as well as reduced material and labour costs — at least for a crew trained in these techniques)
Here, 2x6 @ 24" is a pretty standard method even if most don’t go the full OVE route (with single top plates, header clips instead of jack studs etc.). And continuous external insulation is now a code requirement, so it is in addition to increasing the thermal efficiency of the wall cavity — not instead of. All of these methods are necessary in our climate zone (6) to produce walls that are strong, healthy and efficient.
My experience has been that the framing is better-engineered in OVE projects as all the load paths are lined-up and designed-in, and the structural issues are fully thought through ahead of time — instead of simply throwing additional materials at the problems on-site (over-engineering headers, posts, corners etc) by the builder.
As for the shear wall module, I agree with the others that the squash blocks should be generated and included as the default, as should any integral component of the structure.
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That extra top plate in the walls helps tie everything together, especially as you have walls teeing into each other. Hangers are great but nothing beats a solid (positive) bearing like a jack stud for headers and even beams.
Thermal bridging is a factor but some additional insulation applied to exterior of the wall can go a long ways in alleviating this problem in my opinion. Insulated headers can also be used, I kind of like those sandwich headers with the foam in the center. I don’t like how some people put the foam on the inside with no nailing surface for the interior of the wall.
I agree OVE requires that more time is spent checking things out to make sure it all works, so there is that. I don’t think standard framing needs to over engineer things but some of that does happen when you leave it to the contractor to decide what to do (what choice do they have? Better over engineered than under engineered).
I’m not saying OVE doesn’t work or doesn’t have a place within the construction ecosystem but I’m just not a huge fan, especially in areas where there are high wind loads or seismic events are common. Better to be structurally sound than to save a few pennies in your heating or cooling bill. Nobody wants or needs a bunch of cracks in their sheetrock when a freak windstorm blows through.
P.S.
I’ve often heard the term “Value Engineering” bantered around as well. In my mind that term simply means let’s make it as cheap as possible while still maintaining proper code compliance. No thanks. When it comes to certain things like deflection criteria you really don’t want just the bare minimum. Yes, it will work and your structure probably won’t fail, but who wants their floor to fill like a trampoline every time your walk on it. Sometimes it is better to over engineer things just a little bit for comfort or performance.
When I go to the hardware store and pick out a hammer I don’t buy the cheapest Chinese hammer I can find, unless I only want to spend $3.99. I will typically purchase a hammer that I know will last and serve its purpose well, so I spend my hard earned cash on a $25.00 American made Estwing. The same logic should be applied when building a house in my opinion.
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Instead you can generate entire layout documents from within Sketchup. You could then export the documents as a pdf or as a jpg. The resulting image could be displayed in SketchUp inside of an HTML dialog.
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I’m going to have to look into this further.
I would like to be able to generate a shearwall schedule that can then be utilized within construction documents that are being created within Layout.
I’m not really sure if this is possible or what convoluted hoops one would have to jump through to make this work but it would be really nice if the user could just push a single button (click a tool icon) and the plugin automatically tabulates all of the shearwalls in the model and then somehow is able to bring this information into Layout as a table/schedule.
Tabulating the actual data and properties of each shearwall is a piece of cake, I already have tools and algorithms that do that within my electrical plugin etc… the part I don’t know how to do is getting this into Layout, and up until now I didn’t think this was really possible.
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Would exporting schedules to excel be more practical, or possible? Might be easier for the user to modify to their own needs.
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I’m not sure why I hadn’t thought of that option.
I’m already doing this with the estimating module of the Wall and Electrical plugin.
Give the user an HTML preview and then the ability to download the CSV version that can then be brought directly in Excel.
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Wow, interesting video put out just yesterday:
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