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Wood Shear Wall Software or Spreadsheets
2

Wood Shear Wall Software or Spreadsheets

Wood Shear Wall Software or Spreadsheets

(OP)
For residential design I typically run with segmented shearwalls that I manually calculate and check using the SDPWS-2008. However, I am wondering what if any specialized software or spreadsheets that others might use for looking at shearwalls (segmented, perforated, force transfer) or possibly recommend. What is common practice in this area?

RE: Wood Shear Wall Software or Spreadsheets

I recommend Woodworks software if you don't already have it. Given the amount of wood that you do, the $1000 investment seems as though it would be worthwhile. It's starting to get good for 3D modelling too. With that being the case, it might be worth it just to streamline load take downs.

My wife designs a lot of wood buildings. She has comprehensive spreadsheets that do all of the calculations including the tie down anchors. Pretty slick. I think it's a must if you're doing it on a regular basis.

The greatest trick that bond stress ever pulled was convincing the world it didn't exist.

RE: Wood Shear Wall Software or Spreadsheets

A mechanical guy doing residential shear wall design? That strikes me as odd. Please explain. :)

Perforated design is easy, you just follow the rules in the SDPWS... like a cookbook. No special analysis, no special detailing.

FTAO (force transfer around openings) is a good bit more complicated. Both in the analysis and in the detailing. There are a few hand calc examples (SEAoC seismic design manual, Breyer, et cetera) out there, but I'm not a fan of any of them. It seems to me that these hand calc methods don't work for any but the simplest of walls.

Personally, I like using an FEM based method for determining the shear in each panel of an FTAO wall. This is automated in the RISA-3D program (disclaimer: I actually work for RISA-3D, so I'm not exactly an unbiased observer). In my opinion the RISA treatment works really well for single shear walls with a wide variety of openings. Much better (and more accurate and rational)than the simplified hand calc methods.

For years I've been telling myself that I need to write up a white paper on the subject comparing the FEM solution to the hand calc examples and pointing out apparent errors in some of their simplifying assumptions. But, I never seem to find the time. Hopefully, I'll finally get around to it this coming year.

RE: Wood Shear Wall Software or Spreadsheets

(OP)
Typically I look at the unit shear and uplift (neglecting gravity loads, conservative) to determine the sheathing and nail spacing per SDPWS. Based on the uplift I determine the appropriate holdowns to use which brings me to my Simpson catalog. The holdown choice will dictate the thickness of the chord member that I need to nail or screw into (SDS screws) which I have found is usually more than adequate for the tension and compression chord forces I will encounter.

I typically don't look at the shearwall deflections too much unless there is something particularly interesting going on. The shearwall ratio is also checked but since I usually deal with governing wind loads the 3.5:1 is where I'm at for 90% of my projects.

Most of my shearwalls are segmented, so pretty run of the mill calcs. I could use perforated shearwalls more but I've read somewhere in the literature that perforated shear walls tend to have a "brittle" nature to them which makes me a bit less likely to use them.

Basically, up until this point I've utilized the methodology as laid out in Breyer's book for shearwall design which I find fairly comprehensive but I'm looking at ways to streamline the process and automate my calculations. I find a good spreadsheet or calculator not only saves time but also helps eliminate typos and manual calculation errors.

At the same time I don't like a blackbox approach because it is nice to have a good feel for typical numbers, once your loose touch with this you are no longer an engineer but merely a technician.

RE: Wood Shear Wall Software or Spreadsheets

(OP)
I made the move into the Residential Structural Engineering field about 6 months ago and I've never regretted it once. The only downside is the money is not as good but personal and professional satisfaction is far more important to me at this point.

RE: Wood Shear Wall Software or Spreadsheets

(OP)
KootK does your wife use Woodworks for a lot of her work or is it more custom spreadsheets? I've looked at Woodworks briefly but maybe I should give it a second more detailed look.

RE: Wood Shear Wall Software or Spreadsheets

She uses it extensively: load take down, member sizing, simple connections, shear walls... If you're an 80 person firm, you probably don't need a license on everyone's computer. If you're a one man show doing a lot of wood, it's a must.

I believe that you bought a $100 foundation book on my recommendation. Now maybe a $1000 software package. Next, you should hire KootK! A mere $100K per annum. What's an order of magnitude or two between friends?

The greatest trick that bond stress ever pulled was convincing the world it didn't exist.

RE: Wood Shear Wall Software or Spreadsheets

Try out woodworks before you buy. I thought it was too input intensive.

When I am working on a problem, I never think about beauty but when I have finished, if the solution is not beautiful, I know it is wrong.

-R. Buckminster Fuller

RE: Wood Shear Wall Software or Spreadsheets

I find the woodworks series the best available. It is obviously not perfect however with a quick learning curve it is quite functional. No software is perfect.

I haven't done much wood design as of late but when I have jobs with wood I am always using it. Literally always open on my computer during the design stage.

RE: Wood Shear Wall Software or Spreadsheets

We have been using Woodworks for many years. The shearwalls program is a little clunky in my opinion, but you get used to its idiosyncrasies after a while.

RE: Wood Shear Wall Software or Spreadsheets

(OP)
For sizing beams and joists I've found that Weyerhauser's Forte and Boise Cascades BC Calc to be pretty good. I've also created my own beam calculator that I still used for simple supported beams. The Woodworks Sizer program seems fairly decent however I agree that the interface is a bit clunky, the other software listed here are better in that regard.

I've been playing with the shearwall program from Woodworks this morning which I think would be the most useful tool for me to add to my growing list of tools however the learning curve is a little steeper on this one, okay much steeper...

RE: Wood Shear Wall Software or Spreadsheets

(OP)
I've noticed with Woodworks that unit shear is not uniform for all shear panels along the same shearwall. For example if I have two shear panels with one slightly wider than the other the wider one will have a higher unit shear and higher holdown forces. Has anyone else noticed this? Breyer's book makes the assumption that as long as the aspect ration (h/b) is not greater than 2, then the unit shear is generally assumed to be uniform throughout (WSP segmented shearwall).

A confused student is a good student.

RE: Wood Shear Wall Software or Spreadsheets

It sounds like Woodworks is distributing the line load according to the ratio of the stiffness of each segment.

RE: Wood Shear Wall Software or Spreadsheets

(OP)
My inexperience is showing. Under settings there is an option to distribute the forces to the different panels based on deflection or assume equal rigidity, among a host of other options. It actually looks like a pretty decent piece of software. I could definitely see the utility with more complex structures where the manual calcs would get tedious. Its ability to crank out the wind loads is impressive. I was just comparing the envelope procedure wind loading to my own wind load calculator and it matches perfectly except for a small discrepancy when a windward overhang is present. I've probably got it wrong in my own calculator but I haven't determined what is causing the difference yet. Details like this bug me so I'll probably be up all night until I figure it out.

A confused student is a good student.

RE: Wood Shear Wall Software or Spreadsheets

(OP)
Just one other interesting point. Take a 30 x 30 x 10 building with a 6/12 gable roof. If you compare the wind loads in Woodworks the directional procedure gives loads that are 150 - 170% larger than the envelope procedure. I never realized there was such a discrepancy between the two methods. So which is more correct for a typical residence? They can't be both correct not when they differ by such a large margin.

A confused student is a good student.

RE: Wood Shear Wall Software or Spreadsheets

Does Woodworks design the diaphragms for additional forces caused by irregular (non-rectangular) diaphragms and partial depth shear walls/collectors in flexible diaphragms? I've found the only way to properly account for the additional forces is to use transfer diaphragms as outlined in the visual shear transfer method. The Wood Products Council (also called WoodWorks) has some good white papers about this method, so I was curious if the software from AWC incorporated it (they are contributors to the Wood Products Council). It can get pretty daunting for complex layouts, but it helps develop a "feel" for the load path through irregular diaphragms. Software that could calculate the discontinuous chord forces, transfer diaphragm shears, etc. could save a lot of time.

For what it's worth, the Wood Products Council recommends RISA for wood design. I've had good success with using it for some Force Transfer shear walls, but most of my wood design is done in spreadsheets.

RE: Wood Shear Wall Software or Spreadsheets

Yes, there is a big difference in simplified wind loading vs. analytical wind loading. It is not little. I am told that this is due to measured data vs. calculated (conservative data). Once you get over 60', your loads jump up.

You are getting into the nitty gritty of wood shear wall design. In my opinion, it is one of the most complicated designs that you can get into.

There are a lot of assumptions that you can make that can make the design range greatly: Are shear values distributed assuming flexible or rigid? or both? or semi-rigid? Is shear distributed to walls by stiffness or by linear foot? How is stiffness calculated? 3 factor equation or 4 factor equation?

I'm working on 5+ story wood structures in 110 mph wind areas and I'm making my best guesses. Add in the fact that your exterior walls are 90% glass, and you can see the problem.

It is extremely complicated since the walls are not monolithic and there are many moving parts. Woodworks has a taken a lot of these variables into account as user settings.

I have looked at RISA and was not impressed. Woodworks was clunky for me, although I intend to give it another shot. I do hand calcs combined with some big spreadsheets. I do wind distribution based on a flexible diaphragam for the wide sections and rigid for the narrow sections.

When I am working on a problem, I never think about beauty but when I have finished, if the solution is not beautiful, I know it is wrong.

-R. Buckminster Fuller

RE: Wood Shear Wall Software or Spreadsheets

(OP)
My next job is a shearwall nightmare. Using a flexible diaphragm there is no way for this residence to calc. out, at least not without some very expensive steel moment frames. I am seriously thinking of biting the bullet and purchasing a license for Woodworks and see if I can get it to make this particular floorplan work.

A confused student is a good student.

RE: Wood Shear Wall Software or Spreadsheets

(OP)
Can RISA 3D generate the seismic and wind loading to shear walls like the Woodworks software?

A confused student is a good student.

RE: Wood Shear Wall Software or Spreadsheets

(OP)
Does anyone have a sample wood framed residence RISA 3D file that I can use to test out this software with?

A confused student is a good student.

RE: Wood Shear Wall Software or Spreadsheets

Our sales engineers probably have something they could show you if you contacted them directly. I'll try to dig something up later today and post a link, if I can.

RE: Wood Shear Wall Software or Spreadsheets

@ medeek:

Are you saying complicated because of lack of wall? or complicated because of many vertical irregularities?

Look in the simpson stron-wall catalogs. You can get away with some pretty slender walls using their systems. Just make sure you design the foundation to take it. They also have moment resisting frames that you can either use, or get ideas from.

RE: Wood Shear Wall Software or Spreadsheets

Okay, we (RISA Technologies) have got a few resources related to wood buildings:

This first one is a power point presentation that accompanied a webinar on the subject:
http://risa.com/documents/webinars/Wood%20Building...

This 2nd one is a link you You Tube where you can see the actual webinar:
http://youtu.be/3HTtICAWQ5A

Note:
This webinar is very specifically geared towards commercial wood buildings, not residential. In fact, RISA's implementation is geared much more towards commercial structures. The concepts are basically the same as residential. But, the geometry of residential structures tend to be a lot more problematic. Roof modeling with multiple hips and gables and such is always trickier. Also, you have a lot more discontinuities with residential. Meaning that shear walls don't stack nicely, et cetera.

RE: Wood Shear Wall Software or Spreadsheets

(OP)
This particular plan has no walls in one direction for about half of the structure. A picture is worth a 1000 words here. I've got to draw it up anyhow. Once I get the floor plan outline at least put together I'll post a screenshot and let everyone weigh in.

The funny thing is the designer told me that even though this particular plan has never been engineered it has been built 5 or 6 times in town and he has never had a problem. Before our new building inspector was hired apparently just about anything and everything flew through their office.

A confused student is a good student.

RE: Wood Shear Wall Software or Spreadsheets

@ medeek:

An option to also considered is a "3" sided diaphragm if you have no wall on the one side. We use the methodology for hotels sometimes.

RE: Wood Shear Wall Software or Spreadsheets

(OP)
That is exactly what I'm thinking is going to have to work in this case however looking at the SDPWS-2008 Fig. 4A and section 4.2.5.1.1 the diaphragm length is in excess of 25'. I am probably missing something here though.

A confused student is a good student.

RE: Wood Shear Wall Software or Spreadsheets

(OP)
Three sided rigid diaphragm?

Note I've tentatively notated where I can get some shearwalls in. The walls are 9ft. high.

This one is going to be fun...

Larger Image

A confused student is a good student.

RE: Wood Shear Wall Software or Spreadsheets

Any chance of putting a moment frame in on the side where you can't have shear walls? Or, cantilever columns, or something?

I seem to recall this type of system failing in some apartment garages during the northridge earthquake. Something where the gravity only system on the open side deflected a good amount then P-Delta effects made it unstable and.... collapse.

RE: Wood Shear Wall Software or Spreadsheets

(OP)
It would be really nice to put a moment frame on the living room wall, that might be a possibility:

A confused student is a good student.

RE: Wood Shear Wall Software or Spreadsheets

Don't get too complicated, there are solutions:

1) Northwest (plan view) bedroom, use the closet wall as a shear wall. Easy to add in a drag truss.
2) For living room elevations, see attached Simpson product for "Raked Wall Applications" as well as typical shear wall applications.

This house isn't THAT bad :)

RE: Wood Shear Wall Software or Spreadsheets

This house would typically fall under the IRC in the US.
Note that the northeast corner of the master bedroom violates the IRC in that there isn't a minimum width of wall at the corner. I don't have the IRC handy but typically you can't have a small segment of wall at corners without having specialty details to create adequate hold down at the corner against uplift. The fear is that the uplift load at the corner would overwhelm a single stud pack.

I think the IRC has a table that lists minimum widths at corners.

Of course - if a PE designs out the shear walls then the IRC goes out the window.

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RE: Wood Shear Wall Software or Spreadsheets

(OP)
I am a licensed PE not an SE.

A confused student is a good student.

RE: Wood Shear Wall Software or Spreadsheets

(OP)
One of these days I would like to sit for the SE exam however as a practicing PE and running my own small business I have no SE who regularly reviews my work and therefore I do not have a sponsor for the work experience portion of the application.

A confused student is a good student.

RE: Wood Shear Wall Software or Spreadsheets

If you can claim rigid diaphragm without violating any code limits in your jurisdiction, three sided might work. If you go that route, you might consider taking the east and west walls of the living room to make things wicked stiff in torsion and to help stabilize that bit of the living room that juts out north of the rest. Grab CBSE's closet wall for good measure although I don't see that as alleviating the three-sided-ness. If one of the north bedrooms could have it's windows swapped to the side walls, that would be great. I imagine that there's a view being maximized however. Moment frames may well be the way to go.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

RE: Wood Shear Wall Software or Spreadsheets

Quote (Medeek)

I have no SE who regularly reviews my work and therefore I do not have a sponsor for the work experience portion of the application.

I'll do it if it's legit to do so. Frankly, I spend more time working through things with you than my supervisors ever did with me. And don't everybody freak out by my offer. If it's legit to do so.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

RE: Wood Shear Wall Software or Spreadsheets

(OP)
How come I've never seen the SB shearwall before, I thought I had all of the literature. I'm really liking the chance to grab some shear with one of these on each side of the living room window wall. The ASD allowable shear for wind is pretty decent for a SWSB24x12 = 2965 lbs, but then the red flags come up when I look at the anchor tension at 21685 lbs, wow! My stemwall is going to snap right in two with that amount of uplift. I haven't run my wind loads yet so I don't know what the actual shear is going to be, but hopefully a lot less than the allowable.

I've just ordered a copy of Woodworks and I will put the whole structure into it and throw as many shearwalls in as I can and see what I get. I'm hoping to avoid steel moment frames otherwise my designer will probably fire me. :)

KootK, I really appreciate your offer and also all of the advice you continually give me with little or nothing in return. I have found Breyer's book and other texts to be very useful in my transition to the structural field however the input and feedback I have received in this forum from a number of individuals like yourself has far outstripped any book knowledge I have gained thus far. In a couple years after I've broadened my horizons into concrete and steel I might take you up on your offer if it still stands. I've been doing residential work for about 8 months now and I've yet to take the training wheels off even for wood, but I think I'm getting there.

A confused student is a good student.

RE: Wood Shear Wall Software or Spreadsheets

@ medeek:

If you place a shear wall in the bedroom like I suggested, then the uplift on the Simpson walls shouldn't be THAT bad. Test it and see what happens, should be a pretty quick calc.

The Simpson SB walls are relatively new and a fantastic alternative to the steel strong walls. I have had good success and contractors seem to like them a little more so far.

RE: Wood Shear Wall Software or Spreadsheets

It hasn't been a one way exchange at all Medeek. Your adventures have gone along way towards helping me stay current in an area where I don't get much practice. Plus I rip details off of your website.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

RE: Wood Shear Wall Software or Spreadsheets

(OP)
I'm glad that you are getting something of value as well from these discussions, KootK. However, I would take some of my older details on the website with a grain of salt, I really need to go back through all of them and update and/or correct a few of the more offending ones.

The ability to cut the Strong-Wall SB is a huge plus, can't do that with a steel strong wall. Okay, I think we have a game plan here, now to execute.

A confused student is a good student.

RE: Wood Shear Wall Software or Spreadsheets

Make sure to pay attention to the foundation requirements for the walls...basically the same as you would do for the steel strong walls.

On another note, not related to shear walls but beams, Boise Cascade produces a "King Beam". It's a great product and cheaper than other engineered beams if you need something other than a typical glulam. Just thought I would throw that out there since you are relatively "new" to wood design. Lots of designers don't know about it.

RE: Wood Shear Wall Software or Spreadsheets

(OP)
Here is how the wall looks with a couple of SWSB18 on either end (not all the notes are added yet, so forgive the mess):





A confused student is a good student.

RE: Wood Shear Wall Software or Spreadsheets

(OP)
Note the depth of the footing. The min. embedment is 6" and then you need at least 5" clearance from the bottom of the footing to the anchor bolt nut, so 12" deep, seems a bit overkill to me but thats what I get based on the SWSB catalog.

A confused student is a good student.

RE: Wood Shear Wall Software or Spreadsheets

12" footing? Slightly bigger than my average but not uncommon. However the 16" width seems narrow to me, what kind of bearing capacity do you get in your area?

Pardon my ignorance, I've been following your threads and contributing where I can, a lot of your threads involve the lateral design of residential structures. Are you in a seismic zone or are your designs wind dominated?

I only ask as my experience with residential design is no one pays this much attention to the lateral aspect, however I design in a "non"-seismic (I think they classify it as low seismic now) area. Tall walls get installed all the time with about half the amount of connectors you tend to use in your design. How have you found the acceptance of your detailing by the contractors? The ones around here would laugh me out of the office if I gave them a detail like that. I don't disagree with your detailing and I like that you put this much thought and design into your work I just find it a tad hefty in comparison to what I generally see (and people call me conservative).

RE: Wood Shear Wall Software or Spreadsheets

@medeek: do you know the factored shear and bending moment that you're delivering at the bottom of the strong walls? The capacity of the strong walls are so amazing that I start to worry about the foundation.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

RE: Wood Shear Wall Software or Spreadsheets

@KootK & medeek:

In the Simpson manuals, shear reinforcement and longitudinal reinforcement are required to be designed by the EOR. It is a concern to be aware of and should be checked for loads acting on the concrete in tension and compression.

If medeek has Enercalc, this can easily be done.

RE: Wood Shear Wall Software or Spreadsheets

Too bad they will not re-visit the window layout. I bet the SB moment frame option would relieve much of the uplift.

Good you are in WA or UT. Nowhere to fit insulation. :)

RE: Wood Shear Wall Software or Spreadsheets

It looks like his wall will be 5.5" wide as is...so he can get 2" of rigid insulation in there :) The SB walls are only 3.5" wide.

There are so many windows anyways that they probably won't notice the minor insulation in the walls.

RE: Wood Shear Wall Software or Spreadsheets

CBSE, I agree. The best window on the market is around R8 - 10, so it will not make much difference. I am not a huge fan of the great room, but that is what everyone wants.

RE: Wood Shear Wall Software or Spreadsheets

Quote (CBSE)

If medeek has Enercalc, this can easily be done.

I'm not so sure. For me, this would be less about rebar quantity per se and more about detailing in the disturbed regions at the ends. I see the ends as essentially opening and closing frame corner joints. And those are plenty hard to make work when both members of the corner joint are concrete.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

RE: Wood Shear Wall Software or Spreadsheets

(OP)
I wrote this lengthy response and then the reply box somehow deleted it, argh.

Anyhow it is still a work in a progress, I'm still waiting on the keycodes from Woodworks to get the lateral loads.

For reference:

Basic Wind Speed (Ultimate) = 155 mph
SDS = .98g

Wind speed typically dominates here with single story wood side structures.

Vertical load on columns (P8) is 5,400 lbs. C&C wind load is 51 psf (zone 4), deflection is .55 inches per IBC 1604.3 and IRC Sec. 301.7

Malone's book has some good examples of sizing stemwall foundations below shearwalls and portal frames for bending and shear however this Enercalc software sounds intriguing. I've heard of it but have never looked into it any detail yet. Now might be the time.

I think with a wall of windows the insulation is least of my worries at the moment however as CBSE pointed out some rigid insulation perhaps with some furring should get me there.

CBSE with regards to your corrections I can see what your getting at however with the sheathing I can't guarantee where the builder will put the seams. When the wall is loaded laterally the connections to the SWSB from the two headers will act like a moment frame one will go into tension and the other into compression. Unfortunately, the middle upper window breaks the continuity of the load path slightly but the additional sheathing/wall area through this region should help spread the load.

I'm debating on having them sheath the inside as well but this will be dependent on what kind of shear loads we see.

A confused student is a good student.

RE: Wood Shear Wall Software or Spreadsheets

You're load path goes from the roof, to your dbl top plates and then into your shear walls. I understand the concern about the window, but if you are using shear walls, you can't rely on the area between the shear walls to transfer loads. I would put a note on the detail that requires the contractor to place continuous sheathing over beams and Simosom walls.

As for wind design, you will be okay using the simplified procedure. I have looked at the woodworks program and demo'd it. What it won't do is give you the ability to look at stepped plate heights and other various discontinuities. It looks like a great program, but I have spreadsheets that do all the wall designs for me.

For your footings, you will most likely need pad footings to accommodate compression loads at the Simpson walls. Many designers miss the need for extra support and detailing at hold-downs.

The woodworks program you purchased is the one with shear walls, connections, and beam/column design?

RE: Wood Shear Wall Software or Spreadsheets

(OP)
I can manually get the wind loads, at least that is what I've been doing up until now. I have a nice little spreadsheet that will give me the MWFRS pressures for all of the wall and roof services for both trans. and long. however it is the applying all of these pressures to a cut up roof that becomes problematic especially with shearwall lines all over the place. I'm really hoping that it can do what I want it to do.

If the building is a nice rectangular structure with only ext. shearwalls then I even have a nice web based app. that will generate all of the shear loads using the envelope procedure here:

Medeek Wind Load Calculator

Unfortunately, most of the structures I look at are not so simple.


With the footings isn't the big concern with bending due to the moments that the Simpson walls will exert on the foundation and not so much the compression? The foundation will tend to break due to flexure where the Simpson wall meets the window.



However, with the columns (P8) I can see the need for pad footings, especially if my cont. footing were to remain at the 12" wide, 6" deep footing that is called out for the rest of the structure. If this were the case then a 24"x24"x12" pad footing at these two locations would probably be suitable.

A confused student is a good student.

RE: Wood Shear Wall Software or Spreadsheets

You need to check footing capacity for bending...both tension and compression. You also need to make sure your footing is large enough to support the compression loads.

For the wind loads, my opinion is you are making it way too complicated for the size of house you are dealing with. I have used the simplified procedure on homes from 2,000 sqft to 14,000 sqft and many much more complicated than this one. Is it 100% accurate? No, but it works. You are going to spend a lot of time to get close to the same results. Just my opinion.

RE: Wood Shear Wall Software or Spreadsheets

Quote (Medeek)

With the footings isn't the big concern with bending due to the moments that the Simpson walls will exert on the foundation and not so much the compression? The foundation will tend to break due to flexure where the Simpson wall meets the window.

Yes. However, I believe that the flexure issue presents itself more critically as the anchorage issue shown in detail C below. This is the classic opening/closing joint problem in concrete. Hopefully your flexural bars wind up just being a couple of manageable, small diameter bars.




I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

RE: Wood Shear Wall Software or Spreadsheets

(OP)
This just got more complicated. I need to take some time to digest the concrete detailing suggested above and read a chapter in Malone's book on Shearwall Foundation Issues (Chapter 9.9).

A confused student is a good student.

RE: Wood Shear Wall Software or Spreadsheets

Eh, don't let me freak you out. I'm sure that there will be dissenting opinions. This is just the first question that pops into my head whenever I see those EZ-Bake shear walls. They always seem to be at the far ends of stem walls and/or mounted on flimsy little upstands.

I botched the right hand side crack in my first sketch above. See below for a revision and some supplementary info.



I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

RE: Wood Shear Wall Software or Spreadsheets

I love basements... All your shallow wall worrying is exactly what I had to do on pretty much every job in NZ. Very rare to have basements.

Listen to Kootk. He's bang on with this one!

RE: Wood Shear Wall Software or Spreadsheets

If you look at Simpsons detailing requirements, it pretty much resolves all the worries you guys are looking at with rebar. If you put transverse bars in your footing, and show the anchor below those, you have just engaged much more than a typical shear cone. I will post a detail tomorrow for mid-wall and corner conditions using the Simpson walls.

I really like the KISS principal :) and believe me, I've been told to "KISS" it a lot.

RE: Wood Shear Wall Software or Spreadsheets

@KootK - Not to side track here but... I've often wondered about reinforcement for burst forces when dealing with anchorage design. Are there any references on designing for this or maybe you can shed light on how you approach that situation? Similar to how ACI prestressed concrete strut and tie addresses these forces?

EIT
www.HowToEngineer.com

RE: Wood Shear Wall Software or Spreadsheets

RFeund - I don't know ACI well, but any modern code with Strut and Tie provisions should handle this without issue.

There are a few basic "magic" points to Strut and Tie:

- Determine your B and D regions (this is a fancy way of saying "Design beam like sections as beams, and stout/squat sections as Disturbed regions"). In Strut and Tie, B regions are designed like regular beams, with compressive struts and ties parallel and running the length. Your D regions are where the shear span is less than 2 to 2.5 the beam depth.
- 22.5deg minimum strut angle.
- Check your tiess.
- Check your struts.
- Check your nodes (aka anchorage zones, assumed points of stress flow change).

There are some great resources online for learning this. One of my favourites is a paper from IIT in India.

RE: Wood Shear Wall Software or Spreadsheets

@RFreund: I've actually had a hard time sorting out bursting requirements myself. I've borrowed ideas from PTI and from Widianto's now classic paper on pedestal design. I think Widianto's recommendation amounts to a lateral force to be restrained equal to about 1/4 of the anchored force. What I'd really like is to know at what level nothing needs to be done to restrain bursting stresses. There's gotta be something better than just plain old bearing provisions.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

RE: Wood Shear Wall Software or Spreadsheets

Burst forces are essentially what you're doing at a compressive node. The model is layed out and the reinforcement is detailed to such that the forces involved do not exceed the capacity of the node. The "bursting forces" you're talking about are more applicable when you cannot control the strength of the system, such as with a post-tensioned system.

What am I missing that you two are debating this?

RE: Wood Shear Wall Software or Spreadsheets

Base upon your elevation picture above, I would try a horizontal beam (exterior to exterior) at the top of the lower windows. Designing the above as a wood frame (at the wall studs with wood panels) with posts down to the beam to transfer the lateral force and moments. This way you can transfer the above lateral forces as a shear to the beam with the moment being taken out as an uplift/downward forces on the beam.

Garth Dreger PE - AZ Phoenix area
As EOR's we should take the responsibility to design our structures to support the components we allow in our design per that industry standards.

RE: Wood Shear Wall Software or Spreadsheets

RE Bursting Forces:

I think I may be getting things confused... The bursting forces involved in anchorage design are really geared toward side face blow (or so I think).

Quote (Widianto)

When the reinforcement is used to restraint concrete side-face blowout, it should be
designed to carry the lateral force causing the side-face blowout. Cannon et al. (1981)
indicated that for conventional anchor heads, the lateral force causing side-face blowout
may be conservatively taken as ¼ of the tensile capacity of the anchor steel (based on the
Poisson effect in the lateral direction). A more complex procedure to calculate the lateral
force is given in Furche and Elingehausen (1991). In general, the Furche and
Elingehausen’s procedure gives a smaller lateral load than that recommended by Cannon
et al. (1981).
Also note that

Quote (Widianto)

It should be emphasized that
transverse reinforcement (ties) did not increase the side-face blowout capacity (DeVries
et al. (1998)). Large amount of transverse reinforcement installed near the anchor head
only increased the magnitude of load that was maintained after the side-face blowout
failure occurred

So where my confusion was...
When looking at KootK's sketch on 26 Dec 14 18:47 and seeing the bursting restraint bars, I was wondering how to calculate how much steel is required there. The answer to that seems to be answered by Widianto and KootK (about 1/4 the tension). However to answer the question of "when is it required and how effective is it" is a bit unknown to me. It seems as though it would be required when side face blow out is an issue. It does not effect concrete break-out strength (which I believe I have confused this part in the past). Widianto states that transverse reinforcement does not prevent side face blow out but does "increase the magnitude of the load that was maintained after s-f-b. He also states that "When it is impossible to provide the minimum edge distance of 6do, the side-face blowout strength should be calculated using Section D.5.4 of the ACI 318-05". So it seems as though you don't really gain any strength from a code standpoint by providing "bursting reinforcement" (aka side face blowout reinforcement.

EIT
www.HowToEngineer.com

RE: Wood Shear Wall Software or Spreadsheets

(OP)
Woodman88 the problem I have with putting the beam across the wall at the top of the lower windows is that I then create a hinge point for the columns holding up the central glulam beam. I have about 5000lbs total load on each column I also have strong out of plane wind forces hitting the wall. The bending and hence deflection of this beam along its weak axis would be fairly significant and with no lateral bracing the combination of the columns compression acting near the center where there is max. deflection would be problematic.

A confused student is a good student.

RE: Wood Shear Wall Software or Spreadsheets

(OP)
I kind of have two threads going on here that probably should be merged. Here is the updated stemwall calc. output. The spreadsheet can be downloaded here if anyone is interested:

http://design.medeek.com/resources/footing/2014-02...

http://design.medeek.com/resources/footing/2014-02...

I'm still really new to concrete so if you see something completely amiss please let me know. I based my calcs off of the following references:

ACI318-11
ASCE7-10
Simplified Design of Building Foundations by James Ambrose
Design of Reinforced Concrete 7th Edition by James K. Nelson
The Analysis of Irregular Shaped Structures by R. Terry Malone






A confused student is a good student.

RE: Wood Shear Wall Software or Spreadsheets

(OP)
Woodworks output for the above residence for Flexible and Rigid Wind Loads:





I used the more conservative directional procedure rather than the envelope procedure. As I have found with my own manual calcs the seismic for a one story building does not govern in my locality, wind speeds are 155mph (ultimate).

As you will note, I was unable to correctly model the diagonal walls since Woodworks does not provide this capability. Perhaps someone has a suggestion in this regard or a better method for simplifying the analysis.

I've manually calculated wind loads on cut up roofs on other projects similar to this however my diaphragm loads were probably never quite this granular. There is something to be said for just putting in the geometry and having the program spit out the entire load take down. It still worries me a little as to how the program distributes the loads to the shear walls, I guess I'm not a fan of black box results but I do see the utility of it.

What had me stumped for almost an hour though was why it was giving me such high seismic shear loads. Then I went back through the settings and realized it had my Response Modification Factor set at "2" because of the gypsum on the other side of the ext. shear walls. Once I set this to 6.5 everything was it should have been and my seismic loads made sense.

A confused student is a good student.

RE: Wood Shear Wall Software or Spreadsheets

(OP)
The allowable for my SWSB18 (Simpson StrongWall SB) is 1475 lbs for wind at a 12ft. height I'm over that at about 1880 lbs per the flexible diaphragm wind load however in reality I think the loading will be a semi-rigid diaphragm situation since the tall Simpson walls will deflect and the much stiffer exterior walls will pick up the torsional loadings. This is clearly shown in the rigid diaphragm loading with the much higher loads on the most exterior walls running North and South.

To envelope the design as much as possible I will spec. out the sheathing and holdowns with the worst load case from either the rigid or flexible analysis. This may be overly conservative but I want to try and pick up as much load from the wall of windows as is reasonably possible.

The one other annoying thing about Woodworks that I noticed that I thought might be worth mentioning is that along any given wall line it only allows one type of shearwall to be specified or one type of non-shear wall. It does not seem possible to have two different non-shear wall panels with different sheathing specifications. I don't know if it changes the output significantly or not but on some wall lines I have walls that are exterior and some that are interior (both non-shear). You wondering in anyone else has noticed this and how they have dealt with it.

A confused student is a good student.

RE: Wood Shear Wall Software or Spreadsheets

(OP)
For the wall of windows I get the following with the calculator:

http://design.medeek.com/resources/footing/2014-02...

Which gives me an 8" x 24" stemwall, with a 22" x 12" footing. The stemwall width and footing depth and width are governed by the requirements of the Simpson SWSB. The footing requires two longitudinal #5 bars for shrinkage and temp, no transverse reinf. required. The stemwall, due to the high uplift of the shearwall requires (2) #5 bars at the top and (2) #4 bars at the bottom, with vertical bars in the high shear areas for shear reinforcment (#4 bars vert. @ 12" o/c).

A confused student is a good student.

RE: Wood Shear Wall Software or Spreadsheets

(OP)
Here is the final detail drawing for that wall. I can already see some correction are in order, it is funny how you don't see the errors when it's in AutoCAD but as soon as you print it out they pop out all over the place.

A confused student is a good student.

RE: Wood Shear Wall Software or Spreadsheets

(OP)
I've been giving my shearwall/stemwall calculator some additional thought and I just realized that unlike the bearing pressure of the footing on the soil, the bearing pressure of the stemwall on the footing can also have tensile values because of the vertical bars (typically 24" o/c) between the footing and the stemwall. Currently my calculator treats the interface like there is no vertical bars so only compression is transferred. I guess my question is how does this tensile capacity change the shear and moment diagrams of the stemwall which are driving my concrete reinforcement design. Of course this only becomes an issue when the resultant force is outside the kern of the shearwall.

I have also not determined the best way to deal with contributions from adjacent walls to help counteract the overturning of a footing under a shearwall. The latest residence was able to work out mostly but when I ran the numbers on the interior shearwall at the closet (8.4 feet in length) it did not work out for either overturning or sliding. The only way to make it work in this respect was to assume that the foundation walls and footings it connected to provided enough additional resistance to counteract the high lateral loads. The shearwalls tributary dead loads were not enough. However, how much does one assign from the other connected walls to provide this additional overturning resistance?

A confused student is a good student.

RE: Wood Shear Wall Software or Spreadsheets

If the load falls outside of the kern and the vertical rebar is sufficient to take the footing along for the ride, the footing and a wedge of soil above it become downward load on your stem wall.

You can take as much tie down resistance from perpendicular walls as you need so long as equilibrium is satisfied and there's a capable load path available for the tie down force to develop. Foundations can be a bit nebulous in that there's a lot of continuity and it's tough to know exactly what load goes where.
 

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

RE: Wood Shear Wall Software or Spreadsheets

Just adding concrete is the typical way to make the footing work for uplift. Your CYA vs construction cost savings is better this way.

Garth Dreger PE - AZ Phoenix area
As EOR's we should take the responsibility to design our structures to support the components we allow in our design per that industry standards.

RE: Wood Shear Wall Software or Spreadsheets

(OP)
I really thought this thread was done but a short postlogue is due given some interesting feedback from the contractor building this residence. Apparently he is not a fan of any type of Simpson Shearwall product and has been giving me a bad rap for using it on this particular design. With the aspect ratios what they were and the lack of any shearwall space on the structure I feel that I was forced into this decision otherwise the design would have had to been altered in some way which was not an option.

The worst part is this exact design has been built by him at least 4 other times (prior to any engineering being required by the jurisdiction and an inspector that actually checked the plans) so my calling out shearwalls and special hardware all over the place appears like serious overkill to him.

I think part of the problem here is that most of the contractors are used to building whatever and however they want and I am fighting that right now. So now I've gained the reputation,"His prices are reasonable but construction costs of his engineered designs are high."

A confused student is a good student.
Nathaniel P. Wilkerson, PE
www.medeek.com

RE: Wood Shear Wall Software or Spreadsheets

I feel your pain. Responsibility for public safety + imperitive to compete in free market = perpetual low grade ethical compromise. It's a gods damned race to the bottom I tell you!

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

RE: Wood Shear Wall Software or Spreadsheets

I'm with you on this one as well. In fact, I believe I made a comment about this exact thing earlier in the thread.

Most carpenters (and more specifically residential framers) think anything more than commodity lumber, plywood and a nail-gun is overkill. Once you start making them block shear walls and provide proper connectors and tie downs etc. they call it overkill.

You need to find a happy medium, wood is fairly proficient at load sharing (even if you can't adequately analyze it). One thing I have noted, when you need a hefty simpson product, sometimes it's cheaper to just custom fab a steel plate connector to fit the purpose. A lot of the contractors have a buddy with a steel shop (at least in my experience).

I also in these type of scenarios (tall walls of windows) talk to the contractor the first day about that specific wall. Including describing to him an overkill preliminary framing for the wall and then talk to him about the option of looking into steel framing. That way when the design in finalized he had his say on day 1 and can't grumble about the outcome at the end.

RE: Wood Shear Wall Software or Spreadsheets

"His prices are reasonable but construction costs of his engineered designs are high."

Ultimately, you will have to turn this around and make your prices higher, but the cost of construction easy and cheap.
The more experienced you get, the more it will go this way.

RE: Wood Shear Wall Software or Spreadsheets

@Jsyrod: great advice on the steel. I'm going to test it out this afternoon.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

RE: Wood Shear Wall Software or Spreadsheets

This is the same story on almost every single family home.

Contractors claim that they have "been doing it this way for years". Meanwhile, they don't consider the code updates, improvements in technology, open floor plans, floor to ceiling windows, etc. Houses are not the same floorplan as they used to be, but construction mentality is the same.

Unless it is a custom home, contractors hate the Simpson frames.

medeek, you are too good of an engineer to do the crappy engineering required to make these things look like they work. I don't like working on these things because of situations like this. A near impossible problem, properly solved. However, the solution isn't affordable. Some of the younger engineers here deal with houses like this and I don't know how they make it work without doing something wrong. If I point out an error, I am rocking the boat.

Imagine the same house, but 16' wide with a tuck under garage and 4 stories tall (townhouse). And they are building 100 of them.

A few suggestions:
-Use envelope wind loading, it is much less than analytical wind pressure
-Take all the code reductions that you can get or loading. I don't know where it's located, but you may be able to neglect seismic.
-If possible, use prescriptive IRC design (might not work on this one)
-Try a FTAO frame at that exterior wall. If you can find 2', you can make something work
-Beef up some interior walls to allow the diaphragm to cantilever
-Next time, get with the architect early on and ask for some wall segments to use for shear walls. A lot of time, the Simpson walls are a good "threat".

I didn't read the entire thread, so forgive me if some of this was addressed.

When I am working on a problem, I never think about beauty but when I have finished, if the solution is not beautiful, I know it is wrong.

-R. Buckminster Fuller

RE: Wood Shear Wall Software or Spreadsheets

Doing a little bit of research into recent structural failures can help with that contractor. Put on your "educator" cap and point him towards some examples of similar buildings that failed in past events.

"Yes, a lot of people have done it this way for the last 30 years. Then people died in Northridge or Andrew (or whatever). That's why engineered buildings are not designed that way anymore."

RE: Wood Shear Wall Software or Spreadsheets

Agreed, Josh.

But it's hard to do that when the contractor points across the street and says "same house".

I usually respond with either "Nobody questions my design when they are hiding in a closet during a hurricane" or "It won't be the first time that someone has been doing it wrong for 30 years" if I want to be a jerk.

When I am working on a problem, I never think about beauty but when I have finished, if the solution is not beautiful, I know it is wrong.

-R. Buckminster Fuller

RE: Wood Shear Wall Software or Spreadsheets

I attended an insurance seminar recently were the presenter was very down on residential work, including condo towers. Statistically, the fees are the lowest and the chances of getting sued are the highest. Apparently lawyers, actuaries, and MBA's know better.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

RE: Wood Shear Wall Software or Spreadsheets

(OP)
I'm going to talk with the contractor today and see if I can discuss things a little with him.

I have thought of using the "Envelope" method in the Woodworks software for the analysis however with such crazy geometry and all of the re-entrant corners I was of the understanding that it should not be used in these situations.

Typically I like to envelope the design by taking the largest shear loads due to rigid or flexible diaphragm analysis per Breyer's suggestion in his text, however maybe this is too conservative? Wind loads in this region generally govern, on this design it was all wind.

I think I probably need to be more assertive with the designer and alter the design if it comes to it. A lot of his designs he has been building for years have problems like this one, no room for shearwalls on half of the house or worse. I know that I can make a three sided system or cantilevered diaphragm work but based on empirical data from previous earthquakes we know that they are not going to be as strong as they would be braced on four sides.

A confused student is a good student.
Nathaniel P. Wilkerson, PE
www.medeek.com

RE: Wood Shear Wall Software or Spreadsheets

I'd be inclined not to sweat the seismic really. Wood frame houses do very well in earthquakes. And, in my opinion, that has relatively little to do with any engineering attention that they may have received.

You previously mentioned that you think you suffer some for not having a day-to-day mentor. I suspect that you're right about that. There are a lot of mixed messages out there. All of the literature tells you how to do it by the book and that you should do it by the book. Industry tells you to compromise. This is somewhat institutionalized by IRC and Part 9 in Canada.

I wish that they'd help us out by expanding the scope of these documents. Just say something like "all walls must be 30% solid or tied down with engineered hardware." Leaving the enforcement of good engineering practice to engineers has never been a great formula. Just ask California. I wear khakis to work, not a cape.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

RE: Wood Shear Wall Software or Spreadsheets

Quote (KootK)

I wear khakis to work, not a cape.

This should be your new sig!

RE: Wood Shear Wall Software or Spreadsheets

Perhaps I will. I actually keep a sparkly purple cape at the office left over from a Halloween party. Whoever on the team is getting beat down the worst on any particular day is entitled to don the cape.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

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