Shear wall design in small residential homes 7

[davidl13]

I've just started out doing my own thing on the side and working on some small residential renovations. In this case, the client wants to take down a load bearing wall and have it resupported with a flush beam (wood). I've designed wood beams before but I was wondering if there are any special considerations in terms of the analysis and the detailing for a flush beam vs. a regular drop beam?

In addition, I was wondering how to approach it from a lateral system point of view. I don't have any existing drawings and the house is inhabited so I can't just request to open probes anywhere I want. I don't have that much experience with residential construction, but I assume that any load bearing wall must also act as a shear wall. Is there any way I can justify that ripping down this wall won't have an impact on the integrity of the lateral system in general? Typically, these homes may have been overdesigned and maybe I can justify it numerically that it would still work if we reduce the total length of the shear walls by like 10% for instance?

I'm asking strictly from a safety point of view, less from a permit standpoint.

Any comments/advice would be greatly appreciated!

 

[GaStruct]

For the beam: Design is the same, if not better b/c fully braced. Important part is to make sure you note to shore, cut, and resupport the joists. Residential contractors often don't shore it correctly and the joists drop. Or cut the joists too short.

For the lateral system: If there are a decent amount of walls elsewhere, I would not be concerned about it. Most houses in the US are prescriptive with no SW. Some high wind/seismic exceptions. Look at the IRC BWL section, you don't need much to be compliant.

 

[davidl13]

For the beam: Design is the same, if not better b/c fully braced. Important part is to make sure you note to shore, cut, and resupport the joists. Residential contractors often don't shore it correctly and the joists drop. Or cut the joists too short.

For the lateral system: If there are a decent amount of walls elsewhere, I would not be concerned about it. Most houses in the US are prescriptive with no SW. Some high wind/seismic exceptions. Look at the IRC BWL section, you don't need much to be compliant.

Thanks for the response!

For the flush beam, only the bottom will be fully braced by the joists. The top won't be restrained - I imagine that would still affect the adjustment factors, right? And would a regular Simpson face mount hanger be fine to use for such a flush beam?

This is in Michigan, so not a super high lateral demand. The interior wall that we would be demo'ing is something like 9' long, and there are other interior walls along that line of framing. What is BWL? Would you be able to point where in the IRC that's located?

Thanks again!

 

[GaStruct]

If the beam is flush it can't rotate top or bottom. Joists on both sides will restrain it. Forte is free and will do NDS adjustment factors for you. I would look into that.

BWL = Braced Wall Line. IRC R602.10 is the code section. Simpson has a free calculator to use since doing it by hand is a nightmare. With experience you will eventually be able to just look at plans and know if it complies.

 

[KootK]

Consider a copy of the reference below. It's gross overkill for most of what I do but, at the same time, pretty much everything that you might want to know about light frame wood lateral systems is in there.

It's like having the bible close to hand when your immediate concern is really just whether or not to kill your neighbor.

 

[shacked]

You need to justify removing that wall without increasing and potential lateral loading to the existing walls in the same direction as the existing wall to be removed. Not knowing anything about the existing roof and or ceiling framing I would also verify if the existing adjacent walls extend to the bottom of the roof framing and not just the ceiling framing. Otherwise there is not good shear transfer from the roof diaphragm into the adjacent walls to resist lateral loads.

Just my 2 cents

 

[Eng16080]

I would start by quickly calculating (even just a ballpark) the lateral loads. Then determine what walls you'll have to resist those loads. I'll often add up the total length of solid wall segments (meeting a minimum aspect ratio of 3.5:1) in each line of resistance, and divide that by the lateral load to that wall line. If this works out to something under 300 plf, I'm usually not too concerned. Most of the time for a modest house with plenty of solid wall segments along the exterior, there isn't a problem. It often becomes a problem where there are a lot of large window/door openings in the exterior as well as limited interior walls.

I have a project currently located on the water where a long interior load bearing wall was removed. I determined there was no reasonable means for lateral loads not to be resisted by that wall (despite it not being properly detailed as a shear wall). I ended up designing a steel moment frame to support both the vertical and lateral loads.

 

[lexpatrie]

That you are asking this question as a sole proprietor makes me wonder if you aren't really ready to practice solo. Never mind the liability implications if something goes wrong.

That may sound mean, but keep in mind you accept projects they aren't forced on you, but you are expected to conform to the standard of care and protect health and life-safety, and practice within your area of competence.

 

[XR250]

That you are asking this question as a sole proprietor makes me wonder if you aren't really ready to practice solo. Never mind the liability implications if something goes wrong.

That may sound mean, but keep in mind you accept projects they aren't forced on you, but you are expected to conform to the standard of care and protect health and life-safety, and practice within your area of competence.

I was thinking the same thing.

 

[Eng16080]

That you are asking this question as a sole proprietor makes me wonder if you aren't really ready to practice solo.

While I don't disagree with this comment, based on what I've seen, even asking this question would put OP above the standard of care. My experience has been that many engineers (perhaps the majority) involved in residential work don't even consider lateral design.

Even if OP is perhaps not ready to be doing this work (based on the probably higher than average standards of some of us here), by asking these questions, I think they're on the right path.

 

[KootK]

I celebrate what @davidl13 is doing.

I have little concern for what any engineer does or doesn't know in a particular space. What I'm concerned with is whether or not they recognize their deficiencies and are proactive in addressing them. I take the existence of this thread as @davidl13 doing just that.

Once one hangs out their shingle and becomes an entrepreneur, their primary job responsibility is identifying market opportunities and exploiting them. Competent engineering is important but a distant second. That, no matter what frou-frou gibberish your local association has made you sign to the contrary.

If I had stuck to only that which I already knew how to do, I'd still be pressing the "equals" key incessantly in some truss design software package. You know, slaving away for some entrepreneur who actually grew a pair and took some risks.

I was thinking the same thing.

Et tu Brute? You are a mechanical engineer with one of the highest tolerances for risk of any engineer that I've ever met (love that). Yes, yes... you were once mentored by some other lone wolf. You were also mentored in a number of things by this forum while you were practicing solo. I was there.

 

[phamENG]

I was wondering if there are any special considerations in terms of the analysis and the detailing for a flush beam vs. a regular drop beam?

My advice from your original thread still stands. Heads up for the future - double posting is frowned upon. Also for the future, if you have a structural engineering question, just post it here in the main forum. As you can see, a lot more people hang out on the main forum than the little side fora.

This is where a sketch would help a lot. It's somewhat regional as far as naming goes, but there are often four configurations for a beam in a wood framed structure. Most common three are header (top and bottom unrestrained), drop beam (top restrained, bottom unrestrained), flush (same depth as the joists and so top and bottom are restrained), and upset (much less common, but the bottom is flush with the joist and the top is either up in an attic or perhaps in a wall just above, bottom restrained, top unrestrained). This is an international forum, so don't assume what you call something is what a forum member on the other side of the country or other side of the world is what they'll call it, too.

For lateral, you need to study the difference between braced walls and shear walls. Braced walls come out of the prescriptive residential codes, shear walls are engineered. MOST houses have braced walls if they have any 'designed' lateral system at all. You need to figure out what it is and what they are made of. You need to be intimately familiar with the governing codes in the jurisdiction. IRC, IBC, IEBC, and how your local or state governments have edited them, as well as what version they have adopted currently. Don't count on the contractors to know the code - they don't, generally. The interplay between the IRC and the IEBC (International Existing Building Code) will likely govern how you approach lateral and determine the impact on the existing structure.

I can't just request to open probes anywhere I want.

Yes, yes you can. The homeowner is hiring you as an expert in the field of residential design. If you need to probe something to get information for design, you need to do that. I don't like working for clients that tie my hands behind my back and blindfold me before I start working, and a homeowner that is completely unwilling to let you figure out what you need to know is doing exactly that.

I do applaud that you are seeking help and not just going off half-cocked. But this forum is not enough. You need a mentor that you can lean on locally to help you through things and review your work. Without that, you are dancing very close indeed to an ethical cliff. Most (probably all?) of us around here that are on our own worked on the types of buildings we're working on now under the supervision of an engineer with that same experience.

Michigan State Law (and every other engineering practice law I'm aware of) requires an engineer to undertake only that work for which they are competent. I'm not saying you're not intelligent - the ability to recognize your lack of knowledge and seek help shows you're better than most - but experience matters in measuring competence.

Michigan Administrative Code, PE Rules | Part 3. Standards of Practice and Professional Conduct | R 339.16033 Participation in engineering projects; competence required:

Rule 33. A licensee shall undertake to participate only in those phases of a project in which the licensee is competent. In the areas of a project involving architecture, professional engineering, and land surveying in which the licensee lacks competence, the licensee shall retain licensed professional associates for those phases of that project.

You mentioned this is a side gig. What's you day job (in general, non-doxing terms)? If you're going to join this community, we have to know a little about you. For my part, I have a background in commercial, industrial, residential, waterfront, and historic restoration structural design with a smattering of industrial operations and mechanical stuff. Now I run a solo shop doing mostly high end, custom residential and historic work with a bit of new commercial construction and tenant build out jobs.

 

[XR250]

I celebrate what @davidl13 is doing.

I have little concern for what any engineer does or doesn't know in a particular space. What I'm concerned with is whether or not they recognize their deficiencies and are proactive in addressing them. I take the existence of this thread as @davidl13 doing just that.

Once one hangs out their shingle and becomes an entrepreneur, their primary job responsibility is identifying market opportunities and exploiting them. Competent engineering is important but a distant second. That, no matter what frou-frou gibberish your local association has made you sign to the contrary.

If I had stuck to only that which I already knew how to do, I'd still be pressing the "equals" key incessantly in some truss design software package. You know, slaving away for some entrepreneur who actually grew a pair and took some risks.



Et tu Brute? You are a mechanical engineer with one of the highest tolerances for risk of any engineer that I've ever met (love that). Yes, yes... you were once mentored by some other lone wolf. You were also mentored in a number of things by this forum while you were practicing solo. I was there.

View attachment 2259

Wow, that's flattering One reason I stick mainly with residential is the lack of risk due to the huge amount of redundancy. At this point, I have probably been in 8,000 houses. I have an idea of what fails and what does not (at least in my area) and where to focus my energy. So if I provide advice that seems risky it is because of my experience.

And yes, my BS and MS is in mechanical engineering AND I had a fantastic mentor for 7 years before I went out on my own.

As far as the OP is concerned, I think Pham said it better than I can..

"I do applaud that you are seeking help and not just going off half-cocked. But this forum is not enough. You need a mentor that you can lean on locally to help you through things and review your work. Without that, you are dancing very close indeed to an ethical cliff. Most (probably all?) of us around here that are on our own worked on the types of buildings we're working on now under the supervision of an engineer with that same experience."

 

[GaStruct]

@KootK - Somewhat unrelated but noteworthy.... in the first chapter of that book, they talk about how the LFRS is pretty much ignored on the east coast. They go on to say anyone who bids appropriately knowing the requirements of a properly designed and detailed LFRS will not win the bid.

I have not won a multi-family bid since going out on my own. The only ones I did were as an employee. I have even lost clients who were insulted with my bid

 

[KootK]

Somewhat unrelated but noteworthy.... in the first chapter of that book, they talk about how the LFRS is pretty much ignored on the east coast. They go on to say anyone who bids appropriately knowing the requirements of a properly designed and detailed LFRS will not win the bid.

That is interesting. I probably skipped that part en route to the sexy transfer diaphragm sketches. Good on Malone for his Candor.

Wow, that's flattering

I hope so. When I'm doing work similar to yours, I imagine a mini-you on my shoulder encouraging me to be daring. WWXRD.

Most (probably all?) of us around here that are on our own worked on the types of buildings we're working on now under the supervision of an engineer with that same experience.

I would say that around 20% of my work is stuff that I had no exposure to when working under someone else's supervision. I will also say that such projects also seem to represent the most risk for me for sure. But that risk isn't really technical. The real danger seems to be me not adequately understanding what "normal deliverables" look like in unfamiliar spaces. I've learned the hard way that I do best when I have a sample or two to use as a go-by.

What's you day job (in general, non-doxing terms)?

I'm going to guess: industrial structures.

I am actually of the opinion that light frame construction is one of the most specialized and non-obvious things to dive into as a structural engineer if you lack exposure to that kind of thing. With braced steel towers, shear wall CIP condos etc, most any fool can probably look at the skeleton and have a pretty good idea of how things work.

With light frame, the bits that we use look nearly identical the bits that we don't. And there are a lot of bits. And you want to do WHAT with OSB? Surely you jest...

 

[EngDM]

If the beam is flush it can't rotate top or bottom. Joists on both sides will restrain it. Forte is free and will do NDS adjustment factors for you. I would look into that.

BWL = Braced Wall Line. IRC R602.10 is the code section. Simpson has a free calculator to use since doing it by hand is a nightmare. With experience you will eventually be able to just look at plans and know if it complies.

You wouldn't happen to know if IRC braced wall lines are the same as NBCC part 9 would ya?

 

[KootK]

You wouldn't happen to know if IRC braced wall lines are the same as NBCC part 9 would ya?

So similar as to make any differences pretty trivial.

 

[fp23]

@davidl13

I live/work in a high wind area. My process for this is to do a quick lateral analysis of the building using the SDPWS (once you've done this a few times you can do it pretty fast). Most of the houses around here pre 2000's are primarily held up by drywall from a lateral perspective. I use 120plf (60plf 2 sides per the SPDWS) for any walls that meet the drywall aspect ratios (1.5:1). It's not uncommon for me to get a house that doesn't have adequate lateral capacity to begin with, especially houses built in the 90's. In this case, I make sure that I'm adding ply sheathing somewhere else and maybe holdowns to replace the strength I'm taking out or improve the condition. Buy yourself a laser at home depot and get out there and start measuring!

I think the IEBC says that you can increase the lateral load on any element by up to 10% without modifications. So I could see the logic that if you remove less than 10% of the wall in a level (assuming it's drywall) then you don't need to justify it any further.

 

[lexpatrie]

While I don't disagree with this comment, based on what I've seen, even asking this question would put OP above the standard of care. My experience has been that many engineers (perhaps the majority) involved in residential work don't even consider lateral design.

Even if OP is perhaps not ready to be doing this work (based on the probably higher than average standards of some of us here), by asking these questions, I think they're on the right path.

I don't quite follow the semantics of this argument but I'll just skip that. "don't disagree" means you agree, but....

I know this is going to shock everyone, but NO.

If this were a hypothetical question, then sure, fine, that exceeds the standard of care, asking about something you don't know how to do properly, but in this case, the project has already been agreed upon, the assignment accepted, and now the most basic questions are being asked. I'm not on board that that is "exceeding" the standard of care, and I never will be.

This scenario is the one upon which collapses are "built."

CACI No. 401. Basic Standard of Care

Justia - California Civil Jury Instructions (CACI) (2024) 401. Basic Standard of Care - Free Legal Information - Laws, Blogs, Legal Services and More

www.justia.com

https://docs.acec.org/pub/18803059-a2fd-2d06-cc39-a6d1dd575265

Standard of Care, if you ask me, is the weakest possible argument. Practicing in the area of competence is a much clearer definition.

Why?

You might be able to convince yourself (or be willing to testify in front of a jury) that taking on an assignment you're not competent and capable of doing at the outset is commonly done by "reasonably careful professional engineers" in your area, (standard of care isn't generally the same as statutory requirements, although CACI seems to incorporate the statutory "competence" requirement into it as part of the definition, [thankfully] but it a) standard of care and statutory requirements are different things, and you can violate the statutory requirement to practice within your area of competence, yet still conform to the "standard of care" especially if nobody in your area cares..... b) "standard of care" is generally pure opinion. It isn't generally founded on a letter survey from engineering peers or firms within a 500 mile radius (or whatever) indicating 65% of engineers would do this (Texas is a bit of an exception as the board asks for volunteers on some engineering subjects, but that's for satutory stuff, not standard of care stuff, I think). It's usually two photogenic engineers in court trying to out-grandpa the other. Unless your attorney can't find an expert witness willing to support whatever outlandish "standard of care" scenario is needed to support their client's claim/defense (argument).

This level of questioning indicates a basic lack of knowledge and competence to me. If it were asked before a project is undertaken, then sure, eight random people on the internet whose credentials are not known can "augment" this person's competence in the subject up to the statutory requirement. But here's the thing, the project is already accepted and underway, from what I read.

So, No.

Now we come to the part of my post where I wonder why I even bother, because I know nobody involved is likely to listen.

As Kootk said:

I have little concern for what any engineer does or doesn't know in a particular space. What I'm concerned with is whether or not they recognize their deficiencies and are proactive in addressing them. I take the existence of this thread as @davidl13 doing just that.

Well, that's nice. Only about twenty ethical/legal problems with that.

By the way, this is an affirmative defense, in other words, you're (legally) agreeing to the premise (what you said reads to me like you don't care about competence or experience, I don't see how that can be read any other way). The issue is, your stated requirement to wash it away: "and are proactive in addressing them" isn't met. This isn't Proactive, this is retroactive, DURING the project, after it was agreed to undertake. So the argument falls apart. Now that the helicopter is off the ground, let's read the instruction manual.

Once one hangs out their shingle and becomes an entrepreneur, their primary job responsibility is identifying market opportunities and exploiting them. Competent engineering is important but a distant second. That, no matter what frou-frou gibberish your local association has made you sign to the contrary.

NO. This attitude is dangerous and negligent and I'm asking you to stop advocating it. This is the "fake it until you make it" and it does not ethically fly in engineering. I'll unhappily point to OceanGate (six dead was it?) and Harbour Cay (11 deaths as it happened during construction), the Kansas City Hyatt collapse (114 deaths), and Berkmann Plaza II ("only" one death, again, during construction) where the record is quite clear, and we can put the FIU Bridge Collapse (6 deaths, again, during construction), and Champlain Towers South (98 deaths) in the at least maybe category where four out of five dentists think there were issues that were fairly obvious.

Oh, and the New Orleans Hard Rock Hotel collapse (4 deaths, as I recall, again, during construction) in that category.

This is not some ride-share app.

It also blatantly violates the requirement that engineers practice within their area of competence. If one hypothetically identifies a "market opportunity" this is not enough, one must be competent to offer services. Just for argument's sake, Minnesota:



I'm not even going to bother addressing your attitude about "frou-frou" gibberish (i.e. Legal Requirements). That sounds very very like Stockton Rush and his attitude toward the testing requirements for PVHO.

If I had stuck to only that which I already knew how to do, I'd still be pressing the "equals" key incessantly in some truss design software package. You know, slaving away for some entrepreneur who actually grew a pair and took some risks.

Basically an admission that you've routinely practiced outside your area of competence. Where did you say you were practicing again? Or were you intending to self-report as this is also a "frou-frou" legal requirement?


GaStruct:

They go on to say anyone who bids appropriately knowing the requirements of a properly designed and detailed LFRS will not win the bid.

I don't care and it doesn't legally matter. You can't produce an unsafe or inadequate design to ensure a profit on the job.

There is no constitutional right to a profit in any business. What this really says is either a) people underbid this all the time and rely on "worker expolitation" for profitability, or some other issue, like violating either the standard of care or other ethical cannons. Or they lose money selectively and work on profitable jobs to offset, or they bleed slowly to death and close the company. Shrug. It doesn't matter. One must hold paramount life-safety as an engineer. sadly most states don't actualy have this language in their statutes, it's in the NSPE ethical canons and not anywhere else, I thought for sure it was until I started looking for it in statutes about a year ago.

What Does it Mean to "Hold Paramount the Safety, Health, and Welfare of the Public”? — Training For Engineers

To hold paramount simply means to set as more important. In this canon, the recipient is the public, and the objects are safety, health, and welfare. This seems like a difficult responsibility that could involve thousands of moving parts, any one of which could escape a careful engineer’s attent

www.training4engineers.com

I'll have to go looking for that Simpson tool as it would come in handy now that I'm doing a "check" of a braced wall plan done by others.

10,000 character limit, that feels new.

 

[lexpatrie]

10 attachment limit, too.

KootK:

I am actually of the opinion that light frame construction is one of the most specialized and non-obvious things to dive into as a structural engineer if you lack exposure to that kind of thing. With braced steel towers, shear wall CIP condos etc, most any fool can probably look at the skeleton and have a pretty good idea of how things work.

With light frame, the bits that we use look nearly identical the bits that we don't. And there are a lot of bits. And you want to do WHAT with OSB? Surely you jest...
fp23:

My god, something I can agree with.

I think the IEBC says that you can increase the lateral load on any element by up to 10% without modifications. So I could see the logic that if you remove less than 10% of the wall in a level (assuming it's drywall) then you don't need to justify it any further.

If only the IEBC actually counted as residential code, which outside of Florida (who specifically amends to include residential structures), this isn't quite viable as a strategy. It's also not engineering, it's hand waving.



Florida Building Code, Existing, 2023, eighth edition




2021 International Existing Building Code

Let's step back a second, because we need to classify the work first:



Furthermore, as of 2021 IEBC, now that we are talking about it, it's 5%, and it is in Alterations Level 1 - (this is pretty restrictive) and the language is as follows, this particular provision is related to snow drifts and design dead and live loads, and it's strictly interpreted as applicable to alterations, i.e. you aren't removing lateral or gravity load elements:


This does not fit what is described here by the OP.



Alterations level 2 is based on a work area, less than 50%, so it would seem to apply to deleting a loadbearing wall or a shear wall. There are at least provisions in that portion that seem to make some sense for such work, as well.




This doesn't really fit, thematically, with deleting a load-bearing wall..... but the 5% increase wording is still in there.

As far as deleting a shear wall, alterations level 2 states: "alteration that decreases the capacity of the existing lateral load-carrying structural element......




Still not quite seeing a load-bearing wall, but there's some discussion of substantial structural alteration in Alterations - Level 3.



Substantial Structural Alteration is defined as:


Well, Level 3 is less useful than Level 2. Language pertains to lateral load resisting elements and points at the IBC.

I think the answer to the load-bearing wall question lies in Chapter 3. (When it is not a shear wall).

"New structural members" added "as part of the alteration" shall comply with the IBC.