Residential Lateral Design Philosophy 3

[SarBear]

Hi, thanks for taking the time to read my post. I wanted to put some thoughts I have about residential lateral design out here and see if anyone has some advice or words of comfort lol.

I've been working at this engineering firm for a couple of years, and thus far my training has mostly been on small commercial buildings and small residential projects (tract housing). We have started to get an influx of large (like 10,000 square feet plus) custom residential homes with features including:
- 12:12 roof pitches
- Plate height changes galore
- Jogs, jogs, and more jogs
- Windows, windows, and more windows
- 3-sided glass dining nooks that stick out 15' from the rest of the house
- Covered decks that extend 15' away from the rear wall of the house
- Wings of the house at a 45 degree angle from the rest of the house
- Second floors with exterior bearing walls that are offset from main floor bearing walls below
- Rear walls of the home with a second floor, a main floor, and a walkout basement

We are in a heavy seismic area and have developed Excel spreadsheets for our lateral design. As I use our spreadsheet I can't shake the feeling that the formulas and calculations we have created are not even close to approximating what would really happen in an earthquake. Our spreadsheet or any other spreadsheet can't possibly capture the effect of 12:12 roof pitches, bearing walls that are offset from below, multiple jogs in each wall line, numerous plate height changes, etc. In my opinion if we were honest about really trying to analyze these structures and understand their true behavior in an earthquake then we'd need to do something way more robust than use our spreadsheet. Don't get me wrong, our spreadsheet is great for looking at rectangular-shaped buildings with flat roofs. But these custom homes we're working on are ridiculously complex. In my opinion, using our spreadsheet is just a way for us to say "See look, we ran some numbers". Well I think that those numbers are a sham and that it's dishonest to pretend that those numbers are anything besides eyewash. I've brought this up with my bosses. Their response usually boils down to "This is how all the other firms around here do it", with the reason for that being that's it's most cost-effective. Sure, we could build a scale model of the home and test it on a shake table, but who's going to pay for that?

So I guess some questions I have for you all are:

1) In my opinion, as engineers we should be able to "prove" mathematically that everything we call out on the plans and every construction detail we draw "works". Am I wrong? If I'm right, then I think that any engineer involved in residential engineering is not actually doing that.
2) What programs or solutions are you residential engineers using on these super complex custom homes? I looked at Woodworks, but from what I understand they don't have an option for changing plate heights on a level. In my mind that eliminates Woodworks from being a robust solution, considering that many of the homes we're seeing now have a 10' plate height, but then a 12' plate height in the master bedroom, and then a 19' plate height in the great room, etc.
3) Do you have any advice for someone just starting out in this field? I'm starting to feel a little disappointed in my career choice. In school we focus so much on calculating things and getting the right answer. In the field things are never as simple as they were in school, but even so it feels like there are a lot of things that we continue to do because they've always been done that way even if they don't "calc out", or we run these lateral design numbers just to say we did it rather than really trying to understand the true behavior of the structure.
4) Any other thoughts about lateral design on residential structures?

Thanks again for your time.

 

[driftLimiter]

Yea I have to agree with Pham on just that one line. A young engineer should be concerned with their work product. They should be 'pushing' their own boundaries and the boundaries of their boss.

However a young engineers responsibility is both to the public and to their employer. MSL said that he brought his concerns to the attention of the boss, but the boss insisted it be done a specific way.
Whatever the reason, it is the boss's responsible charge and engineering judgement to make that decision and not yours. I am not saying to stay silent but rather provide sufficient information about your concern, and provide an estimation of the consequences of not following up on your concern.

I have worked with these types of bosses before and the best advice is:

find a mentor who will.

Bosses that are in the habit of handwaving stuff are unlikely to ever change. A better form of this type of boss is someone who knows from experience that something is going to be okay, but instead of telling you to just do it their way, they give you an opportunity to sharpen your pencil and give it your best effort.

I know that this is fairly uncommon in light-frame residential outfits and I think its a shame.

 

[driftLimiter]

Something else I'd like to add is on the construction side of things. We do a few custom homes a year and we put forth a very considerable effort in the detailing and load path. But what we find more often then not is a big percentage of our well thought out details and load path considerations are ignored or overlooked by the builder.

The last job my colleague did a code-required structural observation of roof diaphragm nailing.
1) The requirement for structural observation was ignored and finishes placed before calling us out.
2) Building official 'signed off' on the work. Builder was curious why we had to go out after that.
3) The guys in the field said we have been doing this for 30 years and never heard of a structural observation.
4) We made them take off the finishes to inspect the roof nailing. And what do you know... None of the drag beam had boundary nailing in them. None of the blocking that was indicated with boundary nails was present. They ignored nearly half of the details we provided and very clearly showed.

They gave us a big shpeel about how their framers dont speak english, and the foreman has been doing this for 30yrs+.

The point is, its not just engineers but Building Officials and Builders they are all lax about requirements on homes.

 

[SarBear]

Thank you all for your thoughts. I am glad to know that I am at least in good company with some of the thoughts I've had about residential engineering and construction.

Let's be honest, how many lateral failures do we see in houses?

Haha, I have spent a large amount of time reading papers and other information about the seismic performance of wood-framed structures to ease my mind. Some of these custom homes we see are so full of glass that I struggle to view them as wood-framed. I live in a 2500 square foot wood-framed house that was built in the 1970s. I'm sure there was no engineering done, but I'm not worried about how my house will do in an earthquake since it's a rectangle with a lot of shear wall. I do have some doubts about a lot of the massive custom homes in this area with 20' tall great rooms with a 14' wide window and 2' of wall on either side.

a big percentage of our well thought out details and load path considerations are ignored or overlooked by the builder.

I've been out on site to see about 4 or 5 of the big custom homes we've engineered when the framing is nearly complete. I cringe when I compare our structural plans to what was actually built. It's a really disappointing feeling.

 

[milkshakelake]

@phamENG I like you too, lol. I have a lot of respect for your opinions. I agree in essence. But if you bring it up to your boss and they don't do anything, I think the junior engineer has done their part. Further pushing back could cost them their job, and they have to feed their family and stuff. I agree with you and driftLimiter that the best way forward is to get a better mentor.

One of the major reasons I started my own company was because I had too many moments like what OP is having (maybe similar to you). Back then, I'd bring up a problem, get shot down, and had to do it the wrong way in two different companies. I was losing sleep over it, and had to defend bad designs against clients. But I wasn't in a position financially to do something against my boss and risk my job.

In my current practice, if a junior engineer brings up a good point, we'll follow it. It's good to learn. If it's not a good point, I'll let them do the calculations or I'll argue with logic and code references, or have a senior argue it. I have someone in my office who makes few legit points but keeps bringing up bad ones, and will defend the bad points a lot. I can't just say, "I won't argue this; do it my way," because that's a disservice to the employee. It would be falling into the same vices I hated about my previous bosses. Yet, it becomes a chore to argue and constantly find references to shoot down the bad points, so she will be the first to be laid off if I need to. That's where my point of view is coming from.

 

[kissymoose]

But what we find more often then not is a big percentage of our well thought out details and load path considerations are ignored or overlooked by the builder.

I like to say residential engineering is an oxymoron.
[ul]
[li]The level of detailing and design can't match that of commercial to stay competitive, unless you're doing high end homes.[/li]
[li]Many design aspects, such as the prescriptive LFRS methods, are empirically based, and have stayed thanks in part to lobbying from builder's associations.[/li]
[li]Decks, one of the house components most prone to structural failure, weren't even addressed in the IRC until 2012.[/li]
[li]Basement walls, another component most prone to structural failure, are still only required to be attached to the framing with anchor bolts at 6 feet on center. This hardly ever calcs out.[/li]
[li]Most importantly, the requirements for builders are whatever the AHJ wants, and due to the scale of residential construction, this bar can be low. It always just comes down to the inspector. In my neck of the woods, the only inspection for residential construction is by the AHJ, unless the contractor has a question or wants to pay for a quicker inspection. I remember one house in particular I went back and forth with the city for weeks about a relatively simple rake framing detail (how it shows on the plans), went out months later for an unrelated issue, and noticed that the entire roof framing in that area was different than what was specified. The inspector hadn't even noticed. All sorts of things get missed or covered up and moved on from.[/li]
[/ul]
Due to the level of detailed design that's common to residential structural design and the lack of adequate inspections and compliance to the drawings, residential engineering can be hard to navigate for engineers.
On the other hand, I will add that my area does not have high seismic or high winds. Additionally, I have been on plenty of residential inspections for real-estate transactions and what-not, enough to get a feel for common failure modes (at least for my area). Those inspections have done more than anything else in giving me confidence in how to approach residential design and where to focus energy.

 

[XR250]

Well put, kissymoose. That pretty much echos my experience in residential.
I have been on over 5,000 inspections so, yea, I have a good feel of the typical "failures".
Have had some tornadoes and a direct hit from Fran in that time period.

 

[phamENG]

milkshakelake - fair enough. Digging down, it sounds like we agree. The wording of the initial statement just rubbed me wrong, I guess. EDIT: I'm also in an idealist's paradise right now. I'm on my own, so I have broken free of the restraints of somebody else's dubious engineering choices, but also don't have the responsibility of training a new engineer while also keeping the lights on and food on both of our tables.

And yes, I branched out on my own for much the same reasons. I was working with good engineers, but some of them (in high positions in the firm) were a little to....sloppy?...for my liking. There was very little QC and a lot of reliance on "these don't fail anyway". Considering a design level wind event hasn't occurred in this region since the early 50s (and even that was probably limited to right on a small stretch of the coastline), I've often found the hand waving of lateral design here a bit...inappropriate. If you take issue with the probabilities used to determine the reliability ratings of our designs, that's fine, but convince other engineers of your position and take it to the code writers and adoption committees in your state. (But I'm also the one who says if you want the speed limit higher you should petition your city council, while most people will just speed...I understand that I'm in the minority on these sorts of issues a lot.)

kissymoose - I'll second XR: well put. Things have gotten a little better around here. There was some sort of scandal several years ago (I don't remember the particulars) that implicated several inspectors and a big developer in the area. There was a big crackdown and inspections have gotten a whole lot tighter since then. Of course that can just mean the inspector actually puts his/her boots in the mud on the site...doesn't mean they actually look at anything in particular. Most of the time they just look for code minimum. Spans look about right? Check. Anchor bolts at 6'? Check. Nails in the sheathing? Looks okay. Climb on the roof? Fat chance...check. Oh there are engineered drawings? Hmm...okay. Have the engineer come out and sign off on it. But don't worry about waiting to hang drywall. They'll just stamp it for you.