How often are y’all doing any calcs for single-family residential? 7

[ANE91]

Had a friendly lunch with some sorta-competitors in my market who were very frank about never doing calcs for their work. Work ranges from design to repairs/retrofits, almost all wood. Are they messing with me or what? Obviously, a practitioner can output more work without pausing to do any pesky analysis.

 

[phamENG]

I guess it depends. I could see getting to a point where you have everything pretty well tabulated or write up a simple spreadsheet. Enter a few parameters and spit out a conservative joist size and beam tables for various spans. Designs won't be very economical and most high end custom architects would hate you, but could be done.

On the other hand, I've known of several guys who just assume that it's wood so it'll work. Maybe size a couple of the longer beams. I've also seen them listed on court cases more often than others in the area.

I do an analysis. I don't have to submit formal calcs, but I size (nearly) every beam and run the numbers on my diaphragm and shear walls. Lots of things are "typical" and if I don't exceed those capacities, I don't check them every time, but if I need a new connection detail or a deviation from the 'norm', I'll check it and file it away in the hopes nobody ever asks for it.

 

[phamENG]

(When I say nearly every beam, I mean I don't run an individual check for every hip or valley on the house - I'll usually pick the longest one with the most load and make sure the 'standard size' that reaches the full depth of the cut rafter works. if it does, I use that everywhere.)

 

[Tomfh]

I’d be surprised if they literally never do any. But it wouldn’t surprise me at all if they rarely do calculations for the bulk of the work. A lot of the houses get built by carpenters without any engineering input at all, let alone detailed analysis.

 

[TRAK.Structural]

I'm somewhere in the middle. I calc out all atypical girders/beams, gable end wall studs, built up posts for point loads, track down wind uplift when necessary. I haven't been in the residential market for long enough to just know what will work in all scenarios. Honestly I do think this slows me down as compared to others in my area, but I stress less this way.

 

[GaStruct]

I put almost every house I do into Risa to get the gravity design. Tracing loads in a house that doesn’t stack is more tedious than a 10 story mixed use building.

I “eyeball” lateral. If the house lacks walls, I look more closely and run numbers for shear walls. Honestly a waste of time IMO because detailing lateral in wood to actually work is insane. Read Terry Malone’s book and you’ll see. Else, I use prescriptive. Even if not perfect.

All this being said, MANY houses get “designed” by the lumber supplier without a PE on staff or simply framed by what feels right from the framer.

There’s little problems in residential because there’s usually only a small number of people in the house and lateral is kind of fake anyway. I’m in a low wind and seismic region too.

Residential is a bear because you need to toe the line between engineering that calcs out and what has actually worked since the late 1700s.

 

[XR250]

I do calcs mainly for tall studs, longer beams, beams with complicated loading and joists with offset loads. Also for moment frames and complex 2D roof systems. I do most on my calculator or spreadsheet or my 2D frame program.
I don't actually save most of the calcs though.

 

[ANE91]

I “eyeball” lateral. If the house lacks walls, I look more closely and run numbers for shear walls. Honestly a waste of time IMO because detailing lateral in wood to actually work is insane. Read Terry Malone’s book and you’ll see. Else, I use prescriptive. Even if not perfect.

Thanks for the suggestion. This’ll be my next read. For others, it’s “The Analysis of Irregular Shaped Structures Diaphragms and Shear Walls.”

 

[ANE91]

I don't actually save most of the calcs though.

Never been asked by a building department to produce calcs? I haven’t, but I save it all, just in case.

 

[ANE91]

I guess it depends. I could see getting to a point where you have everything pretty well tabulated or write up a simple spreadsheet. Enter a few parameters and spit out a conservative joist size and beam tables for various spans. Designs won't be very economical and most high end custom architects would hate you, but could be done.

Can’t say I’ve enjoyed working with them, anyway. All this is starting to make me feel like I should leave the residential market behind.

 

[Eng16080]

For gravity, I calc. just about every unique condition. For lateral, if the exterior walls aren't swiss cheese with window/door openings, I usually do a quick ballpark check. With lots of openings, I'll look closer.

Most projects I trace loads manually. If it's really complex, then I might also create a RISA3D model of the major elements. Checking individual beams/columns usually doesn't take me that long, maybe around 3 to 5 minutes in woodworks on average.

I don't get a lot of projects that are the same or are simple. If I did, then I'm sure I'd streamline my procedure a bit and maybe do less calcs. Still, to never calc. anything seems real sketchy to me. When I do run calcs. I usually ballpark the member size in my head first. I'm usually pretty close but not always.

 

[SE2607]

I practice in California and I mostly do residential remodels. Most of my projects are high end and the building officials believe they have more liability than I do, so I do full calcs and detailed structural drawings on whatever modifications are made to the existing building.

 

[driftLimiter]

I practice in California and I mostly do residential remodels. Most of my projects are high end and the building officials believe they have more liability than I do, so I do full calcs and detailed structural drawings on whatever modifications are made to the existing building.

This is also my situation. I've produced mountains of detailed lateral calcs for complex residence. And the fees are rarely there. I'm actually quite fascinated that so many are saying they do so little calcs. I've never been allowed to use the irc before and seismic almost always controls.

I guess this is why some engineers can afford to have such low fees. I prefer commercial/institutional construction.

 

[ANE91]

the building officials believe they have more liability than I do

On what basis? My understanding is that building officials basically can’t be sued for anything. I guess they could lose their jobs and maybe their licenses.

 

[SE2607]

On what basis? My understanding is that building officials basically can’t be sued for anything. I guess they could lose their jobs and maybe their licenses.

One other thing that California has besides earthquakes is a LOT of attorneys. Here, the thinking is that "anyone can be sued for anything" and cities have been sued for building failures (balcony decks come to mind). I believe it goes to the "deep pockets" theory with the thinking that city governments have more money than a consulting engineer. I had one situation where, according to my calculations, a beam was 1% overstressed. I posted that experience here and, amazingly, the majority of the responses concluded that I MUST have a CSR less than or equal to 1.00. I am normally ok with a CSR less than 1.04 (actually 1.0446, rounding to a number less than 1.05). The plan checker, a third party consultant to the city, wouldn't approve the calculations as written. When I talked to him, he used the point I made at the beginning of this paragraph. Normally, I would just change the beam size and move on. The problem with this particular situation, a stronger beam was going to cost a LOT and I didn't see the value in making that change, not even to mention the change of connections, etc. I ended up shaving some "pad" in my dead load and it got approved.

 

[XR250]

Never been asked by a building department to produce calcs? I haven’t, but I save it all, just in case.

I have been asked but generally just for one item of the build. I just re-create the calc for that particular item.

 

[ANE91]

One other thing that California has besides earthquakes is a LOT of attorneys. Here, the thinking is that "anyone can be sued for anything" and cities have been sued for building failures (balcony decks come to mind). I believe it goes to the "deep pockets" theory with the thinking that city governments have more money than a consulting engineer. I had one situation where, according to my calculations, a beam was 1% overstressed. I posted that experience here and, amazingly, the majority of the responses concluded that I MUST have a CSR less than or equal to 1.00. I am normally ok with a CSR less than 1.04 (actually 1.0446, rounding to a number less than 1.05). The plan checker, a third party consultant to the city, wouldn't approve the calculations as written. When I talked to him, he used the point I made at the beginning of this paragraph. Normally, I would just change the beam size and move on. The problem with this particular situation, a stronger beam was going to cost a LOT and I didn't see the value in making that change, not even to mention the change of connections, etc. I ended up shaving some "pad" in my dead load and it got approved.

Thank you for sharing your experience. I acknowledge that California is its own ball o’ wax.

 

[ResidentialStructGuy]

I also focus on residential structures in California and have to provide a pretty detailed lateral/vertical analysis for almost every project.

 

[driftLimiter]

Thank you for sharing your experience. I acknowledge that California is its own ball o’ wax.

It's not just CA I would say the west coast states in general. Most houses I work on here in Nevada are not allowed to be designed by IRC and applying the IBC to a wood frame custom home is tougher than it should be.

 

[jerseyshore]

In Forte it's so damn easy to copy and link loads so I'll create calcs for more members than generally needed just as insurance for future changes (which are inevitable).

But for the most part I'm calc'ing out the bigger beams or unique loading, longer joist spans, etc. Checking the shear wall on the wall full of glass. Pretty similar to what the majority of structural engineers are doing.

There are some who go the architect route and use the span tables, IRC prescriptive sections, and let 84 Lumber design the majority. There's always someone willing to work cheaper.