The dangers of software and code changes 1

[Eng16080]

I use WoodWorks Sizer for sizing most wood members. I must have installed an update recently or inadvertently changed program settings because I just noticed the default code is set to ASCE 7-22 and not ASCE7-16 therefore using the snow load combo: D+0.7S rather than D+S. Fortunately this came to light while manually checking a beam calc. and noticing the end reactions were off.

I realize this is ultimately my error, but it makes me wonder how often errors like this occur, and if the code writers realize the potential problems caused by messing with these loads seemingly every other code cycle. I'm sure there are software users who wouldn't suspect any great harm in using the newest code in the analysis. (I'm not necessarily defending them.)

Sometimes I feel like it would be safer to write my own software for some of this stuff and just lock it to the codes I'm currently using (ASCE 7-16, etc.) and then use these same codes for the next 20 years or so (until I retire). Maybe it's not a perfect approach, but I doubt I'd ever be more incorrect than I was today due to the rather large difference between 0.7S and S.

I don't really have a question here, but wanted to mention today's screw up in the hopes that somebody else might avoid the same error. I always try to be careful but this one certainly caught me off guard.

 

[driftLimiter]

This is one of many issues that will arise due to the change in snow load to ultimate levels. I don't think the code writers really care that much about us little guys. And realistically the engineers are going to be the first to adopt these changes, the rest of the industry (products, specifications etc) is going to take a while to catch up. I am sure you are aware of this but it isn't just the load combination factor that changed, the magnitudes of the loads increased as well. Care to guess how much? lol. Hint (1/0.7).

Seismic loads are up 15% in my region on the 7-22 vs 7-16. Its going to eliminate some construction methods around here unfortunatley. People are already talking about traditional tilt-up warehouses no longer penciling out are suggesting moving to a steel frame supported wall system.

 

[Flotsam7018]

Same exact thing happened to me in Enercalc a few weeks back.

 

[human909]

Codes change. Physics stays the same. This has been the case long before computers and engineering software.

It really is up to the user to know the limitations of their tools. Be it their pencil, their slide rule or their software. Most importantly you need to know the limitations and coverage of the calculation rules your are applying and in general this is often codes. But plenty of structural engineering still can default to 'rational analysis' rather than a codified recipe.

The above isn't meant to be a elitist superiority statement. Simply a statement of fact. Just last I spent around half a day trying to get my head around concrete beam shear calculations. Looking at the code and the output of two different software packages. I am just inexperienced and ignorant in the breadth of my understanding when in comes to beam shear and it takes plenty of work to even partially get my head around the complexities of the code (let alone the theoretical/empirical research that guides the code).

The point is always have healthy doubt. It sounds like your software changed the game on you slightly here which is a bit rude.

 

[Eng16080]

Same exact thing happened to me in Enercalc a few weeks back.

I've been on the fence about purchasing Enercalc. Having used it in the past, I always seemed to find discrepancies when checking calculations manually.

The point is always have healthy doubt.

Agreed, and this is what I often tell people. The fact I missed it this time is somewhat embarrassing.

It sounds like your software changed the game on you slightly here which is a bit rude.

It was likely my fault. I don't blame woodworks. I likely installed an update and didn't anticipate it would change the default code, ultimately resulting in the snow loads only being about 70% of what they should be per the newer code.

 

[jerseyshore]

For people who use ram structural system know the struggle of installing an update and then your previously working model now has 25 slab edge warnings.

Enercalc has had some issues in the past but I love that program. Chris is always quick to respond and address potential bugs.

I've just gotten used to checking codes and defaults on new projects. Changing an existing project is diabolical tho. I'd report that immediately because a lot of people won't notice.

 

[XR250]

Codes change. Physics stays the same. This has been the case long before computers and engineering software.

For sure.
Honestly, I know some old-timers who still just throw 15 PSF on everything for wind and 5% mass for seismic and call it a day.

 

[Eng16080]

Honestly, I know some old-timers who still just throw 15 PSF on everything for wind and 5% mass for seismic and call it a day.

While I don't fully agree with this approach, the longer I do this profession, the more I can see the logic in it.

 

[jerseyshore]

For sure.
Honestly, I know some old-timers who still just throw 15 PSF on everything for wind and 5% mass for seismic and call it a day.

NYC code was 20 psf wind for all buildings up to 100 ft tall. Just a nice flat wind pressure. No wasted time going thru the code just to come up 18.7 psf or something like that. The code guys must get paid by the page because half of ASCE7 feels like wind chapters now.

 

[JAE]

This reveals the great danger of we engineers using software.

I'm just as prone as others to simply plug and grind and get answers and draw those answers onto my plans.
Any software needs to be checked by hand several times before trust begins. Tough to do on large models but some checking is necessary.

 

[GregLocock]

We used to do a regression analysis on each iteration of the app when it was released. This would run through a standard suite of models and we'd then check the results remained the same. Or not. Problem is it's a non production task, so nobody has time to do it, so we just carry on with the old code. But then every time we'd raise a bug report the developer would say, oh we fixed that in 2024.1, you are using 2023.2.

So we more or less stopped doing the regression check, stay up to date with the releases, and I suppose assume our correlation activities will raise any problems..

 

[IRstuff]

We used to do a regression analysis on each iteration of the app when it was released. This would run through a standard suite of models and we'd then check the results remained the same. Or not. Problem is it's a non production task, so nobody has time to do it, so we just carry on with the old code. But then every time we'd raise a bug report the developer would say, oh we fixed that in 2024.1, you are using 2023.2.

So we more or less stopped doing the regression check, stay up to date with the releases, and I suppose assume our correlation activities will raise any problems..

The potential pitfall, which may not occur in other industries, is the possibility that the software update missed a code change, and the regression wouldn't catch that unless the engineer is aware that the code change should produce a different result, but the software did not.

 

[GregLocock]

True we didn't work to code, correlation is the main game, although I did used to have to sign an actual official report that said , in essence, vehicle model xyz has been tested in accordance with procedure abc and it passed.

 

[GaStruct]

NYC code was 20 psf wind for all buildings up to 100 ft tall. Just a nice flat wind pressure. No wasted time going thru the code just to come up 18.7 psf or something like that. The code guys must get paid by the page because half of ASCE7 feels like wind chapters now.

And you will get a different pressure with each method you use - it's ridiculous

 

[IRstuff]

One might suppose that at some time, relatively soon, AI's like Poe and Claude will be able to "read" the code and automatically fill in the correct parameters for each calculation relatively quickly, so only thing required is to feed it the latest code.

 

[jerseyshore]

And you will get a different pressure with each method you use - it's ridiculous

Absolutely. I worked with a lot of old timer engineers and some would use an old BOCA code or blanket 20 psf wind like NYC did. They've been thru so many code changes that they don't care to worry about all the different changes every 3 years. Jack the wind speeds but add a 0.6 factor. Apparently now they are jacking the snow load but adding 0.7 factor. Just want to sell new books.

 

[Eng16080]

They've been thru so many code changes that they don't care to worry about all the different changes every 3 years.

I'm not even that old, and I'm starting to feel this! With wind loads, I usually start with some blanket conservative value and then only refine it if I'm having difficulty getting a reasonable design to work.

The tricky part with this most recent change is that not only did the load combinations change, but so did the actual snow load calculation, from allowable to ultimate (if I have the terminology correct). I think a lot of engineers might assume in general that using a newer code in a piece of software should cause no harm, but this is one case where it definitely can, since the newer code essentially makes any previously entered snow load values invalid (roughly only 70% of what they should be, on average). This would be similar to the wind load change from ASCE 7-05 to 7-10.

 

[jerseyshore]

I'm not even that old, and I'm starting to feel this! With wind loads, I usually start with some blanket conservative value and then only refine it if I'm having difficulty getting a reasonable design to work.

The tricky part with this most recent change is that not only did the load combinations change, but so did the actual snow load calculation, from allowable to ultimate (if I have the terminology correct). I think a lot of engineers might assume in general that using a newer code in a piece of software should cause no harm, but this is one case where it definitely can, since the newer code essentially makes any previously entered snow load values invalid (roughly only 70% of what they should be, on average). This would be similar to the wind load change from ASCE 7-05 to 7-10.

Agreed. And I remember what a pain it was for everyone in my old office to change their mindset for wind at the time. Especially because NJ and NY and NYC all have different codes referencing different standards. Why must they change the snow ugh.

 

[Celt83]

Be careful with the new snow in a few locations it is more than just a change to LRFD, the ground snow loads have also received a considerable boost. There was a structure magazine article covering it, https://www.structuremag.org/article/ground-snow-loads-for-asce-7-22/

 

[Rabbit12]

I can't wait to deal with 3rd party/vendor designs for the new snow loads.

I recall a conversation with an OH door vendor a few years ago when the wind load changed from allowable to ultimate. They were all up in arms about the wind load on my drawings. We wanted windows in the door and the only windows they could get to work were like 1" high (due to the high wind). I asked them if they were using allowable or ultimate wind load and they had no clue.

Anyone who has worked with FM Global knows they still utilize wind loads using an importance factor, but they are pushing to update to 7-22 snow loads. Pick one or the other please! We haven't used importance factors with wind loads since 7-10!