The dangers of software and code changes 2

[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.

 

[Eng16080]

And I remember what a pain it was for everyone in my old office to change their mindset for wind at the time.

Same here. I had conversations with other engineers at the time who weren't aware that the new higher wind loads were only to be used with the new load combinations. They thought the resulting wind demand on a structure was suddenly much higher. They'd say things like: "It's going to be harder to get this building to work with the new wind loads." Overall, it's just confusing for everyone.

Plus you lose (at least temporarily) an intuitive sense of what a reasonable wind load value is. It would be like if they changed the typically residential floor live load of 40 psf to something like 60 psf halfway through an engineer's career. For me, it would be difficult to unlearn "40 psf" and I'm sure I might make some mistakes as a result.

 

[Eng16080]

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/

Good call. I was aware of this from another thread here a few months ago. I'm sure it won't be for another 5-10 years anyway before my state adopts a building code which requires ASCE 7-22 or newer. I'll probably forget all of this by then.

 

[XR250]

Same here. I had conversations with other engineers at the time who weren't aware that the new higher wind loads were only to be used with the new load combinations. They thought the resulting wind demand on a structure was suddenly much higher. They'd say things like: "It's going to be harder to get this building to work with the new wind loads." Overall, it's just confusing for everyone.

Plus you lose (at least temporarily) an intuitive sense of what a reasonable wind load value is. It would be like if they changed the typically residential floor live load of 40 psf to something like 60 psf halfway through an engineer's career. For me, it would be difficult to unlearn "40 psf" and I'm sure I might make some mistakes as a result.

I agree. I think the push to make building design more structurally efficient and reliable probably does the opposite in some cases. I really think we should go back to ASD for everything. (coming from someone who still uses the Green Book).

 

[JoshPlumSE]

There is constant tinkering with codes. Some of them are essential for safety. Like when we added confinement requirements for concrete columns, or re-did the seismic weld criteria for steel moment frames.

Some are relatively minor. Where they adjust load factors, resistance factors, allowable stresses based on testing.

The ones that frustrate most of us are the ones that are merely intended to "modernize" the code.... Like switching from ASD level forces to ultimate level forces. Heck, ASD 9th edition was in 1989 and the industry didn't really switch over to LRFD until 2007 when the 13th edition started gaining steam. Maybe switching from fastest mile wind speeds to 3 second gusts. A lot of these changes are made because the engineering codes no longer match what the government and academic researchers are doing. If the USGS doesn't collect fastest mile wind speed data anymore, then the codes will eventually be changed. It might take 10 or 20 years, but that change will eventually happen. Ideally, it makes it's way into the code commentary and appendices for a couple of code cycles before it gets incorporated into the main body of the code. But, it's going to happen eventually.

Caveat: I sympathize with all of you dealing with code changes. However, I've been on the software side for the majority of my career. Therefore, I tell you unequivocally that code updates REALLY help sell software. So, while a sympathize with other engineers, my frustration is tempered by the fact that these code changes help my company's bottom line greatly.

 

[JoshPlumSE]

I should also mention that I attended code meetings (AISC mostly) twice a year for 10 years. And, I can attest that there is a lot of effort made to listen to everyday engineers. However, relatively few of them are involved in the code writing process. In general, I'd say that there are a few types of people that attend these meetings:

a) Academics who are eager to get funding for new research and like to see their research affect the codes. They're not bad guys. Though (IMO) a lot of them have very little concept of what regular engineers do from day to day.

b) Industry representatives. They represent manufacturers, trade groups, software companies and such. They are there to keep an eye out on any code changes can affect their company. Again, these aren't bad guys. They understand a lot about the industry niche(s) their companies occupy. They also tend to have a much better understanding of what engineers do. Many of them are former engineers and / or speak regularly with their engineering customers. This was the group I was in when I was there.

c1) "Real Engineers". I put this in quotes because I'd guess half of these engineers are more academic or business types. We're talking about the presidents and vice presidents of large engineering companies that no longer do much day to day engineering. They're no longer slogging through calculations and drawings on a day to day basis. That being said, they know EXACTLY what engineers do on a day to day basis. They've just moved past it. Think of them as Jack Welch type of guys. They went to school and got advanced degrees, then went into the private sector and used their academic credentials to climb the corporate ladder. They probably spent 5 or 10 years doing the day to day work that most engineers do. But, now they're 10 years removed from that. They peek their noses into it now and then. But, just as likely they're publishing journal papers or sponsoring research on pet projects of theirs.

c2) Same as item c1, but removing the quotes. These folds tend to own their own smaller companies. They may still be in responsible charge for every project that goes through their office. They are doing well, but they don't want to give up the day to day engineering because they LOVE what they do. They also care intensely about the profession which is why they spend so much time at these committee meetings.


I'd say that (a) and (b) each represent about 1/3 of the members of the code committees I saw. While c1 and c2 are equal components of the rest..... Meaning that about 2/3 of the code committees have a really good idea about what working structural engineers do and the struggles we have. However, only about 16% of them still do this type of work.

I don't think any one of these groups "dominate" the code committee meetings. In fact, I'd say it's a pretty congenial balance between the groups striving for shared goals. That being said, the Academics have the most time and energy to spend on the code provisions. They may have grad students that they can assign to do the work they volunteer for.

 

[plausibly_civil]

I just ran into a similar situation when reviewing the 2021 SDPWS changes for my firm. The changes overall made a lot of sense to me and added a lot of clarity to certain sections, but I can see a younger engineer definitely stumbling with a handful of the changes. Specifically, the choice to combine the previously separate wind load and seismic load capacities for shear walls from Table 4.3A and use different ASD reduction factors for each (2.0 and 2.8 respectively) I think is a great change. The table is way easier to read now and it always looked clunky in a landscape orientation so I appreciate this effort to modernize the code. We have so many resources telling us as engineers what changes happen in each code (StructureMag, SK Ghosh, the standards themselves, etc.) that I don't see the changes as much of an issue. It probably takes me about half a day every 3-6 years per standard to get up to speed on the changes relevant to my practice.

The only big exception in my opinion is ASCE 7 because there's so many stakeholders involved with loading criteria. I'm not sure how it is outside of high seismic areas, but jurisdictions around here really do not put much effort into updating their prescriptive loading requirements. It's a complete toss-up whether the AHJ will require 85 mph, 98 mph, or 110 mph wind speeds and often I've had to correct reviewers on their own loading requirements or the relevant code changes.

 

[JAE]

I just ran into a similar situation when reviewing the 2021 SDPWS changes for my firm. The changes overall made a lot of sense to me and added a lot of clarity to certain sections, but I can see a younger engineer definitely stumbling with a handful of the changes. Specifically, the choice to combine the previously separate wind load and seismic load capacities for shear walls from Table 4.3A and use different ASD reduction factors for each (2.0 and 2.8 respectively) I think is a great change. The table is way easier to read now and it always looked clunky in a landscape orientation so I appreciate this effort to modernize the code. We have so many resources telling us as engineers what changes happen in each code (StructureMag, SK Ghosh, the standards themselves, etc.) that I don't see the changes as much of an issue. It probably takes me about half a day every 3-6 years per standard to get up to speed on the changes relevant to my practice.

The only big exception in my opinion is ASCE 7 because there's so many stakeholders involved with loading criteria. I'm not sure how it is outside of high seismic areas, but jurisdictions around here really do not put much effort into updating their prescriptive loading requirements. It's a complete toss-up whether the AHJ will require 85 mph, 98 mph, or 110 mph wind speeds and often I've had to correct reviewers on their own loading requirements or the relevant code changes.

Yes - I've seen city websites provide their "custom" loading criteria and mandate 90 mph wind using ASCE 7-16. I called them to suggest that the 90 mph wasn't valid as it was a service level wind and the 16 version used ultimate wind speeds. They didn't even understand what I was talking about.

 

[Eng16080]

I just ran into a similar situation when reviewing the 2021 SDPWS changes for my firm. The changes overall made a lot of sense to me and added a lot of clarity to certain sections, but I can see a younger engineer definitely stumbling with a handful of the changes. Specifically, the choice to combine the previously separate wind load and seismic load capacities for shear walls from Table 4.3A and use different ASD reduction factors for each (2.0 and 2.8 respectively) I think is a great change.

I agree. This is a good example of a code change that makes sense.

It's a complete toss-up whether the AHJ will require 85 mph, 98 mph, or 110 mph wind speeds...

Yes - I've seen city websites provide their "custom" loading criteria and mandate 90 mph wind using ASCE 7-16. I called them to suggest that the 90 mph wasn't valid as it was a service level wind and the 16 version used ultimate wind speeds. They didn't even understand what I was talking about.

These are perfect examples of the detrimental effects these code changes can have. The requirements become somewhat incomprehensible (especially for non-engineers). If I ever participated in an ASCE7 code meeting, I'd imagine it would be rather hopeless trying to argue this point. Hopefully at this point, all loads subject to change from service to ultimate have already been done, and maybe we can get some consistency for the next 10 years.

 

[RWW0002]

Yes - I've seen city websites provide their "custom" loading criteria and mandate 90 mph wind using ASCE 7-16. I called them to suggest that the 90 mph wasn't valid as it was a service level wind and the 16 version used ultimate wind speeds. They didn't even understand what I was talking about

Just one example of many of why consistency is important in the "language" of engineering. I maintain that changing wind and snow loading to ultimate-level was/is a mistake. I understand the reasoning behind ultimate-level loading and reliability-based methodologies, however loads have historically been communicated to the public at a Service-level and should continue to be (and no W_asd on the drawings is not adequate in my mind.) The public, especially contractors, suppliers, inspectors, end up "speaking the language" of the current code cycle, without fully understanding it, and the ensuing mess only causes more work for engineers and more confusion overall.

I am both an "ASD" guy and an "LRFD" guy depending on the project, material, and workflow. Factoring up or down load to ultimate-level or service-level is one of the easiest tasks that I might have to do on a project. But trying to communicate the ever-changing loading (that sometimes actually changed and sometimes only looks like it changed and sometimes both) is a nightmare. Even worse are the projects that may not have someone involved to help navigate the semantics. It is now 15 years since wind started using ultimate-level wind speeds and I still have issues with component suppliers and others with "90 mph" components.

"Communicated" loads have been allowable loads ( pre-factor-of -safety loading) in every US code and manual I am aware of until recently. We have basically been saying that after considering a proper margin for safety "This is what your building can be safely expected to resist." Wind speeds reported on the news or measured at home could be fairly closely correlated to the allowable wind speeds on drawings. Similarly snow depths could be measured and correlated to the allowable ground snow load and you could get a sense of how safe your building is in an event. Now that we are talking in terms of ultimate laods I feel like it gets the general public farther from understanding the limits of their building (which, in my opinion, is half of the point of our job!!)

We would never tell someone a floor live load in ultimate terms "This is the absolute max load your floor can resist, but I wouldn't recommend putting that much on it..." and I maintain that we should not be talking wind or snow at ultimate level either.

 

[phamENG]

and no Wasd on the drawings is not adequate in my mind

I had a long, drawn out fight with a plan reviewer once because the city ordinance said that no building could be designed for less than 115mph, but my Vasd was only 92mph (or something like that). Such a mess lol. I had to teach their boss the difference between Vult and Vasd, and that Vasd is only used in 4 very specific cases while use 4 very specific design standards. Took two weeks or arguing about it to get them to admit I didn't actually have any comments and they issued the permit.

Wind speeds reported on the news or measured at home could be fairly closely correlated to the allowable wind speeds on drawings.

Yeah, but they haven't been presented that way....ever? Originally, it was just a blanket design pressure, then evolved to Fastest Mile, and then in 1995 transitioned to 3-second gust. Wind speeds reported on the news is a 2-minute average (unless it's a hurricane, then they do 1-minute average).

Similar issue with snow. How deep is 10psf of snow? How deep is 40psf of snow? And what about the fact that I don't actually design for that? I design for a sloped roof snow load modified for exposure and heating/insulation of the building. So regardless of what 'level' of snow is presented, it's not immediately intuitive. Translation of 'psf' loading to real life loading is difficult for even engineers to visualize - just look at all the posts about "what does 40psf live load really mean?"

which, in my opinion, is half of the point of our job!!

I disagree on this one. I don't see the point of my job as helping owners and occupants understand the limit of their building - it's to make sure they don't need to worry about the limits, because except in a truly extreme event that would have necessitated evacuation anyway, their building will perform at least to the minimum requirements of the code. Now, if they want to know, I'm happy to explain it to them. But the average person - whether an owner or not - isn't going to get it and doesn't really want to. They just want to know that it's 'safe.' So I think it's appropriate to prioritize maximizing the reliability of a building over communicating what you can rely on it to do.

After all, how many of us wonder at what speed our car will no longer adequately protect us in a crash? We trust that it was designed and manufactured in accordance with standards that we may or may not understand if we read them, and we (mostly) obey the laws regarding their use and modification. Are there exceptions? Sure. But they're exceptions, not the rule.

 

[RWW0002]

Yeah, but they haven't been presented that way....ever? Originally, it was just a blanket design pressure, then evolved to Fastest Mile, and then in 1995 transitioned to 3-second gust. Wind speeds reported on the news is a 2-minute average (unless it's a hurricane, then they do 1-minute average).

I agree that wind has not been straightforward, and that I oversimplified a bit, but most wind reports I see relating to a storm are gust speeds as I understand it ( mostly because it is more sensational and this is the news.. ha!). This has roughly correlated to the code wind since IBC adoption (around the last 25 years for most locations). In other words if you hear that you have a storm with 90 mph guests you know you are getting close to your 90 mph buildings limits. But now that same building is 115 mph.. "so we are easily good in that same 90 right... right???" While the wind values have been in a constant state of transition they have always been based on actual measurements at allowable level, not fictions ultimate wind speeds with uncertainty, factors of safety and probability of failure mixed in. That is the important distinction for me.

With snow - again a little education was necessary but ground snow can definitely be converted to inches of snow (in fact the reverse was done to produce the ground tables - as they are based on field measurements of snowfall as I understand it).

I disagree on this one. I don't see the point of my job as helping owners and occupants understand the limit of their building - it's to make sure they don't need to worry about the limits, because except in a truly extreme event that would have necessitated evacuation anyway, their building will perform at least to the minimum requirements of the code

I intentionally said half the point of the job. I agree that meeting code and ensuring public safety is the job, but communicating the limits of the design to the public is also a huge part of our responsibility ( Just talk to anyone who has had to testify in court..). Don't sell the general public short just because they aren't engineers. Many are perfectly capable of understanding basic limits , as long as it is not a constantly moving target. This is especially true in some sectors. Owners understanding building limits and the cost-benefit relationship of additional strength and/or reliability is very much a part of our jobs! Even more so with code officials, municipalities, local politicians.. etc. By complicating the historic use of "allowable load" in the conversation, we are risking a couple of things

1. Those who have successfully followed along with code language to date may get fed-up with keeping-up
2. Those who do not and have not kept up will now suddenly think that building are "stronger" than they were
3. Meaningful conversations about building performance are more complicated because you have to spend the first 30 minutes rehashing and re-educating.. after which you have mostly "lost 'em"

I like your car analogy, but the difference in building is that we are not delivering a "here it is take it or leave it" product but a custom product designed for a specific end-user and use. We tailor loads and performance to proposed use and communicate those loads with owners for the future. If there is a change in use or circumstances, an informed owner should know that the building may have to be altered or strengthened to perform reliably. The more complicated we make the code and the more cumbersome we make the loading information that goes on the drawings, the further we get from that important conversation.

As engineers, "If we err in communication, may we err on the side of conservatism.. "

As an aside, I am not advocating that we either use reliability-based design or communicate loads at allowable level. Both are possible and practical, just with potentially a few more moving parts involved in the background..

 

[RWW0002]

By the way phamENG - We've hashed this out before .. https://www.eng-tips.com/threads/asce-7-22-snow-load-revisions-big-load-increases.502736/

This thread hit on two "rant topics" of mine at once.. Ultimate-level loading and constantly updating software/subscription models (to the extent that validation is impractical or impossible), both of which I have gotten a bit long-winded about on here in the past. I told myself I was going to sit this one out, yet here I am...

 

[phamENG]

Don't sell the general public short just because they aren't engineers.

I'm not. When somebody expresses a desire a to know how the sausage is made, I gladly explain it. Somebody around here once said that inside every engineer is a repressed teacher, and I heartily agree. I enjoy the challenge of meeting a person on their level - whether they know nothing about physics or math or anything useful in understanding what we do or if they have a PE but they just don't do what I do. I flatter myself to think that, under different circumstances, I would have thrived in medical or law school. But due to certain life choices and resulting priorities, I became an engineer and not a doctor or a lawyer. I know enough about health/medicine to get by, and the same with law (a little more so because I own a business), but I'm not a doctor or a lawyer, so I depend on those professionals to guide me through medical and legal situations. I try to give everyone I work with the credit that they could do what I do if they devoted the time and effort to it (at least until they prove me otherwise...).

I get what you're saying. I think we work with different types of clients - most of mine now don't know and, while they care, they just want to know that the building won't fall down. It's been a while since I've worked with a truly sophisticated client, but even then most employed their own engineers, so I was talking with the owner's engineer and not the owner him/herself.

My experience with explaining things to people is that, if they're actually interested, I don't lose them. If they're just bringing it up to complain or to 'prove they know it better than me' then I don't even have their attention at the beginning. I usually start with something along the lines of "because data collection on environmental loads has improved and our ability to test materials has also become more refined, we're moving toward a design process that improves the overall reliability of new buildings to resist hurricanes, earthquakes, etc. In most cases, the end result will be the same as it was before but in some cases it will either result in a more reliable building or a less expensive one." An intelligent and inquisitive interlocutor will be able to pick some part of that and ask questions that drive a constructive conversation. Or, they'll accept it and we'll move on. It also keeps the conversation positive. If I complain about the changes, then I'm not doing anything to help them accept the fact that it has changed and we have to deal with it.

Do you have any proposals for how to communicate the capabilities of a building to the owners in an intuitive way while still using the probabilistic methods being developed to increase reliability and/or make reliability more consistent? What about dealing with the backlash when we say "you shouldn't stay in this house if more than 18" of snow is going to fall" only to have them evacuate 20 apartments for a 2.5' snow storm and they come back to zero damage?

 

[phamENG]

By the way phamENG - We've hashed this out before .. https://www.eng-tips.com/threads/asce-7-22-snow-load-revisions-big-load-increases.502736/

This thread hit on two "rant topics" of mine at once.. Ultimate-level loading and constantly updating software/subscription models (to the extent that validation is impractical or impossible), both of which I have gotten a bit long-winded about on here in the past. I told myself I was going to sit this one out, yet here I am...

Ha. So we did.

 

[RWW0002]

Do you have any proposals for how to communicate the capabilities of a building to the owners in an intuitive way while still using the probabilistic methods being developed to increase reliability and/or make reliability more consistent? What about dealing with the backlash when we say "you shouldn't stay in this house if more than 18" of snow is going to fall" only to have them evacuate 20 apartments for a 2.5' snow storm and they come back to zero damage?

We already do this to an extent. We factor loads all day. Design maps should be based on reliability design but "factored" to service level, similar to Vasd. Load factors should be put back on ultimate (LRFD) load cases. Most of the conversation around design criteria (during design, with code officials, with component designers, or post-design) is around "Design Values" so this is what we should focus efforts of communication and consistency around. Design Values, maps etc, should all be factored (via whatever method necessary) to service-level loading. (I know I am over-simplifying a bit risk factors etc make this a bit more difficult than I am making it sound, but not significantly in my opinion)

 

[phamENG]

That's the thing, though - we went away from that because it results in less predictable and less consistent reliability. If you look at the maps for various return periods of wind, they don't all line up. I imagine it's the same for the new snow maps, though I haven't looked at them closely. Granted, for most of the country it probably doesn't matter as the contour lines are spread states apart in some cases. I live within an hours drive of 4 different wind contour lines. Some of the maps shift enough so that entire cities fall on one side of the line for one return period, and the other side for the next. So it's not a matter of a simple multiplier.

Maybe it would be best to add something to the drawings translating it: "The structure is expected to withstand the following environmental and weather effects with little to no damage or loss of use: <list them in a way that a layman understands>" That way we can maintain our esoteric expression of design level events that more accurately describes things to future engineers who need to use the drawings to interpret the design intent for whatever reason, and any casual observer can see the box and understand what their building is meant to do.

 

[ANE91]

I gotta say, I was pretty “don’t mess with the code” (wrote a whole thesis about it) until I took a graduate-level reliability class. Knowing the very little that I do, now, about Turkstra’s Rule and Code Levels and such, I can’t find it in me to complain.

The code-writers know this sucks for us:

 

[ANE91]

Maybe it would be best to add something to the drawings translating it: "The structure is expected to withstand the following environmental and weather effects with little to no damage or loss of use: <list them in a way that a layman understands>"

Table 1.3-1 in ASCE 7 does this beautifully. I’ve had great success pointing laypersons to it.

 

[phamENG]

Table 1.3-1 in ASCE 7 does this beautifully. I’ve had great success pointing laypersons to it.

Really? You know a layperson who understands reliability theory? Really? I doubt most users of this site really understand it. Hey...I'm not even confident I can say that I really understand all the ins and outs.

I meant more like depth of snow, scale of a hurricane, etc. The stuff that RWW0002 was talking about.

 

[JoshPlumSE]

PhamEng: Do you have any proposals for how to communicate the capabilities of a building to the owners in an intuitive way while still using the probabilistic methods being developed to increase reliability and/or make reliability more consistent?

It's just being able to communicate effectively. There is nothing wrong with saying something like:

"This structure does not meet the current code requirements for snow loads in your area. For such a load condition, the structure is 30% 'overstressed'. Keep in mind that this includes safety and resistance factors that give about us a decent safety factor. So, it doesn't mean that the roof is going to collapse, especially under normal levels of snow. But, the crazy snow levels that occur in a once in 50 year snow storm could use us most of that safety factor"


Then maybe adding something later along the lines of:
"I know it sounds scary. But, look at it like a restaurant where you see an A, B, or C on a placard in the window. You see an A rating and you know there aren't any problems and it's safe to eat there. You can still get a bad shrimp or something. That's just life, but you know there isn't anything that is PREDICTED to cause problems. You know if you see a C rating that restaurant has major issues and is in danger of losing its license if it doesn't correct them quickly. So, even if you've eaten there in the past, you see that C rating and probably move to a different place.... Well, if we had a similar rating system for this building, it would probably warrant a B. You might see this placard and think twice about eating there, but the issues are correctable and don't approach what it takes for to shut the restaurant down. If you really liked that restaurant back when it was an A, you might still eat there when it's a B, it just makes you ask yourself what the problems were. In this case, know the issue is entirely related to snow, you should feel perfectly comfortable living there in normal situations. But, if there is a really bad snow storm then maybe for that brief time when snow is really piled up on the roof, living there is like the way you'd feel eating at a restaurant with a C rating. "