The dangers of software and code changes 6

[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.

 

[Ron247]

if LRFD is truly the more accurate/consistent method

I don't know that it is more accurate or consistent, but it is more accepted. ASD will be dead and gone when all of us that learned it first are taking our dirt naps. When everyone left learned LRFD first, it will be king. Like I said earlier, my main reason for liking ASD is that I learned it first.

There is no real way to compare them fairly. ASD designs provide more steel, hey they must be stronger. Well, what if all the extra steel is not where you need it? Both methods have pros and cons but I know I can explain ASD to a layman easier than I can USD. But the nice thing about these conversations going back and forth, is that I learn to explain something better than I could before. And that is worth a lot to me.

 

[jerseyshore]

Are younger engineers learning LRFD and actually using it? Yes we learned LRFD in college, but the firm I first worked at everyone used ASD so I still do now. The LRFD-only steel manual (from early 90's?) was a great paperweight. My professor in 2010 said ASD is old news, but here we are in 2025 and feels like everyone is still using ASD.

 

[human909]

Are younger engineers learning LRFD and actually using it? Yes we learned LRFD in college, but the firm I first worked at everyone used ASD so I still do now. The LRFD-only steel manual (from early 90's?) was a great paperweight. My professor in 2010 said ASD is old news, but here we are in 2025 and feels like everyone is still using ASD.

Well it is kinda like the metric system. For some reason the US doesn't seem to want to change while the rest of the world has.

I'm not from North America and I do look at the stubborn use of both with continued surprise.

I see LRFD as dressed up ASD. Strip off the statistical costume and it’s largely the same safety buffer for most structures. ASD was less overt about the reliability stats, but the reliability was baked in all the same. People forget LRFD was designed to mirror ASD reliability for most cases. They’re not fundamentally different animals.

I believe we might have butted heads on this before.... Your claim here is like claiming that the metric system is dressed up Imperial units.

Sure when you make the change you might convert the old system to the new system. Why resurvey the road when changing the road sign? Just change the sign to ShelbyVille 10Miles to ShelbyVille 16km {EDIT CORRECTED MISTAKE}.

Moving to an improved system doesn't mean you MUST throw out everything you have learnt from the old system. Nor does keeping and converting significant knowledge from the old system mean that the new system is simply a 'dressed up version of the old'.

But there have been a very good bases for developing both LRFD and the metric system. Deriding either needs some stronger arguments than just claiming that some aspects newer system are similar or that outcomes are similar. It seems be deliberately ignoring the very good reasons for developing the newer system.

They’re not fundamentally different animals.

Well if they aren't different animals (they are both structural codes) they are vastly different species.

 

[human909]

And here is a paper from 1981. The arguments haven't changed, what has changed is who has chosen to adopt LFRD or stay using ASD.

Load and Resistance Factor Design (THEODORE V. GALAMBOS)

 

[Tomfh]

Why resurvey the road when changing the road sign? Just change the sign to ShelbyVille 10Miles to ShelbyVille 10km.

I think there’s been a misunderstanding of what I’m saying.

I’m not comparing ASD to LRFD as if it’s akin to just changing a sign from “10 miles to Shelbyville” to “10 kilometres” without moving the sign.

What I’m saying is this: switching from ASD to LRFD is like changing that sign from “10 miles” to “16 kilometres,” or updating a speed limit from 50 mph to 80 km/h. The numbers look different, but the distance, or in this case, the intended safety level for normal structures, stays the same.

That’s how LRFD was developed. The LRFD factors were chosen to reproduce the same safety levels that ASD already provided for typical structures. For example, dead load is factored at 1.2 and live load at 1.5 because, like 80 km/h matching 50 mph, those numbers give the same result as the ASD approach, which had already proven reliable. There are of course tweaks to LRFD to make it all more consistent. But the reliability basics were ripped straight out of ASD.

So no, LRFD wasn’t built from scratch. It piggybacks off the ASD system that came before it, and was directly calibrated to align with it.

 

[SWComposites]

So I’m in a different industry, and have watched (read about) the ASD vs LRFD debate for some time, with a mixture of amusement and confusion. As a note, ASD is essentially what we use in aerospace. Reading the start of the paper linked above, the only difference seems to be that ASD uses one fudge factor, while LRFD uses two fudge factors. I can see where the academic types would like LRFD as it allows then to get fancier with more factors, allowing more papers to be written, and allowing the methods to be made more complex and less intuitive. And the whole reliability argument seems to be based on a very flimsy set of real data, if anything at all. Cheers from the peanut gallery.

 

[human909]

I think there’s been a misunderstanding of what I’m saying.

I’m not comparing ASD to LRFD as if it’s akin to just changing a sign from “10 miles to Shelbyville” to “10 kilometres” without moving the sign.

What I’m saying is this: switching from ASD to LRFD is like changing that sign from “10 miles” to “16 kilometres,” or updating a speed limit from 50 mph to 80 km/h. The numbers look different, but the distance, or in this case, the intended safety level for normal structures, stays the same.

Sorry the cause of this aspect of misunderstanding is all mine. My post was meant to say 16km. But I mistyped.

That’s how LRFD was developed. The LRFD factors were chosen to reproduce the same safety levels that ASD already provided for typical structures. For example, dead load is factored at 1.2 and live load at 1.5 because, like 80 km/h matching 50 mph, those numbers give the same result as the ASD approach, which had already proven reliable. There are of course tweaks to LRFD to make it all more consistent. But the reliability basics were ripped straight out of ASD.

Well of course when you have centuries of evolution, development and research you are going to use rather than deliberately forget about it and start restart your material testing again.

And interesting that you chose the word 'reliability'. As the variance in reliability of outcomes of ASD is one of the key the advantages of LRFD and this is shown quite clearly in the graphs above and the paper from 1981 linked.

So no, LRFD wasn’t built from scratch. It piggybacks off the ASD system that came before it, and was directly calibrated to align with it.

Align with it only on SOME points in the curve. Your continued suggestion that because LRFD uses data from the time of ASD that it is therefore just a more complicated version of the same thing doesn't demonstrate the evolution and improvement that is present in LRFD.

Again this is akin to deriding Kelvin as a measurement of temperature because Kelvin was calibrated to align with Celsius, Which is absolutely true (the pun was accidental). But that doesn't mean that it 'piggybacks' off Celsius therefore not an improvement. Kelvin is clearly superior from a scientific perspective thus it has gained acceptance as the standard on which temperature is defined and now defines Celsius and Fahrenheit.

It is no different with LRFD. This is a scientifically more robust approach which gives more consistent results than ASD approaches before it. Now when codes change and ASD is still offered as an option, then the ASD is modified to align with changes to LRFD.

Standards evolve and sometimes make evolutionary leaps. LRFD is an evolutionary leap over ASD.

 

[Tomfh]

If you read those documents properly, you’ll see that LRFD was pegged to the reliability established by ASD. That’s why the LRFD reliability index curve closely follows the ASD curve and intersects it near the middle, because LRFD was deliberately calibrated to match ASD for normal design work.

LRFD didn’t reinvent the wheel. It preserves the reliability level of ASD for normal structures. Yes, it flattens the reliability curve slightly to smooth out inconsistencies at the extremes, such as very large tributary areas or unusually high live loads; but in practical terms, the change is marginal. For typical structures, you’re still working with a reliability index around 3, and the designs come out much the same.

LRFD didn’t independently arrive at this level of safety. It copied the reliability levels that were already embedded in ASD. So no, it’s not some independent evolutionary leap. It’s a technical refinement built directly onto the reliability backbone that ASD had already established.

 

[human909]

So now it has gone from your deriding description of "I see LRFD as dressed up ASD." to "It’s a technical refinement."
So you seem to be moderating you language somewhat. I'm still a little confused if it was a merely a technical refinement why is this even a discussion? It clearly involves is a significant change in method and approach.


I might as well start defining "ASD" as a technical refinement of the Calvin and Hobbs bridge building guide.

 

[Tomfh]

So now it has gone from your deriding description of "I see LRFD as dressed up ASD." to "It’s a technical refinement."

You’re reading too much into the wording. Calling LRFD a “dressed-up ASD” and a “technical refinement” is just two ways of saying the same thing: that LRFD didn’t create new safety benchmarks, it simply inherited and tweaked the ones already established by ASD. That’s why the LRFD factors are what they are; they were calibrated to match the safety of the designs ASD was already producing. ASD had already arrived at reliable safety levels, and LRFD simply broke that down and formalised it into explicit factors. By separating out the factors and allowing for fine tuning, LRFD improves consistency and transparency, but the core safety margin was already in place. It was carried over directly from ASD and remains embedded in LRFD, whether people acknowledge it or not.

 

[phamENG]

but the core safety margin was already in place.

I'd rephrase this to say the core target safety margin was already in place. I don't think there's any argument about LRFD creating new benchmarks. As @human909 said several times, and you agreed with it, the new method is based on what you have learned from the old.

So we saw that "normal" structures - by which I mean Risk Category 2 (ASCE) structures in the low to mid-rise category - have an acceptable performance and reliability history. Admittedly, that probably makes up most of the building stock around the world and, by extension, most of what the majority of us deal with. Which is why the continued use of ASD in most situations is fine, and has limited impact on the end result.

But we also saw that smaller, heavily loaded structures, and very large structures fall outside the desired reliability/safety margins that we want to see. The smaller and heavily loaded ones being too low, and the large structures being too high, meaning there's likely some savings to be had. And so, working from what was already deemed as an acceptable level of reliability, we reformulated the means by which we determine loading levels and capacity of members to bring those two ends of the spectrum in line with the previous targets. ASD wasn't capble of doing it, so we had to create a new method that evolved out of the method that came before it. But as single celled organisms didn't instantly evolve into humans, ASD and LRFD are not distant, unique relatives. It's more like Homo erectus and Home sapiens - there's some obvious differences and certainly improvements, but ultimately it's a bipedal homined that walks around and beats on things with a club.

 

[RWW0002]

...without digging up too many old battles between ASD and LRFD..

Whelp there goes that.. Ha!

At the end of the day, whether ASD or LRFD in design, the hill I am fighting to defend (and likely a battle lost before I was even aware it was a fight) is design criteria being discussed and communicated to the public around service-level loading/events.. I know I have beat this one to death, but it seems that loading is trending towards ultimate-level and I think that is a shame. It only confuses the public (and designers honestly) and puts us at odds with historic practice.

 

[XR250]

I think if we dig deep enough we will find that the PEMB folks are behind the push for strength design in order to save $100 on a building

 

[Tomfh]

It's more like Homo erectus and Home sapiens - there's some obvious differences and certainly improvements, but ultimately it's a bipedal homined that walks around and beats on things with a club.

A fair analogy. Closely related species. As opposed to completely different species.

 

[RenHen]

This has been an illuminating thread, definitely a topic I'll have to read more about! To answer an earlier question of "what are students getting taught" in a way I don't think anyone will like... my professor just showed us the xkcd comic on competing standards and told us that LRFD is for concrete and ASD is for everything else lol. that was back in 2017 so hopefully students these days are getting a more thorough explanation, but I know my alma mater is still teaching both with a similar description on what to use each for

 

[Ron247]

Yes we learned LRFD in college, but the firm I first worked at everyone used ASD so I still do now.

Maybe it was because the older people in your firm were ASD and did not want to learn USD to check newer hires work. Like I said, till we are all dead and gone.

Well it is kinda like the metric system. For some reason the US doesn't seem to want to change while the rest of the world has.

I graduated high school in 1975, the target year that we were going to convert to the metric system if I am not mistaken. I am fairly sure the reason for rather than actually converting to the metric system we just went to double listing details like 12 oz & 354 ml is purely economics. Unless there is ever going to be a severe government subsidy for a VERY long length of time, no private sector corporation is going to invest in metric size anything. From carpentry, 16" centers yields 48"x96" sheeting material, not the values used in the metric system for sheeting and framing spacings. Base cabinets are 2' deep and 3' tall, not 300mm x 400mm as the metric system uses. Try remodeling a 1985 house with metric materials. Both systems try to use nice round numbers when possible for standards. It is not the inability of America to figure out metric values, it is already having trillions of dollars of Imperial infrastructure. We did convert to metric rebar, but it has never been a problem, mostly uses lap splices and bend dimensions. The lack of demand means there is no need for supply. A blank graph is an example of supply and demand curves for metric components in many industries except maybe rebar and automotive.