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.

 

[human909]

With USC units, I need scientific notation about twice a year. Lol

Lol that is one of the best arguments against the metric system I've every read!

Yeah, we our trailing powers of 10 can be a bit of a handful when you first start engineering. But you quickly learn to either deal with them not even write bother writing them down. You can even mix and match your dimensions and drop your trailing units and be fairly safe as you know your answer if wrong will be out by and a multiple of 10^3.

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Eg a 200mm channel 5m long has an I=19.1 (x10^6 mm^4). If we load that with a 10kN in the centre I would calculate the simply supported deflection like so:

d=PL^3/48EI = 10*5^3/(48*200*19.1) = 1250 / 183360 =0.0068 Oop... I was sloppy with my units and I dropped my scientific notation. Lets just move the decimal place to fix it. 6.8mm DONE.

Want to know how heavy a 1m x 0.5m x 8mm piece of plate is? 4 x7.8 = 31.2.... 31.2kg Yep that checks out. I could have done 4 x 7860 = 31440. I know it isn't 31440kg so I just move the decimal place. 31.44kg.

~~~~~

 

[ANE91]

You can even mix and match your dimensions and drop your trailing units and be fairly safe as you know your answer if wrong will be out by and a multiple of 10^3.

Fairly common for prestressed concrete design — we speak in terms of tens or hundreds of microstrains and don’t bother with the 10^-6.

 

[Ron247]

That’s why our I-beams are still based on imperial dimensions, just expressed in millimetres.

I do not see that as converting to the metric system, that is restating everything in metric units such as 12 oz = 355 ml. Converting to the metric system, is adopting their standards such as rafters on 60cm spacings (23.62"), not 24" on center and drinks in 400 ml containers. Canada is supposed to be metric but I think they still use imperial units for a lot of construction. The US has converted to full metric in parts per million. computations.

 

[human909]

I do not see that as converting to the metric system, that is restating everything in metric units such as 12 oz = 355 ml. Converting to the metric system, is adopting their standards such as rafters on 60cm spacings (23.62"), not 24" on center and drinks in 400 ml containers. Canada is supposed to be metric but I think they still use imperial units for a lot of construction. The US has converted to full metric in parts per million. computations.

That is certainly converting to the metric system. Things don't have to be nice round numbers to be converted. It just has to be use of the metric system.. Sure nice round numbers are "nice to haves" but they don't make or break the massive advantages through the use of a coherent unit system. If it wasn't for the largest economy in the world being a hold out we'd probably already have moved to nicer 'round' numbers.

Here in Australia cans of soda or beer have long been 375ml. But microbreweries often are now 355ml and you've just explained the reason. I guess we buy canning equipment intended for the US market.

The US has converted to full metric in parts per million. computations.

I don't see how that is overly metric. That is simply a multiple of 10^6. That doesn't even have units. We have been group things in multiples of 10 and 10^3 for far longer than the metric system has been around.

 

[Tomfh]

I do not see that as converting to the metric system, that is restating everything in metric units such as 12 oz = 355 ml.

That’s how it works in practice when countries go metric. Some things are too hard to start from scratch.

And things like plywood, we still have 2440 sheets of ply. The old imperial system is still there in many ways.

 

[Ron247]

I don't see how that is overly metric. That is simply a multiple of 10^6. That doesn't even have units. We have been group things in multiples of 10 and 10^3 for far longer than the metric system has been around.

Parts per million was just intended to be a joke like saying I can convert imperial time to metric time. And no offense, but I guess we just have to agree to disagree on what "converting to the metric system means". To me, it meant converting to the standards used in the metric system.

 

[human909]

Parts per million was just intended to be a joke like saying I can convert imperial time to metric time. And no offense, but I guess we just have to agree to disagree on what "converting to the metric system means". To me, it meant converting to the standards used in the metric system.

No offense taken.

I'll occasionally point out what I see as absurd stubbornness. I know it's an argument I won't "win". And I am kinda picking a fight.

Eng-Tips, is a international forum though primarily populated by US engineers. I value the forum and I value the discussion, help and feedback regardless of whether the participants prefer ASD/LFRD or metric or USC units.

I am here because I respect the engineering intelligence of many of the users here including those who I might have contrasting opinions.

 

[Ron247]

Human909, I agree, having a variety of viewpoints and perspectives is very enlightening and helpful.

Let me relay what I recall from 1975. The president, Ford I think, passed the law. It did not mandate private business had to change but the government "encouraged" industry to adopt metric standards also. I was just getting into construction. I had learned metric system in school. Math was easy, but their choice of "routine quantities" seemed strange like gas being in liters which was about a quart rather than something close to a gallon. Length was over a yard, and other than football, no one ever mentioned a yard.

Government actually had an agency to facilitate industry in the conversion, but still not mandatory. Government talked with lumber mills, lumber mills talked to distributors, distributors talked to lumber yards and finally, lumber yards talked to contractors. That is when you did not hear "no", you heard "Hell No". They learned if they made lumber solely in metric standards, no one was willing to buy if someone else had customary sized lumber and other materials.. And it was not the typical; "we don't like change", it was "I don't need that kind of aggravation". You also need to understand, while this transition was supposed to go on, the country had a recession, and money was REAL tight for a few years. Interest rates on houses was 14% or more and cars were well over 20%.

I remember one plumber wanting someone to tell him how he could splice a damaged drain pipe with metric standard pipe since there is a rule that drain lines cannot decrease in diameter in the direction of flow. Splice any pipe with a different diameter and you have that situation.

Eventually, it just became converting the values, not the standards, but that is all the law actually mandated, converting the values. The rest of what they hope for just became a dream more than a reality. And even government did not follow their own mandate, most things that interfaced with John Q Public were still imperial, like speed limit signs and "Stay Back 100 ft".

As far as people just fighting change, I remember plumbers who were still using lead pipe for water lines well after copper became the norm. I also remember electricians wiring new houses with ungrounded wire well after grounded wire became the norm.