Structure Mag......Code Article 15

"Experienced engineers (5 to 40+ years) produced design wind forces that varied from 3.9 kips to 24.2 kips with a standard deviation of 42% in the results."

This agrees with what I have been figuring for some time now based on seeing other engineers work. I know I have unintentially missed things as well. All the west coast engineers seem to be currently having a hard time adjusting to ASCE wind, but seismic is even worse to me-especially getting all the special detailing right.

"Why have we as practicing engineers allowed the codes to become so complex? I propose the single biggest answer is apathy"

I agree with this one too, and apathy seems to fit our fees as well. But I am also guilty on the code part because I have never been to a committee meeting on anything and argued for simplification. A good one would be, why now does it have to take 4 hours to design a couple of anchor bolts by hand?

http://www.structuremag.org/Archives/2007-12/D-Editorial-Nuttal-Dec07.pdf

 

[vincentpa]

This is a good wind code gripe. I am designing a strip mall. The eave height is 16.5' and there is a 4' parapet. The wind load on the parapet increases the wind force to my frames by a factor of 2. That is ridiculous. You cannot tell me that a 4' parapet doubles the wind load on my building. I think we need another research project and at least 10 more variables to calculate to rectify this problem.

Did you hear that ASCE 7 is now making a new simplified simplified method of calculating wind. I thought the simplified method was simple and supposed to be faster. I did a problem with the simplified method and the analytical method. I arrived within 0.5% the same load. Both methods took me the same amount of time to calculate both. I hope the new simplified simplified method is truly simplified.

I am going to write a paper on ACI Appendix D in one of the journals soon. I have been studying the history and method of Appendix D for some time now. I have stumped people on the committee with questions. It is time to expose it with hardcore numbers. Appendix D is driven by one person. Yes that's right, one person. I am going to contact this person and set things straight.

I am also going to contact my old professors whom I stil have relations. I am also going to contact local professors at the universities to try to talk some sense to them. It might be the only way. I also encourage all of you; when you attend seminars, gripe, gripe and gripe. Make them feel uncomfortable. It may be the only way to get our points across.

The wind code is hopeless.
The seismic worse.
Our computer models are not accurate enough to model buildings for the precision calculations that are required.

"Structual engineering is the art of molding material we do not wholly understand into shapes we cannot precisely analyze to withstand forces we cannot totally assess; in such a way that others have no reason to suspect the extent of our ignorance."

 

[UcfSE]

vincent, how did you calculate the wind loads, by hand? What were your numbers for the walls and parapet, if you don't mind?

 

[vmirat]

What scares me is the potential for frustration to overcome code compliance, just like over-regulated speed limits. If the codes get so complex that they are too difficult to comprehend, people are going to start taking shortcuts or ignoring the requirements just to get the work done.

Regional building departments amend/append model building codes, either because of their local area conditions or because they disagree with the code requirements. Our building department didn't adopt the 2000 IBC/IRC because it was a total mess. They finally did adopt the 2003 code (with lots of changes of their own) but still use the UPC for plumbing.

I would like to think that the code writers have an honest interest in protecting the public. Seismic is a good example. However, I would rather people spend a little more on construction of a conservatively designed structure than save half a penny by calculating down to the nth degree the capacity of a structure whose variability in actual capacity exceeds the level of detail you figured it to handle.

 

[FEMdude]

Here's a code for you:

For buildings lower than 15 m / 50 ft:

Add a constant pressure of 500 N/m2 to all outer surfaces of the building (walls & roof); check that bending won't break the walls or open the roof.

Then remove the pressure from one side of the building and check that the walls perpendicular to it won't fall down due to shear. Repeat this procedure for all walls.

 

[vincentpa]

MWFRS
Wall: 10 psf total (minimum)
Parapet: 17.5 psf and -11.6 psf

 

[271828]

LOL. I worked as a designer for many years and re-entered academia 3 years ago.

A lot of you fellows have a very distorted view of a professor's life and motivations! That's ok--we all see the world through our own little glasses. I'm one of the only people I know who has two sets of glasses, LOLOL.

For one thing, they don't serve on committees because they have more time than designers. After getting a closer look, I'm not sure good professors have more time at all. Deadbeat ones have more time, but these guys aren't pushing or creating anything that will ever affect a designer.

Good professors are VERY interested in what they're doing, so pitch in craploads of their "spare" time--it's more like a hobby than a job. It also has little to do with tenure in most cases.

I do not believe that any committee seeks more professors. I dare say that any PE or SE with a decent resume and >=10 years of experience can get on a committee.

In my experience, the truth is that most designers want to put in a day's work, go home at 5-6pm and spend the evening and weekends with family (noble goals--no argument there).

To a person, the designers I know say they don't have time for committee work. BOLOGNA!! They have the time, but choose to do other things with it. If they don't want to spend a few weekends and evenings per year volunteering time for committee work, then they don't have much of a leg to stand on while complaining, IMO.

It's about like someone complaining about politics, but not voting.

 

[271828]

Just for clarification, I claim that "any PE or SE with a decent resume and >=10 years of experience can get on a committee" through personal experience.

I only had 7 years of experience, a very nice resume, a MS, and a SE license and that was plenty enough to get me on a very non-trivial committee. It took a couple of years to learn the ropes, but I've even been able to have an impact.

Imagine the impact of a >20 year guy doing the same thing!

This stuff just ain't that hard.

 

[vmirat]

It's worthless to exhort everyone to join a committee. They can only take so many people on a committee. What we need is the ability to voice our opinion on these codes and assurance that our comments will be considered, kind of like Congressional representatives. Perhaps committee members should be voted on by the industry. They could go around the country lobbying for our vote. OK, maybe that's too tongue in cheek. However, I have made many many calls to various code organizations over the years including AISC, ASCE, ICBO, etc., about their codes and suggestions that I've had for improvement (although I've never seen anything implemented).

 

[271828]

vmirat, I respectfully disagree. I do not believe that everyone should join a committee, but any who gives a rip about what happens should! It's just not that much work--if one's interested... It IS a lot of work for someone who just wants to complain (NOT saying this you--just speaking in general).

I agree that some committees seem non-responsive at times. I've sent good questions to ASCE 7 and IBC-supposed-gurus and received nothing but crickets.

FWIW, our committee spends a substantial chunk of meetings on comments, mostly from folks from outside the committee. Some of these go somewhere and some don't for various reasons. The ones that go nowhere usually have some other consequence that the author didn't think of.

At the end of each discussion, someone agrees to get in touch with the author and let him know what happened and why. Perhaps this is forgotten at times, but it is supposed to happen.

 

[271828]

Back to the original post: "Experienced engineers (5 to 40+ years) produced design wind forces that varied from 3.9 kips to 24.2 kips with a standard deviation of 42% in the results."

Granted, the wind load provisions are unnecessarily complex, but (I'm going to risk sounding arrogant. Really, I'm not.) how could ANY engineer worth his salt, with >5 years of experience sit down in front of that problem and miss it by a wide margin?

I mean, come on, it is a box, without ANY of the issues that actually are confusing (parapets, penthouses, canopies, partially open, etc.). I'd bet a fair sum that I would come up with the right (or otherwise easily defensible) answer to that and that every other decent engineer with >1 year of experience in my last office would.

The article didn't say either way, but was there a time limit placed on the problem? If someone was given a tight time limit to solve it, then it's understandable.

And I meander further: I'd like to know how much of this has to do with widespread use of automated design software. I dare say that it plays a HUGE part, allowing people who don't study to still design buildings. Remove the need to study and many won't. Our old office hired one SE with 10 years of experience a few years ago who had been using RAM for several years. He literally could not calculate wind or seismic loads manually. We calculated this stuff manually at times, so everybody had to get good at it.

Sorry. I really don't want to come off as arrogant, but something besides code complexity is wrong if THAT many >5 year people couldn't figure it out.

I vote for widespread use of automated software.

 

[MGMtulsa]

This thread is generating some off line discussions.

271828 (Structural)sounds a little defensive. The point of the thread is -- Codes are getting Complex --

So if the codes are getting complex, what is the downside? The consensus is running that there is a lot of work being required. And any engineer, worth his salt, knows that complexity and more work equate to more sources of error.

For a moment of reality, let's not forget the first rule of structural engineering:

------ When in doubt, make it stout. ---------

And if anyone wants to debate that rule, be sure and include the cost of only the structure, versus the whole project.

3 cheers to -- haynewp (Structural)-- for starting this discussion.
And 3 cheers to -- BRGENG (Structural) -- for an excellent summary.

Now, let's come back to the original (understood) question. What should we do about getting the codes back to a more simple set of rules?

 

[vmirat]

I think there are two issues here. The original post by haynewp referred to an article in Structure Magazine. In that article, the writer described the problem of structural engineering getting complicated and went on to espouse the virtues of their trial problem system with an added note of joining a committee, so 271828 is within their rights to lobby for the committee approach.

However, I suggest an alternate solution that can involve everyone/anyone, since we ALL can't be on a committee, especially ones like those at ASCE. We should have a third party union that can speak for us proletariat masses with those organizations that are making the rules. Hey, maybe Eng-Tips will act as our advocate!

 

[Rici]

In the March 2007 issue of the ASCE Journal of Structural Engineering there is a paper entitled “Performance-Based Engineering of Constructed System.” I would recommend it to everyone to study it, because in fact is a FORUM about “the specification-based prescriptive approach to civil engineering design and evaluation practice (which served us well during the last century)” versus the so-called “performance-based approach” which provides alternatives to the current prescriptive code-based practices.

 

[HgTX]

Back to committee membership (whether you're developing a prescriptive or a performance-based spec)--there are some committees whose membership is tightly controlled but even most of those have subcommittees or task groups that do the real work and have more open membership. But most committees that I come into contact with are starving for members, and some will even accept comments and run ballots by email.

Everyone on those committees is a volunteer.

And what professors need to do for "publish or perish" is PUBLISH--meaning issue a research report. A CV lists publications. It doesn't list code provisions. Most research reports that *could* result in code changes never get implemented. Why? Because the professor has delivered their deliverable and if they're not on the relevant committee, then it's up to other people to get it into the code. They lobby because they think they have the right answer. They're not lobbying because they think they'll get more funding; more funding comes from NEW questions, not implementing the old ones.

Hg

Eng-Tips policies: faq731-376

 

[DRC1]

I do a lot of work around several railroads- which experience high wind pressure from passing trains. One has a wind that can't go wrong. rectangular distribution full strucure height one face 30psf. Been around over 20 years never heard of a problem. Does not get any easier!

 

[hokie66]

So the kindly professors are exonerated. That leaves only the greedy publishers of codes and the seminar conductors who teach us how to use them at exorbitant rates. Come to think of it, the kindly professors have their nose in that trough also.

And the thing is, even if the more extensive code provisions result in better design practices, which not many of us seem to think is the case; does this improve the resulting structures? I think not.

 

[BRGENG]

I think we need to take up a collection for vincentpa for his fight against ACI Appendix D. If he is successful in the long run it will save our clients money. Just wait until you calculate the embedment depth of an anchor bolt and discover you need to extend your footing well beyond the frost depth to accommodate the required length per ACI. I have yet to see a column or footing pull itself out.

 

[sdz]

ACI318 AppD is an interesting case. The old method based on uniform stress over a pull out cone was easy to visualise, and apply, but didn't reflect actual behaviour very well. The new method is more complicated but better represents actual test results.

BRGENG, if you find you need to extend embedment depth "well beyond the frost depth" maybe you are doing something wrong.

 

[271828]

sdz brings up some good points IMO. App. D is difficult, but I've never seen the results to be simply insane. For the huge uplift cases I've looked at, sure it gave some large embedments, but they seemed reasonable (it takes quite a bit to hold down a few hundred kips using plain concrete...). Use reinforcement in those cases to resist the load.

 

[271828]

I guess it would be better to ask vincentpa and BRGENG the question (not being combative, I promise LOL, really interested in what you've run across).

Can you give the details of a specific ACI App. D result that was unreasonably severe?

I have not done an exhaustive study of this Appendix, so might not have run into any really stupid answers.