How to handle uncomfortable technical disagreement/concern over design 3

[Lion06]

I have a situation in my office where I'm involved in a design and disagree with a principle that, in my mind, could have significant safety considerations. I've already aired my opinion, but others disagree, because it's just been done in other applications without problems. I just don't buy into that philosophy, especially when there is no technical literature on the subject.

I genuinely have concerns, but I don't know what else to do given that I've already put my concerns on the table and they've been dismissed.

 

[rb1957]

SEIT, your company has used this method before ... has it been tested ? to say it's acceptable 'cause we accepted it before is abit "off", to say it's acceptable 'cause we've proved that it works is something completely different. maybe a scale test ??

 

[Lion06]

No, it hasn't been tested.

 

[asixth]

You have a duty of care to the community. I was once pressured into a engineering design which I know doesn't conform with the building codes. It was the most unethical thing I have ever done. If you know something is incorrect you have got to argue the point until the cows come home.

 

[steellion]

SEIT, I also respect your knowledge based on your posts on this board. You should not simply "let it go" because you're an EIT and you're talking to PE's. If you present your argument in a respectful way, the PE should not get angry, they should respect you for your ethics and have more confidence when you will soon become a PE yourself.

One piece of advice I would give you, is approach the PE with a SOLUTION, not just a problem. If you can say, "hey I've done a lot of research, and we may be able to do it better using this detail", you're likely to get a lot further than throwing your hands in the air and saying "it doesn't work, and I don't know how to make it work"

 

[slickdeals]

SEIT:
As others have said, stick to your guns.

But I am questioning if the detail can be slightly modified for it to work. I am assuming that you have nuts at the ends of these threaded rods. The failure mechanism is by pulling shear cone failure.

Per Appendix D, if you are able to provide U bands that are developed past the shear plane, then you are okay to transfer the tension from the anchor rod (by nut bearing) into rebar. If you remember, we had discussion on this very topic not too long ago.

Just lapping anchor rods to rebar does not sound too convincing.

 

[slickdeals]

Try this

http://fsel.engr.utexas.edu/publications/docs/53-1F.pdf

 

[Lion06]

I appreciate the input from all. I've presented a solution, but it is not desired to have a plate (or even a nut) on the threaded rods. I honestly can't get a reason why from anyone other than, "it's been done before".

Believe me, I am by no means a "chicken little" proclaiming that the sky is falling, but I like to have a good gut reaction to details.

slick- it is proposed to have no nuts or plates at the ends of the rods, just straight up lapping them with rebar.

I'm trying to find out if there are any "threaded" rods that have been tested to comply with A-615. Maybe some have been tested for this purpose, but it didn't jump out in my search on development of threaded rods.

 

[dik]

Dywidag threadbar... bar is cheap... but nuts are expensive...

Dik

 

[Lion06]

threadbar only goes up to number 14, and the capacity isn't high enough. I'll try to rework the detail to get more of them in there to get it to work.

That 2000k is service, the factored uplift is near 3000k.

 

[rb1957]

SEIT, there comes a time when arguing with an engineer is like tilting at windmills.

you say they've analyzed it but you're worried about a combination loadcase ... maybe their opinion is that the combination is improbable (what we'd call a double failure case ... doesn't happen)

they've used this in the past, so they'd be reluctant to test it now ... a failure now would result in considerable and expensive rework to existing structures.

is there some oversight group you can go to ?

can you Prove it bad, or do you just think it's not good ? to prove it bad, are you assumptions too conservative ?

could you interest a nearby university into studying it as a thesis ??

good luck, and when it's your turn, you can design it properly.

 

[PEinc]

Threadbars are available in sizes much larger than #14. Williams has up to #28 (3.5") Grade 75. and 2.5" Grade 150. DSI also has large threadbars.

Per FHWA-RD-96-017, Drilled and Grouted Micropiles: State -of-Practice Review, Page 91, the typical ultimate design bond value for grout and a deformed steel bar is 2.0 to 3.0 MPa. 3.0 MPa = 435 PSI.

http://www.PeirceEngineering.com

 

[IRstuff]

"It hasn't failed yet," was the attitude at NASA that essentially led to both of the Space Shuttle disasters; the complacency arises from skirting the line and surviving. But the law of large numbers will eventually get you.

Is there any way to do a small scale test?

TTFN

FAQ731-376

 

[vandede427]

this is a very interesting thread. usually we're all about "how do i check bending on a blah blah." but a disagreement with your employer over a detail which has life-safety implications is very serious.

obviously you've brought this to attention and been "shot down" repeatedly. i would document your concerns like Ron said, but by email to multiple people in your company. keep it in house.

i agree that "it's how we've always done it" is the worst answer in the world for your question. it's moronic and uses no engineering ration. but make sure you maintain honor and respect when dealing with your employer. always maintain that respect so no one can ever say you were hot-headed or a finger pointer (i'm not implying that your are, just saying).

plead your case, give your reasons, back it up with calculations, and let them make the ultimate decision. do everthing necessary and in your power so that you can sleep at night knowing you did everything you could do.

what i'm having a hard time understanding is why are they so resistant to putting a nut on the end of the threaded bar? how expensive can nuts be in relation to the cost of a structure that has 2000 kip uplift column forces? IMO, putting nuts on the threaded bars solves the issue.

p.s. i saw an advertisement in recent SEA magazine for 97ksi #20 bar used in new WTC tower. it seems like the ceiling for threaded bar size/strength of has been raised.

 

[jt12]

What reason does you P.E. give for not putting a nut on the threaded rod? Is their only response that we haven't done this in the past, so it isn't necessary, or is there some other reason?

 

[Lion06]

I'm the only one who's done any engineering on this detail. When I came back with the nut and plate detail I was told that we're not going to do that because they've never done it before.

I have looked at the Williams bars and they say that they meet A-615 for deformations.

That makes me feel a lot better and I think that is the direction that we're heading after a recent conversation I initiated.

 

[Lion06]

jt-
That and "the threads have some ability to develop the bar, so it's contribution isn't nothing" is all I was given.
I agree it isn't nothing, but there's nothing I can find that gives a rational way to quantify it.

 

[LSPSCAT]

Lets not act like just because this is not in Appendix D we cannot validate the design. People in geotech, tunneling, and deep foundations use similiar techniques. As stated, it might not be the preferred method and I would agree it would be nice to have a nut and washer. I also agree its a good challenge to have with your colleauges. Good luck and keep it safe!

 

[Lion06]

LSP-
I'm not saying we can't validate the design because it's no in App. D, but I wasn't being anything to make me feel comfortable about it. The fact that it may have been done a thousand times before does not make me sleep any better at night.

It looks like the Williams bars, however, put the issue to rest.

 

[ToadJones]

EIT-
How many anchors are we talking about here?
I have not read the thread thoroughly, and I didn't catch the diameter of the rods either.

My concerns with the threaded rods has always been that the load is transferred through the threads to the concrete anywhere there are threads. So, there can be load transferred to the concrete near the surface. To me, this is a poor detail.
I routinely design anchor rods/bolts with an anchor plate and a nut. The lapping of the rods and foundation bars is to ensure that the load is properly transferred to the foundation system. I usually use smooth anchor material and only thread the portion that extends above the pier or foundation. This helps ensure that the load engagement is at the anchor plate depth, not near the surface.
AISC DG1 has a table for the pullout strength of rods with jsut single embedded nuts, but even that scares me because often the bearing area of the nut is small. If you to due a straight bearing check on the area of the nut, the bearing stresses are are very high. A small anchor plate usually is more than enough to completely eliminate this concern.

 

[ToadJones]

BTW-for a braced frame with uplift forces in that range, you must also have some incredibly high shear forces at the column bases...just a thought.

I agree with you that there are concerns ....foundations are a hard thing to fix; if not impossible.