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.

 

[TXStructural]

EIT v PE. One seals the drawing, one doesn't.

I agree that "the old guys" often seem to dismiss "the young guys" as a matter of course, but virtually all of these situations can be resolved by asking the senior, "OK, so what am I missing?"

 

[Ron]

SEIT...in looking at your posts and answers for quite some time, I have a sense that you are quite sharp.

You need to let those who don't listen understand that because there has been no repercussion in the past does not mean that the approach is correct. That's considered anecdotal evidence, not supporting corroboration. Anecdotal evidence is often a "one-time"occurrence. It does not establish precedence.

Document your objection in writing to your principals. It only takes one of these issues to completely sink a firm...and it's usually because someone didn't pay attention to reality.

Stick to your guns...you seem to know what you're doing.

 

[nutte]

First, are you sure you're right? Keep discussing it with people to make sure you aren't mistaken.

As far as "it's worked all along," is this something that is particular to your company, or is this some industry-wide standard?

 

[msquared48]

SEIT...

I have to agree with Ron here. You can push your point, but only so far. Without your PE, after you have voiced your opinion, you have to CYA in writing, then move on with your life. It's their decision and their responsibility at that point. You have done your due dilligence.

Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask

 

[Lion06]

I've asked what I'm missing - the answer doesn't satisfy me. Stating that "we've applied this in x application with no problems" and saying it's an office decision to apply this just doesn't do anything to address my basic and fundamental concerns.

I understand that some things come down to judgment, and I also understand that I'm not signing or sealing anything and I'm just an EIT, but, again, THAT, in and of itself, does nothing to address my concern.

Using it in x application means little to me. There's no telling how "overdesigned" using their principle, or what % of the design load it's ever seen.

Thanks for the vote of confidence, Ron. I'll try to do some more research to demonstrate the lack of literature on the topic and bring it up again.

 

[Lion06]

Nutte-
I can't say I'm right for sure, there's no literature on the subject, but a previous.post on this forum suggests that I'm certainly not wrong. I admit there is definitely some judgment involved, but the criticality of the condition along with the forces involved and the fact that this is a global stbaility of the structure issue makes me uncomfortable.

 

[dhengr]

SEIT:
There isn’t technical literature on every detail and every situation, so you can’t count on that in every case. You might explain the problem here in detail and get some outside ideas or direction. Maybe someone outside your office has run into this issue before. But, you do have a gut feeling that you should get resolved. You seem smart enough to me too, so that I would give you a listen if you came to me with your concerns. And, I would try to explain to your satisfaction, but you better come with evidence, because I know that what we have been doing has worked in the past. We all hate to admit that we were wrong or could do it better, all at the hands of the young guy.

I agree with TXS when he says that the boss is signing the plans and has ultimate responsibility. You usually do have trouble arguing with success, when it has worked before. But, most good bosses will explain their thinking when asked properly, and presented with sound, logical well reasoned concern, given a little time so cooler heads prevail. We want you to succeed, you’re the best asset we’ve got, we secretly want you to keep us on our toes, we’re not infallible. Approach each of the ‘others’ individually to air and explain your concerns. Sometimes you get a better hearing, one-on-one, when the group thinking thing, agree with the boss mentality isn’t prevailing.

I agree with Ron, but would say it a bit differently. You must present your best case, explaining your concerns, with whatever corroborating evidence you can find. Explain your gut feeling with the best evidence you can muster, and dissect what they are doing with your best examples and disproofs at every step along the way as to why you think their way is unsafe or wrong. I don’t think Ron meant notarized letter, by certified mail.

Good Luck

 

[Ron]

dhengr...thanks. Nope, didn't mean anything "official", just good research and statement of position. With good references and corroborating evidence, the argument can be persuasive.

 

[Lion06]

Ok, here's the scoop. I appreciate all opinions.

We have some braced frame columns subject to net uplifts on the order of 2000 kips (that's not a typo). It is being suggested to lap anchor rods with rebar in a drilled pier with no consideration of any other failure mechanism from App. D (specifically, pullout). It is suggested that you can lap the threaded rods directly with rebar with no nut on the threaded rods (or an inadequate nut by pullout capacity) and all is good.

I suggested that App. D is written specifically for this type of application and that we can get out of the tension breakout calcs by lapping with rebar, but we still need to comply with the pullout requirements.

I was told that micropiles are done all the time with threaded bars with no nuts on the ends and that the rod just develops in the concrete.

I've done a pretty exhaustive search, but can't find any literature on development lengths of threaded rods. The thing that concerns me most is the magnitude of the loads and the fact that this type of failure could literally cause the building to topple over. I just don't feel comfortable lapping extremely heavy threaded rods (Gr. 105) with rebar as though the transfer mechanism into the concrete is equivalent.

Any thoughts?

 

[nutte]

I would also be skeptical of that detail. The anchor rod has to be properly embedded into the concrete for the lapped rebar to take hold. To me, "properly embedded" means plate washers or something of that sort, not bond between the threads and the concrete.

 

[LSPSCAT]

The threaded bar can develop bond in the concrete. Check out Williams Form Engineering for concrete and rock anchors and basic application of the Uniform Bond Stress Model and the 45 DEG cone method. I know its "antiquated" but it worked for the US Nuclear Industry for many years. With work I have done I have assumed that the 45 DEG breakout cone starts at half of the effective embedment. You can also check out Dwyidag for similiar uses. In my dealings with Williams they have stayed away from Appendix D, stating that large scale tests have not been completed on anchors greater than 1" and that ACI has not published new material on post installed grouted anchors. Williams posts basic information from ACI 349 which is the old code for Nuclear Work, it may be enough to get you started. A conservative value for the bond at the grout concrete interface can be taken as 300 psi. These same values have been used at the grout to rock interface. The grout or concrete steel interface will exceed this value. Williams shows a hex nut which is typically used to insure the the failure is at the grout concrete interface and not at the steel interface. This same method can be used for the hollow core bars they show with or without mechanical anchorage. I did find two papers at work that may help you. Once again...these are not inline with Appendix D...so you may have to move outside the code to perform your analysis.

http://www.williamsform.com/Contact_Us/PDFs/High_Capacity_Concrete_Anchors.pdf

 

[LSPSCAT]

I gained comfort using this for underwater applications. Owner would not allow any adhesive epoxy style anchors, owner would not allow mechanical anchorage (concerned that anchorage may relax over design lifespan), and we were applying large loads 100-200 kips / anchor to existing structures. Divers performed all work underwater. The comfort for me was that all anchors were pull tested. Tensions and elongations were recorded.

I am not sure how that 2000 kips is getting distributed so you may still have major concerns.

 

[abusementpark]

StructuralEIT,

How bad does it fail if you check pullout?

 

[RonRoberts]

I'd review ACI 12.15.6 -splices in tension ties. I think the drilled pier with a net uplift of 2000 kips meets the characteristics of a tension tie member as described in R12.15.6. I wouldn't rely on a lap splice to transmit the load from the anchor rods to the drilled shaft.

 

[Lion06]

Well, with no nut it has zero pullout capacity, so..............

 

[hokie66]

I don't believe that the situation described here is a tension tie member unless the loading is always there. If transitory due to wind or earthquake, it is a normal connection, not a tension tie.

The threaded rod obviously has capacity, else adhesive anchors don't work. I would look at the ratio of capacity of threaded rods to reinforcing bars using the same adhesive, then apply this ratio to the splice length required in the concrete. Testing of this type splice would help, but I would be comfortable with this logic in the interim.

 

[abusementpark]

Well, we wouldn't say that a lapped rebar (with no nut) has zero pullout capacity. Something doesn't seem right about saying a threaded rod lapped with a rebar has no pullout capacity.

Isn't the difference here that you are providing a threaded rod? There will be a superior bond around the rod due to the threads (similar to a deformed bar). Aren't most typical anchor bolts that are smooth most of the length and thus need the nut at the end for pullout capacity?

 

[LSPSCAT]

See attached for quick discussion on grout bonded anchors. It seems you are not anchoring in grout rather directly in the concrete. However, you could extrapolate that the concrete is your grout. Now analyze the bar / concrete interface. The bar has pullout capacity.

Put down Appendix D for the day and play devil's advocate.

See if some of the information provided can develop the capacities you are looking for. Call Williams...tell them you are planning to embed 2" DIA. 150 KSI All Thread Bar in concrete and see what they say. Then call DSI Dwyidag and get the European feel for what you are doing.

It might not be the perfect application or the 100% correct way of doing things in a perfect world...but lets see if it works with some basic analysis techniques. You need to build a case either for or against your argument.

 

[dik]

I've always treated threaded rod the same as rebar for development, except, for heavy tensile loads I invariably use Dywidag threadbar for the anchor rods. This product is like rebar...