US Codes compared to Eurocodes 2

[ThomasH]

Hi all

I have a question that may or may not have an answer.

I work in Europe and say that I want to design a structure in the US. Of course I would have to design it according to US codes and that would be it. I think it is a fair assumption that the US codes would be required. I have done designs for the American market and it has always been according to US codes. I think that is reasonable.

But now I an on a different situation. The structure will be in Europe the the US consultant want to use US codes because he feels more comfortable with that. I can sympathize with the idea but the US codes don't apply in Europe. The question is, is there a utilization level x %. Below x % we can be sure that and design according to US codes will also meet the requirements in the Eurocodes?

I think the questing is a bit odd but regardless, has anyone seen any comparisons regarding this? I have seen comparisons between different national codes when the Eurocodes were introduced but never any comparisons US vs Eurocode.

Note: This is not an attempt to value which of the codes is "better". I just wonder if anyone has a feeling regarding the security levels.

Input would be appreciated.

Thomas

 

[BAretired]

The question almost certainly has an answer, but without doing a rigorous comparison, nobody on this forum can provide anything more than an educated guess. The law requires that the appropriate code be used and I suspect the authorities in Europe would not accept a design done to x% of the US code.

BA

 

[ThomasH]

BAretired

I agree, it is the "educated quess" I am after. I have some experience but I would like to see it anybody has anything else they would like to contribute.

When Europe made the transition to Eurocode I heard that the utilization changed +/- 10%. For some details the Eurocode was more stringent, for others less stringent then the previous national codes. But the numbers varied with different countries.

The idea behind the Eurocode is to get a more consistent approach i Europe.

Thomas

 

[ukbridge]

The philosophy of the Eurocodes in parts will clearly differ from AASHTO et al., so IMO it is not reasonable to simply do a utilisation above % exercise.

A good example is for box girders. Pre-BS5400 shear lag was neglected at ULS because some plasticity was allowed for in the concrete flanges. Unfortunately due to the Eurocodes we must also account for this at the ULS as well as SLS. As another example the Eurocodes has resulted in the use of much greater lap lengths than were ever required in the BS5400 days (UK pre-EC code). The country specific annexes also have various nationally determined parameters (NDP's) appropriate to the meterological, climatic and quality of workmanship/materials.

I've heard a similar 10% margin on a trial basis for a number of composite bridges, but of course the differential could be very different depending on the structure. I really can't recommend enough using the proper code, think of the consequences if the structure were to fail and you were found not to have used the proper code.

 

[ukbridge]

I'd also like to add that the UK does have some very good published guidance for the design of structures to the Eurocodes. It is mostly very clear, no-nonsense, industry-focused stuff (I've been using them for a while so am probably biased, but I'm quite proud of the UK Structural Engineering literature). If you want anything specific recommended that'll make your life a lot easier for bridges, buildings etc let me know and I'll give you some recommendations.

 

[dik]

Check with a Eurocode website... like below:

http://www.designtoeurocodes.com/forums/activity.php

Dik

 

[IDS]

At least for concrete, if you wanted to apply a single factor that would guarantee a design to US codes would comply with EC2, the result would be very conservative.

See below for a comparison of results for combined bending and axial load with high strength concrete:

http://newtonexcelbach.wordpress.co...einforced-concrete-as-aci-and-european-codes/

There are also significant differences in design for shear.

In my opinion the Eurocode provisions for combined axial load and bending are not overly-conservative, but if you used a reduction factor low enough to ensure that design to ACI was OK for this condition, everything else would be over-conservative (and also unlikely to be accepted by the client).

Doug Jenkins
Interactive Design Services

http://newtonexcelbach.wordpress.com/

 

[ThomasH]

Hello again

First of all, Thanks for your input.

I should start with that I agree with most of what you say. A simple answer is: When in Europe, apply the Eurocodes. Or, whwerever you are apply the valid codes. That is reasonable and very hard to argue against. It is also the answer I have already given to the project manager.

But as an engineer I was also a bit qurious regarding the differences. And I think Doug (IDS) is spot on. It can't be done with a single factor AND a reasonable amount of conservatism. There are differences in the approach on a detailed level. I know that things have changed significantly in some specific areas and it is probably reasonable to think that if we compare entire codes that can become a serious problem.

Anyway, its always nice with a second opinion.

Thomas

 

[Agent666]

I have only ever done one job where it was in New Caledonia, whereby the client was happy for us to design in New Zealand/Australian codes (because working with the French codes (pre eurocode)) was near on impossible for our office due to the language barrier and local engineers simply didn't have the expertise to do the job. The only qualification to this was that the design was checked by a local French engineer to ensure the design was compliant with the French standards.

Part of the justification of this at least internally within the company was that structures in France, and structures in New Zealand essentially stood up if designed correctly with similar margins of safety implied in the design standards.

Otherwise I would just insist on the design being done to eurocodes. The principles are the same, just different equations to get you to the same results. You have to remember that some different requirements exist that aren't as simple as comparing percentages on the capacity. There is plenty of guidance out there now that eurocode are more mainstream to pick it up really quickly.

I would imagine the final word might come from the fact that it's quite hard to convince the authorities to accept an alternative countries standards when they have there own perfectly good standards.

 

[TLHS]

I wouldn't accept structural design to American codes and I'm in Canada. Our codes are significantly closer than Eurocode and the American codes are.

The stuff that gets you in different codes isn't generally overall strength. It's determination of loading, required load combinations and detailing requirements. There can be reasonably significant differences in these practices.

Sure, you'll probably have basic strength cases right, but have you dealt with snow piling the way the other country requires, or seismic detailing, and when you've applied local environmental criteria into your design do the values actually mean what you think they do? Do the safety factors in your code make sense given the material types that are in use? When you've gone and called up a weld, is it leg, some dimensional value, effective throat, or something else?

Codes are based on piles of assumptions. Those assumptions are carried into the way that design criteria are communicated, material specs are written, and construction is performed. If you aren't using the code that ties in to the set of assumptions being used in a given place, you're not putting in the diligence you should.

From a client or permitting standpoint, I'd reject it because (a) it straight up probably isn't legal if it's a structure that requires engineering (b) I couldn't check if it meets requirements without doing a code study and detailed review of everything (c) it shows that the engineer isn't putting reasonable care into the work and would make me suspect that they don't have any idea what local requirements are

The proper way to do this and be comfortable is to do preliminary design to the code that you're most knowledgeable and then go and do the detailed design checks to the actual governing code. That way you're comfortable that the structure is generally safe before you start using an unfamiliar tool and you've also done your due diligence for local requirements.