Help with ASTM C1577 Precast Reinforced Concrete Monolithic Box Sections....

[fel3]

We have a project in San Diego County, California, that includes about 800 ft of 11 ft x 4 ft (inside) precast concrete box for a storm drain. Except for a little bit at each end, the entire alignment is in a residential street (the ends are "in dirt"). Cover ranges from about 18 inches to 6 feet. The standard we are using for this item is ASTM C1577, "Standard Specification for Precast Reinforced Concrete Monolithic Box Sections for Culverts, Storm Drains, and Sewer Designed According to AASTHO LRFD."

Although I had a significant role during the design phase, most of the design work itself was performed by our engineering team in San Diego (I'm in Fresno). I served mostly as a technical resource/mentor/QA-QC engineer/project humorist (every project needs a humorist, especially this one....for reasons I won't go into here). The project is now in the very beginning of the construction phase and our San Diego team is handling construction phase services and I am on call to help, much like before but more limited. At this point, they are mostly dealing with submittals and RFIs.

Now, with this preamble out of the way....

One of the project engineers asked me yesterday to take a look at the submittal for the precast concrete box. The submittal includes a copy of ASTM C1577-14 (I have already questioned why not a more recent version because there are NINE newer ones available).

As I read through ASTM C1577-14, I don't see anything that requires or even implies a seismic design approach. My question to those in the group who have experience with ASTM C1577, is there anything in this standard, especially in Table X1.1, that covers seismic? What am I missing?

When I designed buried cast-in-place vaults in the remote past, I always included a lateral seismic force to the walls. I did a Google search on this subject and found several published papers regarding seismic forces on buried structures and several relevant Eng-Tips threads. Everyone agrees that seismic forces need to be considered....because they exist. Seems simple enough.

On the other hand, the State of Washington DOT limits the requirement for applying seismic forces to buried spans > 20 ft:

https://wsdot.wa.gov/eesc/bridge/designmemos/09-2012.htm

and

https://dot.wa.gov/publications/fulltext/Bridge/designmemos/06-2014.pdf.

Is this perhaps a reasonable practice for small structures?

Thanks in advance for your help.



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"Is it the only lesson of history that mankind is unteachable?"
--Winston S. Churchill

 

[r13]

I think you need to check state/local DOT for their requirement.

 

[fel3]

Retired13…

Thanks for your reply. This is a County project, not a DOT project. I had already checked Caltrans just in case that's what the County uses (I don't know the County standards, so I had tasked the project engineer with figuring out what standard or standards governs for this item. BTW, I just learned that we didn't specify ASTM C-1577, the box culvert manufacturer did.)

I checked the Caltrans "Highway Design Manual", various documents from their structures department, standard plans and details, etc. The only relevant thing I found was a detail in the Caltrans "Standard Plans" that requires box culverts to be designed per AASHTO LRFD. But, no mention of seismic requirements or ASTM C-1577. I have never used AASHTO LRFD, so I don't know how seismic is handled, especially with respect to box culverts. Since ASTM C-1577 refers to AASHTO LRFD, the latter is ultimately the standard. This is why I am asking.

Fred

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"Is it the only lesson of history that mankind is unteachable?"
--Winston S. Churchill

 

[BridgeEI]

Underground structures are not designed for seismic forces unless they are crossing an active fault line. This is all per AASHTO LRFD.

 

[fel3]

BridgeEI....

Thank you. That's what I needed to know. If it was my design, I would include seismic forces because the structure will be subject to them. But, this is a delegated design and if the code doesn't require it, then I'm going to be OK with it.

Fred

============
"Is it the only lesson of history that mankind is unteachable?"
--Winston S. Churchill

 

[BridgeEI]

You can always design it for the loads if you want to, but the issue with AASHTO is that it doesn’t describe how to design for seismic on culverts. There’s a NCHRP report that kind of explains seismic design but it’s very cumbersome and it’s mostly trying to address racking in the culvert.

I’ve got a monster of a structure in Los Angeles and it isn’t being designed for seismic because there’s basically no accepted practice to do it. It’s really a soil structure interaction problem so you have to have the geotech involved....

I think AASHTO basically defaults to that if it is underground it will follow the ground motion so it doesn’t actually accelerate like a span structure.

 

[robyengIT]

may be it can help

https://www.concretepipe.org/wp-content/uploads/2015/05/CP-Info-Precast-Concrete-Box-Sections.pdf

 

[r13]

fel3,

1) ASTM C-1557 is a material specification, not concerning structural design.
2) Does this project require permit? That's where you should start to track it down the answer you are seeing.
3) In the past we have used " Mononobe-Okabe Method" to estimate earth pressure in seismic event. Link below takes you to a SEAOC technical paper that might help you on this issue.

Link

 

[fel3]

RobyengIT - Thanks for the document. I will take a look.

Retired13 -
1) ASTM C-1577 includes design criteria (just no obvious mention of seismic) and rebar tables for different size boxes, so somebody did some design to come up with the rebar tables. It's not just a material spec.
2) No permits because this is a County project (i.e., the County is Owner and our client). The RCB is a delegated design, but I don't know yet what the design is supposed to be based on (Caltrans, County, ASTM, wishful thinking, etc.). I am still waiting to hear from the project engineer about this. Per BridgeEI's post above, it appears that the standard or practice is to ignore seismic for buried structures like this.
3) I have heard of the Mononobe-Okabe Method although I have never used it. I will take a look at the document you linked. Thanks.

============
"Is it the only lesson of history that mankind is unteachable?"
--Winston S. Churchill

 

[r13]

fel3,

From the linked paper you may find out that seismic force is rarely critical for underground structures, thus the logic to ignore it.
However, WSDOT says otherwise,

Link

I really doubt CADOT does not have similar requirements.

 

[r13]

Another lead for answer should be the local geotechnical consulting offices.

 

[fel3]

Retired13....

I came across the WSDOT memo during my research prior to posting here. They ignore seismic for spans up to 20 feet (ours is 11 ft) and include it for longer spans.

So far, I have been unable to find anything useful from Caltrans.* But, the project engineer appears to have found something, which he will be sending me after lunch. Our firm did the geotechnical engineering for this project, but I don't have the report in hand. It is also on its way.

* My Google search turned up many possible links to what I needed from the Caltrans website. Unfortunately, they all took me to a page that doesn't have what Google's description says it has. Perhaps Caltrans rearranged this page recently and the descriptions are out-of-date. Anyway, I am continuing to search for my own edification.

Thanks for your help.

============
"Is it the only lesson of history that mankind is unteachable?"
--Winston S. Churchill

 

[r13]

I don't know your specific role in this project, but someone (EOR for instance) needs to be concerned enough to send letter/email to the owner/client (its designate person in charge) for clarification. Note, albeit the county might not have adequate knowledge/experience on this, it is still considered the authority on this project (a public work), unless the county has delegated all responsibility to you, and waived your company's liability, which are unlikely scenarios. You have done well so far, but may need a little luck to get to the bottom of this though.

 

[fel3]

I'm not the EOR. My role was providing on-call help, QA-QC, etc. as needed, as noted above. Our EOR is a hydrology/hydraulics/storm drainage person with virtually no structural background. The County people we are working with are non-engineers with construction backgrounds. They are relying on us. During the design phase, our EOR had a couple technical questions on unrelated matters and asked our primary contact with the County to run them past his department's engineers. For whatever internal reasons, he didn't/couldn't get the County's engineers involved. So, we had to make the decisions ourselves, inform him about them, and ask for his blessing. This is just one of the many reasons that my role included being the project humorist, as noted above. BTW, our primary contact with the County is a good guy to work with and he's frustrated with his own organization.

I'm actually not as worried about this as I may seem, especially since it appears to be common (but not universal) practice to ignore seismic for small-ish buried structures. I'm just trying to close the loop. In addition, the manufacturer is proposing 6,000 psi concrete and 70,000 psi steel vs. the C-1577 requirements of >= 5,000 psi concrete and >= 65,000 psi steel, and he's using the same steel areas required in C-1577 based on those lower design requirements (well, except for one typo in his submittal). C-1577 assumes the soil has a unit weight of 120 pcf, but ours is about 110 pcf. So, our structure will be stronger than the design in C-1577. The other items in Table X1.1 (at least the 2014 version of C-1577) seem to be conservative enough. Finally, our vertical span is only four feet and I suspect an added seismic force would not increase the bending moment in the walls enough to invalidate the design in the C-1577. But, I don't like to guess.

============
"Is it the only lesson of history that mankind is unteachable?"
--Winston S. Churchill

 

[r13]

Looks like we are at the end of the rope. My last comment, if can be seen as advice, is geotechnical engineer's inputs are very important for your success. If you find anything interesting later on, please do come back and let us know.

 

[cvg]

You need to obtain the AASHTO LRFD Bridge Construction Specifications

there is essentially no base shear as the structure is not free standing, it is supported on all sides. settlement is likely the biggest concern. you should have checked for liquefaction, maybe that is covered in the geotech report. Liquefaction can cause flotation which is never pretty. you should also verify that there is no active fault crossing the culvert alignment. that should also be addressed by the geotech.

 

[fel3]

Thanks for the additional suggestions. Fortunately, there are no active faults crossing the alignment and liquefaction is not an issue. I will have the project engineer track down the AASHTO publication. We're a big company, so a copy is certain to be found somewhere internally. Regardless, since the manufacturer proposes to follow a recognized standard and for the other reasons I outlined above, I think that when we get to the end of this little detective exercise, we will be OK with a C-1577 box.

============
"Is it the only lesson of history that mankind is unteachable?"
--Winston S. Churchill