trench concrete detail 1

[Jandra11]

is there a possibility not to put any reinforcement on the concrete considering the concrete can withstand the load itself? any advise and comments are very much welcome. thank you.

 

[TehMightyEngineer]

You could but I wouldn't. The reinforcement to do this properly is so minimal to the cost as to be negligible.

Professional Engineer (ME, NH, MA) Structural Engineer (IL)
American Concrete Industries

https://www.facebook.com/AmericanConcrete/

 

[haynewp]

The bottom section will get poured and then the walls. Without any reinforcing you will have a joint at the interface with only the bond of the concrete resisting any lateral pressure from the soil and paving.

 

[TLHS]

You'll have some lateral loads from traffic next to it (less than Rankine will tell you given that depth and setback, but still). Also, you're going to get freeze/thaw in anywhere in the high or low latitudes and you have constant dynamic loading and unloading from traffic.

You need the reinforcement for durability even if you can make it calc out for strength.

 

[Jandra11]

thank you for all the inputs. one more question what will be the minimum possible reinforcement beside from the temp bars=.002bh

 

[Jandra11]

@tme i agree with that but my boss want to save everything he can save. and the length of this project is 18km
@haynewp @tlhs what is the minimum possible reinforement

 

[dik]

and to increase costs, I'd add joints... Is your boss? sealing this? Added: Any drains? 6" walls don't retain very much...

Dik

 

[Jandra11]

@dik i have no idea he just ask me if there will be a possibility to reduce the steel reinforcement or make it a plain concrete.

 

[Jandra11]

instead of using steel bars, is it more economical to use steel fibers, considering the right amount of fibers to resist concrete shrinkage?

 

[Jandra11]

any thoughts on this details? what will be the problem disadvantages of this detail?

 

[TehMightyEngineer]

Not to toot the horn of my current industry too much but since I design a lot of it, why not go with a precast trench if you're making that many of them? A precaster could pour them in a single pour with high quality concrete and some wire reinforcement for not too much money more than cast-in-place. You might spend more on the concrete but the time and labor to install would be way lower.

is it more economical to use steel fibers

Possibly, some brands of steel fibers can replace reinforcement. But, if you do the trench in two pours then steel fibers would not work. Also, if these need to meet ASTM requirements for utility structures they likely cannot be reinforced only with fibers. Overall I'd say steel fibers may work but they will add some labor on the mix placement side, so might end up being a wash.

any thoughts on this details? what will be the problem disadvantages of this detail?

That may work. The lack of reinforcement in the bottom of the trench may be an issue, but likely not a problem given the size. Possible corrosion/spalling issue with the rebar extending through the pour but for a trench I doubt it's a show stopper unless you need a long service life out of this trench.

Professional Engineer (ME, NH, MA) Structural Engineer (IL)
American Concrete Industries

https://www.facebook.com/AmericanConcrete/

 

[TLHS]

Yeah, if you're installing kilometers of these things, buy precast or some of the other premade drain products. This is not worth forming. The embedded angles and the tight reinforcement are a pain to do in the field. Cast in place is fine for small trenches when you're trying to fit a specific condition of some sort, but if you have lots of them and can design to make it work go with precast.

You can cast them with a varying invert, or you can screed them to give a slope if you really need to. There are plastic and metal options too. CSP slot drains could be an idea as well depending on the exact application.

 

[dik]

What sort of climate and do the soils vary over the distance? Precast is a good way to go... can you tolerate movement?

Dik

 

[Jandra11]

Helo guys. the client is asking me to design this according to the loads stated in aashto. can someone give me an idea of what loads should I consider? thank you very much in advance

 

[dik]

'big' truck loading?

Dik

 

[bridgebuster]

16k wheel load plus impact

 

[amlinerrichard]

Search 'precast trench drains'.

 

[Jandra11]

the load i consider before is the capacity of the grating above it. but they want the aashto loading requirement I dont have any idea on using aashto.

 

[bridgebuster]

There isn't any AASHTO loading requirement. 16K is an AASHTO wheel load. Many gratings are rated for HS20 or H20, which is a 16K wheel load.

 

[TLHS]

I still think that you really shouldn't be reinventing the wheel on this. The traffic rating of the purchased item should be documented.

Look at the following items in this order:
-Local jurisdiction's department of transportation standard drawings
-Standard drawings of nearby local municipalities
-Local precast concrete/CSP vendor catalogs