One-Way Slab Concentrated Load - Shear Design/Detailing

[echobs]

I am working on designing a one-way slab with a concentrated point load on the slab due to vehicle traffic. Running this, I find the Vc is not enough to resist the large shear loads seen in the one-way slab. I don't want to increase the slab thickness to get this to work, so I would like to use reinforcement to resist this shear. I'm aware that typically for beams, this shear could be taken care of by using stirrups. However, I am struggling to find resources on how to reinforce a one-way slab and the necessary design guides. Any direction on this topic would be appreciated. Thanks!

 

[WesternJeb]

What strip width are you using? AASHTO let's you take more than just a 12" strip width that is typical of slab design.

Shear is usually what controls my one way slab designs for trucks as well and increasing thickness is about the only option.

 

[echobs]

I am just doing a typical 1 ft strip width using the design following ACI 318 for Vc. What section of AASHTO are you following?

 

[WesternJeb]

For the 9th edition, it is 4.6.2.3, the "E" value. This is a pretty big section of AASHTO with a some exceptions.

This is also dependent upon using a certain amount of distributed reinforcement in the transverse direction to distribute it. I am thinking this is 9.7.3.2 but there might be another section.

I am a vertical guy who has done a handful one one way precast bridge decks, usually 15' or less. So take these recommendations with a grain of salt but it should be what you need to justify your design.

 

[echobs]

Thanks for your help! This design is for an underground tunnel with a concrete lid. The lid is to be designed to withstand vehicle traffic loading. To stay on the conservative side, I am just going to design the concrete with a 12" strip width. Following ACI 318 (22.5.5.1) Vc = 2*b*d*(sqrt(f'c))*(phi). Per your wisdom, it sounds like there is no way to effectively design a one-way slab with additional reinforcement for shear in the slab and thus I will be using a thicker slab until I can get what I need.

 

[WesternJeb]

Let's take a few steps back here. You are saying underground.. Is the concrete lid buried beneath soil at all or is it exposed directly to traffic? Is it multilane?

There are a handful of items in AASHTO I didn't mention that might need to be brought up if this is a busy roadway. There is a 540 plf lane load to be used in addition to the typical wheel loads.

A 12" strip width is far, far too conservative but if it helps you sleep better at night then be my guest!

 

[echobs]

This is a concrete lid that is buried under ground that spans 8'-0". The amount of soil cover ranges from 0' - 4'-0". There is a single lane going in each direction. This roadway is not a busy roadway and is pretty much a low traffic service road.
One piece of literature I found online, is another design guide I will be using to help determine my loads on the tunnel. See link below.

https://f.hubspotusercontent10.net/...7e8c8dd6|0affadd8-7b2a-40dd-9f72-5c7b29054aa2

Do you have any other recommendations?

 

[WesternJeb]

See pdf for Kentucky Transportation Cabinet's standard 8'-0" box culvert that should serve you well (it looks like you are in the United States). This is designed per AASHTO loading + 25% per KYTC standards, so it might be slightly conservative for your state. Use at your discretion to check yourself. All of these documents for different spans are available for engineer's use on their website.

[URL unfurl="true"]https://res.cloudinary.com/engineering-com/image/upload/v1703697914/tips/BSC003_dqatcc.pdf[/url]

 

[echobs]

Thank you! I will review this and compare my results with this document.