Catch Basin Rehab - for additional heavy truck loads

[njain]

I have several 30" x 34" (5" wall thickness) precast catch basin in a parking lot.
Owner wants to use the parking lot for heavier loads (Wheel load = 40 kips)

I would like to know -
- How to increase capacity of existing catch basin to take additional wheel loads without digging into the ground.
- Is adding a top CIP concrete slab, one and the only solution?
- Is the cocnrete top slab effective in acting as a beam at top of precast wall?
- How do you design such slab - as a beam to take reaction due to surcharge load at top? Check punching shear? what else?

please advice.

 

[ACtrafficengr]

Just out of curiousity, What kind of truck has individual wheel loads equal to half of legal road weight?

 

[njain]

Hyster H450 Lift Truck, this is for lifting heavy containers

 

[bridgebuster]

How deep are your catch basins? Do they have a metal frame and grate or is the top presently a slab? A little more info please.

 

[njain]

Catch basin is 10' deep (total height) with a top metal frame that I am planning to replace with a stronger one as part of rehab.
We will be raising the catch basin up.

 

[bridgebuster]

Normally, we design the top slab as a concrete beam; given that your plan dimensions are small, how much solid area is left after deducting the grating?

You also need to check the walls due to increased live load. Usually manholes are designed for HS-20 or a heavy surcharge. A fully loaded fork lift, as you describe, has a much larger axle load. Check the wall as a beam spanning horizontally between two side walls, then check it as a vertical cantilever wall.

If your catch basin is precast it should/may have been designed per loads specified in ASTM C890.

If you need to strengthen the walls, they can be thickened - I've seen it done - assuming you can live with the reduced hydraulic capacity. If not, there are ways to isolate the catch basin but it could be more trouble than it's worth to replace them.

 

[njain]

Thanks Bridgebuster for the response. I have To determine the top slab dimension as well. How do yu base that upon? Do you find the influence of a point load beyond which there will be no effect on the CB?

 

[bridgebuster]

The top slab of a catch basin (in plan) is the same size as the catch basin (in plan). What I said earlier is that your CB has a small plan area; after you deduct for the grate there probably isn't going to be much slab left.

 

[njain]

Bridgebuster:
No, the slab is going to be much larger. That is the intent for top slab as I said in my first post.I looked at a previous rehab detail. They are using 12'X12' slab 30" thick over a 72" diameter Manhole. Their loads are about 215 kip per wheel, much higher then what I have (40 kip per wheel). any recommendation on how to determine required slab dimension and thickenss to protect existing CB?
Thanks in advance

 

[bridgebuster]

Njain,

This is the first time you mentioned a 12x12 slab; 72" manhole, and a 215 kip wheel load. Are you sure it's 215? Can you post a sketch of what you're trying to do?

 

[njain]

Bridgebuster:

Load is 40 kips wheel load not 215. The detail that I saw is designed for 215 kips, with a 12x12, 30" thick.
I am trying to find what slab dimension (LXBXh)I need to protect the 34"x30" CB from 40 kip wheel load.
See attached

 

[njain]

The detail I am referrring to.
How do I estimate the slab dimension and thickness required?

Assuming the wheel load as a column load, I can design the slab as a isolated footing?

 

[bridgebuster]

njain

First, your slab, if needed, will be less than 12x12 x 30" thick; 40k is a lot less than 215k.

Here's what you do, (a little trial and error):
Treat the 40k as a point load next to the CB and see what affect it has on the wall. If the CB isn't overstressed, you're good to go.
If not, treat the 40k as a strip load along the CB, pick some dimensions, say 2' wide and 6' long; then see what affect it has on the CB. Adjust the dimensions as needed.
Then design it as a slab on grade. I wouldn't rest the supplementary slab on the catch basin, in case of differential settlement.

 

[njain]

Thanks bridgebuster.
I ended up with a 10'x10'x18" thick slab based on designing it as a beam.
The isolated squre footing check passsed without difficulty for above slab (beam design governs)
Then I checked the slab on grade design for heavy lift truck loading using COE curves.

I am now going to check the catch basin walls, as supported by above slab.

Thanks for your input and help.

 

[bridgebuster]

You're welcome