Grade beam modifications

[Ipetu]

There is a 10" x 24" deep concrete grade beam reinforced with 2-30M (#9) bars top and bottom and 10M (#4 - 0.16 sq. in) stirrups at 24" o.c. The grade beam is supported on concrete piles (piers) at 20'-0" on center. Total length of grade beam is 100'-0". The total factored uniformly distributed load on the grade beam is 38 kN/m (2.6 klf). The yield strength of the reinforcing steel is 400 MPa (58 ksi) and the 28 day compressive strength of the concrete is 30 MPa (4.4 ksi). Concrete cover is approx. 2".

Problem: A 5" deep x 36" wide notch (for a new door way) is required on the top of the grade beam at a location 7'-0" away from the pile center line. The center line of the 5" x 36" notch is 7'-0" from the pile center line.

Does anyone have experience with this sort of a challenge? What are the options available? Thanks in advance for the help.

 

[dik]

Sorry BA... but, if you get any shear in that beam, it will generate a tension in the top fibre... and, I'd just as soon have some rebar across the crack... even a bigger problem if you have any pattern loading...

I think I'd reinforce it...

Dik

 

[BAretired]

dik,

Shear in a beam does not generate tension in the top fiber. Frost heave generates tension in the top fiber. Without frost heave, the top fiber at midspan is in compression.

The only way to get rebar across the door recess is to cut deeper into the beam, drill and embed bars each side of the recess, then fill with concrete, a questionable strategy in my opinion. It is better to reinforce externally as I suggested in my earlier post.

BA

 

[PMR06]

The detail does show voidform under the gradebeam. Unless they solve the stirrup/shear issue, the entire grade beam might lower itself 5" on its own!

There's no way I would use code tricks to take the design right to the edge when shear is the failure mode holding up multistory brick and load bearing wall. I still think sistering on a properly reinforced grade beam is the way to go. I just believe in getting the foundation right from the start.

 

[BAretired]

Another way to resolve the problem is to add an offset pile each side of the door recess. The piles would need to be tied to the grade beam to resist uplift. Then you could forget about top steel across the opening.

In the remaining bays, you could add one pile at midspan in order to reduce the shear stress.

BA