Grade Beam With Isolated Footing

[TekEngr]

I am designing a grade beam which is connected with the isolated footing pedestal both side, furthermore the grade beam is carrying the self-weight of block wall so I have few confusion as mentioned below can someone please suggest in this regards.
1: grade beam is carrying the self-weight of block wall, so will this grade beam transfer the load on isolated pedestal, however the grade beam is fully supported by the block wall below??
2: internal slab should be monolithic with the grade beam or there should be isolation between grade beam and slab which option will be good in this circumstances??

 

[oldestguy]

If the "footing" under the wall will carry the entire wall, why use a grade beam? Or lower the grade beam so most of the wall is carried by it.

 

[hokie66]

1. I wouldn't call that a grade beam. A grade beam sits on the grade. Build the grade beam down at the level of the isolated footing.

2. Isolate the slab, but ensure the fill beside the wall is well compacted.

 

[TekEngr]

@oldestguy
Below wall is for holding the soil under the salb and this grade beam/plinth beam is also acting like a tie beam as it is connected from both side with pedestal of isolated footing.
I think the above wall selfweight will transfer to the footing column through grade beam/plinth beam ,
is my understanding is correct?

 

[jayrod12]

The gradebeam won't transfer the load to the footing until the wall below settles slightly.

 

[hokie66]

So how do you build that block wall 1500 into the ground? Why do you need it so deep? You say that it is "holding the soil under the slab", but what does that mean? What kind of soil do you have?

 

[dhengr]

Shahg123:
You do yourself a significant disservice when you are too damn lazy to do your sketches in proper proportions and when they don’t show all you are talking about. Your cross section shows 5000, 350, & 1500mm vert. dimensions, which bear no resemblance to the proportions of the sketch which does not show the footings or large conc. columns. You will discover that experienced engineers glean a great deal of firsthand basic info. on a problem from what you draw and say, so be careful, or you may seriously mislead them. A 5’ high wall acts far differently than a 16’ high wall, but the 5’ high wall in your sketch is taller than the 16’ high wall, then you don’t show the grade on the outside. It appears that you are building a reinf’d. conc. frame and then the (conc.?) blk. is just infill in that frame. Why not just build a grouted and reinforced conc. blk. wall and make your grade beam a conc. blk. bond beam for the tie purposes, and put the whole wall on a strip footing? Then you don’t have to dig a larger hole every 20’ for the spread footing; you already have to dig the trench for the wall and can use that std. strip footing forming. You indicate nothing that suggest you have concentrated loads every 20’, except you put columns there.

 

[KootK]

It appears to me that the lower block wall is a retaining wall resisting soil pressure across an elevation change.

1: grade beam is carrying the self-weight of block wall, so will this grade beam transfer the load on isolated pedestal, however the grade beam is fully supported by the block wall below??

I would say that any vertical load applied to the top of the grade beam is likely to get transferred to the block wall below the grade beam. Or laterally out to the footings via masonry arching action. As such, unless the soil doesn't provide vertical restraint to the block wall, I don't think that the grade beam will see much vertical load.

2: internal slab should be monolithic with the grade beam or there should be isolation between grade beam and slab which option will be good in this circumstances??

This will depend on:

1) If you're worried about the SOG moving deferentially relative to the grade beam due to frost heave, settlement, expansive clays etc.

2) If you're relying on the SOG to restrain lateral movement induced by the retained soil loads. Based on your proportions, I suspect this may be the case and this would necessitate a hard connection between SOG and grade beam.

3) What your geotechnical engineer thinks.

 

[hokie66]

I don't know how a retaining wall would work like that. I think he has soil both sides, with only a 350 difference inside to out.

 

[derim01]

This detail is used often in the Middle East with sand soil.

The beam is usually named tie beam, and block below it used to contain sand below slab on grade since there are differences between outside and inside levels (usually up to 350 mm). In that case, only 3 layers of 200mm solid concrete block are used since placing more is just a waste of money. However, some Consultants are insisting to place a block from the bottom foundation level.

Slab on grade is usually disconnected from the tie beam. Tie beam height is typically 600 to 700mm since concrete block is widely used for the walls.

 

[TekEngr]

@derim01. Your observation is correct this project is based in UAE and yes 1.5m deep block work is consultant requirement.
I designed the beam as a grade beam as it is resting on the block wall and i assumed that all the vertical load will transfer to the soil through block work below and no vertical load will transfer in to the column of footing through beam, the purpose of the beam connection with column footing to resiste overturning and stabilize footing only.