Grade Beam on Piles with Torsional Load 3

[chrisrosebud2001]

I am designing a 4 story building with a basement that will be placed on auger cast piles. The perimeter of the building will be placed on grade beams to support the basement wall as well as a brick facade above. With the exception of the basement wall, the support structure is steel. So, any columns will be placed in the center of the grade beam, but the basement wall and facade will placed to the exterior of the grade beam creating a torsional moment. What is the best way to handle this load? My initial idea was to ensure a moment connection at all pile/grade beam interfaces so that I can assume the beam fixed against torsion at these locations and then design the piles for the additional moment. Does anyone have a better suggestion?

Thanks in advance for any help.

 

[chrisrosebud2001]

Ok, I have attached a wall detail. Maybe this will help.

 

[PUEngineer]

What is happening perpendicular to this section? Do you have a regular grid where you could tie in perpendicular grade beams at the column locations? This could take any torsion out of the grade beam shown in the section as a concentrated moment in the perpendicular grade beam. Then you could use the standard floating slab on grade. This would add another pile to help resist any lateral load at the base of the wall also. If you have a narrow building, you could just run the grade beam from wall to wall.

If you're putting moment into the top of the pile, then you would need obviously need hooked steel from the pile into the grade beam. It wasn't shown on your detail, so I thought I would throw that out there.

 

[Ltwine]

toadjones:

Above all, I don't do residential, even the exception of my only such design was applied to a light industrial facility with odd pre-existing wall footings buried deep into the soil, not much choice there.

I like the solid feel of reinforced floor, no need to worry about joint details/material, cracks, seepage, running mud after flood, and potential of change of use.

After all, the OP's section might not have much torsion after successful back filling. Torsion could be critical during the stage of wall construction.

 

[chrisrosebud2001]

There is a grid perpendicular to this section. The building is approximately 82' wide and the interior columns are on spread pile cap foundations. The only grade beams running perpendicular to this section are at the ends of the building. I would prefer not to add in additional perpendicular grade beams if there is a simpler solution such as structurally connecting the slab to the beam as someone else mentioned above. Does anyone agree with that solution?

 

[PUEngineer]

What's in the basement? Heavily loaded? Typically, do you use an unreinforced floating slab?

 

[BAretired]

I would not use the detail shown at all. It would be better and more economical to provide a pilaster from basement to Main Floor at each column location, i.e. start the steel column just below Main Floor beams.

Delete the grade beam. The concrete wall is more than adequate to act as a beam on its own. Instead, use a pile cap at each pile and extend the cage from the pile into the pile cap. Center each pile under the center of gravity of applied loads to reduce moment in the pile. The grade slab can be tied laterally to each pile cap but it does not need to resist moment.

Do you really need 16" thick walls? How is the top of wall tied into the structure? There is no vertical reinforcement on the inside face of the 10" block where it meets the 16" wall, so it can't span vertically. If the wall spans horizontally between pilasters, the pilasters must be tied to the Main Floor structure to resist lateral loads.





BA

 

[chrisrosebud2001]

Actually, this slab will be reinforced with wwf. Sorry that it wasn't indicated on this particular detail. The heavier loads on the floor slab are around 150 psf live load.

 

[chrisrosebud2001]

There are pilaster columns in the structure, but this detail only shows the wall section between columns. The steel columns will be placed at the top of the 16" block and the wall will also be braced at that elevation. That's the reason why there is no reinforcement on the inside face of the 10" block.

 

[BAretired]

If there are pilasters, there is no issue with torsion. But why bother with a grade beam at all? The wall is much stiffer than the beam and will carry its own weight.

BA

 

[Ltwine]

If you are going to stick to current details, plan well on shoring to take out unbalanced conditions during construction. I sometimes dictate construction sequence and ask for necessary construction support be installed during certain period/stage, or ask the contractor submit his plan for review. The requests do not mean to interfere with the ways and means of how the contractor doing his business, but to identify and find solution for potential catches/problems, early and in a timely manner.

 

[hokie66]

The nomenclature on the detail bothers me. All the reinforcement is shown as "dowels" of one kind or another. The only ones I would call dowels are the ones at the wall to slab junction called "2-#3 dowels cont", but they are not continuous, and are not desirable as they restrain the slab from shrinking. I would carry the sand onto the grade beam to further prevent restraint.

I agree that with pilasters, there is no concern with torsion on the grade beam. I would still use the grade beams, as they give a good platform for the rest of the construction. The pile reinforcement should at least extend a decent length into the grade beam.

At the top, I assume brick veneer continues above. The slab should be carried through to support the veneer backup rather than depending on the 6" CMU.

 

[BAretired]

hokie,

I agree that the nomenclature on the drawing is questionable. It needs to be revised to make the intent of the drawing clearer.

I don't have a problem with using a grade beam, but a 2'-9" by 3'-0" continuous beam is an expensive way to provide a platform for wall forming. I would not do it and I don't think you would either.

BA

 

[hokie66]

The grade beam does seem to be a big larger than required. I would probably reduce the depth. If it were a concrete wall, you could omit it, but with a block wall, you need a footing to start on.

 

[chrisrosebud2001]

Thanks for all your suggestions. I agree that this detail needs to be revised and I'm not sure why the bars are called out as dowels. I was brought in on this project part way through and this was how the detail had been shown before.

 

[ToadJones]

ltwine-

What difference would it make if the floor were plain concrete or reinforced as far as seepage goes?
Where is this mud coming from ?
We usually pour basement slabs on a layer of 6 mil plastic.
If you can feel the reinforcing in the slab you must have some sensitive toes!!!!!