RAM concept mat foundation

Hi all,

I am designing a very, very large mat foundation. I have modeled 2500mm deep raft, with some 6000mm deep areas. I have modelled columns above (and have applied large G & Q Loads). I have also modeled some tension piles beneath the mat using point supports to tie down the mat in the uplift load case. 

1. Should my design strips span between the point supports below the mat, or between the columns above the mat? Or do I need to model both scenarios for different load cases?

2. By increasing my zero-tension iterations to 12, I see on the max Soil Bearing pressure plan that my negative stress has gone from approx -50kPa to -1.5kPa. Is this the indication I'm looking for to guarantee zero soil tension, and that any tension force will be taken by the piles?

2. Is there a known issue with very deep sections and walls modeled above being cropped..? I have 3m walls above, but they are being trimmed very short over the deep sections, see attached. EDIT: I cant seem to attach a picture.

 

Any help would be great. 

 

thank you

 

Parents
  • 1. Design strip layout takes a lot of engineering judgement, but as general advice I think you will want strips that stop at columns/supports below as well as columns/point loads above (assuming the point loads are large).

    2. Right. As long as the structure is stable you should be able to eliminate tension with enough iterations, but practically speaking a small amount of tension is allowable. Modeling the piles as elastic columns or point springs might also be more realistic than using a rigid point support.

    3. Walls above the mat are considered as starting at the slab Center Line (CL) and extending from there. So the top half of the slab thickness and the wall overlap and the slab occludes the wall.  For more on wall above behavior, check the manual FAQ or this wiki:  

    The program does not implement any special concrete design requirements for thick slabs. If the slab span to depth ratio is less than around 3 then many of the assumptions we make in our design are no longer valid.  In this scenario, an arching mechanism becomes more predominant over the typical beam bending and shear mechanisms and a strut-and -tie model is more appropriate.



    Answer Verified By: Graeme West 

Reply
  • 1. Design strip layout takes a lot of engineering judgement, but as general advice I think you will want strips that stop at columns/supports below as well as columns/point loads above (assuming the point loads are large).

    2. Right. As long as the structure is stable you should be able to eliminate tension with enough iterations, but practically speaking a small amount of tension is allowable. Modeling the piles as elastic columns or point springs might also be more realistic than using a rigid point support.

    3. Walls above the mat are considered as starting at the slab Center Line (CL) and extending from there. So the top half of the slab thickness and the wall overlap and the slab occludes the wall.  For more on wall above behavior, check the manual FAQ or this wiki:  

    The program does not implement any special concrete design requirements for thick slabs. If the slab span to depth ratio is less than around 3 then many of the assumptions we make in our design are no longer valid.  In this scenario, an arching mechanism becomes more predominant over the typical beam bending and shear mechanisms and a strut-and -tie model is more appropriate.



    Answer Verified By: Graeme West 

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