Moment distribution
Moment distribution
(OP)
A few times I have encountered the problem of a structure, rectangular in plan view, which is supported at its four corners by piles (I guess from a conceptual level they could be columns instead). If V-Hx-Hy-Mx-My-T loading is given at the centre of the rectangular structure, how would you go about resolving the moment taken at each of the corners?
I think it's okay to assume the V, H and T components could be divided equally between the four corners. For the moments, what I have seen in the past is to assume a 'push-pull' mechanism whereby one corner goes up and the opposite goes down; the other two corners would have to be treated as pivots which practically don't move, which probably isn't quite right. This means the Mx and My get resolved as additional vertical loads. I've been led to believe that the 'push-pull' resolution is conservative which is probably why it has been used.
Are there better ways of resolving the moments? Are there any better simple methods out there? I don't mind if it's iterative - I can program something up. Similarly if it requires some basic FE code. I just wanted to know what you guys would do and whether there are any better methods out there (short of doing a full in-place structural analysis)
I think it's okay to assume the V, H and T components could be divided equally between the four corners. For the moments, what I have seen in the past is to assume a 'push-pull' mechanism whereby one corner goes up and the opposite goes down; the other two corners would have to be treated as pivots which practically don't move, which probably isn't quite right. This means the Mx and My get resolved as additional vertical loads. I've been led to believe that the 'push-pull' resolution is conservative which is probably why it has been used.
Are there better ways of resolving the moments? Are there any better simple methods out there? I don't mind if it's iterative - I can program something up. Similarly if it requires some basic FE code. I just wanted to know what you guys would do and whether there are any better methods out there (short of doing a full in-place structural analysis)






RE: Moment distribution
Personally, I would model the pile cap on RISA-3D, with a support near each corner.
DaveAtkins
RE: Moment distribution
another day in paradise, or is paradise one day closer ?
RE: Moment distribution
An alternative visualisation could be to consider a slab supported at its corners by columns.
RE: Moment distribution
https://en.wikipedia.org/wiki/Couple_(mechanics)
RE: Moment distribution
Given the above, the comment by rb1957 seems to suggest replacing a moment at the centre with a 'couple' (i.e. a pure moment) at the supports. I don't understand that. Can anyone else explain?
RE: Moment distribution
In your case a moment at the center of the pile cap is the same thing as a couple, with the equal and opposite couple forces acting at the piles. Just like you said in your original post.
DaveAtkins
RE: Moment distribution