Moment distribute to Tie beam

[snoar]

Dear Sir
I am Structure Engineer.
I want to know how to calculate about moment distribution from column eccentric load to Tie beam.
From above this problem occurred from piling construction was deviate from centroid point,
And now I need to consider about moment from column(Pier) to tie beam for re-design new tie-beam.
Thank you.

 

[rb1957]

is the tie beam fixed or pinned to the column ?

this sounds like a problem where a FBD would help alot.

Quando Omni Flunkus Moritati

 

[Archie264]

Are you referring to a pile cap? If so then it becomes a strength of materials problem making use of the equation, stress = P/A + Mc/I and the Parallel Axis Theorem, I + Ad^2. Except in this case instead of area you use piles in an analogous fashion. That is, do the following:

Find the applied vertical force P as well as Mx and My.

Calculate I_x and I_y of the pile groups. But, since this only refers to the piles themselves only the Ad^2 portion of the parallel axis theorem overwhelms the other part of the equation so use only that portion for a reasonable approximation. And instead of "A" use number of piles. Also, note that for odd numbers of rows of piles in a rectangular configuration the center piles are ignored when calculating I since they are at the center.

Then use those numbers in the classic formula, P/A + M_xc_x/I_x + M_yc_y/I_y but instead of calculating force per area you’ll be calculating force per pile.

I couldn’t find a good example of this online but there probably is one. Beyond that maybe a geotech engineer can chime in.

 

[BAretired]

Provide a sketch. We are not mind readers.

BA

 

[KootK]

I'll take the bait. My assumptions regarding your post are as follows:

1) We're talking about a column that is supported by a single, concrete pile.
2) The concrete pile that we're talking about is connected to its neighbours with concrete, at grade, tie beams.
3) The plan eccentricity between the pile and the column above is more than you anticipated.
4) You're trying to find a home for the moment caused by #3 and are looking at dumping some of it into your tie beams.

Assuming that there are competent connections, the load will distribute to the piles and grade beams (and supported columns) in proportion to their relative stiffness. My first check would be to see I you can deal with the entire moment in the piles alone. They tend to be the stiffest element for several reasons:

1) They're often large sections compared to tie beams and columns.
2) The piles are stiffened as a result of being continuously supported along their length by the surrounding soil.
2) The piles are stiffened by the effective pre-stressing force resulting from supported axial loads.

Much will depend on your detailing. Things like the dimensions of your tie beams an whether or not they rest on void form.



The greatest trick that bond stress ever pulled was convincing the world it didn't exist.

 

[snoar]

Thank you Sir
I was upload sketch drawing for my problem.
From now i know about reaction to pile from stress equation.
And then i want to know about moment distribution to tie beam, i try to simply calculate from Eq. Mtotal = Pe
and distribute to any tie-beam by M = Mtotal/No.of tie beam which connect pier.
So moment has been very much ,then calculate adding rebars to tie-beam ,has over cost.
From my thinking , moment distribute to tie-beam that little value, because actual behavior of tie-beam design to resist
Axial load when pile deviation, But i don't have any reference paper ,code, or booking to confirm my thinking.
Please help me to finish this problem and i need to reference paper or code of practice to confirm with owner.

* My English is not so good, please recommend to me
Thank you very much.

 

[KootK]

Damn, that's a great sketch snoar. I'd definitely assume that all of the moment goes into the pile group. From there, follow Archie's instructions. I doubt that you'll be able to reference anything other than "generally accepted structural analysis principles".

The greatest trick that bond stress ever pulled was convincing the world it didn't exist.

 

[BAretired]

Please see attached sketch.

If the tie beams take no moment at all and if your sketch is to scale, it appears to me that piles A and D will carry P/4 or 0.25P each. Pile C will carry approximately P(0.25 + 0.7/9) = 0.328P and Pile B will carry P(0.25 - 0.7/9) = 0.172P. The eccentricity 'e' between the green and black diagonal is 0.7 units and the c/c dimension between piles C and B is 9 units (scaled off the computer screen).

In the worst case, Pile C is carrying about 131% of its design value while Pile B is loafing with only 69% of design value. If Pile B is considered adequate to carry that excess in load, there may be no need to do anything.

The tie beams could be regarded as strap beams to take out the eccentric moment. They will presumably each take a moment in proportion to their stiffness. It will not be possible to remove all the eccentric moment from the pile cap because the beams will deflect, but hopefully they can improve the situation for Pile C.

Why is there a gap between the pile cap and underside of tie beams? I would prefer to see them tied together but perhaps there was a reason for the gap of which I am unaware.

BA

 

[BAretired]

Why the gap between tie beam and pile cap?

BA