Tie beam to pile caps

[sag04]

Hi
It is the usual practice in Middle East that pile caps are tied to the adjacent pile by means of tie beams. Some designers provided this only to single pile and two pile groups others providing this to almost all the pile cap?. For single pile, two tie beams in perpendicular direction and two pile group in their least dimension. What is the purpose of this tie beam?It is not mentioned in any of the design book I read!!! Is it part of seismic design? Could anyone suggest any link to any publication on this? or good design book?
Thanks
Regards

 

[cap4000]

The way your describing your post is exactly the way I have typically seen it done here in NJ and NY. I believe the reason is to simply brace the cap from any lateral movement. I have also designed it, where the slab on grade IF on good soil material I do not use the tie beams, but a thicken haunched slab around the cap with 8 # 7 rebars dowelled from the cap to the slab haunch for the restraint of the cap. I don't think there is a code specific horizontal force in terms of percentage of your pile axial load. Incidentally, as long as you have a min. 2 piles in any one parallel direction within the cap that direction does not need bracing. This is solely my take, on this not so well researched issue. Nice Thread. Good Luck.

 

[STR04]

In addition to any seismic requirements the grade beams are placed to resist eccentric loads from a misplaced pile group. This force M=Pe will need to be resisted by your grade beam for 1 & 2 PC's. 3 or more are braced by themselves but need to resist the misplacement of piles. I've used 1" of eccentricity for the pile group. Check your building code for additional information.

 

[trilinga]

It is a normal practice to tie the pile cap in the direction along which no lever arm is available to resist moments.

In a pile cap with two piles, the moment in the plane containing the two piles is resited by the push-pull on the two piles.

The other direction has no such capacity. The tie beam between the two adjacent pile caps in that direction carries the moment and converts it into the push-pull between the piles of the two pile caps.

The tie beam shall hence be desiged to carry the algebraic sum of the moments from both the columns in the direction, transferred at its ends.