dowels for shear transfer in slabs

huangyhg

dowels for shear transfer in slabs
for slab on ground it is recommended that for construction joints square dowels be used.  round ones are not recommended except for only light loads.  im wondering for old concrete to new pours do you just overdrill a larger hole so that square dowels can be inserted?  
would appreciate comments on this !

the reason square dowels are used is so you have flat surfaces on the sides of the dowels for compressible material.  this allows the new concrete to shrink without stress parallel to the joints from the embedded dowels.  so yes, drilling holes in the old slab large enough to insert and grout square dowels is a good way to do it.
thanks hokie66
up till now i just thought that square bar had a  greater load transfer capability than round bar dowels.
so what your saying is that the square dowels (with their flat surfaces on the sides) will allow the concrete to shrink without stress parallel to the construction joint?  if so, how so?

you have to have a compressible material beside the dowel for it to work.  have a look at the danley construction products website, where they have a couple of types of dowel covers which allow this movement.
the beauty of a square dowel is that it will also permit relative slab movements due to shrinkage.  by this i mean that the two slabs can travel past each other, similar to plates during an earthquake, without stress.
ys
b.eng (carleton)
working in new zealand, thinking of my snow covered home...