Dowel Bars In Shear 2

[Ginger]

Dear all,

I have a cast concrete section against which I am casting fresh concrete. I wish to form a shear connection between the two using steel pins drilled and grouted into the cast section and acting in shear across the joint

Is the shear capacity of the joint :

a) equal to the shear strength of the steel dowel bar cross section at the joint.
b) Bearing capacity of the concrete where the dowel bar is in contact with the concrete.
c)bursting stresses in the concrete.

or is it a combination of these effects/

Thanks in advance

Andy Machon

 

[Taro]

I typically disregard the dowel shear/bearing strength and use a shear friction approach. This assumes that the potential slip plane has some degree of roughness to it and in order for slip to occur, the concrete must separate slightly and the dowels must elongate. The dowels resistance to elongation creates a "clamping" force so that friction develops. This mechanism can be improved by roughening the surface of the existing concrete. The U.S. code reference for this is ACI 318 section 11.7.4.

 

[Taro]

Also, for the shear friction approach the dowels must be developed for the tension force on each side of the slip plane. If the dowels are not developed in tension, then your approach of checking the failure modes mentioned is applicable.

 

[ishvaaag]

Yes, shear friction needs full development of the required capacity in both sides of the joint. Full develpment length embedment is feasible in some cases but since long not the preferred option when just a known force is to be passed in shear, for which the correct approach is to check/design them as anchors without head.

EPCON has table with generic capacity in tension and shear of the inserts from which you can build interaction the UBC-94 way.

HILTI gives free program for the calculation.

ETAG 001
Edition 1997
GUIDELINE FOR EUROPEAN TECHNICAL APPROVAL OF METAL ANCHORS FOR USE IN CONCRETE

http://www.eota.be

go to endorsed ETAGS

 

[Imagineer]

I would say that it is the minimum strength of all of those. If the dowels are shallow, i. e. less than 8 inches, you might also have a pull-out problem.
Imagineer