Anchor Shear with Eccentricity

[Flotsam7018]

When special provisions are not provided to ensure shear transfer to all anchor rods, via plate washers or sim., it is often assumed in the design that only half of the anchors will resist the shear. This much I can agree with, considering only the front or back half of the anchors is logical, however, I have also seen calculations consider the case as shown in the sketch which correlates to Case 1 & 2 of Figure R17.7.2.1b in ACI 318-19. That is, all the shear would go to the side anchors only and the eccentricity between the centroid of the column and the engaged anchors is considered in the calculations. This often will significantly decreases the capacity and in my opinion is not realistic. However, I would be interested in getting other peoples thoughts on the matter.

Thank you

 

[HTURKAK]

Dear FLOTSAM, i have never seen any calculations based on all the shear would go to the side anchors only.. will you pls post the subject figure R17.7.2.1b in ACI 318-19 ?. In this case, the anchors are designed for (shear + torsion) similar to bolts ..is that true ? and if the anchors are for columns of a frame ( rather than self standing solo column) , the column would experience torsion ..

My suggestion will be ;

- Anchors should not be designed for shear if you can show that the factored shear loads are transmitted through friction..
- If there is shear load in excess of the amount that can be transmitted with friction , either use shear lug or use welded washers to transnit the excess shear to the anchors..

Good Luck..