Shear with Lever arm

Posted by Andrew C. on 2023-01-16 16:58

EC-2 part 4 clause 6.2.2.3 states that if a mortar bed is greater than 0.5 d, that shear force with lever arm must be taken into account, but neglects the contribution from the mortar (apart from in a very specific case). Even when discounting direct shear transfer via the mortar bond, the mortar will prevent bending of the anchor rods by acting in compression, which would eliminate much of the shear force acting with a lever arm. In this sense, the composite action of the threaded rods and the mortar will act more like an RC beam (where the reinforcement is not considered to be subject to any direct bending moments.

As the Eurocode discounts all of this, the result of that clause is extremely conservative and impractical: if a 25mm mortar bed is pretty typical, then to avoid consideration of the lever arm, you'd need 50mm bolts (for example). As soon as the shear with lever arm component is considered, the shear capacity drops sharply.

Any advice on this would be appreciated.

Posted by Stephane P. on 2023-01-16 17:36 ( Modified on 2023-01-16 17:37 )

Hi Andrew,

For limited force values, it is possible to rely on shear transmission of the anchor rods in the concrete.
Otherwise, it is recommended to ensure the transmission to the concrete of the shear force at the column base plate using a block shear connector (eg : HEA shear nibs), as soon as the mobilization of friction at the steel-concrete interface is not sufficient.
An explanatory document can be consulted here.

However, Eurocode 2 is not my specialty, any additional opinion on the subject will be welcome.

Stéphane

Posted by Andrew C. on 2023-01-18 14:32

Hi Stephane,
Thanks for that, will have a read of the document you linked to.