Designing an anchor plate connection: how concrete anchors fail and how to prevent it (as an engineer) – part 2

Maybe you read the article on how anchors can fail under tension and are waiting to know more about what happens to a fixing point when the force is perpendicular to the anchor direction. This article will provide you with a greater understanding of shear load applications and share some tips for your next anchor design.

1. Steel failure under shear

Failure might occur if the anchor size is too small, the number of fixing points is not enough or simply due to the steel strength capacity. To increase the resistance, select a more resistant steel material and/or increase the size and the number of anchors. Please be advised that some anchor design codes (i.e. AS 5216-2018/SA TS 101) only allow the designing of selected anchor arrangements and a limited number of anchors: In many cases, you can rely on the Hilti Design Method for some configurations that are not covered in the above-mentioned codes, to support your engineering judgement.

2. Steel failure with lever arm

The anchor plate detached from the concrete surface (sometimes through a ground pad) implies the deflection of the steel rod due to the lever arm. There is no general rule here: stand-off anchor plate anchor design can vary according to design standard use. For this, we strongly recommend that you get in touch with our experts (you can simply leave a comment or post a question on our discussion board) when you are dealing with this application.

In stand-off applications, steel failure with lever arm

should be considered in the design

3. Concrete edge failure

A lateral concrete break-out might occur under shear load, when the anchors are close to the edges. As per concrete cone failure under tension, the resistance of the cone depends mainly on the concrete class, the concrete condition (cracked or uncracked) and the volume of concrete cone engaged by the anchor.

Bear in mind that the main design standards permit consideration of only the first row of anchors closest to the edge to take the full load and transfer it to the base material.

Just a word of advice, in case this failure is limiting the design, position the first row of anchors further from the edge (or foresee a slotted hole for the closest row), increase the embedment depth and increase the spacing from the anchors, if too close.

4. Pry-out

The concrete can also break out far from the edge, especially with shallow embedment. The resistance regarding this failure can be improved by increasing the embedment depth or the volume of concrete engaged (i.e. increasing the spacing between anchors).

After reading this article and the one about tension failure mode, you should have a better understanding of how anchors can fail: These failures are the failures considered in most of the international standards for anchor design in multiple conditions (i.e. static, seismic, fire, fatigue), which require the checking of both load conditions and their combinations.

You can find out more through our Webinars or start designing with more confidence by using our anchor design software PROFIS.

Should you have any questions, simply leave a comment here or in our Q&A section.