Combined Cast-in and Post-installed anchor bolt group design

[jochav52802]

Good Day,

I've got an existing base plate for a fixed-based steel moment frame structure that is supporting some new and higher seismic loads under the jurisdiction of the 2019 California Building Code.

As a result, the existing cast-in anchors aren't sufficient to carry the uplift forces. Therefore, I'm considering having new post-installed anchors installed in between the existing anchors to achieve the desired capacity.

I'm unable to find any supporting design materials that allow or consider cast-in anchors combined with post-installed anchors.

I'd appreciate any support or references that you can provide on whether this is conventional and how I might go about the design; thank you!

 

[SJBombero]

If breakout is the controlling capacity, in order for new post-installed anchors to increase the uplift capacity, they would have to be added outside the existing bolt pattern since the breakout cone already includes all the area in between each existing anchor.

If breakout isn't the controlling capacity, I would check out the latest structuremag article on grouted anchor rods. The existing rod could be core-drilled out and replaced.

 

[canwesteng]

I would say it definitely isn't conventional, and you need to consider how the anchors work together. For steel capacity and concrete breakout, you have a good argument for treating them as one group - but how about for bond strength/anchor pullout, and side face blowout?