I'm looking for some advice on designing post-fixed anchors/resin anchors. I'm often fixing into existing masonry and blockwork a lot and I have been using PROFIS to verify the base material failure modes and I've found the results surprisingly weak. 1kN in tension on an anchor is enough to fail all the resin anchor rods offered by the software regardless of embedment length due to breakout of the block/masonry. I could be dealing with a standard cavity wall or a 500mm thick solid brickwork wall.
I'm wondering if there's a better way of approaching this if I can't get the capacity I need from resin anchors? I would increase the bolts or increase my lever arm to reduce the forces but this isn't normally possible due to site constraints.
How can I get more capacity out of existing blockwork/ masonry walls in terms of these base material failure modes?
Thanks for the question. The limitation you are describing is the governing factor of the base material. It does sound though at 1kN in the relation to the Profis Engineering software it is the selection of the modelled brick unit and the masonry bond selected.
Regarding fixing across a cavity wall, it is not considered by the design code, but common sense would dictate the limit being the lesser of the two i.e. is the wall structure, brick – brick, block – brick or even timber frame - brick. Of course, you would have to conduct additional checks around the fixing point to ensure the masonry structure can resist the load you wish to safely transfer.
You mention thicker solid walls again this is possible using deeper embedment depth with the resin anchors but again due to the variations in masonry units, mortar strength, condition, stability of the structure you would need to test onsite to establish the allowable resistances – any results would also be site specific and not transferable.
Regarding onsite testing either BS8539:2012 or the latest state of the art publication ‘Onsite Testing’ Guidance note published by The Construction Fixings Association which expected to be in the next review of the BS document as this was the basis of the original.