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Looking for a bit of guidance on fire rating of post installed mechanical or chemical anchors.

We currently have a project where we are providing steel support beams to the underside of an existing suspended slab to provide support due to a large number of penetrations being cut in from above. The beams span between drop panels bolted to the face of the drop panels with restraint fixings to the underside of the slab above at nominal centres.

The slab has requirement for a 120/120/120 fire rating. Our initial advice was to box the support beams and connection with fire rated material. This option is not viable as space is very tight and the mechanical ducting can not fit within the ceiling space under the beams if the boxing of the beams occurs.

The architect is proposing an in tumescent paint system Nullifire sc902 which will be sufficient for the fire rating of the beams however we are concerned with the rating of the connection to the existing concrete at each end. Nullifire advised that the heads of the anchors could be post treated by painting or casting a plug over the bolt head (but have no testing to confirm this would be an appropriate method). International have fire rated caps available from the UK - http://www.international-pc.com/ProductLiterature/..., they indicate that they keep the temperature below the cap to 550 deg C targeting the loss of strength point of structural steel.

Have not had any luck with the anchor suppliers as yet - advice to date is that the treatment idea seems sound but they have not done testing so will only refer us the the untreated fire rated values they publish which are alot less than the shear values required. Stainless anchors appear to have better performance values.

Wondering if anyone has dealt with as similar issue or can point me in the right direction to find a solution.



If fire is a concern for design, I doubt you will have much luck using post installed adhesive anchors. They are VERY sensitive to temperature during installation and in service. The adhesive/epoxy tends to melt or creep and the load capacity drops very quickly. I am not an expert on intumescent paint, but I would guess that it would simply prevent direct contact with a flame or fire but probably not insulate it sufficiently from heating the adhesive to a dangerous temperature. You may want to look into UL rated assemblies to see if they include any sort of post installed anchors and what those assemblies are rated for. If the anchor suppliers are not willing to stick their neck out, I certainly would not stick my neck out on this.


For anything that requires stringent fire protection or presents a life safety problem-to-be-solved in the event of a fire, I would RUN away from chem anchors.

Even if you can prevent flame damage to the parts, you cannot prevent every part of the system from getting hot (including the concrete) and anything getting hot will fail the anchors quickly.

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