Concrete Mechanical Anchors - Exterior Use

[TopKnot]

I am looking at a few exterior deck failures in which ledgers have been inadequately attached to concrete or masonry walls. (These connections were horrible and not worth discussing here.) The wood requirements generally govern anchor spacing (i.e. 2-rows of 5/8" anchors at 16" o.c. or similar). I need to specify a concrete anchor for ledger attachment. I want to specify screw anchors (i.e. Titen HD or HILTI HUS-S). But the ICC literature says they are only approved for interior dry aplications. This seems to be the case on every mechanical anchor I've looked at. Are epoxy anchors the only anchors we can specify for exterior applications?

Another side of this argument is that since there are so many anchors required by the wood ledger, the actual bolt to concrete loads are very small (25% of design load). In my head, I divide by a safety factor of 5 to imagine in the worst case, I load these bolts to about 5% of the load it would likely take to pull them from the wall. Thoughts? Experiences? Anyone seen actual failures by exterior use mechanical anchors? Ever considered using them and specifying a sealant or epoxy just to keep water out of the hole?


Tony Krempin
TopKnot Engineering

 

[a2mfk]

I have used Simpson SET/ET and similar for years for this type of application with no complaints or problems. I don't like expansion bolts in CMU, especially near an edge, I have seen too many problems with spalling.

I have never been a fan of any type of screw bolt into concrete, and this is just a gut thing. It seems like it would be easy to mess up in the field. Tap cons for light loads I am fine with, but when the loading is above a few hundred pounds I go with epoxy.

 

[hokie66]

Exterior anchors need to be hot dipped galvanized, or if in a severe environment, stainless steel. They are available, but not in all types or sizes of mechanical anchors.

 

[TopKnot]

I guess my point was that ICC-ES says that (maybe all) mechanical anchorages are not rated for exterior use. Epoxy anchors only. So, no expansion bolts, wedge anchors, screw anchors, etc for outdoor use. That really surprised me, but I hadn't read that in the literature. No one else I have talked to so far was aware of that either.

It seems like a CYA limitation. Has anyone actually seen a failure of an exterior mechanical anchorage attributed to moisture?

Does anyone know specifically of a mechanical anchor approved by ICC-ES for exterior use?

_________________________
Tony Krempin, PE
TopKnot Engineering

 

[hawkaz]

I don't know the anchorage method, but a slab of cladding fell off a Chicago skyscraper a few years ago. Made a mess out of a car parked below.

I believe this was blamed on corrosion of the anchorage

 

[hokie66]

This may be relevant, but it sounds like the adhesive anchors are under the microscope rather than the mechanical ones. Perhaps you can cite the ICC reference which you are interpreting as prohibiting mechanical anchors.

http://www.icc-es.org/News/Articles/IBC_Anchor_Changes.pdf

 

[anchorengineer]

You can get stainless steel expansion anchors but, like stated earlier, they assume a solidly grouted CMU which frequently have voids. The closest thing to an exterior mechanical anchor is the Hilti HUS-H anchor. It is not approved for "exterior" use but it does have a special coating, tested at 240 hours of salt spray, that makes it better than standard 5 mil zinc plated anchors. Instead of 50 years protection you get something like 30 years. I figure this should be fine for residential decks that are not near the ocean.

Clarke Engineering Services, PC
Jobsite Engineering and Consulting

http://www.anchorengineer.com

 

[alihoop]

All expansion bolts are zinc coated electronically and not hot dip galvanized. Thickness of such coating are in microns and not good enough for exterior use. See them every day on cheap barbecue grilles... etc.

Use Hilti epoxy anchors with SS threaded rods or hot dipped galvanized rods. For CMU block Hilti has special screen caps that get inserted in hole first and then epoxy is extruded through the back side when rod is inserted.

Best of luck.

 

[hokie66]

alihoop,
It is not true that hot dipped galvanized and stainless steel mechanical anchors do not exist. They are not available in all sizes, and may be more difficult to procure in some locations, but they exist.

 

[alihoop]

You are correct in a sence that they do exist, but very very hard to find. Most likely by special order. Specify one and hope that the subcontractor will get it. The problem is by the time you catch the sub placing the wrong type it is too Late. Once they are placed, it is impossible to take them Out.

I was told that due to the gringing nature of their anchorage, There is a good possibility that the galvanizing will get stripped leaving the steel will corrode at the most vonroble pressure point.

They are simply not worth the risk.