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bolts in fire tower

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Gary,
 
Were these bolts expansion, embedded, thru, or epoxy?
 
Most applications where we use these bolts are in static loading, or the occasional dynamic loading (wind, seismic). But rappelling would exert a mixture of tension and shear forces in a very dynamic manner. During the course of a year who knows how many times a firefighter, loaded up with equipment, has gone down the cable, stopping and starting, exposing those bolts to lots of dynamic cycles. It doesn't surprise me at all to find that after some time the masonry has started to crack, as it is still a relatively brittle material and I am sure the forces exerted on the bolt and wall result in some tensile force in the masonry. I could see this repeated dynamic loading also loosening up the bolt some, as it bears against the sides of the bolt holes crushing the grout/CMU or causing cracks.
 
I would suggest simply overengineering a fix. If the cells on the parapet are not all filled solid, I would grout them all. Then I think I would do a sandwich plate type connection with plates on each side of the CMU and (2) or (4) 5/8" diameter thru-bolts. Now the tension force is spread out into the back plate into a compressive force, and the bolts are in bearing/shear. A U-bolt could be welded to the face of the plate for them to connect to. The thru bolts should be nice and snug and use lock washers or tack welded in place, to prevent movement or slippage that could result in increased movement and local crushing at the holes.
 
My dos pesos....
 
Andrew Kester, PE
Longwood, FL