huangyhg

ej sacrificial ledge--opinions please
the expansion joint thread reminded me of something. i'd like to see what folks here think of "sacrificial ledges."
i've designed buildings with expansion joints from 2" to about 8". some of these are very difficult to sell to architects, especially where they cross corridors.
i was discussing this with a fellow from another firm a while back and he said something like: "why don't you just use a sacrificial ledge?" i'd never heard of one.
say i need a 12" ej, which wouldn't be hard to imagine. the idea would be to keep a 12" gap between the edges of slab except at specific locations such as corridors where there'd be no way to hide the 12" gap by placing it between two partitions.
at corridors, etc., use a very flimsy piece of slab, closing the gap to 2" or whatever. perhaps this could be a very thin piece of composite slab. in a seismic or wind event, this piece of slab might be smashed, but the overall effect on the diaphragms and lfrs would be insignificant.
the first thing that occurred to me was that it might suck to be standing on the sacrificial ledge! would that make one a "sacrificial live load"?
so what say ye? safe? ok idea? just plain stupid? i should lose my pe and se licenses for just asking the question?! lol.
he said his firm used sacrificial ledges very frequently.
does guidance exist for these? i've never heard of it, but then again, i never went looking for it either.
cant say ive ever done this before, but it does make sense.
strength design and serviceability are two separate service levels.
it is a form of risk based seismic design i suppose.
you would need to make this clear to the client that this is what will happen in a semi-extreme event.
you need to put sufficient reinforcement in it to tie it back to the structure and make sure it doesnt fall onto people below.
you still need to allow for enough movement so that the sacrificial ledge wont need replacing every year.

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