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RE: Unit weight of precast roof plank from 1960

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Title: RE: Unit weight of precast roof plank from 1960

I have a 1944 copyrighted Welded Wire Fabric Manual that describes typical concrete plank as "made from a combination of lightweight aggregate mixed with a foam compound to produce an aerated concrete which is nailable and can be cut in the field."  A newer catalog (1990) for 2" nailable concrete plank gives the weight as 12 psf.

I think the key question regarding your deck is is it nailable?  It can't be very dense and nailable.

Ed Marshall, PE

-----Original Message-----
From:   mark swingle [SMTP:mswingle(--nospam--at)]
Sent:   Friday, June 02, 2000 4:44 PM
To:     seaint(--nospam--at)
Subject:        Unit weight of precast roof plank from 1960

We are investigating an existing building in Massachusetts, built in 1959 and 1964, to which an addition is currently being attached.  It is a one-story building which framing consists of open-web joists at 4' oc supported by steel beams and columns on spread and strip footings.  Exterior walls are CMU infill.

The existing drawings call out <3" PRECAST ROOF PLANK> spanning the 4 ft between joists.  Does anyone know the unit weight of this material?  Breyer's 3rd edition lists <concrete plank> at 6.5 psf per inch, which is 78 pcf.  Regular-weight concrete is 145 pcf.

Is Breyer correct?  Is this the same thing?  In other words, was light-weight concrete in use for roof planks in 1959 and 1964?

By the way, if I use 145 pcf, some of the existing joists and beams are overstressed, which seems unlikely.

Any history lessons from you old-timers will be greatly appreciated.


Mark Swingle, PE, SE