There is a lot of good information already provided by other contributors. My added information has to do with the common occurrence of "increased loads" in private residences and apartments that I have witnessed. These increased loads are due to storing books and equipment in living rooms and bedrooms. Sometimes, what I see in actual residences look more like a Library (Reading room LL=60 psf) or storage facility (Light LL=125 psf).
My general sense is that the older 30 psf and 40 psf code-prescribed loads should probably be increased by designers, architects, and engineers to take into account the likelihood of such increased loads which may happen sometime in the next few decades, long after the designer is no longer in the picture.
As for fish tanks, one never really knows when and where such tanks will be positioned, short term or long term (creep effects, etc.). So, here's one more uncertainty that may lead us to increase the design live load.
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Franz Rad Ph.D., P.E., F.ASCE
Portland State Univ
Portland OR
(503) 725-4205
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Original Message:
Sent: 02-03-2019 12:51
From: Gary Osborne
Subject: What is a typical allowance for live loads on residential floors?
You might want to also consider that the IRC floor loads do not include direct consideration of long-term creep. In my experience, with older wood-framed floor systems, heavy loads such as tanks will cause noticeable deflection over time. Therefore the flooring under the tanks probably should be reinforced.
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Gary Osborne M.ASCE
Principal Engineer
Foundation Doctor, Inc.
Highland Village TX
(972) 318-8800
Original Message:
Sent: 02-01-2019 11:12
From: Peter Mc Conaughy
Subject: What is a typical allowance for live loads on residential floors?
Several previous responses have correctly identified the 30 psf Live Load for sleeping rooms above the main entry level, but the question is more complicated because the fish tanks do not qualify as live load. This "water" loading is not transient, but rather continuously applied for a long duration of time, more like a dead load. (This same discussion applies more frequently to water beds in an upstairs bedroom). Wood as a structural material handles short-term loads much more efficiently than sustained loading, and experiences significant creep over time as it permanently yields away from continuously applied loads. This characteristic is accounted for in the National Design Specification For Wood Construction (NDS) which adjusts the allowable bending strength downward by a Load Duration Factor Cd=0.9 for load combinations including only dead loads, as opposed to 1.0 for live load combinations. In other words, a live load allowance of 30 psf is equivalent to a continuously applied "water" load of .9 x 30 = 27 psf. And if the water loading does not fully displace ALL the live load (as in the case of a waterbed that may or may not have people in it) you still need to allow for that loading as well. In my experience, most of the turn of the century row homes in Baltimore and Washington do not meet the required 30 psf second floor loading, often calculating in at around 15 - 22 psf. But on the plus side, your friend's fish tanks are likely against the walls, and (hopefully) near the bearing ends of the floor framing where the bending stresses will be minimal, rather than out in the middle of the span like most waterbeds.
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Peter Mc Conaughy P.E., M.ASCE
Structural Engineer
MCCON ENGINEERING INC
KINGSVILLE MD
(410)5939535
Original Message:
Sent: 01-31-2019 12:22
From: Rodolfo Perez
Subject: What is a typical allowance for live loads on residential floors?
A friend has multiple fishtanks in a room on the second floor of his home, a residence built during the 1950's (wood floor over joists) in the Washington, D.C. suburbs. I can calculate the additional live load (psi) that these aquariums impose over the floor system but I need a quick reference to check this load against the typical live load allowances for this type of house. I appreciate advice on what live load values/references we could use to assess the safety of this situation because I have not worked on residential floor systems for years. Thanks!
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Rodolfo Pérez P.E., M.ASCE
Independent Consultant
Silver Spring MD
(301) 5024024
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