19th century floor span tests

[acesumper]

Hi, can anyone tell me if there were methods to test floor bounce in the 19th century. Now there's NHBC span tables, but what about in days of old. I've heard of the Span/360 test, but that seems to be for engineering.

 

[foxhole]

19th-century practices often relied on experience and empiricism, rather than rigorous calculations, to manage floor vibrations and sagging

 

[cdbe]

The old rule used to be half the span plus 2.

 

[mrrusty]

What I can tell you is that an otherwise sound floor does get a bit bouncier if you forget to put the herringbone bracing back before the floorboards. Don't ask me how I know...

 

[GhostIntMachine]

OP, why do you need to know? The sort of method given by @cdbe is certainly quoted as a "rule of thumb" calculation in some late 19th Century texts, but another issue is that until the 20th century my understanding is that there were no consistent reliable grading methods for structural timbers (that rule of thumb is predicated on the assumption that your joists will be to a minimum of something equivalent to a modern C16 specification). As an example I worked on one historic building where the 20 x 10in softwood primary beams (which carried the actual joists in a double floor structure) were so weak that the dendro man refused to grade them. It cost the developer well over a £1m in steel flitch plates to make the building meet BC requirements (other remedials to the floors and joist were also required).

There is actually major variation in the structural timbers used in Victorian buildings with anything from really strong pitch pine to relatively weak yellow pine being found as joists in buildings. Other factors which affect floor performance (apart from strutting to reduce bounce) include double or triple flooring skins (where two or more layers of sub-flooring are applied at right angles to each other - sometimes with the first layer laid diagonally to the joists rather than at right angles), the use of lath and plaster ceilings (the lath certainly seems to stiffen the structure, especially if applied green - it shrinks slightly as it dries ending up in tension) and the insertion of stud walls below (Victorians were adept at using "structural" stud walls which aren't always that structural). A Victorian floor with 1-1/8 to 1-1/4in T&G floorboards on top and a lath an plaster ceiling below, with herringbone strutting) can often be a lot stiffer and stronger than you think it would be