Fourth power and floor chipboard/joists

[Ben47]

Just learned ( ? ) that floor deflection increases with the fourth power of length. If you have beams that are BB wide and on them rests floor board with CC width (center to center on the beams), how significant (small, larger, none, ...) can the BB width be for the deflection of the floor board? (The extreme case could be that the floor board rests on beams with a 1 mm spacing ;-). :-D ) (The board does not just rest in the middle of the beams.)

 

[Lennart12]

Hello, usually you always count on c/c between the joists and set it as the length. But yes theoretically it has some impact, but then it would probably require that there is flooring on both sides of the joist that loads the edges equally, otherwise the joist will get an uneven load and then the load will creep towards the center joist since the joist is usually not very torsionally rigid.

But as an example, if you have a 45-rule on c/c 600 mm with flooring that lies on the edge of the rule instead of the center, the difference in deflection should be L1^4/L2^4=600^4/(600-45)^4=1.37, so 37% greater deflection with a span of 600 mm than 555 mm.