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**To**:**<Aquatic-Plants at actwin_com>****Subject**:**Adding to More Floor Loading for large tanks..****From**:**"Adam Shaw" <adams1 at comcen_com.au>**- Date: Sat, 19 Oct 2002 22:09:24 +1000
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- In-reply-to: <200210181924.g9IJOnvY016149 at mailhub_actwin.com>

Just adding to what Scott.H said about floor loading with timber joists and columns etc - it is well worth noting that the long term strength of timber is reduced and failure stresses are 57% of the short term strength. Thus for long-term loading situations (i.e. a big mother tank), the beams and supporting columns' dimensions stated in the standards need to be well exceeded. The general 'standards' available for residential housing construction are generally determined using average short term random or uniform loading patterns. With a long term stress concentration at one point, structural integrity and serviceability will be an issue if the standards are used. Stresses due to shear can most likely be neglected unless the tank is situated closely to a column, where the tank is not over the column. The beams that the tank sit on will experience a large shear stress if the tank weight is not supported by having columns attached to the beam directly beneath the tank. Stresses due to bending (bending shear) are the concern with larger spans where the tank is not very close to a column (i.e. within say, 200mm). This is the most likely cause of problems. Scott said that bending may be a problem not necessarily structurally, but only with leveling the tank. Wood is a natural fibre and like I said above, long term failure stresses are 57% of the short term strength. This is due to 'unravelling' of the fibres (even in the densest hardwoods). So structural significance may be a larger problem than initially thought - the wood may appear fine, but over a few years the tank will sink more and more as the beam bends more and more, possibly until failure. There is a lot to add to the topic, and there are equations that can be put into use to calculate the size beams, columns etc (My/I, Euler buckling load, etc) but for simplicity I will only say this; if you have a large tank and are at all unsure about the flooring system and the capacity of the floor structure to bear the loads - I strongly recommend that you employ the use of a qualified structural engineer. Adam Shaw

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