huangyhg

grp structural desige code and fos
can someone please help me with recommendation for design code for structural grp.
we have a grp post ( cantilevered column, 1.0m height) subject to working load of 80kg (horizontal point load at the top end)
we have carried out a number of destruction tests and they break at 90kg to 120 kg. (different samples fail at different load)
is this sufficient? what should be the factor of safety? what is the governing international code to support the requirement for the fos?
thank you
funnyam
your approach is simplistic and i don't think a design code can cover such design without knowing exact composition of the grp.
as far as i am aware one can analyse a grp section using the exact number of glassfibre filament strands embedded in the defined resin cross section. the structural properties of glassfibre and polyester/epoxy resins are well known and hence the bending resistance of a grp post, assumed to have been manufactured by carefully controlled materials, can be established accurately
i have seen grp pipe designers play around with the number of filament layers and resin thickness, sometimes with ribs, to achieve an economic design. it is a specialised area but the principle is no different from reinforced concrete design except the resin binder in this case has both compressive and tensile strength (concrete's tensile strength is ignored in the reinforcement design). the fibreglass is the equivalent to rebar and the resin is the equivalent concrete.
so it should be possible to prove theoretically the design of your grp post. generally one can add more glassfibre to improve strength untill the amount of resin becomes inadequate to bond all the fibres fully.
in pipe products awwa controlls the grp load carrying capacity by deflection generally around 5% maximum. a safety factor of 1.5 is used for bending.
i am not familiar with any grp code but here goes.
to be consistent with limit state design you should do enough tests (at least 30)to establish that your samples has a normal distribution of failure. once you know statistically that the distribution is normal you can determine the level that 95% of samples would exceed.say f1
fave -(1.645 std dev)f1 should be divided by a partial safety factor to allow for the care in manufacturing, local weaknesses and the criticality of failure.
a live load factor of say 1.5 on your load must give a total less than your calculated f1/fos.
it is therefore evident that this approach would indicate your member needs to be stronger.

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