camber requirements

huangyhg

camber requirements
i wanted to find out minimum span required for 'beam" and "truss" when camber must be provided.
will appreciate a response.
camber in beams and trusses are usually specified according to load and deflection criteria. while there is no minimum, per say, the camber in shorter spans will be less than for longer spans (but in proportion).
as an example:
a beam (or truss) 36' long with a deflection criteria of say l/360, would have camber of 1". while a beam (or truss) 4.5' long with the same deflection criteria would have a camber of 1/8".
beams shorter than 25 feet are typically not cambered because they may not fit in the fabricator's machine and also it is not economical or practical to provide such a small camber.
camber is usually provided to minimize total deflection due to applied loads accordingly it depends on span, cross section moment of inertia and dead load. so, theoretically you calculate the deflection occur due to dead load only and provide camber with approx. same value.
practically, camber is not appreciated by most fabricators since it is expensive, time consuming process and the end result accuarcy is rarely close to your calculation specially when the camber is very small (less than an inch).