pedestrian bridge natural frequency

huangyhg

pedestrian bridge natural frequency
analytical solutions only exist for a few simple structures. failing that you'll get in the right ball-park for the first vertical bending mode by calculating the vertical stiffness at mid span, and using a mass equal to half the bridge's mass, in the sdof frequency equation. this could give errors as large as 200% quite easily, but usually works.
these days you are probably better off using an fe model, which are occasionally quite accurate.
cheers
greg locock
rcheli (visitor)19 sep 01 16:13
check out a publication from aisc engineering journal, an article written by thomas m. murray, phd, from virginia tech.  i believe it was circa 1991.  dr. murray's expertise is in floor vibrations subject to human occupancy.  if you can't find the publication, he can be reached at the civil engineering dept. at virginia tech, blacksurg, va.  i'm sure he can provide the appropriate technical guidance to you.
if of constant section you can find formula (and example, i think to re  
the simple formula for natural frequency is
    f = 16/sqrt(d)
where f = frequency in hertz
      d = maximum self-weight deflection (at 1.0 g)
if you want the frequency for lateral vibration, then simply analyse the structure for gravity in a different direction.
cheers
rhk
russell keays