design load to check lateral stiffness of walkway

huangyhg

design load to check lateral stiffness of walkway
i'm designing a walkway that spans 18 ft with a 100 psf load.  i want to ensure that the walkway is stiff and does not sway too much side to side.  i've seen and walked on too many long span walkways that have significant lateral movement.  although it's structurally safe, the movement makes people nervous.  what load should be applied in the lateral direction to check the stiffness in this direction?  
have you checked wind loading on it?
indoors.  no wind load.  i could apply an arbitrary wind load to it, but there is not that much surface area to apply this to, thus the overall effect will be small.  the walkway is simply two channels or beams with grip strut planks as the walking surface and handrail along the sides.
the steel joist institute has studied floor vibration extensively and developed a proceedure for checking the "bounce" in joist supported floor slabs.  sji technical digest #5 (1988) and aisc/cisc steel design guide 11 (1997) discuss in detail the methods.  while they apply to joist supported floors, you could adapt the method to beam supported floors too.  you can check the sji website for more info.
osha requires that the handrail system resist a 200 pound load anywhere in any direction.  perhaps this could be the basis for a side load.  you might also want to determine the resonant frequency of the assembly and make sure that it is well out of the frequency of normal walking / running.
how about seismic loads? those would induce lateral movements.
what loads do you think will generate lateral movement? perhaps a percentage of the live load. maybe 5%.
the 50#/lineal foot icc code for handrails is probably a more accurate model.  a person swaying might generate that.  i would think a zig zag diagonal tie on the underside should take care of it.
provide a horizontal bracing scheme between your two beams. attach the web   
what kind of main supports do you have?  instability in those   
i always provide lateral supports for the grating that are a minimum of 3/4 the depth of the main   
at the end of the day, you could apply several imaginary loads and still not ensure you've met the requirements that you've specified for yourself.  
if you've noted lateral displacement to be an issue then what you really want to do is limit lateral displacement.  you need a lateral deflection limit, not more load.
i'm sure there are several articles written on the subject as there are deflections limits for beams in flooring as well as limits on vibration characteristics.
another example is that highway bridges with pedestrian traffic are limited to l/1000 in deflection.
look to the codes for examples of where deflection limitations are provided and see how they can be applied in your case.
regards,
qshake
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