Pedestrian comfort?
Pedestrian comfort?
(OP)
I am designing a platform and I want to use 3/16" floor plate for the decking. The platform will be an I beam structure with the decking welded down. What is a good span for the floor plate for "pedestrian comfort"? I checked a bar grating span chart and it states that there should be less than 1/4" deflection for a uniform load of 100 lbs/sq. ft., for pedestrian comfort. When I check AISC manual for allowable stress design it gives a maximum span between 24 and 30 inches to achieve that deflection. That seems like way too tight of spacing. I am considering using 1/4" plate but the spans are not much better.
I checked some of the calculations and it seems that the chart in the ASD manual assumes that the plate is simply supported on the ends and is only supported in two places, which is not realistic (the plate is supported on four sides).
Does anyone know of a more realistic span for this situation? Possibly a chart.
Thanks,
I checked some of the calculations and it seems that the chart in the ASD manual assumes that the plate is simply supported on the ends and is only supported in two places, which is not realistic (the plate is supported on four sides).
Does anyone know of a more realistic span for this situation? Possibly a chart.
Thanks,






RE: Pedestrian comfort?
Have to buy the grating, but may save a lot on reduced quantity of support framing.
www.SlideRuleEra.net
RE: Pedestrian comfort?
RE: Pedestrian comfort?
For the continuous case (fixed ends), the allowable deflection would be .067" (24/360) for a 24" span and .083" for a 30" span. The actual deflection under 100psf would be .038" at a 24" span and .092" at a 30" span. From this you can see that they're in the ballpark.
RE: Pedestrian comfort?
Swearingen,
The ASD manual assumes a simply supported beam. It gives a deflection of 0.195" at 24" and 0.462" at 30". I get the same results as you when I model the plate as a beam fixed on the ends. I suspect however that the deflection will be even lower than the values you give. The plate is not really a beam in the sense that it is supported on four sides not just two.
RE: Pedestrian comfort?
For comfort I would look at limiting the natural frequency of the floor to something, say, greater than 3Hz or greater than 5Hz, or whatever you prefer or can find out. This is equivalent to limiting deflection to a given maximum depending on the assumptions made in the process. Limiting deflections is probably easier than calculating frequencies on top of everything else you're calculating.
RE: Pedestrian comfort?
RE: Pedestrian comfort?
RE: Pedestrian comfort?
RE: Pedestrian comfort?
If you are using 3/16" plate for 30" spans, then do you use 1/4" plate for just a 33" (2'-9") span? Is that a typo or are you suggesting that for the deflection/comfort issue. I agree that angles used for stiffeners is probably the most economocal way of constructing a platform for industrial purposes. By using differing sizes for longer and shorter spans they will frame into each other nicely too.
My experience with plates and allowable deflections has is that it is hard to predict what people will find acceptable. What's good for one is unacceptable for another.
Regards,
-Mike
RE: Pedestrian comfort?
The idea is to get acceptable levels for everybody.
Use 1/4" PL for <= 2'-6" span and get back to designing those WFs! Leave 3/16 stuff for the step up to the pickup truck.
Going the Big Inch!
http://virtualpipeline.spaces.msn.com
RE: Pedestrian comfort?
There are different requirements for different applications. What is acceptable for a seldom used maintenance platform in a manufacturing facility might not be acceptable in a shopping center.
Mike
RE: Pedestrian comfort?
Going the Big Inch!
http://virtualpipeline.spaces.msn.com
RE: Pedestrian comfort?
3/16" FLPL is our standard design for maintenance platforms. We use 30" spans for that with success. Some customers desire 1/4" FLPL. When we use that we go to 33" spans. I know it doesn't seem like much, but it might get rid of a stiffner or two. I guess the reason for the tighter spacing has to do with the fact that a customer specifying 1/4" FLPL instead of the STD 3/16" is already more aware of the deflection. With the 3/16" FLPL we are allowing L/65 deflection at 100psf. When we use the 1/4" we decrease deflection limits to L/100. I know it probably doesn't make sense, but that is what we do.
RE: Pedestrian comfort?
That makes sense to me. Where I work now we generally have more problems with our platforms bouncing than with deflection of the individual floor plate panels. We don't use 3/16" plate but I think it would have its applications.
Thanks,
-Mike