Step loads of a human on a structure

[jaggmi]

We have a requirement to provide a 4 foot long cantilevered structure that must withstand a 250 lb person stepping on it, mid span (2 feet)to reach into the machine. If not for this requirement the beam would only support its own weight which would be about 50 lb. We will need to make it much stiffer but have very limited space so we can not do an over kill add a lot of section just to play it safe.

If a person raised one foot onto the beam and raised his full weight by loading the beam with that foot, what load would you use to design the beam? After he steps off the beam must still function. The beam is supporting an optical device that is at a set focus. A few thousands of an inch set would be ok but total operating distance is only +/- 1 MM (~+/-.040&quot.

 

[flamby]

250 lb human may be unpredictable at times and may opt to 'hop' instead of placing his foot gently onto the structure. I would design it for at least 325lb "point load". Would like to increase it more if chances of jumping are real.

In fact even gently put foot will also exert impact due to stoppage of inertial force of the human. So you got to consider full load + impact.

 

[exchange]

I would use 250x1.3(Impact)x1.5(unknown of the prob). Also, I suggest a welded connection to ensure no sudden movement.
Tubular member sounds like the way to go.