Live load on a slope
Live load on a slope
(OP)
If you have a steep ramp carrying people with a live load of 100psf, does the 100psf apply to the projected length or on the length along the slope? For example, if I have a plank 10ft long and I tilt it at 45 degrees, is the total vertical live load 1000lb or 707lb? Wind loads are clear because they are always normal to the surface.
This may sound like splitting hairs, but it makes a difference for my design. Assume US codes (IBC etc).
This may sound like splitting hairs, but it makes a difference for my design. Assume US codes (IBC etc).






RE: Live load on a slope
RE: Live load on a slope
Definitely projected length. I always reduce load to sloping rafter members, but use the longer slope too in doing so. Gives a much more reliable deflection.
Mike McCann, PE, SE (WA)
RE: Live load on a slope
I am designing a slippery slide.
RE: Live load on a slope
RE: Live load on a slope
Dead load : actual length
RE: Live load on a slope
Am I screwing that up?
RE: Live load on a slope
But I've been wrong before.
RE: Live load on a slope
Faith is taking the first step even when you can't see the whole staircase. -MLK
RE: Live load on a slope
RE: Live load on a slope
1- apply the load on the projected length or surface and continue like regular.
2- you can project the applied load to two loads one is perpendicular to the sloped
length or surface and the second will be parallel to the sloped length and then design
like regular situation. In this case one of the load will act like a friction that we
always have in design of piles. keep in mind in this situation this load creates axial
forces in the member too so the supporting reactions have to be calculated too.
RE: Live load on a slope
RE: Live load on a slope
Mike McCann, PE, SE (WA)
RE: Live load on a slope
This, of course, is true whether you apply it as a verticla force or break it into perpendicular- and along-the-member components.
RE: Live load on a slope
If we ignore dynamic load on the rafter for now there will be no difference when a person standing on
a treadmill or a roof top unit on the rafters.
the treadmill is just a transformer of load to the rafter, like a roof curb for roof top units.
If you solve the problem with the second approach then the friction between the treadmill and the
rafter has to be greater than the sloped force projection along the rafter in order to keep the treadmill in place.