## How does RISA calculate a Distributed load?

## How does RISA calculate a Distributed load?

(OP)

I have mainly been in Land Development, but due to the economy I am trying to diversify and learn RISA 3D. I was trying to verify a result from RISA 3D. I just applied a load of 0.06 kips/ft to a beam 20 feet long with pinned connections. Per my 98 second edition LRFD Steel Design Manual, I had calculated that the moment(M) should be:

M=(wl^2)/8. So I would get M=(0.06 kips/ft*(20ft)^2)/8, which should equal -3 ft kip.

However, RISA calculates a value that is close, but not close enough for me. It calculates the Moment to equal -1.392 ft kip.

Can someone explain to me how it is calculating this value?

M=(wl^2)/8. So I would get M=(0.06 kips/ft*(20ft)^2)/8, which should equal -3 ft kip.

However, RISA calculates a value that is close, but not close enough for me. It calculates the Moment to equal -1.392 ft kip.

Can someone explain to me how it is calculating this value?

## RE: How does RISA calculate a Distributed load?

I would recommend either sending your model into RISA tech support, or posting here on this forum.

## RE: How does RISA calculate a Distributed load?

## RE: How does RISA calculate a Distributed load?

Mike McCann

MMC Engineering

http://mmcengineering.tripod.com

## RE: How does RISA calculate a Distributed load?

In this sort of situation, the total difference between positive and negative moment should equal WL^2/8. In your case the w is actually 0.0701 k/ft (that includes the applied self weight of the beam). So, we're looking for the total moment to be 3.505 k-ft

RISA gives 2.126 k-ft at the column support and 1.378 at mid-span. = 3.504 k-ft total. That should be within a reasonable round-off error.

## RE: How does RISA calculate a Distributed load?