Q: I have a rectangular barge modeled as a line of beams with a uniform load distribution. Why are the structural bending moments and shears not what I get from statics?
REV 7.00

A: The difference is the way the loads are applied. The weight is divided equally among the nodes. The buoyancy forces, however, are "lumped" to the nodes at the ends of the panels. Now, suppose that you have N+1 nodes and a weight (or buoyancy) of L. We have

-L/(N+1) force applied to each node due the weight, and

for each interior nodes

L/N force due to buoyancy.

At the ends, however, you do not get to add the contribution due to a panel on each side. Here you have

L/(2N). Thus you have a net force on each node of

L [ 1/N - 1/(N+1) ] in the interior, and

L [ 1/(2N) - 1/(N+1) ] at the ends. Using your data, this

is

12500 [ 1/100 - 1/51 ] = 120