Force Balances on a Truss

make members under tension red and under compression green

show member forces

center point load (kN)

10

right point load (kN)

15

This Demonstration calculates the forces on the members of a planar truss.

Use the sliders to set the two point loads at the center and the right (forces in negative

y

direction,

F

D

and

F

). Check "show member forces" to show the truss member forces. Check "make members under tension red and under compression green" to show the red and green arrows.

Arrows that point outward (green) represent the member response to compression forces, and arrows that point inward (red) represent the member response to tension forces. Compression acts to shorten the member and tension acts to lengthen the member.

The black members are zero members; that is, these members are neither in tension nor in compression, so the force is 0 kN. The purpose of zero members is to provide stability and extra support to the structure in the event of another member failing.

When the boxes "make trusses under tension red and under compression green" and "show member forces" are checked, move the mouse over a pivot point to show arrows that represent forces (and the values of the forces) in the

x

and

y

directions at that point. This breaks the forces in the diagonal members into their

x

and

y

components.