# Determining a zero force member visually

## Main Question or Discussion Point

Hello,

When given a truss structure, how does one tell visually just by looking at the structure which members are zero force members?

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PhanthomJay
Homework Helper
Gold Member
From Wiki:

• "If only two members meet in an unloaded joint, both are zero-force members.

• If three members meet in an unloaded joint of which two are in a direct line with one another, then the third member is a zero-force member.

• If two members meet in a loaded joint and the line of action of the load coincides with one of the members, the other member is a zero-force member."

An unloaded joint is a joint where no external forces are applied , or a joint where there is no external reaction force.

A loaded joint is a joint where external forces are applied , or a joint where there is an external reaction force.

nvn
Homework Helper

So that means if you have 4 members at a joint, then none of the members can be zero force members? I am looking at a homework problem and this is the case where 4 members meet and yet one or more of the members is a zero force member. I thought it was only 3 members meeting

AlephZero