Structural Analysis
A rigid-jointed plane frame is stable and statically determinate if (where m is number of members, r is reaction components and j is number of joints)

(m + r) = 2j
(m + r) = 3j
(m + 3r) = 3j
(3m + r) = 3j

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Structural Analysis
The effective length of lacing is the distance

Between the inner ends of effective lengths of welds connecting the members
0.7 of the distance between the inner end rivets of the bar for double lacing
All of these
Between the inner end rivets of the bar for single lacing

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