When making truss influence lines, note that:
(1) When the load acts on the upper and lower strings, the influence lines are different;
(2) The equations affecting the column are the same as the internal force of the truss (node method, section method), and the isolator is also the same;
(3) When using the node method, pay attention to whether the load acts on the node;
(4) When using the cross section method, note that the left and right influence line equations are different;
(5) The influence lines between nodes change according to a straight line law. The line of influence between the nodes changes according to a straight line.
When making truss influence lines, it is necessary to distinguish between upper and lower chord bearing. The distinction between upper and lower chord bearing is mainly to determine the interval of load, because under normal circumstances the members of the upper chord and the lower chord are not aligned, and the truss member influences. Lines often make a transition at the node of a chord. Therefore, only the interval where the load is applied (upper chord bearing or lower chord bearing) can obtain the influence line of the truss.