Attention should be paid to the truss influence line:
(1) when the load is applied to the upper and lower strings, the influence line is different;
(2) the linear equation is the same as the internal force of the truss (node method and section method), and the isolator is the same;
(3) when using the node method, pay attention to whether the load ACTS on the node;
(4) when using section method, it is important to note that the equation of the left and right affects the equation;
(5) the influence line between nodes changes according to the linear rule. The internode influence line changes according to the linear law.
Make truss influence line, to distinguish between wind load and lower chord load, to distinguish the bottom chord on bearing primarily to determine the range of load, because normally bent bar and the bottom chord bar is not aligned, and the influence of the truss bar line often turn in a chord node position. Therefore, the influence line of the truss can only be obtained by determining the range of the load, which is carried by the upper chord or the lower chord.