What is Influence Line Diagram?
It’s a diagram which shows the reactions, Shear force and Bending moment at each and every section or instant at any distance of any span that you want to find out.
In short, Influence Line Diagram shows the influence or effect of loads or reaction on the span.
Importance of Influence Line Diagram:
Since, its very time consuming and tedious to find out the reactions, shear force and bending moment with our regular or conventional method of analysis. But ILD is the quick and simple method to find out these all things as quick as possible and anywhere as you want to find out on the considered span. This method is more helpful in entrance exams where time is most important factor. Because you can easily find out reactions, S.F. & B.M. as quickly as you can for the efficient utilization of your precious time.
As the live loads or impact loads are moving on the spans or structures like highway bridges, moving cranes in industrial buildings, etc will produce different reactions, shears force and bending moment for their different positions. Any structure or structural element shall have to be designed the most severe stress condition that can occur on the structure. Structure designer finds out the load positions that produce maximum stress in the and that can be determined by Influence Line Diagrams.
Basic Formulas with diagrams
I.L.D. for Reactions:
I.L.D. for Shear Force:
I.L.D. for Bending Moment:
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