Simply supported beam subjected to a vertical point load
Enter the data to view support-reaction and internal-force influence lines, or shear-force and bending-moment diagrams, for a simply supported beam under a unit point load.
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Current response
Moment influence line
- At the section, x = 8 m
- 4.800 m
- At the load position, z = 7 m
- 4.200 m
\[M_I(z)=\begin{cases}\dfrac{z(L-x_c)}{L},&z\le x_c\\[6pt]\dfrac{x_c(L-z)}{L},&z\ge x_c\end{cases}\]
Method and sign convention
The influence-line ordinate equals the response caused by a moving unit downward load along the beam. Positive shear is the algebraic sum of vertical forces to the left of the section, with upward forces taken as positive. At z = x, the shear influence line has two one-sided values whose difference is exactly 1.
View the formula derivation