Structure Analysis I Lecture 14 Influence Line for

Structure Analysis I

Lecture 14 Influence Line for Statically Determinate Structure Ch. 6 in text book

Influence lines • Influence lines provide a systematic procedure of how force in a given part of structure varies as the applied loads moves along the structure

Procedure for Analysis • Place a unit load at various locations, x along the member, and at each location use static to determine the value of the function ( Reaction, Shear, Moment) at the specified point. • If the IL for a vertical force reaction at a point on a beam is to be constructed, consider the reaction to be positive at the point when it acts upward on the beam • If a shear or moment IL is to be drawn for a point, take the shear or moment at the point as +ve according to the same sign convention used for drawing shear and moment diagram.

• All statically determinate beams will have IL that consist of straight line segments. After some practice one should be able to minimize computations and locate the unit load only at points representing the end points of each line segment

Example 1 Draw the IL for the Reaction at A

IL Equation

Example 2 Draw the IL for the Reaction at B

Example 3 Draw the IL for the Shear at C

Load from A to C Load > C

Example 4 Draw the IL for the Moment at C

Load from A to C Load > C

Group Work 1 Draw the IL for the Shear & Moment at B

Group Work 2 Draw the IL for the Shear & Moment at C

0. 5

Group Work 3 Draw the IL for the Shear & Moment at D