Blog Archives

How to Draw Shear Diagrams

Shear diagrams are an easy way to visualize shear values along a beam or member and also reveal the maximum positive and negative shear values.

The first step will always be to simplify any and all load distributions into point loads and to solve for all exterior reactions.

Begin the shear diagram by drawing a horizontal line, this is the line for zero shear. I like to draw my shear diagrams directly below the actual member so that they line up and I designate my shear diagrams with a big V.

The beam is 20ft long divided into 5 foot sections.

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How to Solve for Reactions

The first step in many problems is solving for reactions, here is an example of some situations that you may encounter.

Simplify the distributed load into a point load:

Since this distribution is constant the load is applied at the midpoint, 2.5 ft to the left of B. (If the distributed load was not linear the point load should be applied at wherever the "center of mass" of the distributed load is; the center of mass of a constant distributed load is the midpoint). Click here to continue reading

Zero-Force Members

Zero force members are members in a truss/frame that theoretically have no force in them. Being able to identify these members swiftly will aid you on the PE Exam and in life in general (possibly).

There are two rules to look for when identifying zero-force members.

  1. Joints with three members where two of the members are parallel, and there is no external load. The third member will be zero-force.

  2. Joins with two members and no external load. Both members are zero force.
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Method of Joints

When analyzing a joint you will solve for the forces in all of the members connected to it.

Lets start with H, draw the two unknown forces and in tension (away from H). Click here to continue reading