How to determine whether a beam is determinate or indeterminate

In this construction video tutorial, you will come to know about definition of determinate and indeterminate beam as well as the criterion for verifying whether a beam is determinate or indeterminate.

It should be noted that a beam is called determinate beam if equilibrium equations are used to completely analyze that beam. Given below, the details of equilibrium equations :-

∑Fx= 0 (some of the forces in x direction should be zero)
∑Fy= 0 (some of the forces in y direction should be zero)
∑Ma= 0 (some of the forces at point a should be zero)

A beam is called indeterminate beam when it is not possible to analyze it completely by applying only equilibrium equations.

The following formulas are applied to define whether a beam is determinate or indeterminate :-

If R = 3n, the beam will be defined as Determinate beam

If R is greater then 3n, then the beam will defined as indeterminate beam
If R is less then 3n, beam will be defined as Not stable

Here,

R denotes number of unknown reactions.
n denotes number of beam segments
and 3 belongs to equilibrium equations

To get more details, watch the following video tutorial presented by S.L. Khan.