How to Calculate shear force in Simply Supported Beam

 Shear Force is the algebraic sum of all vertical forces acting on either side of the point on the beam. Shear force is to shear off the beam along with the point where it is acting.

                                                            Shear Off Diagram

Here submitting an example of shear force acting on the simply supported beam.

Loading Diagram 

1- Calculate Reactions

we will use Minus (-) Sign for downward forces (Loads) and Positive (+) Signs for Upward Forces (Reactions or Supports)

Taking Moment at Reaction "A"

+RAx0 - (1200x60)-(3000x20)-(4000x47)+(RBx60)

-(72000)-(60000)-(188000)+RBx60

RB =  320000/60 =  5333.333 Lbs

We know that (RA+RB) = Total Load

RA+RB =  (3000+4000)+(1200x60)

RA+RB =  79000 Lbs_________Eq.1

Putting value of RB in Eq.1

RA+(5333.333) =  79000 Lbs_________Eq.1

RA = 73666.667  Lbs

Now Calculating Shear forces at different points

Shear force at point "a" due to reaction A = +73666.667 Lbs

Shear force at point "b" = 73666.667-(1200x20)-(3000) 

SF due to UDL              =73666.667-(24000)= +49666.667 Lbs

SF due to Point Load   =49666.667-(3000)= +46666.667 Lbs     

Shear force at point "c" = +46666.667-(1200x27)-(4000)

SF due to UDL               =+46666.667-(1200x27)=  +14266.667 Lbs

SF due to Point Load     =+14266.667-(4000)       = +10266.667 Lbs

Shear force at point "d" = +10266.667-(1200x13)+(5333.333)

SF due to UDL               = +10266.667-(1200x13) = - 5333.333

SF due to Reaction RB  =  -5333.333+5333.333  =0

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