Calculating Reaction Forces in a Beam - Moment About Point B

[feedingjax]

I am calculating the all reaction forces in this beam.
However, I want to ask:
By taking moment about point B, why does the moment of the UDL become 15*7*5.5 instead of 15*7*4.5

Thanks !

 

[SteamKing]

I am calculating the all reaction forces in this beam.
However, I want to ask:
By taking moment about point B, why does the moment of the UDL become 15*7*5.5 instead of 15*7*4.5

Thanks !

It's not clear where the 4.5 is measured from in the second expression.

The UDL is a constant 15 kN/m applied over a distance of 7 meters in total, therefore, the center of this load is 3.5 meters from either the LHS or the RHS of the UDL.
By taking point B as the moment reference, the moment of the UDL becomes 15 kN/m * 7 meters * (2 + 3.5) meters, where 2 + 3.5 = 5.5 meters is the distance from point B to the center of the UDL.

 

[PhanthomJay]

When determining the moment of a distributed load about a point, you may find the moment by replacing the distributed load with a resultant concentrated load acting at the cg of the load distribution. Where is the cg of that load located along its 7 foot length?