Support Reactions: Identifying Moments & Forces

[princejan7]

I have trouble identifying what moments and forces are due to a support

http://postimg.org/image/a2xux5qjx/

Can someone explain the moments and forces (and their directions) due to the support in this picture?
http://postimg.org/image/kto0b0ft3/

Why isn't there a MAx and Ax due to the bearing in this problem?http://postimg.org/image/b5va9kq45/
Or for this one, why doesn't the support at B prevent rotation about any of the axii's?

 

[Simon Bridge]

I. Start by locating the pivot, then use your intuition to guide you about which way things will try to move if not supported. i.e. if the cord DE did not exist, the plate would rotate about pivot B.

It helps to sketch the plate with nothing else, then draw arrows for all the linear forces and their points of action.
Resolve the forces into components through the center of mass and perpendicular to that line.

II. If they were there - what would their magnitudes be?

III. Support B is a hinge - it is designed to allow rotation.

 

[princejan7]

It helps to sketch the plate with nothing else, then draw arrows for all the linear forces and their points of action.
Resolve the forces into components through the center of mass and perpendicular to that line.

So, for example, when considering the reactions due to the thrust bearing, should I imagine the plate without the rope and the friction-less bar AC?

I. Start by locating the pivot, then use your intuition to guide you about which way things will try to move if not supported. i.e. if the cord DE did not exist, the plate would rotate about pivot B.

I'm still not sure about the F2,M2,Fx and M1x reactions
Could you explain the reasoning behind them?

 

[Simon Bridge]

1. yes - isolate the component you are analyzing - replace any constraining objects, like bearings, pivots, and so on, by their corresponding linear forces.

I'm getting a "gateway time out" error o those images right now.