Shear Force Due to Bending HW question

[patpiesek]

Homework Statement

My prof gave us this take home quiz to complete to prepare for our actual quiz. We are studying Shear force due to bending of beams (2nd year mech eng). In this question he told us that the shear force (V) can be applied at any of the points and that we would need to find the shear force due to bending (Tau). I am having the hardest time just even starting out, I need some direction on how the problem would change depending on which force point is chosen. Note: only one force will be present, either at A,B,C,D,or E.

this is the cross section given:
http://img714.imageshack.us/img714/4721/mechimage.th.png

Homework Equations

Tau= VQ / Ib

V = max shear force (which u find from the Shear force diagram)
Q = first moment of area
I = second moment of area
b= thickness of cross section

The Attempt at a Solution

 

[chrisk]

Do you mean a force can be applied at the given points rather than a "shear force"? A shear force is a result of applied external forces. If your professor meant to apply a force at a given point then shear force and bending moment diagrams can be generated. Keep in mind with point loads the shear force and bending moment curves are not smooth at the force point. How is the object supported? Knowing the support points will provide the reaction forces for static equilibrium. Also, an applied load can be replaced by an equivalent force-couple system.

 

[patpiesek]

Do you mean a force can be applied at the given points rather than a "shear force"? A shear force is a result of applied external forces. If your professor meant to apply a force at a given point then shear force and bending moment diagrams can be generated. Keep in mind with point loads the shear force and bending moment curves are not smooth at the force point. How is the object supported? Knowing the support points will provide the reaction forces for static equilibrium. Also, an applied load can be replaced by an equivalent force-couple system.

From what the teacher let us know, he would either apply a force onto the beam and then have us calculate the shear force with an SFD, as you said, which in my opinion would be easy. OR, he would apply a shear force on the cross section in one of the points; A,B,C,D or E and then we would have to work from there. I have been looking at the problem more and My real problem is understanding how to deal with the shear force at basically any point other than A. How would the equation change depending on the points? I am aware of a moment and a shear force being applied if the shear force is at D for example. How would I go about dealing with something like this??

 

[chrisk]

View this website. It may help you understand how to approach the problem.

http://emweb.unl.edu/negahban/em325/13-shear-stress-in-beams/shear stress in beams.htm