AC is a T-joint: because there is no outside force acting on joint C and members CD and BC are collinear, then the non-collinear member (AC) is a zero force member. To express this mathematically, draw a free-body diagram of a joint with three forces coming out of it in the shape of a capital T. The collinear ones must balance each other out. But there is nothing to balance out the non-collinear member, thereby defaulting it to 0. (This would not be true if there was any other load acting on the joint!!) Since there is no force in AC, there is no force acting on the A joint in the y-direction (notice: the support reaction is a roller that acts in the negative x-direction, if it was say a pin for example, the solution would change). Therefore, there is no need to compensate for a y-component in the AB member, defaulting it to 0. Zero force members are intended for stability, support if load conditions change over time, bracing of tensile members, aesthetics, etc.
You could do that, however it is not necessary because you have enough information to start at joint D without the support reactions and the question does not ask for the support reactions. Those types of questions were asked in an earlier chapter of this textbook (rigid body equilibrium) and are used later on in the topic of frames and machines.
Yes, AC is only zero by default if: - 2 collinear & 1 non-collinear members are connected at a joint (T joint) - AND there is no force or support reaction acting on the joint (outside of the three members) If there were a 300 lb force acting on joint C in the diagram, you would have to make a free body diagram and solve by writing 2 force equations in the x and y directions.
Since there is no force in AC, there is no force acting on the A joint in the y-direction (notice: the support reaction is a roller that acts in the negative x-direction, if it was say a pin for example, the solution would change). Therefore, there is no need to compensate for a y-component in the AB member, defaulting it to 0. Zero force members are intended for stability, support if load conditions change over time, bracing of tensile members, aesthetics, etc.
Can you explain more in depth as to why members AC and AB are considered zero force members?
after 1 year still he didn't answer it he is kind of .....
AC is a T-joint: because there is no outside force acting on joint C and members CD and BC are collinear, then the non-collinear member (AC) is a zero force member. To express this mathematically, draw a free-body diagram of a joint with three forces coming out of it in the shape of a capital T. The collinear ones must balance each other out. But there is nothing to balance out the non-collinear member, thereby defaulting it to 0. (This would not be true if there was any other load acting on the joint!!)
Since there is no force in AC, there is no force acting on the A joint in the y-direction (notice: the support reaction is a roller that acts in the negative x-direction, if it was say a pin for example, the solution would change). Therefore, there is no need to compensate for a y-component in the AB member, defaulting it to 0.
Zero force members are intended for stability, support if load conditions change over time, bracing of tensile members, aesthetics, etc.
@@mohamedarab6187 2 Years now
@@dominicnikon6276 5 years now
@@jadrianrodriguez2156 6 years now
Why there is no horizintal force on B?
how about working out the reaction forces at A and B
You could do that, however it is not necessary because you have enough information to start at joint D without the support reactions and the question does not ask for the support reactions.
Those types of questions were asked in an earlier chapter of this textbook (rigid body equilibrium) and are used later on in the topic of frames and machines.
Great
what if you were to move the force of 300 lb from joint D to joint C? Would that change anything in the solution?
Yes, AC is only zero by default if:
- 2 collinear & 1 non-collinear members are connected at a joint (T joint)
- AND there is no force or support reaction acting on the joint (outside of the three members)
If there were a 300 lb force acting on joint C in the diagram, you would have to make a free body diagram and solve by writing 2 force equations in the x and y directions.
@@lentil68 ur so nice, answering everyone's questions :)
Thank u
@@lentil68 thank you so much for this!
The angle you used is incorrect
Why AB is zero force member??
Since there is no force in AC, there is no force acting on the A joint in the y-direction (notice: the support reaction is a roller that acts in the negative x-direction, if it was say a pin for example, the solution would change). Therefore, there is no need to compensate for a y-component in the AB member, defaulting it to 0.
Zero force members are intended for stability, support if load conditions change over time, bracing of tensile members, aesthetics, etc.
how did he come up with the 500 pounds?...
300lb/sin36.9°