# Reaction at the pinned support

1. Jan 11, 2017

### fonseh

1. The problem statement, all variables and given/known data
The modulus of elasticity of each member is E = 20kN/(mm^2) and the cross section of each member is 1000(mm^2) , except member EB and EC is 40(mm^2) , determine :
a) The vertical displacement at joint C
b) The horizontal dispalcemnet at joint C

at A , it's a pinned support , so there must be 2 reactions , right ?

2. Relevant equations

3. The attempt at a solution
Why the author showed one reaction( horizontal reaction) only ? Is it wrong ?

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2. Jan 12, 2017

### haruspex

Suppose there is a vertical reaction. What do the force and moment sums tell you?

3. Jan 12, 2017

### fonseh

what do you mean ? Can you please explain further?

4. Jan 12, 2017

### haruspex

You can determine the horizontal force at A easily. Take moments about D. What do you deduce about the vertical reaction at A?

5. Jan 12, 2017

### fonseh

what do you mean ? Can you please explain further?

6. Jan 12, 2017

### fonseh

what do you mean ? Can you please explain further?

7. Jan 12, 2017

### fonseh

what do you mean ? Can you please explain further?

8. Jan 12, 2017

### fonseh

The vertical reaction at A create clockwise moment about D

9. Jan 12, 2017

### haruspex

Yes, but write the equations. First, find the horizontal force at A. Then take moments about D to find the vertical force.

10. Jan 12, 2017

### fonseh

HA = 20kN to the left . moment about D = VA(2) -20(1) = 0 , VA = 10kN(upwards) , is it correct ?

11. Jan 12, 2017

### haruspex

The equation must include moments due to all the forces, including those at B.

12. Jan 12, 2017

### fonseh

moment about D = -20(1) +VA(2) -20(1)+20(2) = 0 , Thus VA = 0 ?

13. Jan 12, 2017

Right.