# [static equilibrium] pin and link support type

1. Oct 10, 2011

### kougou

Hello every one

I am confused between two support type:

On the textbook, it says, the pin prevents the object from translating vertically and horzontally, therefore, it provides fx and fy reaction forces.

but another type of support is much identical to the pin, which is the link support, the photo is here: http://imageshack.us/f/105/pinconnectiontw4.jpg/

at point A, the beam AB is subjected to the pin support, so it has two components of reaction forces, namely fx and fy

but what about at point G, how come it only provides one force components, namely fx, but not fy as well? is the point G also classified as pin support?
i am very confused; instructor said that whenever u see a pin support, there's two force components; how come this is not a case here?

2. Oct 10, 2011

### kougou

Re: [engineer need help] to understand support type of static equlibrium

is the link support the beam which connects from GB, and pin support the node at G and A?

3. Oct 10, 2011

### hotvette

Re: [engineer need help] to understand support type of static equlibrium

G is a pinned support as well as A. The reason there is reaction in x only at G is because member GB can support axial loads only.

4. Oct 10, 2011

### PhanthomJay

Yes, point G is a pin support. In general, there are 2 force components at a pin, in the x and y direction, but in some cases, such as joint G, there is only one. This is due to equilibrium considerations for so called '2-force' members. A 2-force member is a member subjected to a force (applied or a reaction force) at each end with no forces applied in between. All members of a truss are 2 force members when loads are applied at the joints only. Member BG is a 2-force member. As such, it can only take axial loading in tension or compression along its longitudinal axis. Thus , the reaction at G must be entirely horizontal; otherwise, the resultant reaction force could not be directed along the BG axis.

EDIT: I notice you are posting the same question in the ME sub-forum. You should stick to that forum and communicate further with the responder if you have additional questions.

Last edited: Oct 10, 2011
5. Oct 10, 2011

### kougou

apologize, this is my first time to use this forum... . I will never do that again.