Why does a truss need both a pinned support and a roller support?

The short answer is : to allow for movements usually occur due to thermal contraction and expansion. Stresses occur due to movement being resisted, so if you resist the expansion/ contraction movement, say by pinning the roller support, additional thermal stresses will be induced in the members accordingly.

What is the difference between pinned fixed and roller supports?

Roller supports prevent normal (vertical) translations, but capable of tangential (horizontal) translations and/or rotations. There is a single linear reaction force either upward or downward. Pinned supports are just capable of rotation, and prevent from normal or tangential translations.

Why is one end of a truss structure typically supported on a roller?

Roller supports are commonly located at one end of long bridges. This allows the bridge structure to expand and contract with temperature changes. The expansion forces could fracture the supports at the banks if the bridge structure was “locked” in place. A roller support cannot provide resistance to a lateral forces.

Why one end of beam is placed on the roller?

Explanation: Roller support reaction is normal to the axis of the beam. In case the beam subjected to trust or to avoid temperature stresses in the beam, one end of the beam is placed on roller because it facilitate free horizontal movement of end. It is similar to simple support.

Is a simply supported beam pinned?

Figure: A simply-supported beam. The beam is also pinned at the right-hand support. free to rotate and does not experience any torque. In real life, there is usually a small torque due to friction between the beam and its pin, but if the pin is well-greased, this torque may be ignored.

What is simply support?

Simply supported – a beam supported on the ends which are free to rotate and have no moment resistance. Fixed or Encastre – a beam supported on both ends and restrained from rotation. Over hanging – a simple beam extending beyond its support on one end.