A portal frame consists of a beam resting over two columns. The junction of the beam and the column behaves like a rigid joint. In general , there are two types of portal frame namely:
- Sway frame
- Non – sway frame
Identification of sway and non – sway frame
The following conditions certify that a frame is sway and non – sway frame:
- If columns of the frames are symmetrical
- Loading should be symmetrical
- The support of the column should be symmetrical
If any of the conditions is avoided, the given frame is said to be sway frame.
Looking at the fig 1 you will see that all the conditions were met, so in this regard the frame is non – sway
In (fig 2) two conditions were met, the support is not symmetrical. The frame is sway
In (fig. 3) the frame is sway because the column is not symmetrical
How to convert sway frame to non – sway frame regardless of the conditions
Looking at the above structure the frame is sway in nature but it can be converted to non sway by placing a reaction in the direction of the beam
Non sway frame is the most typical form of frame found in practice since sway can cause large moments in structures. Any frame that has lateral load resisted by other structure is considered braced.