A symmetric frame

    
(a)                                                                                                                 (b)
Fig. 12-7: A symmetric frame subjected to an asymmetric load

Fig. 12-7 shows a simple symmetric plastic frame unloaded (a) and carrying an asymmetrically concentrated load positioned close to the right hand column (b). It can be observed that the horizontal member deflects vertically and the loaded frame moves to the left. Note that the movement is to the left for the load placed to the right of the centre line of the frame. If the vertical load was a harmonic dynamic load and its frequency matched the natural frequency of the frame in its horizontal direction, resonance with significant horizontal movements of the frame would occur.