Handbook of Civil Engineering Calculations

These results may be combined and expressed verbally thus: If a point is displaced

along a virtual circular arc, its displacement as projected on the u axis equals the displace-

ment angle times the length of the radius as projected on an axis normal to u.

GABLE-FRAME ANALYSIS BY USING

THE MECHANISM METHOD

For the frame in Fig. 3 Ia, assume that plastic hinges form at D and F. Calculate the plas-
tic moment associated with this assumed mode of failure by applying the mechanism
method.

Calculation Procedure:

1. Indicate the frame configuration following a virtual
   displacement
   During collapse, the frame consists of three rigid bodies: ABD, DF 7 and GF. To evaluate
   the external and internal work performed during a virtual displacement, it is necessary to
   locate the instantaneous center of rotation of each body.
   In Fig. 33 indicate by dash lines the configuration of the frame following a virtual dis-

FIGURE 33. Virtual displacement of frame.