PRACTICAL 2ND-ORDER INELASTIC ANALYSIS OF SEMIRIGID FRAMES

The stability behavior of rigid and semirigid frames bent in the weak axis is investigated using a hardening plastic hinge method. The stabi lity limit load of frames is usually overpredicted by the simple plast ic hinge analysis neglecting the effect of partial plastification. The plastic zone analysis can predict the limit load more accurately but a large number of elements must be used. Hence, it is costly and time- consuming. An alternative method called the ''hardening plastic hinge method'' is developed here for practical use. In the proposed method, one element is used per beam-column. The initial yield surface includi ng residual stress is first determined from the normalized moment-curv ature-thrust relationship of W8 x 31 section. The member stiffness is then modified to simulate the effect of partial plastification through the concept of work-hardening in which the average degradation of tan gent stiffness of a cross section is calibrated against the slopes of the exact moment-curvature-thrust relationship. The stability limit lo ads of planar steel frames predicted by this and several other methods are compared. The results predicted by the hardening-hinge method are found close to that of the plastic-zone method and experimental resul ts.