Ground Motions and Structures - Earthquake Engineering for Structural Design - page 324

324 Earthquake Engineering for Structural Design

member rotation capacity. This proposal has been given for the steel structures, but similar
classification is proposed also for reinforced concrete elements;
- analyzing the plastic rotation capacity of steel members by using a specialized
computer program DUCTROT M (Petcu and Gioncu, 2003, Gioncu and Mazzolani,
2002). This program is developed on the base of local plastic mechanism methodology
(Fig. 8.26a) and it allows the evaluation of the plastic rotation and the rotational ductility
under static or seismic actions, as a function of cross-section type, geometrical member
dimensions, mechanical properties of steel. Figure 8.26b shows the rotation capacity for a
wide-flange beam, using this methodology.
The rotation capacity reduces due to the influence of seismic cycles when the number
of important cycles exceeds a given value. The program DUCTROT M for seismic actions
considers the superposition of plastic mechanisms for positive and negative moments
(Fig. 8.27a,b), resulting in the moment-rotation curve for cyclic loading. One can see that
this curve is divided in two parts: (i) in the first, the cyclic loads have no influence on the
rotation capacity, because the plastic rotation occurs in the moment-rotation plateau; (ii)
after a number of important cycles, a significant reduction of rotation capacity arises (Fig
.8.27c).
For the ground motion types characterized by short duration and reduced number of
important cycles (for instance, intraplate crustal earthquakes), no reduction of rotation
capacity must be considered. Contrary, for earthquakes with long duration (intraslab
earthquakes) and large number of important cycles, the erosion of rotation capacity can be
dramatic (Fig. 8.27c).

(a)

Figure 8.26 (continues)