* Mom and Vort Irr
ao t 1 OZ C3 (H 04 te il OS B.t 1 & 1 1 UIJ a«ID.I a2D.a D^USQ&I-?!]!«.! ID 1.1 12 12 0) lb)
Figure 8. Characteristic curves of pier panel 2.1: (a) positive seismic verse; (b) negative seismic verse.
line, in the non proportional elastic field, where reacting sections are reduced; (iii) a third non linear branch, in the plastic field, related to the ductility of the panel. These curves of the whole level allow to assess the maximum bearable shear force and stop at the displacement in which the weakest panel, belonging to each floor, is at failure. Finally, the equilibrium of the spandrel strips has been checked, with a tolerance of 5% of the maximum acting stress.
In the following, the comparison of the pier walls of level 2 in the four typologies under study is reported.
The panel reaches the failure condition for composed flexural and axial load in both verses of the seismic action for almost all kinds of irregularity (Fig. 8). Only the horizontal irregular wall (and consequently the horizontal and vertical wall) shows a smaller shear value due to the different distribution of the seismic weight.
In this panel the influence of the seismic verse can be easily detected. In the regular and vertical irregular wall, under positive horizontal actions (from left to right) the eccentrical normal load determines the failure. Conversely, the introduction of the horizontal irregularity decreases the height of the pier panel from 2.8 m to 1.8 m, making it stocky and causing a shear failure (Fig. 9.a). As expected, when the considered seismic force has a negative verse (from right to left), the height of the panel stay unchanged and the collapse occurs in all the kinds of walls because of the composed flexural and axial load (Fig. 9.b).
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