Page 6 - KS_materijal za vezbe_2015

Introduction to the RC building example. Modeling and analysis of the design example.
P. Fajfar and M. Kreslin

six modes would be sufficient to satisfy the requirements in EN 1998-1/4.3.3.3(3) (the sum of the
effective modal masses amounts to at least 90% of the total mass).

Table 2.5.1 The elastic periods (T), the effective masses and the effective mass moments (M eff )

T M eff,UX M eff,UY M eff,MZ
Mode
(s) (%) (%) (%)
1 0.92 80.2 0.0 0.2
2 0.68 0.0 76.3 0.0
3 0.51 0.2 0.0 75.2
4 0.22 15.0 0.0 0.2
5 0.15 0.0 18.5 0.0
6 0.12 0.2 0.0 17.6
6 M eff = 95.7 94.7 93.1

Figure 2.5.1 Three fundamental modes of vibration

2.5.3 ACCIDENTAL TORSIONAL EFFECTS

The torsional effects were considered by means of the torsional moments (M Xi and M Yi ) about the
vertical axis according to EN 1998-1/4.3.3.3.3. They are determined as a product of the horizontal
forces in each horizontal direction (F Xi and F Yi ) and the corresponding accidental eccentricity (e Xi and
e Yi ). The horizontal forces are obtained by the Lateral force method of analysis (see section 2.6.3).
Accidental eccentricities are equal to 5% of the floor-dimensions (L Xi and L Yi , see Figure 2.1.1).
Torsional moments as well as horizontal forces and accidental eccentricity are shown in Table 2.5.2.
Only torsional moments above level 0 were considered in the analysis.

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