Analysis and modelling of the seismic behaviour of high ... - Ingegneria

5. SEISMIC BEHAVIOUR OF RC COLUMNS EMBEDDING STEEL PROFILES
in the design tables, for what concerns the material specific weights. A uniformly
distributed live load of 3.0 kPa was assumed at each storey level (mechanical
equipments, finishes, etc.). Different values of the dead and live loads were
calculated for the roof; in this case the live load is equal to 2.0kPa.
Subsequently, the horizontal seismic forces acting at each storey height according
to Eurocode 8 have been determined; being the structure regular both in plan and
in height (prEN 1998-1, 2001), it is allowed to carry out a simplified planar static
analysis, the so-called Lateral Force Method Analysis. The equivalent horizontal
seismic forces, represented as nodal forces acting at each storey height, have
been determined for the seismic study cases denominated above as A and B. For
the two load combinations we assumed the same peak ground acceleration, i.e.
0.20g, which implies that the construction site belongs to a low seismicity area.
Only the main aspects that are relevant to the seismic resistance of the moment
resisting frames in the direction of loading are summarised herein.
The design seismic loads at each level, Fi, were determined using the simplified
modal response spectrum analysis method:
182
F = F ⋅
i b
z ⋅ m
i
i i
( z ⋅ m )
i i
( 5.4 )
where Fb is the seismic base shear, and zi and mi are respectively the height from
the ground level and the masses at each storey of the building. The seismic base
shear force is given by:
F = S ( T ) ⋅W ⋅ λ
( 5.5 )
b d
1
where Sd(T1) is the ordinate of the design spectrum at the fundamental period of
vibration of the structure for translational motion in the direction considered, T1, W
is the total weight of the building, and is a correction factor. The equations and
the values of the soil parameter, S, and the reference periods TB, TC, and TD that
are required to construct Types 1 and 2 design spectra are given below. For this
project, the following key parameters were adopted:
• Type 1 spectrum;
• Peak ground acceleration, ag = 0.20 g;
• Subsoil Class A (Rock site, or alike, with Vs,30 > 800 m/s);
• Behaviour factor, q = 1.5 for Ductility Class LOW and q = 3.9 for Ductility
Class MEDIUM.
Therefore, S = 1.0 and the reference periods TB, TC, and TD are respectively equal
to 0.15 sec, 0.5 sec, and 2.0 sec. The fundamental period T1 of the structure was