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

5. SEISMIC BEHAVIOUR OF RC COLUMNS EMBEDDING STEEL PROFILES
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Design case: LOW DUCTILITY Design case: MEDIUM DUCTILITY
Total base shear force = 8716 kN Total base shear force = 3353 kN
Floor
level
Fx
(kN)
Fy
(kN)
Floor
level
Fx
(kN)
Fy
(kN)
1 477.0 477.0 1 180.0 180.0
2 933.0 933.0 2 359.0 359.0
3 1399.0 1399.0 3 539.0 539.0
4 1866.0 1866.0 4 718.0 718.0
5 2332.0 2332.0 5 897.0 897.0
Roof 1722.0 1722.0 Roof 633.0 633.0
Table 5.2. Lateral seismic forces obtained for the two ductility design cases
5.3.3 3D frame modelling
After a rough estimation of the geometry of all the structural elements by simplified
drafts and schematic diagrams, a simulation of the building behaviour was
implemented applying both vertical and horizontal forces to a 3D model drawn by
the finite element program SAP2000 (see Figure 5.6).
The contribution of a single masonry in-fill was taken into account by an equivalent
compression diagonal model endowed the following stiffness:
K
w
2
cos
0.6 w E ⋅ w⋅ t ⋅ θ
= ( 5.8 )
d
in which the value 0.6 accounts for the presence of openings, doors, etc. Two
different models have been considered:
• the first one (see Figure 5.6a) in which the structure was modelled with the
masonry in-fill present on each floor of the building (Structure I);
• the second one (see Figure 5.6b) in which the structure was modelled without
the masonry infill on the first floor. This case, named Pilotis Case (Structure II),
was considered with the purpose of maximizing the design action on the base
columns and of incrementing the second order effects (inter-storey drift
sensitivity). ). In fact, this model implements the aforementioned Soft Storey
situation.
From these analyses it was found that the most adverse conditions applied to three
representative base columns of the building labelled as n° 260, n° 302 and n° 309
(as indicated in Figure 5.4); we also paid particular attention to how the masonry