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

4. SEISMIC RESPONSE OF PARTIAL-STRENGTH COMPOSITE JOINTS
University of Pisa acts as responsible of the design and execution of the 3D tests
in the framework of the ECSC project 7210-PR-250 “Applicability of composite
structures to sway frames”, coordinated by RWTH, Aachen, while University of
Trento is the coordinator of a Ecoleader-Jrc project for access to the ELSA
infrastructure entitled “Cyclic and PsD testing of a 3D steel-concrete composite
frame”.
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 uniformly distributed gravity dead load at both floors, wD, was taken equal to
4.68 kPa, including the weight of the floor slab-steel deck assembly (3.18 kPa) and
an additional dead load of 1.5 kPa (mechanical equipments, finishes, etc.). The
weight of the beams and columns must be added to these values: IPE300 beams =
0.42 kN/m, IPE240 beams = 0.31 kN/m, HEB260 partially encased columns = 2.33
kN/m, and HEB280 partially encased columns = 2.67 kN/m. A uniformly distributed
imposed live load, wL, of 5.0 kPa was assumed at both levels.
The design seismic loads at each level, Fi, were determined by using the simplified
modal response spectrum analysis method:
108
F = F ⋅
i b
z ⋅ m
i
i i
( z ⋅ m )
i i
( 4.1 )
where Fb is the seismic base shear, and zi and mi are respectively the height from
the base and the masses at each level. The seismic base shear is given by:
F = S ( T ) ⋅W ⋅ λ
( 4.2 )
b d
1
where Sd(T1) is the ordinate of the design spectrum at the fundamental period of
vibration of the building for translational motion in the direction considered, T1, W is
the total weight of the building, and is a corrective 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 for different subsoil
conditions. For this project, the following key parameters were adopted:
• Type 2 spectrum
• Peak ground acceleration, ag = 0.40 g
• Subsoil Class A (Rock site, or alike, with Vs,30 > 800 m/s)
• Behaviour factor, q = 6.0 (Concept a, Structural ductility Class S dissipative
composite structure, with assumed multiplier αu/α1 = 1.2)