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

4. SEISMIC RESPONSE OF PARTIAL-STRENGTH COMPOSITE JOINTS
When analysing the possible structural solutions, it becomes immediately evident
that the use of composite columns and beams, by stiffening the structural elements
and therefore significantly limiting second-order effects, can allow the erection of
buildings of considerable height without the need to use bracings. This advantage,
combined with the introduction of partial strength joints, guarantees the formation
of global dissipative frame mechanisms for seismic loadings, and it avoids
unwanted storey or local mechanisms. If associated to suitable constructional
solutions, such structural types can undoubtedly provide significant advantages in
terms of both economy and performances (Braconi et al., 2003).
Clearly, the choice of such structural systems in current design practice cannot
leave out the preliminary evaluation and mechanical definition of the different
possible connection types and the associated structural details.
The present study illustrates the results of a European research (Ecoleader-ECSC
joint Project) aimed at evaluating the rotational and dissipative capacities of a
particular type of connection between a concrete partially encased column and a
steel-concrete composite beam. The design of the connection, successively
verified on the basis of experimental substructure tests, has been conducted by
extending to the inelastic range the method described in Section 8 of Eurocode 4
(Bursi et al, 2003). From the obtained knowledge on connection and member
response, a numerical model of the prototype structure has been developed to
examine its seismic behaviour through non-linear static (push-over) and dynamic
analyses. Simulated ground motion time histories that match the design response
spectrum were used in the dynamic analyses. This analytical work permitted to
predict the performance of the frame and to propose an appropriate magnitude
level of ground motion for the pseudo-dynamic tests on a full-scale model of a
frame building expressly designed using the connections and structural details
suggested by the results of the analyses.
4.2 The Ecoleader-ECSC joint project
The objective of the Ecoleader-ECSC joint project is to develop an experimental
database on the behaviour of low-rise steel-concrete composite structures with
partial strength semi-rigid connections subjected to gravity and lateral loads. In
particular, information was needed on the behaviour of the beam-to-column joints
and the structural overstrength exhibited by composite frames. Moreover, in order
to evaluate the feasibility and effectiveness of the composite construction with
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