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

4. SEISMIC RESPONSE OF PARTIAL-STRENGTH COMPOSITE JOINTS
From the processing of the experimental results it could be observed that the
beam-to-column joints rotated more at the first level. Some remarks can be made:
• at the interior joints the web panels in shear contributed more than the
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connections while on the contrary at the exterior joints the connections rotated
more;
• the joints A1 and A3 (the exterior joints on the exterior instrumented frame)
worked quite in the same way as in the PsD tests.
Although we tested a composite structure the behaviour of all the joints was quite
symmetric. This phenomenon was probably due to the damage induced during the
PsD tests on the concrete slab.
4.11 Conclusions
The objective of this study has been the investigation of the seismic performance
of a realistic size moment resisting frame structure of high ductility class according
to Eurocode 8 (2002) under various levels of earthquake. Dissipative elements
were conceived to be partial strength beam-to-column joints and column base
joints at later stages. Some full-scale substructures, representing the interior and
exterior joints, have been subjected to monotonic and cyclic tests at the Laboratory
for Materials and Structures Testing of the University of Pisa in Italy.
Moreover, a new mechanical model of the partial strength beam-to-column joint
has been described. The model, which still relies on experimental data, is capable
of simulating the behaviour of the steel-concrete composite partial strength joints
subjected to monotonic loading. In detail, the model is capable of defining yielding
and failure evolution of different components. The component models of the slab
have indicated clearly that the compressive strut strength of the composite slab
bearing on the column flange depends on the shear stiffness of the column web
panel. Moreover, the activation of diagonal compressive struts on column sides
induced by transversal reinforcing bars is hindered by the direct bearing of the
compressive strut. Some force-displacement relationships provided by the
proposed mechanical model have been compared with analytical formulae and
current European standards. The principles set forth have then been applied to the
design of beam-to-column joints and columns of a full-scale frame structure that
has been built and subjected to pseudo-dynamic tests at the ELSA Laboratory of
the Joint Research Centre in Ispra. The construction of the full-scale structure
proved that the construction of steel-concrete composite structures with partial
strength beam-to-column joints and partially encased columns is highly efficient.