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

4. SEISMIC RESPONSE OF PARTIAL-STRENGTH COMPOSITE JOINTS
4.8 Cyclic tests of full-scale composite joint subassemblages
This Section presents results obtained from tests carried on three full-scale
composite beam-to-column joint subassemblages, which were replicas of parts of
the two-storey prototype structure. One monotonic test and one test in cyclic
regime both on an interior (CJ-INT) and an exterior (CJ-EXT) joint were conducted.
The steelwork connection consists of an extended end plate welded to the beam
end and bolted to the column flange. As illustrated in Figure 4.16 and Figure 4.17,
all the specimens had steel deck supported concrete slab acting compositely with
the beam and partially encased steel-concrete composite columns. Moment–
rotation curves obtained from the tests are compared with those predicted by an
analytical model. Plastic analysis based on the theoretical developments of the
previous sections is used to develop the analytical model for the prediction of
moment capacity. A rotational spring model for the composite beam, as proposed
in revised Annex J of EC4, combined with a translational spring model for the steel
web panel, is used to assess the strength and the stiffness of the composite joints.
The model tends to over-predict the behaviour of the joint. To better understand
the transfer mechanism activated in the composite beam and in the web panel
numerical finite element (FE) analyses were carried out by means of the ABAQUS
code. The FE model was calibrated and the stress and strain state of the
aforementioned connections was simulated in the monotonic displacement regime.
4.8.1 Test set-up and procedure
The basic set-up included a test frame and a loading system (Figure 4.18). The
test frame was designed to be sufficiently stiff to minimize the lateral movement of
the system. The lower hinges were fastened directly to the test floor. The horizontal
displacement-controlled load was applied by a hydraulic jack at the upper end of
the composite column. The jack was mounted on the pedestal and was connected
to the column through a load cell. The height of the columns of the test specimens,
measured from the point of load application to the center of the hinge, was 3500
mm, which was the storey height of the prototype structure. This selection was
made by assuming that the points of contra-flexure occurred at the midheight of the
adjacent stories.
In order to characterize the behaviour of the specimens under hysteretic loading a
predefined representative displacement history was applied. The procedure follows
the ECCS recommendation n° 45 (1986), as illustrated in Chapter 2. The
instrumentation of the specimens was designed to determine the applied loads, to
127