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

5. SEISMIC BEHAVIOUR OF RC COLUMNS EMBEDDING STEEL PROFILES
The analytical values obtained from the previous equations well agree with the true
joint shear resistances obtained from the experimental tests in the case that, an
increase in the shear resistance of the steel web panel (when subjected to high
cyclic strains) is allowed. Hence, in equation 5.18, the factor 1/√3 is substituted by
a value equal to unity:
240
f ym, d , cw
Vj , wps = 0,7 ⋅ ⋅min( Av ; tcw ⋅ ds ) + ∆ Vj
, swp
( 5.74 )
1
Note that, in this phase, the single mechanism resistance evaluated by means
of the analytical model, does not take into account the partial safety factor value
equal to 1,3 as prescribed by the Capacity Design Principle. Furthermore, the
resistance values are determined considering the real material strengths obtained
from specific tests conducted on concrete and steel samples. In fact, it is intended
to make a direct comparison to establish the precision of the proposed analytical
equations. Of course, at the design stage, it is necessary to account for all the
relevant safety factors as already foreseen in the equations previously presented.
By means of these modifications it was possible to calibrate the proposed
analytical formulas: a substantial increase in the accuracy of the predicted joint
shear resistance compared with that obtained from the experimental results. The
difference between the analytical and experimental results has been modified from
a 20% to a 5% of error, as reported in the Table.
5.8 Conclusions
This part of the Ph.D. thesis has been written with the intent of underlining the
importance of the studies conducted on Innovative Beam-to-Column Composite
Joints in order to provide the reinforced concrete structures of the necessary
amount of ductility in those critical zones usually strongly affected by the
occurrence of seismic events. The general recommendation is to reinforce some
strategic points of the building, as the joints of the 1 st storey, allowing in this
manner to save the structure from a global collapse due to localised brittle type of
failures. Both the solutions studied, with long and short steel profile encased in the
concrete column, as expected, revealed to be effective in order to greatly improve
the performance of the concrete members in terms of strength and ductility at large
deformations. In fact, it can be stated that also the short steel profile stump is able
to guarantee an adequate amount of resistance and ductility at the joint critical