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

5. SEISMIC BEHAVIOUR OF RC COLUMNS EMBEDDING STEEL PROFILES
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M = V ⋅ d
( 5.43 )
Rd , j, b j, b s
It is assumed that bond failure occurs in the outer elements when the sum of the
forces is equal to the bond strength of a set of main reinforcing bars.
Tcb + Ttb = Tbf
( 5.44 )
The bond failure strength should be calculated as follows:
T = f ⋅φ ⋅ d
( 5.45 )
bf bd b s
The design value of the ultimate bond stress fbd for ribbed bars may be taken as:
where:
η1
2
2/ 3
0.7 ⋅0.3 ⋅ fck
fbd = 2.25⋅η1 ⋅η2 ⋅ fctd
= 2.25⋅η1 ⋅η2 ⋅ ( 5.46 )
γ
is a coefficient related to the quality of the bond condition and the
position of the bar during concreting:
1,0 when good conditions are obtained;
0,7 for all other cases and for bars in structural elements built
with slip-forms, unless it can be shown that good bond
conditions exist;
is a coefficient related to the bar diameter φ equal to:
1.0 for φ 32 mm
(132 - φ)/100 for φ > 32 mm
Where not otherwise indicated in Eurocode 8, for frame systems the beam-to-
column joints are required to have an increased moment resistance Mjoint,Rd in order
to enhance the ductile capacity of the columns avoiding, in this way, the local
formation of plastic hinges. Provided that, at the design stage, the plastic hinge
formation in the beams is envisaged, it is necessary in any case to take into
account the increase in the beam moment values in order to derive the design joint
forces. Focusing the attention on the behaviour of an internal beam-to-column joint
belonging to a frame free to deform in plane and subjected both to gravitational
c