(1)P Moment resisting frames shall be designed so that plastic hinges form in the beams or in the connections of the beams to the columns, but not in the columns, in accordance with 4.4.2.3. This requirement is waived at the base of the frame, at the top level of multi-storey buildings and for single storey buildings.
(2)P Depending on the location of the dissipative zones, either 6.5.2(4)P or 6.5.2(5)P applies.
(3) The required hinge formation pattern should be achieved by conforming to 4.4.2.3, 6.6.2, 6.6.3 and 6.6.4.
6.6.2 Beams
(1) Beams should be verified as having sufficient resistance against lateral and lateral torsional buckling in accordance with EN 1993, assuming the formation of a
--`,`,,,`,``,,,```````,,`,,`,,-`-`,,`,,`,`,,`---
plastic hinge at one end of the beam. The beam end that should be considered is the most stressed end in the seismic design situation.
(2) For plastic hinges in the beams it should be verified that the full plastic moment of resistance and rotation capacity are not decreased by compression and shear forces.
To this end, for sections belonging to cross-sectional classes 1 and 2, the following inequalities should be verified at the location where the formation of hinges is expected:
0 , 1
Rd pl,
Ed ≤ M
M (6.2)
15 , 0
Rd pl,
Ed ≤ N
N (6.3)
5 , 0
Rd pl,
Ed ≤ V
V (6.4)
where
M Ed, G Ed,
Ed V V
V = + ; (6.5)
NEd is the design axial force;
MEd is the design bending moment;
VEd is the design shear;
Npl, Rd , Mpl, Rd , Vpl, Rd are design resistances in accordance with EN 1993;
VEd,G is the design value of the shear force due to the non seismic actions;
VEd,M is the design value of the shear force due to the application of the plastic moments Mpl,Rd,A and Mpl,Rd,B with opposite signs at the end sections A and B of the beam.
NOTE VEd,M = (Mpl,Rd,A+Mpl,Rd,B)/L is the most unfavourable condition, corresponding to a beam with span L and dissipative zones at both ends.
(3) For sections belonging to cross-sectional class 3, expressions (6.2) to (6.5) should be checked replacing Npl, Rd, Mpl, Rd, Vpl, Rd with Nel, Rd, Mel, Rd, Vel, Rd.
(4) If the condition in expression (6.3) is not verified, the requirement specified in (2) of this subclause is deemed to be satisfied if the provisions of EN 1993-1-1:2004, 6.2.9.1 are satisfied.
6.6.3 Columns
(1)P The columns shall be verified in compression considering the most unfavourable combination of the axial force and bending moments. In the checks, NEd, MEd, VEd
should be computed as:
E Ed, ov G
Ed, Ed
E Ed, ov G
Ed, Ed
E Ed, ov G
Ed, Ed
1 , 1
1 , 1
1 , 1
V V
V
M M
M
N N
N
Ω γ
Ω γ
Ω γ +
=
+
=
+
=
(6.6)
where
NEd,G (MEd,G, VEd,G) are the compression force (respectively the bending moment and shear force) in the column due to the non-seismic actions included in the combination of actions for the seismic design situation;
NEd,E (MEd,E, VEd,E) are the compression force (respectively the bending moment and shear force) in the column due to the design seismic action;
γov is the overstrength factor (see 6.1.3(2) and 6.2(3))
Ω is the minimum value of Ωi = Mpl,Rd,i/MEd,i of all beams in which dissipative zones are located; MEd,i is the design value of the bending moment in beam i in the seismic design situation and Mpl,Rd,i.is the corresponding plastic moment.
(2) In columns where plastic hinges form as stated in 6.6.1(1)P, the verification should take into account that in these plastic hinges the acting moment is equal to Mpl,Rd. (3) The resistance verification of the columns should be made in accordance with EN 1993-1-1:2004, Section 6.
(4) The column shear force VEd resulting from the structural analysis should satisfy the following expression :
5 , 0
Rd pl,
Ed ≤ V
V (6.7)
(5) The transfer of the forces from the beams to the columns should conform to the design rules given in EN 1993-1-1:2004, Section 6.
(6) The shear resistance of framed web panels of beam/column connections (see Figure 6.10) should satisfy the following expression:
0 , 1
Rd wp,
Ed
wp, ≤
V
V (6.8)
where
Vwp,Ed is the design shear force in the web panel due to the action effects, taking into account the plastic resistance of the adjacent dissipative zones in beams or connections;
Vwp,Rd is the shear resistance of the web panel in accordance with EN 1993- 1-8:2004, 6.2.4.1. It is not required to take into account the effect of the stresses of the axial force and bending moment on the plastic resistance in shear.
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Figure 6.10: Web panel framed by flanges and stiffeners
(7) The shear buckling resistance of the web panels should also be checked to ensure that it conforms to EN 1993-1-5:2004, Section 5:
Vwp,Ed < Vwb,Rd (6.9)
where
Vwb,Rd is the shear buckling resistance of the web panel.
6.6.4 Beam to column connections
(1) If the structure is designed to dissipate energy in the beams, the connections of the beams to the columns should be designed for the required degree of overstrength (see 6.5.5) taking into account the moment of resistance Mpl,Rd and the shear force (VEd,G
+ VEd,M) evaluated in 6.6.2.
(2) Dissipative semi-rigid and/or partial strength connections are permitted, provided that all of the following requirements are verified:
a) the connections have a rotation capacity consistent with the global deformations;
b) members framing into the connections are demonstrated to be stable at the ultimate limit state (ULS);
c) the effect of connection deformation on global drift is taken into account using non- linear static (pushover) global analysis or non-linear time history analysis.
(3) The connection design should be such that the rotation capacity of the plastic hinge region θp is not less than 35 mrad for structures of ductility class DCH and 25 mrad for structures of ductility class DCM with q > 2. The rotation θp is defined as
θp = δ / 0,5L (6.10)
where (see Figure 6.11):
δ is the beam deflection at midspan ; L is the beam span
The rotation capacity of the plastic hinge region θp should be ensured under cyclic loading without degradation of strength and stiffness greater than 20%. This requirement is valid independently of the intended location of the dissipative zones.
Figure 6.11: Beam deflection for the calculation of θp.
(4) In experiments made to assess θp the column web panel shear resistance should conform to expression (6.8) and the column web panel shear deformation should not contribute for more than 30% of the plastic rotation capability θp.
(5) The column elastic deformation should not be included in the evaluation of θp. (6) When partial strength connections are used, the column capacity design should be derived from the plastic capacity of the connections.