Joints - The Behaviour and Design of Steel Structures to EC3 - page 405

9.4.2.4 Rotation capacity
When rigid plastic analysis is used in the design of a frame (Section 8.5.3.7),
each plastic hinge location must have sufficient rotation capacity to ensure that
theplasticmomentcanbemaintaineduntilthecollapsemechanismisdeveloped.
Clause6.4ofEC3-1-8[1]providesmethodsofdeterminingwhetherjointsbetween
I-section members have sufficient rotation capacity.
9.4.2.5 Joint classification
Thebehaviourofastructureisinfluencedasmuchbythebehaviourofitsjointsas
bythebehaviourofitsindividualmembers.Flexuralframesarethereforeanalysed
asbeingsimple,semi-continuous,orcontinuous(Section8.3.1),dependingonthe
resistance and stiffness classifications of their joints.
Clause 5.2.3 of EC3-1-8 [1] classifies joints according to strength as being
nominallypinned, ofpartialstrength, oroffullstrength.Ajointmaybeclassified
asfullstrengthifitsdesignmomentresistanceisnotlessthanthatoftheconnected
members. A joint may be classified as nominally pinned if its design moment
resistance is not greater than 0.25 times that required for a full strength joint,
provided it has sufficient rotation capacity. Ajoint which cannot be classified as
either nominally pinned or full strength is classified as partial strength.
Clause 5.2.2 of EC3-1-8 classifies joints according to stiffness as being nomi-
nallypinned,semi-rigid,orrigid.Ajointinaframethatisbracedagainstsignificant
sway may be classified as rigid if S j ≥ 8 EI b / L b where EI b is the flexural rigidity
of the beam connected and L b is its length. A joint may be classified as nom-
inally pinned if S j ≤ 0.5 EI b / L b . A joint which cannot be classified as either
nominally pinned or rigid is classified as semi-rigid.
9.4.3 Force and moment joints
Joints which are required to transfer both force and moment may be analysed
elasticallybyusingthemethodofsuperposition,asshowninSection9.9.Thus,the
individualboltforcesintheeccentricallyloadedin-planeplateconnectionsshown
in Figure 9.7 can be determined as the vector sum of the components caused by a
concentric force Q and a moment Qe . Similarly, the individual connector forces
in a joint loaded out of its plane as shown in Figure 9.11b may be determined
from the sum of the forces due to the out-of-plane force N x and the principal axis
moments M y and M z in which the centre of compression is used to determine the
connector lever arms.
Theconnectorforcesinjointssubjectedtocombinedloadingsmaybeanalysed
elastically by using superposition to combine the separate effects of in-plane and
out-of-plane loading.
The following section provides simplified descriptions of the response of
common joints.