Classification according to stiffness for Hong Kong Code

Joints are classified according to joint stiffness to:

• Rigid – joints with insignificant change of original angles between members,
• Semirigid – joints which are assumed to have the capacity to furnish a dependable and known degree of flexural restraint,
• Pinned – joints which do not develop bending moments.

Joints are classified according to the EN 1993-1-8 – Cl. 5.2.2.

• Rigid – \( \frac{S_{j,ini} L_b}{E I_b} \ge k_b \)
• Semirigid – \( 0.5 < \frac{S_{j,ini} L_b}{E I_b} < k_b \)
• Pinned – \( \frac{S_{j,ini} L_b}{E I_b} \le 0.5 \)

where:

• S_j,ini – initial stiffness of the joint; the joint stiffness is assumed linear up to the 2/3 of M_j,Rd
• L_b – theoretical length of the analyzed member; set in member properties
• E – Young's modulus of elasticity
• I_b – moment of inertia of the analyzed member
• k_b = 8 for frames where the bracing system reduces the horizontal displacement by at least 80 %; k_b = 25 for other frames, provided that in every storey K_b/K_c ≥ 0.1. The value of k_b = 25 is used unless the user sets "braced system" in Code setup.
• M_j,Rd – joint design moment resistance
• K_b = I_b / L_b
• K_c = I_c / L_c