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 that 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:
- Sj,ini – initial stiffness of the joint; the joint stiffness is assumed linear up to the 2/3 of Mj,Rd
- Lb – theoretical length of the analyzed member; set in member properties
- E – Young's modulus of elasticity
- Ib – moment of inertia of the analyzed member
- kb = 8 for frames where the bracing system reduces the horizontal displacement by at least 80 %; kb = 25 for other frames, provided that in every storey Kb/Kc ≥ 0.1. The value of kb = 25 is used unless the user sets "braced system" in Code setup.
- Mj,Rd – joint design moment resistance
- Kb = Ib / Lb
- Kc = Ic / Lc