Joint classification according to SP

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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 – \( \frac{S_{j,ini} L_b}{E I_b} \le 0.5 \)


  • 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

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