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The rotational stiffness is calculated with the component method according to EN 1993-1-8 Article 6.3, considering bolt-rows located above center of compression (See also chapter: "Center of compression"). Bolt-rows used only for shear are not used for stiffness calculation.
Stiffness model for strong-axis bending:
For bolted end-plate connections, the basic components related to each single bolt row, are represented by a single effective stiffness coefficient keff,r as given by EN 1993-1-8 Article 6.3.3.1 (2). These effective stiffness coefficients for each bolt-row are, based on EN 1993-1-8 Article 6.3.3.1 (1), transformed to the equivalent stiffness coefficient keq, to be used finally in the final stiffness formula specified by EN 1993-1-8 Article 6.3.3.1 (4). The leverage arm zeq is given by EN 1993-1-8 Article 6.3.3.1 (3).
The basic formula for calculation of rotational stiffness specified in EN 1993-1-8, Article 6.3.1 (4) is used, independently of the 5% Npl,Rd limit defined by the same article.
The program makes a distinction between three stiffness types:
As specified µ is the stiffness ratio Sj,ini/Sj. Determination of this stiffness ratio is specified by EN 1993-1-8, Article 6.3.1 (6). The value of coefficient ψ is given by Table 6.8.
The moment-rotation diagram is based on the values of Sj,ini and Sj,MRd.
