The simple alternative (7-15)/(H.8) is sufficiently accurate in most cases, compared to other uncertainties like the effect of stiffness variations within and between members due to cracking etc. It should be observed that variation in the degree of cracking between first and following steps does not have to be considered, if reduced stiffness values according to are used; these values are intended to be valid for the final stage of deformation. However, if values for uncracked section are used in early steps, although cracking might occur in later steps, then more steps have to be included in the analysis, like in expression (7-16); k-values for early steps would otherwise be too low for later steps. This would apply generally when a more refined analysis is used, where gradual cracking is taken into account.

When the structure is analysed for the equivalent horizontal force HEd, the relevant second order effects can be obtained everywhere in the structure.

To magnify all moments with the same factor, as in expression (7-6)/(5.30), would not be correct in for instance a frame or a shear wall with large openings.

5.8.8 Method based on nominal curvature

C5.8.8. Method based on curvature Basic relationships

This method is basically the same as the previously so-called "model column" method in the ENV. The second order moment is expressed in the following way, cf. equation (6-1):

1 I2

As mentioned in 6.5, 1/r is estimated on the basis of reaching yield strain in tensile and compressive reinforcement. Here correction factors Kr and Kw are included:

0 0

Post a comment