Leaderboard

What I have read about drift is that codes (Im talking about ASCE & ACI) intention is to limit all these three states; serviceability, damage, and collapse. Codes distinguish and set criteria only for horizontal component of drift (horizontal racking) whereas in a building vertical component of drift also exists. We have Damage Index to know the extent of damage that's been done. Damage Index takes into account the effect of both horizontal and vertical components of drift like shear strain. This is one of my favourites about drift. See the attachment. Dan Berding Thesis.pdf

Centre of rigidity is a measure of 'torsional susceptibility' of buildings, and is computed by calculating stiffness of vertical members, at a particular floor level, to lateral loads. Hence, in elastic range, it is independent of loading. But loading can change the state of member: can push a member into inelastic region. In in-elastic region, center of rigidity will change continuously because stiffness of some members will diminish, depending on the state of members and their mechanical properties, which will depend on loading condition. In design offices, and as far as building codes is concerned, you, primarily, deal with elastic response, and hence it is independent of loading.