Accounting for residual deformation and simple approaches to their mitigation

Recent developments in performance-based seismic design and assessment approaches have emphasised the importance of properly assessing and limiting the residual (permanent) deformations, typically sustained by a structure after a seismic event, even when designed according to current code provisions. Recent investigations have led to a proposed Direct Displacement-Based Design (DDBD) approach which includes an explicit consideration of the expected residual deformations accounting for 2-dimensional and MDOF effects. Having estimated the possible residual deformations in a structure, it remains to implement specific design features to reduce them to an acceptable level. Previous studies have identified post-yield stiffness as being critical to residual deformation behaviour, therefore a series of simple approaches are proposed to increase this element and system parameter. These methods do not utilise re-centring post-tensioned technology. First, the effects of changes in material stress-strain behaviour and section design in the primary seismic-resisting system are considered, and then the design and introduction of a secondary elastic frame to act in parallel with the primary system is demonstrated. Using moment-curvature and non-linear time-history analyses, the proposed approaches are shown to be effective at achieving their intended goal of residual deformation reduction.