Seismic design of hybrid rocking timber frames: An energy-based perspective

Protecting buildings against earthquakes increasingly means controlling damage rather than merely preventing collapse. Systems that pair self-centering with replaceable energy-dissipating devices pursue exactly this goal, and hybrid rocking timber frames are a particularly compelling case: built from lightweight engineered timber, they concentrate the earthquake’s inelastic response in a few replaceable devices, while the timber frame itself is meant to remain essentially undamaged. Designing them, however, exposes a mismatch with current practice. Force-based procedures do not represent energy dissipation explicitly, and displacement-based procedures target a peak deformation rather than the energy accumulation that ultimately drives damage, leaving the designer without direct control over how that damage distributes through the structure. This paper develops an energy-based design (EBD) framework for multi-storey timber buildings with hybrid rocking systems. Instead of a single global target, the method apportions the seismic energy demand storey by storey, so that cumulative damage is spread more evenly over the height rather than concentrating at a few critical levels. The framework is demonstrated on a multi-storey glulam frame, designed in parallel by the proposed EBD approach and by conventional direct displacement-based design (DDBD), in both bare and hybrid rocking configurations. Nonlinear time-history analyses compare the designs in terms of inter-storey drift, the location and severity of damage, and the distribution of inelastic demand along the height. The results show that the hybrid rocking configuration markedly limits deformation demand and channels the inelastic response into replaceable elements, and that the energy-based formulation delivers a more uniform height-wise damage distribution than its displacement-based counterpart, clarifying what each design philosophy does, and does not, control.