Multi-hazard design of low-damage high-rise steel–timber buildings subjected to wind and earthquake loading

This work focuses on the design trade-off aspects related to the structural behavior of tall buildings subjected to the actions of wind and earthquake and on the feasibility of adopting innovative low-damage structural systems and connections combining engineered wood and steel. A multi-hazard approach is developed and proposed, through the use of an efficient equivalent baseline reference to compare the structural performance under two independent whilst competing hazards. Following a capacity-vs-demand approach an Acceleration Displacement Response Spectrum (ADRS) domain, well established in the earthquake engineering environment, is suggested to be extended and adapted to wind design. The innovative procedure is developed and implemented with reference to two case study tall buildings, 18 storey and 36 storey high, respectively. The use of either traditional steel-only connections or innovative low-damage steel-timber hybrid - unbonded post-tensioned rocking-dissipative – connections are employed and compared. Two difference constructions sites are considered: 1) a high seismicity and low wind zone and 2) low seismicity and high wind zone. A Direct Displacement Based Design (DBDD) procedure is firstly implemented to design the structural system targeting the desired level of seismic performance. Then the effects of wind loading are estimated through the analytical procedure provided by the Italian National Research Council (CNR), which allows to calculate wind-induced forces and peak floor accelerations. Peak interstorey drifts are selected as seismic performance indicator, while peak floor accelerations are selected as wind performance indicator with the intent to focus on the building occupants’ comfort serviceability limit state. The predicted structural performances are then numerically validated through time series/history analyses under earthquake and wind loading with a lumped plasticity global model of the case-study buildings. Finally, the structural responses under the two actions are compared within the proposed innovative common baseline ADRS domain, allowing to establish the governing design hazard depending on the intensity levels and adopted return periods. Based on these developments, a true multi-hazard approach is proposed for the preliminary design phase of a building subjected to wind and earthquake loading.