Timber vertical additions for improving seismic resilience of existing buildings

This PhD research investigates the seismic behaviour of existing reinforced concrete (RC) buildings subjected to timber vertical additions (VAs), with a focus on Cross-Laminated Timber (CLT) and Light Timber Frame (LTF) systems. The study addresses the growing need for sustainable urban densification strategies while ensuring seismic safety in aging building stocks. Vertical extensions are typically considered critical interventions in seismic regions due to the increase in mass and the modification of structural properties. However, this research demonstrates that timber VAs, when properly designed, can induce beneficial dynamic interactions with the host structure, potentially reducing seismic demand rather than amplifying it. The work combines nonlinear finite element modelling, seismic fragility analysis, simplified analytical approaches, and design optimization techniques. A case study-based fragility analysis shows that CLT vertical additions do not necessarily worsen seismic performance and may reduce the probability of exceeding severe damage states. A simplified equivalent two-degree-of-freedom (2-DOF) model is developed to predict the period shift and variations in seismic demand, providing an efficient and practical tool for preliminary design assessments. A key contribution of the research is the development of a comprehensive optimization framework for LTF vertical additions, demonstrating that properly tuned configurations can achieve reductions in interstorey drift of up to 20%, while maintaining robustness against record-to-record variability.