There is a range of innovative energy dissipation method available to modify the seismic response of both new and existing structures. Viscous damper and friction brace are two well- known types of energy dissipators that have attracted interests from practitioners and researchers for many years. However, current design methodologies for friction braces rely on the past experimental results that were carried out at a component level, and current viscous damper design frameworks do not specifically consider the flexibility of the damper system and connections. Such design approaches may be considered as unconservative and can cause the devices to behave different than expected under large load reversals. This thesis presents the findings of the research carried out to achieve better understanding in the energy dissipation mechanism of friction braces and viscous dampers, which lead to an improved design frame for structures equipped with friction braces and viscous dampers.

Quasi-static testing of Asymmetrical Friction Connection (AFC) and Symmetrical Friction Connection (SFC) braces was conducted. The braces were tested alone, where an axial load was applied directly to the specimens, as well as within a one storey full scale steel frame. It was found that the friction braces developed stable sliding behaviour with repeatable hysteresis loops. The average effective friction coefficient of 0.18 for the AFC braces and 0.31 for the SFC braces. It was also found that due to bolt slackening and surface degradation, the maximum strength degradation in the AFC and SFC braces was 10% and 15%, respectively. Additionally, frame compatibility actions caused brace bending in-plane with bolt bearing on the slotted hole sides, and prying and p-delta effect caused bracing member to deform out-of- plane. Based on the observed mechanisms of AFC and SFC within a bracing system, a simplified numerical hysteresis model has been developed as a part of this thesis and implemented into OpenSees as a tool to approximate the hysteretic behaviour of a friction connection.

The inherent elastic flexibility of viscous dampers can alter the phasing of damper and structural forces. This thesis also investigates how damper sub-system stiffness affects overall seismic response. By undertaking a suite of analyses with damped single degree-of-freedom systems it is shown that a damper with significant flexibility can experience median peak displacements 40% higher than those of a damper with rigid support, depending on the added damping, damper sub-system stiffness, and period of vibration. To limit the impact of phasing effects, the damper sub-system stiffness should be five to ten times the stiffness of the main lateral load resisting system. A design example has been carried out to present how the damper sub-system to main structure lateral stiffness ratio can be calculated. Additionally, a modified design frame has been proposed as a part of this study to account for damper sub-system stiffness.