Seismic Response of Green Roofs

Green roofs consist of vegetation with a light-weight substrate planted over a drainage layer and waterproof membrane. The green roof retains rainwater in the plants and substrate and releases the water through evapotranspiration and some surface drainage. This research explored the green roof's ability to resist seismic forces and the potential for the green roof to be used as an energy dissipater to reduce the response of the building to lateral dynamic loading, such as wind loading. Shake table tests showed the substrate layer was capable of resisting most seismic events and with the addition of plants it became resistant to all but the most severe earthquake events. Varying the moisture conditions showed that up until the substrate started responding to excitations as a liquid, the additional water was beneficial to the survivability of the substrate layer. The mixing and sloshing of free water within the drainage layer will provide additional damping to a structure. Laboratory-scale dynamic tests proved the concept of using free water within the drainage layer as a source of additional damping and enabled quantification of the damping effects. Numerical simulations demonstrated that significant additional damping could be achieved in full-scale buildings susceptible to excessive wind-induced vibrations.