Multihazard Performance and Design of Ecoroofs

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The proliferation of "green roofs" or more generally, ecoroofs in the United States has increased dramatically in the last ten years and has radically expanded the historical function of a roof. Ecoroofs offer new opportunities to provide environmental, economical, and social benefits. However, ecoroofs carry higher gravity loads and must support long-duration transient fluid loading compared to traditional systems. This shift in roof design demands has outpaced building codes and regulations, and more importantly exceeded our fundamental understanding of roof structural behaviors under these nontraditional loads. Regrettably, conventionally engineered roofs account for a disproportionately large number of structural failures with over $1 billion in damages since 1990 for a single insurer. Proper design of ecoroofs to ensure structural safety and serviceability of these relatively "sensitive" structural components requires research to address these three critical questions: 1.Under earthquake induced roof shaking, does the ecoroof planting material mobilize? To what degree is the ecoroof planting material coupled to the structure? Can roof dead load imbalances be expected after an earthquake?2.During rain events, what are the load effects produced on ecoroofs and over what time-scales? How loads are distributed in ecoroofs and will traditional design approaches ensure ponding stability and prevent overloading? 3.What are the engineering properties of typical ecoroof planting materials? Which properties are most critical to achieving ecoroof performance during seismic and rain events?This project is the first to examine the structural, geotechnical, and planting interactions on ecoroof seismic performance. The research focuses on system response to demonstrate the important interactions of the design elements. An ecoroof structural simulator will be developed to test full-scale laboratory ecoroof prototypes and will be integrated with field survey and component laboratory data to produce new knowledge on fluid-structure interaction at the roof including: planting material mobility during lateral shaking, water retention and drainage characteristics, and long-term service performance. These will provide background material for development of a structural guide for ecoroof designs in seismic zones.