Final answer:
The importance factor in wind load design is applied to ensure structures can withstand extreme wind events that might occur over a specified mean recurrence interval, which is not provided in the question. The importance factor relates to the level of risk and reliability required by the structure during its lifetime.
Step-by-step explanation:
The importance factor in engineering, particularly with regards to wind load design, is used to ensure that structures can withstand extreme wind events that may occur over a specified mean recurrence interval. The importance factor of 1.15 is applied to account for the increased reliability required for buildings that may be subject to higher-than-normal risk levels due to windstorms.
While the specific mean recurrence interval associated with an importance factor of 1.15 isn't provided in the question, it typically corresponds to extreme wind events that buildings need to be designed to withstand. This statistical measure is used to estimate the probable intervals or return periods of windstorms of a certain intensity, influencing building codes and design practices.
For example, let's say a wind turbine is built with an energy return on energy invested (EROEI) of 20:1 over a 40-year lifetime. It means that two years’ worth of the energy it produces is required for its construction and installation, leaving the other 38 years of operation as net energy gain.