ADDITIONAL ECCENTRICITY AND BUILDING IMPORTANCE FACTOR IN EXISTING BUILDINGS

In accordance with Earthquake Code Chapter 7 Article 7.4.8, additional eccentricity shall not be applied in assessment and retrofit projects of existing buildings. When the option "This project is an existing building assessment and/or retrofit project" is checked on the project general settings/performance page, the program automatically disables the 5% additional eccentricity option.

Earthquake Code Chapter 7 Article 7.4.2 states: "In the definition of seismic action, the elastic (unreduced) acceleration spectrum given in Section 2.4 shall be used; however, modifications made to this spectrum according to Section 7.8 for different exceedance probabilities shall be taken into account. The Building Importance Factor defined in Section 2.4.2 shall not be applied in the seismic analysis (I = 1.0)." Therefore, when the option "This project is an existing building assessment and/or retrofit project" is checked on the project general settings/performance page, the program automatically sets the building importance factor to 1.0 and does not accept any change.

In addition, for Section 7.8, different earthquake hazard levels can be selected on the project general settings/performance page: the earthquake with a 2% probability of exceedance in 50 years, the earthquake with a 10% probability of exceedance in 50 years, and the earthquake with a 50% probability of exceedance in 50 years. The analysis performed for the earthquake with a 2% probability of exceedance in 50 years yields the same result as using I = 1.5 or Ao = 0.6 for a first-degree seismic zone.