New nonhistorical additions which impose vertical or lateral loads on an existing structure shall not be permitted unless the affected part of the supporting structure is evaluated and strengthened, if necessary, to meet regular code requirements.
Note: For use of archaic materials, see Chapter 8-8.
Strength-level seismic forces used to evaluate the structure for resistance to seismic loads shall be based on the R-values tabulated in the regular code for similar lateral-force-resisting systems including consideration of the structural detailing of the members where such R-values exist. Where such R-values do not exist, an appropriate R-value shall be rationally assigned considering the structural detailing of the members.
- The forces need not exceed 0.75 times the seismic forces prescribed by the regular code requirements.
- For Risk Category I, II or III structures, near-fault increases in ground motion (maximum considered earthquake ground motion of 0.2 second spectral response greater than 150 percent at 5 percent damping) need not be considered when the fundamental period of the building is 0.5 seconds in the direction under consideration.
- For Risk Category I or II structures, the seismic base shear need not exceed 0.30W.
- For Risk Category III or IV structures, the seismic base shear need not exceed 0.40W.
Evaluation and seismic improvement of unreinforced masonry bearing wall buildings shall comply with the California Existing Building Code (CEBC), Appendix Chapter A1 2013 Edition, and as modified by the CHBC.
- Alternative standards may be used on a case-by-case basis when approved by the authority having jurisdiction. It shall be permitted to exceed the strength limitation of 100 psi in Section A108.2 of the CEBC when test data and building configuration supports higher values subject to the approval of the authority having jurisdiction.
- CEBC Section A102.2 shall not apply to Qualified Historical Buildings in Risk Category III buildings and other structures whose primary occupancies are public assembly with an occupancy load greater than 300.
Parapets and exterior decoration shall be investigated for conformance with regular code requirements for anchorage and ability to resist prescribed seismic forces.
An exception to regular code requirements shall be permitted for those parapets and decorations which are judged not to be a hazard to life safety.