.010 General. Every structure within the scope of this Division shall be analyzed and constructed to resist minimum total lateral seismic forces assumed to act nonconcurrently in the direction of each of the main axes of the structure in accordance with the following equation:
V=ZIKCSW
The value of IKCS need not exceed the values set forth in Table No. 15.07-D based on the applicable rating classification of the building.
.020 Lateral Forces on Elements of Structures. Parts or portions of structures shall be analyzed and designed for lateral loads in accordance with subsections .010 of this section and UBC Section 2312(e) but not less than the value from the following equation:
Fp=ZICpSWp
For the provisions of this subsection, the product of IS need not exceed the values as set forth in Table No. 15.07-E.
Exception: Unreinforced masonry walls in buildings not having a rating classification of I may be analyzed in accordance with Section 15.07.080.
The value of Cp need not exceed the values set forth in Table 15.07-F.
.030 Anchorage and Interconnection. Anchorage and interconnection of all parts, portions and elements of the structure shall be analyzed and designed for lateral forces in accordance with Table No. 15.07-F of this code and the equation Fp=ZICpSWp as modified by Table No. 15.07-E. Minimum anchorage of masonry walls to each floor or roof shall resist a minimum force of two hundred pounds per linear foot acting normal to the wall at the level of the floor or roof.
.040 Level of Required Repair. Alterations and repairs required to meet the provisions of this chapter shall comply with all other applicable requirements of the UBC unless otherwise specifically provided for in this chapter.
.050 Required Analysis.
(a) General. Except as modified herein, the analysis and design relating to the structural alteration of existing structures within the scope of this chapter shall be in accordance with the analysis specified in Chapter 23 of the UBC.
(b) Continuous Stress Path. A complete, continuous stress path from every part or portion of the structure to the ground shall be provided for the required horizontal forces.
(c) Positive Connections. All parts, portions or elements of the structure shall be interconnected by positive means.
.060 Analysis Procedure.
(a) General. Stresses in materials and existing construction utilized to transfer seismic forces from the ground to parts or portions of the structure shall conform to those permitted by the UBC and those materials and types of construction specified in Section 15.07.080.
(b) Connections. Materials and connectors used for interconnection of parts and portions of the structure shall conform to the UBC. Nails may be used as part of an approved connector.
(c) Unreinforced Masonry Walls. Except as modified herein, unreinforced masonry walls shall be analyzed as specified in UBC Sections 2406, 2407, 2408 to withstand all vertical loads as specified in Chapter 23 of the UBC in addition to the seismic forces required by this chapter. The fifty percent increase in the seismic force factor for shear walls as specified in UBC Section 2407(h)4F may be omitted in the computation of seismic loads to existing shear walls.
No allowable tension stress will be permitted in unreinforced masonry walls. Walls not capable of resisting the required design forces specified in this chapter shall be strengthened or shall be removed and replaced.
Exception No. 1: Unreinforced masonry walls in buildings not classified as a Rating Classification I pursuant to Table No. 15.07-A may be analyzed in accordance with Section 15.07.080.
Exception No. 2: An unreinforced masonry wall which carries no design loads other than its own weight may be considered as veneer if it is adequately anchored to new supporting elements.
.070 Combination of Vertical and Seismic Forces.
(a) New Materials. All new materials introduced into the structure to meet the requirements of this section which are subjected to combined vertical and horizontal forces shall comply with UBC Section 2303(f).
(b) Existing Materials. When stresses in existing lateral force resisting elements are due to a combination of dead loads plus live loads plus seismic loads, the allowable working stress specified in the UBC may be increased one hundred percent. However, no increase will be permitted in the stresses allowed in Section 15.07.080, and the stresses in members due only to seismic and dead loads shall not exceed the values permitted by UBC Section 2303(d).
(c) Allowable Reduction of Bending Stress by Vertical Load. In calculating tensile fiber stress due to seismic forces required by this chapter, the maximum tensile fiber stress may be reduced by the full direct stress due the vertical dead loads. (Ord. 5076 § 1 (part); November 14, 1989.)