SEC. 91.1900. BASIC PROVISIONS.

   (Amended by Ord. No. 186,488, Eff. 12/27/19.)

   Chapter 19 of the CBC is adopted by reference, except that CBC Sections 1905.1, 1905.1.7, and 1906.1 are not adopted; and, in lieu, LAMC Subsections 91.1905.1, 91.1905.1.7, 91.1905.1.9, 91.1905.1.10, 91.1905.1.11, 91.1905.1.12, and 91.1906.1 are added.

91.1905.1. General. The text of ACI 318 shall be modified as indicated in CBC Sections 1905.1.1 through 1905.1.8 and as modified by the LAMC.

91.1905.1.7. ACI 318, Section 14.1.4. Delete ACI 318, Section 14.1.4, and replace with the following:

   14.1.4 - Plain concrete in structures assigned to Seismic Design Category C, D, E or F.

   14.1.4.1 - Structures assigned to Seismic Design Category C, D, E or F shall not have elements of structural plain concrete, except as follows:

   (a)   Concrete used for fill with a minimum cement content of two (2) sacks of Portland cement per cubic yard.

   (b)   Isolated footings of plain concrete supporting pedestals or columns are permitted, provided the projection of the footing beyond the face of the supported member does not exceed the footing thickness.

   (c)   Plain concrete footings supporting walls are permitted provided the footings have at least two continuous longitudinal reinforcing bars. Bars shall not be smaller than No. 4 and shall have a total area of not less than .002 times the gross cross-sectional area of the footing. A minimum of one bar shall be provided at the top and bottom of the footing. Continuity of reinforcement shall be provided at corners and intersections.

   EXCEPTION: In detached one- and two-family dwellings three stories or less in height and constructed with stud-bearing walls, plain concrete footings with at least two continuous longitudinal reinforcement bars not smaller than No. 4 are permitted to have a total area of less than .002 times the gross cross-sectional area of the footing.

91.1905.1.9. ACI 318, Section 18.7.5. Modify ACI 318, Section 18.7.5 by adding Section 18.7.5.8 to read as follows:

   18.7.5.8 - Where the calculated point of contraflexure is not within the middle half of the member clear height, provide transverse reinforcement as specified in ACI 318 Section 18.7.5.1 Items (a) through (c), over the full height of the member.

91.1905.1.10. ACI 318, Section 18.7.5. Modify ACI 318, Section 18.7.5, by adding Section 18.7.5.9 to read as follows:

   18.7.5.9 - At any section where the design strength, P n , of the column is less than the sum of the shears V e computed in accordance with ACI 318 Sections 18.6.5.1 and 18.7.6.1.1 for all the beams framing into the column above the level under consideration, transverse reinforcement as specified in ACI 318 Section 18.7.5.1 through 18.7.5.3 shall be provided. For beams framing into opposite sides of the column, the moment components may be assumed to be of opposite sign. For determination of the design strength, P n , of the column, these moments may be assumed to result from the deformation of the frame in any one principal axis.

91.1905.1.11. ACI 318, Section 18.10.4. Modify ACI 318, Section 18.10.4, by adding Section 18.10.4.6 to read as follows:

   18.10.4.6 - Walls and portions of walls with P u > 0.35P o shall not be considered to contribute to the calculated strength of the structure for resisting earthquake-induced forces. Such walls shall conform to the requirements of ACI 318, Section 18.14 for wall piers.

91.1905.1.12. ACI 318, Section 18.12.6. Modify ACI 318, Section 18.12.6, by adding Section 18.12.6.2 to read as follows:

   18.12.6.2 - Collector and boundary elements in topping slabs placed over precast floor and roof elements shall not be less than 3 inches (76 mm) or 6d b thick, where d b is the diameter of the largest reinforcement in the topping slab. [CBC Section 1909.3.5]

91.1906. Footings for Light-Frame Construction. (Added by Ord. No. 187,719, Eff. 1/23/23.)

91.1906.1. Plain Concrete Footings. (Amended by Ord. No. 187,719, Eff. 1/23/23.) The design and construction of structural plain concrete, both cast-in-place and precast, shall comply with the minimum requirements of ACI 318, as modified in CBC Section 1905.

   EXCEPTION: For Group R-3 occupancies and buildings of other occupancies less than two stories above grade plane of light-frame construction, the required footing thickness of ACI 318 is permitted to be reduced to 6 inches (152 mm), provided that the footing does not extend more than 4 inches (102 mm) on either side of the supported wall. This exception shall not apply to structural elements designed to resist seismic lateral forces for structures assigned to Seismic Design Category D, E, or F.