§ 91.1905 — SEISMIC PROVISIONS

SEC. 91.1905. SEISMIC PROVISIONS.

(Added by Ord. No. 188,797, Eff. 12/31/25.) Section 1905 of the CBC is adopted by reference with the following exceptions, modifications and additions: 91.1905.1. General. In addition to the provisions of ACI 318, structural concrete shall comply with the requirements of CBC Section 1905 and LAMC Section 91.1905. 91.1905.6.2. Seismic Design Categories C, D, E and F. Structures assigned to Seismic Design Category C, D, E or F shall not have elements of structural plain concrete, except as follows: 1. Concrete used for fill with a minimum cement content of two (2) sacks of Portland cement per cubic yard. 2. 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. 3. 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. 91.1905.8. 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. 91.1905.9. 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, φ 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 Sections 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, φ P n , of the column, these moments may be assumed to result from the deformation of the frame in any one principal axis. 91.1905.10. ACI 318, Section 18.10.4. Modify ACI 318, Section 18.10.4, by adding Section 18.10.4.7 to read as follows: 18.10.4.7 - 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. 91.1905.11. 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]