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(Amended by Ord. No. 185,587, Eff. 7/16/18.)
Section 1806 of the CBC is adopted by reference, except Section 1806.2 of the CBC is not adopted; and, in lieu, LAMC Subsection 91.1806.2 is added.
91.1806.2. Presumptive Load-bearing Values. The load-bearing values used in design for supporting soils near the surface shall not exceed the values specified in CBC Table 1806.2 unless data to substantiate the use of higher values are submitted and approved. Where the Department has reason to doubt the classification, strength or compressibility of the soil, the requirements of CBC Section 1803.5.2 shall be satisfied.
Presumptive load-bearing values shall apply to materials with similar physical characteristics and dispositions.
Mud, organic silt, organic clays, peat or uncertified fill shall not be assumed to have a presumptive load-bearing capacity.
(Amended by Ord. No. 182,850, Eff. 1/3/14.)
Section 1807 of the CBC is adopted by reference, except Sections 1807.1.4 and 1807.1.6 the CBC are not adopted; and, in lieu, LAMC Subdivisions 91.1807.1.4 and 91.1807.1.6 are added. (Amended by Ord. No. 185,587, Eff. 7/16/18.)
91.1807.1.4. Permanent Wood Foundation Systems. (Amended by Ord. No. 186,488, Eff. 12/27/19.) Permanent wood foundation systems shall be designed and installed in accordance with AF & PA PWF and as otherwise approved by the Department. Lumber and plywood shall be treated in accordance with AWPA U1 (Commodity Specification A, Use Category 4B and Section 5.2) and shall be identified in accordance with CBC Section 2303.1.9.1. Permanent wood foundation systems shall not be used for structures assigned to Seismic Design Category D, E or F.
EXCEPTION: Accessory buildings not used for human occupancy and less than 120 square feet (11.1 m2) in area may be supported on treated wood mud sills.
91.1807.1.6. Prescriptive Design of Concrete and Masonry Foundation Walls. Concrete and masonry foundation walls that are laterally supported at the top and bottom shall be permitted to be designed and constructed in accordance with this Section. Prescriptive design of foundation walls shall not be used for structures assigned to Seismic Design Category D, E or F.
(Amended by Ord. No. 182,850, Eff. 1/3/14.)
Section 1808 of the CBC is adopted by reference.
91.1808.7.1.1. Exception to CBC Section 1808.7.1. (Added by Ord. No. 186,488, Eff. 12/27/19.) An Exception to CBC Section 1808.7.1 is an open deck or patio not covered with a roof or other overhead structure, which shall not be considered a building for the specific application of the building clearance pursuant to CBC Section 1808.7.1 and CBC Figure 1808.7.1.
(Amended by Ord. No. 182,850, Eff. 1/3/14.)
Section 1809 of the CBC is adopted by reference, except Section 1809.3, 1809.4 and 1809.12 are not adopted; and, in lieu, LAMC Subsections 91.1809.3, 91.1809.4, 91.1809.7 and 91.1809.12 are added. (Amended by Ord. No. 185,587, Eff. 7/16/18.)
91.1809.3. Stepped Footing. (Amended by Ord. No. 185,587, Eff. 7/16/18.) The top surface of footings shall be level. The bottom surface of footings shall be permitted to have a slope not exceeding one unit vertical in 10 units horizontal (10-percent slope). Footings shall be stepped where it is necessary to change the elevation of the top surface of the footing or where the surface of the ground slopes more than one unit vertical in 10 units horizontal (10-percent slope). For structures assigned to Seismic Design Category D, E or F, the stepping requirement shall also apply to the top surface of grade beams supporting walls. Footings shall be reinforced with four 1/2 inch diameter (12.7 mm) deformed reinforcing bars. Two bars shall be placed at the top and bottom of the footings as shown in LAMC Figure 1809.3.
91.1809.4. Depth and Width of Footings. (Amended by Ord. No. 185,587, Eff. 7/16/18.) The minimum depth of footings below the surface of undisturbed soil, compacted fill material or CLSM shall be 12 inches (305 mm). Where applicable, the requirements of CBC Section 1809.5 shall also be satisfied. The minimum width of footings shall be 12 inches (305 mm).
91.1809.7. Prescriptive Footings for Light-Frame Construction. (Amended by Ord. No. 185,587, Eff. 7/16/18.) Where a specific design is not provided, concrete or masonry-unit footings supporting walls of light-frame construction shall be permitted to be designed in accordance with LAMC Table 1809.7. Prescriptive footings in LAMC Table 1809.7 shall not exceed one story above grade plane for structures assigned to Seismic Design Category D, E or F.
NUMBER OF FLOORS SUPPORTED BY THE FOOTING
f | WIDTH OF FOOTING (inches) | THICKNESS OF FOOTING (inches) |
1 | 12 | 6 |
2 | 15 | 6 |
3 | 18 | 8
g |
For SI: one inch = 25.4 mm, one foot = 304.8 mm a. Depth of footings shall be in accordance with CBC Section 1809.4. b. The ground under the floor is permitted to be excavated to the elevation of the top of the footing. c. Not adopted. d. See CBC Section 1908 for additional requirements for footings of structures assigned to Seismic Design Category C, D, E or F. e. For thickness of foundation walls, see LAMC Subdivision 91.1807.1.6. f. Footings are permitted to support a roof in addition to the stipulated number of floors. Footings supporting roof only shall be as required for supporting one floor. | ||
91.1809.12. Timber Footings. Timber footings shall be permitted for buildings of Type V construction and as otherwise approved by the Department. Such footings shall be treated in accordance with AWPA U1 (Commodity Specification A, Use Category 4B). Treated timbers are not required where placed entirely below permanent water level, or where used as capping for wood piles that project above the water level over submerged or marsh lands. The compressive stresses perpendicular to grain in untreated timber footings supported upon treated piles shall not exceed 70 percent of the allowable stresses for the species and grade of timber as specified in the AF&PA NDS. Timber footings shall not be used in structures assigned to Seismic Design Category D, E or F.
(Amended by Ord. No. 182,850, Eff. 1/3/14.)
Section 1810 of the CBC is adopted by reference, except Sections 1810.3.1.5, 1810.3.2.4, 1810.3.3.1.4, and 1810.3.10.4 of the CBC are not adopted; and, in lieu, LAMC Paragraphs 91.1810.3.1.5, 91.1810.3.2.4, 91.1810.3.3.1.4, 91.1810.3.10.4, and Subdivision 91.1810.4.8 are added. (Amended by Ord. No. 185,587, Eff. 7/16/18.)
91.1810.3.1.5. Helical Piles. Helical piles shall be designed and manufactured in accordance with accepted engineering practice to resist all stresses induced by installation into the ground and service loads. Helical piles shall not be used for support of new structures. Helical piles may be used to underpin foundations of existing structures or retrofit or remediate deficient foundations of existing structures. Helical piles shall not be used to resist any horizontal loads.
91.1810.3.2.4. Timber. Timber deep foundation elements shall be designed as piles or poles in accordance with AF&PA NDS. Round timber elements shall conform to ASTM D 25. Sawn timber elements shall conform to DOC PS-20. Timber shall not be used in structures assigned to Seismic Design Category D, E or F.
91.1810.3.3.1.4. Allowable Frictional Resistance. (Amended by Ord. No. 186,488, Eff. 12/27/19.) The assumed frictional resistance developed by any uncased cast-in-place deep foundation element shall not exceed one-sixth (1/6) of the bearing value of the soil material at minimum depth as set forth in CBC Table 1806.2, up to a maximum of 500 psf (24 kPa), unless a greater value is allowed by the Department on the basis of a geotechnical investigation as specified in LAMC Section 91.1803 or a greater value is substantiated by a load test in accordance with CBC Section 1810.3.3.1.2. Frictional resistance and bearing resistance shall not be assumed to act simultaneously.
91.1810.3.10.4. Seismic Reinforcement. (Amended by Ord. No. 185,587, Eff. 7/16/18.) For structures assigned to Seismic Design Category C, a permanent steel casing shall be provided from the top of the micropile down to the point of zero curvature. For structures assigned to Seismic Design Category D, E or F, the micropile shall be considered as an alternative system in accordance with LAMC Subdivision 91.104.2.6. The alternative system design, supporting documentation and test data shall be submitted to the Department for review and approval.
91.1810.4.8. Hollow-stem Augered, Cast-in-Place Elements. An indicator pile program shall be performed to confirm the installation procedure and to determine the pile capacity by static load testing. Upon completion of the pile load testing, at least one test pile shall be entirely exhumed to examine the pile integrity. Prior to the installation of production piles, the results of the testing, and confirmation or revision to the pile capacity shall be determined. Where concrete or grout is placed by pumping through a hollow-stem auger, the auger shall be permitted to rotate in a clockwise direction during withdrawal. As the auger is withdrawn at a steady rate or in increments not to exceed 1 foot (305 mm), concreting or grouting pumping pressures shall be measured and maintained high enough at all times to offset hydrostatic and lateral earth pressures. Concrete or grout volumes shall be measured to ensure that the volume of concrete or grout placed in each element is equal to or greater than the theoretical volume of the hole created by the auger. Where the installation process of any element is interrupted or a loss of concreting or grouting pressure occurs, the element shall be redrilled to 5 feet (1524 mm) below the elevation of the tip of the auger when the installation was interrupted or concrete or grout pressure was lost and reformed. Augered cast-in-place elements shall not be installed within six diameters center to center of an element filled with concrete or grout less than 12 hours old, unless approved by the building official. If the concrete or grout level in any completed element drops due to installation of an adjacent element, the element shall be replaced.
(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.
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.
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.
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.
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.
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]
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.
(Division Title Amended by Ord. No. 179,324, Eff. 12/10/07, Oper. 1/1/08.)
Section
91.2000 Basic Provisions.
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