(Amended by Ord. No. 171,175, Eff. 7/25/96.)
91.8809.1. General. All materials permitted by this Code, including their appropriate allowable stresses and those existing configurations of materials specified herein, may be utilized to meet the requirements of this division.
91.8809.2. Existing Materials.
91.8809.2.1. General. (Amended by Ord. No. 171,939, Eff. 4/15/98.) Unreinforced masonry walls analyzed in accordance with this section may provide vertical support for roof and floor construction and resistance to lateral loads.
All units of both bearing and nonbearing walls shall be laid with full shoved mortar joints; all head, bed and wall (collar) joints shall be solidly filled with mortar; and the bonding of adjacent wythes of multiwythe walls shall be as follows:
The facing and backing shall be bonded so that not less than 4 percent of the wall surface of each face is composed of headers extending not less than four inches (102 mm) into the backing. The distance between adjacent full-length headers shall not exceed 24 inches (610 mm) either vertically or horizontally. In walls in which a single header does not extend through the wall, headers from the opposite sides shall overlap at least four inches (102 mm), or headers from opposite sides shall be covered with another header course overlapping the header below at least four inches (102 mm).
Wythes of walls not bonded as described above shall be considered as veneer. The veneer wythe shall not be included in the effective thickness used in calculating the height-to-thickness ratio and the shear capacity of the wall.
Tension stresses due to seismic forces normal to the wall may be neglected if the wall does not exceed the height-to-thickness ratio in Table No. 88-G and the in-plane shear stresses due to seismic loads as set forth in Table No. 88-J.
If the wall height-to-thickness ratio exceeds the specified limits, the wall may be supported by vertical bracing members designed in accordance with Division 16 of this Code. The deflection of such bracing member at design loads shall not exceed one tenth of the wall thickness.
EXCEPTION: The wall may be supported by flexible vertical bracing members designed in accordance with Section 91.8808.2 if the deflection at design loads is not less than one quarter or more than one third of the wall thickness.
All vertical bracing members shall be attached to floor and roof construction for their design loads independently of required wall anchors. Horizontal spacing of vertical bracing members shall not exceed one half the unsupported height of the wall or 10 feet (3048 mm).
The wall height may be measured vertically to bracing elements other than a floor or roof. Spacing of the bracing elements and wall anchors shall not exceed six feet (1829 mm). Bracing elements shall be detailed to minimize the horizontal displacement of the wall by components of vertical displacements of the floor or roof.
91.8809.2.2. Veneer. (Amended by Ord. No. 181,758, Eff. 8/8/11.) Veneer shall be anchored with approved anchor ties conforming to the required design capacity specified in Section 91.1405 of this Code and placed at a maximum spacing of 24 inches (610 mm).
EXCEPTION: Existing veneer anchor ties may be acceptable provided the ties are in good condition and conform to the minimum size, maximum spacing and material requirements specified in the provisions of the Los Angeles Building Ordinances in effect prior to October 6, 1933. Said provisions specified that veneer anchor ties shall be corrugated galvanized iron strips not less than one inch (25 mm) in width, eight inches (203 mm) in length and 1/16 inch (1.6 mm) in thickness and shall be located and laid in every alternate course in the vertical height of the wall at a spacing not to exceed 17 inches (432 mm) on center horizontally. As an alternate, said provisions specified that such ties may be laid in every fourth course vertically at a spacing not to exceed nine inches (229 mm) on center horizontally.
The existence and condition of existing veneer anchor ties shall be verified as follows:
1. An approved testing laboratory shall verify the location and spacing of the ties and shall submit a report to the Department for approval as a part of the structural analysis.
2. The veneer in a selected area shall be removed to expose a representative sample of ties (not less than four) for inspection by the Department.
91.8809.2.3. Existing Roof, Floors, Walls, Footings and Wood Framing. Existing materials, including wood shear walls utilized in the described configuration, may be used as part of the lateral load-resisting system, provided that the stresses in these materials do not exceed the values shown in Table No. 88-H.
91.8809.3. Strengthening of Existing Materials. New materials, including wood shear walls, may be utilized to strengthen portions of the existing seismic resisting system in the described configurations, provided that the stresses do not exceed the values shown in Table No. 88-I.
91.8809.4. Alternate Materials. Alternate materials, designs and methods of construction may be approved by the Department in accordance with the provisions of Article 8, Chapter IX of the Los Angeles Municipal Code.
91.8809.5.1. General Provisions. (Amended by Ord. No. 171,939, Eff. 4/15/98.) All unreinforced masonry walls utilized to carry vertical loads and seismic forces parallel and perpendicular to the wall plane shall be tested as specified in this section. All masonry quality shall equal or exceed the minimum standards established herein or shall be removed and replaced by new materials. Alternate methods of testing may be approved by the Department. The quality of mortar in all masonry walls shall be determined by performing in-place shear tests or by testing eight-inch (203 mm) diameter cores.
The vertical wall joint between wythes (collar joints) shall be inspected at the test location after the in-place shear tests, and an estimate of the percentage of wythe-to-wythe mortar coverage shall be reported along with the results of the in-place shear tests. Where the exterior face is veneer, the type of veneer, its thickness and its bonding and/or ties to the structural wall masonry shall also be reported.
Alternative methods of testing may be approved by the Department. Nothing shall prevent pointing with mortar of all the masonry wall joints before the tests are first made. Prior to any pointing, the mortar joints must be raked and cleaned to remove loose and deteriorated mortar. Mortar for pointing shall be Type S or N except masonry cements shall not be used. All preparation and mortar pointing shall be done under the continuous inspection of a registered deputy inspector. At the conclusion of the inspection, the inspector shall submit a written report to the licensed engineer or architect responsible for the seismic analysis of the building setting forth the result of the work inspected. Such report shall be submitted to the Department for approval as part of the structural analysis.
All testing shall meet Department-approved testing method parameters (including rate of load application) and shall be performed in accordance with the requirements specified in this section by a testing agency approved by the Department.
An accurate record of all such tests and their location in the building shall be recorded and these results shall be submitted to the Department for approval as part of the structural analysis.
91.8809.5.2. Number and Location of Tests. (Amended by Ord. No. 171,939, Eff. 4/15/98.) The minimum number of tests shall be as follows:
1. At each of both the first and top stories, not less than two per wall line or line of wall elements providing a common line of resistance to lateral forces.
2. At each of all other stories, not less than one per wall element providing a common line of resistance to lateral forces.
3. In any case, not less than one per 1,500 square feet (139.4 m2) of wall surface and a total of eight.
The shear tests shall be taken at locations representative of the mortar conditions throughout the entire building, taking into account variations in work quality at different building height levels, variations in weathering of the exterior surfaces and variations in the condition of the interior surfaces due to deterioration caused by leaks and condensation of water and/or by the deleterious effects of other substances contained within the building. Where the higher h/t ratios allowed in Footnotes Nos. 4 and 5 of Table No. 88-G are to be used, the in-place shear tests taken at the
top story shall be included in the 80 percent of the shear tests used to determine the minimum mortar shear strength.
The exact test or core location shall be determined at the building site by the licensed engineer or architect responsible for the seismic analysis of the subject building.
91.8809.5.3. In-Place Shear Tests. (Amended by Ord. No. 186,488, Eff. 12/27/19.) The bed joints of the outer wythe of the masonry shall be tested in shear by laterally displacing a single brick relative to the adjacent bricks in that wythe. The mortar in the opposite head joint of the brick to be tested shall be removed and cleaned prior to testing. The minimum quality mortar in 80 percent of the shear tests shall not be less than the total of 30 psi (206.9 kPa) plus the axial stress in the wall at the point of the test. The shear stress shall be based on the gross area of both bed joints and shall be that shear stress at which movement of the masonry is first measured or at which cracking first appears.
An internal caliper, graduated in 0.001 of an inch (0.025 mm) increments shall be used to measure movement of the masonry unit. A hydraulic jack equipped with a pressure gauge graduated in increments of 50 psi (345 kPa) or less shall be used. The jack load shall be applied at a rate not exceeding 5,000 pounds (22 240 N) per minute.
The test shall be conducted by a minimum of two technicians. Load and displacement readings shall be recorded at the following intervals:
1. At a caliper reading of 0.001 inch (0.025 mm);
2. At first visually observed sign of movement or cracking of the mortar or masonry unit;
3. At a caliper reading of 0.02 inch (0.51 mm); and
4. The ultimate load on the unit.
The masonry unit to be tested shall not be located adjacent to a bond course in a brick wall laid in common bond. Tests to evaluate the mortar quality of structural walls shall not be conducted in masonry veneer.
Walls with mortar values which are consistently low and do not meet the minimum quality values specified in this Section shall be entirely pointed per Chapter A1, Section A103 and A106.2.3.9 of the 2019 California Existing Building Code except that the depth of joint penetration shall be 1-1/2 inch (38 mm) in lieu of the 3/4 inch (19 mm) specified.
91.8809.5.4. Core Tests. (Amended by Ord. No. 171,939, Eff. 4/15/98.) A minimum number of mortar test specimens equal to the number of required cores shall be prepared from the cores and tested as specified herein. The mortar joint of the outer wythe of the masonry core shall be tested in shear by placing the circular core section in a compression testing machine with the mortar bed joint rotated 15 degrees from the axis of the applied load. The mortar joint tested in shear shall have an average ultimate stress of 20 psi (138 kPa) based on the gross area. The average shall be obtained from the total number of cores made. If test specimens cannot be made from cores taken, the shear value shall be reported as zero.
1/2-inch-diameter bolts or dowels – 40 foot-pounds.
5/8-inch-diameter bolts or dowels – 50 foot-pounds.
3/4-inch-diameter bolts or dowels – 60 foot-pounds.
For SI: 1 inch = 25.4 mm, 1 foot-pound = 1.356 Nm
No bolts exceeding 3/4-inch (19.1 mm) shall be used. All nuts shall be installed over malleable iron or plate washers when bearing on wood and heavy cut washers when bearing on steel.
91.8809.7. Determination of Allowable Stresses for Design Methods Based on Test Results.
91.8809.7.1. Design Shear Values. (Amended by Ord. No. 171,939, Eff. 4/15/98.) Design seismic in-plane shear stresses shall be substantiated by tests performed as specified in Section 91.8809.5.3 and 91.8809.5.4.
Design stresses shall be related to test results obtained in accordance with Table No. 88-J. Intermediate values between 3 and 10 psi (20.7 kPa and 69 kPa) may be interpolated.
91.8809.7.2. Design compression and tension values. (Amended by Ord. No. 171,939, Eff. 4/15/98.) Compression stresses for unreinforced masonry having a minimum design shear value of three psi (20.7 kPa) shall not exceed 100 psi (690 kPa). Design tension values for unreinforced masonry shall not be permitted.
91.8809.8. (Amended by Ord. No. 171,939, Eff. 4/15/98.) Five percent of the existing rod anchors utilized as all or part of the required wall anchors shall be tested in pullout by an approved testing laboratory. The minimum number tested shall be four per floor, with two tests at walls with joists framing into the wall and two tests at walls with joists parallel to the wall. The test apparatus shall be supported on the masonry wall at a minimum distance of the wall thickness from the anchor tested. The rod anchor shall be given a preload of 300 pounds (136 kg) prior to establishing a datum for recording elongation. The tension test load reported shall be recorded at 1/8-inch (3.2 mm) relative movement of the anchor and the adjacent masonry surface. Results of all tests shall be reported. The report shall include the test results as related to the wall thickness and joist orientation. The allowable resistance value of the existing anchors shall be 40 percent of the average of those tested anchors having the same wall thickness and joist orientation.
91.8809.9. Qualification tests for devices used for wall anchorage shall be tested with the entire tension load carried on the enlarged head at the exterior face of the wall. Bond on the part of the device between the enlarged head and the interior wall face shall be eliminated for the qualification tests. The resistance value assigned the device shall be 20 percent of the average of the ultimate loads.