(A) General. All materials permitted by the Uniform Building Code, including their appropriate allowable stresses and those existing configurations or materials specified herein may be utilized to meet the requirements of this chapter.
(B) Existing materials.
(1) Unreinforced masonry falls.
(a) Unreinforced masonry walls analyzed in accordance with this section may provide vertical support for roof and floor construction and resistance to lateral loads. The facing and backing of such walls shall be bonded so that not less than 4% of the exposed face area is composed of solid headers extending not less than four inches into the backing. The distance between adjacent full-length headers shall not exceed 24 inches vertically or horizontally. Where the backing consists of two or more wythes the header shall extend not less than four inches into the most distant wythe, or the backing wythes shall be bonded together with separate headers whose area and spacing conform to the foregoing.
(b) Tension stresses due to seismic forces normal to the wall may be neglected if the walls do not exceed the height to thickness ratio in Table G and the in-plane shear stresses due to seismic loads as set forth in Table J.
(c) If the wall height-thickness ratio exceeds the specified limits, the wall may be supported by vertical bracing members designed in accordance with § 15.64.090. The deflection of such bracing member at design loads shall not exceed one-tenth of the wall thickness.
(d) Exception: The wall may be supported by flexible vertical bracing members designed in accordance with § 15.64.090(B) if the deflection at design loads is not less than one-quarter nor more than one-third of the wall thickness.
(e) 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 nor ten feet.
(f) 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. Bracing elements shall be detailed to minimize the horizontal displacement of the wall by components of vertical displacements of the floor or roof.
(2) 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 H.
(C) 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 I.
(D) Alternate materials. Alternate materials, designs and methods or construction may be approved by the Building Official in accordance with the provisions of the Uniform Building Code.
(E) Minimum acceptable quality of existing unreinforced masonry walls.
(1) General provisions. 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 subsection. 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 Building Official. The quality of mortar in all masonry walls shall be determined by performing in-place shear tests or by testing eight inch diameter cores. Alternative methods of testing may be approved by the Building Official. 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 leaned to remove loose and deteriorated mortar. Mortar for pointing shall be Type S or N except that masonry cements shall not be used. All preparation and mortar pointing shall be done under the continuous inspection of a registered Deputy Building 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. The report shall be submitted to the Building Official for approval as part of the structural analysis. All testing shall be performed in accordance with the requirements specified in this subsection by a testing agency approved by the Building Official. An accurate record shall be kept of all such tests and of their locations in the building, and these results shall be submitted to the Building Official for approval as part of the structural analysis.
(2) Number and location of tests. The minimum number of tests shall be two per wall or line of wall elements resisting a common force, or per 1500 square feet of wall surface, with a minimum of eight tests in any case. 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.
(3) In-place shear tests. 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 opposite head joint of the brick to be tested shall be removed and cleaned prior to testing. The minimum quality mortar in 80% of the shear tests shall not be less than the total of 30 psi 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 at which movement of the brick is first observed.
(4) Core tests. 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 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, then the shear value be reported as zero.
(F) Testing of shear bolts.
(1) One-fourth of all new shear bolts and dowels embedded in unreinforced masonry walls shall be tested by a special inspector using a torque calibrated wrench to the following minimum torques:
(a) ½" diameter bolts or dowels = 40 foot-lbs;
(b) 5/8" diameter bolts or dowels = 50 foot-lbs;
(c) ¾" diameter bolts or dowels = 60 foot-lbs.
(2) No bolts exceeding three-fourths inch 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.
(G) Determination of allowable stresses for design methods based on test results.
(1) Design shear values. Design seismic in-plane shear stresses shall be substantiated by tests performed as specified in § 15.64.100(E)(3) and (4). Design stresses shall be related to test results obtained in accordance with Table J. Intermediate values between three and ten psi may be interpolated.
(2) Design compression and tension values. Compression stresses from unreinforced masonry having a minimum design shear value of three psi shall not exceed 100 psi. Design tension values for unreinforced masonry shall not be permitted.
(H) Existing rod anchors to be tested. 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 prior to establishing a datum for recording elongation. The tension test load reported shall be recorded at one-eighth inch 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% of the average of those tested anchors having the same wall thickness and joist orientation.
(I) Qualification tests. 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% of the average of the ultimate loads.
(`78 Code, § 15.64.100.) (Ord. 1967 § 1 (part), 1989.)