SECTION 413B – DETAILED SYSTEM DESIGN REQUIREMENTS

413B.1  Wall Anchorage.

413B.1.1  Anchor locations.  All unreinforced masonry walls shall be anchored at the roof and floor levels as required in Section 410B.2. Ceilings of plaster, gypsum board or similar heavier materials, when not attached directly to roof or floor framing, and abutting masonry walls, shall be either anchored to the walls at a maximum spacing of 6 feet (1.829 m) or removed.

413B.1.2  Anchor requirements.  Anchors shall consist of bolts installed through the wall as specified in Table 4B-E, or by an approved equivalent at a maximum anchor spacing of 6 feet (1.829 m). All existing wall anchors shall be secured to the joists to develop the required forces.

413B.1.3  Minimum wall anchorage.  Anchorage of masonry walls to each floor or roof shall resist a minimum force determined in accordance with San Francisco Building Code Chapter 16 or 200 pounds per linear foot (298 kg/m), whichever is greater, acting normal to the wall at the level of the floor or roof. Anchor spacing shall not exceed 6 feet (1.829 m) on center. Existing through-the-wall anchors, if used, must meet the requirements of this chapter or must be upgraded.

413B.1.4  Anchors at corners.  At the roof and floor levels, both shear and tension anchors shall be provided within 2 feet (0.609 m) horizontally from the inside of the corners of the walls.

413B.1.5  Anchors with limited access.  When access to the exterior face of the masonry wall is prevented, wall anchors conforming to Item 4.b. in Table 4B-E may be used.

413B.1.6  Anchors at interior and party walls.  When floor or roof framing aligns vertically at party and interior masonry walls, continuous anchors shall be utilized to directly connect the floor or roof framing on either side of the wall. Where the roof or floor framing is offset more than the least depth of any adjacent framing, the intervening wall section shall be investigated for cross wythe shear assuming that the diaphragm to wall tensions on either side of the wall are acting in opposite directions.

413B.2  Diaphragm Shear Transfer.  Bolts transmitting shear forces shall have a maximum bolt spacing of 6 feet (1.829 m) and shall have nuts installed over malleable iron or plate washers when bearing on wood and heavy cut washers when bearing on steel.

413B.3  Collectors.  Collector elements shall be provided which are capable of transferring the seismic forces originating in other portions of the building to the element providing the resistance to those forces.

413B.4  Ties and Continuity.  Ties and continuity shall conform to SFEBC Section 301.2.

413B.5  Wall Bracing.

413B.5.1  General.  Where a wall height-to-thickness ratio exceeds the specified limits, the wall may be laterally supported by vertical bracing members per Section 413B.5.2 or by reducing the wall height by bracing per Section 413B.5.3.

413B.5.2  Vertical bracing members.  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 10 feet (3.048 m). Deflection of such bracing members at design loads shall not exceed one-tenth of the wall thickness.

413B.5.3  Intermediate wall bracing.  The wall height may be reduced by bracing elements connected to the floor or roof. Horizontal spacing of the bracing elements and wall anchors shall be as required by design but shall not exceed 6 feet (1.829 m) on center. Bracing elements shall be detailed to minimize the horizontal displacement of the wall by the vertical displacement of the floor or roof.

413B.6  Parapets.  Parapets and appendages not conforming to this chapter shall be removed, or stabilized or braced to ensure that the parapets and appendages remain in their original position.

   EXCEPTIONS:

      1.   Parapets, appendages and roof-to wall-tension anchors which have already been removed, stabilized or braced to comply with Chapter 4C of this code or previous codes pursuant to an application filed before the effective date of this ordinance need not be reanalyzed or restrengthened.

      2.   Parapets whose heights do not exceed 3 times their thicknesses need not be removed, stabilized or braced, provided they are located either immediately adjacent to a normally inaccessible court or yard or another building. In the case of an adjoining building, the top of the parapet of the building under consideration shall not be more than 12 inches (0.305 m) above the top of the parapet of the adjoining building. In order to qualify for this exception, the owner must execute an agreement with the Department to voluntarily abate any hazard that may arise as a result of changed conditions such as demolition of the adjacent building or development or occupancy of the adjoining court or yard. The owner must record the agreement with the County Recorder on a form satisfactory to the Department and supply a copy of the recorded agreement to the Department.

   Parapets previously exempted that would not be exempted under Exception 2 above shall be removed, or stabilized or braced when the building is strengthened.

   The maximum height of an unbraced unreinforced masonry parapet above the lower of either the level of tension anchors or roof sheathing shall not exceed 1½ times the thickness of the parapet wall. If the required parapet height exceeds this maximum height, a bracing system designed for the forces determined in accordance with San Francisco Building CodeChapter 16 shall support the top of the parapet. Parapet corrective work must be performed in conjunction with the installation of tension roof anchors.

   The minimum height of a parapet above any wall anchor shall be 12 inches (0.305 m).

   EXCEPTION: If a reinforced concrete beam is provided at the top of the wall, the minimum height above the wall anchor may be 6 inches (170.44 mm).

413B.7  Veneer.

413B.7.1  Anchorages.  Veneer shall be anchored with approved anchor ties, conforming to the required design capacity specified in this code and placed at a maximum spacing of 24 inches (610 mm) with a maximum supported area of 4 square feet (0.372 m2).

   EXCEPTION: Existing anchor ties for attaching brick veneer to brick backing may be acceptable, provided the ties are in good condition and are corrugated galvanized iron strips not less than 1 inch (25.4 mm) in width, 8 inches (203.2 mm) in length and 1/16 inch (1.59 mm) in thickness or equal.

413B.7.2  Verification.  The location 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 Building Official for approval as 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 Building Official.

413B.8  Nonstructural Masonry Walls.  Unreinforced masonry walls which carry no design vertical or lateral loads and are not required by the design to be part of the lateral force resisting system shall be adequately anchored to new or existing supporting elements. The anchors and elements shall be designed for the out-of-plane forces specified in San Francisco Building Code Chapter 16 . The height or length to thickness ratio between such supporting elements for such walls shall not exceed 13.

413B.9  Truss and Beam Supports.  Where trusses and beams, other than rafters or joists, are supported on masonry, independent secondary columns shall be installed to support vertical loads of the roof or floor members.

413B.10  Adjacent Buildings.  Where elements of adjacent buildings do not have a separation of at least 5 inches (127 mm), the allowable height-to-thickness ratios for “all other buildings” per Table 4B-B shall be used in the direction of consideration.