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The purpose of this chapter is that stated in Section 401A.
402B.1 General. The seismic strengthening of unreinforced masonry bearing wall buildings shall comply with the provisions of this chapter when strengthening either is mandated by Chapter 4A or is done voluntarily under Section 405A.6. The elements regulated by this chapter shall be determined in accordance with Table 4B-A. Except as provided herein, other structural provisions of this code shall apply.
402B.2 Essential and Hazardous Facilities. The provisions of this chapter are not intended to apply to the strengthening of buildings or structures in Risk Categories III and IV of ASCE 7-10 Table 1.5-1. Such buildings or structures shall be strengthened to meet the requirements of this code for new buildings of the same occupancy category or to such other criteria as has been established by the Building Official.
402B.3 Unreinforced Masonry Private School Buildings. The strengthening of unreinforced masonry private school buildings shall comply with Sections 17320-17336 of the California Education Code.
402B.4 Qualified Historical Buildings. Qualified historical buildings shall be strengthened to comply with this chapter or the alternative provisions contained in Title 24, California Code of Regulations, Part 8, the State Historical Building Code.
402B.5 Party Wall Buildings. In buildings separated by party walls, all segments sharing the party walls shall be strengthened at the same time whenever feasible. When such action is not feasible, a party wall in any segment undergoing strengthening shall be provided with the capacity to resist a reasonable estimate of the shear forces generated by the adjacent unstrengthened segments.
402B.6 Buildings of Mixed Construction. When buildings having at least one bearing wall of unreinforced masonry also utilize other structural systems, the following requirements shall apply:
402B.6.1 Masonry-wood or steel mix. When the lower stories of the building are of unreinforced masonry bearing wall construction and the upper stories are of wood frame or steel stud construction, the unreinforced masonry stories shall be strengthened to meet the requirements of the general procedure of this chapter and the other stories need not be strengthened.
402B.6.2 Masonry-concrete mix. When a building is of mixed unreinforced masonry bearing wall construction and reinforced concrete or masonry construction, the entire building shall be strengthened in accordance with a program developed by the owner’s architect or engineer and approved by the Building Official.
For the purpose of this chapter, the applicable definitions in this code shall also apply.
COLLAR JOINT is the vertical space between adjacent wythes and may contain mortar.
CROSSWALL is a new or existing wall that meets the requirements of Section 411B.3. A crosswall is not a shear wall.
CROSSWALL SHEAR CAPACITY is the allowable shear value times the length of the crosswall, vcLo.
DIAPHRAGM EDGE is the intersection of the horizontal diaphragm and a shear wall.
DIAPHRAGM SHEAR CAPACITY is the allowable shear value times the depth of the diaphragm, vuD.
ESSENTIAL FACILITY is any building or structure classified in Risk Category IV of ASCE 7-10 Table 1.5-1.
HAZARDOUS FACILITY is any building or structure classified in Risk Category III of 7-10 Table 1.5-1.
NORMAL WALL is a wall perpendicular to the direction of seismic forces.
OPEN FRONT is an exterior building wall line, without vertical elements of the lateral force resisting system in one or more stories.
PARTY WALL is a wall common to two or more buildings located on separate parcels of land.
POINTING is the partial reconstruction of the bed joints of an unreinforced masonry wall as defined in Section 416B.
QUALIFIED HISTORICAL BUILDING is a building or structure as defined in the June 1, 1990, Edition of Title 24, California Code of Regulations, Part 8, Section 8-302.
UNREINFORCED MASONRY includes burned clay, concrete or sand-lime brick, hollow clay or concrete block, plain concrete and hollow clay tile. These materials shall comply with the requirements of Section 406B.
UNREINFORCED MASONRY WALL is a masonry wall in which the area of reinforcing steel is less than 25 percent of the minimum steel ratios required by this code for reinforced masonry. To qualify, reinforcing steel must have been installed in grouted cells within the masonry.
UNREINFORCED MASONRY BEARING WALL is an unreinforced masonry wall which provides the vertical support for a floor or roof for which the total superimposed load exceeds 200 pounds per linear foot (298 kg/m) of wall.
YIELD STORY DRIFT is the lateral displacement of one level relative to the level above or below at which yield stress is first developed in a frame member.
404B.1 For the purpose of this chapter, the applicable symbols and notations in this code shall apply.
A = cross sectional area of unreinforced masonry pier or wall, square inches.
Ab = total area of the bed joints above and below the test specimen for each in-place shear test.
Cp = numerical coefficient as specified in Table 4B-C for Special Procedure diaphragm shear transfer.
D = in-plane width dimension of pier, inches, or depth of diaphragm, feet.
DCR = demand-capacity ratio specified in Section 411B.4.2.
Fwx = force applied to a wall at level x, pounds.
H = least clear height of opening on either side of a pier, inches.
h/t = height-to-thickness ratio of an unreinforced masonry wall. Height, h, is measured between wall anchorage levels and/or slab-on-grade.
L = span of diaphragm between shear walls, or span between shear wall and open front, feet.
Lo = length of crosswall, feet.
Li = effective span for an open front building specified in Section 411B.8, feet.
PD = superimposed dead load at the location under consideration, pounds. For determination of the rocking shear capacity, dead load at the top of the pier under consideration shall be used.
pD+L = stress resulting from the dead plus actual live load in place at the time of testing, pounds per square inch (psi).
Pw = weight of wall, pounds.
Va = vaA, the allowable shear in any unreinforced masonry pier, pounds.
Vca = total shear capacity of crosswalls in the direction of analysis immediately above the diaphragm level being investigated, åvcLo, pounds.
Vcb = total shear capacity of crosswalls in the direction of analysis immediately below the diaphragm level being investigated, åvcLo, pounds.
Vp = shear force assigned to a pier on the basis of its relative shear rigidity, pounds.
Vr = pier rocking shear capacity of any unreinforced masonry wall or wall pier, pounds.
Vtest = load at incipient cracking for each in-place shear test per Section 414B, pounds.
Vwx = total shear force resisted by a shear wall at the level under consideration, pounds.
va = allowable shear stress for unreinforced masonry, pounds per square inch (psi).
vc = allowable shear value for a crosswall sheathed with any of the materials given in Table 4B-D or 4B-E, pounds per foot.
vt = mortar shear strength as specified in Section 406B.3.3.4, pounds per square inch (psi).
vto = mortar shear test values as specified in Section 406B.3.3.4, pounds per square inch (psi).
vu = allowable shear value for a diaphragm sheathed with any of the materials given in Table 4B-D or 4B-E, pounds per foot.
vuD = sum of diaphragm shear capacities of both ends of the diaphragm, pounds.
vuD = for diaphragms coupled with crosswalls, vuD includes the sum of shear capacities of both ends of diaphragms coupled at and above the level under consideration.
W = total seismic dead load as defined in San Francisco Building CodeChapter 16, pounds.
Wd = total dead load tributary to a diaphragm, pounds.
wd = total dead load to all the diaphragms at and above the level under consideration, pounds.
Ww = total dead load to an unreinforced masonry wall above the level under consideration or above an open front building, pounds.
Wwx = dead load of an unreinforced masonry wall assigned to Level x halfway above and below the level under consideration, pounds.
405B.1 General. All buildings shall have a seismic resisting system conforming with ASCE 7-10 Section 12.2, except as modified by this chapter.
405B.2 Alterations and Repairs. Alterations and repairs required to meet the provisions of this chapter shall comply with all other applicable structural requirements of this code unless specifically provided for in this chapter.
405B.3 Requirements for Plans. In addition to the requirements of San Francisco Building Code
Section 106A.3.3 of this code, the following construction information shall be included in the plans required by this chapter:
1. Dimensioned floor and roof plans showing existing walls and the size and spacing of floor and roof framing members and sheathing materials. The plans shall indicate all existing and new crosswalls and shear walls and their materials of construction. The location of these walls and their openings shall be fully dimensioned and drawn to scale on the plans.
2. Dimensioned wall elevations showing openings, piers, wall classes as defined in Section 406B.3.3.6, thickness, heights, wall shear test locations, and cracks or damaged portions requiring repairs. 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 noted.
3. The type of interior wall and ceiling materials and framing.
4. The extent and type of existing wall anchorage to floors and roof when used in the design.
5. The extent and type of parapet and appendage corrections which were previously performed, if any.
6. Repair details, if any, of cracked or damaged unreinforced masonry wall walls required to resist forces specified in this chapter.
7. All other plans, sections and details necessary to delineate required retrofit construction.
8. The design procedure used shall be stated on both the plans and the permit application.
9. Details of the anchor prequalification program required by Section 415B, if utilized, including location and results of all tests.
10. In buildings with party walls, the details of construction on both sides of each party wall shall be shown. Where required by Section 411B.1, Item 5 the owners’ consent statements shall be included with the plans.
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