The purpose of this chapter is to promote public safety and welfare by reducing the risk of death or injury that may result from the effects of earthquakes on existing unreinforced masonry bearing wall buildings. The provisions of this chapter are intended as minimum standards for structural seismic resistance established primarily to reduce the risk of life loss or injury. Compliance with these standards will not necessarily prevent loss of life or injury or prevent earthquake damage to rehabilitated buildings.
(§ 1, Ord. 678, eff. July 12, 1991)
The provisions of this chapter shall apply to all existing buildings having at least one unreinforced masonry bearing wall. Except as provided herein, all other provisions of the Uniform Building Code shall apply.
(§ 1, Ord. 678, eff. July 12, 1991)
This chapter shall not apply to detached one- or two-family dwellings and detached apartment houses containing less than five dwelling units and used solely for residential purposes, garages and sheds, this chapter does not require alteration of existing electrical, mechanical or fire safety systems.
(§ 1, Ord. 678, eff. July 12, 1991)
For the purposes of this chapter, the following terms shall be used in this chapter with such meanings. (Other terms defined in the Uniform Building Code and used herein shall be used with the meanings set forth in the Uniform Building Code):
"Board of Appeals"
shall mean the City Council. The Building Official shall serve as ex officio secretary but shall not be a member of the Board.
"Building Official"
shall mean the designated authority charged with the administration and enforcement of this Code.
"Collar joint"
shall mean the vertical space between adjacent wythes and may contain mortar.
"Cross wall"
shall mean a wall that meets the requirements of Section 9-12.603(c) of this chapter. A cross wall shall not mean a shear wall.
"Cross wall shear capacity"
shall mean the length of the cross wall times the allowable shear value, voLo.
"Diaphragm edge"
shall mean the intersection of the horizontal diaphragm and a shear wall.
"Diaphragm shear capacity"
shall mean the depth of the diaphragm times the allowable shear value, vuD.
"Flexible diaphragm"
shall mean a diaphragm of wood or other construction of similar flexibility.
"Historical building"
shall mean any building designated an historical landmark by an appropriate Federal, State or City jurisdiction.
"Normal wall"
shall mean a wall perpendicular to the direction of seismic forces.
"Open front"
shall mean an exterior wall plane without vertical elements in one or more stories which resist the required lateral forces.
"Pointing"
shall mean the partial reconstruction of the bed joints of a URM wall as defined in Uniform Building Code Standard No. 24-9.
"Unreinforced masonry bearing wall"
shall mean a URM wall which provides the vertical support for a floor or roof for which the total superimposed load is over one hundred pounds per linear foot of wall.
"Unreinforced masonry ("URM") wall"
shall mean a masonry wall in which the area of reinforcing steel is less than 25% of that required by the Uniform Building Code for reinforced masonry.
"Yield story drift"
shall mean the lateral displacement of one level relative to the level above or below at which yield stress is first developed in a frame member.
(§ 1, Ord. 678, eff. July 12, 1991)
For purposes of this chapter, the applicable symbols and definitions in the Uniform Building Code shall also apply.
A
=
Area of URM pier, square inches.
Ab
=
Area of the bed joints above and below the test specimen for each in-place shear test.
Cp
=
Numerical coefficient specified in Table 12-A of this chapter.
D
=
In-plane width dimension of pier, inches or depth of diaphragm, feet.
DCR
=
Demand-capacity ratio specified in Subsection 9-12.604 of this chapter.
Fp
=
Wall anchor tension force, pounds.
Fwx
=
Force applied to a wall at level x, pounds.
H
=
Least clear height of opening on either side of pier, inches.
h/t
=
Height/thickness ratio of URM wall. Height h is measured between wall anchorage levels.
L
=
Span of diaphragm between shear walls or span between shear wall and open front, feet.
Lo
=
Length of cross wall, feet.
Li
=
Effective span for an open front building specified in Section 9-12.604(d) of this chapter, feet.
PD
=
Superimposed dead load at the top of the pier under consideration, pounds.
PD + L
=
Actual dead plus live load in place at the time of testing, pounds.
PW
=
Weight of wall, pounds.
V
=
Total lateral seismic base shear.
Va
=
VaA, the allowable shear in any URM pier, pounds.
Va
=
VoLo
Vr
=
0.5PD(D/H), the rocking shear of any URM wall or wall pier, pounds.
Vwx
=
Total shear force resisted by a shear wall at the level under consideration, pounds.
Vp
=
Shear force assigned to a pier on the basis of its relative shear rigidity, pounds.
Vtest
=
Load in pounds at incipient cracking for each in-place shear test per Uniform Building Code Standard 24-7.
Va
=
Allowable shear stress for unreinforced masonry, psi.
Vc
=
Allowable shear value for a cross wall sheathed with any of the materials given in Tables 12-C or 12-D of this chapter, pounds per foot.
Vt
=
Mortar shear strength as specified in Section 9-12.303(c)(iv) of this chapter.
Vto
=
Mortar shear test values as specified in Section 9-12.303(c)(iv) of this chapter.
Vu
=
Allowable shear value for a diaphragm sheathed with any of the materials given in Tables 12-C or 12-D of this chapter, pounds per foot.
Wd
=
Total dead load tributary to a diaphragm, pounds.
Wp
=
Wall dead load tributary to an anchor, pounds.
Ww
=
Total dead load of an unreinforced masonry wall above the level under consideration or above an open front of a building, pounds.
Wwx
=
Dead load of a URM wall assigned to Level × halfway above and below the level under consideration.
Z
=
The seismic zone factor equivalent to 0.25.