Bakersfield Municipal Code Ch. 15.40 Earthquake Hazard Reduction in Existing Unreinforced

MASONRY BEARING WALL BUILDINGS*

• Prior ordinance history: Ords. 3302 and 3464.

The purpose of this chapter is to promote public safety, health and welfare by reducing the risk of death or injury that may result from the effects of earthquakes on unreinforced masonry buildings.

The provisions of this chapter establish minimum standards for structural seismic resistance primarily to reduce the risk of death or injury, but cannot prevent loss of life or injury or prevent earthquake damage to an existing building even though it complies with these standards. (Ord. 3552 § 1, 1993)

The provisions of these requirements shall apply to all buildings having unreinforced masonry bearing walls as defined herein. It is recognized that strengthening was done to many unreinforced masonry buildings following the 1952 Kern County earthquake. The engineer or architect retained by the building owner and the city building official shall give full consideration to any strengthening done when analyzing the existing condition of the building as required by this chapter. Where strengthening was done which may not fully comply with the provisions of this chapter, approval may be granted by the city building official if the building’s condition complies with the intent of this chapter.

Nothing in this chapter shall prevent the building owner, his or her architect or engineer from employing accepted alternative methods to prove the minimum seismic safety of a building. In the event an alternative method is employed by the building owner, his or her architect or engineer which is not accepted by the city building official, the building owner shall have the right to appeal that decision to the board of building appeals. (Ord. 3552 § 1, 1993)

For the purpose of this chapter, certain terms are defined as follows:

A. “Cross walls” means interior walls of masonry or wood stud construction. In order to be considered as a cross wall within the intent of this chapter, cross walls shall be not more than forty feet apart in each story, and shall be full story height between diaphragms. Existing cross walls shall be a minimum length of one and one-half times the story height. Existing wood frame cross walls shall be sheathed with one of the following: wood lath and plaster, one-half inch thick gypsum wallboard two sides, or solid one inch nominal thickness straight or diagonal wood board sheathing. New cross walls shall have a rational shear path to the ground, and shall be constructed of materials that are assigned allowable shear values in Chapter 25 or 47 of the Building Code, and shall have a total shear capacity equivalent to that of a wall one and one-half times the story height that is sheathed with a material that has an allowable shear value of one hundred fifty pounds per foot.

B. “Unreinforced masonry bearing wall” means a masonry wall having all of the following characteristics:

1. Provide the vertical support for a floor or roof.

2. The total superimposed load is over one hundred pounds per linear foot.

3. The area of reinforcing steel is less than twenty-five percent of the minimum steel ratios required by the
Building Code for reinforced masonry.

C. “Architect or engineer” means California licensed architect or California licensed civil or structural engineer in responsible charge of the structural design work for the project. (Ord. 4715 § 1, 2012; Ord. 3552 § 1, 1993)

A. Existing Materials. All existing materials utilized as part of the lateral force resisting system shall be in sound condition or shall be removed and replaced with new materials.

B. Existing Unreinforced Masonry.

1. General. Unreinforced masonry walls shall be tested as specified in this subsection. Masonry that does
not meet or exceed the minimum standards established by this chapter shall be removed and replaced by

new materials and anchored to supporting elements; design of anchorage shall comply with requirements for anchorage of masonry veneer of Section 15.40.070(G).

2. Lay-Up of Walls. The facing and backing shall be bonded so that not less than four percent of the wall
surface of each face is composed of solid headers extending not less than four inches into the backing. The
distance between adjacent full-length headers shall not exceed twenty-four inches either vertically or
horizontally. In walls in which a single header does not extend through the wall, headers from opposite sides
shall overlap at least four inches, or headers from opposite sides shall be covered with another header
course overlapping the header below at least four inches. 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 of the wall unless it is bonded and anchored to the backing in a
manner acceptable to the city building official.

3. Mortar.

a. Tests. The quality of mortar in unreinforced masonry walls shall be determined by performing in-
place shear tests in accordance with Building Code Standard (24-7). Alternative methods of testing to
establish compliance with the minimum requirement of Section 15.40.040(B)(3)(d)(iv) may be approved
by the city building official.

b. Location of Tests. Shear tests shall be taken at locations representative of the mortar conditions
throughout the entire building. The exact test location shall be determined at the building site by the
architect or engineer. An accurate record of such tests and their location in the building shall be
recorded and these results shall be submitted to the city building official for approval as part of the
structural analysis.

c. Number of Tests. The minimum number of tests per wall or line of wall elements providing a
common line of resistance to lateral forces shall be as follows: Two tests per wall with a minimum total
number of eight tests or one test per one thousand five hundred square feet of wall area, whichever
results in the greater number of tests.

d. Minimum Quality Mortar.

i. Mortar shear test values, vto, shall be obtained for each in-place shear test in accordance with the following equation:

Vto = (Vtest - PD+L)/AW (7-1)

Where:

Vto = Mortar shear test value, in psi.

Vtest = Shear stress at incipient cracking for each in-place test per Standard No. 24.7.

PD+L = Actual dead plus live load in place at the time of testing, in pounds.

AW = Area of the wall supporting PD+L at each in-place shear test.

ii. Individual unreinforced masonry wall with vto less than thirty psi shall be pointed prior to
retesting.

iii. The mortar shear strength, vto is the value in psi representing a minimum of eighty percent of
all of the mortar shear test values, vto.

iv. Unreinforced masonry with mortar shear strength, vt less than thirty psi shall be removed or
pointed and retested.

e. Pointing. All deteriorated mortar joints in unreinforced masonry walls shall be pointed according to
Standard No. 24-9. Nothing shall prevent pointing with mortar of all masonry wall joints before the tests
are made. (Ord. 4715 § 1, 2012; Ord. 3552 § 1, 1993)

A. Pointing. Special inspection shall be provided during preparation and mortar pointing.

Exception: pointing may be performed without special inspection where approved by the architect or engineer.

B. Existing Floor or Roof Level Wall Anchors.

1. Floor Level Tension Anchors Embedded in Brick. If existing rod anchors embedded in brick are to be utilized
as all or part of the required wall anchorage system at the floor level, not less than five percent of such
existing rod anchors shall be tested by an approved testing laboratory or under the supervision of the architect or engineer. The minimum number of anchors 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 but not less than five
percent of the total number of existing tension anchors at each level. 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 three hundred 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. Ends of existing anchors shall be secured into the wood
framing by a positive mechanical attachment.

2. Floor or Roof Level Anchors Embedded in Concrete. Existing rod anchors at floor or roof levels that are
embedded in existing concrete or gunite applied to the opposite side of the wall need not be tested provided
such embedment is verified by observation and report by an approved testing agency or the architect or
engineer for at least one anchor, and all anchors observed, in each wall at each level for which such the
anchors are to be utilized as all or part of the required wall anchorage system. Other evidence of such

embedment may be approved by the city building official.

C. Testing of Bolts. One-fourth of new embedded bolts in unreinforced masonry walls shall be tested by a testing laboratory or architect or engineer using the procedure of Building Code Standards No. 24-8.

Exception: special inspection in accordance with the building code or continuous observation by the architect or engineer may be provided during installation in lieu of testing.

D. Required Reports. The architect or engineer or testing agency shall submit a signed report to the city building official for each test, observation or inspection required by Sections 15.40.050 and 15.40.070(G). The report shall state the test, observation, or inspection performed, the date, the results of each individual test, observation or inspection, (including those that fail to satisfy the intent of this chapter) and whether to the best of the knowledge of the preparer of the report, the results indicate compliance with this chapter. (Ord. 4715 § 1, 2012; Ord. 3552 § 1, 1993)

A. Tension Anchors. Allowable values for tension anchors are given in Table No. 1-B. A one-third increase is not allowed for values listed in this table.*

B. Other Materials. Allowable values not specified in this chapter shall be as specified elsewhere in the 1991 Building Code. (Ord. 4715 § 1, 2012; Ord. 3552 § 1, 1993)

• Editor’s Note: The tables referred to herein may be found in Section 15.40.080.

A. Lateral Force on Elements of Structures and Nonstructural Components. Parts or portions of structures, nonstructural components and their anchorage to the main structural system shall be designed for lateral forces in accordance with the following formula:

Fp = Cp Wp (10-1)

Wp shall be as defined in Section 2332. The value of Cp need not exceed the values set forth in Table No. 1-C.*

B. Height to Thickness Limitations. Unreinforced masonry wall height to thickness ratios shall not exceed the ratios set forth in Table 1-D.* If a wall height to thickness ratio exceeds the specified limits, the wall shall be laterally supported by bracing members complying with subsection (C)(1) or (C)(2). Bracing systems shall be designed in accordance with subsection A. The wall thickness may include the thickness of plaster, stucco or concrete that is determined by the architect or engineer to be bonded to the full height of the wall between wall anchors.

C. Bracing Methods.

1. Vertical Bracing Members. Vertical bracing members shall be attached to floor and roof construction for
their design loads independent of required wall anchors. Horizontal spacing of vertical bracing members shall
not exceed one-half the unsupported height of the wall nor ten feet. Deflection of such bracing members at
design loads, shall not exceed one-tenth of the wall thickness.

2. Wall Bracing. The wall height may be measured to bracing elements other than a floor or roof. Horizontal
spacing of the bracing elements and wall anchors shall not exceed six feet on center nor six times the wall
thickness, whichever is less. Bracing elements shall be detailed to minimize the horizontal displacement of
the wall by the vertical displacement of the floor or roof.

D. Wall Anchorage.

1. Anchor Locations. Unreinforced masonry walls shall be anchored at the roof and floor levels in order to
resist the forces specified in this section.

2. Tension Anchor Requirements. Tension anchors shall have a maximum spacing of six feet or six times the
wall thickness, whichever is less, and shall comply with the requirements set forth in Table No. 1-B.* Tension
anchors used to resist required forces may be assumed to develop the allowable values listed in Table No.
1-B.* Tension anchors shall be secured to the rafters or joists to transfer the required forces into the roof or
floor sheathing.

3. New Tension Anchors. New tension anchors installed to meet the requirements of this section shall be
combination tension and shear bolts, and shall be secured to the roof or floor framing to develop tension and
shear forces into the diaphragm.

4. Minimum Wall Anchorage Forces. New or existing tension anchors shall anchor masonry walls to each floor or roof with a capacity to resist a minimum tension force determined by Formula (10-1) or two hundred pounds per linear foot whichever is greater, acting normal to the wall at the level of the floor or roof. In addition, new combination tension and shear bolts shall be connected to the framing to resist a shear force of two hundred pounds per foot acting parallel to the wall at the level of the floor or roof.

   Exception: where the roof or floor sheathing consist only of one inch nominal thickness single board sheathing, new combination tension and shear bolts may be connected to the framing to resist a shear force of one hundred pounds per foot acting parallel to the wall.

   The city building official may approve an analysis by the architect or engineer that demonstrates that the required shear capacity is less than required by this section.

   5. Anchors at Corners. New combination tension and shear bolts at the roof and floor levels, if required by this section, shall be provided within two feet horizontally from the inside of the corners of the walls.

E. Parapets. Parapets and exterior wall appendages not capable of resisting the forces specified in this section shall be removed, stabilized or braced to ensure that the parapets and appendages remain in their original position.

The maximum height of an unbraced unreinforced masonry parapet above the level of tension anchors shall not exceed one and one-half times the thickness of the parapet wall. If the required parapet height exceeds this maximum height, a bracing system designed for the force determined by formula (10-1) shall be installed to support the parapet. Parapet corrective work shall be performed in conjunction with the installation of tension roof anchors.

The minimum height of a parapet above the wall anchor shall be twelve inches.

Exception: If a reinforced concrete beam is provided at the top of the wall, the minimum height above the wall anchor may be six inches.

F. Mortar Joints. All deteriorated mortar joints in unreinforced masonry walls shall be pointed with Type S or N mortar. Masonry cements shall not be used. Prior to any pointing, the wall surface must be raked and cleaned to remove loose and deteriorated mortar. All preparation for pointing shall be inspected by the architect or engineer or their representative.

G. Masonry Veneer.

1. Veneer shall be anchored to the structure of the building with approved anchor ties conforming to the
required design capacity specified in the building code and placed at a maximum spacing of twenty-four
inches with a maximum supported area of two square feet.

a. Exception:

1. Existing masonry veneer anchor ties may be acceptable provided the ties are in sound condition and conform to the following minimum size, maximum spacing and material requirements: Existing masonry veneer anchor ties shall be corrugated galvanized iron strips not less than one inch in width, eight inches in length and one-sixteenth inch 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 seventeen inches on center horizontally. As an alternate, such ties may be laid in every fourth course vertically at a spacing not to exceed nine inches on center horizontally. 2. Masonry veneer, no portion of which six feet is above grade need not be anchored.

   2. The location and condition of existing veneer anchor ties shall be verified as follows:

      a. The architect or engineer shall determine the location and spacing of the ties.

      b. The veneer shall be removed from not less than four locations designated by the architect or engineer for the architect or engineer’s evaluation.

      c. The architect or engineer shall report to the city building official the veneer anchor tie locations and spacings, their evaluation of the condition and effectiveness of the veneer anchor ties, and their recommendations whether or not the existing veneer anchor ties need to be supplemented with new veneer anchor ties.

   3. Unreinforced masonry walls which carry no loads other than their own weight may be considered as veneer if they are adequately anchored to new supporting elements. (Ord. 3552 § 1, 1993)

• Editor’s Note: The tables referred to herein may be found in Section 15.40.080.

For time limits and technical specifications see Table Nos. 1-A, 1-B, 1-C, and 1-D; Standard Nos. 24-7 and 24-9.

TABLE NO. 1-A
TIME LIMITS FOR PROCEEDINGS FOLLOWING DECEMBER 31, 1998
DEADLINE

Required Action By Obtain Building Commence Complete
Owner Permit Within Construction Within Construction Within

Anchorage 1 Year(1) 180 Days(2) 1 Year(2)
Installation

Buildings to be 1 Year(1) 180 Days(2) 1 Year(2)
Demolished

(1) Measured from the date of the order.

(2) Measured from the date of building permit issuance.

(3) These time limits shall not apply to a change of occupancy involving a Group A Occupancy having an occupant load of 100 or more.

TABLE NO. 1-B
ALLOWABLE VALUES FOR TENSION ANCHORS

Type of Installation Allowable Values(1)

EXISTING TENSION ANCHORS: Anchors at Allowable shall be 40% of the average of
floor level embedded in brick (to be tested the tests for anchors having same wall
per Section 15.40.050B). thickness and joist orientation.

Anchors at floor or roof levels embedded 1800 lb. per anchor.
in existing concrete or gunite on the
opposite side of the wall.(2)

TENSION BOLTS: Bolts extending entirely 1800 lbs. per bolt. 900 lbs. for 2 wythe
through unreinforced masonry walls walls.
secured with bearing plates on far side of
a 3 wythe minimum wall with a bearing
plate having an area of at least 30 square
inches.(2)(3)

COMBINATION TENSION AND SHEAR Same as for tension bolts.
BOLTS: Combination tension and shear
bolts are tension bolts centered in a 2½
inch diameter by 8 inch minimum depth
hold with dry-pack or nonshrink grout
around the circumference of bolt.

EMBEDDED BOLTS: Bolts extending to the 1200 pounds.
exterior wall with a 2½ inch round plate
under the head and drilled at an angle of
22½ degrees to the horizontal. Bolts shall
be centered in 2½ inch diameter holes
with dry-pack or non-shrink grout around
circumference of bolts. Bolts shall be
tested per Section 15.40.050C.

(1) A one-third increase in allowable stresses is not allowed for the tabulated values. The allowable capacity shall not be greater than the capacity of the connection to the floor or roof framing.

(2) Bolts to be ½ inch minimum in diameter.

(3) Drilling for bolts and dowels shall be done with an electric rotary drill. Impact tools shall not be used for drilling holes or tightening anchors and shear bolt nuts.

TABLE NO. 1-C
HORIZONTAL FORCE FACTOR “Cp” FOR PARTS OR PORTIONS OF
BUILDINGS OR OTHER STRUCTURES

Part or Portion of Buildings Direction of Force Value of Cp

Exterior bearing and nonbearing walls; interior Normal-to-flat 0.3
bearing walls and partitions; interior nonbearing walls surface
and partitions over 10 feet in height.

Cantilever parapet and other cantilever walls, except Normal-to-flat 1.00
retaining walls. surface

Exterior and interior ornamentations and Any direction 1.00
appendages.

Prefabricated structural elements, other than walls, Any horizontal 0.30
with force applied at center of gravity of assembly. direction

Connections for exterior panels or elements. Any direction 2.00

TABLE NO. 1-D
ALLOWABLE VALUE OF HEIGHT-THICKNESS RATIO OF
UNREINFORCED
MASONRY WALLS WITH MINIMUM QUALITY MORTAR

Buildings with All Other Buildings
Crosswalls As
Defined by Section
15.40.030

Walls of one-story 16 13
buildings

First-story walls of 16 15
two-story buildings

Walls in top story of 14 9
multi-story
buildings

All other walls 16 13

(Ord. 3552 § 1, 1993)