1990-021-Establishing Procedures For Investigation Of UnreinforcedRESOLUTION 1990 - 21
RESOLUTION OF THE TOWN OF LOS GATOS ESTABLISHING
PROCEDURES FOR INVESTIGATION OF UNREINFORCED
MASONRY BEARING WALL BUILDINGS
BE IT RESOLVED BY THE TOWN COUNCIL OF THE TOWN OF
LOS GATOS that procedures for investigation of unreinforced masonry bearing wall
buildings shall be in accordance with Exhibit A, attached hereto and incorporated by
reference herein.
PASSED AND ADOPTED at a regular meeting of the Town Council of the Town
of Los Gatos, California, held on the 16th day of January, 1990 by the following vote.
COUNCIL MEMBERS:
AYES:
NAYES:
ABSENT:
ABSTAIN:
Joanne Benjamin, Eric D.
Robert L. Hamilton, Brent
Mayor Thomas J. Ferrito
None
None
None
SIGNED:
MAYOR OF 'I
LOS GATOS,
ATTEST:
CLERK OF THE TOWN OF LOS G OS
LOS GATOS, CALIFORNIA
Carlson
N. Ventura
WN OF LOS GATOS
FORNIA
t1
PROCEDURES FOR INVESTIGATION OF URN BEARING WALL BUILDINGS
(a) Preliminary Field Survey. From existing plans or from
field investigation prepare framing plans for roof and upper floors
noting all beams, trusses, and major lintels at bearing walls.
Prepare elevations of all URM walls noting the location and size of
all openings in the walls.
(b) Items for Special Investigation.
(1) Identify and include on the plans all parts of the
vertical load carrying system that may act as ties to lateral load
resisting elements, to determine the elements that may control the
relative displacement between the building's base and roof.
(2) Identify and include on the plans all undamaged
interior crosswalls that are continuous between the ground floor and
roof noting if these are connected to the upper floor or roof by
methods other than attachment of wall and ceiling finishes.
(3) Examine and draw the relationship of the roof or
floor framing to the ceiling framing (if separate) to determine the
method if any of their interconnection.
for any
building
frame) .
(5) Identify and include on the plans a description of
the floor and roof sheathing and their attachment. Note any
difference in materials on a given level that could lead to
substantial variations in diaphragm stiffness. Note the sizes and
locations of openings in diaphragms adjacent to URM walls. Identify
the roof covering system used and note if there are locations where
it is on a cricket or other superimposed deck.
A thorough investigation of the roof diaphragm is necessary to
permit the evaluation of the compatibility of its stiffness with the
out -of -plane stability of the URM walls of the story immediately
below the roof as required in section (c) of the analysis procedure
of this appendix.
(4) Identify and include on the plans the support system
URM walls that are not continuous to the base of the
noting the materials used for this support. (e.g. steel
Exception: Where the damage conditions of a building prevent
adequate investigation of any of the items listed
above the Director of Building Services may exempt
those upon request from the engineer performing the
investigation. Assumptions regarding structural
conditions or materials not directly observed or
taken from existing plans must be clearly noted in
the investigation report and analysis.
(c) Investigation of Existing Anchorage of URM Walls to Upper.
Floor and Roof. Indicate the locations of all existing
wall anchors on the roof /floor framing plans and specify their
spacing, size and method of connection. If existing anchors are to
be utilized as connections for resisting lateral force in the
analysis these will require testing as specified in section (e)1.
(d) Investigation of Existing URM Walls. Investigate the
following items if they occur in the building, and determine:
(1) The thickness of URM walls at all levels and location
of any changes in thickness. Substantial changes in wall thickness
or stiffness shall be considered in the analysis for out -of -plane
and in -plane wall stability. Variations in wall stiffness caused by
nominal openings such as windows and doors need not be considered.
(2) The materials used for lintels or arches at openings
and their bearing area and connection to supporting columns or
piers. The materials used for columns or piers supporting lintel
beams or arches.
(3) The heights of parapets, cornices and gable ends of
URM walls above the uppermost existing anchorages.
(4) The anchorage or bonding of terra cotta, cast -stone
brick veneer or similar facing materials to the backup wythes of
brickwork at cornices and other architectural appendages.
(5) The coursing of exterior wythes of masonry, the
bonding of wythes of masonry, and the materials used in each wythe.
An examination of the wall joint between wythes (collar joint) must
be made at each in -plane shear test location to estimate the
percentage of wythe to wythe mortar coverage and the estimate shall
be reported with the results of the tests.
Wythes of walls not bonded as described below shall be
considered veneer. The veneer wythe shall not be included in the
effective thickness of the wall used to calculate the height -to-
thickness ratio and the shear capacity of the wall and methods for
its adequate anchorage must be devised.
All units of URM bearing and non - bearing walls shall be laid
with full shoved mortar joints; all head, bed and collar joints
shall be solidly filled with mortar; and the bonding of adjacent
wythes of multi -wythe walls shall be as follows:
The facing and backing shall be bonded so that not less than 4
percent of the wall surface of each face is composed of 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. In walls where a single header does not
extend through the wall, headers from the 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.
(6) The condition of mortar joints and the location of
any existing cracks or damaged portions of wall elements.
Exception: Where the damage conditions of a building prevent
adequate investigation of any of the items listed
above the Director of Building Services may exempt
those upon request from the engineer performing the
investigation. Assumptions regarding structural
conditions or materials not directly observed or
taken from existing plans must be clearly noted in
the investigation report and analysis.
(e) Testing. The testing of existing anchorage systems must
be made to determine an average capacity where these anchors are to
be used in the analysis of the building's current resistance to
lateral forces. The testing of existing URM walls to determine the
allowable bed -joint shear is required for all buildings.
(1) Existing Wall Anchors in URM Walls. Five percent of
the existing rod anchors shall be tested in pullout by an approved
testing laboratory. The minimum tested quantity shall be four per
floor or roof level with two tests where framing is perpendicular to
the wall and two where framing is 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.
Where due to obstructions this is not possible, details of the
condition encountered and the alternate method used must be included
in the test report, with calibration adjustment for conditions where
the reaction of the test apparatus contributes to the tension value
of the anchor. The rod anchor shall be given a preload of 300
pounds prior to establishing a datum for recording elongation. The
tension load reported shall be recorded at 1/8 inch relative
movement of the anchor to the adjacent masonry wall surface.
(2) In -Place Shear Test of Brick Masonry. 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. Steel bearing plates
of the full dimension of the brick shall be inserted at each end of
the test jack. The bearing plates shall not contact the mortar
joints. The shear stress shall be based on the gross area of both
bed joints and shall be that at which movement of the adjacent brick
is first observed.
The minimum quality mortar in 80 percent of the shear tests
shall not be less than the total of 30 psi when reduced to an
equivalent zero axial stress. If the larger height -to- thickness
ratios allowed by footnotes #5 and #6 of Table A -2 are to be
utilized in the analysis, all shear tests taken at the top story
must be included in the 80 percent of the shear tests used to
determine the minimum mortar shear strength.
The minimum quantity of tests shall be as follows: At each
story not less than two per wall line or line of wall elements
providing a common line of resistance to lateral forces, with not
less than one per 1500 square feet of wall surface and not less than
a total of eight per building. In single story buildings the wall
above the lintel beam at an open storefront need not be tested.
The exact test locations shall be determined by the engineer
responsible for the investigation and noted on the documents
submitted to the Town. The tests should be conducted at least two
brick courses above or below the bond course and be distributed
vertically to include a variety of dead load surcharge conditions.
Test locations shall be representative of the mortar conditions
throughout the entire building, taking into account variations in
workmanship, variations in weathering of exterior surfaces and
variations of interior surfaces due to deterioration caused by leaks
and condensation of water and /or by other deleterious substances
contained within the building.
(a) Structural Analysis Procedures
(1) The total seismic forces should be computed in
accordance with the following equation: V = ZIRCSW
WHERE: The value of RCS need not exceed .100 for one story
buildings with an occupant load of less than 100; and need not
exceed .133 for buildings over one story above grade or those one
story buildings with 100 or more occupants.
The value of Z and I shall equal 1.0.
The value of W_ shall be as defined in Chapter 23 of the 1985
Uniform Building Code (UBC).
(2) Parts or portions of the building shall be analyzed
for lateral loads in accordance with Chapter 23 of the 1985 UBC but
not less that the value from the following equation: Fp = ICpSWp
WHERE: The product of IS need not exceed 1.0.
The value of CCp shall be as set forth in Table 23 -J of
the 1985 UBC.
The value of WWp shall be as defined in the 1985 UBC.
Exception: URM walls may be analyzed as indicated in Section
(b) below.
(3) The structural elements of the building required to
be analyzed shall include the following:
Wall height -to- thickness ratio and in -plane shear forces.
Tension bolts (in bending) if used to resist lateral forces.
Parapets for out -of -plane loading.
Diaphragm stress and diaphragm chords at floors and roof.
(4) Anchorage and interconnection of all parts, portions
and elements of the structure resisting lateral forces shall be
analyzed in accordance with the 1985 UBC and the formula in
Subsection (2) above.
A complete and continuous load path from every part or portion
of the structure to the foundation shall be shown to exist for the
required lateral forces. All parts, portions and elements of the
structural systems shall be shown to be interconnected by an
adequate positive means.
(5) Except as modified herein, the lateral analysis of
the building shall be in accordance with the analysis specified in
the 1985 UBC.
Stresses in existing materials and construction utilized to
transfer seismic forces shall conform to either those permitted by
the 1985 UBC or those permitted for types of materials and
configurations specified in Table A -3 or those described in Section
(b) below. When calculating shear or diagonal tension stresses due
to seismic forces, existing masonry shear walls may be allowed to
resist 1.0 times the required forces in lieu of the 1.5 factor
required by the 1985 UBC.
(6) Masonry walls shall be anchored to all floors and
roof to resist a minimum of 200 pounds per linear foot acting normal
to the wall at the level of the floor of roof or must be considered
inadequate. No allowable tension stress will be permitted in URM
walls, except as provided by section (b)1 below. URM walls not
capable of resisting the required design forces specified in this
section shall be deemed inadequate.
In addition to seismic forces, URM walls shall be analyzed as
specified in Chapter 24 of the 1985 UBC to withstand all vertical
loads.
Exception: URM Walls which carry no design loads other than
their own weight may be considered veneer if they
adequately anchored to elements which are not part
of the existing lateral force resisting system. See
section (d) 5 under Procedures for Investigation to
determine if existing walls must be considered as
veneer.
(7) When stresses in existing lateral force resisting
elements are due to a combination of dead and live plus seismic
loads, the allowable working stress specified in the 1985 UBC may
increased by 100 percent. However, no increase will be permitted in
the stresses allowed in Section (b) below and the stresses in
members due to only seismic and dead loads shall not exceed the
values permitted in the 1985 UBC. In addition, the calculated
tensile fiber stress due to seismic forces may be reduced by the
full direct stress due to vertical dead loads.
(b) Materials of Construction Standards
(1) Unreinforced masonry walls analyzed in accordance
with this section may provide support for roof and floor
construction and resistance to lateral loads under the conditions
set forth below.
The bonding of such walls shall conform to those specified in
Section (d) 5 of the Procedures for Investigation.
Tension stresses due to seismic forces acting normal to the
wall may be neglected if the wall does not exceed the height -to
thickness ratio and the allowable in -plane shear stresses due to
seismic loads set forth in Tables A -2 and A -4 respectively.
If the wall height -to- thickness ratio exceeds the specified
limits, the wall will be considered inadequate unless braced by
vertical members designed to satisfy the requirements of the 1985
UBC. The deflection of such bracing members at design loads shall
not exceed one -tenth of the wall thickness.
Exception: The wall may be supported by flexible vertical
bracing members that comply with the requirements of Section (a) 2
of the analysis procedure if the deflection at design loads is not
less than one - quarter nor more than one -third of the wall thickness
in the story under consideration.
Any existing or new vertical bracing used for this purpose
shall be attached to floor and roof construction independently of
existing wall anchors and the horizontal spacing of the members
shall not exceed one -half the unsupported height of the wall or ten
feet, whichever is greater.
(2) Minimum Acceptable Quality of Existing URM Walls. 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 Section (e) 2 of the Procedures for
Investigation. All masonry used to resist seismic forces shall be
undamaged by shear failure cracking and be of a quality not less
than the minimum standards established or shall be considered
inadequate.
Pointing of all masonry wall joints may be performed prior to
the testing if joints are raked and cleaned to remove loose and
deteriorated mortar. Mortar pointing shall be Type S or N, except
masonry cements shall not be used. All preparation and pointing
shall be done under the continuous inspection of a special inspector
whose reports shall be included in the testing report.
The design seismic in -plane shear stresses shall be related to
test results in accordance with Table A -4. Intermediate values
between 5 and 10 psi may be interpolated.
Compression stresses for unreinforced masonry having a minimum
design shear value of 3 psi shall not exceed 100 psi and design
tension values shall not be permitted.
(3) Existing Roof, Floors, and Walls. Existing undamaged
materials, including wood shear walls may be analyzed as part of the
lateral load resisting system, provided that the stresses in these
materials do not exceed the values shown in Table A -3. New plywood
shear walls designed in accordance with the 1985 UBC may be
recommended to strengthen portions of the existing seismic resisting
system.
Diaphragm chord stresses of horizontal diaphragms shall be
developed in existing materials or be considered inadequate.
(4) Minimum URM Wall Anchorage. All URM walls shall be
anchored at both floors and roof by existing rod anchors at a
maximum spacing of six feet and be secured to the joists or rafters
to develop the required forces. At the building corners at roof and
floor levels combination shear and tension anchors shall be located
not more than two feet horizontally from the inside corners of the
wall. Testing of existing rod anchors shall be conducted according
to Section (e) 1 of the Procedures for Investigation. Walls without
anchors having the necessary locations, spacing or capacity will be
considered inadequate.
(5) Minimum Vertical Support. Where trusses or beams
other than rafters or joists and beams supporting walls above open
storefronts are supported on URM piers, these piers must be
evaluated and shown to provide adequate vertical support during
seismic loading or shall be independently supported by a vertical
element other than the URM wall pier.
(6) Minimum Parapet Bracing. Parapets and exterior wall
appendages not capable of resisting the forces specified in Section
(a) shall be considered hazardous. The maximum height of an
unbraced URM wall parapet above the roof sheathing, shall not exceed
one and one -half times the thickness of the parapet wall.
(c) Design Check for Compatibility of Roof Diaphragm Stiffness
to the Out -of -Plane Stability of URM Walls.
(1) General. The requirements of this section are in
addition to the other analysis requirements of Section (a). This
section contains a procedure for the evaluation of the out -of -plane
stability of unreinforced masonry walls anchored to wood diaphragms.
The relative stiffness and strength of a diaphragm governs the
amount of amplification of seismic ground motion by the diaphragm,
and therefore, a diaphragm stiffness and strength related check of
the out -of -plane stability of URM walls must be performed.
(2) Definitions. The following definitions are
applicable to this section:
CROSS WALL is a wood framed wall having a height -to- length
ratio complying with 1985 UHC Section 4713(d) or Table 25 -1 and is
sheathed with any of the materials described in Table A -1. The
total strength of all cross walls located within any 40 feet length
of diaphragm measured in the direction of the diaphragm span shall
not be less than 30 percent of the strength of the diaphragm in the
direction under consideration
DEMAND CAPACITY RATIO (DCR) is a ratio where:
Demand equals lateral forces due to 33 percent of the combined
weight of the diaphragm and the tributary weight of walls and other
elements anchored to the diaphragm.
Capacity equals the diaphragm's total shear strength in the
direction under consideration as determined using the values in
Table A -1.
D = the depth of the diaphragm, in feet, measured perpendicular
to the diaphragm span.
h/t = the height -to- thickness ratio of an unreinforced masonry
wall. The height shall be measured between wall
anchorage levels and the thickness shall be measured
through the wall cross section at the level under
consideration.
L = span of diaphragm between masonry shear walls or steel
Vc the total shear capacity of cross walls in the direction
of analysis immediately below the diaphragm level being
investigated as determined by using Table A -1.
vu = Maximum shear strength in pound per foot for a diaphragm
sheathed with any of the materials given in Table A -1.
Wd = total dead load of the diaphragm plus the tributary weight
of the walls anchored to the diaphragm, the tributary
ceiling and partitions, and the weight of any other
permanent building elements at the diaphragm level under
consideration.
(3) Design Check Procedure. The demand - capacity ratio
(DCR) shall be calculated by the following equations:
Buildings without crosswalls
0.33 Wd
2 vu D
Buildings with crosswalls
0.33 Wd
DCR = ----- - - - - --
2 vu D + Vc
Diaphragm Deflection. The calculated DCR shall be the left of
the curve in Figure A -5. Where the calculated DCR is outside (to
the right) of the curve, the diaphragm's deflection limits are
exceeded and cross walls are needed to reduce the deflection.
URM Wall Out -of -Plane Stability. The DCR shall be calculated
discounting any existing cross walls. If this DCR value
corresponding to the diaphragm span is to the right of the curve in
Figure A -5, the region within the curve at and below the
intersection of the diaphragm span with the curve may be used to
determine the allowable h/t values per Table A -2.
TABLE A -1
ALLOWABLE VALUES FOR EXISTING WALLS AND DIAPHRAGMS
ONLY FOR DETERMINATION OF THE DIAPHRAGM DEMAND / CAPACITY RATIO
1. Horizontal Diaphragms I
a. Roofs with straight sheathing
and roofing applied directly
to the sheathing.
b. Roofs with diagonal sheathing
and roofing applied directly
to the sheathing.
2. Crosswalls I
a. Plaster on wood or metal
lath
b. Plaster on gypsum lath
C. Gypsum wallboard unblocked
d. Gypsum wallboard edges blocked
Footnotes:
100 PLF for seismic shear
250 PLF for seismic shear
200 PLF per side for
seismic shear
175 PLF per side for
seismic shear
75 PLF per side for
seismic shear
125 PLF per side for
seismic shear
1. Materials must be undamaged and in good condition.
TABLE A -2
ALLOWABLE VALUE OF HEIGHT -TO- THICKNESS (H /T) RATIO
OF URM WALLS WITH MINIMUM QUALITY MORTAR 1, z
One Story Building Walls
First Story Walls of
Multi -Story Buildings
Walls in Top Story of
Multi -Story Buildings
All Other Walls
---------- -------- - - -- --
Footnotes:
Buildings with
Complying Crosswalls
13 - 16 4, a, 1
16
9 - 14 4, s, 6
16
All Other
Buildings
13
15
9
13
-------- --- - - - - --
1. Minimum quality mortar shall be determined by testing described
in Section (e) 2 of the Procedures for Investigation and shall
include all top story tests in the 80 percent of tests used if
the higher ratio values permitted in footnotes 5 and 6 are used.
2. See section (c) for determination of the demand capacity ratio
values to be used in conjunction with Figure A -5 to determine if
the building can qualify as a building containing crosswalls.
3. Qualifying crosswalls are defined as interior walls of masonry
or wood frame construction with surface finish of wood lath and
plaster, 1/2 inch thick gypsum board, or solid horizontal wood
sheathing. They may not exceed 40 feet horizontal separation,
must be continuous through all stories and have a minimum length
of 1 -1/2 times the story height.
4. The minimum mortar strengths required in footnotes # 5 and 6
shall be the test shear strength reduced by the effect of axial
stress in the wall at the point of the test.
5. The larger height -to- thickness ratio may only be used when
mortar shear tests establish a minimum mortar shear strength of
not less than 100 psi or when the tested mortar shear strength
is not less than 60 psi and a. visual examination of the vertical
wythe- to -wythe (collar) joint indicates not less than 50 percent
mortar coverage.
6. Where a visual examination of the collar joint indicates not
less than 50 percent mortar coverage and the minimum mortar
shear strength is greater than 30 psi but not less than 60 psi,
the allowable h/t ratio may be determined by linear
interpolation between the larger and smaller values given in
direct proportion to the mortar shear strength.
TABLE A -3
ALLOWABLE STRESS VALUES FOR EXISTING MATERIALS
FOUND TO BE UNDAMAGED AND IN GOOD CONDITION
1. Horizontal Diaphragms
a. Roofs with straight sheathing
with the roof covering applied
directly to the sheathing.
b. Roofs with diagonal sheathing
with the roof covering applied
directly to the sheathing
C. Floors with straight tongue
and groove sheathing
d. Floors with straight sheathing
and finished wood flooring
e. Floors with diagonal sheathing
and finished wood flooring
f. Floors or roofs with straight
sheathing and plaster applied
to the joists or rafters below
2. Shear Walls
a. Wood stud walls with lath and
plaster in undamaged condition
3. Plain Concrete Footings
4. Douglas Fir Wood P
5. Reinforcing Steel 1
6. Structural Steel 1
Footnotes:
100 PLF for seismic shear
400 PLF for seismic shear
150 PLF for seismic shear
300 PLF for seismic shear
450 PLF for seismic shear
Add 50 PLF to the allowable
values for items la and 1c.
100 PLF each side for
seismic shear
f'c = 1500 PSI unless
otherwise shown by tests
Same as 1985 UBC values for
No. 1 Douglas Fir i
f't = 18,000 PSI maximum 1
f't = 20,000 PSI maximum i
1. Stresses may be increased for combination of loads as specified
in Section (a) 7 of the Standards for Analysis and Evaluation.
TABLE A -4
ALLOWABLE SHEAR STRESS FOR TESTED URM W ALLS
80 Percent of Test Results Allowable In- P1_ane Shear
in PSI Not Less Than: in PSI Based ont Gross Area 1
--------------------------------------- ----- --- ---- ------------ - - -- --
30 + Axial Stress
40 + Axial Stress
50 + Axial Stress
100 + Axial Stress or more I
----- ------------ ---------- -- - - - - --
Footnotes:
3.0
4.0
5.0
10.0 (maximum)
----- -- --- ----- --- - - - - - --
1. The allowable shear stress may be increased by addition of 10
percent of the axial stress due to the weight o f the wall
directly above.
120 O3
60 O
0` I I I i I i
0 1 2 3 4 5 6
DEMAND /CAPACITY RATIO = 0.33Wd / 2vuD OR 0.33Wd / (2vuD + Vc)
FIGURE A -5
12
540
Oi
REGION OF DEMAND /CAPACITY
RATIOS WHERE CROSSWALLS
480
MAY BE USED TO INCREASE
H/T RATIOS
O2
REGION OF DEMAND /CAPACITY
RATIOS WHERE H/T RATIOS OF
"WITH
420
CROSSWALLS" MAY BE
USED
o
O3
REGION OF DEMAND /CAPACITY
360
RATIOS WHERE H/T RATIOS OF
"ALL OTHER BUILDINGS" SHALL
BE USED
H
W
W
z
300
z
6
\
�
240
E
\
c5
z
�
x
6
180
0
120 O3
60 O
0` I I I i I i
0 1 2 3 4 5 6
DEMAND /CAPACITY RATIO = 0.33Wd / 2vuD OR 0.33Wd / (2vuD + Vc)
FIGURE A -5
12