This document provides an overview of masonry structures and materials. It discusses the mechanical behavior of masonry walls, arches, vaults and domes. Traditional masonry construction techniques are compared to modern methods. Various masonry elements like walls, columns and beams are examined. Finally, common masonry materials like fired clay units are described in terms of their manufacturing, properties and testing standards. The document serves as teaching material for a course on seismic design and assessment of masonry structures.
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Lesson1
1. Seismic design and assessment of
Seismic design and assessment of
Masonry Structures
Masonry Structures
Course taught by:
Daniel P. Abrams
Professor of Civil Engineering
University of Illinois at Urbana-Champaign
and
GuidoMagenes
Associate Professor of Strutural Design
Università di Pavia and ROSE School
October 2004
Masonry Structures, lesson 1 slide 1
Introduction
Masonry construction is the oldest and most
common building technique, together with timber
construction.
The word “masonry” actually encompasses
techniques which may differ substantially
depending on type and shape of materials and
construction methods.
A screening of the hystorical masonry heritage
shows the wide variety of construction systems
which fall under the name of “masonry”.
Masonry Structures, lesson 1 slide 2
3. Introduction – Stone masonry
Masonry Structures, lesson 1 slide 5
Introduction – Masonry w. clay units
early sundried mud
elements
Masonry Structures, lesson 1 slide 6
4. Introduction – Mixed stone-clay units
“sacco” wall
Masonry Structures, lesson 1 slide 7
Mechanical behaviour of masonry
Good behaviour under vertical compression
Low or negligible tensile strength; in particular the
tensile strength of a mortar joint can be of the order of 1/30
of the compressive strength of masonry
- problems for the resistance to horizontal loading (wind,
earthquake)
- horizontal structures were traditionally built with timber or were
arched or vaulted; nowadays floor slabs and roofs are usually built
with materials which can resist tensile stresses and therefore
flexure (r.c., steel, timber..).
Masonry Structures, lesson 1 slide 8
5. Mechanical behaviour of masonry structural elements - Walls
R ⋅ r = W ⋅ a + Vy / 2
Vy
r =a+
2W
Equilibrium of mud brick wall at Palace of Ctesiphon, Iraq
Masonry Structures, lesson 1 slide 9
Mechanical behaviour of masonry structural elements - Walls
Effect of wind pressure on the line of thrust
Masonry Structures, lesson 1 slide 10
6. Mechanical behaviour of masonry structural elements - Walls
Consider a wall subjected to a uniformly distributed horizontal pressure q (e.g. wind) and to self weight
(γ=18 kN/m3).
Assuming zero tensile strength at the base of the wall, where a crack is assumed to develop under the
effect of horizontal forces, evaluate the value of q which leads to overturning of the wall.
Consider a wall strip of unit length (l = 1 M ov − M res = 0
m): q ⋅ h2 t
− P⋅ = 0
2 2
h h/2
P = γ ⋅ t ⋅ h self weight of wall (l = 1)
Q = q ⋅ h resultant horizontal force (l = 1)
q P
t
Qu = P ⋅
q h
h/2 if t = 0.12 m h = 3 m
we have overturning for Qu = 0.259 kN
Rh
l
Rv if l = 3 m Qu = 0.777 kN
t t/2
Masonry Structures, lesson 1 slide 11
Mechanical behaviour of masonry structural elements - Walls
Same wall with vertical load N at the top, with some eccentricity e w. respect to centreline of wall:
e
Considering a wall strip of unit length (l = 1 m):
N
M rib − M stab = 0
q ⋅ h2 t ⎛ t⎞
− P ⋅ − N ⋅⎜e + ⎟ = 0
h/2 2 2 ⎝ 2⎠
P = γ ⋅ t ⋅ h self weight of wall (l = 1)
q P
Q = q ⋅ h resultant horizontal force (l = 1)
h/2 the presence of a vertical load increases
the resistance to overturning
t ⎛ t + 2e ⎞
Rh
Qu = P ⋅ + N ⋅ ⎜ ⎟ high h/t reduces the resistance to
h ⎝ h ⎠ overturning
Rv
In general, resistance of unreinforced masonry (urm) to out-of-plane
t/2 loading is low.
Masonry Structures, lesson 1 slide 12
7. Mechanical behaviour of masonry structural elements - Walls
On the contrary, the resistance of walls to in-plane loading can be high, and
therefore the structural conception of an urm building must be similar to a “box”,
where walls are positioned along at least two orthogonal directions.
Touliatos, 1996
Masonry Structures, lesson 1 slide 13
Mechanical behaviour of masonry structural elements – Spanning
across: beams or lintels
Lions Gate in Mycenae (1250 B.C.) equilibrium relies on
tensile strength of stone
Masonry Structures, lesson 1 slide 14
8. Mechanical behaviour of masonry structural elements – Spanning
across: primitive arch
Position of the thrust line at
midlength of one of the stones:
WL W ⎛L⎞ L
a+ ⎜ ⎟ =W
4h 2 ⎝8⎠ 4
3
a= h
4
By considering other sections, it can be
shown that if the thickness of the stones
Solid abutments are necessary to is approximately constant, then the
provide horizontal restraint complete thrust line is parabolic
Masonry Structures, lesson 1 slide 15
Mechanical behaviour of masonry structural elements – Spanning
across: primitive arch
even
bearing at
abutments
more likely
situation
Masonry Structures, lesson 1 slide 16
9. Mechanical behaviour of masonry structural elements – Spanning
across: true arches
Masonry Structures, lesson 1 slide 17
Mechanical behaviour of masonry structural elements – Spanning
across and enclosing spaces: vaults and domes
corbelled
dome: tomb of
Agamennon
(1300 BC)
true domes
Pantheon, Rome, AD 123
Masonry Structures, lesson 1 slide 18
10. Mechanical behaviour of masonry structural elements – Collapse
of masonry arch
Limits of a “working
stress” approach: the
stress at a point at a
section does not tell us
how far we are from
collapse
Masonry Structures, lesson 1 slide 19
Masonry buildings: from single-storey to multistorey
Contemporary single-story masonry buildings are very similar to simple
ancient domestic buildings such as those built by the Romans. Stability was
achieved using thick walls that were buttressed by orthogonal end walls
apartment block
or “insula” in
Ostia
Multistorey masonry buildings were constructed by Romans as early as the
1st century AD. They had a cellular layout with brick-faced concrete walls
about 1 m thick.
Masonry Structures, lesson 1 slide 20
11. Masonry buildings: from single-storey to multistorey
When multistorey commercial
buildings developed, open space
was required internally, and internal
walls were replaced by timber and
then iron columns to support the
floors.
Walls had variable thickness to
attain stability under wind forces..
This solution, however has lower
stability vs. horizontal loads when
compared to the “cellular” solution
Masonry Structures, lesson 1 slide 21
Modern masonry buildings: what solution for stability against
horizontal loads
HORIZONTAL LOADS
UNREINFORCED
use of reinforcement
MASONRY
REINFORCED MASONRY
cellular layout (many
walls, less free surface) or
thicker walls, limited CONFINED MASONRY
interstorey height, low
slenderness, to avoid out-
of-plane collapse
Masonry Structures, lesson 1 slide 22
12. Modern masonry construction
Classification of Modern Masonry Construction
• engineered construction vs. non-engineered construction
• structural masonry vs. non-structural masonry
• reinforced masonry vs. unreinforced masonry
• partially or fully grouted vs. ungrouted
• clay-unit masonry vs. concrete-unit masonry
• solid units vs. hollow units
• single wythe vs. multiple wythe
• cavity walls vs. composite walls
• bearing walls vs. nonbearing walls
• running bond vs. stack bond
• working stress design vs. strength design
Masonry Structures, lesson 1 slide 23
Main typologies of modern structural masonry
unreinforced
masonry
confined masonry
reinforced masonry
Masonry Structures, lesson 1 slide 24
13. Masonry elements - Walls
single-leaf
running
bond
stack bond:
bad structural
behaviour
Masonry Structures, lesson 1 slide 25
Masonry elements - Walls
Solid walls
Composite
walls
Masonry Structures, lesson 1 slide 26
14. Masonry elements - Walls
Reinforced masonry
walls: examples
f) Reinforcement in vertical holes and in
bedjoints
Masonry Structures, lesson 1 slide 27
Masonry elements - Walls
Cavity walls:
examples
The two wythes share the structural
function
Masonry Structures, lesson 1 slide 28
15. Masonry elements - Walls
Veneer walls
(non
structural)
Nonstructural partition
walls
Masonry Structures, lesson 1 slide 29
Masonry elements - Walls
Diaphragm
walls or
utility walls
The longitudinal wythes are connected by masonry webs to
achieve composite structural action in compression and
vertical bending
Masonry Structures, lesson 1 slide 30
16. Masonry elements – Columns and pilasters
Columns
Pilasters
Masonry Structures, lesson 1 slide 31
Masonry elements – Columns and pilasters
Reinforced
masonry
columns and
Pilasters
Masonry Structures, lesson 1 slide 32
17. Masonry elements – Beams and lintels
Reinforced
masonry
beams and
lintels
Masonry Structures, lesson 1 slide 33
Masonry materials
fired clay
units
of most
units (bricks, blocks) interest
concrete
usually with approx. units
parallelepiped shape
calcium
silicate units
+
stone units
mortar
sand + binder (cement, in case reinforcement and
+ grout (reinforced masonry)
lime) + water
Masonry Structures, lesson 1 slide 34
18. Masonry materials. Units
mechanical
properties
ease of
construction
durability and properties of the
resistance to unit
weather
fire resistance
thermal and acoustic
insulation, healthiness
Masonry Structures, lesson 1 slide 35
Masonry materials. Fired clay units
Normal or lightweight (better for thermal insulation).
They have holes (vertical or horizontal) to reduce weight/ allow grip/
accommodate reinforcement (reinforced masonry)
Fired clay as a material can have a very high compression strength (up
to 130 N/mm2), however units, especially when perforated, show a lower
strength.
Compressive strength (fb ) in Europe is usually referred to the gross area of
the element normal to the bed face, regardless of hole percentage.
However, especially for perforated units in structural masonry, also the
strength parallel to bedjoints (f'b) is of interest.
Typical values of compressive strength for fired clay units: 2-3 N/mm2
for lightweight units with 50-55 % percentage of holes; 30-50 N/mm2 for
holes percentages around 30-40%;
Masonry Structures, lesson 1 slide 36
19. Masonry materials. Fired clay units
Eurocode 6
requirements
for the
grouping of
masonry units
(all types of
material)
Masonry Structures, lesson 1 slide 37
Raw Materials used in Clay Units
• surface clays
• shales
• fire clays
• iron oxides
• hydrated silicate of alumina
• miscellaneous impurities: calcium, magnesium, sodium,
titanium, potassium
Ref: ASTM C62 Standard Specification for Building Brick
Masonry Structures, lesson 1 slide 38
20. Manufacturing of Clay Units
• Stiff mud process: (12% – 15% water)
pug mill
pug mill mixer
mixer extruder
extruder wire cutter
wire cutter kiln
kiln
grind clays mix clays form clay strip cut bricks fire at 1400-2370oF
• Soft mud process: (20% – 30% water) bricks are formed in molds
• Dry press process: ( 7% – 10% water) bricks are pressed with
500 – 1500 psi pressure
Ref: BIA Tech Note 9 Manufacture, Classification and Selection of Brick
Masonry Structures, lesson 1 slide 39
Engineering Properties of Clay Units
• absorption
• durability
• volume change
• compressive strength
• flexural strength
• thermal conductivity
• acoustics
• fire resistance
• elastic modulus
Masonry Structures, lesson 1 slide 40
21. Physical Characteristics of Clay Units
• color
• texture
• form
• size
• dimensional tolerance
Masonry Structures, lesson 1 slide 41
Durability Grades for Clay Units
Weathering Index = number of freeze-thaw days times winter rainfall (inches)
< 50 50–500 > 500
vertical surfaces
in contact with earth MW SW SW
not in contact with earth MW SW SW
horizontal surfaces
in contact with earth SW SW SW
not in contact with earth MW SW SW
SW severe weathering resists frost action
MW moderate weathering freeze, but not subjected to water
NW no weathering no freeze
Compressive strength and water absorption are both good indexes of freeze-thaw resistance
because both are related to firing and fusing of clay particles, and porosity.
Masonry Structures, lesson 1 slide 42
22. Water Absorption
ASTM C67: Standard Test Methods for Sampling and Testing Brick
weight of water absorbed after 24 hours in cold water
cold water absorption =
dry weight
primary pores
C
saturation coefficien t = filled by cold
secondary pores
B water
filled by boiling
water
C = absorption after 24 hours in cold water
B = total absorption after boiling for 5 hours and
24 hours in cold water
Saturation coefficient is one measure of freeze-thaw durability.
Masonry Structures, lesson 1 slide 43
Water Absorption
ASTM C67: Standard Test Methods for Sampling and Testing Brick
30 in 2
initial rate of absorption = IRA = ( W1 − W ) ≤ 30 grams
Anet
where: IRA = initial rate of absorption
W1 = weight of brick after 1 minute in 1/8” of water
W = dry weight of brick
Anet = net area of unit
high IRA is undesirable because of:
• rapid drying of mortar
• poor bond strength between brick and mortar
• poor water penetration of masonry
• pre-wetting of unit may be required if IRA > 30 grams/minute
Masonry Structures, lesson 1 slide 44
23. Unit Compressive Strength (North America)
ASTM C67: Standard Test Methods for Sampling and Testing Brick
strength is dependent on:
• clays
• type of manufacturing process
• degree of firing P
• hole pattern
flat - wise compressive strength = f'a = P
Anet
If Anet > 75% Agross then use Anet = Agross
since cores will add strength because of:
• uniform drying and shrinkage
• keying action between mortar and brick
Compressive strength of North American bricks can range from 3,000 to
30,000 psi. Nominal strengths are typically in the range of 8,000 to 15,000 psi.
Masonry Structures, lesson 1 slide 45
Unit Properties
ASTM C67: Standard Test Methods for Sampling and Testing Brick
Modulus of Elasticity of Clay-Masonry Units
Eb = 1400 ksi to 5000 ksi
Modulus of Rupture of Clay-Masonry Units
P
t
M = P L = PL
2 2 4
f r = mod ulus of rupture = M = PL/4 = 1.5 PL
L S bt 2 /6 bt 2
b
Masonry Structures, lesson 1 slide 46
24. Expansion Coefficients for Clay Units
Coefficient of Thermal Expansion
2.8 x 10-6 per °F to 3.9 x 10-6 per ºF
Moisture Expansion
200 in/in x 10-6
Freezing Expansion
148 in/in x 10-6
Ref: Grimm, Clayford T., Design of Masonry for Volume Changes, The Masonry
Society Journal, October 1999, pg. 12.
Masonry Structures, lesson 1 slide 47
Concrete Masonry Units
Most common typologies:
•units with normalweight aggregates,
obtained mixing cement, selected aggregates
and admixtures;
•units with lightweight aggregates (e.g.
expanded clay, expanded clayey schist,…)
Typical compressive strength (referred to
the gross area) : from 2-3 N/mm2 in the
case of lightweight concrete, up to about
20-30 N/mm2 .
Masonry Structures, lesson 1 slide 48
25. Concrete Masonry Units
ASTM C90: Standard Specification for Load-Bearing Concrete Masonry Units
Dimensions of CMU’s
Nominal dimensions are specified in sequence
of width times height times length. Specified
dimension is 3/8” less than nominal
dimension. Actual dimension of unit is height
within 1/8” of specified dimension.
For example, an 8” x 8” x 16” unit is
specified to be 7 5/8” x 7 5/8” x 15 5/8” width
length
and actual block may be plus or
minus 1/8” from these dimensions.
Ref: NCMA TEK 2-1A Typical Sizes and Shapes of Concrete Masonry Units
NCMA TEK 2-3A Architectural Concrete Masonry Units
Masonry Structures, lesson 1 slide 49
Concrete Masonry Units
Raw Materials used in Concrete Masonry Units
• Portland Cement
• pozzolans: reduce expansive characteristics and aggregates; add sulfate
resistance
• other admixtures: air entrainment, pigments, water repellents, etc.
• aggregates: normal weight and lightweight
Ref: NCMA TEK 1-1A ASTM Specification for Concrete Masonry Units
NCMA TEK 18-2 Sampling and Testing Concrete Masonry Units
Masonry Structures, lesson 1 slide 50
26. ASTM Designations of Concrete Masonry Units
1. ASTM C90: load-bearing CMU’s
Type I: moisture controlled units
Type II:non-moisture controlled units
lightweight units: less than 105 pcf
medium weight units: from 105 to 125 pcf
normal weight units: more than 125 pcf
2. ASTM C55: building brick: Grades N and S
3. ASTM C129: non-load-bearing units
4. ASTM C744: prefaced concrete and calcium silicate masonry units
5. ASTM C73: calcium silicate face brick
Masonry Structures, lesson 1 slide 51
Method of Manufacture: Concrete Masonry Units
separate and
separate and
weigh
weigh mixing
mixing molding
molding ejection
ejection curing
curing
aggregates
aggregates
Aggregates are stored Cement, aggre- Mix is fed into Units in sets of 3 Units are put in a
separately by density gates, water, pig- a mold and con- are ejected from kiln for 6 to 8 hours.
and gradation, then ments and other solidated by vibra- molds while be- Curing is done under
weighed and trans- admixtures are tion (feed time); ing supported on saturated conditions.
ported by conveyor to combined to a head lowers to steel pallets. The Temperature may be
mixer. form damp, but press the mix into pallets form the elevated to accelerate
not wet, zero- the mold; a second bottom of the cement hydration.
slump mix. vibration cycle mold cavities. Units are stored out-
consolidates the side for continued
mix (finish time). curing.
Masonry Structures, lesson 1 slide 52
27. Engineering Properties of Concrete Units
ASTM C140: Standard Methods for Sampling and Testing Concrete Masonry Units
absorption: weight change after 24 hour immersion in cold water, 13 to 18 pcf
total linear drying shrinkage: up to 0.065% for Type I units
moisture content: 25 to 45% for type I units, Type II units not controlled
compressive strength: f’ut ranges from 1900 to 6000 psi
tensile strength: frt ranges from 250 to 500 psi
deformational properties: Em = 750 f’m Gm = 0.4 Em v = 0.28
creep: kc = 2.5 x 10-7 per psi
thermal expansion: 4.13 in/in per oF
Masonry Structures, lesson 1 slide 53
Mortar
History
• first mortars were used to fill voids between stones unit
• first mortars were mud and then tar mortar
• early mortars consisted of lime and sand
• early admixtures: egg whites, clays, urine, oxblood unit
Basic Ingredients of Modern Mortars
• cements: Portland Cement, Masonry Cement
or Mortar Cement (according to ASTM classification)
• hydrated lime: hydrated calcium oxide (Ca(OH)2) improves workability
and bond
• hydraulic lime: better workability than cement, hardens under water
and faster than common lime
• sands: natural or manufactured sands are used
• pozzolans
Masonry Structures, lesson 1 slide 54
28. Types of Mortar Mixes (US)
The following mortar designations took effect in the mid-1950’s:
M a S o N w O r K
strongest weakest
Relative Parts by Volume (approximate)
Mortar Portland Hydrated Sand
Type Cement Lime
M 1 ¼ 3½
S 1 ½ 4½
N 1 1 6
O 1 2 9
Sum should equal 1/3 of sand volume
(assuming that sand has void ratio of 1 in 3).
Masonry Structures, lesson 1 slide 55
Types of Mortar Mixes (Italy)
Designation of mortars according to composition in volume
Class Type Cement Hydrated Hydraulic Sand Pozzolan
lime lime
M4 Hydraulic 1 3
M4 Pozzolanic 1 3
M4 Mixed 1 2 9
M3 Mixed 1 1 5
M2 Cementitious 1 0.5 4
M1 Cementitious 1 3
Masonry Structures, lesson 1 slide 56
29. Types of Mortar Mixes
Equivalence in terms of mean compressive strength (Italy):
M1 : 12 N/mm2
M2: 8 N/mm2
M3: 5 N/mm2
M4: 2.5 N/mm2
Eurocode 6 classifies mortars on the basis of the mean compressive
strength: e.g. M10 refers to a mortar with 10 N/mm2 compressive
mean strength.
Masonry Structures, lesson 1 slide 57
Water Content of Mortar
• Water is added to mortar mix to hydrate cement and make it workable.
• Too much water will result in mortar too fluid to support weight of a few courses.
• Good water retention is important:
– to keep water from bleeding out of mortar
– to prevent mortar from stiffening before units are laid
– to ensure proper hydration of cement
• Desirable to have consistent IRA of unit and water retentivity of mortar
– low IRA with low water retentivity or high IRA with high water retentivity
unit If water migrates too quickly from
mortar to the unit, cement may not
mortar hydrate fully resulting in reduced bond
strength.
unit
Masonry Structures, lesson 1 slide 58
30. Mixing of Mortar
ASTM C270: Mortar for Unit Masonry
• Use paddle type mixer.
• Cementitious materials and aggregate mixed for 3 to 5 minutes with
maximum amount of water to produce workable consistency.
• Sand is typically measured by counting number of shovels, however,
• Preferred method is to measure sand amounts in calibrated box.
• Add water as needed for proper flow. Rely on judgment and experience
of mason.
• Place mortar before it starts to set up (could be as short as 20 minutes).
• Retempering of mortar (replacing water lost due to evaporation) on the
board is allowed within 2.5 hours after mixing.
Masonry Structures, lesson 1 slide 59
Mortar Compressive Strength (US)
2” cubes cast in brass molds 2” cylinders in steel molds
(laboratory test method) (field test method)
P P
4”
2”
2”
Mortar compressive strength is significantly affected by its water content at the time of
molding test specimens. Laboratory samples may have water removed by suction to simulate
the water content of mortar placed between masonry units. Field mortar samples are often
prepared by placing mortar on top of a unit for one minute before placing in molds.
Ref: NCMA TEK 18-5 Masonry Mortar Testing
Masonry Structures, lesson 1 slide 60
31. Grouting Masonry
Grout Placement Methods
Low Lift:
• grout is placed and consolidated as masonry is constructed
– maximum grout height = 5 feet per TMS 602 Sec. 3.5C
High Lift:
• grout is placed after a story height is constructed vibration needed
• clean-out holes are required at:
– every vertical bar location
– minimum spacing of 32” for all grout pours over 5 feet
Ref: NCMA TEK 3-2 Grouting for Concrete Masonry Walls
Masonry Structures, lesson 1 slide 61
Grout Mix Proportions (US)
ASTM C476 Standard Specification for Grout for Masonry
Constituents:
Portland Cement: Fine Aggregate: Coarse Aggregate: Hydrated Lime
(sand) (pea gravel)
Grout Portland Fine Coarse Hydrated
Type Cement Aggregate Aggregate Lime
(3/8” max. size)
Fine 1 2¼-3 - 0.0 – 0.1
Grout
Coarse 1 2¼-3 1–2 0.0 – 0.1
Grout
Note: Proportions are by volume.
Ref: NCMA TEK 9-4 Grout for Concrete Masonry
Masonry Structures, lesson 1 slide 62
32. Grout Compressive Strength (US)
ASTM C1019 Standard Method of Sampling and Testing Grout
P
31/2” x 31/2” x 6”
grout specimen
porous paper 7”
1
32 quot; 31quot;
2
Note: Method also applies to clay-unit masonry.
Masonry Structures, lesson 1 slide 63
Reinforcing Steels (US)
Longitudinal and transverse reinforcing bars
#3 through #11 bars: Grade 40 or Grade 60* (ASTM 615*, A616, A617 and A706)
* more common
Grade 60
fy= 60 ksi
Tensile Stress
Grade 40
fy = 40 ksi
0.005 0.010 0.015 0.020
Tensile Strain
Ref: NCMA TEK 12-4A Steel for Concrete Masonry Reinforcement
Masonry Structures, lesson 1 slide 64
33. Joint Reinforcement
ASTM A-951:
Standard specification for cold-drawn wire for joint reinforcement
ladder type
truss type
Ref: NCMA TEK 12-2A The Structural Role of Joint Reinforcement in Concrete Masonry
Masonry Structures, lesson 1 slide 65
Differential Movements
• One common cause of cracking is differential movement between
wythes.
• Different materials expand or contract different amounts due to:
– temperature
– humidity
– freezing
– elastic strain
• Cementitious materials shrink and creep
• Clay masonry expands
• Consider differential movements relative to steel or concrete frames
shrink expand
Ref: BIA Tech. Note 18 Movement - Volume Changes and Effect of Movement, Part I
Masonry Structures, lesson 1 slide 66
34. Coefficients of Thermal Expansion
Ave. Coefficient of Thermal Expansion
Material Linear Thermal Expansion (inches per 100’ for
(x 10-6 strain/oF) 100oF
temperature increase)
Clay Masonry
clay or shale brick 3.6 0.43
fire clay brick or tile 2.5 0.30
clay or shale tile 3.3 0.40
Concrete Masonry
dense aggregate 5.2 0.62
cinder aggregate 3.1 0.37
expanded shale aggregate 4.3 0.52
expanded slag aggregate 4.6 0.55
pumice or cinder aggregate 4.1 0.49
Stone
granite 4.7 0.56
limestone 4.4 0.53
marble 7.3 0.88
Thermal coefficients for other structural materials can be found in BIA Technical Note 18.
Masonry Structures, lesson 1 slide 67
Moisture Movements
• Many masonry materials expand when their moisture content is
increased, and then shrink when drying.
• Moisture movement is almost always fully reversible, but in some
cases, a permanent volume change may result.
Moisture Expansion of Clay Masonry = 0.020%
Moisture Expansion of Clay Masonry = 0.020%
Freezing Expansion of Clay Masonry = 0.015%
Freezing Expansion of Clay Masonry = 0.015%
Masonry Structures, lesson 1 slide 68
35. Moisture Movements in Concrete Masonry
• Because concrete masonry units are susceptible to shrinkage, ASTM
limits the moisture content of concrete masonry depending on the
unit’s linear shrinkage potential and the annual average relative
humidity. For Type I units the following table is given.
Moisture Content, % of Total Absorption
(average of three units)
Linear Shrinkage, % Humidity Conditions at Job Site
humid intermediate arid
0.03 or less 45 40 35
0.03 to 0.045 40 35 30
0.045 to 0.065 35 30 25
Masonry Structures, lesson 1 slide 69
Control Joints in Concrete Masonry
• Control joints designed to control shrinkage cracking in masonry.
Spacing recommendations per ACI for Type I moisture controlled units.
Vertical S pacing of Joint Reinforcement
Recommended control None 24” 16” 8”
joint spacing
Ratio of panel length 2 2.5 3 4
to height, L/h
Panel length in feet 40 45 50 60
(not to exceed L regardless of H)
Cut spacing in half for Type II and reduce by one-third for solidly grouted walls.
Masonry Structures, lesson 1 slide 70
36. Control Joints in Concrete Masonry
Control joints should be placed at:
– all abrupt changes in wall height
– all changes in wall thickness
– coincidentally with movement joints in floors, roofs and
foundations
– at one or both sides of all window and door openings
Masonry Structures, lesson 1 slide 71
Control Joint Details for Concrete Masonry
paper grout fill
control joint unit
raked head joint
and caulk
Ref. NCMA TEK 10-2A Control Joints in Concrete Masonry Walls
Masonry Structures, lesson 1 slide 72
37. Expansion Joints in Clay Masonry
Pressure-relieving or expansion joints
Pressure-relieving or expansion joints
accommodate expansion of clay masonry.
accommodate expansion of clay masonry.
expansion joint
Ref: Masonry Design and Detailing, Christine Beall, McGraw-Hill
BIA Tech. Note 18A Movement - Design and Detailing of Movement Joints, Part II
Masonry Structures, lesson 1 slide 73
Spacing of Expansion Joints
For brick masonry:
W = [ 0.0002 + 0.0000045( Tmax −Tmin )] L
where W = total wall expansion in inches
0.0002 = coefficient of moisture expansion
0.0000043 = coefficient of thermal expansion
L = length of wall in inches
Tmax= maximum mean wall temperature, °F
Tmin = minimum mean wall temperature, °F
24 ,000( p )
S=
Tmax −Tmin
S = maximum spacing of joints in inches
p = ratio of opaque wall area to gross wall area
Masonry Structures, lesson 1 slide 74
38. Expansion Joint Details for Brick Veneer Walls
20 oz. copper silicone or butyl sealant
neoprene extruded plastic
Masonry Structures, lesson 1 slide 75
Vertical Expansion of Veneer
flashing with
weep holes
rc
steel shelf beam
angle
1/4” to 3/8”
min. clearance
concrete block
compressible
filler
joint reinforcement
clay-brick or wire tie
veneer
Masonry Structures, lesson 1 slide 76
39. Expansion Problems
In cavity walls, cracks can form at an external corner because the
outside wythe experiences a larger temperature expansion than the
inside wythe.
sun
Masonry Structures, lesson 1 slide 77
Expansion Problems
• Diagonal cracks often occur between window and door openings if
differential movement is not accommodated.
Masonry Structures, lesson 1 slide 78
40. Expansion Problems
• Clay-unit masonry walls or veneers can slip beyond the edge of a
concrete foundation wall because the concrete shrinks while the clay
masonry expands. As a result, cracks often form in the masonry at
the corner of a building.
Brick
Veneer
Concrete
Foundation
Masonry Structures, lesson 1 slide 79
Expansion Problems
• Brick parapets are sensitive to temperature movements since they are
exposed to changing temperatures on both sides.
Elongation will be longer
than for wall below.
parapet sun
roof
Masonry Structures, lesson 1 slide 80