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Dan Abrams + Magenes Course on Masonry

Dan Abrams + Magenes Course on Masonry

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    Lesson1 Lesson1 Presentation Transcript

    • 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
    • Introduction – Stone masonry Masonry Structures, lesson 1 slide 3 Introduction – Stone masonry Masonry Structures, lesson 1 slide 4
    • Introduction – Stone masonry Masonry Structures, lesson 1 slide 5 Introduction – Masonry w. clay units early sundried mud elements Masonry Structures, lesson 1 slide 6
    • 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
    • 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
    • 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
    • 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
    • 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
    • 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
    • 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
    • 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
    • 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
    • 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
    • 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
    • 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
    • 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
    • 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
    • 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
    • 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
    • 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
    • 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
    • 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
    • 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
    • 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
    • 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
    • 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
    • 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
    • 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
    • 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
    • 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
    • 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
    • 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
    • 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
    • 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
    • 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
    • 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
    • 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
    • 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
    • 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
    • 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