Design and detailing of Movement Joints

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Technical Notes 18 - Volume Changes and Effects of Movement, Part 1Rev [Jan. 1991]Abstract: This Technical Notesdescribes the various movements that occur within buildings.Movement induced by changes in temperature, moisture, elastic deformations, creep, and otherfactors develop stresses if the brickwork is restrained. Restraint of these movements may resultin cracking of the masonry. Typical crack patterns are shown and their causes identified.Key Words: brick, corrosion, cracks, differential movement, expansionINTRODUCTIONThe various materials and elements that are used to construct a building are in a constant state ofmotion. All building materials change in volume due to internal or external stimuli. These stimulimay be changes in temperature, moisture, elastic deformations due to loads, creep, or otherfactors. Restraint of these movements may cause stresses within the building elements which inturn may result in cracks.To avoid cracks, the design should minimize volume change, prevent movement oraccommodate differential movement between materials and assemblies. A system of movement

joints can eliminate cracks and the problems they cause. Movement joints can be designed byestimating the magnitude of the several types of movements which may occur in masonry andother building materials.This Technical Notesdescribes the various volume changes in brick masonry and other buildingmaterials. It also describes the effects of volume change when the materials are restrained. OtherTechnical Notesin this series address the design and detailing of movement joints and the typesof anchorage which permit movement.MOVEMENTS OF CONSTRUCTION MATERIALSThe design and construction of most buildings does not allow precise prediction of movements ofbuilding elements. Volume changes are dependent on material properties and are highly variable.Age of material and temperature at installation also influence expected movement. When meanvalues of material properties are used in design, the actual movement may be underestimated oroverestimated. The designer should use discretion when selecting the applicable values. Thetypes of movement experienced by various building materials are indicated in Table 1.Temperature Movements

All building materials expand and contract with variations in temperature. For unrestrainedconditions, these movements are theoretically reversible. Table 2 indicates the coefficients ofthermal expansion for various building materials.


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Unrestrained thermal movement is the product of temperature change, the coefficient of thermalexpansion, and the length of the element. The stresses developed by restrained thermalmovements are equal to the change in temperature multiplied by the coefficient of thermalexpansion and the modulus of elasticity of the material. The temperature change used forestimating thermal movements should be based on mean wall temperatures. For solid walls,temperatures at the center of the wall should be used. In cavity walls and veneers, thetemperature at the center of each wythe or component should be used. In discontinuous


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construction, the wythes will have different temperatures due to the separation of the wythes byan air space.Surface temperatures of brick walls may be much higher than the ambient air temperature. Wallorientation, wall type and color are governing factors. It is possible for a dark, south facing wall toreach surface temperatures as high as 140

oF (60

oC), while the ambient air temperature is well

below 100

o

F (37.7

o

C). The mean wall temperature of a 4 in. (100 mm) thick insulated brickveneer wall is very close to the surface temperature of the brick. A thicker or non-insulated wallmay experience a smaller temperature difference between the outside and inside surfaces.Other materials such as metals or wood will expand and contract at rates different from that ofbrick masonry. These differences are important in applications such as window frames, railings,or copings which are attached to brick masonry. Distress may occur in either material.Moisture MovementsWith the notable exception of metals, many building materials tend to expand with an increase inmoisture content and contract with a loss of water. For some building materials these movementsare reversible; while for others they are irreversible or only partially reversible.Clay Products. Brick units expand slowly over time upon exposure to water or humid air. Thisexpansion is not reversible by drying at atmospheric temperatures. A brick unit is smallest in sizewhen it cools after coming from the kiln. The unit will increase in size due to moisture expansionfrom that time. Most of the expansion takes place quickly over the first few weeks, but expansionwill continue at a much lower rate for several years (see Figure 1). The moisture expansionbehavior of brick depends primarily on the raw materials and secondarily on the firingtemperatures. Brick made from the same raw materials that are fired at lower temperatures willexpand more than those fired at higher temperatures.

Projected Moisture Expansion of Fired Brick vs. Time

Fig. 1Moisture expansion of individual brick or brick masonry can be measured for a given length oftime. Predicting the total moisture expansion of brick is much more difficult. At present there areno standard tests to predict moisture expansion or measure moisture expansion which occurs inservice. Based on past research, long term moisture expansion of brick can be estimated atbetween 0.0002 and 0.0009. A design value of 0.0003 should be used when designing composite


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masonry walls. A design value of 0.0005 should be used in veneer walls where an upper boundof movement is estimated.Concrete Masonry. Concrete masonry units experience shrinkage as a result of moisture lossand carbonation. Shrinkage of concrete masonry is affected by method of curing, aggregate type,change in moisture content, cement content, and wetting and drying cycles. Total shrinkage is

determined by ASTM C 425 Test Method for Drying Shrinkage of Concrete Block whichmeasures shrinkage from a saturated condition to a 17% moisture condition. Typical total linearshrinkage values range between 0.0002 to 0.0007. Type I concrete masonry units must conformto moisture content requirements found in the material specifications which limits wall shrinkage.Concrete. Concrete shrinks as it cures and swells as it becomes wet. Shrinkage of concrete isinfluenced by the water cement ratio, composition of the cement, type of aggregate, size ofconcrete member, curing conditions, and amount and distribution of reinforcing steel. Values offinal shrinkage for ordinary concretes are generally of the order of 0.0002 to 0.0007 depending onthe factors listed.Wood. Wood will shrink during the natural seasoning process as the moisture content drops fromthe fiber saturation point (28 to 30%) until it reaches equilibrium moisture content with local

atmospheric conditions. Shrinkage occurs differently in the tangential, radial and longitudinaldimensions of the member. Table 3 indicates the range of shrinkage values for commonly usedwoods. Moisture expansion and contraction continues with changes in moisture content.

1Adapted from Reference 10

2Dried from 30% moisture content to 0%Elastic DeformationIn the structural design of a building, the designer must consider all forces imposed on thestructure. These include dead loads, live loads, snow loads, and such external lateral forces aswind, soil, earthquake and blast. All of these forces create stresses in the building materialsresulting in deflections of the building elements.All materials, when subjected to a force, respond to stress with an associated strain. The stress-strain relationship for masonry materials is approximately linear and is defined by the modulus ofelasticity. Axial deformation is determined by dividing the stress by the modulus of elasticity and

multiplying the quotient by the length under load. The deflections of horizontal elements, lateraldeflections of walls and columns, and reductions in lengths of axially loaded structural elementsdue to design loads must be considered.CreepCreep, or plastic flow, is the continuing deformation of materials under load or stress. Themagnitude of movement due to creep in masonry and concrete depends on the stress level,material age, duration of stress, material quality, and environmental factors.


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Brick. Creep in brick masonry primarily occurs in the mortar joints and is negligible. The ACI530/ASCE 5 "Building Code Requirements for Masonry Structures" suggests 0.7 x 10 -7 in./in. perpsi of load.Concrete Masonry. Concrete masonry exhibits more creep than brick masonry because of thecement content in the units. The ACI 530/ASCE 5 code suggests a value of 2.5 x 10-7 in./in. perpsi of load.Concrete. Creep is most significant in concrete frame structures. Creep in concrete begins afterload is applied and proceeds at a decreasing rate. High-strength concretes show less creep thanlow-strength concretes. Creep is slightly greater in lightweight aggregate concretes than normal-weight concretes. In high-rise buildings, the total elastic and inelastic shortening of columns andwalls due to gravity loads and shrinkage may be as high as 1 in. (25.4 mm) for every 80 ft (24.4m) of height.Corrosion of SteelCorrosion of steel embedded in masonry can cause cracking or spalling of masonry. The volumeof rust is greater than that of the steel from which it is formed. This volume increase causespressure on the surrounding masonry. Metals embedded in grout, such as reinforcing bars, areless susceptible to corrosion than ties and joint reinforcement embedded in mortar joints sincethey are protected by the grout and not exposed. Other items in masonry susceptible to corrosion

are steel lintels, steel shelf angles, joint reinforcement, anchor bolts and other metal fasteners inmasonry. To minimize corrosion, do not use additives in mortar, such as calcium chloride, whichwould accelerate corrosion. See Technical Notes44B for more on corrosion resistance of metalwall ties.Other Causes of MovementThere are other causes of movement in building elements which may occur under givenconditions. These include freezing expansion, carbonation of concrete and mortars, drift of thebuilding frame, deflection of building elements, and the action of unstable soils. It is beyond thescope of this Technical Notesto discuss these items in detail. However, the designer shouldrecognize and consider these factors.Masonry materials exhibit expansion due to freezing when saturated. Freezing expansion has asmall effect on total expansion of masonry. Based on limited data, the freezing expansion forbrick ranges from 0 to 10.3 x 10 -4 in./in. A design value for brick masonry of 2 x 10-4 in./in. is

recommended. The expansion occurs when saturated brick are subjected to temperatures at orbelow 14oF (-10

oC).

Carbonation is the chemical combination of hydrated portland cement with carbon dioxide presentin air. Although it is known that materials containing portland cement shrink upon carbonation,little is known about the extent of the carbonation or the resulting shrinkage.The drift or side-sway of a structural frame may cause distress to brick masonry used as in-fillwalls or exterior cladding. Wind or earthquake loads will be transferred to the more rigid brickworkif attached rigidly to the frame. The same is true for deflection of floor slabs or spandrel beams.Masonry built up in contact with these elements will be loaded due to the deflection of themember. Masonry intended to be non-loadbearing may become loadbearing.Foundation movements and differential settlement often cause cracking in masonry wallssupported on foundations. Unstable soils or expansive soils are of special concern. Properfoundation design should be performed to ensure a stable support or allow uniform settlement.EFFECTS OF MOVEMENTChanges in building design have affected the design and behavior of many building components,including masonry walls. The most significant change for brick masonry is the shift fromloadbearing masonry walls to skeleton frame construction. Other factors include the use ofthinner walls, composite walls and insulated walls. The increased use of portland cement mortarsand the tendency to specify high compressive strength mortars have become common. Althoughstronger units and mortars increase the compressive strength of the masonry, they do so at theexpense of other important properties. Thus, masonry walls are thinner and more brittle than theirmassive ancestors. These thinner walls are more susceptible to cracking and spalling ifprovisions for differential movement are not accounted for properly.


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Cracking and SpallingCracking is probably the distress which occurs most often in masonry walls. Cracks result frommany different sources, but there are typical shapes and patterns of cracks. Often the type andmagnitude of cracking will indicate the cause.It is more beneficial to show what can happen if movement is not considered in design than toshow a properly designed and detailed project. Following are some typical locations where cracksoccur in masonry walls and the major cause of each. Technical Notes18A will describe ways toavoid these problems.Long Walls. Long walls or walls with large distances between expansion joints may causedistress within the wall. The expansion of the brickwork may force sealant material out of theexpansion joint or crack the brickwork between expansion joints (see Fig. 2). Diagonal cracksoften occur in piers between window or door openings. Such cracks usually extend from the heador sill at the jamb of the opening, depending upon the direction of movement and the path of leastresistance.

Expansion of Long WallFIG. 2

Corners. An insufficient amount or improper location of expansion joints in walls can lead tocracking at the corners. Perpendicular walls will expand in the direction of the corner causingrotation and cracking near the corner. This typically occurs at the first head joint from either sideof the corner (see Fig. 3).


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Crack at CornerFIG. 3

Offsets and Setbacks. Vertical cracks are quite common at wall setbacks or offsets if movementis not accommodated. When parallel walls expand towards the offset, the movement producesrotation of the offset causing vertical cracks (see Figs. 4 and 5).

Crack at OffsetFIG. 4

Rotation at OffsetFIG. 5


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Shortening of Structural Frames. In frame structures, predominately concrete frame buildings,vertical shortening due to creep or shrinkage of the structural frame may impose high stresses onthe masonry. These stresses may develop at window heads, shelf angles, and other points wherestresses are concentrated. Fig. 6 shows brick veneer supported by a steel shelf angle on aconcrete frame. Over time the concrete frame has shrunk and caused the steel shelf angle tobear on the masonry below. Because a horizontal expansion joint was not provided, stressesbecame concentrated on the mortar joint directly below the angle causing crushing of themasonry below. This phenomena can also cause bowing of brickwork between floors, if thebrickwork is not adequately attached to the backing, or the backing is not sufficiently rigid.

Spalling Due to Shortening of Structural FrameFIG. 6

Parapet Walls. Parapets exposed on three sides are subjected to extremes of moisture andtemperature which may be substantially different from those in the wall below. Also, parapets lackthe dead load of masonry above to help resist movement. Expansion can cause parapets to bowif restrained at both corners or move away from corners if restrained only at one end (see Fig. 7).

Bowing of Parapet Due to ExpansionFIG. 7

Foundations. Masonry walls above grade built on concrete foundations will expand while theconcrete foundation will shrink. This differential movement will cause shear at the foundationinterface if bonded together. Movement of the brick away from the corner or cracking of theconcrete often results (see Fig. 8).

Crack at Foundation CornerFIG. 8


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Deflection and Settlement. Deflection and settlement cracks are identified by a tapering shape.Fig. 9 shows a deflection crack due to insufficient support of the brickwork on a lintel. The crack iswider at the steel angle and tapers to nothing. Technical Notes31B Revised, Structural SteelLintels, details the proper design of steel lintels supporting masonry. Deflection cracks may alsooccur at steel shelf angles attached to spandrel beams that deflect.

Crack Due to DeflectionFIG. 9

Fig. 10 shows a crack due to differential settlement of the foundation. If all settlement is equal,then little harm is done. Cracking occurs when one portion of a structure settles more than anadjacent part.

Crack Due to Differential SettlementFIG. 10

Encased Columns. Where structural elements are rigidly encased in masonry, any movement ofthe column is transferred to the masonry, causing cracks. These movements may be due to driftof the building frame or lateral expansion from creep. These cracks occur on the exterior as wellas the interior of the building (see Fig. 11).


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Encased Column

FIG. 11Curling of Concrete. If a concrete slab is cool and dry on top and warm and moist on thebottom, the top may become shorter than the bottom causing the slab to curl upward. Cast-in-

place concrete slabs also curl up at the corners due to deflection when the forms are removedand loads applied. This curling can lift masonry attached to or laid on the concrete slab (see Fig.12).

Crack Due to Curling of Concrete SlabFIG. 12

Embedded Items. Items embedded in or attached to masonry may cause spalling or crackingwhen they move or expand. Joint reinforcement that is continuous across an expansion joint may

buckle, pushing out adjacent mortar (see Fig. 13). Corrosion of metal elements within masonrycauses volume increases of such a magnitude as to crack or spall the masonry.


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Spalling Due to Buckling of Joint ReinforcementFIG. 13SUMMARYThis Technical Notesdescribes the various movements that occur within all building materialsand constructions. It also explains the effects of these movements. Cracking in brickwork can beeliminated if all factors are taken into consideration and the anticipated movement isaccommodated.The information and suggestions contained in this Technical Notesare based on the availabledata and the experience of the engineering staff of the Brick Institute of America. The informationcontained herein must be used in conjunction with good technical judgment and a basicunderstanding of the properties of brick masonry. Final decisions on the use of the informationcontained in this Technical Notesare not within the purview of the Brick Institute of America andmust rest with the project architect, engineer, owner or all.REFERENCESMore detailed information on subjects discussed here can be found in the following publications:

1."Building Code Requirements for Masonry Structures (ACI 530/ASCE 5)", AmericanConcrete Institute, Detroit, MI, 1988.2."Building Movements and Joints", Portland Cement Association, 1982.3.Fintel, M., Ghosh, S.K., Iyengar, H., "Column Shortening in Tall Structures-Predictionand Compensation", Portland Cement Association, 1987.4.Grimm, C.T., "Masonry Cracks: A Review of the Literature," Masonry: Materials,Design, Construction, and Maintenance, ASTM STP 992, H.A. Harris, Ed., ASTM,Philadelphia, PA, 1988, pp. 257-280.5.Grimm, C.T., "Probablistic Design of Expansion Joints in Brick Cladding", Proceedingsof the 4th Canadian Masonry Symposium, University of New Brunswick, Canada, 1986,pp. 553-568.6.Robinson, G.C., "The Reversibility of Moisture Expansion", American Ceramic SocietyBulletin, Vol. 64, 1985, pp.712-715.7.Scheffler, M.J., Chin, I.R., Slaton, D., "Moisture Expansion of Fired Bricks", Fifth NorthAmerican Masonry Conference, June 1990, pp. 549-562.8."Shrinkage Characteristics of Concrete Masonry Walls", Housing Research Paper No.34, Housing and Home Finance Agency, April 1954.9.Winter, G. and Nilson, A.H., "Design of Concrete Structures", McGraw-Hill BookCompany, 1979.10."Wood Handbook: Wood as an Engineering Material", Agricultural Handbook 72, U.S.Department of Agriculture, Washington, D.C., 1987.


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11.Young, J.E., and Brownell, W.E., "Moisture Expansion of Clay Products", Journal ofthe American Ceramic Society, Vol. 42, No. 12, 1959, pp. 571-581.


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Technical Notes 18A - Design and Detailing of Movement Joints, Part 2[December 1991] (Reissued Sept. 2001)Abstract: Expansion joints are used in brick masonry to allow for movement and avoidcracking. This Technical Notesdefines the different types of movement joints used inbuilding construction. Equations are given to determine the proper size and spacing ofbrick expansion joints. Examples show the proper placement of expansion joints toavoid cracking of brick masonry. Information is also included on bond breaks, bondbeams and flexible anchorage.

Key Words: brick, differential movement, expansion joint, flexible anchorage, sealants.

INTRODUCTION

Because all materials in a building experience changes in volume, a system ofmovement joints is necessary to allow these movements to occur. Failure to permitthese movements may result in cracks in brickwork as discussed in Technical Notes18. The type, size and placement of movement joints is critical to the properperformance of the building. This Technical Notesdefines the different types ofmovement joints and discusses the proper design of expansion joints within brick

masonry buildings. Details of expansion joints are provided for loadbearing and non-loadbearing applications.

MOVEMENT JOINTS

There are various types of movement joints in buildings: expansion joints, control joints,building expansion joints, and construction joints. Each type of movement joint isdesigned to perform a specific task, and they should not be used interchangeably.

An expansion jointis used to separate brick masonry into segments to prevent crackingdue to changes in temperature, moisture expansion, elastic deformation due to loads,and creep. Expansion joints may be horizontal or vertical. The joints are formed ofhighly elasticmaterials placed in a continuous, unobstructed opening through the brickwythe. This allows the joints to close as a result of an increase in size of the brickwork.Expansion joints must be located so that the structural integrity of the brick masonry is

not compromised.A control jointis used in concrete or concrete masonry to create a plane of weaknesswhich, used in conjunction with reinforcement or joint reinforcement, controls thelocation of cracks due to volume changes resulting from shrinkage and creep. A control

joint is usually a vertical opening through the concrete masonry wythe and may beformed of inelasticmaterials. A control joint will open rather than close. Control jointsmust be located so that the structural integrity of the concrete masonry is not affected.

A building expansion (isolation) jointis used to separate a building into discretesections so that stresses developed in one section will not affect the integrity of theentire structure. The isolation joint is a through-the-building joint.

A construction joint (cold joint) is used primarily in concrete construction whereconstruction work is interrupted. Construction joints are located where they will leastimpair the strength of the structure.

Expansion Joints

Although the primary purpose of expansion joints is to accommodate movement, thejoint must also resist water penetration and air infiltration. Figure 1 shows various waysof forming vertical expansion joints. A copper waterstop, a premolded foam pad or aneoprene pad may be included


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Vertical Expansion JointsFIG. 1

as a barrier to keep mortar or other debris from clogging the joint and aids in resistingwater penetration. Fiberboard and other similar materials are not suitable for thispurpose because they are not highly compressible and, after being compressed, theywill not expand to their original size.

When placing expansion joints in brick, materials such as mortar or joint reinforcementshould not bridge the expansion joint. If this occurs, movement will be restricted andthe expansion joint will not perform as intended. Expansion joints should be formed asthe wall is built, as shown in Fig. 2.

Expansion Joint ConstructionFIG. 2

Sealants are used on the exterior side of the expansion joint to act as a seal againstwater and air penetration. Many different types of sealants are available, althoughthose which exhibit the highest movement capabilities are best. Elastomeric sealantsmust be highly elastic, resistant to weathering (ultraviolet light) and have high bond toadjacent materials. These elastomeric sealants are classified by three generic types:urethanes, silicones and polysulfides. Sealant manufacturers should be consulted forthe applicability of their sealants as expansion joint materials. The sealant shouldconform to ASTM C 920 Specification for Elastomeric Joint Sealants. Many sealantsrequire a primer to be applied to the masonry surface to ensure adequate bond.Compatibility of the sealant with adjacent materials such as flashings, metals, etc. mustbe taken into consideration.

A backer rod, which is a circular foam rod, is used behind the sealant to keep thesealant at a constant depth and provide a surface to tool the sealant against. Thesealant must not adhere to the backer rod. The depth of the sealant should beapproximately one-half the width of the expansion joint, with a minimum sealant depthof 1/4 in. (6 mm). Increased resistance to water and air infiltration can be achieved by

designing a two-stage joint as shown in Fig. 3. A two-stage joint is often used in a rainscreen wall providing a vented or pressure-equalized joint. The space between thesealants must be vented to allow drainage. This is achieved by leaving a hole or gap inthe sealant at the top and bottom of the joint.

Two-Stage Expansion JointFIG. 3

Vertical Expansion Joints

Spacing of Vertical Expansion Joints. No single recommendation on the positioningand spacing of expansion joints can be applicable to all structures. Each building

should be analyzed to determine the extent of movements expected within thatparticular structure. Provisions should be made to accommodate these movements andtheir associated stresses by a series of expansion joints. Generally, spacing ofexpansion joints is determined by considering the amount of expected wall movementand the size of compressibility of the expansion joint and expansion joint materials.

Unrestrained expansion of the brickwork may be estimated by the following formula:

mu = (ke + kf +kt?T) L Eq. 1

where:


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mu = total unrestrained movement of the brickwork, in.

ke = coefficient of moisture expansion, in./in.

kf = coefficient of freezing expansion, in./in.

kt = coefficient of thermal expansion, in./in./F

?T = temperature change in brickwork, F.L = length of wall, in.

The design value of the coefficient of moisture expansion for clay masonry is usually0.0005 in./in. The coefficient for thermal expansion is 0.000004 in./in./F. Thecoefficient of freezing expansion is taken as 0.0002 in./in. Freezing expansion does notoccur until wall temperatures go below 14F ( -10C). Further, the units must besaturated when frozen to cause expansion. Local conditions must be considered todetermine if freezing expansion will occur, but is usually considered negligible.

Equation 1 provides an estimate of the amount of movement occurring in a wallsystem. In addition to the amount of movement, there are other variables which mayaffect the size and spacing of expansion joints. These include wall restraint, elasticdeformation due to loads, shrinkage and creep of mortar, construction tolerances and

wall orientation.The following equation relates spacing between expansion joints to total unrestrainedmovement of the brick work and the expansion joint width.

where:

Se = spacing between expansion joints, in.wj = width of expansion joint, in.ej = extensibility of expansion joint material, %

The expansion joint is typically sized to resemble a mortar joint, usually 3/8 in. (10 mm) to 1/2

in. (13 mm). The maximum size of the expansion joint may depend on the sealant capabilities.

Extensibility of highly elastic expansion joint materials are typically in the range of 25 % to

50%. Compressibility of backing materials can range up to 75%.The temperature change in brickwork used in Eqs. 1 and 2 is based on mean wall temperatures.

The theoretical change in temperature is equal to the maximum or minimum mean wall

temperature minus the mean wall temperature at the time of installation. Although this

theoretical temperature difference is precise, it is difficult to accurately predict the temperature

at the time of installation, and the minimum and maximum temperatures. Therefore, it is

conservative to calculate the temperature variation based on the difference between the

maximum and minimum mean wall temperature.Maximum mean wall temperatures vary from the maximum ambient air temperature to as high

as 140F (60C) depending on wall orientation, location of insulation, color and density of the

wall. Minimum mean wall temperatures will typically be close to the winter design temperature.Therefore, wall temperature differences, ?T, can vary from less than 50F (10C) to about 160F

(71C).As an example of the use of Eq. 2, consider a brick veneer wall which is facing south. The color

of the brick is a light red and the desired size of the expansion joint is 3/8 in. (10 mm). The

extensibility of the sealant is 50%. Assuming appropriate values and no freezing expansion, Eq.

2 would give the following expansion joint spacing:


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Therefore, the maximum spacing for vertical expansion joints in a straight wall would be17ft-4 in. (5.3 m). This spacing does not take into account window openings, corners orother material properties that may reduce the spacing of the expansion joints. The

extent to which precautions should be taken to prevent masonry cracking will dependupon the intended use of the structure and its exposure. In most instances it isdesirable to be conservative, but it may be economically desirable to exceed themaximum spacing as a calculated risk. An example would be when calculations show aneed for expansion joints every 18 ft (5.5 m) but the expansion joint spacing is set at 20ft (6.1 m) to match the spacing of the structural columns. Generally, vertical expansion

joints should not exceed 30 ft (9.1 m) in walls without openings.Placement of Vertical Expansion Joints

The actual location of vertical expansion joints in a structure is dependent upon theconfiguration of the structure as well as the expected amount of movement. In additionto adequately placing expansion joints within long walls, consideration should be givento placement of expansion joints at: corners, offsets, openings, wall intersections,

changes in wall heights and parapets.Corners. Walls perpendicular to one another will expand towards their juncture,typically causing distress at the first head joint on either side of the corner (Fig. 4a).Expansion joints should be placed near corners to alleviate this stress. It is often notaesthetically pleasing to place expansion joints at the corner, although this is the bestlocation. In such instances, an expansion joint should be placed within 10 ft (3.0 m) ofthe corner in either wall, but not necessarily both. The spacing of expansion jointsaround a corner should not exceed the spacing of expansion joints in a straight wall(Fig. 4b). For example, if the spacing between vertical expansion joints on a straightwall is 25 ft (7.6 m), then the spacing of expansion joints around a corner could be 10 ft(3.0 m) on one side of the corner and 15 ft (4.6 m) on the other side. Jointreinforcement may be added around wall corners to provide added tensile strength tothe corner. Joint reinforcement should not bridge the expansion joint.


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Expansion Joints at CornersFIG. 4

Offsets and Setbacks. Parallel walls expand towards the offset rotating the shortmasonry leg, or causing cracks within the offset (Fig. 5a). Expansion joints should be

placed at the offset to allow the parallel walls to expand (Fig. 5b).


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Expansion Joints at OffsetsFIG. 5

Openings. Cracks often appear at window and door openings when the spacingbetween expansion joints is too large. In structures containing punched windows anddoor openings, more movement occurs above or below the openings. Less movement

occurs along the line of windows since there is less masonry. This differentialmovement may cause cracks which emanate from the corners of the opening as in Fig.6. This pattern of cracking does not exist in ribbon window structures.

Window and door openings weaken the wall yet act as "natural" expansion joints. It isoften desirable to locate vertical expansion joints along the edge or jamb of theopening. In cases where the masonry above an opening is supported by shelf anglesattached to the structure, a vertical expansion joint can be placed alongside theopening, continuing through the horizontal support.


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Cracking In Structure With "Punched" WindowsFIG. 6

In cases where the masonry above the opening is supported by loose lintels(unattached to the structure), special detailing and construction is required. If the

expansion joint runs along side the opening as shown in Fig. 7a, the loose steel lintelmust be allowed to expand independently of the masonry. To accomplish this a slipplane is formed with flashing placed above and below the angle. A backer rod andsealant is placed in front of the toe of the angle, and space left at the end of the angle.Thus, a pocket will be formed which will allow movement of the steel angle within thebrickwork. If the joint cannot be built in this manner, then the vertical expansion jointshould not be placed alongside the opening. An alternative may be to place it halfwaybetween the windows. Location of the expansion joint alongside the window willinfluence the dead weight of the masonry bearing on the lintel. Instead of the usualtriangular loading, the full weight of the masonry above the angle should be assumedto bear on the lintel. See Technical Notes31Bfor more information on steel linteldesign.

Expansion Joint at Loose LintelFIG. 7

Intersections and Junctions .Expansion joints should be located at intersections ofmasonry walls and walls which serve different functions. If the masonry is not requiredto be bonded at the intersection, an expansion joint should be incorporated. Wallswhich intersect at other than right angles are also vulnerable to cracking at theintersection. It may be necessary to separate adjacent walls of different heights toavoid differential movement. This is especially true if the difference is very large.Examples are shown in Fig. 8.


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Expansion Joints at JunctionsFIG. 8

Parapets.Parapets are exposed on three sides to extremes of moisture andtemperature which may cause substantially different movement from that of the wallbelow. Parapets also lack the dead load of masonry above to help resist movement.Therefore, all vertical expansion joints should be carried through the parapets.Additional expansion joints may be necessary halfway between those running fullheight, unless the parapet is reinforced. These additional expansion joints mustcontinue down to a horizontal expansion joint, or continue to the base of the wall.

Aesthetic Effects.Expansion joints are usually noticeable on flat walls of masonrybuildings. There are ways to reduce the obvious demarcation. The use of a coloredsealant which matches the brick helps to hide the joint. Also, mason's sand can berubbed into new sealant to remove the sheen, making the joint blend in more. Someprojects have used toothed expansion joints where the expansion joint follows the bondpattern. This type of joint is not suggested because it is more difficult to keep debris outof the joint during construction which could interfere with movement. Further, mostsealants do not perform well when subjected to both shear and tension.

Conversely, it may be desirable to accentuate the expansion joint instead of trying tohide it. This is possible by recessing the brickwork at the expansion joint, or usingspecial-shaped brick units as shown in Fig. 9. Architectural features such as quoins,recessed panels of brickwork or a change in bond pattern reduce the visual impact of

vertical expansion joints. Also, expansion joints are less noticeable when located atreentrant corners.


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Accentuated Expansion JointFIG. 9

Symmetrical placement of expansion joints on the elevation of buildings is usually mostaesthetically pleasing. Further, placing the expansion joints such that wall areas andopenings between expansion joints are symmetrical will reduce the likelihood ofcracking.

Other Considerations .Location of vertical expansion joints will be influenced byadditional factors. Spandrel sections of brickwork supported by a beam or floor maycrack due to deflection of the support. Reduced spacing of expansion joints will permitdeflection to occur without cracking the brickwork. Wall segments which have differentclimatic exposure conditions will respond with different movement. An expansion jointshould separate wall areas with different exposures. Thus, an exterior wall whichcontinues past a glass curtainwall perpendicular to the wall should have an expansion

joint at the curtainwall intersection.

Movement joints must be provided in multi-wythe brick and concrete masonry walls.Expansion joints must be placed in the brick wythe and control joints must be placed inthe concrete masonry, although they do not necessarily have to be aligned.

Horizontal Expansion Joints

Horizontal expansion joints may be required when brickwork is a non-loadbearingelement. Horizontal expansion joints are needed if the brick wythe is supported on ashelf angle outside the frame or used as an infill wall within the frame. Horizontalexpansion joints are located at steel shelf angles by providing space beneath the anglefor movement to occur. In low-rise masonry buildings (below three stories) andbuildings with shear walls it is not necessary to provide horizontal relief, but differentialmovement should be accounted for in the tie system, window details, and at the top ofthe wall. High-rise frame structures typically have horizontal expansion joints located atevery floor level or every other floor level. Figure 10 is a typical detail of a horizontalexpansion joint on a brick veneer building. Notice that a clear space or highlycompressible material is placed beneath the angle, and that a backer rod and sealantare used at the toe of the angle to seal the joint.


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Expansion Joint at Shelf AngleFIG. 10

The size of the horizontal expansion joint should take into account movements of thebrickwork and movements of the frame. These frame movements include both materialand load induced movements, including deflection of the shelf angle. In some

instances, the size of the expansion joint may get rather large and not aestheticallypleasing. An alternate detail shown in Fig. 11 allows more room for movement whileproviding a smaller-appearing joint. The special-shaped brick unit, sometimes calledlipped brick or rabbeted brick, could also be placed below the steel angle and turnedupside down. To avoid problems with chipping and breakage, the lipped portion of thebrick should be at least to in. (13 to 19 mm) in length in either direction.

Alternate Expansion Joint DetailFIG. 11

Horizontal expansion joints are suggested when brick is used as an infill material withinthe frame of the structure. Expansion joints must be provided between the top courseof masonry and the member above. Deflections of the frame should be consideredwhen sizing the expansion joint.

Shelf angles are required by model building codes in most locations especially thoseareas of high seismic risk. They are advisable in buildings with a flexible structuralframe and are recommended when the backing is steel studs.

BOND BREAKS

Concrete and concrete masonry have moisture and thermal movements which areconsiderably different than those of brick masonry. Also, floor slabs and foundationsare usually under different states of stress due to loading than are walls. Therefore, itmay be important to separate these elements by bond breaks such as building paper or


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flashing. With bond breaks between foundations and walls; between slabs and walls;and between concrete and clay masonry, each element will be able to move somewhatindependently while still providing the necessary support. Typical methods of breakingbond between walls and slabs, and walls and foundations are shown in Fig. 12.

Bond Breaks in loadbearing Cavity WallFIG. 12

When bands of clay brick are used in concrete masonry walls, or when bands ofconcrete masonry are used in clay brick walls, joint cracking may result due to thedifference in material properties. It may be prudent to have the bond broken betweenthe two materials with building paper or flashing, or to provide additional movement

joints to eliminate this cracking.

Breaking bond does not affect the compressive strength of the wall and generally doesnot affect the stability of veneer wythes. The weight of the masonry, anchorage and thefrictional properties at the interface provide for stability.

When it is necessary to anchor a masonry wall to the foundation and to the roof, it isstill possible to detail the walls in a manner which allows some differential movement.Such anchorage will be required for loadbearing walls subjected to high winds orseismic forces (Fig. 13).


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Bond Break at FoundationFIG. 13

LOADBEARING MASONRY

The potential for cracking in loadbearing masonry members is less than in non-loadbearing masonry members since compressive stresses resulting from dead andlive loads help offset the effects of expansive movement. Adding reinforcement atcritical sections such as parapets, points of load application and around openings toaccommodate or distribute high stresses will also help control the effects of movement.Reinforcement may be placed in bed joints or in reinforced bond beams (Fig. 14). Itshould be noted that historically, old loadbearing structures did not have expansion

joints, and did not crack. However, the walls were thicker and made of homogeneousmaterials as compared to structures built today.

Bond Beams

FIG. 14NON-LOADBEARING MASONRY

Non-loadbearing walls are usually thinner than loadbearing walls. The exterior wythe isoften thermally isolated from the building by insulation and therefore is subjected tomore differential movement. For these reasons, a series of vertical and horizontalexpansion joints should be designed to permit differential movement.

Brick veneer can be self-supporting up to a maximum height of 100 ft (30.5 m) providedthe building has shear walls or rigid structural frames with stiff backing materials. For


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such a system, the structural frame provides the walls with lateral support and carriesall other vertical loads. The wall is tied to the frame by flexible anchors or adjustableties which permit differential movement. Allowance for differential movement betweenthe exterior brickwork and the structure is provided at any openings and at the tops ofwalls. Vertical expansion joints as discussed earlier must be incorporated.

Flexible Anchorage

Where anchors tie walls to the structural frame or the backing to provide lateralsupport, the anchors and ties should be flexible; i.e. resist movement perpendicular tothe plane of the wall (tension and compression) but not parallel to the wall (shear). Thisflexibility permits differential movements between the structure and the wall. Figure 15shows typical methods for anchoring masonry walls to columns and beams. Details ofanchoring brick to the backing are shown in Technical Notes44B.

Flexible Anchorage to Beams and ColumnsFIG. 15

The size and spacing of anchors and ties are based on tensile and compressive loadsinduced by lateral loads on the walls. Technical Notes44Blists recommended tiespacing based on application. Anchors and ties must be able to accommodate theexpected movement without obstruction and without becoming disengaged.

SUMMARY

This Technical Notesdefines the types of movement joints used in buildingconstruction. Details of expansion joints used in brickwork are shown. Therecommended size, spacing and location of expansion joints are given. By using the


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suggestions in this Technical Notes, the possibility of cracks in brickwork can bereduced.

Expansion joints are used in brick masonry to allow for the movement generated bymaterials as they react to their own properties, environmental conditions and loads. Ingeneral, vertical expansion joints should be used to break the brickwork intorectangular elements which have the same support conditions, the same climatic

exposure and the same through-wall construction. The maximum spacing for verticalexpansion joints is 30 ft (9.1 m). Horizontal expansion joints must be placed at shelfangles supporting brick masonry.

The information and suggestions contained in this Technical Notesare based on theavailable data and the experience of the engineering staff of the Brick IndustryAssociation. The information contained herein must be used in conjunction with goodtechnical judgment and a basic understanding of the properties of brick masonry. Finaldecisions on the use of the information contained in this Technical Notesare not withinthe purview of the Brick Industry Association, and must rest with the project architect,engineer and owner.

REFERENCES

1. ASTM C 920-01, Standard Guide for Use of Elastomeric Joint Sealants, Annual

Book of Standards, Vol. 04.07.

2. Beall, C., "Sealant Joint Design", Water on Exterior Building Walls: Problems andSolutions, ASTM STP 1107, T.A. Schwartz, Ed., ASTM, Phila., 1991.

3. "Building Movements and Joints", Portland Cement Association, 1982.

4. Rainger, P., "Movement Control in the Fabric of Buildings", Nichols Publishing Co.,New York, 1983.

5. Szoke, S.S., Carrier, G.J., "Accommodating Movement in Brickwork", Applicationsand Performance of Structural Materials and Exterior Facades, ASCE Convention,Boston, MA, October 27, 1986.

Design and detailing of Movement Joints

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