Structures 2 (2015) 1–7

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Analysis of brick veneer on concrete masonry wall subjected toin-plane loads

Stephen A. Marziale, Elias A. Toubiaa EIT, University of Dayton, Dayton, OH, United Statesb Department of Civil and Environmental Engineering and Engineering Mechanics, University of Dayton, Dayton, OH, United States

E-mail addresses: marziales@gmail.edu (S.A. Mar(E.A. Toubia).

http://dx.doi.org/10.1016/j.istruc.2014.11.0012352-0124/© 2014 The Institution of Structural Engineers

a b s t r a c t

a r t i c l e i n f o

Article history:Received 14 August 2014Received in revised form 22 November 2014Accepted 24 November 2014Available online 2 December 2014

Keywords:SeismicComposite actionShear-wallVeneerWytheTiesConcrete masonry

Brick veneers are commonplace in modern building construction. Current building codes require veneers to beanchored to a structural backing in order to transfer out-of-plane loads. However, for in-plane loads buildingcodes assign brick veneers as nonparticipating elements. This study exploits an analytical method to examinethe in-plane coupling between brick veneers and concrete masonry shear walls. The amount of load transferredthrough wall ties depends on factors such as tie spacing, tie stiffness, reinforcement, etc. Results indicate thatsome degrees of composite action exist; around 12% to 37% of the applied shear load is transferred to the brickveneer. Veneers should be isolated in their own plane from the seismic-force-resisting system. An optimumlocation of the isolation joint is proposed to minimize the rocking behavior and limit design story drift.

© 2014 The Institution of Structural Engineers. Published by Elsevier Ltd. All rights reserved.

1. Introduction

Historically, masonry has been a reliable material for centuries andstill prevalent in modern construction. Some of the benefits of masonryinclude ease of construction, durability, and fire resistance. Masonryis also attractive as a sustainable building material that can earn signif-icant credits in Leadership in Energy and Environmental Design (LEED).Due to its high thermal mass and specific heat, masonry provides anexcellent insulation and thermal properties, which reduce the overallheating and cooling loads of buildings [1].

Brick masonry is a common material for veneer walls. A veneer is awythe of masonry used as an exterior façade connected to a backingmaterial such as steel studs, wood, or concrete masonry. The veneercan be anchored to the backing wall with metal ties, or adhered to thebacking with a bonding agent. The two walls are separated by an airgap, typically 50 mm to 100 mm wide, allows moisture to drain fromthe wall assembly without penetrating the backing material. This airgap further enhances a veneer wall's thermal properties by allowingheat to dissipate more quickly. A veneer wall is a type of cavity wallthat exhibits non-composite behavior. The veneer directly transfersout-of-plane loads to the backingmaterial without adding any strengthor stiffness to the wall system. However, the backing material is as-sumed to carry the entire in-plane load, and any transfer of in-plane

ziale), etoubia1@udayton.edu

. Published by Elsevier Ltd. All rights

loads and stresses from the shear backing to the veneer is considerednegligible by most building codes, specifically the Masonry StandardsJoint Committee (MSJC) code [2]. Fig. 1.1 visualizes a typical detail ofan anchored brick veneer connected to a backing of concrete masonryunits (CMUs).

In order to limit cracking and other failures in the veneer, the MSJCrequires designers to limit the deflection of the backing wall but doesnot specify an exact deflection design limit. Instead, in the commentaryof Section 6.1.2 of the TMS 402-11 [2], the MSJC references limitsrecommended by other organizations such as the Brick Industry As-sociation (BIA) [3]. The BIA suggests that designers choose a backingdeflection limit of either L/720 or L/600 [3]. Section 1604.3 of theInternational Building Code (IBC) [4] recommends a deflection limit ofL/240 for brittle exterior walls and interior partitions that utilize brickmasonry.

The TMS 402-11 [2] recognizes that nonparticipating elementsshould be isolated from the seismic force-resisting system of a struc-ture, but fail to specify a specific method for determining an appro-priate width of isolation. Section 1.18.3.1 of the TMS 402-11 [2]acknowledges the need for further research on design options thatallow non-isolated, nonparticipating elements with correspondingchecks for strength, stiffness, and compatibility. This paper presentsan analytical model to quantify and predict the degree of compositeaction between the backup shear wall and the brick veneer facade(non-isolated, non-participating elements). A rational design ap-proach is also proposed to locate the isolation joints in the brickveneer.

reserved.

Fig. 2.2.1. Load-displacement of various wall ties.

Fig. 1.1. Typical cross section of a brick veneer anchored to a CMU wall.

2 S.A. Marziale, E.A. Toubia / Structures 2 (2015) 1–7

2. Background

2.1. Related code requirements

In addition to the aforementioned recommended deflection limits,the TMS 402-11 [2] sets forth other requirements for brick veneerconstruction. The requirements pertaining to dimensions of adjustablewire ties are presented in Table 1. This table compares theMSJC code re-quirements for tie spacingwith theCanadian andNewZealand standardtie spacings.

Section 7.1.1 of the Canadian Standards Association CAN/CSA-A370-04 [5] limits maximum vertical spacing to 600mm and horizontal spac-ing to 800 mm. Interestingly, the CSA [5] further reduces the limits forthe corrugated metal strip ties. Corrugated ties can be spaced at either:600 mm vertically and 400 mm horizontally, or 400 mm vertically and600 mm horizontally [5]. In Section 2.9.7.1 of SNZ HB 4236:2002 [6],Standards New Zealand (SNZ) restricts tie spacing to 400mm verticallyand 600 mm horizontally.

2.2. Related literature survey

Large scale experimental testing performed by Moore [7] showed asignificant increase in the strength and stiffness of the walls with veneer,

Table 1International building code standards for maximum tie spacing.

MSJC codesection

Category Requirement CAN/CSA-A370-04code section

Category

6.2.2.5.6.3 Max. vertical spacing 635 mm 7.1.1 a. Max. vertical sp6.2.2.5.6.3 Max. horizontal spacing 813 mm 7.1.1 b. Max. horizontal

6.2.2.5.6.1 Max. area per anchor 0.25 m2 10.5.1.4 Max. vertical spcorrugated strip

10.5.1.4 Max. horizontalcorrugated strip

which can be over 4 times the stiffness compared to the wood shear wallwithout brick veneer. Additional testing done by Thurston [8] showedthat for an isolated wall panel with masonry veneer, the veneer wallwould continue to resist load until it would slide along the joint betweenthe brick mortar and the concrete foundation. Their testing also showedthat for walls with closed corners (no joint), themovement of the veneerwall was caused entirely by the rocking of the wall and not sliding,presumably due to the extra weight of the veneer from around thecorner. In all of their testing presented, no sliding occurred along thehorizontal cracks between brick rows. Full scale shake table testingdone by Okail [9] showed similar results to the testing done by Thurston[8]. The movement of wall segments with closed corners and a largeheight to length ratio was caused almost entirely by rocking instead ofsliding, while for other segments of the wall, deflection was mainly dueto sliding. Zisi [10] found that the most important factors contributingto the performance of the wall assembly were tie type and tie spacing.Choi [11] tested small sub-assemblies of brick connected to wood with22 gauge corrugated metal ties. They applied monotonic and cyclic load-ing patterns on the subassembly and determined that the ties deflectedbased on an initial stiffness, but after a certain deflection the ties wouldbegin to twist and switch to a lesser secondary stiffness. Zisi [12] also test-ed the strength and stiffness of 22 gauge corrugatedmetal ties with brickand wood subassemblies. They reported similar twisting tendencies asChoi [11]; however, their values for initial and secondary tie stiffnesswere far less than Choi's stiffness values.

Williams and Hamid [13] tested a variety of adjustable wire tiesconnecting brick and a CMU backing. Two types of ties included intheir study are the eye& pintle tie, which restricts horizontalmovementbut allows free vertical movement, and a slotted block tie, which allowsmovement in both the horizontal and vertical planes. These adjustableties allow the brick and CMUwalls to expand and shrink independentlywhile maintaining a reliable connection between the two walls.Williams and Hamid [13] labeled the eye & pintle tie as T1 and theslotted block tie as T2. The average stiffness values of both ties arecompared in Fig. 2.2.1.

Requirement SNZ HB 4236:2002code section

Category Requirement

acing 600 mm 2.9.7.1 Max. vertical spacing 400 mmspacing 800 mm 2.9.7.1 Max. horizontal

spacing600 mm

acing ofties

600 mmor400 mm

spacing ofties

400 mmor600 mm

Fig. 3.1. Diagram of model using springs to represent brick and tie stiffness (shown only top two tie rows).

3S.A. Marziale, E.A. Toubia / Structures 2 (2015) 1–7

Lintz and Toubia [14] created an analytical method to estimate theamount of load transferred through ties and predicted the resulting re-action of the brick veneer. After analyzing a variety of wood shear walldesigns, they found that an unreinforced brick veneer can overturn orslide along the flashing plane at the base of the wall before the woodshear wall reaches its anticipated capacity. This conclusion is in parallelwith the experimental failuremodes observedby Thurston [8] andOkail[9]. To account for sliding and overturning, they proposed to developvertical steel reinforcements on each side of the thru-wall flashing(See Lintz and Toubia [14]).

Fig. 3.1.2. Diagram showing details o

3. Analytical method

The method for calculating load transfer in brick veneer backed byCMU is a slightly modified version of the method proposed by Lintzand Toubia [14]. This model assumes that the ties and brick veneercan be represented by springs. Since each tie is assumed to deflecthorizontally (in-plane), ties located in the same horizontal row areconsidered to act in parallel. Therefore, the total stiffness of a horizontalrow of ties is equal to the stiffness of an individual tie multiplied by thenumber of ties in the row. Then, each tie row stiffness is placed in series

f CMU and brick reinforcements.

Fig. 4.1.2. Deflected veneer shape at 100% of CMU shear capacity — CMU and brickreinforced.

4 S.A. Marziale, E.A. Toubia / Structures 2 (2015) 1–7

with a corresponding brick stiffness at that level. Fig. 3.1 shows a simpli-fied version of this method with two rows of ties.

The total stiffness of the effective spring at each row can then becalculated using Eq. (1).

1keff

¼ 1ktie row

þ 1kbrick

ð1Þ

Using superposition, the total deflection of the spring equals thedeflection caused by the applied load minus deflection caused by theresisting force of the ties and brick at each row. This principle is repre-sented in Eq. (2).

ΔT ¼ ΔP−ΔF ð2Þ

ΔT total deflection of the springΔP deflection of the spring due to the applied load PΔF deflection of the spring due to the force in the spring.

As more rows are added, the model becomes more complex sincethe resisting force in the spring at one row will cause a deflection atevery other row. Eq. (2) is applied at each row and modified to createEqs. (3) and (4), assuming two rows of springs.

ΔT1 ¼ ΔP1−ΔF11−ΔF12 ð3Þ

ΔT2 ¼ ΔP2−ΔF21−ΔF22 ð4Þ

ΔT1 total deflection of the spring at row 1ΔP1 deflection of the spring at row 1 due to the applied load PΔF11 deflection of the spring at row 1 due to the force in the spring

at row 1ΔF12 deflection of the spring at row 1 due to the force in the spring

at row 2ΔT2 total deflection of the spring at row 2ΔP2 deflection of the spring at row 2 due to the applied load PΔF21 deflection of the spring at row 2 due to the force in the spring

at row 1ΔF22 deflection of the spring at row 2 due to the force in the spring

at row 2.

This process can be extrapolated for any number of rows to form asystem of linear equations that describe the total deflection at eachrow. These deflections are calculated by combining traditional deflec-tion equations for a cantilever beam and specific deflection equationsfor masonry. Lintz and Toubia [14] used a modified version of Eq. 4.3-1 from the 2008 National Design Specification (NDS) Wind & Seismiccode [15] to describe the deflection of a wood shear wall. The modifiedequation is presented as Eq. (5). The first term expresses deflection due

Fig. 4.1.1. Load in tie rows at 100% of CMU shear capacity — CMU and brick reinforced.

to bending, the second term expresses deflection due to shear, and thethird term expresses wall deflection due to anchor pullout as the baseof the wall.

δsw ¼ 2PH3

3EAL2þ PHGaL

þ PH2Δa

L2Tallowð5Þ

Deflection of masonry is defined by Eq. (6), where Av = (5/6) ∗ Ag

and Gm = (2/5) ∗ Em for clay brick masonry.

Δm ¼ Ph3

3EmImþ PhAvGm

ð6Þ

After developing the equations to represent the deflection of thebrick and masonry walls at each row, the equations are substitutedinto a linear system based on Eqs. (3) and (4), and the only unknownvariables remaining are the forces in each spring. Once the forces ineach spring are found, the deflection of the brick veneer at each levelcan be calculated. A more detailed explanation of this method can befound in Lintz and Toubia [14].

Their proposed method is based on an unreinforced brick veneerconnected to a wood shear wall. In order to reduce the sliding of thebrick veneer, reinforcements are required to counter act this failuremode. Such reinforcements are depicted in Fig. 3.1.2.

To account for steel reinforcement in the brick (proposed solution toprevent sliding), the area of steel was transformed using the modularratio n (n = Es/Em) to create an equivalent area of masonry. The areaof transformed steel was then incorporated into the moment of inertiaof the wall, Im, as shown in Eq. (7).

Im ¼ 112

th3 þ thd12 þ nAsd2

2 ð7Þ

Fig. 4.1.3. Percentage of applied load transferred to veneer— CMU and brick reinforced.

Table 4Adjustable wall tie stiffnesses.

T1N/mm

T2N/mm

kinitial 54.25 170.6ksecondary 21.70 54.29Δk change 0.0025 0.0118

Table 2Spacing cases for analysis using a CMU shear wall (Note: Sv = vertical spacing, Sh =horizontal spacing).

Spacing case Sv Sh

mm mm

A 406.4 406.4B 406.4 812.8C 609.6 406.4D 812.8 406.4

5S.A. Marziale, E.A. Toubia / Structures 2 (2015) 1–7

where t = thickness of the masonry wall, h = length of masonry wall,d1 = distance from centroid of masonry to neutral axis (N.A.), andd2=distance from centroid of transformed section to N.A. Additionally,a term similar to the anchor pullout term in Eq. (5) was added to Eq. (6)to simulate deflection due to reinforcement pullout (acting as anchorsat each corner of the wall). The adjusted equation for masonry deflec-tion is shown in Eq. (8). Themaximum tension force in the steel anchor,Tallow, was controlled by the bond strength between the steel and grout,assuming a bond strength of 1103 kPa according to Section 2.1.7.2 of theTMS 402-11 [2]. The corresponding maximum allowable deflection, Δa,is the deflection of the steel reinforcement at Tallow.

Δm ¼ Ph3

3EmImþ PhAvGm

þ PH2Δa

L2Tallowð8Þ

Another modification incorporates the steel reinforcement anchorsinto the equation for sliding along the flashing plane.

Eq. (9), proposed by Ahmadi et al. [16], is used to account for thefriction between the flashing and the veneer aswell as the additional re-sistance provided by the steel reinforcement. Ahmadi et al. [16] deter-mined an approximate coefficient of friction, μ, of 0.63 (reinforcedCMU and concrete foundation). The following analysis presents resultsusing coefficients of 0.35 and 0.65 to account for various flashing mate-rials.

Vs ¼ μ As fy þ Pn� �

ð9Þ

First, this method was used to analyze the effects of reinforcing abrick veneer attached to the CMU shear wall. Then, tie spacing and tietype were varied to develop an understanding of how influential eachfactor is to the overall strength and stiffness on the double-wythe wallassembly. For each trial, load is applied to the shear wall in incrementalsteps to account for the change in stiffness of the ties until the failuremodes are reached. The load step is relative to the total shear capacityof the backing wall. This paper accounts for strength and serviceabilityrequirements. The Allowable Stress Design (ASD) directly addresses

Table 3Load to failure for various tie spacings.

Wall type (a) Spacingcase

Brick sliding μ =0.35 (b)

Brick sli0.65

kN kN

2.44 m × 2.44 m, all unreinforced A 24.14 58.852.44 m × 2.44 m, all unreinforced B 48.85 106.972.44 m × 2.44 m, all unreinforced C 39.06 90.112.44 m × 2.44 m, CMU reinf., brick unreinf. A 29.35 68.862.44 m × 2.44 m, CMU reinf., brick unreinf. B 58.39 127.082.44 m × 2.44 m, CMU reinf., brick unreinf. C 51.54 112.592.44 m × 2.44 m, CMU reinf., brick reinf. A 162.96 324.112.44 m × 2.44 m, CMU reinf., brick reinf. B 289.33 559.962.44 m × 2.44 m, CMU reinf., brick reinf. C 252.71 486.42

(a): Typical CMU construction: f′m=13,790 kPa ,thickness= 203.2mm , reinforced at 1220m10 Grade 240 (no 3, Grade 60 US bars) bar at each end.(b): μ = coefficient of static friction between the brick wall and the flashing material.(c): Δ = deflection limit.

these limit states. Consequently, all calculations of masonry wallstrength and serviceability use the Allowable StressDesign and conformto Chapter 2 of the TMS 402-11 [2].

4. Results and discussion

4.1. Influence of tie spacing

The wall used in this analysis is 2.44 m tall and 2.44 m long. The tieused in this section features the T1 stiffness values found by Williamsand Hamid [12]. The baseline values for the specified compressivestrength were 13,790 kPa for CMU and 10,340 kPa for brick. Thesevalues represent commonmasonry strength used for industrial and res-idential constructions. The tie spacing needs to reflect the geometry ofthe CMUwhich dictates vertical spacing of 203.2mm intervals. Tie spac-ing cases B and D violate Section 6.2.2.5.6.1 of the TMS 402-11 [2], butare included in this analysis to study any trends of increasing tie spacing.

For each tie spacing case, the wall assembly was studied with bothwalls unreinforced, CMU reinforced and brick unreinforced, and bothwalls reinforced. The CMU wall was reinforced with Grade 420 (Grade60), no. 13 (no. 6 US bar) placed at 1220mmon the center. The brick ve-neer was reinforced with one no. 10 (no. 3 US bar) bar at each edge ofthewall. Figs. 4.1.1 and 4.1.2 display the load transfer and veneer deflec-tion patterns at an applied load equal to themaximum shear capacity ofthe CMU wall. These figures are taken from the case of both walls rein-forced. Figs. 4.1.1 and 4.1.3 demonstrate that the closest tie spacing, caseA (horizontal and vertical), transfers the greatest load. Case B transfersthe lesser load due the large horizontal spacing of the ties and the effec-tive stiffness flexibility of the tie rows.

Fig. 4.1.3 shows howmuch of the applied load is transferred throughthe ties to the veneer when bothwalls are reinforced. The brick resists asignificant load immediately at low loads before settling to a constantrate. This is due to the high initial stiffness of the wall ties (seeFig. 2.2.1). After the ties begin to yield or locally deform, their secondarystiffness will engage and less load is transferred to the brick.

Table 3. presents the applied load to failure for various tie spacingand reinforcement cases. Although CMU shear failure and overturningare possible failure modes, the model ignores any vertical axial loadon the CMU wall. In reality, the CMU wall would support the loads of

ding μ = Brickoverturning

Load at Δ = L/600(c)

Load at Δ =L/240

Max. % of loadtransferred tobrick

kN kN kN

63.34 13.27 31.92 19.16%114.55 12.67 30.91 12.38%97.43 12.79 31.14 14.03%74.49 15.59 38.05 17.30%

137.04 15.03 37.01 10.83%121.99 15.08 37.09 12.28%220.56 15.59 38.05 17.30%384.86 15.03 37.01 10.83%339.48 15.08 37.09 12.28%

m on center (o.c); Typical brick construction: 10,340 kPa , thickness= 101.6mm , one no.

Fig. 4.2.1. Load in tie rows using T1 and T2 ties.

6 S.A. Marziale, E.A. Toubia / Structures 2 (2015) 1–7

floors and roofs above its level which increases the CMUwall's ability toresist overturning and shear (CMU-URM shear capacity of 130 kN).Therefore, these CMU failure modes are unlikely. In most cases, thebrick veneer slides before it overturns; particularly if the brick is unrein-forced (Table 3.). It is interesting from a design perspective to observethat the L/600 limit governs the design, and the L/240 limit addressedby the IBC code [4] is not conservative, since in most cases brick slidingmode occurs before reaching this limit.

4.2. Influence of tie stiffness

Using spacing case A as a baseline (Table 2), two of the adjustablewall ties tested byWilliams andHamid [12] can be compared. The initialand secondary stiffness of each tie are displayed in Table 4.

The T2 ties are far more rigid than the T1 ties, and therefore it is ex-pected that the T2 ties transfer more load to the veneer. This is clearlydemonstrated in Fig. 4.2.1. This plot was generated with an appliedload equal to the shear capacity of the CMU wall.

Since a rigid tie forcesmore load on the brick, the veneer with the T2ties carries a higher percentage of the total applied load (column 9,Table 5). This justifies the observation that the load to failure using arigid tie (T2) is much less than the load to failure of a flexible tie (T1)(Column 4 and 5, Table 5). Another interesting observation is the largedifference at load to failure in brick sliding mode at η = 0.35 and η =0.65 for T1 and T2 ties. For the low coefficient of friction case (η =0.35), as the shear load is applied at the CMU, the wall slides at approx-imate close values when using T1 or T2 ties (unreinforced case;24.14 kN vs. 20.27 kN). However, for a rough flashing surface (η =0.65), the T1 tie demands more load to slide the brick veneer than theT2 tie (unreinforced case; 58.85 kN. vs. 37.65 kN), since the T2 tie offersa rigid coupling connection between the backing and the brick veneer.

Table 5Load to failure for veneers with rigid adjustable wall ties.

Wall type (a) Spacingcase

Tietype

Brick sliding μ= 0.35 (b) B

kN k

2.44 m × 2.44 m, all unreinforced A T1 24.142.44 m × 2.44 m, all unreinforced A T2 20.272.44 m × 2.44 m, CMU reinf., brick unreinf. A T1 29.352.44 m × 2.44 m, CMU reinf., brick unreinf. A T2 22.452.44 m × 2.44 m, CMU reinf., brick reinf. A T1 162.96 32.44 m × 2.44 m, CMU reinf., brick reinf. A T2 68.64 1

(a): Typical CMU construction: f′m=13,790 kPa , thickness = 203.2 mm , reinforced at 1220 mUS bars) at each end.(b): μ = coefficient of static friction between the brick wall and the flashing material.(c): Δ = deflection limit.

4.3. Width of isolation

As discussed in the introduction section, there is no consensusmeth-od for calculating an appropriate width of isolation. It is understood thatnon-isolated, nonparticipating elements can influence a structure'sstrength and stiffness. Therefore, placing the isolation joints close tothe corners of the brick veneer façade can prevent rocking behaviorunder cyclic loading. Based on the results discussed in the previous sec-tions, significant amounts of load can be transferred through the ties.If thewidth of isolation is too narrow, these transferred forces could de-flect the isolated section.

Using the model developed in Section 3, the loads in each tie rowwere calculated at a certain applied load. For this example, a loadequal to 25% of the CMU shear capacity (within the elastic responserange) was imposed on a 2.44 m by 2.44 m reinforced shear wall witha case A tie spacing. The loads in each tie row were then reduced by aratio of L1/L and applied to a brick wall with length L1 and height H,where L1 is the length of the isolated section. A diagram of an isolatedwall section including applied tie row forces transferred to the brickveneer is shown in Fig. 4.4.1.

The deflection at each tie rowwas calculated based on the applied tierow forces. This process was repeated for various widths of isolation.Then, the loads in each tie row and the corresponding deflections ateach row were plotted, and the result is shown in Fig. 4.4.2.

As L1 increases, H/L1 decreases, and the lines begin to converge to-ward a point where the isolated wall section does not deflect due totransferred forces. Investigating Fig. 4.4.2, one can notice that an opti-mum design target would consider a minimal deflection (story drift)and small load in the top tie row. A large deflection will crack the bedand head thin joints, causing the serviceability of the veneer to degrade.Additionally, a large load transferred can locally deform the tie, or spalloff and break the interface bond between the mortar and the tie. Thiswill weaken the out-of-plane stiffness and affect the serviceability andwater tightness of the brickwall. Using this rational approach, a design-er can choose an approximate width of isolation based on a H/L1 ratiobetween 3 and 4. For example, for a 3-meter veneer wall, an isolationjoint should be placed at approximately 1 m from the edge of eachcorner.

5. Conclusion

This researchwork presents an analyticalmethod to calculate the in-plane load transferred through wall ties as well as the deflection of abrick veneer caused by these forces. Using the model of a brick veneeranchored to a CMU shear wall, tie stiffness and spacing were found tosignificantly influence the failure modes of the brick veneer, whereasCMU compressive strength and wall thickness had minimal effects.Close tie spacing and stiff ties forms a rigid coupling between the CMU

rick sliding μ= 0.65 Brick overturning Load atΔ = L/600 (c)

Load atΔ = L/240

Max. % of LoadTransferredto Brick

N kN kN kN

58.85 63.34 13.27 31.92 19.16%37.65 38.03 13.27 38.98 37.35%68.86 74.49 15.59 38.05 17.30%41.69 41.95 15.88 47.15 36.43%24.11 220.56 15.59 38.05 17.30%06.20 76.48 15.88 47.16 36.44%

m ; Typical brick construction: 10,340 kPa , thickness = 101.6 mm , one no. 10 bar (no. 3

Fig. 4.4.2.Width of isolation analysis for various H/L1.

Fig. 4.4.1. Diagram of an isolated section of brick veneer.

7S.A. Marziale, E.A. Toubia / Structures 2 (2015) 1–7

and brick, and some composite action occurs. As shown in Table 4.,a brick veneer anchored with rigid adjustable wall ties spaced at400 mm horizontally and vertically, can be subjected to approximately37% of the load applied to the shear wall. Using the largest tie spacingpermissible by the TMS 402-11 [2] (defined as case C in Section 4.2),an unreinforced veneer will still resist approximately 12% of the appliedload. Since the veneer exhibits composite action, it is recommended thatbrick veneers be isolated or include some form of reinforcement as aprecaution.

Designers should limit deflection of the backing to L/600when brickveneer façade is used. This limit prevents sliding and overturning of thebrick veneer while maintaining the serviceability of the wall system.The IBC's suggested limit of L/240 is not recommended, since in certaincases, the brick failed due to sliding before reaching the L/240 limit.In order to prevent the veneer from sliding, a flashing material with acoefficient of friction of 0.65 should be used. In addition, in active seis-mic regions, the ends of thewalls should be isolated at a length approx-imately H/3 or H/4 from the edge.

Notations and abbreviationsAg gross cross-sectional area of masonryAs cross-sectional area of steelAv net shear area of masonryASD allowable stress designBIA Brick Industry AssociationCMU concrete masonry unitCSA Canadian Standards AssociationEs modulus of elasticity of steelEm modulus of Elasticity of masonryf′m specified Compressive strength of the masonryfy yielding stress of steel reinforcementGa apparent wood shear wall stiffnessGm shear modulus of masonry

H total vertical height of the wallh height from ground to tie rowI moment of InertiaIBC International Building Codek stiffnesskbrick stiffness of brick veneerkeff net effective stiffnessktierow total stiffness of all brick ties in a single rowL total in-plane length of the wallL1 in-plane length of an isolated wall sectionLEED leadership in Energy and Environmental DesignMSJC Masonry Standards Joint CommitteeNCMA National Concrete Masonry Associationn ratio of elastic modulus of steel and masonry, Es/EmNDS National Design SpecificationP applied in-plane load on the CMU wallRM reinforced masonrySh horizontal spacing between wall anchorsSv vertical spacing between wall anchorsSNZ standards New ZealandTallow maximum allowable tensile load of shear wall anchorTMS The Masonry SocietyURM unreinforced masonryVs frictional forceΔa maximum allowable elongation of shear wall anchorΔF deflection of the spring due to the force in the springΔk change deflection at which ties switch from initial to secondary

stiffnessΔP deflection of the spring due to the applied load PΔT total deflection of the spring at a tie rowδsw deflection of a wood shear wallμ coefficient of static friction

References

[1] National Concrete Masonry Association. TEK 6-9C: concrete masonry & hardscapeproducts in LEED 2009. Herndon, VA: National Concrete Masonry Association; 2009.

[2] The Masonry Society. Building code requirements and specifications for masonrystructures. (TMS 402-11/ACI 530-11/ASCE 5-11). Longmont, CO: The Masonry Soci-ety; 2011.

[3] Brick Industry Association. Technical note 18A: accommodating expansion of brick-work. Technical notes on brick construction. Reston, VA: Brick Industry Association;2006.

[4] International Code Council. International building code. Country Club Hills, IL: Inter-national Code Council, Inc.; 2011.

[5] Canadian Standards Association. CAN/CSA-A370-04: connectors for masonry. Toron-to, ON, Canada: Canadian Standards Association; 2006.

[6] Standards New Zealand. SNZ HB 4236:2002: masonry veneer wall cladding.Wellington, New Zealand: Standards New Zealand; 2002.

[7] Moore JFA. Some preliminary load tests on brick veneer attached to timber-framedpanels. Proceedings of the British Ceramic Society Symposium; 1978.

[8] Thurston SJ, Beattie GJ. “Seismic performance of brick veneer houses”. 2008 NZSEEconference. New Zealand: New Zealand Society for Earthquake Engineering.Wairakei; 2008.

[9] Okail Hussein O, Shing P Benson, McGinley W Mark, Klingner Richard E, JoSeongwoo, McLean David I. Shaking-table tests of a full-scale single-story masonryveneer wood-frame structure. J Earthq Eng Struct Dyna 2011;40(5):509–30.

[10] Zisi NV. The influence of brick veneer on racking behavior of light framewood studwalls. Ph.D. thesis, Knoxville, TN: University of Tennessee, Knoxville; 2009.

[11] Choi YH, LaFave JM. Performance of corrugated metal ties for brick veneer wall sys-tem. J Mater Civ Eng May/June 2004:202–11.

[12] Zisi NV, Bennett RM. Shear behavior of corrugated metal tieconnections in anchoredbrick veneer-wood frame wall systems. J Mater Civ Eng February 2011:120–30.

[13] Williams CR, Hamid AA. Plane stiffness and strength of adjustable wall ties. 10th Ca-nadian Masonry Symposium; 2005.

[14] Lintz JM, Toubia EA. In-plane loading of brick veneer over wood shear walls. Mason-ry Soc J December 2013;31(1):15–27.

[15] American Forest Paper Association. Special design provisions for wind and seismic.Washington, D.C.: American Forest and Paper Association; 2011

[16] Ahmadi F, Hernandez J, Scheid G, Klinger RE. Sliding shear resistance of reinforcedmasonry shear walls. Masonry Soc J December 2013;31(1):45–57.