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ALTERNATE BRICK VENEER OESIGHS ANO INSTALLATIONS By Walter L. Oickey Consultino Engincer 7f

Higgins Brick Company

ABSTP.ACT

The Uniform Bullding Code (UBC) of the International Conference of Building Officials (IC(30) provides for brick vencer installation by "Per­formance," i.e.,design, ~lÍth the option of using ' ·Prescription",or specifi­cation of timc provcn methods. In general, this discussion is based on the excellent codification in the UBC, which contains one of the best and logic­ally sound codes on Veneer. It simply states,in brief, certain general I imitations or requirements, defines the two types of veneer, requires that they be designed and states the design criteria for each. In lieu of design it permits use of certain time proven standard or specification alternate installation.

Adhered Vencer. The UBC design criteria is,desiçn to develop 50 psi in shear. This may seem large for a 15 psf maximum load but is valid be­cause it is easily developed if workmanship is proper. Other economical aJ­ternate methods have bcen tested and are recommerded .

Anchored Veneer . The UBC "Performance" design criteria is 2 times its weight. Although this is Jarge, it is easiJy achieved and provides a good factor of safety for thermaJ andother dcfJections with no economic penalty.

Examples of design are clarified. The true dcsign of brick anchored to (flexible) steel studs for wind and quake is outl ined based on computer­ized building and wall dynamic response to quakes, as well as wind, and de­termines the more correct value of capacity of ties required.

The investigation confirms that the UBC provisions are, in general, satisfactory if followed properly, and notes reasons for some failures of improper installations.

* ' Past President, Structural Engineers of Northern California; Past Presldent The Hasonry Society; Life Hember, American Society Civil Engineers; Hon. l1~mber, American Concrcte Institute ; Member, American Society Testinç Mate­~ials C1S, Hasonry; Member, Consulting Engineers Association, American Con­sulting Engineers Council; Member, Structural Engineers of Southern Cali- · fornia; Professional Hember, International Conference of Building Officials; Irstructor, Cal-Poly; Lecture r , University of California,Los AngeJes; flon­orary Member, Instituto de Mexico; Commander, U.S. Navy Civil Engineers Corps; Licensed Engineer, California, Oregon, Washington, Hawai i, Nevada, Utah, Texas, and Florida.

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INTRODUCTION

As expressed and demonstrated in previous papers [1] [i] [3] [4][S] the Masonry Veneer Chapter of the Uniform Building Code (OBC) is one of the simplest,must direct and 10gically organized. [S]

It is, in essence, the Veneer Chapter as revised for 1967 Edoition of UBC and:

1. Lists certain general limitations or requirements, such sizes, heights, consideration of differential deflections, shrinkage, creep, temperature.

2. Defines the two types of veneer as Adhered and Anchored. 3. Requires that they be desiogned; 4. States the Adhered design criteria as "SO psi in shear." S. States the Anchored criteria as "2x weight." 6. In 1 ieu of performance design, permits use of prescriptive

specified Standard time-proven alternates.

The purpose of this discussion is to clarify some of those limita­tions and to indicate some alternates that may be used. Also to clarify some of the structural design aspects of these 50 called non-structural installations, especially for brick veneer on steel studs.

This latter system is an especially complex, rather indeterminate, structural problem which warrants more explanation, especially since many who specify or install non-structural veneer may not >be highly skilled In indeterminate principIes of structural design, and beca use even greater use of the system seems imminent due to its many benefits.

Also some failures will be discussed to further clarify proper in­stallation methods.

The UBC Chapter is rather brief, it can be put on a page, with the Standards requiring only a few more (compared to other verbose chapters.)

GENERAL LIMITATIONS

"Limitations: Exterior veneer shall not be attached to wood-frame construction at a point more than 30 feet in height above the non-combus­tible foundation except the 30' limit may be increased when special con­struction is designed by the Building Official.'o[l]This limit is intended to provide for the accumulated differential settlement of wood especial-Iy in side bearing and cross grain shrinkage compared to the negligible settlement in the rigid veneer plane. The excessive settlement of the wood backing, especial1y with platform construction, would destroy the ties or attachment to the backing.

Alternate to prescriptive height limit.

Alternate constructions may minimize that problem. Flexible joints may be placed at calculated leveIs to provide for the vertical motion of the backing. For example, at floor leveIs there may be side grain double top plates on studs + floor joist + flooring + bottom stud plates permlt­ting a side grain settlement of perhaps over 1/2". Calculated expansion joints may be installed at these levels,-to provide for settlement with­out distress. Vertical support for adhered veneer is by adhesion to the backing.

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For the anchored veneer support may be by shelf angles in ~lIdi a manner that distress due to deflection does not occur, e.g., by speclal angle support or by sltding type anchors.

Construction Limitations

Materiais, Loading, method of design and of weatherproofing and con­struction are as covered in other appropriate chapters of the Code, e.g., 17, 23, 24, 26, 47.

;f

The simple term "corrosion resistant" states a very important quality frequently not awarded the respect due it. In addition to g~lvanizing, which is a limited duration sacraficial protection, there are metaIs which may be used for more permanent protection.

I rI' When the terms "corrosion resistan!" or "noncorrosive" are used in this

chapter they shall mean having a corrosion resistance equal to or greater than a hot-dipped galvanized coating of 1.5 ounces of zinc per square foot of surface area. When an element is required to be corrosion resistant or noncorrosive. alI of its parts shall be corrosion resistant, such as screws, nails, wire, dowels. bolts, DUts, washers, shims, anchors, ties and attachrnents. \"

ADHERED VENEER

-,) L

The requirement for developing a shear "bond of 50 psi" is much greater than a structural design would indicate for a material that weighs less than I psi. However, it is easily developed and it is to provide a measure for good workmanship. Less than 50 psi might indicate poor work­manship. The Standard prescriptive method and several alternates will de­velop 3 or more times that value with good workmanship. The high bond value also provides for resistance to secondary thermal stress miscellane­ous deflection etc. I. A paste of neat portland cement shalJ be brushed on the backing and the

back of the veneer uni!. li'pe S mortar then shalJ be applied to the backing and the veneer uni!. Sufficient mortar shalJ be used to create a slight ellcess to be forced out the edges of the units. The units shalJ be tapped into place so as to completely filJ the space between the units and the backing . The resulting thickness of mortar in back of the units shalJ be not less than 1/2 inch nor more Ihan 11/. inch o

One improvement to the Code might be the addition of more standard methods to include clearly the more recently developed bond enhancers such as latex and thin set nrethods as Standards. Some of these are included In IC60 Research Evaluation or Approvals, obtained on a proprietary basis, upon the approval of Ceramic Tile Institute as an approved testing labora­tory for evaluating the bond capacities. Several are accordino to American National Standsrds Institute standards,e.g., ANSI II&and 10& r 6].

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This would increase the possible optional prescriptive alternates to the simple design performance stipulation of "50 psi." [UBC]

One must recognize that placing of Adhered Veneer is a hand operation and may be imperfect in some way, e.g., there may be dust or paint or oil on the unit or on the backing; the amount of bonding mortar may not fill the bond spacej the bonding layer may have set somewhat before contact with the unit; the units might be moved for positioning after placing; the mois­ture content of units or of backing might not be optimum; etc. etc.

Therefore, it is well to place tooled mortar joints. The tooling when "thumb print firm" provides that the mortarwill bond to the backing and to the sides of the units, to a degree adequate to support the light weight of the unit even if the units were not bonded to the backing. This provides an additional fattor ·of , safety since . fal~ures in one ·system will not occur at the same place as failures in the ~ther (as in appllcation of two coats of paint),as ' well as adding resistance to water penetratlon.

There have been many failures of installation of thin units in which the tooled mortar was not placed. The consequent joint space between units was considered a "raked joint" in appearance. Water could enter and could cause internaI efflorescence and there was no redundancy for factor of safety. There were consequently many fai lures of such installations.

ANCHORED VENEER

The options for Anchored Veneer are the design (performance) or "in lieu of design use satisfactory standard (prescriptive) methods." The de­sign criteria of 2x weight is actually a rather prescriptive method since in certain systems, e.g., the stiff brick veneer anchored to limber steel studs, it invokes a rather complex design to give proper "consideration of ... deflection." Research by WSCPA [1], BIA [e] and others shows that in some cases a valid design method may show greater loads on ties.

Also, in order to be more complete, and for clarification, there should be additional prescriptive Standard methods listed in the Code, some which have been developed since the 1966-67 writing of the Chapter.

The brick veneer on steel studs warrants a more expansiwe clarifi­cation of "Consideration should be made of .... deflection," however simple that true statement may be.

This subject emphasizes what the IC80 Committee had in mind when they imposed the requirement for design of the veneer to include consid­eration of those factors of secondary indeterminancy.

Considera!ion shall be given for differen!ial movemen! of supports . including lha! caused by !empera!ure changes. shrinJcage, creep and deflection.

This differential stiffness and deflection consideration was an item frequently overlooked by designers in a quick skimming of the Code, espe­cially since most designers of this non-structural item were not skilled structural engineers.

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Study of this subject suggests, perhaps, that not only should there be additional satisfactory alternate standards added but that the design recolTfT1endation of "2x the weight" should be considered a tentative perform­ance design with a prescriptive criteria, and that the true performance re­quirements be added to the Chapter in more detail. Actua"y this subject of differential deflections is important beca use the backing of st€el studs is relatively limber, whereas backing of concrete or masonry is relatively stiff 50 that the problem does not warrant much consideration.

BRICK VENEER ON STEEL STUOS

Although the UBC Standard for brick on steel studs will generally comply with the specified prescriptive design, i.e., 2x thp. weight, WSCPA [7] and BIA [8] and others realized it was necessary to analyze the sub ject further as a truly indeterminate structural design problem consldering seismicity response and differing stiffnesses.

The seismic reactions and response of brick/steel stud systems were uncertain initia"y. There was the possibility that the veneer wall period would be much stiffer than the building stiffness and hence the veneer wall response would be much less than the building seismic response due to the building response factor. This would have been similar to the early prin­cipie of "Flexible First Story," or modern "Base I·solation."

In order to evaluate the seismic effect, especia"y for Zone 4, and the indeterminate load distribution between brick and steel studs and the tie or connection loadings, WSCPA,[ 7] sponsored a report "WINO ANO EARTH­QUAKE FORCES ON BRI CK VENEER WITH STEEL STUOS" by Computech and KPFF ,Ref. [ 1] and REPORT ON BEHAVIOR ANO OESIGN OF ANCHOREO BRICK VENEER METAL STUO SYSTEM BY KPFF [ 9].

Wind arid EartHquake Loads on System

The project Report [7] was to develop guidelines to ensure that brick veneer cladding systems will be able to safely resist wind and earth­quake loadings.

The response to quakes was determined by a series of typical building computer models, 2 and 4 stories)subjected to quake and wind loadings, then more detailed modeling of veneer panels to determine deflections, cracking and effect of varying stiffness of brick, ties, and studs.

Simplified Oesign Summary

Since the seismic and wind loads and the brick stresses and the tie stiffnesses are intrinsica"y not precise factors in actual construction the complexities of precise design calculations are not warranted in real life and the procedure may be simplified for general practice. However, although certain design parameters are not precise in value they must be correct in principie and system.

The seismic Cp factor for the building should be used for the seismic wall panel loading. In general the magnitude of loading will be governed , by wind loading.

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The uncracked brick and stud framing will deflect very nearly equal­Iy, due to the tie function.

The ties impose the load on the studs, with the top and bottom one or two tie leveis imposing the brick span reactions.

The load distribution between the uncracked brick and the stud fram­ing is proportional to their stiffnesses, i.e., based on

IOf 12

lí8d

The conventional basic deflection equation is extendcd above for con­venience in different calculations and comparisons.

Since the uncracked brick and the studs deflect similarly to resist the total lateral load

Moment (Stud)

Moment (Brick)

Total M x E I (stud) E'TTstü"d) + EI (bri ck)

Total H x Er (brick) E I ( 5 t ud) + E' ( b r i ck)

At maximum loading conditions, and service deflection, the brick and studs will have shared the load and deflection in proportion to their stiffness until the brick cracks, then the studs carry the total load.

In general, for a serviceability deflection limit the stud stress wi 11 not governo

In general, it is practical to recognize that the brick will crack 50

the anchors, ties, etc. must be corrosion resistant. Perhüps the proper term should be corrosion proof!

Tie Loading

The ties transfer the load between the brick and the studs. The stiffness of the ties will influence their loading. The stiffness will consist of the elastic, plus consideration of inelastic deformation and this is an item that tie manufacturers must determine by test and furnish to the designer.

Example Calculation

A calculation of a typical example would be, as shown in Reference [ 9 J.

I. Assume: 144" 6" steel joi st @ 16" wind w 35 ps f I = 2.65 zone No.= 4 s = .65

d = 3-'1'12" ti es @ 16" hor.12, 12" verto f b= 180

max t; = I = 0.40 ~

Veneer weight = 35 psf: Cp 0.3, w 0.3 x 35 11 psf

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2. Verify stud size and spacing for adequacy after brick crack

3. Determine maximum tie force at top and bottom

Moment in brick @ cracking

fx' = f x ud 2 = IDO x 12 x 3.S2 4410"# 368'# c 6 6

w = _fi x 36& = 20.4 psf 122

4~ Determine tie stress at top and bottom

T = 20 . 4 x 12/2 = 122

Tie ultimate capacity reg. = 122# x (F.S . = 1.2S) = 153#

Since after cracking the ties will carry nearly the simple tributary area or 16 x 12 x 3S# = 46#, this will not governo

Ilowever, it must be recognized that actually the reactioll at top and bottom will probably be shared in some degree by the end two ties rather than entirely by one tie, i.e., 80# per tie, for a value practically a maximum.

However, for this rather maximum condition one might ask the ti e manufacturer to provide ties to develop a confirmed load capacity of, say, ISO I bs.

Another criticai area for " cons ideratioll of differential deflections\\ is at corners of facing veneers, the inplane and out cf plane stiffness varying so greatly. This requires judicious use of e xpansion joints.

CO~ICLUS IOtl5

I. The UBe Veneer Chapter is valid in providing sound general limitations, performance design criteria,and in lieu thereof alternate prescriptive methods. 2. Other alternates are available. 3. The brick on steel stud system seismic factors as the building. reasonable.

should be designed for the same wind and A deflection service limit of 1/360 is

4. Exterior veneer connections, ties, anchors etc. should be (really)corrd­s i on res i 5 tan t . S. In geHeral the chapter performance and prescriptive provisions are quite adequate, if read carefully and appl ied. Pe 'riiaps installations above rub­I ic ways or areas should be continuously inspected for protection against damage, injury, and lawsuit.

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•••••• .... I~ • ••• a ... .. . .. .... 1 .. ..

A venéer facing that is supported,from top of parapet to bottom,on the fo~ndation. Lateral ties are long bolt' strut-ties , which provide out-of-plane support but permit in-plane move­ment relative to building by end rotation.

REFERcllCES

l. "Uniforr.1 [luilúing Code,"19(i7 and 1988 edition. PuLlished by the Inter­national Confercnce of Building Officials.

2. \.-:.L. Dickey I : r~asonry Veneer Dcsign Under lhe lJniform Building Code,' ; Pub 1 i shed in 5 I BMaC, 1981.

3. w. L. Dickey, 1 ; ~lasonry Veneer" publ ished in 1968 by 11J1,SONP.V RESEJI,RCH, 2600 ~;ilshire óoulevard, Los Angeles Caliornia 90057

4. I,.i. L. Dickey, "/1asonry Veneer," published in 1974 by 11asonry Institute of America, 2550 Heverly Boulevard, Los Angeles, Cal ifornia 90057

5. ~!. L. Dickey, "Higgins 13rick Vencer;" published by Higgins Brick Company, ~G45 ~Iena Street, Redondo Beach, California 90277

6. ANSI, 108; 118; Standards publ ished uy Americar, IJati onal Standard Insti­tute,

7. "\;' ind and Earthquake Forces on orick Veneer with Steel Studs," prepared for Western States Clay Products Association by Computech Engineering Services, 2855 Telegraph Avenue, Berkeley, California 94705 and KPFF.

8. Tech Notb, 28, BV Brick Institute of America

9. "Report on Behavior and Design of Anchored Brick Veneer/11etal Stud Systems" by KPFF, . 2121 Cloverdale Boulevard, Santa Monica, Cal ifornia, 90404.