1632

Tests of Tie Reinforcement for Composite and Cavity Masonry Wall Construction

Dr. James Colville,

by

Associate Dean of Engineering and Professor of Civil Engineering, University af Maryland~

College Park, Maryland 20742 (U.S.A.)

and

Dr. Donald W. Vannoy, Associate Professor of Civil Engineering University af Maryland

College Park, Maryland 20742 (U. S.A.)

ABSTRACT

A variety af continuous and individual wall tie systems are available for interconnection of multiple wythe walls. One such system is an adjustable, 5in­gle unit masonry reinforcement system consisting af a 0.076 em by 2.54 em cor­rugated steel, hot-dipped galvanized, ties which are preattached to the chords af conventional ladder on truss type joiot reinforcement.

The paper presents the results af a series af tests to determine basic io­formation on the strength of this tie system in transmitting tension, compres­sion and shear between interconnected masonry wythes.

A total of 4S specimens were tested considering combinations of the fol~ lowing parameters: type of test, (eompression , tension, shear) magnitude of space between wythes, (2.2 em, 7.3 em, and 9.8 em), and tie alignrnent condition , i.e., zero misalignment and maximum misalignment.

Details of the test speeimen and method of eonstruction are presented along with a thorough deseription of the test precedures.

Test results are presented and discussed in detail . Reeornrnended design equations are developed and presented for eaeh failure mechanism.

Introduetion:

In both cavity and composite masonry wall construction, it is desirabl eto intereonnect the briek and bloek wythes with meehanieal anehoring devices. re­ferred to as wall ties. A variety of eontinuous and individual wall tie sys­tems are available for interconnection of multiple wythe walls, ineluding an adjustable, single unit masonry reinforcement system consisting of a 0.076 em by 2.54 em corrugated steel, hot-dipped galvanized, ties which are preattaehed to the ehords of eonventional ladder or truss type joint reinforeement.

This paper describes a test program designed to provi de lower bOlD1d values of the capacity of such a tie system in transmitting compression, tension, and shearing forces between wythes of masonry wall construction eonsisting of eon­crete bloek and brick .

Deseription of Test Speeimen

AlI test specimens eonsisted of two eonerete bloek units interconnected with two briek units as shown in Figures 1 and 20

Figure 3 shows the typieal plaeement of the reinforcement system in the eOncrete bloek bed joint.

Conerete masonry units were nominal 20 em x 20 em x 40 em expanded shale, lightwei~ht, hollow, load bearing units eonforming to ASTM C90, Type N-l (f~ = l3.8N/mm ). Brick used were facing briek, 5~7 em x 8.9 em x 20 CID, ASTM C2l6, grade SW, Type FBS, havin g an absorption by 5-hr boil of arO\md 4 pereent, a saturation coeffieient of 0.591, and an average of f~ = 57o l N/mm2. Type S mo~ t ar , consisting of 1 part port1and cement (Type I), 1/2 part hydrated lime, and 4 parts sand, by volume was used for alI specimens. AlI mortar was mea­sured and mixed in a mortar mixer in aeeordanee with ASTM C270.

lhe major var iables in the tes t program were the magnitude of the eavity and the a1ignment of the brick and eonerete block bed joints.

a) Magnitude of the Cavi ty.

lhree values of overa11 wall thiekness were considered, namely, 30.5 cm, 35.6 e~, and 38 em. The resulting magnitudes of the cavity separating the two masonry wythes were 2.2 em, 7.3 em, and 9.8 em, respective1y. The 2.2 em cav­ity represents an upper bound on the gap that can be expected in composite masonry wal1 construction. lhus, these specimens wil1 be referred to as com­posite walls.

b) Vertical MisaIignment of the Masonry Wythes.

It was considered important, particular1y for the compression te st s, to investigate the effeet of lack of initia1 straightness of the tie on the tie capaci ty. The 1ack of straightness of the tie depends primari1y on the mis­aIignment of the bed joints of the masonry wythes.

Two extreme conditions were considered, name1y, a zero misalignment pro­ducing a straight interconnecting tie, and a maximum misa1ignment equal to on~ half of the brick height . In the latter case, the tie was hand bent down the face of the conerete block and bent again to, align with the brick masonry bed joint.

AlI specimens were prepared by the same mason in a single day. The mor­tar was retempered as necessary during fabrication of the specimens. Face she1I bedding was used for the ho110w block wythes. The workmanship was con­sidered excel1ent throughouto A total of 45 specimens were constructed. Prior to testing alI specimens were air cured in the laboratory for 28 days.

Description of Tests

A description of the number of specimens tested and a code for specimen

1633

identificatian is presented in Table lo

DetaiIs af each of these tests are given below:

a) Compression Tests

AlI compression tests were performed in a compression testing machineo The specimens were carefully handled to minimize damage to the bond between the tie and mortar . The tie was visually aligned with the upper cross-head of the machine and load was applied until failure occurred . Figure 4 illustrates the test set-up.

b) Tension Tests

AlI tension tests were performed using the arrangement shown in Figure S. Load was applied using a 220 KN hydraulic jack. A calibrated load cell was used to measure the applied loading. lt should be noted that specimen 2A3Twas damaged prior to testing and the failure load for this specimen is not reported herein.

c) Shear Tests

The test set-up for the shear tests is illustrated in Figure 6. Load was applied to the brick wythe using the hydraulic jack and load cell. · lhe con­crete block wythe was supported during testing to eliminate horizontal movement of the units . Plywood shims were placed between the brick and block wythes to minimize twisting of the brick wythe and thereby maintain a parallel alignrnent of the brick and block during the application of load .

Test Result s

Failure loads in compression, tension and shear are presented for each specimen in Tables 2, 3, and 4, respectivelYD

AlI specimens failed in compression by buckling. For the tension tests, the failure mechanism consisted of a splitting apart of either the brick ar block courses. The shearing failure mode consisted af buckling of the tieo

Discussian af Test Results

l. Out-of-Plane Capacity

a) Compression Tests

The average failure Ioads in compression are summarized in Table 5, along with the standard deviation camputed for each af the five tests. and the cor­responding coefficients af variationo

With the exception of specimens 2~t, the coefficients of variation are relatively large, indicating a significant scatter of the test data. It is believed that this results from the sensitivity af the tie strength to align­ment of the campression load along the tie axis.

Slenderness ratios 333, and 100.4. Due to this end may be assumed

1634

(L/r) for the the length of to be fixed.

three cavity sizes considered are 449. embedment of the tie in the brick wythe , The attachment of the tie to the trus s

reinforcement is essentially pinned . The theoretical effective length for these end conditions is 0.7L, in which L = aetual unsupport ed tie length. Using E = 200 GN/m2, the following estimates of buekling stress may be determined for the 9.8 em and 7.3 em eavities, respeetively, 20 N/mm2• and 36.3 N/mm2•

corr~sponding avera~e test values for speeimen with zero misalignment are 19.8 N/mm and 39.7 N/mm •

For the misaligned specimen, the test results indicate a reduction in buckling strength. Using a theoretical effective length of 0.9L. estimates

20f

buckling sress for 9.8 cm and 7.3 em cavities, are 12.1 N/mm2 and 22.0 N/mm , respeetivel y. Corresponding average test values are 16.6 N/mm2 and 21.5 N/mm2•

Beeause of the sensitivity of the compression test results to minor varia­tions in actual eavity size, initial straightness of the tie, and alignment of the tie and load, etc., the above agreement between test and theory is consid­ered excellent .

For the composite wal1 construction, the effective slenderness ratio of the tie is less than 100, and am empirical relationship is needed to determine acr. Using a parabolic equation of the form ocr = ao - c(KL/r)2 and matching results at a 7.3 em eavity with the Euler buckling stress equation gives:

(2)

For the composite wall specimen, Eq. vcr y close to the average test value

b) Tension Tests

2 (2) gives a value of 74.1 N/mm which is of 75.4 N/mm2•

The tension fai1ure 10ads given in Table 3 indieate that the tie capacity in tension is not strongly dependent on the cavity size or alignrnent configu­ration of the tie. The average failure load in tension for alI specimens tested is 2763 newtons. The standard deviation is 427 newtons, giving a co­efficient of variation of 0.154.

In the 9.8 cm cavity specimens, failure occurred by splitting of the brick courses. In these speeimens the larger overall wall thicknes s resulted in an incomplete penetration of the tie through the brick wythe . Thi s was a1so true in the specimen series 2~1. For specimen series 2A and the eomposite wall spec­imens, the failure initiated in the block masonry. 1t is believed that axial wal1 stress would tend to prevent the type of fa i lure noted in the tests, 50 that the capacities obtained in the tests deseribed herein are conservative.

11. In-Plane Capacity

The capacity of the Uni-Tie in shear is 1730 N, based on an average of five (5) testso The standard deviation of the tests is 96 N, with a coeffi­cient of variation indicates that the shear capacity of the tie may be ac­eurately determined from the average test value.

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Recommended Design Procedure

I . Out -of-Plane Loads

Based on the data presented herein, the capacity of the tie in transfer­ring out-of-plane loads between brick and block wythes is governed by com­pressiono Because of the relatively high coefficients of variation obtained in the tests described herein, it is recommended that a factor of safety of 2.0 be used to determine working load values for design o

The fOllowing equations are, therefore, recommended for computation of the tie allowabl e load capacity:

in which

P a

P a

37.8 - .00034(kL/ r )2 for kL/r < 233

for kL / r > 233

Pa = allowable design load, in newtons; A = cr05S 5ectional area of tie, in mm2; r = t//i2, in mm; t = thickne55 of tie, in mm; E = mod­ulus of elasticity, L = actual space between masonry wythes, in mm; k = 0.7 in Eq. (I); 0.9 in Eq. (2).

(I)

(2)

The amount of load to be transferred through the tie depends on the relative rigidities of the masonry wythes . However, it is recommended herein that each tic bc capablc of transferring the full loading between wythes.

It i5 also recommended, herein, that current individual tie spacing re­quirements contained in Building Code Requirements for Concrete Masonry Struc­tures (ASI 531-79) and Commentary - ACI53IR-79, published by the American Con­crete Institute be followed.

II . In-Plane Loads

A recommended safe working load value for tie design in tran5ferrin g in­plane loads between block and brick masonry wythes i5 890 newtons. This pro­vides a factor of safety against failure of 1.94.

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". , Spec:iwn T)-pe of .pitude Ti. AU.,..nt Spec.i.n •• 11 ...... , T.tt of C.vity Conditlen Tesud "... ...is!l.

3M , C ec.pression ••• _:d_ , 3" C.v i t r

" , C Co.pression ••• -tni_ , 3" C,vil )'

" , C COIIpreuion 7.3 _xi •• , 2" '1\'1 t)'

2A li C eo.pru5ion 7.3 II1n1_ , 2" C.vi r )'

, C ~"ssion 2.' aini_ , Col!pOsi U

'" " fens10n ••• _d_

3 3" c.vit y

" " Tension ••• aini_ 3 ) " Ca vit y

" " Tendon 7.3 -"'- 3 2" C.vH)'

lA , T Tendon 7.3 aini_ , 2" Cnit)'

, T Tension 2.2 II1n1_ 3 Co..,osiu

, 5 She.r 2.2 tini_ , CoIlllPOS ite

c:avity •• 11, - .bJ.d; c:o-posite ... Us - ad

d· T)'pe 01 Ult: C. cClÇrudon, T· tpsiem; S • ,I\e.r

r,h}. 2 - Coapression Failu:re Lo.d, in Newton'

Noainal Speci_n Clvit)' AI i p.nt N~er Avenif' , , 3 • , , " 15. '00 .00 '67 '" 3"

A '"' '" SS6 24' ... '" , " '" '" '" .67 '" '"

A '" 53. lO' '" ... 76S

, A "'. 10PO 1<191 U13 1"6 !<ISS

. Inc.hadu , 20 n.-.tons aUow.u for dw hric:1t .. d,M.

1637

1638

Tahh 1 - T«Ision hilure Loads in N-..tool

Noain.l C.vity AlilJl_nt Specilllm NJalbrr , 2 , ,

" 2510* 2710· 349S'

A 5425· 2915* 2760·

2 " 2315· 1190. 3070'

A 2"90· 2"00+ ,

O A 2760+ 21100- 300S.

Denate~ Iplittinó: hUure af the block course s.

·Deoates splittioó: hi1ure of tlle bTi ck course s .

T.ble" - SlleaTine Fdlure t.oads in Newtoos

Nolllinal C.vit )' AlipeM Speti_n NUlllbe T , 2 , .. 5

O A 1869 "" 1785 nos ".,

Tabh 5 - S_TY (lf Col!pression Test Resulu

Coeffitient Nomioal Alleraee Standard of C.vi ty Al ilJlaent c.p.tity Devinion Varinioo

(in newton s )

, " 'lO .. 0.263

A m ,,, 0.325

2 " ." " 0.090

A 165 - '" 0.21 4

O A 1'55 SII 0.213

Avenó:e

2950

"" 2"2S

2US

28S5

Average

1730

Aveuge FailuTt StTess

N/'.?

16.6

19.8

21. 5

39.7

75.4

'Block

,caVi ty (see

ick

Fig. 2) Brick

End View Elevation

FIGURE 1 ZERO MISALIGNMENT SPECIMEN ('A')

See Fig. 3

End View Elevation

FIGURE 2 HAXIMUM ~lISALIGNMENT SPEClHEN ( 'I~' )

FIGURE 3 DETAlL or PLACHIEH OF UNI - TlE REI.~FORCEMENT I N

CONCRETE BLOCK BED JOINT

1639

1640

r-__ I--'1-_ Loading head

Brick

Machine Base

a) 'A" Specimen

Block

Loading head

Brick

Block

Machine Base

b) IM' Specimen

FIGURE 4 DETAILS OF COMPRESSION TESTS

~

'" ...

/ / /

t- --I-- Loading - Loadin g t- beam

bea m

rJL r- Load ce ll -I-Jack Jack

- P-

~ Cr oss ..-- Stee I beam Strap .-

- - -

I---- Chann e I Chann el -......

hl r, JI--

I---AngI e l: I I L-lJ I , SUppOrl H- -

........ - I- 1----

... .--BIock BIock _

/ / / ////////////////////// / /

FIGURE 5 DETAILS DF TENS IDN TEST SET-UP

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Load cell

Load cell

...... /

I-I'

Elevation

'<l ....

"-"- ....

Jack 7

Plan

Block

Brick

Steel Post

Block J /

/ /

/ "- / ',.,,' .-

I I I L.J

'- Brick

FIGURE 6 SHEAR TEST SET-UP

2x4' 5

Post

71 plywood sh ims