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106 Vth International Brick Masonry Conference 11-13. Shear Strength of Brick Masonry Joints R.G. Drysdale Professor, Department of Civil Engineenng and Engineering Mechanics, McMaster University, Hamilton, Ontano R. Vanderkeyl M. Eng. Candidate, Department of Civil Engineenng and Engineering Mechanics, McMaster University, Hamilton, Ontano A.A. Hamid Post-Doctoral Fellow, Department of Civil Engineenng and Engineenng Mechanics, McMaster University, Hamilton, Ontario. ABSTRACT The results of 74 shear tests of clay bnck masonry assemblages are reported. These test specimens were designed to transmit pure shear along the bed joints either with or without normal compressive stress. Constant levels of precompression ranging from O to 30% of the compressive strengths of the corresponding prisms were used in the tests. Also the influence of the mortar properties was investigated using types M, S, and N mortars. In addition, bricks with substantially different initial rates of absorption were used. The shear bond failure capacities of the bed joints were influenced by the mortar type but were not proportional to the compressive strengths of either the mortars or the corresponding masonry prisms. Under compressive stresses normal to the bed joints, th e type and strength of mortar have more significance for the shear strength. Also the additional shear resistance obtained by increasing the normal compressive stress was not proportional to the level of compr essive stress and the so-called coefficient of fnction along the bed joint decreased with increased normal compressive stress. The results also illustrate the influence of the initial rate of absorption of the bnck on the shear bond capacity. Cet article contient les résultats de 74 essais de cisaillement sur des assemblages de briques d'argile, jointes à l'aide de maconnene. Ces échantillons étaient concus pour transmettre du cisaillement pur le long des joints honzontaux, avec ou sans contrainte normale de compression. Des niveaux constants de pré-compression allant e O à 30% de la résistance en compression de la brique ont été utilisés lors de ces essais . Egalement, l'influence des propriétés du mortier a été étudiée en employant des mortiers de type M, S et N. De plus, des briques ayant des taux initiaux d'absorption substantiellement différents ont été utilisées. Les capacités en cisaillement du lien dans les joints honzontaux ont été influencées par le type de mortier, mais n'étaient pas proportionnelles aus résistances en compression du monter ou des prismes de maconnerie correspondants. Sous de contrainnes de compression normales aux joints honzontaux, le type et la résistance du mortier ont plus d'influence sur la résistance au cisaillement. Egalement, les résistances additionnelles au cisaillement obtenues par l'accroissement de la contrainte normale de compression n'étaient pas proportionnelles aux niveaux de cette dernWre. Le coefficient de friction le long des joints honzontaux décroissait avec l'augmentation de la contrainte normale de compression. Les résultats illustrent éga lement l'influence du taux initial d'absorption de la brique sur la capacité en cisaille- ment du lien. Die Resultate von 74 Schubversuchen on Mauerverbindugen von Ziegelsteinen aus Ton. Diese Versuchspe- zimens wurden entworfen um reinen Schub zu übertragen auf die Bettungsfugen entweder mit oder o/me Normaldruckspannungen. In den Versuchen wurde konstante Grossen von Normaldruckspannungen zwichen zero und 30% der Druckstarke der korrespondierenden Prismas benutzt. Der Einfluss der Morteleigenschaften wurde untersucht für die M, S and V Morteltypen. Auch Ziegelsteine mil wesentlichen unterschiedlichen initialen Absorptionsraten wurden benutzt. Die Schubverbundstarke der Bettungsfugen waren vom Morteltype beeinflusst aber waren nicht proportional zur Druckstarke von beiden des MorteLs oder de korrespondierenden Mauerwerk- prismas. Unter Druckspannungen normal zu der Bettungsfugen, der Type and die Starke des ' Mortel haben grossere Wichtigkeit fiá die Zugstarke. Auch der zusatzliche Schubwiderstand hervorgerufen durch eine zuneh- mende Normaldruckspannung war nicht proportional zur Hohe der Druckspannung. Der sogenannte Reibung- skoeffizient entlang der Bettungafuge nahm zu mit abnehmender Normaldruckspannungen. Die Resultate illus- trieren den Einfluss der initialen Absorptionsraten der Zeigelsteine auf der Schubverbundstarke. INTRODUCTION failure must be considered. The shear forces in the plane of the walI may be accompanied by only very low vertical compressive stresses due to the self -weight of the walI. Alternately, if the walI shares in carrying the floor loadin g, this compressive stress may be fairly large. Due to l ateral loading on buildings, masonry walIs must often be designed to resist the shear forces in the plane of t he wa ll. Where the capac ity of the walI is not limited by tension or compressio n failure caused by the combi- nation ofaxia l load and bending, th e possibility of shear Previous investigations:!·4.0.H have shown that shear fail- ure wilI be by slip along one 01- more of the bed joints

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106 Vth International Brick Masonry Conference

11-13. Shear Strength of Brick Masonry Joints R.G. Drysdale

Professor, Department of Civil Engineenng and Engineering Mechanics, McMaster University, Hamilton, Ontano

R. Vanderkeyl M. Eng. Candidate, Department of Civil Engineenng and Engineering Mechanics, McMaster University, Hamilton, Ontano

A.A. Hamid Post-Doctoral Fellow, Department of Civil Engineenng and Engineenng Mechanics, McMaster University, Hamilton, Ontario.

ABSTRACT

The results of 74 shear tests of clay bnck masonry assemblages are reported. These test specimens were designed to transmit pure shear along the bed joints either with or without normal compressive stress. Constant levels of precompression ranging from O to 30% of the compressive strengths of the corresponding prisms were used in the tests. Also the influence of the mortar properties was investigated using types M, S, and N mortars. In addition, bricks with substantially different initial rates of absorption were used. The shear bond failure capacities of the bed joints were influenced by the mortar type but were not proportional to the compressive strengths of either the mortars or the corresponding masonry prisms. Under compressive stresses normal to the bed joints, the type and strength of mortar have more significance for the shear strength. Also the additional shear resistance obtained by increasing the normal compressive stress was not proportional to the level of compressive stress and the so-called coefficient of fnction along the bed joint decreased with increased normal compressive stress. The results also illustrate the influence of the initial rate of absorption of the bnck on the shear bond capacity.

Cet article contient les résultats de 74 essais de cisaillement sur des assemblages de briques d'argile, jointes à l'aide de maconnene. Ces échantillons étaient concus pour transmettre du cisaillement pur le long des joints honzontaux, avec ou sans contrainte normale de compression. Des niveaux constants de pré-compression allant e O à 30% de la résistance en compression de la brique ont été utilisés lors de ces essais. Egalement, l'influence des propriétés du mortier a été étudiée en employant des mortiers de type M, S et N. De plus, des briques ayant des taux initiaux d'absorption substantiellement différents ont été utilisées. Les capacités en cisaillement du lien dans les joints honzontaux ont été influencées par le type de mortier, mais n'étaient pas proportionnelles aus résistances en compression du monter ou des prismes de maconnerie correspondants. Sous de contrainnes de compression normales aux joints honzontaux, le type et la résistance du mortier ont plus d'influence sur la résistance au cisaillement. Egalement, les résistances additionnelles au cisaillement obtenues par l'accroissement de la contrainte normale de compression n'étaient pas proportionnelles aux niveaux de cette dernWre. Le coefficient de friction le long des joints honzontaux décroissait avec l'augmentation de la contrainte normale de compression. Les résultats illustrent également l'influence du taux initial d'absorption de la brique sur la capacité en cisaille­ment du lien.

Die Resultate von 74 Schubversuchen on Mauerverbindugen von Ziegelsteinen aus Ton. Diese Versuchspe­zimens wurden entworfen um reinen Schub zu übertragen auf die Bettungsfugen entweder mit oder o/me Normaldruckspannungen. In den Versuchen wurde konstante Grossen von Normaldruckspannungen zwichen zero und 30% der Druckstarke der korrespondierenden Prismas benutzt. Der Einfluss der Morteleigenschaften wurde untersucht für die M, S and V Morteltypen. Auch Ziegelsteine mil wesentlichen unterschiedlichen initialen Absorptionsraten wurden benutzt. Die Schubverbundstarke der Bettungsfugen waren vom Morteltype beeinflusst aber waren nicht proportional zur Druckstarke von beiden des MorteLs oder de korrespondierenden Mauerwerk­prismas. Unter Druckspannungen normal zu der Bettungsfugen, der Type and die Starke des' Mortel haben grossere Wichtigkeit fiá die Zugstarke. Auch der zusatzliche Schubwiderstand hervorgerufen durch eine zuneh­mende Normaldruckspannung war nicht proportional zur Hohe der Druckspannung. Der sogenannte Reibung­skoeffizient entlang der Bettungafuge nahm zu mit abnehmender Normaldruckspannungen. Die Resultate illus­trieren den Einfluss der initialen Absorptionsraten der Zeigelsteine auf der Schubverbundstarke.

INTRODUCTION failure must be considered. The shear forces in the plane of the walI may be accompanied by only very low vertical compressive stresses due to the self-weight of the walI. Alternately, if the walI shares in carrying the floor loading, this compressive stress may be fairly large.

Due to lateral loading on buildings, masonry walIs must often be designed to resist the shear forces in the plane of the wall. Where the capacity of the walI is not limited by tension or compression failure caused by the combi­nation ofaxial load and bending, the possibility of shear

Previous investigations:!·4.0.H have shown that shear fail­ure wilI be by slip along one 01- more of the bed joints

Session JI, Paper 13, Shear Strength of Briek Masonryjoints

even where a stepped diagonal cracking occurs due to dif­ferent combinations of vertical and shear forces. This paper is intended to provide some basic information on which to develop a rational basis for establishing design nlues for the shear strength of brick masonry.

CSA Standard S304 1 lists allowable shear stresses for plain brick masonry which are functions of the compres­sive strength of the masonry but with different limits depending on the type of mortar. This form of presen­tation implies that masonry compressive strength and mortar type are the importam characteristics which affect the shear strength of brick masonry. The experimental investigation 7 reported in this paper was designed to examine the validity of the current code approach for dif­ferem combinations of materiais and various leveis of pre­compression normal to the bed joints.

EXPERIMENTAL INVESTIGA TION

MateriaIs

Brieks: Three different types of bricks were used. A pho­tograph of these is presented in Fig. 1 and their basic properties are listed in Table 1. Brick types A and B were from the same manufacturer but by their colours could be separated according to strength and initial rate of absorp­tion (IRA). Type A was a dark brown colour whereas the less highly burned type B was red. Type A tended to show more evidence of fire cracking and although any bricks with obvious fine cracks were discarded, this may account for the slightly lower flexural tensile strength for type A. The type C bricks had larger cores and a much larger initial rate of absorption and therefore provided a strong contrast to the type A bricks.

Mortan: Types M, S and N mortars were used. The proportions are listed in Table 2. Batching was done by weight and the water contents were established by the mason's requirements for workabi:ity and then maintained constam for each type of mortar. The control specimens were 2 in. cubes which were tested under axial compres­sion at approximately the same age as the corresponding assem blages.

Test Specimen

The four brick assemblage shown in Fig. 2 was adopted as the shear test specimen . Since the load is transferred by shear through the joints, this configuration eliminated the effect of flexural stresses which it is argued that other types of specimens incorporate.2 This type of specimen has the added advantage of being easy to fabricate and provides a relatively simple test to perform.

Construction Details and Test Procedure

The test specimens were constructed with the bed joints in a horizontal position and the 3/8 in. mortal' joints were tooled to assure compaction of the joint. For testing, the ends of the central bricks were capped using a sulphur compound. The specimen was centered in a vertical posi­tion in a hydraulic test machine and the shearing load was graduallyapplied .

107

For the specimens with precompression stresses normal to the bed joints, the precompressive load was applied first and maintained constant during the test. The test set-up is shown in Fig. 2. This precompression equipment con­sisted of a series of four 1 in . thick steel plates connected by four 1/2 in. diameter 7-wire prestressing strands which ran through holes near the corners of the plates. Two 1/8 in. thick plywood sheets were placed between the ends of the specimen and the steel plates to relieve any stress concentrations. On one side of the specimen a load cell was positioned between one of these plates and an externai plate and on the other side of the specimen a hydraulic jack was centered between the plate next to the specimen and the remaining plate. By monitoring the load during testing, the normal compressive force was maintained at a constant value using the hydraulic jack.

DISCUSSION OF THE TEST RESULTS

The results of the 74 shear tests are summarized in Table 3 where each series represems from 3 to 5 repetitions of the same test. For each series the type of brick used is idemified along with the levei of precompression stress normal to the bed joints and the type of morta r used. Where brick types A and B are identified for the same series, the two central bricks were always type A and the two exterior bricks were always type B. These series com­prised the first group of tests and they were followed later by tests of specimen containing only one type of brick. The mean compressive strengths from air cured mortar cubes are also listed. Ir should be noted that the propor­tions of the type S mortar differed slightly from the orig­inai type S2. AIso since Series 4 to 6 and 12 to 17 were constructed and cured in the low relative humidity (approx. 20%) of the laboratory in the winter months, the cube strength of the SI mortar is significamly below the original S2 mortar. The average com pressive strengths from 4 repetitions of tests of 6 brick high masonry prisms constructed at the same time as the corresponding shear specimens are also presented. Finally the mean shear strengths based on the gross contact area are listed along with their respective coefficients of variation.

Mode 01 Failure: The failure mode was consistemly a shear slip failure along two of the joints (see Fig. 3). How­ever under high leveis of precompression some signs of mortar failure were observed. This could be taken to indicate that the mortal' strength might have a significant influence on shear capacity for cases of shear-compression states of stress.

Elleet 01 Mortar Type: The average shear strength, T , is calculated as:

T = P/2A (I)

where P is the vertical shear load at failure and A is the gross are a of contact between two bricks. Comparison of the results for Series I, 2, and 3 indicates that the shear bond strength was not proportional to the mortar com­pressive strength , a crn . Inclusion of the results for Series 4, 5, and 6 supported this observation. The results for these 6 Series without precompression (a n = O) are ploued in Fig. 4 to illustrate this poim. Since the code I relates

108

shear strength to the square root of compressive strength, Fig. 5 was drawn using the data in Fig. 4 but with the shear strength normalized by dividing by the square root of the mortar cube compressive strength. The resulting coefficients, k2, do not seem to hold any promise of some basic relationship.

Correlation with Prism Compressive Strength: Figure ti con­tains the individual shear strength results from Series I to 6 plotted against the correspond ing prism compressive strengths, f;". There does not seem to be any strong direct correlation with the prism compressive strength. However, when the mean shcar strengths are normalized by d ividing by the square root of the corresponding prism compres­sive strength, as shown in Fig. 7, a recognizable relation­ship does seem to existo For the range of prism strengths included in this study, the relationship between shear bond strength and the square root of f;" as expressed by the coefficient k" seems to be approximately 1.0.

Other attempts to relate the shear strengths to the com­pressive and tensile strengths of the bricks or to the square root of these values did not reveal any .consistent trends.

Effeet of the lnitial Rate of Absorption: Figures 8(a) and 8(b) illustrate the effect of the initial rate of absorption (IRA) on the shear strength with and without precompres­sion. It is shown that the extremes of either very high or very low absorption coincide with reduced shear strengths. This is as expected since low IRA values will indicate that the mortar will not te nd to be drawn into intimate contact with the brick. In the case of the specimens constructed with both types A and B bricks, the shear fai lure plane always occurred along the surfaces of the dark low absorp­tive type A bricks .

EJJect of Precompression: The resu lts for Series 2, 8, 9 and 10, where types A and B bricks were used with type S2 mortar, indicate the significance of the magnitude of the compressive stress normal to the joint in increasing the capacity. These results are plotted in Fig. 9 along with three additional groups corresponding to specimens made solely with one of the three types of brick. These latter three groups result in nearly linear relationships between shear strengths and precompression stress up to 1000 psi. However, for the higher stresses included in the first group, the nonlinear shape of the curve passing through the data points indicates that the use of Coulomb's theory of internai friction",'; ·H may not be applicable for the full range of compression normal to the bed joints.

Figure 8(b) indicates that as the levei of precompression increases the relative effect of the initial rate of absorption decreases.

REVIEW OF DESIGN PROVISIONS

Utilizing the results presented in this paper, the design provision of CSA S304' concerning the allowable shear stresses for unreinforced brick masonry have been reviewed and lead to the following observations:

I . The provisions do not distinguish between the shear failures controlled by slip or by diagonal tension . It is presumed, in the following discussion, that the

Vth International Brick Masonry Conference

assigned values relate to the joint slip failure along the bed joints.

2. The allowable shear stress for type M or S mortar is \11';;;' but not to exceed 50 psi and the allowable shear stress for type N mortar is ~but not to exceed 35 psi. Except for the N mortar, the test results for zero precompression indicate a safety factor of less than 2.0 compared to the mean values.

3, The results show that the shear bond strength is bet­ter related to the compressive strength of masonry rather than to the mortar compressive strength. In fact for zero precompression there does not appear to be any consistent trend with mortar type or mortar strength.

4. The initial rate of absorption seems to have a signif­icant effect on the shear strength under zero pre­compression. The relationship that the code uses to assign values for allowable shear cannot reflect the effect of such a parameter.

5. This investigation clearly showed that the compres­sive stresses normal to the bed joints (precompres­sion) significantly increase the shear resistances of masonry joints, CSA S304' does allow for an increase in the shear values and the fo llowing relationship is recommended for shear walls:

v = V m + 0.3 fes (2)

where: v = maximum allowable shear stress V m = allowable shear stress at zero precompres­

SlOn

fes = compressive stress due to dead load

The allowable shear stresses from Equation 2 indicate a safety factor ranging from 2 to 3 when compared to the tests for specimens under precompression between zero and 0.3 f;". This approach seems to realistically account for the effect of precompression which exists due to dead loads.

ACKNOWLEDGEMENTS

This research was funded through Operating Grants from the Natural Science and Engineering Research Council of Canada and the Masonry Research Foundation of Canada. The authors appreciate the contribution of mason's time made available through the Ontario Masonry Promotion fund, AIso the supply of bricks by the Clay Brick Association of Canada (Domtar Inc., Clay Products Division and Burnstein Brick Ltd.) are gratefully acknowl­edged.

NOTATION

A = gross area of contact between two bricks fes = compressive stress due to dead load f;" = prism compressive strength of masonry P = vertical shear load at failure v = maximum allowable shear stress V m = allowable shear stress at zero precompression (Tem = compressive strength of mortar cubes (T n = precompressive stress normal to the bed joints T = ultimate shear strength along the bed joints

Session 11, Paper 13, Shear Strength o[ Brick Masomyjoints

REFERENCES

I. CSA Standard S304-1977, "Masonry Design and Construction for Buildings", Canadian Standards Association, Rexdale, Ontario, 1977. 2. Hamid, A.A., "Behaviour Characteristics of Concrete Masonry," thesis presented to McMaster University in Hamilton, Ontario, Canada, in 1978 in partial fulfillment of the requirements for the degree of Doctor of Philosophy. . 3. Jolly, R., "Shear Strength: A Predictive Techmque for Masonry Walls ," thesis presented to Brigham Young Umverslty, Provo, Utah , in 1976 in partial fulfillment of the requirements for the degree of Doetor of Philosophy. 4. Pieper, K. and Trautsch, W., "Shear Tests on Walls," Proc. of the Second International Brick Masonry Conference, Stoke-on­Trent, Apr. 1970, pp. 140-143.

A B

109

5. Sinha, B.P. and Henley, A. W., "Racking Tests on Storey Height Shear-Wall Structures with Openings Subjected to Pre­compression," Design, Engineering and Constru.cting with Masonry Pmdu.cls. Proceedings of the International Conference on Masonry Structural Systems, Austin, Texas, Fulf Publishing Co. , Houston , Texas, 1969. Paper No. 23 . 6. Stafford-Smith, B. and Carter, C., "Hypothesis of Shear Fail­ure of Brickwork, Journal of the Structural Division , Proc. of ASCE, ST4, vol. 97, April 1971, pp. 1055-1062. 7. Vanderkeyl , R., "Behaviour Characteristics of Brick Masonry," M.Eng. thesis submitted to McMaster University, Hamilton, Ontario, Canada in 1979. 8. Yokcl , F. and Faltai, C., "Failure Hypothesis for Masonry Shear WalIs," Journal of the Structural Division, Proc. of ASCE, ST3, vol. 102, March 1976, pp. 515-532.

c Figure 1. Photograph of Bricks (Left to right types A, B

and C)

Type

A B C

Pereent Solid

92 92 82

T ABLE l-Brick Properties

IRA gm/30 in 2/min

2.9 9.2

37.5

Compressive Strength

(ksi)

19.6 16.8 18.7

Flexural Tensile Strength

(ksi)

1.40 1.55 1.72

110 Vth lnternational Brick Masonry Conference

TABLE 2-Mortar Proportions

Mortar Type

M

S,

N

Cement

Figure 2. Photograph of Test Set-up for Precompression Loading

a) Withollt Precompression

Figure 3 . Photograph or Shear T est Specimen arter Failllre

Proportions by Volume (Weight)

Lime Sand Water

0.25 2.81 (0. 1) (2.98) (0.64)

0.5 4.0 (0.2 1) (4.24) (0.90)

0.5 3.375 (0.21) (3.59) (0 .77)

1.25 6.75 (0.53) (7.1 6) ( 1. 50)

b) With Precompression

Session lI, Pape7' 13, Shear Strength of Brick MasonryJoints

125~----r-,----~1----~----~--~

I/)

0.100 - o -J: 0 r-<.!)

0 • Z w a:: 75- -r-(/)

a:: <t W J: (/) 50- -w O -BRICK A <.!) <t .-BRICK B a:: w 6-BRICK C > <t 25 - 0-BRICK A+B -

Each point represents on overoge of

ot leost 4 tests .

I I I I

2 3 4 5

MORTAR COMPRESSIVE STRENGTH I ksi

Figure 4. Shear Strength versus Mortar Compressive Strength (a n = O)

III

2.5~----~1~_'----~1----~1------r-,--~

2.0 ~ -

• ~ "- 1.5 ~ . -....

11 I • N

.x

r-1.0 z - -

w U ~ lL.. w O

0 .5 ü r- -

I I I I

2 3 4 5

MORTAR COMPRESSIVE STRENGTH I o-cm I ksi

Figure 5. Correlation Between Shear Strength and the Square Root of Mortar Compressive Strength (an = O)

T ABLE 3 -Summary of the Shear Test Results

Mortar Prism Comp. Mean Shear Coef. of

Ser. No. No.ofSpec. Type of Brick Pre-Comp. (psi) Type Slr. psi Slr. f;" (psi) Slr. (psi) Varo

I 5 A+B O M 4750 9350 92 17.0 2 5 A+B O 52 45 10 7500 97 12.5 3 5 A+B O N 1210 5500 87 15.0 4 4 A O 5, 2340 5450 65 14.5 5 4 B O 5, 2340 7070 88 10.0 6 4 C O 5, 2340 6330 66 19.9 7 5 A+B 1870 M 4750 9350 1560 7.9 8 5 A+B 750 5, 4650 7500 870 4.9 9 5 A+B 1500 5, 4720 7500 1300 5.0

10 5 A+B 2250 5, 4530 7500 1640 9.6 11 5 A+B 1100 N 1210 5500 860 6.5 12 4 A 500 5, 2340 5450 500 4.3 13 4 B 500 5, 2340 7070 580 8.3 14 4 C 500 5, 2340 6330 520 9.5 15 3 A 1000 5, 2340 5450 910 6.0 16 3 B 1000 5, 2340 7070 1100 3. 1 17 4 C 1000 5, 2340 6330 950 6.6

112

125.-~--r-,----r-----'-,----,-,----'

cn Co

:J:

100 I • •

~ 75- • z ~ . ti; • a: 50-<{ W :J: (f)

W (!)

<{ 25-a: w > <{

,

• •

I

6

• • •

I

7

• I •

I

8 I

9

I _

• • -

-

-

10

PRISM COMPRESSIVE STRENGTH, f~ , ksi

Figure 6. Shear Strength versus Masonry Compressive Strength (<Tn=O)

100~----~------~------~----~

cn 80 Co

:J: ~ <.!) Z w 60 a: ~ (f)

a: <{

~ 40 (f)

w <.!) <{ a: ~ 20 <{

o O

8

• • •

0- BRICK A

.- BRICK B

t::. - BRICK C

o 10 20 30 40 INITIAL RATE OF ABSORPTION,gm/30in~/min 1) Without Precompression

Vth lnternational Brick Masonry Conference

2.5.--+---r-----"T,----___,r------r--' ----.

2.0r -

s ~ 1.5 -

11

• ~

~ 1.0r U •

• • • • -

u.. u.. w O u 0.5- -

Â. J I , , 6 7 8 9 10

MASONRY COMPRESSIVE STRENGTH, fm, ksi

Figure 7. Correlation Between Shear Strength and the Square Root of the Masonry Compressive Strength (<T n = O)

1250.-----~,-------.-,------.-1-------,

·iiiIOOOr Co

:J: ~ <.!) Z ~ 750r r-(f)

a: <{

* w O

• •

:J: 500~ e • i 2>Á~n ~ 250"" L{jJ

I

o 10

O"n = BRICK 500psi

A

B

o

• c t::.

, I

-

O"n = 1000psi

.. -

• A 20 30 40

INITIAL RATE OF ABSORPTION,gm/30in2/min

b) With Precompression

Figure 8. Effect of lnitial Rate of Absorption on Shear Strength

Session li, PapeT /3 , Shear StTength of 8Tick Masonryjoints

2.0~--------~--------~--------~--------~------~

.. I O"n t; 1.5 c) z w a::: ~ cn

~ 1.0 w I cn W (!) <{ 0.5 a::: w ~

o

-o-BRICK A ,5, MORTAR

-.-BRICK B ,5, MORTAR

--.6--BRICK C ,5, MORTAR

-·e--BRICK A+B ,52 MORTAR

0.5 1.0 1.5 2.5 PRECOMPRE5510N 5TRE55, O"n , ksi

FiguTe 9. Effect of Precompression on Shear Strength

2.5

113