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Ser TRl N21d

no. 1405 National Research Conseil national C . 2 I+ Council Canada de recherches Canada BLDO - - Institute for lnstitut de

Research in recherche en Construction construction

Compressive Strength of Hollow Concrete Blockwork

by A.H.P. Maurenbrecher

Appeared in Proceedings 4th Canadian Masonry Symposium Department of Civil Engineering University of New Brunswick June 2, 3, 4, 1986, Vol. 2, p. 997- 1009 (IRC Paper No. 1405)

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BLDG. RES. L I B R A R Y 1

La nouvel le Bdi t ion de l a norme canadienne r e l a t i v e au c a l c u l de l a masonnerie u t i l i s e l a su r face de l ' a s s i s e de mort ier p l u t 8 t que l a su r face n e t t e pour c a l c u l e r l a fo rce por t an te des murs en b locs creux. La su r face de l a s e c t i o n u t i l e de b locs creux, jo in toyes au mort ier seulement l e long des pa ro i s de f ace , e s t par consgquent rgdu i t e , e t l a f o r c e por t an te s e t rouve a l o r s diminuik s i l e s con t ra in te s a d d s e s son t basdes s u r l e s va leu r s t a b u l a i r e s ex i s t an tes . On a donc dO modifier c e s va leu r s pour determiner l a rBsis tance 3 l a compression des ouvrages en b locs de S t o n .

COMPRESSIVE STRENGTH OF HOLLOW CONCRETE BLOCKWORK

A.H.P. Maurenbrecher I n s t i t u t e f o r Reeearch i n Conetruction, National Reeearch Council of Canada,

Ottawa, Canada, KlA OR6

ABSTRACT

The new e d i t i o n of t h e Canadian masonry design s tandard uses mortar-bedded a r ea ins tead of ne t a r ea i n determining t h e load capaci ty of hollow block walls. The e f f e c t i v e cross-sect ional a r e a of hollow blockwork wi th mortar on t h e face-shel ls only i s thereby reduced, i n t u rn reducing t h e load capac i ty i f allowable stresses are baaed on e x i s t i n g t abu la r values. This has l e d t o a review of the t abu la r values f o r compressive s t r eng th of concrete blockwork.

INTRODUCTION

Several changes i n t h e new e d i t i o n of t h e Canadian masonry design s tandard [ 11 af f e c t the load-bearing capaci ty of hollow concrete blockwork walls. Two of t he changes a l t e r t h e e f f e c t i v e cross-sect ional a r e a of a wa l l and t h e t abu la r values f o r compressive s t rength . This paper examines the t abu la r values and compares them wi th d a t a from tests on small hollow-concrete blockwork specimens (prisms). Prisms a r e used i n preference t o wal l s because more test da t a a r e ava i l ab l e and s lenderness e f f e c t s a r e small. Furthermore, Canadian and U.S. design codes permit prism s t r e n g t h ins tead of t abu la r values t o be used f o r design.

EFFECTIVE CROSS-SECTIONAL AREA

The a x i a l load capac i ty of wa l l s i n t h e 1978 Canadian masonry design standard [2] and the American Concrete I n s t i t u t e concrete masonry code [31 is based on t h e ne t cross-sect ional a r e a of t h e concrete block used i n t h e wall . I n con t r a s t , t h e mortar-bedded a r ea is used f o r shear and tens ion ( t he Commentary t o t he A C I code seems t o con t r ad i c t t h i s s i n c e i t reconmends use of t h e ne t block area) . In near ly a l l cases mortar is l a i d on the f langes ( face-she l l s ) of t he block, and t h i s "mortar-bedded" a r e a i s o f t e n considerably smaller than t h e n e t a r ea of t he block. (Even i f mortar i s l a i d over t he whole block, the load-bearing a r e a i s l e s s than t h e n e t block a r e a because t h e webs of modern two-core blocks normally do not a l i g n when b u i l t i n t o a wall .) The ne t block a r ea has, never the less , been used because of t r a d i t i o n and because i t is e a s i e r t o determine than t h e mortar-bedded area. The l a t t e r is defined i n t h e new e d i t i o n of t h e Canadian s tandard a s t h e ho r i zon ta l a r e a of mortar i n a bed j o i n t i n f u l l contact with both t he masonry u n i t above and the masonry u n i t below, and includes t he ho r i zon ta l a r e a of t h e voids i n s o l i d u n i t s and grouted voids i n hollow u n i t s ( a "so l id" u n i t is defined a s a u n i t with a ne t a r ea of a t l e a s t 75% of i t s gross a rea) .

The convenience of us ing ne t a r e a could be j u s t i f i e d i f t h e r a t i o between net and face-shel l a r ea were roughly constant , but t he r a t i o increases a s block width increases: from 1.05 f o r a 90mm block t o 1.60 f o r a 290-m block (assuming t h a t t he face-shel l a r ea is based on the minimum face-shel l width plus 20%). For example, a 290-mm block wi th a compressive s t r e n g t h of 10 MPa i s allowed a t abu la r blockwork u l t imate stress of 7.7 MPa, based on ne t a r ea (M o r S type mortar); i f t h e mortar-bedded a r e a is used, t h i s stress w i l l have t o be increased t o 12.3 MPa t o give t he same load capaci ty: t h a t is , a s t r e s s higher

than the block f a i l u r e stress ! Wider blocks were, theref o re , i n d i r e c t l y allowed higher e t r e s se s . The use of mortar-bedded area i e more l og i ca l , but means s s i g n i f i c a n t decrease i n load capaci ty f o r f ace-shell bedded blockwork i f t he e x i s t i n g tabular values a r e re ta ined , a decrease varying from 5% f o r 90 -m blocks t o 38% f o r 290-mm blocks. This reduct ion has prompted a review of t he t abu la r values f o r t he s t r e n g t h of concrete blockwork.

I EXISTING TABULAR VALUES

The t abu la r values f o r concrete blockwork i n t h e 1978 Canadian design s tandard and the ACI code a r e t h e same a s those i n t h e Nat ional Concrete Masonry Associat ion (NCMA) spec i f i ca t i on , a p a r t from minor d i f f e r ences 12-41. I n a commentary, t he NCMA [5] show t h a t t h e values f o r blockwork using M o r S type mortars were obtained from ASA A41.2-1960, "Building code requirements f o r re inforced masonry" [61. This gives one set of t abu la r values f o r masonry using s o l i d o r hollow c l ay o r concrete u n i t s up t o a s t r e n g t h of 83 MPa (12 000 p s i ) ; i t is not , therefore , l im i t ed t o concrete blockwork. The NCMA adopted these values f o r u n i t s t r e n g t h up t o 41 MPa (6000 ps i ) . The commentary does no t s t a t e how values were obtained f o r blockwork using type N mortar.

PRISM TEST DATA

Appendix 1 provides test da t a on t h e a x i a l compressive s t r e n g t h of small masonry specimens made of M and S type mortars o r N type mortars (equivalent t o 1:0.25:3, 1:0.5:4.5 and 1:1:6 cement:lime:sand mixes by volume). It inc ludes specimens i n both s t ack and running bond up t o a height-to-thickness r a t i o of 10.

FA C E - S H E L L S

M O R T A R O N F A C E - S H E L L A R E A

M O R T A R - B E D D E D A R E A

M O R T A R N O T I N C O N T A C T W I T H B O T H B L O C K S

Figure 1. Example of mortar-bedded area. Stack bond prism

The values f o r t he c o ~ r e s s i v e s t r eng th of t he block given i n Appendix 1 a r e based on ne t cross-sect ional a r e a ( r a t i o of n e t volume t o gross volume) of air-dry blocks w i th a hard capping [ 7 ] . The s t r eng th of t h e prisms i s based on t h e mortar-bedded area. The average n e t a r e a of t h e blocks was used with prisms having f u l l mortar bedding and a l igned cross-webs. This value, u sua l ly quoted i n t e s t r e s u l t s , g ives a conservat ive estimate of t h e f a i l u r e stress s ince , s t r i c t l y speaking, t h e minimum cross -sec t iona l a r e a should be used ( t h e d i f f e r ence i s of t h e order of 5%). For prisms with face-shel l mortar bedding t h e a r e a i s an estimate based on t h e minimum face-ehe l l width p lu s an inc rease of up t o 20%, depending on t h e shape of t h e block ( t h e f ace-shell width v a r i e s a long t h e length of t h e block, see Figure 1).

DISCUSSION OF TEST DATA

Factors t h a t may a f f e c t t he r e l i a b i l i t y of t h e t e s t da t a i n Appendix 1 include mortar s t rength , age, moisture content , cross-sect ional a rea , height-to-thickness r a t i o and capping. Mortar mixes normally used f o r s t r u c t u r a l masonry ( types M, S and N) have l i t t l e e f f e c t on blockwork s t rength , the e f f e c t becoming l a r g e r with increas ing block s t r eng th (Appendix 1, [8,91). One s e t of t e s t s using M, S and N mortars did show a l a r g e decrease i n s t r eng th with type N mortar, but t h e s t r eng th of t h a t mortar was already m c h lower than normal [ lo] . The small e f f e c t of mortar on blockwork s t r eng th implies t h a t any increase i n s t r eng th with age is raainly due t o t he block. Blocks can increase i n s t r eng th with age [8,111, p a r t l y from a gain i n t h e s t r edg th of t he concrete with time, but a l s o from the drying of t h e block [12,13]. It i s the re fo re important t h a t blocks be t e s t e d a t t h e same time and under the same atmospheric condit ions a s the corresponding prisms t o obta in an accura te r e l a t i o n between block and prism strength. Most recent t e s t programs do not s t a t e a t what age the blocks were t e s t ed ; i t is probable t h a t they were t e s t e d e a r l i e r than t h e prisms and thus may underestimate block s t rength , giving a r t i f i c i a l l y high r a t i o s of prism-to-block s t rength .

Blockwork with face-shel l mortar bedding has been assumed t o f a i l a t s i g n i f i c a n t l y higher s t r e s s e s than blockwork with f u l l bedding [14]. This is not confirmed by the r e s u l t s i n Appendix 1; these show t h a t face-shel l bedding gives values about 2% higher (average of e igh t values ranging from -11 t o +lo%) [15-201. I f t he minimum ins t ead of t he average n e t a r e a were used f o r prisms with f u l l mortar bedding, the r a t i o would be even less . One reference not included i n t he t e s t r e s u l t s cont rad ic t s t h i s , showing 18% higher r e s u l t s , on average, f o r face-shel l bedding [21]. This s t i l l needs t o be explained, but pa r t of t he d i f fe rence may be due t o t he value f o r mortar-bedded area. The assumed r a t i o s of mortar-bedded t o gross a rea ranged from 0.34 t o 0.39; the ac tua l a reas a r e probably c lose r t o t h e higher assumed value f o r a l l t h e t e s t e d prisms. For example, i f a value of 0.40 had been used throughout, the r e s u l t s would be 8% ins tead of 18% higher.

Ratios of height-to-thickness up t o 10 a r e assumed t o a f f e c t t he a x i a l s t r eng th of hollow blockwork by l e s s than 10% [1,3,12,161. The number of blocks and the v a r i a b l i t y i n t h e block s t r eng th w i l l probably be t h e main reason f o r reductions i n s t r eng th over t h i s range [22]. The s t r eng th of the block i t s e l f can be a f f ec t ed by its height-to-width r a t i o , wider blocks giving r e l a t i v e l y higher s t rengths [23]. I f t h i s is t r u e f o r hollow blocks, i t implies t h a t the wider t h e block t h e lower t h e r a t i o of prism-to-block s t rength . The o v e r a l l r e s u l t s i n Appendix 1 follow t h i s t rend, but r e s u l t s from indiv idua l references vary.

The s t r eng th of prisms with s o f t cappings such a s f ibreboard have been found t o give the same (or lower) r e s u l t s a s those with hard cappings such a s denta l p l a s t e r : r a t i o s of 0.92-1.00 [16], 0.88-0.94 [13] , 0.68-1.00 (9,241. The d i f fe rence may be explained by the f a i l u r e mode ( l e s s d i f fe rence i f f a i l u r e i s i n i t i a t e d a t t he mortar j o i n t ) , sur face of t he block (rough sur faces give r i s e t o s t r e s s concentrations when a s o f t capping i s used), and d i f f e r e n t t e s t dates. A s o f t capping has a l a r g e r e f f e c t on t h e compressive s t r eng th of t h e block (e.g. a r a t i o of 0.85 f o r f ibreboard t o plaster-capped block [161).

COMPARISON OF PRISM DATA WITH TABULAR VALUES

The s t r eng th of 71 s e t s of prisms using M and S mortars i s p lo t t ed aga ins t block s t r eng th i n Figure 2. The s e l e c t i o n of da ta was based on the following c r i t e r i a : 1 ) no r a t i o s of prism-to-block s t r eng th g r e a t e r than one; 2) where

Figure 2. Prism versus block strength (M and S mortar)

Figure 3. Basis for new tabular stresses i n S304-M84 (M and S mortar)

Figure 4. Prism strength: N versus M and S mortar

B L O C K S T R E N G T H ( N E T A R E A ) , M P a

5 0

m 4 0 MEAN THROUGH ORlG l

E

x 30

Z W az C - 2 0 a Ln - = 10 n

0 0 10 20 30 40 5 0 6 0 70 80

B L O C K S T R E N G T H ( N E T A R E A ) . M P a

+ M & S MORTAR + +

m n

0 N MORTAR ++

E

i 2 0 - I- C3 Z W 0: C Ln

= 1 0 - Ln - ct La

L

0 1 I I

10 2 0 3 0 4 0 B L O C K S T R E N G T H ( N E T A R E A ) , M P a

there was a choice of specimens wi th in a test program, p r i o r i t y was given t o prisms with harder capping, next , t o t h e one with t h e most t e s t r e p l i c a t e s , then t o t he l a r g e s t prism. A second-order polynomial curve based on a least-squares f i t is shown i n Figure 2 toge ther wi th a lower bound curve below which only 7% of the r e s u l t s f a l l ( t he c h a r a c t e r i s t i c s t r eng th l e v e l used i n t he Canadian masonry design standard). Allowable values i n t h e A C I code and t h e 1978 Canadian s tandard a r e a l s o shown. These i nd i ca t e t h a t t abu la r values a r e t oo l i b e r a l f o r low block s t r eng ths and conservat ive f o r higher ones. The use of t h e lower bound 7% curve as a bas i s f o r new t abu la r values would severe ly reduce t he e x i s t i n g permissible load capac i ty of blockwork wi th low-strength blocks.

An a l t e r n a t i v e , l e s s severe, approach i s t o apply a reduct ion f a c t o r t o a bes t - f i t curve passing through the o r ig in , s o t h a t t he r e s u l t i n g curve w i l l a l s o pass through it. This i n t e r im approach was adopted f o r t h e new e d i t i o n [ l ] of the Canadian masonry design s tandard ( see Table 1 and Figure 3). An a r b i t r a r y reduct ion f a c t o r of 0.8 was adopted. Although higher t abu la r stresses seem j u s t i f i e d f o r high block s t rengths , t h i s change w i l l no t be made u n t i l more information i s a v a i l a b l e on the s t r e n g t h of high-strength blockwork and on t h a t of hollow blockwork under varying e c c e n t r i c loads ( a check on t h e shear s t r eng th of t h e webs). The new t abu la r s t r e s s e s , appl ied t o a cross-sect ional a r e a based on the mortar-bedded a rea , mean an increased u l t ima te load capaci ty f o r most blockwork with f u l l mortar bedding and a decreased capaci ty f o r face-shel l mortar bedding (Table 2). The decrease is p a r t l y o f f s e t i n t h e new e d i t i o n of t he Canadian s tandard by changing t h e allowable a x i a l stress reduct ion f a c t o r from 0.225 t o 0.25 t o conform t o t h e f a c t o r a l ready used f o r brickwork.

TABLE 1 Comparison of Tabular and Prism Data (M and S Mortar)

Prism Strength (MPa) Bes t - f i t Curve

Tabular Strength (Ma)

Through Origin Block

Strength 7% Mean 7% Mean A C I -- S304 -- (MPa Mean l e v e l l e v e l x 0 . 8 79 78 84

More da t a a r e needed f o r prisms us ing type N mortar, e spec i a l l y f o r higher s t r eng th blocks. Nevertheless, t h e co l l ec t ed da ta suggest t h a t t h e e x i s t i n g t abu la r values can be considerably increased t o g ive values t h e same a s those f o r low-strength blocks using M and S mortars and gradual ly reduced values with higher-strength blocks ( see Figure 4 and Appendix 1). The new t abu la r values f o r the Canadian s tandard a r e shown graphica l ly i n Figure 4; a f u r t h e r increase w i l l probably be i n order when more test d a t a become ava i lab le . The low values i n Figure 4 a r e probably t h e r e s u l t of a lower than expected mortar s t r eng th [ lo ] .

CONCLUSIONS

Exis t ing t abu la r values f o r concrete blockwork i n t h e A C I [3] and Canadian masonry [21 codes a r e not d i r e c t l y based on t e s t s on concrete blockwork.

Compared with r e s u l t s from prism tests, t he t abu la r values f o r blockwork with M o r S mortar a r e conservat ive f o r high-strength blocks and too l i b e r a l f o r low-s t rength blocks.

The use of mortar-bedded a r e a i n s t ead of ne t a r e a w i l l mean a s i g n i f i c a n t reduct ion i n the u l t imate a x i a l load capaci ty f o r face-shel l bedded blockwork, using e x i s t i n g t abu la r values. This can be compensated f o r by increas ing t h e t abu la r values and decreasing the reduction f a c t o r f o r t h e allowable a x i a l s t r e s s . The new e d i t i o n of t h e Canadian masonry design s tandard [ l ] has taken t h i s approach, but there is sti l l a s i g n i f i c a n t reduct ion i n allowable a x i a l load f o r face-shel l bedded blockwork using lower-strength blocks. A more d e t a i l e d s a f e t y study is required t o determine whether f u r t h e r changes can be made.

Guidance is needed, too, on t h e values t o be used f o r mortar-bedded area. For example, a value based on the minimum face-shel l width p lus 20% would apply t o many of t he s tandard two-core blocks i n Canada. In f u t u r e t h e block manufacturers w i l l probably suggest values on t h e i r d a t a sheets .

When t e s t i n g concrete blockwork prisms, ca re nust be taken t o ensure t h a t the mortar-bedded a r ea is accura te ly determined and t h a t t h e blocks from which the prisms a r e made a r e t e s t e d a t t h e same time and under t h e same atmospheric condi t ions a s t he prisms.

TABLE 2 Change i n Axial Load Capacity (CAN3-S304-M84 [ I ] ) , 190-mm Concrete Blockwork (M o r S Mortar)

Change i n h a d Capacity ( I )

Face-shell F u l l Block Area* Area

Strength (MPa U l t Allow U l t Allow

*Area based on minimum face-shel l width + 20%

REFERENCES

1 Canadian Standards Association. Masonry design f o r bui ldings. CAN3-S304-M84, 1984.

2 Canadian Standards Association. Masonry design and cons t ruc t ion f o r buildings. CAN3-S304-M78, 1978.

3 American Concrete I n s t i t u t e , Building code requirements f o r concrete masonry s t ruc tu re s . A C I 531-79(rev 83), 1983.

4 National Concrete Masonry Association. Spec i f i ca t i on f o r t h e design and cons t ruc t ion of load-bearing concrete masonry. 1970.

5 National Concrete Masonry Association. Research da ta with commentary i n support of: Spec i f ica t ion f o r t h e design and cons t ruc t ion of load-bearing concrete masonry.

6 National Bureau of Standards. NBS Handbook 74, Building code requirements f o r re inforced masonry. ASA41.2-1960.

7 ASTM. Method of sampling and t e s t i n g concrete masonry un i t s . C140-75, 1975.

8 Copeland, R.E. and A.G. T i m . E f f ec t of mortar s t r e n g t h and s t r e n g t h of u n i t on t h e s t r eng th of concrete masonry walls. A C I Journal, Vol. 28, 1932, p. 551-562.

9 Roberts, J.J. The e f f e c t upon t h e ind ica ted s t r e n g t h of concrete blocks i n compression of rep lac ing mortar with board capping. Proceedings, F i r s t Canadian Masonry Symposium, Calgary, 1976, p. 22-38.

10 Redmond, T.B. and M.H. Allen. Compressive s t r e n g t h of composite br ick and concrete masonry wal l s , &Masonry: Pas t and present . ASTM, STP 589, 1975, p. 195-232.

11 Sturgeon, G.R., J. Longworth and J. Warwaruk. An inves t i ga t ion of re inforced concrete block masonry columns. S t r u c t u r a l Eng. Report 91. University of Alberta. 1980

12 Maurenbrecher, A.H.P. Axial compressive tests on masonry wa l l s ' and prisms. Proceedings, Third North American Masonry Conference, The Masonry Society, Texas, 1985, p. 19-1 t o 19-14.

13 S e l f , M.W. S t r u c t u r a l p rope r t i e s of loadbearing concrete masonry. & Masonry: Past and presen t , ASTM, STP 589, 1975, p. 233-254.

14 National Concrete Masonry Association. Compressive s t r e n g t h of concrete masonry. NCMA, USA, Tek 15, 1969.

15 Hatziniknolas , M., J. Longworth and J. Warwaruk. Concrete masonry wal ls . Dept. of C i v i l Engineering, Universi ty of Alberta , S t r u c t u r a l Engineering Report 70, 1978.

16 Maurenbrecher, A.H.P. Ef fec t of test procedures on compressive s t r e n g t h of masonry prisms. Proceedings, Second Canadian Masonry Symposium, Ottawa, 1980, p. 119-132.

17 Maurenbrecher, A.H.P. Compressive s t r e n g t h of e c c e n t r i c a l l y loaded prisms. Proceedings, Third Canadian Masonry Symposium, Edmonton, 1983, p. 10-1 t o 10-13

18 Richart , F.E., R.B.B. Moorman and P.M. Woodworth. S t rength and s t a b i l i t y of concrete masonry walls. Univ. of I l l i n o i s , Bu l l e t i n 251, 1932.

19 Woodward, K., and F. Rankin. Inf luence of v e r t i c a l compressive stress on shear r e s i s t ance of concrete block masonry walls. NBS, NBSIR84-2929, 1984.

20 Ibid. Inf luence of aspect r a t i o on shear r e s i s t a n c e of concrete block masonry wal ls . NBS, NBSIR84-2993, 1985.

21 Nacos, C.J. Comparison of f u l l y bedded and face-shel l bedded concrete block, Colorado S t a t e Universi ty , USA, CE-495, 1980.

22 Cranston, W.B. and J.J. Roberts. The s t r u c t u r a l behaviour of concrete masonry - re inforced and unreinforced. The S t r u c t u r a l Engineer, Vol. 54, No. 11, Nov. 1976, pp. 423-436.

23 Roberts, J. J. et a l . Concrete masonry des igner ' s handbook, Viewpoint Publ icat ions, Eyre & Spottiswoode, England, 1983, 272 p.

24 Roberts, J.J. The e f f e c t of d i f f e r e n t test procedures upon t h e i nd i ca t ed s t r eng th of concrete blocks i n conrpression. Magazine of Concrete Research. Vol. 25, No. 83, June 1973. pp. 87-98.

APPENDIX 1. COMPRESSIVE STRENGTH OF HOLLOW CONCRETE BLOCKWORK PRISMS (An/& ( 0.75; h / t ( 10)

Block Mortar Prism Ref. S ize (mm) An/Ag Strength ( M P ~ ) Type Size Bedding Strength (MPa) Ratio No. l x h x t P/An n v(%) Am/& P/Ab n v(%) Age(d) ~ r i s m / ~ l o c k

NOTES :

Bard capping (p l an t e r , cement, sulfur ...I except where noted + Values used i n Figures 2-4; * Values used i n Figure 4 Prism size: i n i t i a l number gives course height of prism

following number gtves length of prism i n terms of block length ( i f d i f f e r e n t from 1) lbedded a r e a , f o r blocks wi th two roughly pear-shaped cores , based on minimum face-she l l width + 20% 2blocks t e s t e d a t same t i m e as prisms 3three oval cores; webs al ign i n wall 4block t e s t e d with ffbreboard capping; t e s t values increased by 18% 5author's tests 610w s t r e n g t h f o r N mortar (1.3 W a ; 28 d; m k s t cure) 7assurued value f a r An/Ag 8bedded a rea based on minimum face-shel l width + 14% gbedded a rea , f o r stack bond prisms us ing blocks with two square cores , based on minimum f ace-she l l width + 5%

NOTATION

Ag = gross a r ea Am = mortar bedded a rea An = net a r e a f = f ibreboard capping f b = f u l l bedding f s = face-shel l mortar bedding h = height

1 = length n = number of r e p l i c a t e s P = f a i l u r e load r = running bond s = s t ack bond t = thickness v = coe f f i c i en t of v a r i a t i o n

REFERENCES

A1 Becica, I.J. and H.G. Harris. U l t i m a t e s t r e n g t h behaviour of hollow concrete masonry prisms under a x i a l load and bending. Proceedings, 2nd North American Masonry Conference, 1982, p. 3-1 - 3-20.

A2 Drysdale, R.G. and A.A. Hamid. Behaviour of concrete block masonry under a x i a l compression. A C I Journal , June 1979, p. 707-721.

A3 Drysdale, R.G. and A.A. Hamid. Capacity of concrete block masonry prisms under e c c e n t r i c compressive loading. ACI Journa l , Mar./Apr. 1983, p. 102-108.

A4 F a t t a l , S.G. and L.E. Cattaneo. S t r u c t u r a l performance of masonry wa l l s under compression and f lexure. Nat ional Bureau of Standards. BSS 73, 1976.

A5 Hatzinikolas M., J. Longworth and J. Warwaruk. E f f ec t of j o i n t reinforcement on v e r t i c a l load car ry ing capac i ty of hollow concrete block masonry. Proceedings, North American Masonry Conference, 1978, p. 16-1 - 16-16.

A6 Read, J.B. and S.W. Clements. The s t r e n g t h of concre te block wal ls . Phase 11: Under un i ax i a l loading. Cement and Coqcrete Associat ion, Technical Report 42.473, 1972.

A7 Read, J.R. and S.W. Clements. The s t r e n g t h of concre te block wal ls . Phase 111: Ef fec t s of workmanship, mortar s t r e n g t h and bond pa t te rn . Cement and Concrete Associat ion, Technical Report 42.518, 1977.

A8 Suter-Keller Inc. F i e ld measurements of deformations on a loadbearing masonry h igh r i s e s t ruc tu re . Contract Report SR81-00073, Ottawa, 1984.

A9 Yokel, F.Y., R.G. Mathey and R.D. Dikkers. Compressive s t r e n g t h of s l ende r concrete masonry walls. National Bureau of Standards, BSS 33, 1970.

A10 Yokel, F.Y., R.G. Mathey and K.D. Dikkers. S t rength of masonry wa l l s under compressive and t ransverse loads. National Bureau of Standards, BSS 34, 1971.

A l l Woodward K. and F. Rankin. Behaviour of concrete block masonry wal l s subjected t o repeated c y c l i c displacements. Nat ional Bureau of Standards, NBSIR 83-2780, 1983.

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