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Compressive strength of hollow concrete blockwork
Maurenbrecher, A. H. P.
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TRlN21d
no.
1405
National
Research
Conseil national
C .
2
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Council Canada
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recherches
Canada
BLDO
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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)
A N A L Y Z E D
Reprinted with permission
Price $2.00
NRCC 26362
NRC-
CISTIBLDG.
RES.
L I B R A R Y
1
La n o u v e l l e B d i t i o n de l a norme canadienne r e l a t i v e au c a l c u l d e l a masonnerie u t i l i s e l a s u r f a c e de l ' a s s i s e de m o r t i e r p l u t 8 t que l a s u r f a c e n e t t e pour c a l c u l e r l a f o r c e p o r t a n t e d e s murs e n b l o c s creux. La s u r f a c e d e l a s e c t i o n u t i l e de b l o c s creux, j o i n t o y e s au m o r t i e r seulement l e l o n g d e s p a r o i s d e f a c e , e s t p a r consgquent r g d u i t e , e t l a f o r c e p o r t a n t e s e t r o u v e a l o r s diminuik s i l e s c o n t r a i n t e s a d d s e s s o n t basdes s u r l e s v a l e u r s t a b u l a i r e s e x i s t a n t e s . On a donc dO m o d i f i e r c e s v a l e u r s pour d e t e r m i n e r l a r B s i s t a n c e 3 l a compression d e s ouvrages en b l o c s 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 C o n e t r u c t i o n , N a t i o n a l Reeearch Council of Canada, Ottawa, Canada,
KlA
OR6
ABSTRACT
The new e d i t i o n of t h e Canadian masonry d e s i g n s t a n d a r d u s e s mortar-bedded a r e a i n s t e a d of n e t a r e a i n determining t h e load c a p a c i t y of hollow block walls. The e f f e c t i v e c r o s s - s e c t i o n a l a r e a of hollow blockwork w i t h mortar on t h e
f a c e - s h e l l s only i s t h e r e b y reduced, i n t u r n reducing t h e l o a d c a p a c i t y i f a l l o w a b l e stresses are baaed on e x i s t i n g t a b u l a r v a l u e s . This h a s l e d t o a review of t h e t a b u l a r v a l u e s f o r compressive s t r e n g t h of c o n c r e t e blockwork.
INTRODUCTION
S e v e r a l changes i n t h e new e d i t i o n of t h e Canadian masonry d e s i g n s t a n d a r d [ 11 af f e c t t h e load-bearing c a p a c i t y of hollow c o n c r e t e blockwork walls. Two of t h e changes a l t e r t h e e f f e c t i v e c r o s s - s e c t i o n a l a r e a of a w a l l and t h e t a b u l a r v a l u e s f o r compressive s t r e n g t h . T h i s paper examines t h e t a b u l a r v a l u e s and compares them w i t h d a t a from tests on s m a l l hollow-concrete blockwork specimens (prisms). Prisms a r e used i n p r e f e r e n c e t o w a l l s because more test d a t a a r e a v a i l a b l e and s l e n d e r n e s s e f f e c t s a r e small. Furthermore, Canadian and U.S. d e s i g n codes permit prism s t r e n g t h i n s t e a d of t a b u l a r v a l u e s t o be used f o r design.
EFFECTIVE CROSS-SECTIONAL AREA
The a x i a l l o a d c a p a c i t y of w a l l s i n t h e 1978 Canadian masonry d e s i g n s t a n d a r d [ 2 ] and t h e American Concrete I n s t i t u t e c o n c r e t e masonry code [31 i s based on t h e n e t c r o s s - s e c t i o n a l a r e a of t h e c o n c r e t e block used i n t h e w a l l . I n c o n t r a s t , t h e mortar-bedded a r e a i s used f o r s h e a r and t e n s i o n ( t h e Commentary t o t h e A C I code seems t o c o n t r a d i c t t h i s s i n c e i t reconmends u s e of t h e n e t block a r e a ) . I n n e a r l y a l l c a s e s mortar i s l a i d on t h e f l a n g e s ( f a c e - s h e l l s ) of t h e block, and t h i s "mortar-bedded" a r e a i s o f t e n c o n s i d e r a b l y s m a l l e r t h a n t h e n e t a r e a of t h e block. (Even i f mortar i s l a i d over t h e whole block, t h e
load-bearing a r e a i s l e s s t h a n t h e n e t block a r e a because t h e webs of modern two-core blocks normally do n o t a l i g n when b u i l t i n t o a w a l l . ) The n e t block a r e a h a s , n e v e r t h e l e s s , been used because of t r a d i t i o n and because i t i s e a s i e r t o determine t h a n t h e mortar-bedded a r e a . The l a t t e r i s d e f i n e d i n t h e new e d i t i o n of t h e Canadian s t a n d a r d a s t h e h o r i z o n t a l a r e a of m o r t a r i n a bed j o i n t i n f u l l c o n t a c t w i t h both t h e masonry u n i t above and t h e masonry u n i t below, and i n c l u d e s t h e h o r i z o n t a l a r e a of t h e v o i d s i n s o l i d u n i t s and g r o u t e d v o i d s i n hollow u n i t s ( a " s o l i d " u n i t
i s
d e f i n e d a s a u n i t w i t h a n e t a r e a of a t l e a s t 75% of i t s g r o s s a r e a ) .The convenience of u s i n g n e t a r e a c o u l d be j u s t i f i e d i f t h e r a t i o between n e t and f a c e - s h e l l a r e a were roughly c o n s t a n t , but t h e r a t i o i n c r e a s e s a s block width i n c r e a s e s : 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 h e f a c e - s h e l l a r e a i s based on t h e minimum f a c e - s h e l l width p l u s 20%). For example, a 290-mm block w i t h a compressive s t r e n g t h of 10 MPa i s
allowed a t a b u l a r blockwork u l t i m a t e stress of 7.7 MPa, based on n e t a r e a (M o r S t y p e mortar); i f t h e mortar-bedded a r e a i s used, t h i s stress w i l l have t o be i n c r e a s e d t o 12.3 MPa t o g i v e t h e same l o a d c a p a c i t y : t h a t i s , a s t r e s s h i g h e r
than t h e block f a i l u r e stress ! Wider blocks were, t h e r e f o r e , i n d i r e c t l y allowed h i g h e r e t r e s s e s . The u s e of mortar-bedded
area
i e more l o g i c a l , but meanss
s i g n i f i c a n t d e c r e a s e i n load c a p a c i t y f o r f a c e - s h e l l bedded blockwork i f t h e e x i s t i n g t a b u l a r v a l u e s a r e r e t a i n e d ,
a
d e c r e a s e v a r y i n g from5%
f o r 9 0 - m b l o c k s t o 38% f o r290-mm
blocks. T h i s r e d u c t i o n h a s prompted a review of t h e t a b u l a r v a l u e s f o r t h e s t r e n g t h of c o n c r e t e blockwork.I
EXISTING TABULAR
VALUESThe t a b u l a r v a l u e s f o r c o n c r e t e blockwork i n t h e 1978 Canadian d e s i g n s t a n d a r d and t h e A C I code a r e t h e same a s t h o s e i n t h e N a t i o n a l Concrete Masonry A s s o c i a t i o n (NCMA) s p e c i f i c a t i o n , a p a r t from minor d i f f e r e n c e s 12-41. I n a commentary, t h e
NCMA
[ 5 ] show t h a t t h e v a l u e s f o r blockwork u s i n g M o r S t y p e mortars were o b t a i n e d from ASA A41.2-1960, "Building code requirements f o r r e i n f o r c e d masonry" [61. T h i s g i v e s oneset
of t a b u l a r v a l u e s f o r masonry u s i n g s o l i d o r hollow c l a y o r c o n c r e t e u n i t s up t oa
s t r e n g t h of 83 MPa (12 000 p s i ) ; i t i s n o t , t h e r e f o r e , l i m i t e d t o c o n c r e t e blockwork. The NCMA adopted t h e s e v a l u e s f o r u n i t s t r e n g t h up t o 41 MPa (6000 p s i ) . The commentary does n o t s t a t e how v a l u e s were o b t a i n e d f o r blockwork u s i n g t y p eN
mortar.PRISM TEST DATA
Appendix 1 p r o v i d e s test d a 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 t y p e mortars ( e q u i v a l e n t t o 1:0.25:3, 1:0.5:4.5 and 1:1:6 cement:lime:sand mixes by volume). It i n c l u d e s specimens i n both s t a c k 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 a r e a . Stack bond prism
The v a l u e s f o r t h e c o ~ r e s s i v e s t r e n g t h of t h e block g i v e n i n Appendix 1 a r e based on n e t c r o s s - s e c t i o n a l a r e a ( r a t i o of n e t volume t o g r o s s volume) of a i r - d r y b l o c k s w i t h a h a r d capping [ 7 ] . The s t r e n g t h of t h e prisms i s based on t h e mortar-bedded a r e a . The average n e t a r e a of t h e b l o c k s was used w i t h prisms having f u l l mortar bedding and a l i g n e d cross-webs. T h i s v a l u e , u s u a l l y quoted i n t e s t r e s u l t s , g i v e s a c o n s e r v a t i v e estimate of t h e f a i l u r e stress s i n c e , s t r i c t l y speaking, t h e minimum c r o s s - s e c t i o n a l a r e a should be used ( t h e d i f f e r e n c e i s of t h e o r d e r of 5%). For prisms w i t h f a c e - s h e l l mortar bedding t h e a r e a i s an
estimate
based
on t h e minimum f a c e - e h e l l width p l u san
i n c r e a s e of up t o 20%, depending on t h e shape of t h e block ( t h e f a c e - s h e l l width v a r i e s a l o n g t h e l e n g t h of t h e block,see
F i g u r e 1).DISCUSSION OF TEST DATA
F a c t o r s t h a t may a f f e c t t h e r e l i a b i l i t y of t h e t e s t d a t a i n Appendix 1 i n c l u d e mortar s t r e n g t h , age, moisture c o n t e n t , c r o s s - s e c t i o n a l a r e a ,
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 ( t y p e s M, S and
N)
have l i t t l e e f f e c t on blockwork s t r e n g t h , t h e e f f e c t becoming l a r g e r w i t h i n c r e a s i n g block s t r e n g t h (Appendix 1, [8,91). One s e t of t e s t s u s i n g M, S and N mortars d i d show a l a r g e d e c r e a s e i n s t r e n g t h w i t h typeN
mortar, b u t t h e s t r e n g t h of t h a t mortar was a l r e a d y m c h lower t h a n normal [ l o ] . The small e f f e c t of mortar on blockwork s t r e n g t h implies t h a t any i n c r e a s e i n s t r e n g t h w i t h a g e i s raainly due t o t h e block. Blocks can i n c r e a s e i n s t r e n g t h w i t h age [8,111, p a r t l y from a g a i n i n t h e s t r e d g t h of t h e c o n c r e t e w i t h time,
b u t a l s o from t h e d r y i n g of t h e block [12,13]. It
i s
t h e r e f o r e important t h a t blocks be t e s t e d a t t h e same time and under t h e same atmospheric c o n d i t i o n s a s t h e corresponding prisms t o o b t a i n a n a c c u r a t e r e l a t i o n between block and prism s t r e n g t h . Most r e c e n t t e s t programs do n o t s t a t e a t what age t h e blocks were t e s t e d ; i t i s probable t h a t t h e y were t e s t e d e a r l i e r t h a n t h e prisms and t h u s may underestimate block s t r e n g t h , g i v i n g 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 r e n g t h .Blockwork w i t h f a c e - s h e l l mortar bedding h a s been assumed t o f a i l a t
s i g n i f i c a n t l y h i g h e r s t r e s s e s t h a n blockwork w i t h f u l l bedding [14]. This i s not confirmed by t h e r e s u l t s i n Appendix 1; t h e s e show t h a t f a c e - s h e l l bedding g i v e s values about 2% h i g h e r (average of e i g h t v a l u e s ranging from -11 t o + l o % )
[15-201. I f t h e minimum i n s t e a d of t h e average n e t a r e a were used f o r prisms w i t h f u l l mortar bedding, t h e r a t i o would be even l e s s . One r e f e r e n c e not included i n t h e t e s t r e s u l t s c o n t r a d i c t s t h i s , showing 18% h i g h e r r e s u l t s , on average, f o r f a c e - s h e l l bedding [21]. This s t i l l needs t o be e x p l a i n e d , but p a r t of t h e d i f f e r e n c e may be due t o t h e v a l u e f o r mortar-bedded a r e a . The assumed r a t i o s of mortar-bedded t o g r o s s a r e a ranged from 0.34 t o 0.39; t h e a c t u a l a r e a s a r e probably c l o s e r t o t h e h i g h e r assumed v a l u e f o r a l l t h e t e s t e d prisms. For example, i f a v a l u e of 0.40 had been used throughout, t h e r e s u l t s would be 8% i n s t e a d of 18% h i g h e r .
R a t i o s of height-to-thickness up t o 10 a r e assumed t o a f f e c t t h e a x i a l s t r e n g t h of hollow blockwork by l e s s t h a n 10% [1,3,12,161. The number of blocks and t h e v a r i a b l i t y i n t h e block s t r e n g t h w i l l probably be t h e main reason f o r r e d u c t i o n s i n s t r e n g t h over t h i s range [22]. The s t r e n g t h of t h e block i t s e l f can be a f f e c t e d by i t s height-to-width r a t i o , wider blocks g i v i n g r e l a t i v e l y h i g h e r s t r e n g t h s [23]. I f t h i s i s t r u e f o r hollow blocks, i t i m p l i e s t h a t t h e wider t h e block t h e lower t h e r a t i o of prism-to-block s t r e n g t h . The o v e r a l l
r e s u l t s i n Appendix 1 f o l l o w t h i s t r e n d , but r e s u l t s from i n d i v i d u a l r e f e r e n c e s vary.
The s t r e n g t h of prisms w i t h s o f t cappings such a s f i b r e b o a r d have been found t o g i v e t h e same ( o r lower) r e s u l t s a s t h o s e w i t h hard cappings such a s d e n t a l p l a s t e r : r a t i o s of 0.92-1.00 [ 1 6 ] , 0.88-0.94 [ 1 3 ] , 0.68-1.00 (9,241. The d i f f e r e n c e may be e x p l a i n e d by t h e f a i l u r e mode ( l e s s d i f f e r e n c e i f f a i l u r e i s i n i t i a t e d a t t h e mortar j o i n t ) , s u r f a c e of t h e block (rough s u r f a c e s g i v e r i s e t o s t r e s s c o n c e n t r a t i o n s when a s o f t capping i s u s e d ) , and d i f f e r e n t t e s t d a t e s .
A
s o f t capping h a s a l a r g e r e f f e c t on t h e compressive s t r e n g t h of t h e block (e.g. a r a t i o of 0.85 f o r f i b r e b o a r d t o plaster-capped block [161).
COMPARISON OF PRISM DATA WITH TABULAR VALUES
The s t r e n g t h of 71 s e t s of prisms u s i n g M and S m o r t a r s i s p l o t t e d a g a i n s t block s t r e n g t h i n F i g u r e 2. The s e l e c t i o n of d a t a was based on t h e f o l l o w i n g c r i t e r i a : 1 ) no r a t i o s of prism-to-block s t r e n g t h g r e a t e r t h a n one; 2 ) where
Figure 2. Prism versus block strength
(M
and S mortar)Figure 3. Basis for new tabular s t r e s s e s 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 3 0 Z W az C
-
2 0a
Ln-
=
1 0 n 0 0 1 0 2 0 30 4 0 5 0 6 0 70 8 0 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 ++ Ei
2 0 - I- C3 Z W 0: C Ln=
1 0-
Ln-
ct La L 0 1 I I 1 0 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 at h e r e was a c h o i c e of specimens w i t h i n a t e s t program, p r i o r i t y was given t o prisms w i t h h a r d e r capping, n e x t , t o t h e one w i t h t h e most t e s t r e p l i c a t e s , t h e n t o t h e l a r g e s t prism. A second-order polynomial curve based on a l e a s t - s q u a r e s f i t i s shown i n F i g u r e 2 t o g e t h e r w i t h a lower bound curve below which o n l y 7% of t h e r e s u l t s f a l l ( t h e c h a r a c t e r i s t i c s t r e n g t h l e v e l used i n t h e Canadian masonry d e s i g n s t a n d a r d ) . Allowable v a l u e s i n t h e A C I code and t h e 1978 Canadian
s t a n d a r d a r e a l s o shown. These i n d i c a t e t h a t t a b u l a r v a l u e s a r e t o o l i b e r a l f o r low block s t r e n g t h s and c o n s e r v a t i v e f o r h i g h e r ones. The u s e of t h e lower bound 7% curve as a b a s i s f o r new t a b u l a r v a l u e s would s e v e r e l y reduce t h e e x i s t i n g p e r m i s s i b l e l o a d c a p a c i t y of blockwork w i t h low-strength blocks.
An a l t e r n a t i v e , l e s s s e v e r e , approach i s t o a p p l y a r e d u c t i o n f a c t o r t o a b e s t - f i t curve p a s s i n g through t h e o r i g i n , s o t h a t t h e r e s u l t i n g curve w i l l a l s o p a s s through i t . This i n t e r i m approach was adopted f o r t h e new e d i t i o n [ l ] of t h e Canadian masonry d e s i g n s t a n d a r d ( s e e Table 1 and F i g u r e 3). An a r b i t r a r y r e d u c t i o n f a c t o r of 0.8 was adopted. Although h i g h e r t a b u l a r stresses seem j u s t i f i e d f o r h i g h block s t r e n g t h s , t h i s change w i l l n o t be made u n t i l more i n f o r m a t i o n i s a v a i l a b l e on t h e s t r e n g t h of h i g h - s t r e n g t h blockwork and on t h a t of hollow blockwork under varying e c c e n t r i c l o a d s ( a check on t h e s h e a r s t r e n g t h of t h e webs). The new t a b u l a r s t r e s s e s , a p p l i e d t o a c r o s s - s e c t i o n a l a r e a based on t h e mortar-bedded a r e a , mean a n i n c r e a s e d u l t i m a t e load c a p a c i t y f o r most blockwork w i t h f u l l mortar bedding and a decreased c a p a c i t y f o r f a c e - s h e l l mortar bedding (Table 2). The d e c r e a s e
i s
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 h eCanadian s t a n d a r d by changing t h e a l l o w a b l e a x i a l stress r e d u c t i o n 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 r e a d y used f o r brickwork.
TABLE
1 Comparison of Tabular and Prism Data (M and S Mortar) Prism S t r e n g t h (MPa) B e s t - f i t Curve Tabular S t r e n g t h ( M a ) Through O r i g i n Block S t r e n g t h 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 84More d a t a a r e needed f o r prisms u s i n g t y p e N mortar, e s p e c i a l l y f o r h i g h e r s t r e n g t h blocks. N e v e r t h e l e s s , t h e c o l l e c t e d d a t a s u g g e s t t h a t t h e e x i s t i n g t a b u l a r v a l u e s can be c o n s i d e r a b l y i n c r e a s e d t o g i v e v a l u e s t h e same a s t h o s e f o r low-strength blocks u s i n g M and S mortars and g r a d u a l l y reduced v a l u e s w i t h
h i g h e r - s t r e n g t h blocks ( s e e Figure 4 and Appendix 1). The new t a b u l a r v a l u e s f o r t h e Canadian s t a n d a r d a r e shown g r a p h i c a l l y i n F i g u r e 4; a f u r t h e r i n c r e a s e w i l l probably be i n o r d e r when more test d a t a become a v a i l a b l e . The low v a l u e s i n F i g u r e 4 a r e probably t h e r e s u l t of a lower t h a n expected mortar s t r e n g t h [ l o ] .
CONCLUSIONS
E x i s t i n g t a b u l a r v a l u e s f o r c o n c r e t e 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 c o n c r e t e blockwork.
Compared w i t h r e s u l t s from prism tests, t h e t a b u l a r v a l u e s f o r blockwork w i t h M o r S mortar a r e c o n s e r v a t i v e f o r h i g h - s t r e n g t h blocks and t o o l i b e r a l f o r low-s t r e n g t h blocks.
The u s e of mortar-bedded a r e a i n s t e a d of n e t a r e a w i l l mean a s i g n i f i c a n t r e d u c t i o n i n t h e u l t i m a t e a x i a l load c a p a c i t y f o r f a c e - s h e l l bedded blockwork, u s i n g e x i s t i n g t a b u l a r v a l u e s . This can be compensated f o r by i n c r e a s i n g t h e t a b u l a r v a l u e s and d e c r e a s i n g t h e r e d u c t i o n f a c t o r f o r t h e a l l o w a b l e 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 d e s i g n s t a n d a r d [ l ] h a s t a k e n t h i s approach, but t h e r e
i s
s t i l l a s i g n i f i c a n t r e d u c t i o n i n a l l o w a b l e a x i a l load f o r f a c e - s h e l l bedded blockwork u s i n g lower-strength blocks. A more d e t a i l e d s a f e t y s t u d y i s r e q u i r e d t o determine whether f u r t h e r changes can be made.Guidance i s needed, t o o , on t h e v a l u e s t o be used f o r mortar-bedded a r e a . For example, a v a l u e based on t h e minimum f a c e - s h e l l width p l u s 20% would apply t o many of t h e s t a n d a r d two-core blocks i n Canada. I n f u t u r e t h e block
manufacturers w i l l probably s u g g e s t v a l u e s on t h e i r d a t a s h e e t s .
When t e s t i n g c o n c r e t e blockwork prisms, c a r e n u s t be t a k e n t o e n s u r e t h a t t h e mortar-bedded a r e a i s a c c u r a t e l y determined and t h a t t h e blocks from which t h e 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 c o n d i t i o n s a s t h e 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
S t r e n g t h
(MPa U l t Allow U l t Allow
*Area based on minimum f a c e - s h e l l width
+
20% REFERENCES1 Canadian Standards A s s o c i a t i o n . Masonry d e s i g n f o r b u i l d i n g s . CAN3-S304-M84, 1984.
2 Canadian Standards A s s o c i a t i o n . Masonry d e s i g n and c o n s t r u c t i o n f o r b u i l d i n g s . CAN3-S304-M78, 1978.
3 American Concrete I n s t i t u t e , B u i l d i n g code requirements f o r c o n c r e t e masonry s t r u c t u r e s . A C I 531-79(rev 83), 1983.
4 N a t i o n a l Concrete Masonry A s s o c i a t i o n . S p e c i f i c a t i o n f o r t h e d e s i g n and c o n s t r u c t i o n of load-bearing c o n c r e t e masonry. 1970.
5 N a t i o n a l Concrete Masonry A s s o c i a t i o n . Research d a t a w i t h commentary i n s u p p o r t of: S p e c i f i c a t i o n f o r t h e d e s i g n and c o n s t r u c t i o n of load-bearing c o n c r e t e masonry.
6 N a t i o n a l Bureau of Standards. NBS Handbook 74, B u i l d i n g code requirements f o r r e i n f o r c e d masonry. ASA41.2-1960.
7 ASTM. Method of sampling and t e s t i n g c o n c r e t e masonry u n i t s . C140-75, 1975.
8 Copeland, R.E. and A.G. T i m . E f f e c 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 e n g t h of c o n c r e t e masonry w a l l s . A C I J o u r n a l , Vol. 28, 1932, p. 551-562.
9 Roberts, J.J. The e f f e c t upon t h e i n d i c a t e d s t r e n g t h of c o n c r e t e b l o c k s i n compression of r e p l a c i n g mortar w i t h 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 b r i c k and c o n c r e t e masonry w a l l s , &Masonry: P a s t and p r e s e n t . ASTM, STP 589, 1975, p. 195-232.
11 Sturgeon, G.R., J. Longworth and J. Warwaruk. An i n v e s t i g a t i o n of r e i n f o r c e d c o n c r e t e block masonry columns. S t r u c t u r a l Eng. Report 91. U n i v e r s i t y of A l b e r t a . 1980
12 Maurenbrecher, A.H.P. Axial compressive tests on masonry w a l l s ' a n d prisms. Proceedings, Third North American Masonry Conference, The Masonry S o c i e t y , 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 r o p e r t i e s of l o a d b e a r i n g c o n c r e t e masonry.
&
Masonry: P a s t and p r e s e n t , ASTM, STP 589, 1975, p. 233-254.14 N a t i o n a l Concrete Masonry A s s o c i a t i o n . Compressive s t r e n g t h of c o n c r e t e masonry. NCMA, USA, Tek 15, 1969.
15 H a t z i n i k n o l a s , M., J. Longworth and J. Warwaruk. Concrete masonry w a l l s . Dept. of C i v i l Engineering, U n i v e r s i t y of A l b e r t a , S t r u c t u r a l Engineering Report 70, 1978.
16 Maurenbrecher, A.H.P. E f f e c t of t e s t 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, T h i r d Canadian Masonry Symposium, Edmonton, 1983, p. 10-1 t o 10-13
18 R i c h a r t , F.E., R.B.B. Moorman and P.M. Woodworth. S t r e n g t h and s t a b i l i t y of c o n c r e t e masonry w a l l s . Univ. of I l l i n o i s , B u l l e t i n 251, 1932.
19 Woodward, K., and F. Rankin. I n f l u e n c e of v e r t i c a l compressive stress on s h e a r r e s i s t a n c e of c o n c r e t e block masonry w a l l s . NBS, NBSIR84-2929, 1984. 20 I b i d . I n f l u e n c e of a s p e c t r a t i o on s h e a r r e s i s t a n c e of c o n c r e t e block
21 Nacos, C.J. Comparison of f u l l y bedded and f a c e - s h e l l bedded c o n c r e t e block, Colorado S t a t e U n i v e r s i t y , 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 c o n c r e t e masonry
-
r e i n f o r c e d 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. e t a l . Concrete masonry d e s i g n e r ' s handbook, Viewpoint P u b l i c a t i o n s , 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 n d i c a t e d s t r e n g t h of c o n c r e t e blocks i n conrpression. Magazine of Concrete Research.
APPENDIX 1. COMPRESSIVE STRENGTH OF HOLLOW CONCRETE BLOCKWORK PRISMS
(An/& ( 0.75; h / t ( 10)
Block Mortar Prism
Ref. S i z e (mm) An/Ag Strength ( M P ~ ) Type Size Bedding Strength (MPa) Ratio
NOTES :
Bard capping ( p l a n t e r , cement, sulfur
...I
except where noted+
Values u s e d i n Figures 2-4;*
Values used i n F i g u r e 4P r i s m
size:
i n i t i a l number gives c o u r s e h e i g h t of prismfollowing number gtves length of prism i n terms of block l e n g t h ( i f d i f f e r e n t from 1)
lbedded a r e a , f o r blocks w i t h two roughly pear-shaped c o r e s , based on minimum f a c e - s h e l l width
+
20%2blocks t e s t e d a t same t i m e as prisms
3three o v a l c o r e s ; webs a l i g n i n wall
4block t e s t e d w i t h ffbreboard capping; t e s t v a l u e s i n c r e a s e d 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 c u r e )
7assurued v a l u e f a r An/Ag
8bedded a r e a based on minimum f a c e - s h e l l width
+
14%gbedded a r e a , f o r stack bond prisms u s i n g b l o c k s w i t h two s q u a r e c o r e s , based on minimum f a c e - s h e l l w i d t h
+
5%NOTATION
Ag = g r o s s a r e a Am = mortar bedded a r e a An = n e t a r e a f = f i b r e b o a r d capping f b = f u l l bedding f s = f a c e - s h e l l mortar bedding h = h e i g h t 1 = l e n g t h n = number of r e p l i c a t e s P = f a i l u r e l o a dr
= running bond s = s t a c k bond t = t h i c k n e s s v = c o e f f i c i e n t of v a r i a t i o nREFERENCES
A1 Becica, I.J. and H.G. H a r r i s . U l t i m a t e s t r e n g t h behaviour of hollow c o n c r e t e 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 c o n c r e t e block masonry under a x i a l compression. A C I J o u r n a l , June 1979, p. 707-721.
A3 Drysdale, R.G. and A.A. Hamid. Capacity of c o n c r e t e block masonry prisms under e c c e n t r i c compressive loading. A C I J o u r n a 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 w a l l s under compression and f l e x u r e . N a t i o n a l Bureau of Standards. BSS 73, 1976.
A5 H a t z i n i k o l a s M., J. Longworth and J. Warwaruk. E f f e c t of j o i n t reinforcement on v e r t i c a l l o a d c a r r y i n g c a p a c i t y of hollow c o n c r e t e 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 c o n c r e t e block w a l l s . Phase 11: Under u n i a x i a l loading. Cement and Coqcrete A s s o c i a t i o n , T e c h n i c a l
Report 42.473, 1972.
A7 Read, J.R. and S.W. Clements. The s t r e n g t h of c o n c r e t e block w a l l s .
Phase 111: E f f e c t s of workmanship, mortar s t r e n g t h and bond p a t t e r n . Cement and Concrete A s s o c i a t i o n , T e c h n i c a l Report 42.518, 1977.
A8 S u t e r - K e l l e r Inc. F i e l d measurements of deformations on a l o a d b e a r i n g masonry h i g h r i s e s t r u c t u r e . C o n t r a c t 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 e n d e r c o n c r e t e masonry w a l l s . N a t i o n a l Bureau of S t a n d a r d s , BSS 33, 1970.
A10 Yokel, F.Y., R.G. Mathey and K.D. Dikkers. S t r e n g t h of masonry w a l l s under compressive and t r a n s v e r s e loads. N a t i o n a l Bureau of S t a n d a r d s , BSS 34, 1971.
A l l Woodward
K.
and F. Rankin. Behaviour of c o n c r e t e block masonry w a l l s s u b j e c t e d t o r e p e a t e d c y c l i c displacements. N a t i o n a l Bureau of S t a n d a r d s , NBSIR 83-2780, 1983.T h i s paper
i s
being d i s t r i b u t e d i n r e p r i n t form by t h e I n s t i t u t e f o r Research i n Construction. A l i s t of b u i l d i n g p r a c t i c e and r e s e a r c h p u b l i c a t i o n s a v a i l a b l e from t h e I n s t i t u t e may be obtained by w r i t i n g t o t h e P u b l i c a t i o n s Section, I n s t i t u t e f o r Research i n Construction, National Research C o u n c i l of Canada, O t t a w a , O n t a r i o ,KlA
OR6.Ce document e s t distribui5 sous forme de tir6-8-part p a r 1' I n s t i t u t de recherche en c o n s t r u c t i o n . On peut o b t e n i r une l i s t e d e s p u b l i c a t i o n s de
1'
I n s t i t u t p o r t a n t s u r l e s techniques oules
recherches e nmatisre
de batiment en Bcrivant