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Compressive strength of hollow concrete blockwork

Maurenbrecher, A. H. P.

https://publications-cnrc.canada.ca/fra/droits

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Ser

TRl

N21d

no.

1405

National

Research

Conseil national

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Council Canada

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recherches

Canada

BLDO

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Institute for

lnstitut de

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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

-

CISTI

BLDG.

RES.

L I B R A R Y

1

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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 .

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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

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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 means

s

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 from

5%

f o r 9 0 - m b l o c k s t o 38% f o r

290-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

VALUES

The 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 one

set

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 o

a

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 e

N

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 s

an

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).

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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 type

N

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

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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 0

a

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 ++ E

i

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 a

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t 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 e

Canadian 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 84

More 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.

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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% REFERENCES

1 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.

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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

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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.

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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

(13)
(14)
(15)

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 4

P 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 prism

following 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 d

r

= 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 n

(16)

REFERENCES

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.

(17)

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 ou

les

recherches e n

matisre

de batiment en Bcrivant

hl

l a Section d e s p u b l i c a t i o n s , I n s t i t u t de recherche en c o n s t r u c t i o n , C o n s e i l n a t i o n a l d e recherches du Canada, Ottawa (Ontar Lo),

Figure

Figure  1.  Example  of  mortar-bedded  a r e a .   Stack  bond  prism
Figure  3.  Basis  for  new  tabular  s t r e s s e s   i n   S304-M84  (M  and  S  mortar)
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  --
TABLE  2  Change  i n  Axial  Load  Capacity  (CAN3-S304-M84  [ I ] ) ,   190-mm  Concrete  Blockwork  (M  o r   S  Mortar)

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