UBC Theses and Dissertations

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UBC Theses and Dissertations

Investigation of bond of deformed bars in plain and steel-fiber-reinforced concrete under reversed cyclic… Panda, A. K. 1980

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I N V E S T I G A T I O N OF BOND OF DEFORMED B A R S I N P L A I N AND S T E E L - F I B E R - R E I N F O R C E D C O N C R E T E UNDER . ' ' . R E V E R S E D C Y C L I C L O A D I N G b y A . K . P A N D A B . T e c h ( H o n s ) , I . I . T . ( K h a r a g p u r ) , I n d i a , 1966 M . S c . ( E n g g ) , S a m b a l p u r U n i v e r s i t y , I n d i a , 1975 A T H E S I S S U B M I T T E D I N P A R T I A L F U L F I L M E N T OF THE R E Q U I R E M E N T S F O R THE D E G R E E OF M A S T E R OF A P P L I E D S C I E N C E i n •THE F A C U L T Y OF GRADUATE S T U D I E S ( D e p a r t m e n t o f C i v i l E n g i n e e r i n g ) We a c c e p t t h i s t h e s i s a s c o n f o r m i n g t o t h e r e q u i r e d s t a n d a r d THE U N I V E R S I T Y OF B R I T I S H C O L U M B I A S e p t e m b e r , 1980 © Av Ki: Eandiv 1980 In presenting th i s thes is in pa r t i a l fu l f i lment of the requirements for an advanced degree at the Un ivers i ty of B r i t i s h Columbia, I agree that the L ibrary sha l l make it f ree ly ava i l ab le for reference and study. I further agree that permission for extensive copying of th i s thesis for scho lar ly purposes may be granted by the Head of my Department or by his representat ives. It is understood that copying or pub l i ca t ion of th is thesis for f inanc ia l gain sha l l not be allowed without my written permission. Department of The Univers i ty of B r i t i s h Columbia 2075 Wesbrook P l a c e V a n c o u v e r , Canada V6T 1W5 Date |O,<?.80 i ABSTRACT The i n f l u e n c e of reversed low c y c l i c l oad ing on the bond behaviour of deformed bars i n p l a i n as w e l l as s t e e l - f i b e r - r e i n f o r c e d concre te has been s tud ied expe r imen ta l l y and i s d i scussed i n t h i s t h e s i s . In t o t a l , ten specimens c o n s i s t i n g of two p l a i n concre te and e i gh t s t e e l - f i b e r r e i n f o r c e d specimens were t es ted to f a i l u r e . The v a r i a b l e s were the mix p r o p o r t i o n s , the s i z e and shape of the s t e e l f i b e r s and the p a t t e r n of l o a d i n g . The r e s u l t s i n d i c a t e tha t the most important f a c t o r a f f e c t i n g bond or s t r e s s t r a n s f e r i s the peak s t r e s s reached i n the p rev ious c y c l e . I t was observed tha t s t e e l - f i b e r -r e i n f o r c e d concre te e x h i b i t s h ighe r bond s t r e n g t h , improved s t i f f n e s s and l e s s b o n d - d e t e r i o r a t i o n under reversed c y c l i c l o a d i n g than p l a i n conc re te . I t was a l s o found that s t e e l f i b e r s make a d e f i n i t e c o n t r i -b u t i o n to crack c o n t r o l and b e t t e r s e r v i c e a b i l i t y . i i TABLE OF CONTENTS A b s t r a c t i Tab le of Contents i i L i s t of Tab les : I v L i s t of F igu res v L i s t of P l a t e s v i i Acknowledgements v i i i INTRODUCTION 1 CHAPTER - I 3 Review of E a r l y I n v e s t i g a t i o n a l Works 3 CHAPTER - I I 6 Test Procedure and Specimen Behav iour Under T e s t i n g 6 2.1 Tes t Procedure 6 2 . 1 . 1 Test Programme 6 2 . 1 . 2 Specimen Under Tes t 6 2.1. ! 3 F a b r i c a t i o n of Test Frame 10 2 .1 .4 Ins t rumenta t ion of Rebars 13 2 . 1 . 5 M a t e r i a l s 14 2 .1 .6 Formwork 16 2 .1 .7 Cas t i ng of Specimens 14 2 .1 .8 T e s t i n g Set Up and Ins t rumenta t ion 15 2 .1 .9 T e s t i n g 17 2.2 Behav iour of Test Specimens 18 CHAPTER - I I I 22 A n a l y s i s of Tes t R e s u l t s 22 3.1 L o n g i t u d i n a l D i s t r i b u t i o n of Average Bond 22 S t r e s s 3.2 S t i f f n e s s Loss 23 i i i 3.3 Load - S l i p R e l a t i o n s h i p 27 3.4 R e s i d u a l Bond S t r e s s e s 30 3.5 Comparison of R e s u l t s Obtained by Other 30 I n v e s t i g a t o r s 3.6 Mechanism of Bond D e t e r i o r a t i o n and Crack ing 33 Under Reversed C y c l i c Loading CHAPTER - IV 37 Conc lus ions 37 CHAPTER - V 39 D i s c u s s i o n s 39 References 41 Appendix : 44 Bond S t r e s s D i s t r i b u t i o n Curves S t i f f n e s s Loss - Load R e l a t i o n s h i p Curves Load-Disp lacement R e l a t i o n s h i p Curves L o a d - S l i p R e l a t i o n s h i p Curves R e s i d u a l Bond S t r e s s D i s t r i b u t i o n Cruves F i gu res Showing Crack ing P a t t e r n A f t e r F a i l u r e F i g u r e s Showing V a r i a t i o n of S t resses i n the Specimen i v L I S T OF T A B L E S Page T a b l e I M i x p r o p o r t i o n s 7 T a b l e I I P h y s i c a l p r o p e r t i e s o f r e i n f o r c i n g b a r s 10 T a b l e I I I S u m m a r y o f t h e t e s t r e s u l t s f o r b o n d s t r e s s 20 T a b l e IV C o n c r e t e s t i f f n e s s l o s s a n d b o n d s t r e s s d i s t r i b u t i o n 24 T a b l e V L o a d - s l i p r e l a t i o n s h i p 28 LIST OF FIGURES Page F i g . 1 C y c l i c Bond Test Equipment 8 F i g . 2 Bond Test Specimen (Steel Arrangement) 11 F i g . 3 S t r a i n Gauge F i x i n g Arrangement 12 F i g . 4 Test System 16 F i g . l a Bond Stress D i s t r i b u t i o n with Increase i n Load & Cycles - 45 Specimen B l F i g . 2a' - do - fo r Specimen B l 46 F i g . 3a - do - fo r Specimen B 2 47 F i g . 4a - do - for Specimen B 2 48 F i g . 5a - do - for Specimen B 3 49 F i g . 6 - do - fo r Specimen B 3 50 F i g . 7 - do - for Specimen B 4 51 F i g . 8 - do - fo r Specimen B 4 52 F i g . 9 - do - fo r Specimen B 6 53 F i g . 10 - do - for Specimen B 6 54 F i g . 11 - do - fo r Specimen B 7 55 F i g . 12 - do - for Specimen B 7 56 F i g . 13 - do - for Specimen V 57 F i g . 14 - do -, for Specimen B 8 58 F i g . 15 - do - f o r Specimen B 9 59 F i g . 16 - do - for Specimen B 9 60 F i g . 17 - do - fo r Specimen Bio 61 F i g . 18 - do - for Specimen Bio 62 F i g . 19 Bond Stress D i s t r i b u t i o n (Applied force ±10 k) 63 F i g . 20 Bond Stress D i s t r i b u t i o n (Applied force +10 k) 64 F i g . 21 Bond Stress D i s t r i b u t i o n (Applied force +20 k) 65 F i g . 22 , Bond Stress D i s t r i b u t i o n (Applied force ±20 k) 66 v i Page F i g . 23 B o n d S t r e s s D i s t r i b u t i o n ( A p p l i e d f o r c e ± 3 0 k ) 67 F i g . 2 4 - d o - ( A p p l i e d f o r c e +30 k ) 68 F i g . 2 5 - d o - ( A p p l i e d f o r c e +40 k ) 69 F i g . 26 1 - d o - ( A p p l i e d f o r c e ± 4 0 k ) 70 F i g . .27 S t i f f n e s s L o s s - L o a d R e l a t i o n s h i p 71 F i g . 28 L o a d D i s p l a c e m e n t R e l a t i o n s h i p 72 ( E n v e l o p e o f H y s t e r i s L o o p s ) F i g . 29 L o a d - S l i p R e l a t i o n s h i p 73 F i g . 30. L o a d - S l i p / C y c l e R e l a t i o n s h i p 74 F i g . ,31 R e s i d u a l B o n d S t r e s s D i s t r i b u t i o n . A f t e r . M a x . 1 0 k L o a d 7 5 F i g . 32 R e s i d u a l B o n d S t r e s s D i s t r i b u t i o n A f t e r M a x . 2 0 k L o a d 76 F i g . 33 R e s i d u a l B o n d S t r e s s D i s t r i b u t i o n A f t e r M a x . 3 0 k L o a d 77 F i g . 3 4 C r a c k i n g P a t t e r n A f t e r F a i l u r e 78 F i g . 3 5 V a r i a t i o n i n rj~^f (f^ i n t h e S p e c i m e n D u r i n g L o a d i n g 79 F i g . 36 S t e s s e s B e t w e e n R i b s o f D e f o r m e d B a r a n d C T , Q~" D i s t r i - 80 N y v z bution v i i LIST OF PLATES Plate 1 Test frame set up Plate 2 Test frame set up (close up) v i i i ACKNOWLEDGEMENTS Th is i n v e s t i g a t i o n regard ing "Bond of Deformed bars i n P l a i n and S t e e l - f i b e r - r e i n f o r c e d concre te under reversed c y c l i c Load ing " was c a r r i e d out i n the S t r u c t u r a l Eng ineer ing Labora to ry of the Department of C i v i l Eng ineer ing and was made p o s s i b l e by g ran ts from the N a t i o n a l Research C o u n c i l of Canada. The author expresses h i s indebtedness to P r o f e s s o r s R. A. Spencer and S. Mindess f o r t h e i r v a l u a b l e guidance i n p lann ing and c a r r y i n g out the i n v e s t i g a t i o n . The author wishes to thank the t e c h n i c a l a s s i s t a n t s of the Labora to ry e s p e c i a l l y , Mess rs . B. M e r k l i , D. Pos tga te and G. K i r s c h f o r t h e i r a s s i s t a n c e i n making the t e s t equipment and c a r r y i n g out the t e s t s . September, 1980 Vancouver , B . C . 1 INTRODUCTION Though there has been considerable study of bond between r e i n f o r c i n g bars and concrete by numerous i n v e s t i g a t o r s , the e f f e c t of c y c l i c loading on bond and cracking has not been extensively inves-tigated. Some of the re s u l t s that have been found are contradictory. Further, no attempt has been made to determine the e f f e c t of repeated loading on bond between f i b e r reinforced concrete and deformed r e i n -f o r c i n g bars. Currently, concrete designers are placing more emphasis on two important f a c t o r s : control of cracking and provision.of d u c t i l i t y . The control of cracking i s important f o r the sake of appearance and d u r a b i l i t y . D u c t i l i t y i s important to ensure that the structure behaves i n a d u c t i l e manner i n the event of being loaded to f a i l u r e , g i v ing s u f f i c i e n t warning of f a i l u r e . E s p e c i a l l y f o r structures i n seismic areas, p r o v i s i o n of adequate d u c t i l i t y i s most important as the design philosophy assumes s u f f i c i e n t d u c t i l i t y a f t e r y i e l d i n g to enable the structure to survive an earthquake without collapse. In s a t i s f y i n g the above two c r i t e r i a i n design, bond between r e i n f o r c i n g bars and concrete plays a v i t a l r o l e , and the designer should give i t . s p e c i a l attention. During earthquakes, alternate y i e l d i n g i n tension and compression at a c r i t i c a l section such as a beam-column j o i n t i n t e r f a c e can occur. Due to such repeated loading, there may be a gradual l o s s of bond which can r e s u l t i n penetration of y i e l d i n g into the anchorage zone, thus reducing the e f f e c t i v e development length a v a i l a b l e to develop the y i e l d strength of.the bar. Thus bond becomes c r i t i c a l under such loading conditions. 2 In l i g h t of the above, the aim of the tests reported herein was to study the behaviour of bond of deformed r e i n f o r c i n g bars with p l a i n as w e l l as f i b e r - r e i n f o r c e d concrete under reversed c y c l i c loading, simulating seismic loading conditions. Specimens with f i b e r -r einforced concrete were also tested to explore the f e a s i b i l i t y of using f i b e r - r e i n f o r c e d d u c t i l e frames i n seismic areas. 3 C H A P T E R - I R E V I E W OF E A R L Y I N V E S T I G A T I O N A L W O R K S : A s e a r l y a s 1 9 0 9 , W i t h e y ( 2 9 ) r e p o r t e d t h e r e s u l t s o f s o m e b o n d t e s t s o n b e a m s p e c i m e n s w i t h p l a i n r e i n f o r c i n g b a r s s u b j e c t e d t o r e p e a t e d l o a d i n g . H e s h o w e d t h a t a l o a d e q u a l t o 5 0 t o 60% o f t h e s t a t i c l o a d c o u l d b e r e p e a t e d a n i n d e f i n i t e n u m b e r o f t i m e s w i t h o u t f a i l u r e o f b e a m s . T h i s r a t i o w a s 6 0 t o 70% f o r d e f o r m e d b a r s . H e a l s o r e p o r t e d t h a t b o n d s t r e s s e s f o r p u l l o u t s p e c i m e n s w e r e a s m u c h a s t w o t i m e s t h o s e f o u n d f r o m b e a m s p e c i m e n s . I n 1 9 4 0 , L e a ( 1 0 ) r e p o r t e d t h e r e s u l t s o f b o n d t e s t s u n d e r r e p e a t e d l o a d i n g a n d i n d i c a t e d t h a t t h e l o w e s t l o a d a t w h i c h b o n d f a i l u r e o c c u r r e d i n f a t i g u e w a s a b o u t 50% o f t h e s t a t i c b o n d s t r e s s ( i . e . a p p r o x i m a t e l y t h e same a s t h e f a t i g u e l i m i t f o r c o n c r e t e ) . I n 1 9 4 5 , M u h l e n b r u c h ( 1 6 ) a t t e m p t e d t o d e t e r m i n e t h e e f f e c t o f r e p e a t e d l o a d i n g o n b o n d s t r e n g t h . H e t e s t e d s o m e p u l l o u t s p e c i m e n s w i t h 5 / 8 " p l a i n r e i n f o r c e m e n t b a r s s u b j e c t e d t o a s m a n y a s 5 m i l l i o n l o a d c y c l e s a n d s h o w e d t h a t w i t h a n i n c r e a s e i n t h e n u m b e r o f r e p e t i t i o n s o f l o a d i n g , s t a t i c p u l l o u t s t r e n g t h d e c r e a s e s . H e a l s o s h o w e d t h a t a f t e r 5 m i l l i o n c y c l e s o f l o a d i n g , s t a t i c p u l l o u t s t r e n g t h r e d u c e s t o a b o u t 50% a n d i n g e n e r a l , h e r e p o r t e d t h a t a n i n c r e a s e i n r e p e t i t i o n s c a u s e s a d e c r e a s e i n a v e r a g e b o n d s t r e s s a t f a i l u r e . I n 1 9 6 2 , V e r n a a n d S t e l s o n ( 2 8 ) t e s t e d s o m e b e a m s p e c i m e n s u n d e r r e p e a t e d l o a d i n g a n d r e p o r t e d t h a t t h o u g h i t w a s d i f f i c u l t t o m a k e a p r e d i c t i o n o f b o n d f a t i g u e s t r e n g t h f o r o n e m i l l i o n c y c l e s , i t w a s l e s s t h a n 40% o f t h e s t a t i c u l t i m a t e l o a d . I n 1 9 6 8 , B r e s l e r a n d B e r t e r o ( l ) r e p o r t e d r e s u l t s f r o m c y l i n d r i c a l c o n c r e t e s p e c i m e n s , e a c h r e i n f o r c e d a x i a l l y w i t h a d e f o r m e d s t e e l b a r 4 sub jec ted to repeated c y c l e s of l oad ing and un load ing . They showed that s t r e s s t r a n s f e r at any g iven s t r e s s l e v e l i s i n f l u e n c e d by the p rev ious s t r e s s h i s t o r y and a g i ven maximum peak s t r e s s l e v e l i n s t e e l r e i n f o r c e -ment reduced the s t r e s s t r a n s f e r e f f e c t i v e n e s s at lower s t r e s s e s i n subsequent c y c l e s . They a l s o showed that the r e l a t i v e c o n t r i b u t i o n of concre te to the s t i f f n e s s became n e g l i g i b l e as the number of l oad c y c l e s and the magnitude of peak s t r e s s e s i n c r e a s e d . In 1969, P e r r y and Jund i (20) on the b a s i s of t e s t r e s u l t s f o r e c c e n t r i c p u l l out specimens repor ted tha t there was no ev idence tha t f a i l u r e of a specimen would occur because of an i n c r e a s i n g number of c y c l e s of l oad ing un less the a p p l i e d l oad was at l e a s t 80% of the u l t i m a t e l oad or g r e a t e r . In 1972, I s m a i l and J i r s a ( 8 , 9 ) repo r ted the r e s u l t s of t e s t s on a x i a l l y r e i n f o r c e d concre te pr isms sub jec ted to a l t e r n a t i n g loads and on beam specimens sub jec ted to c y c l i c l o a d i n g . They showed tha t the most impor tant f a c t o r a f f e c t i n g bond or s t r e s s t r a n s f e r i s the peak s t r e s s reached i n p rev ious c y c l e s ; r e p e t i t i o n s of l oad c y c l e s w i t h constant peak s t r e s s produced on ly a g radua l d e t e r i o r a t i o n of s t r e s s t r a n s f e r c a p a c i t y . In 1974, Swamy and A l Noor i (26) c a r r i e d out p u l l - o u t t e s t s on deformed bars of v a r i o u s d iameters embedded i n s t e e l f i b e r r e i n f o r c e d and p l a i n concre te and repor ted tha t the anchorage bond s t r eng th of deformed bars was 40% h igher i n s t e e l f i b e r r e i n f o r c e d concre te than i n p l a i n conc re te . In 1977, V iwathanatepa, Be r te ro and Popov(21a) r e p o r t e d , based on the r e s u l t s of bond t e s t s w i t h reversed c y c l i c l o a d i n g , tha t even below the work ing s t r e s s l e v e l , s e v e r e l y p inched h y s t e r e s i s curves were ob ta ined i n d i c a t i n g cons ide rab le d isp lacements of the r e i n f o r c i n g b a r . 5 They a l s o observed s i g n i f i c a n t r e s i d u a l s t r e s s e s a f t e r a s m a l l number of l o a d i n g c y c l e s . Popov(21b) has emphasized the need f o r a bond-s l i ppage law. L a s t l y , i n 1979, Rehm and E l igehaussen(23) on the b a s i s of t e s t s on p u l l out specimens, showed that the i n f l u e n c e of repeated l o a d i n g on the s l i p and bond s t r eng th of deformed bars i s s i m i l a r to t ha t on the deformat ion and f a i l u r e behav iour of u n r e i n f o r c e d conc re te . The f a t i g u e bond s t reng th corresponds to the f a t i g u e s t r e n g t h of a x i a l l y loaded concre te and no f a t i g u e bond f a i l u r e would occur even a f t e r s e v e r a l m i l l i o n s of c y c l e s i f the upper l oad i s l e s s than about 50% of the s t a t i c p u l l out l o a d . They a l s o repor ted tha t i f no f a t i g u e f a i l u r e o c c u r s , a repeated l oad would have on ly an i n f l u e n c e on the bond behav iour under s e r v i c e l o a d . In the l i g h t of these somewhat c o n t r a d i c t o r y r e s u l t s , i t was cons idered wor thwhi le to f u r t h e r i n v e s t i g a t e bond under reve rsed c y c l i c l oad ing f o r p l a i n as w e l l as f i b e r r e i n f o r c e d conc re te . 6 C H A P T E R - I I T E S T P R O C E D U R E AND S P E C I M E N B E H A V I O U R UNDER T E S T I N G : 2 . 1 T e s t P r o c e d u r e : 2 . 1 . 1 T e s t P r o g r a m m e : T e n c o n c r e t e s p e c i m e n s w e r e t e s t e d i n t h e S t r u c t u r a l E n g i n e e r i n g L a b o r a t o r y o f t h e C i v i l E n g i n e e r i n g D e p a r t m e n t o f U B C . A l l o f t h e s p e c i m e n s w e r e t h e s a m e s i z e a n d s h a p e , w i t h a 1 " d i a m e t e r r e i n f o r c i n g b a r p l a c e d c e n t r a l l y i n t h e s p e c i m e n . Two s p e c i m e n s w e r e o f p l a i n c o n c r e t e a n d t h e r e m a i n i n g e i g h t w e r e o f s t e e l - f i b e r r e i n f o r c e d c o n c r e t e . T h e v a r i a b l e s i n t r o d u c e d w e r e m i x p r o p o r t i o n s , s i z e a n d s h a p e o f s t e e l f i b e r s . T h e n u m b e r o f c y c l e s a t v a r i o u s p e a k l o a d s w a s a l s o v a r i e d . T h e m i x p r o p o r t i o n s a n d o t h e r p a r t i c u l a r s a r e t a b u l a t e d i n T a b l e N o . 1 . T h e a p p l i c a t i o n o f l o a d i n g w a s b y m e a n s o f t w o j a c k s m o u n t e d o n a t e s t f r a m e . T h e l o a d s e t u p w a s s u c h t h a t a c o m p r e s s i o n ( o r t e n s i o n ) f o r c e c o u l d b e a p p l i e d a t o n e e n d o f t h e t e s t b a r w h i l e a t e n s i o n ( o r c o m p r e s s i o n ) f o r c e w a s a p p l i e d t o t h e o t h e r e n d . A n MTS s e r v o - c o n t r o l l e d l o a d s y s t e m w a s u s e d t o a p p l y t h e l o a d s . L o a d s , d i s p l a c e m e n t s a n d s t r a i n s w e r e r e c o r d e d u s i n g a V i d a r 5 4 0 3 D - D A S D a t a A c q u i s i t i o n S y s t e m a n d P D P 1 1 / 1 0 m i n i c o m p u t e r . T h e l o a d i n g a r r a n g e m e n t s a n d t e s t s e t u p a r e s h o w n i n F i g u r e 1 a n d P l a t e N o . 1 a n d 2 . 2 . 1 . 2 S p e c i m e n s U n d e r T e s t : T h e s p e c i m e n s u n d e r t e s t a l l h a d d i m e n s i o n s 1 0 " x 2 0 " x 4 0 " . T h e c y c l i c l o a d i n g w a s a p p l i e d t o t h e e n d s o f a 1 " d i a m e t e r G r a d e 6 0 d e f o r m e d b a r w i t h a n e m b e d m e n t l e n g t h o f 2 0 " . I n o r d e r t o c o n f i n e t h e c o n c r e t e a r o u n d t h i s t e s t r e b a r a n d p r e v e n t l o n g i t u d i n a l s p l i t t i n g o f t h e c o n c r e t e , TABLE 1: MIX PROPORTIONS Specimen Steel Fiber (lb/cu yd)| Fiber Size Water (lb/cu yd) Cement (lb/cu yd) Sand (lb/cu yd)] 3/8" Pea Gravel (lb/cu yd) Water Reducer (fl oz per cu yd)| Air Entralnment ( f l oz per cu yd) | Plain Concrete B3\ 0.75% Steel-s' I Fiber Concrete B5"\ 0.75% Steel-B6 j Fiber Concrete B 7| 1,5% Steel-BgJ Fiber Concrete Bgl 1.5% Steel-B.j Fiber Concrete 100 100 100 100 200 200 200 200 0.5x0.022x0.01" 0.5x0.022x0.01" 1x0.022x0.01" 1x0.022x0.01" 0.5x0.022x0.01" 0.5x0.022x0.01" 1x0.022x0.01" 1x0.022x0.01" 240 240 270 270 270 270 290 290 290 290 675 675 675 675 675 675 675 675 675 675 1480 1480 1425 1425 1425 1425 1390 1390 1390 1390 1480 1480 1425 1425 1425 1425 1390 1390 1390 1390 20 20 20 20 20 20 20 20 20 20 6.67 6.67 8.00 8.00 8.00 8.00 8.00 8.00 8.00 8.00 1. Pozzolith 300N 2. MB-VR NOTE: Steel Fiber % by Volune. MTS JACK T 10 - I •WI4 x 34 •WEBB STIFFENER ' A " •I2"x I2"x V 4"PL.: P L A N FIG. I' CYCLIC BOND TEST EQUIPMENT PLATE 2 : Tes t Frame Setup (Close Up) 10 a n 8 " o u t e r d i a m e t e r s p i r a l m a d e o u t o f h" d i a m e t e r b a r , w a s u s e d f o r e a c h s p e c i m e n . To h o l d t h e s p i r a l , a d d i t i o n a l r e i n f o r c e m e n t b a r s w e r e p l a c e d v e r t i c a l l y a s w e l l a s h o r i z o n t a l l y . A l l o f t h e r e i n f o r c e m e n t e x c e p t t h e t e s t r e b a r a n d s p i r a l w e r e o f V < | > MS b a r s . T h e d i s p o s i t i o n o f t h e r e i n f o r c i n g b a r s i n t h e s p e c i m e n s i s s h o w n i n F i g u r e 2 . T h e y i e l d s t r e n g t h s a t 0 . 2 % o f f s e t f o r t h e 1 " d i a m e t e r d e f o r m e d b a r a n d t h e h" d i a m e t e r b a r a r e t a b u l a t e d i n T a b l e N o . 2 . T A B L E 2 - P H Y S I C A L P R O P E R T I E S OF R E I N F O R C I N G B A R S B a r Y i e l d T e n s i l e D i a m e t e r T y p e A r e a ( i n ) S t r e n g t h ( k s i ) S t r e n g t h ( k s i ) 1 " D e f o r m e d 0 . 7 8 5 4 6 3 9 8 k" P l a i n 0 . 1 9 6 3 6 3 8 0 2 . 1 . 3 T e s t F r a m e : T h e t e s t f r a m e w a s d e s i g n e d a n d f a b r i c a t e d w i t h s t e e l s t r u c t u r a l s e c t i o n s f o r b o n d t e s t u n d e r r e v e r s e d c y c l i c l o a d i n g w i t h m a x i m u m l o a d c a p a c i t y o f ± 1 0 0 k i p s . I n t h e p r e s e n t t e s t s e t - u p , o n e 1 0 0 k i p j a c k a n d o n e 5 0 k i p j a c k w e r e u s e d . T h e s e w e r e m o u n t e d h o r i z o n t a l l y i n t h e t e s t f r a m e . T h e d e f o r m e d b a r w a s l o a d e d u s i n g t h r e a d e d c o n n e c t o r s w e l d e d t o t h e t e s t r e b a r , w h i c h w e r e b o l t e d t o t h e l o a d c e l l s o f t h e j a c k s . T h e s e h a v e b e e n s h o w n i n F i g u r e 3 . T h e c o n c r e t e s p e c i m e n s w e r e l o c a t e d i n t h e c e n t e r o f t h e t e s t f r a m e a n d m o v e m e n t w a s p r e v e n t e d b y m e a n s o f 2 " x 1 " s t e e l f l a t s l o c a t e d b y b o l t s a t t a c h e d t o t h e t e s t f r a m e . T h e t e s t f r a m e w a s b r a c e d a n d s t i f f e n e d t o m i n i m i z e a n y d e f o r m a t i o n d u r i n g t e s t i n g . T h e d e t a i l s o f t h e t e s t f r a m e a r e s h o w n i n F i g u r e 1 a n d P l a t e 1 a n d 2 . XX 6 NOS '/4"cj> BARS ON EACH SIDE '/4"co BARS TO SUPPORT REBAR AND SPIRAL SECTION PLAN A — A F I G . 2 ' BOND T E S T S P E C I M E N -( S T E E L ARRANGEMENT) FIG:3> STRAIN GAUGE FIXING A R R A N G E M E N T . 13 2 .1 .4 Ins t rumenta t ion of Tes t Rebars : The r e i n f o r c i n g bar f o r each bond t e s t specimen c o n s i s t e d of a Grade 60, 1" d iameter , 30" long deformed b a r . Grooves 0 . 2 " wide and 0 . 1 " deep were formed by machin ing on oppos i te s i des of the rebar a long the c e n t r a l 20" l eng th as shown i n F i gu re 3 . A threaded connector was welded to each end of each reba r -as shown i n F i g u r e 3. Due ca re was taken to ensure that the l o n g i t u d i n a l a x i s of the threaded connectors (at both ends) c o i n c i d e d w i t h that of the r eba r . Mount ing of S t r a i n Gauges: S t r a i n gauges used i n the t e s t s were e l e c t r i c r e s i s t a n c e gauges of type CEA-06-062-UW-120. F o r t y gauges were used f o r each spec imen, 20 on each s i d e of the t e s t r e b a r , spaced at 1" i n t e r v a l s as shown i n F i g u r e 3. Be fo re the gauges were a p p l i e d , the r e i n f o r c i n g bars were sand b l a s t e d and then a i r b l a s t e d to remove any d i r t or g rease . Then g lue was app l i ed to the rebar groove a t the app rop r i a te l o c a t i o n s -and to the s t r a i n gauges one at a t ime . A f t e r a shor t p e r i o d , the gauges were p laced on the rebar and cured at 200°C f o r one hour i n an oven. A l l the s t r a i n gauges used were of the same s p e c i f i c a t i o n s , hav ing an e l e c t r i c r e s i s t a n c e of 120±0.3 Ohm and a gauge f a c t o r of 2.1±0.5% at 75°F. Connect ion of Wires to Gauges: Before s o l d e r i n g , the gauge t e rm ina l s were scraped c l ean of any o x i d a t i o n or d i r t . Termina ls and leads were then t i nned and s o l d e r e d . Glue was used to anchor the l e a d w i r e s i n the grooves. For each specimen, w i res from 10 gauges came out at each end of the b a r , 5 above and 5 below the b a r . Wires f o r the remain ing 20 gauges were l e d to the cen t re of the bar and came out from both f a c e s of specimen. The arrangement of the 14 gauges i s shown i n F i gu re 3. P l a s t i c s t r a p s were used to prevent the w i r e s from r i p p i n g out . Th in p l a s t i c tubes were a l s o used over the c e n t r a l w i r e s to p r o t e c t them from the conc re te . Co lour cod ing was used to d i s t i n g u i s h the w i res from v a r i o u s gauges. 2 . 1 . 5 M a t e r i a l s : The cement was h igh e a r l y s t reng th p o r t l a n d cement (Type 30) . The f i n e aggregate was c l ean sand from the F r a s e r R i v e r V a l l e y which was f r e e from harmfu l i m p u r i t i e s . The coarse aggregate used was 3 / 8 " pea g r a v e l . The d e t a i l s of the conc re te mix p ropo r t i ons are shown i n Tab le No. 1. 2 .1 .6 Formwork: The formwork f o r the 10" x 20" x 40" concre te specimens c o n s i s t e d of plywood and 2" x 4" lumber, b o l t e d together f o r easy and e f f i c i e n t s t r i p p i n g . Care was taken to avo id any leakage through j o i n t s , and to keep the forms square and t r u e . 2 .1 .7 C a s t i n g of Specimens: The forms were o i l e d and the r e i n f o r c i n g cage a long w i t h the s p i r a l re in fo rcement t i e d to i t was p r o p e r l y l o c a t e d . The t e s t rebar w i t h s t r a i n gauges f i x e d to i t was supported i n the formwork through ho les p rov ided f o r the purpose. Necessary e l e c t r i c a l connect ions were then made. A pan - type mixer was used and cement, aggregate , sand and water were added i n o r d e r , f o l l owed by the admix tu res : a water reduce r , P o z z o l i t h 300N and an a i r e n t r a i n i n g agent (MB-VR). F i n a l l y , s t e e l f i b e r s were added by shak ing them through a s i e v e , and the concre te was mixed f o r about 5 minutes . The concre te was unloaded i n a t r o l l e y , and p laced i n t o the formwork w i t h a s h o v e l . 15 The concre te was w e l l compacted by means of an immersion v i b r a t o r . Care was taken not to d i s t u r b the re in forcement cage du r ing placement of the concre te and v i b r a t i o n . F i n a l l y , the specimens were f i n i s h e d w i t h a t rowe l and covered w i t h wet bur lap and p l a s t i c to prevent d r y i ng f o r a p e r i o d of f ou r weeks. They were then s t o r e d i n a i r . The specimen age at t e s t i n g was one yea r . 2 . 1 . 8 T e s t i n g Set-Up and T e s t i n g System: Loading System An M .T .S . s e r v o - c o n t r o l l e d l o a d i n g system was used f o r the c y c l i c bond t e s t s . Readings from a l l f o r t y s t r a i n gauges and LVDTs cou ld be recorded u s i n g a V i d a r da ta a c q u i s i t i o n system and a PDP-11 m i n i computer. The t e s t system i s shown d i a g r a m a t i c a l l y i n F i gu re 4. The M . T . S . system i s a c l o s e d - l o o p - s e r v o c o n t r o l l e d two channel system u t i l i z i n g a h y d r a u l i c power supp ly . The h y d r a u l i c a c t u a t o r which serves as a f o r c e genera t ing and/or p o s i t i o n i n g dev ice i s c o n t r o l l e d by the servo v a l v e i n response to a c o n t r o l s i g n a l . The load or d i s p l a c e -ment a p p l i e d by a h y d r a u l i c ac tua to r i s sensed by t ransducers which p rov ide s i g n a l s to t ransducer c o n d i t i o n e r s which supply e x c i t a t i o n v o l t a g e s and c o n d i t i o n the t ransducer output vo l t age to d -c l e v e l s . The output of a p a r t i c u l a r t ransducer c o n d i t i o n e r i s s e l e c t e d by a feed-back s e l e c t o r and s u p p l i e d to a Command Input Module which a t tenua tes the s e l e c t e d f e e d -back s i g n a l and compares i t to a program command s i g n a l . As the program command and feed-back s i g n a l s become e q u a l , the c o n t r o l s i g n a l app l i ed to the servo v a l v e decreases to zero and the loop becomes ba lanced . Data A c q u i s i t i o n and Data P r o c e s s i n g : Computer programmes were w r i t t e n f o r da ta a c q u i s i t i o n and f o r p rocess i ng of t e s t da ta sent from the V i d a r to the PDP-11 Computer. Data f o r each specimen was s to red i n separa te f i l e s on the PDP-11 d i s c . Bridge Co mpletio n C i r c u i t s 5 STRAIN G A U G E S 5 STRAIN GAUGES 5 STRAIN GAUGES 5 STRAIN GAUGES 5 STRAIN G A U G E S 10 STRAIN GAUGES 10 STRAIN GAUGES BRIDGE BOXES 40 STRA IN GAUGES + 4 L V D T S POWER SUPPLY EX - VOLTS Odd DU 0 P I 0 I 0 D I Q B O I D O U O n O D S VIDAR (Data Acquisition) CONCRETE SPECIMEN PDPII COMPUTER! n brrrjnnj n LTD nxM n J 1 fe^l o a a a ••• • •• MTS CONTROL ( L o a d i n g ) ( Data Ana lysis as FI6.4« TEST SYSTEM . 17 Before each t e s t , c a l i b r a t i o n data from LVDTs and Load C e l l s , and gauge f a c t o r s f o r s t r a i n gauges, were entered to the Computer programme. The v o l t a g e s measured by the V i d a r were then d i r e c t l y conver ted i n t o the d e s i r e d u n i t s , and s e l e c t e d va lues were p r i n t e d by the Computer du r ing the t e s t . Data p rocess ing was completed when the t e s t was f i n i s h e d . 2 . 1 . 9 T e s t i n g : F i r s t of a l l , the hardened concre te specimen was p laced i n the cen te r of the t es t - f r ame by means of an overhead crane and p laced i n a t r u l y v e r t i c a l p o s i t i o n such tha t the rebar a x i s was c o n c e n t r i c w i t h both of the Jack axes . Then the rebar connectors were connected to the l oad c e l l s and the b o l t s were t i g h t e n e d . The specimen was f i r m l y h e l d by the c lamping b o l t s and p l a t e s . To reco rd s l i p of the r e b a r , four d isp lacement t r a n s d u c e r s , two on each s i de a t each end of the rebar were f i x e d by magnet ic c lamps. Leads from a l l of the s t r a i n gauges, LVDTs and t ransducers were connected to the V i d a r . Other connect ions from the V i d a r and from the servo v a l v e , j a c k s , e t c . to the M . T . S . C o n t r o l and from the M . T . S . C o n t r o l to the PDP-11 Computer were made as shown i n the b l o c k d iagram, F i g u r e 4. Be fo re running the t e s t a ramp wave form mode of l oad ing was s e l e c t e d . Necessary adjustments i n the V ida r as w e l l as i n the M . T . S . C o n t r o l were made to ensure smooth f u n c t i o n i n g of the system wi thout any e r r o r . Be fo re app l y i ng l o a d , zero scan read ings were reco rded . Peak l oad was i n i t i a l l y ±10 k i p s , then ±20 k i p s , ±30 k, ±40 k, ±45 k, ±50 k, ±51 k, ±52 k, ±53 k and so on t i l l f a i l u r e . For each of the peak l o a d i n g s , s e v e r a l c y c l e s up to a maximum of 14 c y c l e s were run be fo re i n c r e a s i n g the load to the next peak v a l u e . As the l o a d i n g on the specimen p rog ressed , a c a r e f u l watch was kept to l o c a t e 18 t h e a p p e a r a n c e o f c r a c k s o n t h e s p e c i m e n s u r f a c e . T h e l o a d i n g w a s c o n t i n u e d t i l l f a i l u r e o f t h e s p e c i m e n d u e t o e x c e s s i v e s l i p p a g e , t e n s i l e f a i l u r e o f t h e t e s t r e b a r , o r e x t e n s i v e c r a c k i n g o f t h e s p e c i -men t o o k p l a c e . A f t e r e a c h t e s t , t h e g e n e r a l b e h a v i o u r o f t h e s p e c i m e n u n d e r t e s t w a s n o t e d . C o n c r e t e c y l i n d e r s w e r e t e s t e d i n a C o m p r e s s i o n T e s t i n g m a c h i n e a n d s t r e n g t h s n o t e d f o r e a c h s p e c i m e n . 2 . 2 B e h a v i o u r o f T e s t S p e c i m e n s : I n t o t a l , t e n s p e c i m e n s w e r e t e s t e d a n d t h e f o l l o w i n g o b s e r v a t i o n s w e r e m a d e : -T h e f i r s t c r a c k w a s o b s e r v e d i n t h e p l a i n c o n c r e t e s p e c i m e n s B ^ a n d B ^ a t ± 3 0 k i p l o a d ( s t r e s s l e v e l i n t h e r e b a r = 3 8 . 2 k s i ) w h e r e a s u n d e r s i m i l a r l o a d i n g c o n d i t i o n s a r id c y c l e s , a l l t h e s t e e l f i b e r - r e i n f o r c e d s p e c i m e n s s t a r t e d d e v e l o p i n g c r a c k s a t ± 4 0 k i p o r h i g h e r p e a k l o a d s . F u r t h e r , t h e c r a c k p a t t e r n f o r p l a i n c o n c r e t e s p e c i m e n s w a s t r a n s v e r s e s p l i t t i n g , w h e r e a s f o r s t e e l f i b e r - r e i n f o r c e d s p e c i m e n s , t h e r e w a s b u r s t i n g o f a p o r t i o n o f t h e c o n c r e t e n e a r t h e r e b a r e n d . I t w a s a l s o o b s e r v e d t h a t f o r a l l o f t h e f i b e r - r e i n f o r c e d s p e c i m e n s , t h e c r a c k f o r m a t i o n a n d p r o p a g a t i o n w a s m o r e g r a d u a l t h a n f o r t h e p l a i n c o n c r e t e s p e c i m e n s . D u r i n g t e s t i n g , a s the . l o a d p r o g r e s s i v e l y i n c r e a s e d u p t o a b o u t ± 2 0 k i p p e a k l o a d , t h e r e w a s p r a c t i c a l l y n o c h a n g e i n s t r a i n a n d s l i p v a l u e s w i t h i n c r e a s e i n n u m b e r s o f c y c l e s o f l o a d i n g . B e y o n d t h i s p e a k l o a d , t h e r e w a s a s l i g h t c h a n g e i n s t r a i n a n d s l i p v a l u e s , a n d a p p r e c i a b l e c h a n g e w a s n o t i c e d b e y o n d ± 4 0 k i p l o a d ( s t r e s s l e v e l i n t h e r e b a r = 5 0 . 9 3 k s i ) . H o w e v e r , a t t h i s l o a d a n d h i g h e r , m o s t o f t h e s t r a i n g a u g e s w e r e d a m a g e d , a n d t h e r e f o r e t h e v a l u e s o b t a i n e d w e r e e r r a t i c . D e t a i l s r e g a r d i n g s p e c i m e n s , n o . o f c y c l e s r u n , c r a c k i n g l o a d e t c . 19 are indicated i n Table 3. There was t e n s i l e f a i l u r e of the t e s t rebar i n four of the cases, and welding f a i l u r e of the connectors for two of the specimens. These were probably due to fatigue. Testing of each specimen took about one or two days to complete. TABLE 3 : SUMMARY OF THE TEST RESULTS FOR BOND STRESS No. S p e c i f i c a t i o n U i t . C y l . Load Cyc les Max Load at Type of Remarks of S t reng th (K ips ) (To ta l ) S l i p 1st Crack F a i l u r e Specimen (KSI) ( i n ) (K ips) 10 " 1 20 1 Rebar 7.53 30 3 (10) 0.151 30 F a i l u r e 40 3 i n Tension P l a i n 50 . 2 Concrete 10 " 4 20 6 Pro fuse 8.15 30 > 10 (36) 0.18 30 Crack ing & 40 6 S p a l l i n g of 45 5 concrete 50 5 1 0 ' 4 20 6 30 6 Rebar f a i l e d 9.7 40 • 5 (41) 0.186 40 #J1 end at 45 7 52k (41 c y c l e ) 50 8 3/4% 5 2 . • 5 S t e e l F i b e r 20 " 4 h" Long 6.99 30 2 (18) 0.079 - Conta ined 40 2 some honey-50 10 combs Excess i ve F u l l of honey 3/4% 7.91 S l i p combs i n the S t e e l F i b e r specimen 1" Long? 10 ' 4 20 5 Weld f a i l u r e 8.14 30 5 (20) 0.11 45 at #J1 end at 40 5 45k 45 1 TABLE 3 : c o n t ' d Specimen No. '10 > e c i f i c a t i o n U l t . Cy . Load Cyc les Max Load at Type of of S t reng th (K ips ) (To ta l ) S l i p 1st Crack F a i l u r e Specimen (KSI) ( i n ) (K ips) 10" 4 20 6 Weld f a i l u r e 5.92 30 5 (29) 0.142 40 at #J1 end at 40 5 50k h 45 5 1.5% S t e e l 50 4 F i b e r 10" 1 h" Long 20 2 6.26 30 • ' 2 (26) 0.239 40 -40 4 45 3 5 0 . 14, 1 0 ' 10. 20 9 30 7 Rebar f a i l e d 7.30 40 4 0.231 40 at #J1 end at 45 3 (46) 53k 50 8 52 3 1.5% S t e e l 53 2 F i b e r 10 n 4 1" Long- 20 6 30 6 Rebar f a i l e d 6.58 40 6 (37) 0.263 40 at #J1 end at 45 6 52k 50 8 52 1 Remarks 22 CHAPTER - I I I ANALYSIS OF TEST RESULTS 3.1 L o n g i t u d i n a l D i s t r i b u t i o n of Average Un i t Bond S t r e s s : The v a l u e s of the s t e e l s t r a i n s at each gauge l o c a t i o n f o r peak l oad ings w i t h a s m a l l number of v a r i o u s c y c l e s as desc r i bed i n Table 3 were ob ta ined by p rocess ing the data f o r each specimen. A computer programme was used to c a l c u l a t e the average u n i t bond s t r e s s f o r each gauge l o c a t i o n a long the reba r . S t e e l s t r e s s e s f o r each p o i n t were c a l c u l a t e d from the exper imenta l s t r e s s - s t r a i n diagram of the r e b a r . The average u n i t bond s t r e s s was c a l c u l a t e d based on the f o l l o w i n g f o r m u l a : -cr = ( f j - f i ) p : V i j kl. . where ^ . = average u n i t bond s t r e s s between i and j l o c a t i o n s f^ = s t e e l s t r e s s at i th l o c a t i o n ^ = s t e e l s t r e s s at j th l o c a t i o n D = diameter of rebar l^ = l eng th of rebar w i t h i n i and j po i n t = 1" The va lues were p l o t t e d as shown i n F igu re l a to 26. The e f f e c t s of repeated l o a d i n g were as f o l l o w s : 1. The bond s t r e s s d i s t r i b u t i o n diagrams i n d i c a t e a s h i f t of the po i n t of zero bond s t r e s s towards the compression zone ( s t e e l ) from the cen te r . Th is s h i f t i s more w i t h h ighe r peak l o a d i n g s . The t e n s i l e bond s t r e s s zone i s about 20% longer than the compression zone. The l o n g i t u -d i n a l s t e e l s t r e s s d i s t r i b u t i o n a l s o agrees w i t h t h i s . 2 . G e n e r a l l y , the abso lu te maximum bond s t r e s s occurs at the ends of the specimens. 2 3 3 . W i t h i n c r e a s e d p e a k l o a d i n g , b o n d s t r e s s i n c r e a s e s . T h e r e a p p e a r s t o b e some r e d i s t r i b u t i o n o f b o n d s t r e s s o r s h e a r t r a n s f e r a l o n g 4 . U n d e r s i m i l a r l o a d i n g c o n d i t i o n s a n d c y c l e s , b o t h t h e a v e r a g e b o n d s t r e s s a n d t h e m a x i m u m b o n d s t r e s s e s f o r f i b e r - r e i n f o r c e d s p e c i m e n s a r e f o u n d t o b e a b o u t 2 0 t o 30% h i g h e r t h a n t h o s e f o r p l a i n c o n c r e t e . 5 . T h e r e a p p e a r s t o b e n o s i g n i f i c a n t d e c r e a s e i n b o n d s t r e s s w i t h a n i n c r e a s e i n t h e n u m b e r o f c y c l e s a t a c o n s t a n t s t r e s s l e v e l e s p e c i a l l y u n d e r l o w p e a k l o a d i n g . H o w e v e r , a n i n c r e a s e i n p e a k s t r e s s l e v e l p r o d u c e s a r e d u c t i o n i n b o n d s t r e s s a t a l o w e r s t r e s s l e v e l i n t h e s u b s e q u e n t c y c l e s . T h i s r e d u c t i o n r a n g e s f r o m 10 t o 30% a s d e s c r i b e d i n T a b l e 4 . 6 . T h e r a t i o o f m a x i m u m m e a s u r e d b o n d s t r e s s t o t h e a v e r a g e b o n d s t r e s s g e n e r a l l y e x c e e d s t w o . T h i s r a t i o h o w e v e r f a l l s w i t h i n c r e a s e i n l o a d r e p e t i t i o n s o r l o a d i n c r e m e n t . T h i s m a y b e s e e n f r o m T a b l e 4 . 3 . 2 S t i f f n e s s L o s s : ; n e s s o f t h e r e b a r a n d s u r r o u n d i n g - c o n c r e t e c a n b e d e f i n e d a s f o l l o w s : t h e l e n g t h o f t h e r e b a r w i t h i n c r e a s e d l o a d i n g . T h e p e r c e n t a g e c o n t r i b u t i o n o f t h e c o n c r e t e t o t h e a p p a r e n t - s t i f f -X E s w h e r e X = p e r c e n t a g e o f s t i f f n e s s c o n t r i b u t i o n m e a s u r e d t e n s i l e s t e e l s t r a i n a l o n g r e i n f o r c e m e n t s f s = m a x i m u m t e n s i l e s t r e s s a p p l i e d t o s t e e l E = Y o u n g ' s , m o d u l u s f o r s t e e l L = a n c h o r a g e l e n g t h ( t e n s i o n z o n e c o n s i d e r e d ) T h e v a l u e s o f s t i f f n e s s a r e t a b u l a t e d a s i n T a b l e 4 f o r d i f f e r e n t T A B L E 4 : C O N C R E T E S T I F F N E S S L O S S & BOND S T R E S S D E T E R I O R A T I O N S p e c i m e n L o a d S t r e s s C y c l e A v . B o n d A v . B o n d S t r e s s B o n d S t r e s s M a x . B o n d S t r e s s % B o n d N o . ( K i p ) L e v e l ( K s i ) S t r e s s ( T h e o ) ( P s i ) ( M e a s u r e m e n t ) ( P s i ) ( M a x ) ( P s i ) A v . B . S t r e s s (M) D e t e r i o r a t i o n B 2 5 6 . 3 7 1 4 9 . 4 8 1 5 . 9 . 0 1 4 3 . 4 6 + 3 5 7 . 2 6 2 . 4 9 1 0 1 2 . 7 3 1 4 3 . 1 0 3 1 8 . 3 2 8 2 . 5 3 + 5 8 8 . 4 2 2 . 0 8 ( P l a i n C o n c r e t e ) 4 4 3 . 0 4 3 1 8 . 3 2 4 5 . 5 5 + 5 3 2 . 3 8 2 . 1 6 2 0 2 5 . 4 6 6 3 5 . 4 5 6 3 6 . 6 5 3 2 . 2 4 - 1 2 2 5 . 8 7 2 . 3 1 0 3 5 . 3 2 6 3 6 . 6 / 5 0 9 . 3 4 - 1 2 6 0 . 9 0 2 . 4 3 0 3 8 . 2 0 12 3 5 . 5 3 9 5 4 . 9 3 . 7 8 8 . 5 0 - 1 6 7 4 . 1 9 2 . 1 2 18 3 5 . 6 8 9 5 4 . 9 3 7 5 7 . 4 1 - 1 5 1 3 . 0 8 1 . 9 9 4 0 5 0 . 9 3 22 3 0 . 4 6 1 2 7 3 . 2 1 1 1 3 . 3 9 - 1 8 5 6 . 3 2 1 . 6 6 2 0 2 5 . 4 6 2 0 3 5 . 8 5 6 3 6 . 6 4 4 3 . 5 7 - 1 5 0 6 . 0 8 3 . 3 16 5 6 . 3 7 1 6 4 . 9 7 1 5 9 . 0 1 3 0 . 0 7 4 1 3 . 3 0 3 . 1 8 1 0 1 2 . 7 3 1 6 0 . 1 1 3 1 8 . 3 ' 2 6 3 . 4 8 - 6 9 3 . 4 9 2 . 6 3 3 5 7 . 8 3 3 1 8 . 3 2 6 2 . 3 7 - 7 2 1 . 5 2 2 . 7 5 2 0 2 5 . 4 6 4 5 1 . 7 6 6 3 6 . 6 5 4 6 . 3 9 - 1 1 3 4 . 8 1 2 . 0 8 1 0 5 0 . 8 0 6 3 6 . 6 5 3 7 . 2 0 - 1 0 7 1 . 7 6 1.9.9 30 3 8 . 2 0 12 4 7 . 8 5 9 5 4 . 9 8 2 3 . 2 3 - 1 4 7 8 . 0 6 1 . 8 0 16 4 6 . 0 9 9 5 4 . 9 7 5 4 . 2 0 - 1 4 8 5 . 0 6 1 . 9 7 4 0 5 0 . 9 3 17 4 1 . 6 5 1 2 7 3 . 2 1 0 5 6 . 7 3 ' - 1 8 2 8 . 3 1 1 . 7 3 3 0 3 8 . 2 0 2 1 3 8 . 2 2 9 5 4 . 9 7 4 6 . 3 2 - 1 9 3 3 . 3 8 2 . 5 9 10 TABLE 4 : con t ' d Specimen Load S t r e s s Cyc le X% Av.Bond Av.Bond S t ress Bond S t ress Max.Bond S t ress % Bond (K ip) L e v e l ( K s i ) S t ress(Theo) ( P s i ) (Measurement) ( P s i ) (Max) ( P s i ) A v . B . S t r e s s (M) D e t e r i o r a t i o n 5 6.37 1 63.47 159.0 145.88 - 455.32 3.12 10 12.73 1 56.66 318.3 264.28 - 532.38 2.01 3 56.56 318.3 252.03 - 623.44 2.47 20 25.46 4 46.63 636.6 606.25 + 1015.73 1.67 8 43.40 636.6 599.72 + 917.65 1.53 30 38.20 9 42.35 954.9 1005.20 + 1394.00 1.39 13 37.98 954.9 915.42 + 1232.88 1.35 40 50.93 14 36.59 .1273.2 1092.62 - 1527.09 1.40 30 38.20 18 36.68 954.9 698.60 - 1169.83 1.67 30 20 25.46 18 35.07 636.6 560.55 + 1099.78 1.96 8 5 6.37 1 60.74 159.0 160.48 - 637.45 3.97 10 12.73 1 54.19 318.3 303.28 - 770.55 2.54 4 51.57 318.3 25 8.-51 + 658.47 2.54 20 25.46 7 48.36 636.6 591.78 + 910.65 1.53 10 44.95 636.6 531.65 - 1092.78 2.05 30 38.20 11 43.83 954.93 865.12 - 1527.09 1.77 15 36.55 954.93 819.88 + 1351.97 1.65 40 50.93 16 35.31 1273.2 1170.27 + 1926.37 1.65 30 38.20 17 36.35 954.93 772.15 + 1246.89 1.60 11 TABLE 4: con t ' d Specimen Load S t r e s s Cyc le X% Av.Bond Av.Bond S t ress Bond S t ress Max.Bond S t r e s s / % Bond (K ip ) L e v e l ( K s i ) St ress(Theo) ( P s i ) (Measurement) (Ps i ) (Max) ( P s i ) , A v . B . S t r e s s (M) D e t e r i o r a t i o n 5 6.37 1 54.14 159.0 134.85" - 448.32 3.32 10 12.73 1 47.73 318.3 295.48 - 861.61 2.92 47.55 318.3 251.05 - 868.62 3.46 20 25.46 5 42.70 636.6 591.63 - 1120.80 1.89 10 40.44 636.6 555.44 - 1050.75 1.89 30 38.20 11 35.79 954.9 867.31 - 1478.06 1.70 16 35.28 954.9 812.87 - 1590.14 1.96 40 50.93 17 36.81 1273.2 1063.88 - 1919.37 1.80 30 38.20 18 37.12 954.9 756.10 - 1302.93 1.72 13 27 c y c l e s o f l o a d i n g a t v a r i o u s p e a k l o a d s . F i v e s p e c i m e n s i n c l u d i n g o n e p l a i n c o n c r e t e s p e c i m e n w e r e s e l e c t e d w h i c h w e r e t e s t e d u n d e r s i m i l a r c y c l i c l o a d i n g c o n d i t i o n s . T h e s t i f f n e s s l o s s e s f o r t h e s e s p e c i m e n s w e r e c o m p a r e d t o s t u d y t h e e f f e c t o f f i b e r - r e i n f o r c e m e n t o n b o n d s t r e n g t h a n d t h e f o l l o w i n g i n f o r -m a t i o n w a s o b t a i n e d : 1 . W i t h a n i n c r e a s e i n t h e p e a k l o a d o r i n c r e a s e i n l o a d r e p e t i t i o n s u n d e r c o n s t a n t s t r e s s l e v e l , b o t h p l a i n c o n c r e t e a s w e l l a s f i b e r - r e i n f o r c e d c o n c r e t e s p e c i m e n s s u f f e r e d l o s s o f s t i f f n e s s t o a g r e a t e x t e n t . T h e r e d u c t i o n i n s t i f f n e s s m a y b e p a r t l y r e l a t e d t o d e t e r i o r a t i o n o f b o n d a n d c r a c k i n g , i f a n y , d u r i n g s h e a r t r a n s f e r . T h i s may b e s e e n f r o m F i g u r e 2 7 ' a n d 2 8 . 2 . U n d e r s i m i l a r l o a d i n g c o n d i t i o n s a n d c y c l e s o f l o a d i n g , p l a i n c o n c r e t e s p e c i m e n s s u f f e r a g r e a t e r l o s s o f s t i f f n e s s t h a n s t e e l - f i b e r -r e i n f o r c e d o n e s . T h e s t i f f n e s s d i f f e r e n c e a f t e r s i m i l a r c y c l e s o f l o a d i n g b e t w e e n p l a i n a n d s t e e l f i b e r - r e i n f o r c e d s p e c i m e n s i s a b o u t 15% a t a s t r e s s l e v e l o f ± 4 0 k s i , a s may b e s e e n f r o m F i g u r e 2 7 . 3 . 3 L o a d - S l i p R e l a t i o n s h i p : T h e e f f e c t o f c y c l i c r e v e r s e d l o a d i n g o n t h e l o a d - s l i p r e l a t i o n -s h i p h a s b e e n s h o w n i n F i g u r e 2 8 . Some o f t h e s e d a t a a r e a l s o s h o w n i n T a b l e 5 . F i v e s p e c i m e n s i n c l u d i n g o n e p l a i n c o n c r e t e s p e c i m e n w e r e c o m p a r e d , a s t h e s e w e r e t e s t e d u n d e r s i m i l a r l o a d i n g c o n d i t i o n s a n d c y c l e s . T o d e t e r m i n e t h e e f f e c t o f c y c l i c l o a d i n g o n l o a d - s l i p r e l a t i o n s h i p a n d t o s t u d y t h e e f f e c t o f s t e e l f i b e r s , t h e f o l l o w i n g i n f o r m a t i o n w a s o b t a i n e d : 1 . T h e f i b e r c o n c r e t e s p e c i m e n s s h o w m o r e b o n d c a p a c i t y t h a n p l a i n c o n c r e t e o n e s u n d e r s a m e c o n s t a n t s l i p . A t a s l i p o f 0 . 0 3 " , f i b e r -r e i n f o r c e d s p e c i m e n s h a v e 22% ( o n a v e r a g e ) m o r e b o n d s t r e n g t h t h a n p l a i n TABLE 5 : LOAD-SLIP RELATIONSHIP Specimen Load Nos. of S l i p Av . I nc rease Specimen Load Nos. of S l i p A v . I n c r e a s e No. (K ips) c y c l e s ( inches) i n s l i p / c y c l e ( inches) No. (K ips) cyc l es ( inches) i n s l i p / c y c l e ( inches) B l 10 20 1 2 0.0055 0.0125 - B 2 10. 1 4 0.00835 0.0082 -( P l a i n 30 3 0.02065 0.0012 ( P l a i n 20 5 0.019 0.00045 Concrete) 5 0.02298 Concrete) 10 0.02169 40 6 8 0.03187 0.0338 0.0095 30 11 20 0.031 0.0344 0.00034 50 9 10 0.048 0.054 0.003 40 45 50 21 26 27 31 32 35 0.0478 0.0583 0.0738 0.09284 0.118 0.1424 0.0018 0.0027 0.0061 B 3 10 1 3 0.0072 0.0078 0.0002 B 6 ' 10 1 3 0.006 0.0065 0.00017 (3/4% s t e e l -20 4 10 0.0144 - (3/4% • s t e e l -20 4 8 0.01266 0.01450 0.00037 f i b e r , 30 11 0.0144 0.000247 f i b e r , 30 9 0.02146 0.00047 V long) 16 0.0292 1" long) 13 0.02382 40 17 21 0.0327 - 40 14 18 0.0372 0.04591 0.00174 45 22 28 0.1053 0.1118 0.00093 50 29 36 0.14967 0.1640 0.0018 TABLE 5: c o n t ' d Specimen No. Load Nos. of (K ips) c y c l e s S l i p ( i nches) Av . Inc rease i n s l i p / c y c l e s ( inches) Specimen Load Nos. of S l i p No. (K ips) c y c l e s ( inches) A v . I n c r e a s e i n s l i p / c y c l e s ( inches) (1.5% s t e e l -f i b e r , long) 1-" (1.5% s t e e l -f i b e r , 1" long) 10 20 30 AO 50 10 20 30 40 45 50 52 53 1 4 5 10 11 14 15 20 25 28 1 4 5 11 12 21 22 30 31 33 34 41 42 44 0.00884 0.00901 0.0148 0.0158 0.0239 0.0249 0.0340 0.03816 0.095 0.1475 0.0077 0.0081 0.0137 0.0162 0.0216 0.0245 0.0268 0.0297 0.033 0.0345 0.044 0.062 0.0779 0.083 0.00004 0.00017 0.00025 0.0007 0.013 0.0001 0.0003 0.0003 0.0004 0.0005 0.0022 "8 (1.5% s t e e l -f i b e r , k" long) "10 (1.5% s t e e l -f i b e r , 1" long) 10 20 30 40 45 50 10 20 30 40 45 50 1 2 3 4 5 6 9 10 12 13 26 1 4 5 10 11 16 17 22 23 28 29 36 0.007 0.016 0.0168 0.027 0.0287 0.0414 0.0477 0.099 0.01 0.145 0.222 0.0109 0.01158 0.0189 0.0198 0.0278 0.0295 0.0384 0.0444 0.0952 0.1378 0.1599 0.0004 0.00085 0.0016 0.00033 0.0055 0.00017 0.00015 0.00028 0.001 0.0028 30. concrete ones, the highest being 30% f o r . f i b e r - r e i n f o r c e d specimen No - B,. This may be seen from Figure -29'. o 2. The s l i p per cycle (see Figure 30) increases with higher peak loads and the increase i s more for p l a i n concrete than f i b e r -r e i n f o r c e d concrete specimen. The change i n s l i p due to c y c l i c loading under constant load i s generally noticeable a f t e r a stress l e v e l of about ±35 k s i . 3.4 Residual Bond Stresses: A f t e r the a p p l i c a t i o n of.repeated cycles of loading, there were re s i d u a l bond stresses a f t e r the loading was stopped. These stresses were higher for high peak loads i n the previous cycle. The maximum value of r e s i d u a l stresses occur at about % of the development length. The l o n g i t u d i n a l d i s t r i b u t i o n of r e s i d u a l stresses are indicated i n Figure 31 to 33 . Under s i m i l a r load increments and cycles of loading, the r e s i d u a l bond stresses f o r p l a i n concrete specimens appear to be higher than those for f i b e r - r e i n f o r c e d ones ( e s p e c i a l l y i n the tension zone). The l o n g i t u d i n a l d i s t r i b u t i o n of r e s i d u a l bond stress a f t e r repeated cycles of loading i s found to be more or l e s s uniform f o r s t e e l f i b e r - r e i n f o r c e d concrete specimens, e s p e c i a l l y B^ and B^, whereas for p l a i n concrete, the d i s t r i b u t i o n i s non-uniform. The presence of r e s i d u a l stresses a f t e r reversed c y c l i c loading i s probably due to i n e l a s t i c nature of s l i p . This may be caused p a r t l y due to development of negative f r i c t i o n a l resistance on release of load. 3.5 Comparison of Results Obtained by Other Investigators: While the properties of concrete and s t e e l under c y c l i c loading 31 has been s tud ied e x t e n s i v e l y by v a r i o u s i n v e s t i g a t o r s , the e f f e c t of repeated l o a d i n g e s p e c i a l l y of the reve rsed c y c l i c t ype , on the magnitude or d i s t r i b u t i o n of bond s t r e s s has not been e x t e n s i v e l y i n -v e s t i g a t e d and some of the r e s u l t s are c o n t r a d i c t o r y . F u r t h e r , pub l i shed r e s u l t s are not a v a i l a b l e on the i n f l u e n c e of f i b e r - r e i n f o r c e m e n t on bond s t r e n g t h under c y c l i c l o a d i n g . The re fo re , from the l i m i t e d data a v a i l a b l e , some of the r e l e v a n t aspec ts have been compared. There appear to be both d i s c r e p a n c i e s and p o i n t s of agreement i n the r e s u l t s which have been desc r i bed i n t h i s chap te r . The recommendations of ACT Committee 408 i n d i c a t e tha t w i t h deformed b a r s , a p u l l - o u t specimen n e a r l y always f a i l s by s p l i t t i n g , w i t h the concre te s p l i t t i n g i n t o two or three segments ra the r than f a i l i n g by c rush ing aga ins t the lugs or by shea r ing of the c y l i n d r i c a l su r f ace which the lugs tend to s t r i p ou t . A c t u a l t e s t s have shown tha t w i t h deformed b a r s , a s p l i t t i n g type of f a i l u r e may on ly be a p p l i c a b l e to p l a i n concre te specimens, as t h i s type of f a i l u r e was observed f o r p l a i n concre te specimens but not w i t h the f i b e r - r e i n f o r c e d specimens. Wi th the f i b e r - r e i n f o r c e d specimens, f a i l u r e was due to b u r s t i n g out of a p o r t i o n of concre te near the r eba r . Dur ing t e s t i n g , i t was observed tha t under s i m i l a r l oad ing c o n d i t i o n s and c y c l e s , the f i b e r - r e i n f o r c e d specimens developed c racks a t h ighe r load than those f o r p l a i n concre te specimens. F u r t h e r , the crack fo rmat ion and p ropagat ion was found to be more g radua l f o r the former case . Th i s agrees w e l l w i th some of the r e s u l t s obta ined by Swamy(2.p, and Shah and Rangan(24). M indess j Lawrence.and Kes le r (15 ) a l s o showed tha t the r e s i s t a n c e to f r a c t u r e of f i b e r - r e i n f o r c e d c o n c r e t e , as represented by the J - i n t e g r a l was much h igher than tha t f o r p l a i n 32 c o n c r e t e . S i n c e , i n t h i s r e s e a r c h , t h e m i x p r o p o r t i o n s a n d f i b e r c o n t e n t s o f t h e s p e c i m e n s w e r e u s e d i d e n t i c a l t o t h o s e u s e d b y M i n d e s s e t a l ( 1 5 ) a n d t h e a c t u a l c r a c k i n g s t r e n g t h i n b o n d o f f i b e r -r e i n f o r c e d s p e c i m e n s i s h i g h e r t h a n t h o s e o f p l a i n c o n c r e t e o n e s , t h e s e r e s u l t s a r e c o n s i s t e n t . I s m a i l a n d J i r s a ( 8 , 9 ) c o n c l u d e d f r o m t h e r e s u l t s o f b o n d t e s t s , t h a t t h e m o s t i m p o r t a n t f a c t o r a f f e c t i n g b o n d o r s h e a r t r a n s f e r i s t h e p e a k s t r e s s r e a c h e d . i n t h e p r e v i o u s c y c l e s a n d r e p e t i t i o n s o f l o a d c y c l e s w i t h c o n s t a n t p e a k s t r e s s o n l y p r o d u c e s a g r a d u a l d e t e r i -o r a t i o n o f s t r e s s t r a n s f e r c a p a c i t y . T h i s i s i n g o o d a g r e e m e n t w i t h t h e r e s u l t s c a r r i e d o u t i n t h i s i n v e s t i g a t i o n a n d i s a l s o a p p l i c a b l e t o f i b e r - r e i n f o r c e d s p e c i m e n s . I s m a i l a n d J i r s a ( 8 , 9 ) h a v e a l s o r e p o r t e d t h a t a n i n c r e a s e i n p e a k s t r e s s p r o d u c e s m a r k e d r e d u c t i o n i n t h e p e r c e n t a g e c o n t r i b u t i o n o f c o n c r e t e t o s t i f f n e s s o f t h e s p e c i m e n a t l o w e r s t r e s s l e v e l s . T h i s a l s o c o m p a r e s f a v o u r a b l y w i t h t h e r e s u l t s i n t h i s i n v e s t i g a t i o n . Swamy a n d A l - N o o r i ( 2 6 ) h a v e r e p o r t e d f r o m t h e p u l l o u t t e s t r e s u l t s ( u n d e r s t a t i c l o a d i n g ) t h a t t h e a n c h o r a g e b o n d s t r e n g t h o f d e f o r m e d b a r s i s 40% h i g h e r i n s t e e l - f i b e r c o n c r e t e t h a n i n p l a i n c o n c r e t e . H o w e v e r , i n t h i s i n v e s t i g a t i o n , i t w a s o b s e r v e d t h a t u n d e r s i m i l a r l o a d i n g c o n d i t i o n s a n d r e v e r s e d c y c l i c l o a d i n g , f i b e r - r e i n f o r c e d s p e c i m e n s h a v e 20% ( a v e r a g e ) m o r e b o n d s t r e n g t h t h a n p l a i n c o n c r e t e o n e s , t h e h i g h e s t b e i n g 30% f o r s p e c i m e n B^. C o n s i d e r i n g t h e d i f f e r e n c e s i n m i x p r o p o r t i o n s a n d e x p e r i m e n t a l t e c h n i q u e s , t h i s i s i n r e a s o n a b l e a g r e e m e n t w i t h o t h e r p u b l i s h e d d a t a . 3 3 3 . 6 M e c h a n i s m o f B o n d - D e t e r i o r a t i o n a n d C r a c k i n g U n d e r R e v e r s e d C y c l i c L o a d i n g F r o m t h e s t u d y o f e x p e r i m e n t a l t e s t s c o n d u c t e d i n t h i s r e s e a r c h a s w e l l a s r e v i e w o f s t u d i e s b y o t h e r i n v e s t i g a t o r s ( 1 , 1 1 , 1 2 , 1 7 ) t h e f o l l o w i n g m e c h a n i s m o f b o n d d e t e r i o r a t i o n a n d c r a c k i n g b e h a v i o u r i s s u g g e s t e d : T h e b o n d r e s i s t a n c e o f d e f o r m e d r e i n f o r c i n g b a r s i s d u e t o m e c h a n i c a l i n t e r l o c k i n g b e t w e e n c o n c r e t e a n d s t e e l . G e n e r a l l y , t h e b o n d s t r e n g t h d e v e l o p e d b e t w e e n t w o c o n s e c u t i v e r i b s i s a s s o c i a t e d w i t h t h e f o l l o w i n g s t r e s s e s : ( i ) S h e a r s t r e s s , v , a l o n g t h e b a r . s u r f a c e d e v e l o p e d t h r o u g h a d h e s i o n . ( i i ) S h e a r s t r e s s , v , a c t i n g o n t h e c y l i n d r i c a l c o n c r e t e s u r f a c e b e t w e e n a d j a c e n t r i b s , ( i i i ) B e a r i n g s t r e s s f ^ , a g a i n s t t h e f a c e o f t h e r i b . T h e s e h a v e b e e n s h o w n i n F i g u r e 3 6 ( c ) . W i t h t h e i n c r e a s e i n t e n s i l e s t r e s s l e v e l , t h e a d h e s i o n a l o n g t h e b a r s u r f a c e o b v i o u s l y b r e a k s d o w n a n d , f r i c t i o n a l s t r e s s b e i n g n e g l i g i b l e , s t r e s s t r a n s f e r t a k e s p l a c e t h r o u g h t h e b e a r i n g o f t h e l u g s . A s m o r e l o a d i s a p p l i e d , t h e s l i p a t t h e l o a d e d e n d s i n c r e a s e s a n d b o t h t h e h i g h b o n d s t r e s s a n d s l i p e x t e n d d e e p e r i n t o t h e s p e c i m e n . F r o m t h e c r a c k p a t t e r n s o f s p e c i m e n s ( o b s e r v e d e x t e r n a l l y ) , t h e r e a p p e a r t o b e t w o d i f f e r e n t m o d e s o f f a i l u r e - ( i ) s p l i t t i n g t y p e ( i i ) b u r s t i n g o f c o n c r e t e a r o u n d r e i n -f o r c i n g b a r . D u r i n g t e s t i n g , t h e , p l a i n c o n c r e t e s p e c i m e n s f a i l e d i n s p l i t t i n g o f c o n c r e t e , w h e r e a s f o r 1 . 5 % s t e e l . f i b e r - r e i n f o r c e d o n e s , t h e r e w a s b u r s t i n g o f c o n c r e t e a r o u n d t h e r e i n f o r c i n g b a r s a t b o t h e n d s . A t r a n s i t i o n a l s t a t e b e t w e e n s p l i t t i n g a n d b u r s t i n g w a s o b s e r v e d f o r ^ 34 specimens c o n t a i n i n g a f i b e r content of 0.75%. A f t e r the t e s t s , one each from the p l a i n concre te specimens (B^) and f i b e r - r e i n f o r e d ones (B^) were cut open l o n g i t u d i n a l l y u s i n g a masonry saw up to the c e n t r a l r e i n f o r c i n g bar to i n v e s t i g a t e the i n t e r n a l c rack f o rma t i ons . Th is revea led tha t there were no i n t e r n a l t r ansve rse or d i agona l c racks developed a long the r e i n f o r c i n g bar except wide d i a g o n a l c racks at bo th , ends of each specimen. For the p l a i n c o n c r e t e , the development of l o n g i t u d i n a l c racks ( separa t ion ) up t o about 3" to 4 " f rom bo th ends was n o t i c e d . These have been shown i n F i gu re 38. The f o l l o w i n g t h e o r -e t i c a l exp lana t i on of the c r a c k i n g behav iour and the mechanism of bond d e t e r i o r a t i o n i s proposed: As the t ens ion i n the r e i n f o r c i n g bar i s i n c r e a s e d , the. bar d i a -meter i s reduced due to P o i s s o n ' s e f f e c t , caus ing a decrease i n the t r ansve rse p ressure on the c o n c r e t e . S ince the l a y e r of concre te sur round ing the bar i s . i n t e n s i o n , i t would t h e r e f o r e f a i l a t a lower va lue of the bond s t r e s s caus ing some amount of s l i p i n the p r o c e s s . Th is i n tu rn he lps i n m o b i l i z a t i o n of f u l l bea r i ng of concre te aga ins t the r i b s . Wi th a f u r t h e r i n c r e a s e i n t e n s i l e l o a d i n g , there w i l l be bea r ing of the r i b face aga ins t the c o n c r e t e , which w i l l cause c i r c u m -f e r e n t i a l t e n s i o n i n the concre te around the re in fo rcement bar and hence may cause sepa ra t i on a long the conc re te - r eba r i n t e r f a c e . The a c t u a l s t r e s s s t a t e due to the t e n s i l e l o a d , f o r both l o n g i t u d i n a l and t r ansve rse s t r e s s d i s t r i b u t i o n s based on the theory of e l a s t i c i t y (22) f o r dep th - l eng th r a t i o (D/B) of two has been i n d i c a t e d i n F i g u r e (35 ) . F u r t h e r , r e a c t i o n caused a t bo th m i l d s t e e l , f l a t s aga ins t the conc re te due to the p u l l out l o a d , a l s o causes zones of compression and tens ion (7 ) . These have been superimposed as shown i n F i g u r e 40. I t would be 35 evident from the above that an element located i n the v i c i n i t y of the r e i n f o r c i n g bar at the t e n s i l e end w i l l be subjected to b i a x i a l t e n s i l e stresses, the p r i n c i p a l t e n s i l e stress of which may exceed the t e n s i l e strength of concrete at a c e r t a i n p u l l out load and cause diagonal cracking and/or s p l i t t i n g of concrete. Further, high l a t e r a l transverse stresses which are expected to ex i s t within the zone located close to the load point ( p u l l out), contribute to separation. This also depends on the bond stress d i s t r i b u t i o n along the reinforcement. Probably due to the higher t e n s i l e strength and resistance to cracking of f i b e r - r e i n f o r c e d concrete, s p l i t t i n g and separation between the concrete and rebar at the ends of the specimen are prevented. Thus the f i b e r - r e i n f o r c e d specimens do not show the s p l i t t i n g mode of f a i l u r e , but undergo a bursting type of f a i l u r e at c r i t i c a l loads as seen during t e s t i n g . On the compression face of the specimen, the increase i n push-i n (compression) loading may cause swelling of bar owing to Poisson's e f f e c t . This creates an a d d i t i o n a l compressive s t r e s s between concrete and s t e e l , which i s further increased by shrinkage of concrete (7). Guyon(7) shows that pressure exerted by the r e i n f o r c i n g bar i s inadequate to cause c r a c k i n g / f a i l u r e i n concrete. Upon complete release of loading, f u l l recovery of s t e e l elongation i s prevented by f r i c t i o n between the s t e e l and the concrete and by bearing stress against the face of the r i b s . This causes c e r t a i n r e s i d u a l t e n s i l e stress i n the s t e e l and compression i n the concrete. The i n t e r n a l cracks already developed do not close up completely and there remains some r e s i d u a l s l i p even a f t e r release of the load. With further cycles of loading and unloading, there w i l l be d i s r u p t i o n of the concrete 36 adjacent to the steel-concrete i n t e r f a c e and widening of cracks already formed due to damage accumulation. This disruption causing bond d e t e r i o r a t i o n i s mainly due to the loss of s t i f f n e s s of concrete and the Bauschinger e f f e c t i n s t e e l . The amount of dis r u p t i o n or bond d e t e r i o r a t i o n p r i m a r i l y depends on the magnitude of the stress l e v e l i n the s t e e l i n the previous cycle and number of cycles run. 37 C H A P T E R -r. I V  C O N C L U S I O N S B a s e d o n t h e t e s t r e s u l t s o b t a i n e d i n t h i s i n v e s t i g a t i o n , t h e f o l l o w i n g c o n c l u s i o n s may b e d r a w n . 1 . T h e m o d e o f f a i l u r e a n d t h e b e h a v i o u r u n d e r t e s t o f t h e p l a i n a n d f i b e r - r e i n f o r c e d s p e c i m e n s a p p e a r t o b e d i f f e r e n t . T h e f o r m e r u n d e r g o e s a s p l i t t i n g t y p e o f f a i l u r e w h e r e a s t h e l a t t e r f a i l s d u e t o . b u r s t i n g o u t o f a p o r t i o n o f c o n c r e t e n e a r t h e r e b a r . F u r t h e r , f i b e r -r e i n f o r c e d s p e c i m e n s e x h i b i t g r e a t e r r e s i s t a n c e t o c r a c k f o r m a t i o n a n d p r o p a g a t i o n t h a n t h e p l a i n c o n c r e t e o n e s . 2 . T h e r e a p p e a r s t o b e n o s y m m e t r y i n t h e l o n g i t u d i n a l b o n d s t r e s s d i s t r i b u t i o n i n t h e t e n s i o n a n d c o m p r e s s i o n z o n e s , t h e a v e r a g e b o n d s t r e s s i n c o m p r e s s i o n z o n e b e i n g h i g h e r t h a n t h a t i n t e n s i o n z o n e . 3 . W i t h i n c r e a s e i n p e a k l o a d i n g , t h e b o n d s t r e s s i n c r e a s e s a n d t h e r e i s a p p a r e n t l o n g i t u d i n a l r e d i s t r i b u t i o n o f b o n d s t r e s s o r s h e a r t r a n s f e r a l o n g t h e r e i n f o r c e m e n t b a r . 4 . T h e r e s e e m s t o b e n o s i g n i f i c a n t d e c r e a s e i n b o n d s t r e s s w i t h a s m a l l i n c r e a s e i n n u m b e r o f c y c l e s u n d e r c o n s t a n t s t r e s s l e v e l . H o w e v e r , a n i n c r e a s e i n p e a k s t r e s s - l e v e l p r o d u c e s a s i g n i f i c a n t r e d u c t i o n i n b o n d s t r e s s i n t h e s u b s e q u e n t c y c l e s . 5 . W i t h i n c r e a s e i n p e a k l o a d o r l o a d r e p e t i t i o n s u n d e r c o n s t a n t l o a d , b o t h p l a i n a s w e l l a s s t e e l - f i b e r - r e i n f o r c e d c o n c r e t e s u f f e r l o s s i n r e l a t i v e c o n t r i b u t i o n o f c o n c r e t e t o t h e s t i f f n e s s o f t h e s p e c i m e n s . T h e l o s s i n s t i f f n e s s i s g r e a t e r f o r p l a i n c o n c r e t e s p e c i m e n s . 6 . U n d e r r e v e r s e d c y c l i c l o a d i n g w i t h f e w c y c l e s , t h e a n c h o r a g e b o n d s t r e n g t h o f d e f o r m e d b a r s i s a b o u t 20 t o 30% h i g h e r i n s t e e l - f i b e r -38. reinforced concrete than i n p l a i n concrete. 7. Repeated loading r e s u l t s i n c e r t a i n r e s i d u a l bond stresses which may be p a r t l y due to i n e l a s t i c nature of s l i p . 8. Under s i m i l a r loading conditions and r e p e t i t i o n s of loading, there seems to be higher r e s i d u a l bond stresses for deformed bars i n p l a i n concrete than i n s t e e l - f i b e r - r e i n f o r c e d concrete. 9. Anchorage provisions such as embedment length etc. as recommended by various codes need further examination to take into account the reduction i n bond effectiveness at higher stress l e v e l s f or p l a i n concrete as w e l l as f i b e r - r e i n f o r c e d concrete structures subjected to repeated loading. However, before any firm conclusions are drawn, further tests are necessary as only a few t e s t s were c a r r i e d out i n t h i s i n v e s t i g a t i o n . Further, variables l i k e various embedment lengths, diameter of reinforcement bar, mix proportions, shape and s i z e of f i b e r s etc. need be considered to study the e f f e c t of reversed c y c l i c loading on bond strength. 39 CHAPTER - V  DISCUSSIONS Though every e f f o r t was made to carry out the e n t i r e programme of casting specimens, curing and t e s t i n g under s i m i l a r conditions, there were c e r t a i n deviations. These are discussed i n b r i e f below: During casting of specimens B^, B^, B,., i n i t i a l l y the mix was found to be too s t i f f and v i b r a t i o n could not be c a r r i e d out properly. Further, the v i b r a t o r went out of order during.casting of specimen B^. These resulted i n the formation of some honeycombing i n the specimens. Though every care was taken to apply concentric a x i a l t e n s i l e or compressive load to the rebar of the specimens, t h i s could not be ensured i n p r a c t i c e e s p e c i a l l y during t e s t i n g of some specimens. Such eccent r i c loading might have caused c e r t a i n i r r e g u l a r i t i e s i n l o n g i -t u d i n a l bond stress d i s t r i b u t i o n as well as s l i p behaviour. During t e s t i n g of specimens, i t was observed that most of the s t r a i n gauges went out of order when the number of cycles of loading were increased or peak load was increased beyond about 30 kips. Such damage/ disturbance of the s t r a i n gauges gave e r r a t i c readings of s t r a i n s and no actual bond behaviour could be predicted/analysed at higher stress l e v e l s or cycles. This became a serious drawback of the experiment. During t e s t i n g of the specimens, i n two cases, due to s l i p p i n g of magnetic clamps, the displacement recording transducers got disturbed. Though these were reset based on recordings of other transducers, these did not behave well as c e r t a i n i r r e g u l a r i t i e s were observed i n displacement recordings. Further, for some of the specimens, there was gradual welding f a i l u r e at the rebar and connector connection. This might have 40 caused some irregularities in s l i p measurement. For each set of casting of specimens, three cylinders were cast. Probably, due to non-uniformity in compaction, there was wide variation in cylinder strengths in some of the cases. Therefore, correct evaluation of the strength of specimens was d i f f i c u l t to correlate from the cylinder test. 41 R E F E R E N C E S 1 . B r e s l e r , B . , a n d B e r t e r o , V . , " B e h a v i o u r o f R e i n f o r c e d C o n c r e t e U n d e r R e p e a t e d L o a d s " , J o u r n a l o f S t r u c t u r a l D i v . , A S C E , P r o c . V . 6 4 , ST 6 , J u n e 1 9 6 8 . 2 . B r o m s , B . B . , " S t r e s s D i s t r i b u t i o n i n R e i n f o r c e d C o n c r e t e M e m b e r s w i t h T e n s i o n C r a c k s " , A C I J o u r n a l , P r o c . V . 6 2 , S e p t e m b e r 1 9 6 5 . 3 . C l a r k , A r t h u r ^ P . , " B o n d o f C o n c r e t e R e i n f o r c i n g B a r s " , A C I J o u r n a l , P r o c . V . 4 6 , N o . 3 , N o v e m b e r 1 9 4 9 4 . E d w a r d s , A . D . , a n d Y a n n o p o u l o s , P . J . , " L o c a l B o n d S t r e s s t o S l i p R e l a t i o n s h i p f o r H o t R o l l e d D e f o r m e d B a r s a n d M . S . P l a i n B a r s " , A C I J o u r n a l , P r o c . V . 7 6 , M a r c h 1 9 7 9 . 5 . F e r g u s o n , P . M . , a n d T h o m p s o n , J . N . , " D e v e l o p m e n t L e n g t h o f H i g h S t r e n g t h R e i n f o r c i n g B a r s i n B o n d " , A C I J o u r n a l , P r o c . V . 5 9 , N o . 7 , J u l y 1 9 6 2 . 6 . F e r g u s o n , P . M . , a n d T h o m p s o n , J . N . , " D e v e l o p m e n t L e n g t h o f L a r g e H i g h S t r e n g t h R e i n f o r c i n g B a r s " , A C I J o u r n a l , P r o c . V . 62", N o . 1 , J a n u a r y 1 9 6 5 7 . G u y o n , Y . , P r e s t r e s s e d C o n c r e t e , J o h n W i l e y & S o n s , I n c . , New Y o r k , 1 9 6 0 . 8 . I s m a i l , M . A . F . , a n d J i r s a , J . O . , " B o n d D e t e r i o r a t i o n i n R e i n f o r c e d C o n c r e t e S u b j e c t t o L o w C y c l e s o f L o a d s " , A C I J o u r n a l , P r o c . V . 6 9 , J u n e 1 9 7 2 . 9 . I s m a i l , M . A . F . , a n d J i r s a , J . O . , " B e h a v i o u r o f A n c h o r e d B a r s U n d e r L o w C y c l e O v e r l o a d s P r o d u c i n g I n e l a s t i c S t r a i n s " , A C I J o u r n a l , V . 6 9 , N o . 7 , J u l y 1 9 7 2 . 1 0 . L e a , F . C . , " R e p e a t e d S t r e s s e s o n R e i n f o r c e d C o n c r e t e " , S t r u c t u r a l E n g i n e e r ( L o n d o n ) , V . 1 8 , P a r t 2 , 1 9 4 0 . 42 1 1 . L u t z , L . A . , a n d G e r g e l y , P . , " M e c h a n i c s o f B o n d a n d S l i p o f D e f o r m e d B a r s i n C o n c r e t e " , A C 1 J o u r n a l , P r o c . V . 6 4 , N o v e m b e r 1 9 6 7 . 1 2 . L u t z , L . A . , " A n a l y s i s o f S t r e s s e s i n C o n c r e t e n e a r a R e i n f o r c i n g B a r d u e t o B o n d a n d T r a n s v e r s e C r a c k i n g " , A C I J o u r n a l , V . 6 4 , N o . 1 0 , O c t o b e r 1 9 7 0 . 1 3 . M a i n s , R . M . , " M e a s u r e m e n t o f ' D i s t r i b u t i o n o f T e n s i l e a n d B o n d S t r e s s A l o n g R e i n f o r c i n g B a r s " , A C I J o u r n a l , P r o c . V . 4 8 , N o . 3 , N o v e m b e r , 1 9 5 1 . 1 4 . M a t h e y , R . G . , a n d W a t s t e i n , D . , " I n v e s t i g a t i o n o f B o n d i n B e a m a n d P u l l o u t S p e c i m e n s w i t h H i g h - Y i e l d D e f o r m e d B a r s " , A C I J o u r n a l , P r o c . V . 5 7 , N o . 9 , M a r c h 1 9 6 1 . 1 5 . M i n d e s s , S . , L a w r e n c e , F . V . , a n d K e s l e r , C E . , " T h e J - I n t e g r a l a s a F r a c t u r e C r i t e r i o n f o r F i b e r - R e i n f o r c e d C o n c r e t e " , C e m e n t a n d C o n c r e t e R e s e a r c h , V . 7 , 1 9 7 7 . 1 6 . M u h l e n b r u n c h , C . W . , " T h e E f f e c t o f R e p e a t e d L o a d i n g o n t h e B o n d S t r e n g t h o f C o n c r e t e " , A m e r i c a n S o c i e t y f o r T e s t i n g M a t e r i a l s , P r o c . V . 4 5 , 1 9 4 5 . 1 7 . P a r k , R . a n d P a u l a y , T . , " R e i n f o r c e d C o n c r e t e S t r u c t u r e s " , J o h n W i l e y P u b l i c a t i o n , 1 9 7 5 . 1 8 . P a u l , W. A b e l e s , " C r a c k i n g a n d B o n d R e s i s t a n c e i n H i g h S t r e n g t h R e i n f o r c e d C o n c r e t e B e a m s " , A C I J o u r n a l , P r o c . V . 6 3 , N o v e m b e r 1 9 6 6 . 1 9 . P e r r y , E . S . , a n d T h o m p s o n , J . N . , " B o n d S t r e s s D i s t r i b u t i o n i n R e i n -f o r c i n g S t e e l i n B e a m s a n d P u l l o u t S p e c i m e n s " , A C I J o u r n a l , P r o c . V . 6 3 , A u g u s t 1 9 6 6 . 2 0 . P e r r y , E . S . , a n d J u n d i , N a v i l , " P u l l - o u t B o n d S t r e s s D i s t r i b u t i o n U n d e r S t a t i c a n d D y n a m i c R e p e a t e d L o a d i n g s " , A C I J o u r n a l , P r o c . V . 6 6 , 1 9 6 9 . A3 21a. ' V iwathanatepa, S . , Popov, E . P . , and B e r t e r o , V . V . , " D e t e r i o r a t i o n of Re in fo rced Concrete Bond Under Gene ra l i zed L o a d i n g " , A C I , 1977 Annual Conven t ion , San D iego , C a l i f o r n i a , March, 1977 (Unpub l i shed) . 21b. Popov, E . P . , "Mechan i ca l C h a r a c t e r i s t i c s and Bond of R e i n f o r c i n g S t e e l Under Se ism ic C o n d i t i o n s " , P r o c . of a Workshop on ERCBC, J u l y 11 -15 , 1977, V o l . I I . 22. Raab, A . R . , D i s c u s s i o n of the Paper by Broms, B . B . , " S t r e s s D i s t r i b u t i o n i n Re in fo rced Concrete Members w i th Tension C r a c k s " , ACI J o u r n a l , V . 63 , March 1966. 23. Rehm, G . , and 'E l igehausen , R . , "Bond of Ribbed Bars under High Cyc le Repeated L o a d s " , ACI J o u r n a l , P r o c . V. 76, February 1979. 2A. Shah, S . P . , and Rangan, B. V . , " F i b e r Re in fo r ced Concrete P r o p e r t i e s " , ACI J o u r n a l , V . 68, February 1971. 25. Shipman, J . M . , and G e r s t l e , K.H., "Bond D e t e r i o r a t i o n i n Concrete Pane ls Under Low C y c l e s " , ACI J o u r n a l , V . 76, February 1979. 26. Swamy, R . N . , and A l - N o o r i , K., "Bond Stength of S t e e l - F i b e r - R e i n f o r c e d C o n c r e t e " , J o u r n a l of Concre te , August 197A. 27. Swamy, R . N . , and A l - N o o r i , K., " F l e x u r a l Behaviour of F i b e r Concrete w i th Conven t iona l S t e e l Re in fo rcement " , RILEM Sympossium 1975, F i b e r Re in fo rced Cement and Concre te . 28. Ve rna , J . R . , and S t e l s o n , T . E . , " F a i l u r e of Smal l Re in fo rced Concrete Beams Under Repeated L o a d s " , ACI J o u r n a l , P r o c . V. 59, October 1962. 29. Wi they , M .O . , "Tes t s on Bond Between Concrete and S t e e l i n Re in fo rced ;Concrete Beams", B u l l e t i n 321, U n i v e r s i t y of Wiscons in Eng ineer ing Ser ies" , V . 5 , No. 5 , 1909. 44 APPENDIX Bond S t r e s s D i s t r i b u t i o n Curves S t i f f n e s s Loss - Load R e l a t i o n s h i p Curves Load-Disp lacement R e l a t i o n s h i p Curves L o a d - S l i p R e l a t i o n s h i p Curves R e s i d u a l Bond S t r e s s D i s t r i b u t i o n Curves F i gu res Showing Crack ing P a t t e r n A f t e r F a i l u r e F i gu res Showing V a r i a t i o n of S t r esses i n the Specimen . S p e c i m e n - B 2 0 0 0 1000 I did. Rebar I 40k , 6 C y c l e s 4 0 k , 8 — • • -30k, 3Cycles 30k, 5 — » — 20k, 2 — " — I Ok, I Cyc le l r fo.5 1.5 2.5 3.5 4.5^ff 1000 A 2000 i — r 18.5 7.5.J 8,5 9.5 10.5 12.5 14.5 16.5 Distance along Rebar from left- inches \ \ • \ : \ F I G . I a « B O N D STRESS DISTRIBUTION WITH INCREASE IN LOAD AND CYCLES Specimen - B FIG.2a<B0ND STRESS DISTRIBUTION WITH INCREASE IN LOAD AND CYCLES Specimen - B 2 FIG.3a'B0ND STRESS DISTRIBUTION WITH INCREASE IN LOAD AND CYCLES FIG.4CTB0ND STRESS DISTRIBUTION WITH INCREASE IN LOAD AND CYCLES S p e c i m e n - B 3 2 O O O 1 -1 0 0 0 M XJ C o c « O > < - 1 0 0 0 0.5 1.5 2.5 3.5 4.5 5.5 6.5 7.5 8.5 9.5 10.5*, Distance along Rebar from left-inches I2T5 14.5 16.5 18.5 / J20 .0 - 2 0 0 0 L FIG.5a'B0ND STRESS DISTRIBUTION WITH INCREASE IN LOAD AND CYCLES . FIG. 6 *• BOND STRESS DISTRIBUTION WITH INCREASE IN LOAD AND CYCLES FIG. 7 : BOND STRESS DISTRIBUTION WITH INCREASE IN LOAD AND CYCLES . Specimen - B FIG.8= BOND STRESS DISTRIBUTION WITH INCREASE IN LOAD AND CYCLES Specimen - B FIG. 9-. BOND STRESS DISTRIBUTION WITH INCREASE IN LOAD AND CYCLES S p e c i m e n - B 6 40k,14 Cycles 30k, 9 — •• — 30k,13 — . . — 2 0 0 0 r -1000 h 1.5 2.5 3.5 4.5 5.5 6.5 7.5 8 - 1000 9.5 10.5 12.5 14.5 16.5 18.5 Distance along Rebar from left - inches 20.0 /r-rr-•/ ~~ . -- 2000 L-FIG.IO-BOND STRESS DISTRIBUTION WITH INCREASE IN LOAD AND CYCLES Specimen - B 7 2 0 0 0 i -1000 h-40k, ISCycles 30k, II —•• — 30k,15 — " — 20k, 5 — » — 2 0 k , 1 0 — — \ I dio. Rebor 0.5 1.5 2.5 3.5 4.5 5.5 6.5 7.5 8.5 9.5 10.5 Distance along Rebar from left-inches 1000 2000 »-H , 4- 5 16.5 18.5 / A-\ 20.0 FIG.II- BOND STRESS DISTRIBUTION WITH INCREASE IN LOAD AND CYCLES S p e c i m e n - B 7 2 0 0 0 40k, 16 Cycle 30k, II — » — 3 0 k , 1 5 — " — 20k, 7 — ..— 20k,14 - " — 1 0 0 0 r -o f c ) . 5 1 . 5 2 . 5 3 . 5 4.5 5 . 5 6 . 5 7 . 5 J 8 . 5 9 . 5 1 0 . 5 1 0 0 0 2 0 0 0 « -2 0 . 0 Distance along Rebar from left-inches FIG.I2-B0ND STRESS DISTRIBUTION WITH INCREASE IN LOAD AND CYCLES . S p e c i m e n - B 8 FIG.I3'B0ND STRESS DISTRIBUTION WITH INCREASE IN LOAD AND CYCLES Specimen - B 8 F1G.I4-B0ND STRESS DISTRIBUTION WITH INCREASE IN LOAD AND CYCLES . Specimen - B - 2000 L FIG . I5«B0ND STRESS DISTRIBUTION WITH INCREASE IN LOAD AND CYCLES Speci men -F I G . I 6 « B 0 N D STRESS DISTRIBUTION WITH INCREASE IN LOAD AND S p e c i m e n - B FIG.I7« BOND STRESS DISTRIBUTION WITH INCREASE IN LOAD AND CYCLES S p e c i m e n - B l 0 FIG.IS'BOND STRESS DISTRIBUTION WITH INCREASE IN LOAD AND CYCLES . Applied Force ^+iok [stress Level-25.46ksi] Specimens • Nos.of Cycles = B2 5 > - 2000 FIG. 21 « BOND STRESS DISTRIBUTION Appl ied F o r c e Specimens • B -lok [S t ress LeveI -25.46ksi] Nos.of Cycles: 2 0 0 0 r -! O O O r -20.0 0 0 0 2000 L FIG.22« BOND STRESS DISTRIBUTION Applied Force Specimens B : + *SkK[Stress Level-50.93ksi] Nos.of Cycles • 2 0 0 0 r a. ~a c o J3 H 1000 a> o> o w > - 1000 0.5 1.5 2.5 3.5 4.5 5.5 6.5 / \ - 2000 »-9.5 10.5 12.5 14.5 16.5 18.5 Distance along Rebar from left-inches 20.0 F I G . 2 6 « BOND STRESS DISTRIBUTION 71 F IG .27«ST IFFNESS LOSS -LOAD RELATIONSHIP (STIFFNESS C A L C U L A T E D AFTER A L L CYCLES TO LOAD POINT P L O T T E D ) . FIG.28' LOAD DISPLACEMENT RELATIONSHIP (AT JACK-I ). (ENVELOPE OF HYSTERIS LOOPS) FIG.29' L O A D - S L I P REL ATIONSHIP (SLI P A F T E R A L L C Y C L E S • TO LOAD POINT P L O T T E D ). 74 FIG.30 s L O A D - S L I P / C Y C L E RELAT IONSH IP (AVE. INCREASE IN SLIP FOR C Y C L E TO LOAD P L O T T E D ) . Specimens 1 Nos.of Cycles up to 10k load: B 2 B 6 B,o 4 3 4 4 0.5 \ e b a r N f t * i 3 : 4!% 5 ! 5 X 5 \ j j ^ 5 ! ^ ^ j o : 5 ' Distance from' (VTt - inches 8 0 0 L 20.0 FIG.31« RES IDUAL BOND STRESS DISTRIBUTION AFTER MAX. 10k LOAD. Speci mens Nos.of Cycles up to 20k load; FIG.32 'RES IDUAL BOND STRESS DISTRIBUTION AFTER MAX. 20k LOAD. Specimens Nos.of Cycles up to 30k lood: to o. <n at «> m c o £3 O i — > < 8 0 0 600 4 0 0 200 0 - 200 - 400 - 6 0 0 - 8 0 0 • B 6  B 7 • 16 13 14 \ / i / / / Rebar Axis LI \ \ A a 5 \ ! . 5 / 2 l 5 3.'5 4'.5 5.5 6.5 7.5 #5 \5fp.5 ^ \ 1 .^5 Distance from left - inches ; / i\ i V . . . \ y ' S i IV., U j . J - J , J- J . J . ^ - W g & n ' i ' W A V .4.5 ' I els /\l8<f5 / I /V / 20.0 FIG.33' RES IDUAL BOND STRESS DISTRIBUTION AFTER MAX. 30k LOAD. 78 S P E C I M E N - B , (PLAIN CONCRETE) SOUTH FACE NORTH FACE NORTH FACE SOUTH FACE S P E C I M E N - B ? ( 1.5% FIBER REINFORCED C O N C R E T E ) FIG.34' CRACKING PATTERN AFTER FAILURE . ( INTERNAL AND EXTERNAL CRAKS) FIG.35(b)VARIATI0N IN cr y DUE TO APPL IED P U L L 'P'. FIG. 35(c) VARIATION IN a y DUE TO APPLIED PULL P. FI6.35(d) VARIATION IN <ry DUE TO ' R ' » P/2 FI6.35(e)VARIATI0N IN <rz DUE TO 'R'P/Z. FIG.36(a) LONGITUDINAL CONCRETE STRESS DISTRIBUTION (<r2 ). FIG.36 (b) TRANSVERSE CONCRETE STRESS DISTRIBUTION (<Ty ). FIG.36(c) STRESSES BETWEEN RIBS OF DEFORMED BAR. 

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