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A modified technique for short-term laboratory strain measurements in concrete reinforcement using electrical-resistance… Khanna, Jitendra 1962

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A MODIFIED TECHNIQUE FOR SHORT-TERM LABORATORY STRAIN MEASUREMENTS I N CONCRETE REINFORCEMENT USING ELECTRICAL-RESISTANCE STRAIN GAUGES by JITENDRA KHANNA B . S e . ( E n g i n e e r i n g ) Honours , Patna U n i v e r s i t y , I n d i a , 1957 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF APPLIED SCIENCE i n the Department o f C i v i l E n g i n e e r i n g We accept t h i s t h e s i s as conforming t o the r e q u i r e d s t a n d a r d THE UNIVERSITY OF BRITISH COLUMBIA A u g u s t , 1962 In presenting this thesis in partial fulfilment of the requirements for an advanced degree at the University of British Columbia, I agree that the Library shall make i t freely available for reference and study. I further agree that permission for extensive copying of this thesis for scholarly purposes may be granted by the Head of my Department or by his representatives. It is understood that copying or publication of this thesis for financial gain shall not be allowed without my written permission. Department of £ r > ^ „ ^ > * ~ ^ The University of British Columbia, Vancouver 8, Canada. Date <=£-y ^ z-ABSTRACT S t u d i e s i n R e i n f o r c e d Concrete i n v o l v i n g t r a n s f e r e n c e o f s t r e s s e s by bond from s t e e l t o concrete r e q u i r e a method f o r s t r a i n measurement i n c o n c r e t e r e i n f o r c e m e n t which i s r e l i a b l e and f r e e from l o c a l e f f e c t s . A v e r y s imple and economical method based on a t e c h n i q u e f i r s t used by B r i c e ^ , has been developed u s i n g o r d i n a r y etched f o i l e l e c t r i c a l r e s i s t a n c e s t r a i n gauges, a p p l i e d t o the i n t e r i o r o f a s p l i t p i p e , w h i c h i s j o i n e d t o g e t h e r by a room-temperature epoxy a d h e s i v e , be fore embedment i n concrete as r e i n f o r c e m e n t . Experiments performed t o prove the r e l i a b i l i t y o f the Technique have g i v e n i n d i c a t i o n s t h a t s t r e s s t r a n s f e r e n c e by bond i s a f f e c t e d by the volume o f concrete 0urrounding the r e i n f o r c e m e n t . Some s u p p o r t i n g evidence from the r e s u l t s o b t a i n e d by p r e v i o u s i n v e s t i g a t o r s ' i s p r e s e n t e d . A l s o observed d u r i n g the " p r o v i n g exper iments" i s the pronounced e f f e c t o f c r a c k s on s t r a i n measurements, and the r e g u l a r spac ing o f c r a c k s i n t e n s i l e specimens. A c a s t - i n - s i t u j o i n t between p r e c a s t and p r e s t r e s s e d members has been s t u d i e d w i t h the h e l p o f the m o d i f i e d t e c h n i q u e , and the r e s u l t s p o i n t t o the f o r m a t i o n o f m i c r o - c r a c k s d e t e c t e d by l o c a l v a r i a t i o n s i n s t r a i n measurements which precede v i s i b l e c r a c k i n g . These v a r i a t i o n s , however, tend t o d i s a p p e a r on h i g h e r o r c y c l i c l o a d i n g . A l s o observed d u r i n g the j o i n t t e s t i s the composite a c t i o n even a f t e r complete h o r i z o n t a l s l i p between the c a s t - i n - s i t u and precast concrete, provided the two portions are prevented from further sl ipping, and at high loads when s l ip is allowed to occur, i t i s seen that a moment mechanism other than in the composite section governs vert ical forces in the st irrups. ACKNOWLEDGEMENT The a u t h o r wishes t o acknowledge h i s indebtedness t o the v a l u a b l e and i n s p i r i n g guidance p r o v i d e d by h i s s u p e r v i s o r P r o f e s s o r S . L . L i p s o n . He i s g r a t e f u l t o the t e c h n i c i a n s o f the Department who manufactured v a r i o u s components and a s s i s t e d i n s e t t i n g up e x p e r i m e n t s . I n p a r t i c u l a r he wishes t o mention M r . E . M . White who made many w o r t h -w h i l e s u g g e s t i o n s r e l a t i n g to. d e t a i l s and spent a l o t o f t ime g i v i n g them t a n g i b l e shape. A l s o upon M r . W h i t e , f e l l the major burden o f a s s i s t i n g i n v a r i o u s e x p e r i m e n t s , w h i c h r e q u i r e d more t h a n one p e r s o n t o c o n d u c t , and h i s a s s i s t a n c e i s g r a t e f u l l y acknowledged. Acknowledgement i s a l s o due t o h i s t e a c h e r s who spared t h e i r t ime f o r d i s c u s s i o n s and t o h i s c o l l e a g u e s who h e l p e d i n p e r f o r m i n g some o f the e x p e r i m e n t s . T h i s p o s t graduate study was made p o s s i b l e through the award o f a Commonwealth S c h o l a r s h i p t o the a u t h o r by the Government o f Canada, and the r e s e a r c h p r o j e c t was f i n a n c e d by the N a t i o n a l Research C o u n c i l . TABLE OF CONTENTS CBAPTER PAGE 1 INTRODUCTION 1 11 DESCRIPTION OF TECHNIQUE 5 111 EXAMPLES OF APPLICATION . , 1 1 i . Beam T e s t 11 i i . T e n s i o n Test 27 i i i . J o i n t Test 35 IV CONCLUSIONS 51 BIBLIOGRAPHY 53 APPENDIX I Data on M a t e r i a l s i and. Equipment used 54. APPENDIX II A d d i t i o n a l d e t a i l s o f J o i n t T e s t 62 LIST OF FIGURES FIGURE PAGE 1. Strain-Gauges applied to pipe 6 2. Attachment of Leads to the Strain-Gauges 7 3. Water-proofing of Gauges with Dijell-wax 7 4. Bottom half of wooden press 8 5. Pipe-Joint being cured in improvised wooden press 9 6. Beam test 12 7. Crack-Formation in Tension Specimen cut from Beam 24 8. . Shrinkage Strains in 3-Block Tension Specimen 29 9. Joint-Test Details 36 10. Arrangement for Tensioning vertical bars in Joint 37 11. - Joint on Loading Frame 37 12. Loading Cycles on uncracked Joint 42 13. Loading of Joint to Cracking 44 14. Location of Cracks in Joints 43 15. Loading of Joint with complete horizontal cracking of interface 46 16. Measurement of Forces in Vertical rods and surface of Precast Member 47 17. Deflection of Joint 50 18. Stress-strain curve for Standard pipe and Shelby Tubing 57 19. Grading of Aggregate for Concrete Mixes 58 20. Stress-strain curve for Mix 1 (6 in . dia. cylinder) 59 21. Stress-strain curve for Mix 11 (6 in . dia. cylinder) 60 [2.2. Joint Test: Cracks and sequence of formation 62 23. Joint Test: Location of Gauges in pipe and concrete 63 LIST OF TABLES TABLE PAGE 1 Behavior of Tension Specimen cut from Beam 18 2 Bond Stress Data Abstracted from Mathey and Watstein 1 2 21 3 Bond Stress Data Abstracted from Ma-ins^ - 22 4 Behavior of Tension Specimen - Gauge pair 1 31 5 Behavior of Tension Specimen - Gauge Pair 2 33 6 Behavior of Tension Specimen - Gauge Pair 3 34 7 Tests on Scotchweld Structural Adhesive 56 CHAPTER 1 INTRODUCTION A number o f t e c h n i q u e s have been developed f o r measuring s t r a i n s i n c o n c r e t e r e i n f o r c e m e n t w i t h the h e l p o f e l e c t r i c a l r e s i s t a n c e s t r a i n gauges, d u r i n g the l a s t f i f t e e n y e a r s , but a l l o f them a r e c h a r a c -t e r i s e d by the c o m p l e x i t y o f the o p e r a t i o n s i n v o l v e d and i n some c a s e s , the i n t r o d u c t i o n o f u n d e s i r a b l e l o c a l e f f e c t s . The t e c h n i q u e s may be d i v i d e d i n t o two c l a s s e s - those i n v o l v i n g the attachment o f gauges on the s u r f a c e o f a concrete r e i n -forcement and those i n v o l v i n g attachment o f gauges on the " i n s i d e " o f the r e i n f o r c e m e n t . S u r f a c e a p p l i c a t i o n s were developed f i r s t , on account o f t h e i r r e l a t i v e ease , but e f f e c t i v e w a t e r - p r o o f i n g o f the gauges and l e a d s remained a major problem. A l s o l o c a l e f f e c t s i n the s t r a i n measurement were i n t r o d u c e d on account o f a break o f bond i n the w a t e r - p r o o f e d 2 s e c t i o n o f the p i p e , and t o a much s m a l l e r e x t e n t on account o f the passage o f l e a d s through the c o n c r e t e . S h e r l o c k and B e l g i n 1 r e p o r t e d the use o f c y l i n d r i c a l p l a s t i c s h i e l d f o r e f f e c t i v e m o i s t u r e - p r o o f i n g and p r o t e c t i o n a g a i n s t damage. Mc henry and W a l k e r 2 reduced the a r e a o f band d i s t u r b a n c e on the r e i n f o r c i n g b a r by u s i n g a rubber cement o r 3 rubber b u t t o n v u l c a n i z e d l o c a l l y . Hondros attempted f u r t h e r improvement i n the s u r f a c e attachment t e c h n i q u e t o s u i t c l i m a t i c c o n d i t i o n s i n A u s -t r a l i a . Mains^ appears t o be the f i r s t i n v e s t i g a t o r t o a p p l y gauges i n s i d e o f a r e i n f o r c i n g b a r . I n h i s experiments on t e n s i l e and bond s t r e s s e s i n r e i n f o r c i n g b a r s , he s l i c e d the r e i n f o r c i n g b a r l o n g i t u d i -n a l l y w i t h a p r e c i s i o n saw, and a t t a c h e d gauges and l e a d s i n s l o t s m i l l e d i n the l a r g e r s l i c e o f the b a r , and t h e n t a c k welded the s l i c e s t o g e t h e r . Thompson-* t r i e d t o e l i m i n a t e the l o c a l e f f e c t s o f unequal s l i c e s by p l a n i n g two b a r s t o h a l f - r o u n d s e c t i o n s , m i l l i n g s l o t s i n each o f them, a t t a c h i n g gauges and l e a d s , and t a c k - w e l d i n g as b e f o r e , but undoubtedly the s m a l l l o c a l e f f e c t s o f t a c k - w e l d s were not e l i m i n a t e d . B r i c e i n h i s s t u d i e s on bond r e s o r t e d t o the use o f a p i p e which was sawn l o n g i -t u d i n a l l y i n two s y m m e t r i c a l h a l v e s . Gauges and l e a d s were t h e n f i x e d on the i n n e r s u r f a c e , and the two h a l v e s s o l d e r e d t o g e t h e r . Wilkins*^ attempted t o e l i m i n a t e sawing o f the p i p e i n h i s s t u d i e s o f bond s t r e s s d i s t r i b u t i o n i n " p u l l - o u t " specimens by d e v e l o p i n g a technique o f a p p l y i n g gauges i n s i d e o f a p i p e by the p l a c i n g o f the gauge w i t h l e a d s a t t a c h e d , on a wedge a t the end o f a r o d , i n s e r t i n g the r o d i n t o the p i p e a t the r e q u i r e d p o s i t i o n , and u s i n g a complimentary wedge and r o d from the o t h e r end o f the p i p e t o p r e s s the gauge i n p o s i t i o n . The method, w h i l e workable f o r s m a l l p i p e s , l a c k s i n p r e c i s i o n , f o r one cannot be sure o f the exact p o s i t i o n o f the gauge o r i t s o r i e n t a t i o n , n o r o f i p e r f e e t 3 . bonding over the whole gauge a r e a . The t e c h n i q u e , which i s the s u b j e c t o f t h i s t h e s i s , has been developed as a p r e r e q u i s i t e t o the study o f c a s t - i n - s i t u s t r u c t u r a l j o i n t s between p r e c a s t p r e s t r e s s e d members. On account o f the importance o f bond i n d e v e l o p i n g f o r c e s i n r e i n f o r c i n g s t e e l i t was d e c i d e d t o use a technique w h i c h caused no d i s t u r b a n c e i n the bonding o f s t e e l and c o n c r e t e . Consequently an attempt was made t o f o l l o w the t e c h n i q u e d e -v e l o p e d by B r i c e , but d i f f i c u l t i e s were encountered i n r e p r o d u c i n g the r e s u l t s , the s o l u t i o n o f w h i c h l e d t o a s i m p l e r and e q u a l l y a c c u r a t e method. The main snag encountered i n r e p r o d u c i n g the B r i c e ^ technique was the p r o t e c t i o n o f the i n s t a l l e d gauges, gauge-adhesive and l e a d s from the h i g h temperatures d u r i n g the s o l d e r i n g o f the s p l i t p i p e . The heat r e s i s t a n c e o f the gauge assembly was improved by u s i n g h i g h temperature gauges, s p e c i a l ceramic cements, copper sheathed w i r e s w i t h p o r c e l a i n beads as i n s u l a t i o n a t the gauge e n d , and p a r t i a l success was a c h i e v e d , but the e l a b o r a t e and t ime consuming o p e r a t i o n s f o r the heat t reatment o f the cement and gauges, and the c o s t o f the s p e c i a l m a t e r i a l s - a l l f o r the sake o f heat p r o t e c t i o n d u r i n g assembly - caused a r e - e x a m i n a t i o n o f the method and l e d t o the use o f an epoxy-adhesive which c o u l d j o i n the two h a l v e s o f a s p l i t p i p e , a t room t e m p e r a t u r e , w i t h adequate s t r e n g t h , and w a t e r - p r o o f n e s s , so t h a t o r d i n a r y gauge a p p l i c a t i o n t e c h n i q u e c o u l d be used t o p r o v i d e an economical and f a s t method o f s t r a i n measurement w i t h a minimum o f p r o o f i n g ^ , f o r r e l i a b l e r e s u l t s . Tes ts were c a r r i e d out t o prove the e f f i c a c y o f the 4 . t e c h n i q u e , and the r e s u l t s o b t a i n e d ( w i t h p i p e specimens embedded i n concrete) show the complete r e l i a b i l i t y o f the technique i n a v a r i e t y o f a p p l i c a t i o n s , but p o i n t t o c e r t a i n extraneous i n f l u e n c e s on the measurements o b t a i n e d , as a l s o n o t i c e d by M a i n s ^ , o f the m a t e r i a l t h a t i s c o n c r e t e . CHAPTER 11 DESCRIPTION OF TECHNIQUE Standard p i p e s o f 3/4 i n . nominal d i a . , and Shelby-t u b i n g w i t h 1 i n . O . D . , 3/4 i n I . D . were used as r e i n f o r c e m e n t . The l e n g t h r e q u i r e d f o r an experiment was s l i t l o n g i t u d i n a l l y i n a m i l l i n g machine by a l / l 6 i n . c u t t e r , and threaded a t ends t o t a k e g r i p s f o r c a l i b r a t i o n i n a t e s t i n g machine. Centre l i n e s a t o p p o s i t e ends o f a d iameter were marked on b o t h h a l v e s o f the p i p e , and the mounting s u r f a c e s c l e a n e d by hand g r i n d i n g w i t h a b a l l m i l l and emery p a p e r . Degreas ing was then done u s i n g c h l o r o t h e n e , and SR-4 s t r a i n gauges FA-50-12 w i t h 1/2 i n . gauge l e n g t h were i n s t a l l e d , a t the p r e - d e t e r m i n e d s e c t i o n s , as p e r i n s t r u c t i o n s J b r use o f Eastman 910 cement. T e s t s on i n s u l a t i o n r e s i s t a n c e o f the gauges a f t e r attachment showed them t o be i n excess o f 20 x 103 meg ohms. ( F i g u r e l ) FIGURE 1 "A pair of gauges - instailed" To their right may be seen spacers with holes for carrying individual leads. Single core leads, made up of conductors fraaPhillips T-M Style 19 Rural Telephone Distribution cable and of equal lengths were then attached to the gauge tabs and glued to the pipe surface at a few points by Scotchweld epoxy adhesive^ i n order to prevent their being pulled loose from the gauges. (Figure 2) Water-proofing of the gauges and exposed leads was then done, as a second line of defence, by heating D i j e l l wax and pouring over gauges and surrounding leads so as to provide at least 1/8 i n . cover. (Figure 3) 7 . FIGURE 2 "Leads a t t a c h e d t o gauges, and g l u e d , near s p a c e r s , t o p i p e . " FIGURE 3 " D i j e l l wax poured over gauges and s u r r o u n d i n g l e a d s . " The p i p e was now ready f o r c l o s i n g . The cut edges were c leaned by C h l o r o t h e n e . S c o t c h w e l d S t r u c t u r a l Adhesive^ (a two p a r t room c u r i n g l i q u i d adhesive) was then prepared by m i x i n g the two p a r t s i n the g i v e n p r o p o r t i o n s by w e i g h t . 1/8 i n . w i d e and 4- i& i l b r a s s shim s t o c k spacerswere l a i d on the edges a t 6 i n . c/c i n o r d e r t o m a i n t a i n an optimum bond l i n e t h i c k n e s s . The adhesive was t h e n a p p l i e d on the edges by means o f a s p a t u l a . The two h a l v e s were p r e s s e d a g a i n s t each o t h e r , p l a c e d i n a wooden p r e s s t o m a i n t a i n optimum p r e s s u r e and cured a t room tem-p e r a t u r e f o r 4.8 h o u r s . ( F i g u r e s U and 5) FIGURE L "Bottom h a l f o f wooden p r e s s . " FIGURE 5 Pipe i n improvised wooden press." The gauges i n the pipe were then calibrated i n a 60 kips B.T.E. Universal Testing Machine, using special c y l i n d r i c a l grips which were screwed to the threaded ends of the pipe. A 2-arm or a 4 -arm external bridge was formed, with the help of dummy gauges attached to a s i m i l a r pipe, and with the same length of leads as the active gauges f o r temperature compensation, and s t r a i n readings taken using a 3aldwin Type "L" Str a i n Indicator and a 20 channel switching u n i t . The gauges at every section were calibrated up to loads to which the pipe would be subjected, i n p a i r s , to eliminate l o c a l bending e f f e c t s , and also singly so that readings could be obtained at a section i n case one of the gauges went out of order. The ends of the pipe were then f i l l e d with heated " D i j e l l " wax, and the leads coming from the pipe were enclosed i n a "Polyethylene" bag which was taped to the ends of the pipe, so as to p r e v e n t any m o i s t u r e from e n t e r i n g the p i p e d u r i n g c u r i n g . The p i p e was now ready f o r embedment i n c o n c r e t e . CHAPTER 111 EXAMPLES OF APPLICATION Three pipes were prepared and used i n separate tests. It was found on completion of the tests that the pipes could be re-covered from the concrete and reused i f care was taken i n knocking out the concrete. The r e l i a b i l i t y of the technique was checked i n two cases, when re-calibration of the gauges t a l l i e d with calibration be-fore the embedment of the pipe i n concrete. EXAMPLE 1 Beam Test A 3/4 i a . nominal diameter standard pipe 5 f t . 6 i n . long was knurled l i g h t l y , s l i t , threaded at the ends and a pair of gauges attached at the central section. The pipe was then closed up 12. £0,000 -15,000-k *0 /0,000-sooo 0 r 7W£o/z£pcAL / / / CM ACM ££LO'// I / A/-A- ' / / /THaOZ-J/CAL / OM BAS/J o/~ r~c o£ //me- of /esf = 7700yos/ ZZ" r L.OAV 3L. . B£.Aft1 CUT ALOf/c tf£?Z£ FaK • A~£/K Tf'£Z - . -i 15 •f- P/P£ -i-P"\ •©-/ / C/Z.ACK /hi &£AM OA/ /-OADWC • / / G>A £ £$ AT TA. C//£I> ' AT CZMTXAL ^£C/-/cW CAXACA<£rZ) 3£ C.7/OA/ BcTAM /OOO 2.00O 3000 CENTRAL LOAD /AI L8S 4O00 1 3 . f o r embedment, as d e s c r i b e d i n the l a s t c h a p t e r . A beam specimen was prepared by c a s t i n g concrete (Mix 1 d e s c r i b e d i n A p p e n d i x ) , and the beam t e s t e d i n a 200 k i p s O l s o n U n i v e r s a l T e s t i n g M a c h i n e , w i t h a c e n t r a l l o a d and end s u p p o r t s . ( F i g u r e 6) Computations R e l a t i n g t o the Beam T e s t : a . T h e o r e t i c a l s t r e s s e s i n s t e e l f o r uncracked s e c t i o n : m A . 4 . 7 x 10^ p s i (secant modulus f o r £Q <m 2000 p s i from s t r e s s -s t r a i n curve f o r the concrete see A p p e n d i x . ) 2 6 . 6 x 10^ p s i (as measured f o r s t a n d a r d p i p e . ) = 5 .68 - .333 - 2 x 3/16 x .113 - .333 - .014 = .319 s q . i n . y = AO x 5 * £.68 x .319 x 8 - .785 x . 8 2 4 2 x 8 40 * 4 . 6 8 x .319 - .785 x . 8 2 4 2 = 5 .08 i n . 4" L c g 4 x 103 4 40 x . 0 8 2 f 1.49 x 2 . 9 2 2 - .532 x 2.922 12 = 3 4 1 . 7 i n . 4 -Load j u s t be fore c r a c k i n g = 3300 l b s . Moment = 3300 x 44 4 = 36 ,300 i n l b s . Cone, s t r e s s a t l e v e l o f s t e e l = 36.300 x 2.92 3 4 ! . ? •-• ps i S t e e l s t r e s s = 5.68 x 310 = 17.62. p s i M s d . s t r e s s = 1?60' p s i Maximum t e n s i l e s t r e s s i n cone. = 36,300 x 4 .92 = 522 p s i T h e o r e t i c a l s t r e s s i n s t e e l (assuming concrete cracked below N e u t r a l A x i s . ) Moment o f a r e a i n compression about N e u t r a l A x i s = Moment.of e q u i v a l e n t a r e a i n t e n s i o n about N e u t r a l A x i s . o r , 1/2 b n 2 = mA g (d-n) o r , 4/2n2 = 5.68 x .319(8-n) o r , 2n* l . S l n - 14.5 = 0 + j. o r , n - 2.27 i n . . * . l e v e r arm - 8 - 2.27 3 = 7.24 Moment a t c e n t r a l l o a d o f 4>500 l b s . = 4 . 5 0 0 x 44 i n l b s . A S t e e l s t r e s s = 4.500 x 11 7.24 x .319 = 21,400 p s i T h e o r e t i c a l s t r e s s e s i n s t e e l (on b a s i s o f e x t e n t o f c r a c k measured on t e s t specimen.) E s = 26.6 x 106 p s i E = 4.7 x 106 p s i A c (uBcracked) A . eg M A/-- 4-x 3 .25 i n . - 13 s q . i n . = .319 s q . i n . = 13 x 3 .25 .4- >5.68 x .319 x 8 2 _ 13 4 1 .81 - 2.4. i n . - 13 x 3 . 2 5 2 -+13 x , 7 7 5 2 r i 1 .81 x 5 . 6 ' 12 = 76 i n ! A = 4500 x 44 A = A9,5QO l b . i n . = 5 . 6 i n . = mfc = g,68; x 49,500 x 5,6 76 = 20,700 p s i The d i f f e r e n c e i n s t e e l . s t r e s s a t the maximum l o a d t o w h i c h the beam was s u b j e c t e d between the expected v a l u e (on b a s i s o f e x t e n t o f c r a c k measured), and the measured v a l u e was: expected s t e e l s t r e s s = 20,700 p s i measured s t e e l s t r e s s = 11,600 p s i d i f f e r e n c e = 9,100 p s i % d i f f e r e n c e = 9.100 x 100 20,700 ' = LIS 16. I t was obvious t h a t t h i s pronounced d i f f e r e n c e , much g r e a t e r t h a n what Mains4 had observed i n h i s t e s t s , was on account o f a c r a c k w h i c h o r i g i n a t e d 1-3/4- i n . away from the gauge c e n t r e - l i n e and extended up t o 3-1/4 i n . from the top so t h a t 1-3/4 i n . o f the c o n c r e t e next t o the gauge t r a n s f e r r e d a l o a d o f 9100 x .319 = 2 ,900 l b s . by bond from the s t e e l t o the c o n c r e t e . The average bond s t r e s s i n t h a t l e n g t h = 2900  3 .14 x 1.05 x 1.75 = 502 p s i * w h i c h i s w e l l w i t h i n the average bond s t r e s s e s o b t a i n e d by W i l k i n s ' ' ' f o r k n u r l e d p i p e and h i g h s t r e n g t h c o n c r e t e . I t has been suggested by Ashdown i n the d i s c u s s i o n o f the paper by Hondros^ t h a t the s t r a i n energy i n t e n s i o n i n g _ t h e c o n c r e t e around the s t e e l i s t r a n s m u t e d i n some way t o l o w e r the s t r e s s i n s t e e l . T h i s would mean t h a t i f t h e r e were a l a r g e r concrete a r e a c r a c k e d o r o t h e r w i s e around the s t e e l , the r e d u c t i o n i n s t e e l s t r e s s i n a g i v e n l e n g t h would be g r e a t e r , and v i c e - v e r s a . I n o r d e r t o v e r i f y t h i s i d e a o f Ashdown, the c o n c r e t e beam was sawn l o n g i t u d i n a l l y i n a s p e c i a l concrete saw, so as t o l e a v e a s y m m e t r i c a l 4 i n . x 4 i n . concrete s e c t i o n around the p i p e . The p i p e was t h e n l o a d e d i n t e n s i o n and the s t r e s s i n the p i p e a t the gauge n o t e d . I t was noted t h a t the s t r e s s i n the p i p e 1-3/4 i n . away from the c r a c k was l e s s e r t h a n i n the bare p i p e . The concrete s e c t i o n around the c e n t r e l i n e o f the gauges was t h e n reduced by making a 3/4 i n . c u t a l l around the column s e c t i o n , and the p i p e l o a d e d a g a i n . The d i f f e r e n c e i n s t r e s s e s between the bare p i p e , and the c o n c r e t e d p i p e was now s m a l l e r t h a n b e f o r e . A f u r t h e r c u t a l l around the c e n t r a l s e c t i o n up t o w i t h i n l / 8 i n . o f the p i p e s t i l l reduced the d i f f e r e n c e i n s t r e s s e s . F i n a l l y concrete was knocked o f f from the c e n t r a l s e c t i o n and the gauges r e t u r n e d t o t h e i r 17 o r i g i n a l c a l i b r a t i o n . T h i s i n d i c a t e d t h a t the amount o f concrete s u r r o u n d i n g the p i p e r e i n f o r c e m e n t had an e f f e c t on the amount o f f o r c e t r a n s m i t t e d i n t o the c o n c r e t e w i t h i n the 1-3/A i n . d i s t a n c e b e t -ween the c r a c k e d s e c t i o n and the gauge l o c a t i o n . Gr i n o t h e r w o r d s , the bond s t r e s s e s on account o f which a t r a n s f e r e n c e o f f o r c e t a k e s p l a c e from the s t e e l t o the c o n c r e t e are a f f e c t e d by the amount o f c o n c r e t e s u r r o u n d i n g the p i p e . T h i s i s f u r t h e r c o r r o b o r a t e d by the 12 r e s u l t s o f Mathey and W a t s t e i n d u r i n g t h e i r i n v e s t i g a t i o n s o f bond i n Beam and P u l l o u t specimens w i t h h i g h y i e l d - s t r e n g t h deformed b a r s . And t h i s t r e n d i s a l s o p e r c e p t i b l e i n s t u d i e s on bond s t r e s s d i s t r i -b u t i o n a l o n g r e i n f o r c i n g b a r s by Mains4. (Tables 1, 2 and 3 . ) CO H TABLE 1 TABLE SHOWING BEHAVIOUR OF TENSION SPECIMEN GUT FROM BEAM Load. lbs. Strain Indicator Readings - (Indicator Calibrated for a Gauge Factor of 2.00) Cracked seetion as cut from beam  With 3/4 in« deep saw cut a l l around at mid-section With cut to within 1/8 i n . of pipe at mid -3ect ion *  Pipe alone -concrete Calibration of pipe -Loading Unloading Loading Unloading Loading Unloading Loads held steady Loads held steady 0 0 15 -4 20 A 76 0 0 800 78 121 104 180 168 216 170 188 1600 212 254 268 350 328 376 354 371 2400 358 412 438 530 496 554 540 558 3200 518 570 608 710 664 716 725 746 4000 680 721 786 908 860 896 910 1038 4800 842 846 958 1088 1048 1084 1098 1128 5600 - - 1140 1265 1236 1264 - -6400 - - 1318 1430 1428 1456 - -7200 - - 1492 1580 1614 1630 - -8000 - - 1675 1722 1800 1800 - -8800 _ 1850 1855 — — _ 19 . Notes on Table 1 1. Each c y c l e o f l o a d i n g t o o k about 5 m i n u t e s . 2 . L o a d i n g c y c l e marked by an a s t e r i s k was performed w i t h a 2-arm e x t e r n a l b r i d g e whereas the o t h e r s were w i t h a A-arm e x t e r n a l b r i d g e . Therefore r e a d i n g s shown have been doubled f o r compar ison. 3 . Some b l a n k s a r e i n d i c a t e d i n the t a b l e because the specimen was p u l l e d t o d i f f e r e n t maximum l o a d s . A. The d i f f e r e n c e i n f i n a l gauge c a l i b r a t i o n check and o r i g i n a l gauge c a l i b r a t i o n i s on account o f the f a c t t h a t w h i l e k n o c k i n g out the c o n c r e t e , a l e a d had come o f f from the gauge t a b and the p i p e was s p l i t t o r e p a i r i t . The s p l i t p i p e behaves a l i t t l e d i f f e r e n t l y from the g l u e d p i p e because some independent bending o f each h a l f t a k e s p l a c e . 5 . I n o r d e r t o o b t a i n t r u e s t r a i n s the f i g u r e s shown have t o be m u l t i -p l i e d by a f a c t o r o f l/2 x 2.13/2 t o take i n t o account the 4-arm e x t e r n a l b r i d g e , gauge f a c t o r o f 2.13 and i n d i c a t o r c a l i b r a t i o n w i t h a c a l i b r a t i o n u n i t o f gauge f a c t o r 2 . 0 0 . 2D. Mathey and W a t s t e i n determined average bond s t r e s s e s developed i n No. 4 and No. 8 b a i s i n 10 i n . x 10 i n . p u l l - o u t specimens, and 8 i n , x 18 i n . beam specimens, w i t h equal l e n g t h s o f embedment. The p u l l - o u t c o n c r e t e cubes were r e i n f o r c e d a g a i n s t s p l i t t i n g by a c y l i n d r i c a l cage o f w i r e f a b r i c . The r e s u l t s noted from t h e i r T a b l e s 3 and 4 show t h a t c r i t i c a l bond s t r e s s e s ( b e i n g the l e s s e r o f the bond s t r e s s e s c o r -responding t o e i t h e r a f r e e - e n d s l i p o f .002 i n . o r a l o a d e d end s l i p o f . 0 1 i n . ) a r e always g r e a t e r i n the case o f the beam specimens, which has about f i f t y p e r c e n t more concrete t h a n the p u l l - o u t specimens. However u l t i m a t e average bond s t r e s s e s a r e determined t o be g e n e r a l l y l o w e r i n case o f the beam specimens. The r e a s o n i s s e l f - e v i d e n t i n the mode o f f a i l u r e d e s c r i b e d , f o r the beams. I n a l l beams w i t h No. 8 b a r s f a i l u r e was accompanied b y l o n g i t u d i n a l s p l i t t i n g , and i n 3 o f the beams w i t h No. 4 b a r s , i n w h i c h the u l t i m a t e bond s t r e s s e s a r e l e s s e r t h a n f o r p u l l -out specimens, f a i l u r e was s i m i l a r l y accompanied by l o n g i t u d i n a l c r a c k i n g and s p a l l i n g . Therefore the p u l l - o u t specimens i n d i c a t e d g r e a t e r s t r e n g t h a t u l t i m a t e l o a d s on account o f the hoop-re inforcement which prevented s p l i t t i n g ; : . 21:. TABLE 2 DATA OBTAINED FROM TABLES 3 AND A OF PAPER B I MATHEI AND WATSTEIN 1 2 P u l l out specimens 10 i n . x 10 i n . r e i n f o r c e d a g a i n s t s p l i t t i n g , . Beam specimens 8 i n . x 18 i n . C r i t i c a l Bond U l t i m a t e Bond Type o f Length o f S t r e s s e s S t r e s s e s Mode o f b a r Embedment P u l l - o u t Beam P u l l - o u t Beam Beam F a i l u r e 7 i n . 680 1181 1542 1636 E x c e s s i v e S l i p 7 580 1150 1620 1572 S p a l l i n g o f c o n c r e t e No. L 10.5 790 850 1464 1364 E x c e s s i v e S l i p Deformed 10.5 730 833 1464 1362 I I U 475 618 960 1078 it 14 470 605 960 892 II 17 425 540 1008 882 C r a c k 17 475 525 1004 932 C r a c k 7 i n . 585 782 1214 1024 Crack 14 540 610 1372 598 ri No. 8 14 595 683 1394 760 ti Deformed 21 495 495 1256 736 I I 21 395 521 1244 636 tt 28 250 511 966 692 ii 28 270 433 966 644 I I 34 335 526 912 678 n 34 280 470 902 662 C r a c k 22 Type o f TABLE 3 Maximum Bond S t r e s s e s Measured Bar 8 i n . x 12 i n . 8 i n . x 12-1/2 i n . 8 i n . x 18 i n . P u l l o u t Beam Beam Remarks P L - 460 B 16 B 4 I f we omit u n -d e r l i n e d r e a d -P 5 B 17 B 5 • - 950 i n g s w h i c h a r e f r e a k f o r B-26 7/8 i n . P 6 B 18 - 600 B 6 and c o m p l e t e l y P l a i n u n r e l i a b l e f o r P 9 - 375 B 27 - 410 B 10 X - l , X-2 because suddenly the m a x i -P 12 B 28 - .-480 B 11 mum bond s t r e s s e s a r e shown t o be X - l - 3900 B 25 - 1200 g r e a t e r f o r p l a i n bars t h a n f o r the X-2 - 2060 B 26 - m deformed b a r s , t h e t r e n d i s p e r c e p -t i b l e . P 1 B 12 - 1060 B 1 • - 1000 The v a l u e f o r B 13 i s e n t i r e l y P 2 B 13 - 3420 B 2 a l o c a l e f f e c t as shown by P 3 B 14 - 1860 B 3 F i g u r e 13 o f 7/8 i n . p a p e r . Deformed P 7 B 15 - 970 B 7 P 8 - 900 X 3 - 810 B 8 P 10 - 1560 X 4 - 860 B 9 • - 1600 P 11 Notes : 1. The specimen numbers are g i v e n before each va2.ue o f maximum bond s t r e s s . 2 . Specimens X I , X 2 , X 3, and X 4 are specimens w i t h c o n t r o l l e d c r a c k l o c a t i o n a t mid span. 3. A b l a n k i n d i c a t e s t h a t no d a t a was a v a i l a b l e i n the T a b l e s . 23 Mains^ - determined bond s t r e s s e s i n beams and p u l l - o u t specimens by measuring f o r c e s a t d i f f e r e n t p o i n t s o f the r e i n f o r c e m e n t , w i t h o r w i t h o u t h o o k s , and w i t h o r w i t h o u t bent-up b a r s . Data r e l a t i n g t o 7/8 i n . d i a . p l a i n and deformed b a r s , s t r a i g h t and w i t h o u t any bent-up b a r s a r e a b s t r a c t e d from h i s Tables 2 and 3 . (Table 3) The Table g i v e s the maximum bond s t r e s s e s which M a i n ' s o b t a i n e d i n the r e i n f o r c i n g b a r s . The maximum v a l u e s a r e more a f f e c t e d by l o c a l • c o n d i t i o n s a t any p o i n t o f the r e i n f o r c e m e n t , and t h e r e f o r e cannot be as r e l i a b l e as average bond v a l u e s f o r i n d i c a t i n g the e f f e c t o f the volume o f c o n c r e t e on bond. N e v e r t h e l e s s , a g r e a t e r bond s t r e n g t h would g e n e r a l l y be expected i n a specimen showing g r e a t e r maximum bond s t r e s s . I f we t h e r e f o r e s tudy the few maximum v a l u e s o b t a i n e d by Mains w i t h the r e s e r v a t i o n s mentioned e a r l i e r and keep i n view t h a t any c o n c l u s i o n s from t e s t s i n concrete r e q u i r e a l a r g e number o f r e s u l t s , we note t h a t i n the case o f the 7/8 i n . p l a i n b a r - the maximum bond s t r e s s v a l u e s are g r e a t e r f o r the 8 i n . x 18 i n . beam (area IAA i n . ) t h a n f o r the 8 i n . x 12 i n . p u l l out specimen (area 96 s q . i n . ) o r the 8 i n . x 12-1/2 i n beam (area 100 s q . i n . ) . T h i s t r e n d cannot be d e t e c t e d i n the ease o f the 7/8 i n . d i a . deformed b a r s but the r e a s o n may be the g r e a t e r l o c a l e f f e c t s on account o f the m e c h a n i c a l wedging a c t i o n o f the d e f o r m a t i o n s . A l a r g e r number o f r e s u l t s would have been d e s i r a b l e . I t was observed immediate ly before the concrete was s t r i p p e d o f f c o m p l e t e l y from the p i p e , t h a t on account o f the repeated p u l l s t o w h i c h the p i p e was s u b j e c t e d , prominent c r a c k s had appeared i n the concrete a t a p p r o x i m a t e l y 5-1/2 i n . e/c. The p i p e had been l o a d e d up t o a maximum s t r e s s o f 3 0 , 0 0 0 p s i . 24. CONCRETE CUT A WA y FROM HERE 1L 5" 'st'^Y^sF^ '4 J3 | ^8 bS V CRACKS OBSERVED IN 7'ENS/ON J ' P E C / M E N LOAD 3E/NC- TRANSFERRED /NTO CONCRETE BY BOND LOAD IM CONCRETE JCAST EXCEEDS TENJ/LE JTREA/C-TH. CRACK/NG 3EC/NS CONCRETE CRACKED. LOAD IN CONCRETE //V FIRST PORTION REDUCED . CONCRETE BEYOND CRACK -STARTS GETTING LOADED. h - s -CRACK FORMATION JN TENS/OA/ SPECIMENS CUT FROM BEAM F/G. 7 25. This pointed to a mechanism for crack formation in a tensile concrete specimen, which made i t impossible to form cracks, within a cracked distance. Imagine a tensile specimen being pulled gradually (see f i g .7 on preceding page), consider the transference of stress by bond into concrete from one end. When the tensile load in the concrete exceeds a certain maximum value the concrete w i l l crack accompanied, by s l ip at the ends of the cracked concrete in order to balance the changes in deformation of steel and concrete. However, immediately on cracking, the load transferred in length "a" by bond w i l l be reduced by half, while the next crack w i l l start forming from the cracked section. So unless by repeated or prolonged loading there i s a reduction in the tensile strength of the concrete by more than half, the cracks w i l l form only at approimately equal distances. The variations in the distance would be of the same order as expected variations in the strength of concrete from a particular batch or mix. It would therefore be expected that in a tensile specimen of this type there would be a minimum cracking distance which would be a function of: the concrete strength in tension, the area of concrete, and some factor dependant on the bond properties of the steel , such that no major cracks (as distinct from micro-cracks) form in this distance. 'Bjuggren in his discussion of the paper by Mylrea 1^ on 'Bond and Anchorage refers to some Swedish experiments on cracks; in re in-forced concrete beams which showed that the ratio between the greatest distance e between cracks, and the square root of the smallest surrounding area A c was constant; i.e.Jkc was constant. Therefore he speculated , e 26. the g r e a t e s t d i s t a n c e between c r a c k s t o be o f form e where 0 i s a f a c t o r depending upon the bond p r o p e r t i e s o f s t e e l . I n v iew o f the f a c t t h a t the g r e a t e s t d i s t a n c e between c r a c k s i s m o s t l y i n l o c a t i o n s o f maximum moment and minimum s h e a r , where the concrete s u r r o u n d i n g the s t e e l i s i n t e n s i o n t h i s r e s u l t may h o l d even f o r t e n s i l e specimens o f the type i n v e s t i g a t e d by u s , w i t h the d i f f e r e n c e t h a t would r e p r e s e n t the minimum c r a c k i n g d i s t a n c e . The e x i s t e n c e o f a minimum c r a c k i n g d i s t a n c e f o r a t e n s i l e specimen would mean t h a t i f such a specimen has a l e n g t h o f concrete e q u a l t o l e s s t h a n t w i c e the minimum c r a c k i n g d i s t a n c e , t h e n no major t e n s i l e c r a c k s would form on l o a d i n g the specimen, p r o v i d e d o f course t h a t the t e n s i l e l o a d was s u f f i c i e n t . t i o n No. 2 ( d e s c r i b e d l a t e r ) where a p i p e was surrounded by p r e - c r a c k e d concrete o f l e n g t h s 1-1/2 i n . , 3 i n . , and 6 i n . , and no c r a c k s were ob-s e r v e d . I t may be i n t e r e s t i n g t o note t h a t i n a t e s t c a r r i e d out by B i c h a r a , and mentioned by G u y o n 1 1 i n which a 34 nim. O.D. p i p e was e n -c l o s e d by a 8 i n . x 8 i n . c o n c r e t e s e c t i o n , 56 i n . l o n g , no c r a c k s were formed, as shown by the r e s u l t s , i n d i c a t i n g t h a t e i t h e r the 56 i n . was l e s s t h a n t w i c e the minimum c r a c k i n g d i s t a n c e f o r t h a t spec imen, o r e l s e the concrete was not l o a d e d t o i t s u l t i m a t e t e n s i l e s t r e n g t h . T h i s l a c k o f c r a c k f o r m a t i o n was observed i n our A p p l i c a -27. EXAMPLE 2  T e n s i o n Test A 26 i n * l o n g Shelby Tubing 1 i n . O . D . , 3/4 i n . I . D . was prepared f o r embedment i n c o n c r e t e , w i t h l i g h t k n u r l i n g on the o u t s i d e , and w i t h 3 p a i r s o f gauges. The concrete was c a s t i n 3 b l o c k s w i t h the h e l p o f b r a s s s e p a r a t o r s , w i t h the gauge p a i r s a t the c e n t r e o f each b l o c k , and c r a c k s were preformed i n the middle o f each gauge by means o f a 1/16 i n . b r a s s p l a t e . ( F i g u r e 8) I n the Beam Test performed e a r l i e r we had seen t h a t the s t r e s s - s t r a i n c h a r a c t e r i s t i c o f the gauges had remained u n a l t e r e d a f t e r c o n c r e t i n g d u r i n g the one and a h a l f month p e r i o d o f t e s t i n g , i n s p i t e o f the f a c t t h a t Eastman 910 cement, which i s e a s i l y a f f e c t e d by age and m o i s t u r e , was u s e d . However, no o b s e r v a t i o n s were t a k e n r e g a r d i n g the change i n the gauge-zero on account o f creep o f the cement over t h i s p e r i o d o f t i m e . An attempt was t h e r e f o r e made i n t h i s t e s t t o take r e a d i n g s e x t e n d i n g over the c u r i n g and d r y i n g p e r i o d o f 18 days w i t h r e f e r e n c e t o the a b s o l u t e gauge-zero, w h i c h was o b t a i n e d by r e v e r s i n g the a c t i v e and dummy gauge l e a d s , and t a k i n g the mean o f the two r e a d i n g s . These r e a d i n g s gave us the expans ion and shr inkage c h a r a c t e r i s t i c s o f the d i f f e r e n t specimen s i z e s a n d , as may be seen, p o i n t e d t o the l a r g e s h r i n k -age s t r a i n s w h i c h took p l a c e i n the s m a l l e s t b l o c k i n w h i c h the r a t i o o f the e x t e r n a l s u r f a c e t o the volume was l a r g e s t , as compared t o the o t h e r two. I t may be noted t h a t the s t r a i n s measured are l e s s t h a n what one would measure on s i m i l a r specimens w i t h o u t the 1/16 i n . t h i c k b r a s s c r a c k f o r m e r s . 2 8 . An i n t e r e s t i n g o b s e r v a t i o n o f shr inkage s t r a i n s (see accompanying graph) i n the s m a l l e s t specimens d u r i n g c u r i n g and d r y i n g was the p e r i o d i c drop which seemed to be brought about by s u c c e s s i v e s l i p s o f the c o n c r e t e on account o f e x c e s s i v e s t r a i n s . However i n s p i t e o f the s l i p o f the c o n c r e t e , which caused a l o w e r i n g o f the bond s t r e n g t h , the bond c o u l d s t i l l be i n c r e a s e d p o s s i b l y on account o f m e c h a n i c a l wedging, and P o i s s o n ' s e f f e c t i n the p i p e w h i c h expanded l a t e r a l l y on account o f compress ion , by f u r t h e r s t r a i n s . I t was a l s o observed t h a t the middle b l o c k showed an expans ion o f the concrete d u r i n g the c u r i n g p e r i o d , whereas the o u t e r two showed c o n s i s t e n t s h r i n k a g e . T h i s i n d i c a t e d t h a t i f the r > ^ f - J U f loss -cbf m o i s t u r e ' . cn was l a r g e enough, then the c o n c r e t e would s h r i n k even when k e p t humid under b u r l a p . ( F i g u r e 8) The p i p e was then l o a d e d i n t e n s i o n , and i t was observed t h a t the c o n c r e t e around the gauges caused a t r a n s f e r e n c e o f force i n the c o n c r e t e , even though each gauge had around i t a c e n t r a l c r a c k . T h i s d i f f e r e n c e , w h i c h was o f the o r d e r o f L-5% was reduced on c y c l e s o f r e -l o a d i n g . F i n a l l y the c o n c r e t e was knocked o f f from around the p i p e , and the g a u g e - c a l i b r a t i o n s checked e x a c t l y , except i n case o f gauge p a i r 1 i n a t the l o c a t i o n o f which the two h a l v e s o f the p i p e had opened i up c a u s i n g l o w e r s t r a i n s t o be r e c o r d e d than when the two h a l v e s were g lued t o g e t h e r . (Tables L, 5 and 6) The gauge a b s o l u t e zero h a d , however, shown a creep o f 28* in ./ i n . and 2 9 W i n . / i n . i n two p a i r s o f the gauges, and i t i s expected a l s o i n the 3 r d p a i r , but u n f o r t u n a t e l y d u r i n g the l o a d i n g c y c l e s i n which the p i p e was s t r e s s e d up t o about 60,000 p s i , some y i e l d i n g took p l a c e <x/ //me of A-sf = c?,P'80/>s/ SHR/NKA GE SAPA/A/S /A/ EE'MS'/OA/ 6P£C/M£M P~/G 8 ' 30. i n the pipe i n the region of the 3rd gauge, so no check was available. As was pointed out earlier, no external cracks were seen on the specimen, after the loading cycles pointing to the existence of a "minimum cracking length." 31 TABLE 4 SHOWING BEHAVIOR OF TENSION SPECIMEN UNDER LOAD Gauge P a i r No. 1 a t Centre o f Preformed Crack i n 3 i n . Long B l o c k S t r a i n I n d i c a t o r Readings - ( I n d i c a t o r C a l i b r a t e d f o r Gauge F a c t o r o f 2.00)  L o a d i n g L o a d i n g Tube a lone - O r i g i n a l Load i n C y c l e No. 1 C y c l e No. 2 concrete removed c a l i b r a t i o n k i p s L o a d i n g U n l o a d i n g L o a d i n g U n l o a d i n g Loads Steady Loads Steady 0 98 60 101 230 98 100 0.5 147 112 1.0 210 319 2.0 310 288 320 321 3.5 £72 449 4.0 549 649 541 540 5.0 630 610 6.0 761 758 6.5 795 778 7.0 877 970 8.0 962 942 981 975 9.5 1125 1112 10.0 1203 1280 1202 1190 11.0 1298 1280 12.0 1425 1410 12.5 1461 1451 13.0 1549 1594 14.O 1616 1616 1649 1626 32. Notes on Table L 1. Each c y c l e o f l o a d i n g took about 5 m i n u t e s . 2. A l l r e a d i n g s a r e t a k e n w i t h a 2-arm e x t e r n a l b r i d g e . 3 . A t the t ime o f check c a l i b r a t i o n , the j o i n t between the two h a l v e s o f p i p e was open a t s e c t i o n where gauges were a t t a c h e d . 3 3 . TABLE 5 SHOEING BEHAVIOR OF TENSION SPECIMEN UNDER LOAD  Gauge P a i r No. 2 a t Centre o f Preformed C r a c k i n 6 i n . Long B l o c k S t r a i n I n d i c a t o r Readings - ( I n d i c a t o r C a l i b r a t e d f o r Gauge F a c t o r o f 2.00) ' Tube a l o n e O r i g i n a l Load i n L o a d i n g L o a d i n g - c o n c r e t e c a l i b r a -k i p s C y c l e No. 1 C y c l e No. 2 removed t i o n s L o a d i n g Unloading Loading Unloading Loads Steady _ Loads Steady 0 100 105 100 110 100 100 1.0 203 226 2.0 319 330 327 324 2.5 370 392 4.0 540 561 549 550 5.0 650 660 5.5 703 730 6.0 772 773 7.0 870 900 8.0 982 991 995 995 8.5 1036 1069 10.0 1200 1235 1217 1217 11.0 1312 1330 11.5 1368 1392 12.0 1440 1440 13.0 1532 1547 14.0 1648 I642 I664 1667 1663, Notes : . 1. Each c y c l e o f l o a d i n g took about 5 m i n u t e s . 2. A l l r e a d i n g s a r e t a k e n w i t h a 2-arm e x t e r n a l b r i d g e . 3 4 . TABLE 6 SHOWING BEHAVIOR OF TENSION SPECIMEN UNDER LOAD Gauge P a i r No. 3 a t Centre o f Preformed Crack i n 12 i n . Long B l o c k S t r a i n I n d i c a t o r Readings - ( I n d i c a t o r C a l i b r a t e d f o r Gauge F a c t o r o f 2 .00)  Tube a lone O r i g i n a l L o a d i n g L o a d i n g - concrete c a l i b r a -Load i n C y c l e No. 1 C y c l e No. 2 . removed t i o n k i p s L o a d i n g U n l o a d i n g L o a d i n g U n l o a d i n g Loads Steady Loads Steady 0 98 102 100 98 100 100 1.5 260 278 2 . 0 325 324 3 . 0 423 AAA 430 434 4 . 0 548 547 4 . 5 593 613 6 . 0 756 786 764 767 771 771 7 .5 920 953 8 . 0 994 992 9 . 0 1088 • 1118 1090 1104 1 0 . 0 1216 1213 10.5 1252 1278 12 .0 1421 1439 1425 1439 1440 1438 13 .5 1588 1594 1 4 . 0 1643 1663 1662 14.5 1755 1767 Notes : 1. Each c y c l e o f l o a d i n g took about 5 m i n u t e s . 2. A l l r e a d i n g s a r e t a k e n w i t h a 2-arm e x t e r n a l b r i d g e . 35. EXAMPLE 3  J o i n t Test-A c a s t - i n - s i t u j o i n t between two p r e c a s t and p r e s t r e s s e d 4 i n . x 10 i n . x L f t . 0 i n . members, i n the shape o f a Tee, was c a s t on a l o a d i n g frame e s p e c i a l l y prepared f o r the t e s t . ( F i g u r e 9) The j o i n t was r e i n f o r c e d w i t h a 1 i n . O . D . , 3/4 i n . I . D . Shelby Tubing i n one h a l f o f w h i c h e i g h t p a i r s o f s t r a i n gauges had been a t t a c h e d . One h a l f o f the j o i n t had 1/4 i n . d i a . v e r t i c a l 2-^legged s t i r r u p s a t 4 i n . c/c and the o t h e r h a l f had an e q u a l number o f r o d s a t the same s p a c i n g , anchored i n the c a s t i n s i t u concrete but p a s s i n g l o o s e l y through a h o l e formed i n the p r e c a s t member. A m i l l e d s e c t i o n a t the l o w e r end o f the rods c a r r i e d T a t n a l l C6-141-B s t r a i n gauges w h i c h measured f o r c e s i n the r o d s . The ends o f the rods were threaded so t h a t they c o u l d be extended by t u r n i n g a nut b e a r i n g on the p r e s t r e s s e d member through a c y l i n -d r i c a l s l e e v e . ( F i g u r e 10) The l o a d i n g frame made up o f a p a i r o f 8 i n . x 2-1/% i n . x 1/2 i n . channels p r o v i d e d a c e n t r a l l o a d , through a h y d r a u l i c j a c k , on the j o i n t , which c o u l d be measured e x a c t l y through the end rods vrhich were c a l i b r a t e d a f t e r a t t a c h i n g T a t n e l l G6-I4I-8 s t r a i n gauges t o them. The p r e c a s t members were made o f M i x 1 (see Appendix) and were p r e s t r e s s e d a t 21 days by ..four.:: 7 mm w i r e s t o approximate 850 p s i u s i n g , screw j a c k s . They were t h e n supported on the L o a d i n g Frame, w i t h one end r e s t i n g on the l o a d i n g head o f the jack.^ and the o t h e r on temporary wooden s u p p o r t s , and a l i g n e d and l e v e l l e d . A s p e c i a l form w h i c h 36. k ^ - I k ^ -<. IN O I \|c\i / . {( G -\ x $...1 *** • \ X V!> vj <o k ^ <^  ^ k ^ k £ >^ \ i S ^ k 3 FIGURE 11 "The j o i n t on the L o a d i n g Frame." 38. allowed i t ' s removal from the frame without disturbing the joint was set up, and the reinforcing pipe placed in position. Concrete as per Mix II was then cast, and cured under wet burlap for 82 hours, and then allowed to dry for 60 hours. Six pairs of SR-4 gauges Type A-9-4 were then applied? to the sides of the prestressed member on either side of the ins-trumented half ( Fig.23 ). The joint was now ready for loading (Fig.11). Prior calibration of the rods and reinforcing pipe, and the dimensions of the loading frame, gave the following constants which when multiplied to the corresponding Strain Indicator readings gave (R= Strain reading): Force in pipe = 8.98 R l b s . Force in Frame Rods = 3*38 R Force in Vert ical Rods= 2.51 R^ l b s « Concrete stress = 5«3 R^ ps i . Moment at Centre = 6.55 R 2 l b . f t . Moment at Section AA = 4.95 l b . f t . I n i t i a l l y the vert ical rods were tightened to about 1000 lbs . Then the joint was loaded by i t s own self weight by raising the jack without the frame rods bearing on the precast members. A series of tests were then carried out to study the effect of the superimposed central loads. A l l readings were taken with the loads held steady by locking the jack head. F irs t four cycles of loading and unloading in two steps each were performed to within the cracking load. The forces in the pipe at d i f f -erent sections for various maximum central moments are shown in Fig.12, and i t may be observed that the smoothness of the curves i s interrupted 39. by a n g u l a r i t i e s . These are due t o the f o r m a t i o n o f m i c r o - c r a c k s i n the concrete and i n t e r n a l adjustment o f s t r e s s e s and s t r a i n s , and g e n e r a l l y f o r t e l l the f o r m a t i o n o f major c r a c k s i n the v i c i n i t y o f these l o c a l changes, as conf i rmed d u r i n g subsequent l o a d i n g s . W i t h h i g h e r l o a d s o r f u r t h e r c y c l i c l o a d i n g an e q u i l i b r i u m o f the i n t e r n a l f o r c e s i s e s t a b l i s h e d and the r e t u r n t o a r e g u l a r v a r i a t i o n o f f o r c e s i s n o t i c e d . I t i s a l s o seen t h a t w h i l e u n l o a d i n g h i g h e r v a l u e s o f f o r c e s i n the p i p e are r e c o r d e d f o r any p a r t i c u l a r l o a d t h a n when l o a d i n g , presumably on account o f v e r y s m a l l p l a s t i c s t r a i n s i n the concrete d u r i n g the upward l o a d i n g which p r e v e n t the p i p e from r e t u r n i n g t o i t s o r i g i n a l c o n d i t i o n . When the s e c t i o n i s uncracked and e q u i l i b r i u m i s e s t a b l i s h e d i n the i n t e r n a l m i c r o - a d j u s t m e n t s , t h e r e i s c l o s e agreement between the computed and observed v a l u e s o f the f o r c e s i n the p i p e . Thus f o r L o a d i n g c y c l e No. A , the computed and observed v a l u e s o f the f o r c e s a t the c e n t r a l s e c t i o n , and s e c t i o n AA, a t q u a r t e r p t i o f c a s t - i n - s i t u p o r t i o n are as f o l l o w s : C e n t r a l S e c t i o n E e = 26 .6 x 1 0 D p s i E e = 3 . 5 x 1Q 6 p s i m = 2 6 . 6 3 . 5 = 7 .6 A r e a = L x 14 - .785 /• 7 .6 x .328 = 57.71 s q . i n . e . g . = 56 x 7 - .785 x 12 / 2.A9 x 12 57.71 = 7.15 i n . from bottom = 6.85 i n . from top /"0 !£>• 40. I c e = A x 1 4 3 4 A x 1A x .152 A (2 .49 - . 7 9 ) 4 .85 2 6 3 x 4 = 956.2 i n . L Maximum Moment - 2.2.6 k i p f t . . * . Cone, s t r e s s a t l e v e l o f p i p e = 2 2 6 0 x 12 x 4.85 956.2 = 138 p s i . * . s t e e l s t r e s s = 7 . 6 x 13:8 = 1053 p s i S t r e s s measured = 3J£_ .328 p s i S e c t i o n AA E g = 26.6 x 1 0 6 p s i E c ( p r e c a s t ) = 5 x 10^ p s i E c ( i n - s i t u ) = 3.5 x 1 0 6 p s i m = 26.6 5 = 5.3 P r e c a s t s e c t i o n Z.6 4' 4 . ^ 4-A r e a = 10 x 4 - A x 3.14 x . 5 2 4(3 .14) x 5.3 x .0651 ;+ 4(3 .14) , 2 7 6 2 x 5.3 4 / 4 = AA. 8.3 s q . i n . 41. leg = k x IO 3 + 4.34 x 2 2 + 1.27 x 2 2 - 4 x .196 x 2 2 12 = 352.6 i n . ^ '. Cast- in-situ Section Equivalent Area = k x 2.8+ 5.3 x .328 - .78 = 12.16 sq . in . I = 2.8 x 43- .0k91 x 1.0k + .0491 x (1.0^ - .75*) x 5.3 eg Jg— 4 = 15.06 i n . Considered together Area = 44.83 + 12.16 = 56.99 sq . in . e.g. = 44.83 x 5 + 12.16 x 12 56799 = 6.50 i n . from bottom = 7.50 i n . from top I = 352.6 + 44.83 x 1.502 + 15.06 + 12.16 x 5.502 eg r = 825.4 i n . Moment at Section AA = 1.71 kips f t . Concrete stress at level of pipe = 1710 x 12 x 5*50 0^575 = I36 psi Therefore, steel stress= 136 x 5.3 = 722 psi stress measured = 195 .328 = 594 psi 42. /•94P SUPERIAPPOSED JB. M.D. D/STANCE FROM CENTRE IN INS.-LOADING OF UNCRACKFD -SECTION NUMERALS INDICATE LOADING CYCLE NO. DOTTED. LINES SHOW FORCES WHILE UNLOADING FfG. /2 A3 Next the j o i n t was loaded t o c r a c k i n g u n t i l h o r i z o n t a l c r a c k s appeared a t the j u n c t i o n o f the p r e c a s t and c a s t - i n - c i t u c o n c r e t e , and the p l o t t e d r e s u l t s ( F i g u r e 13) a g a i n show a n g u l a r i t i e s which become mani fes t before v i s i b l e c r a c k f o r m a t i o n , and p o i n t t o i n t e r n a l m i c r o -c r a c k i n g . However a f t e r the f o r m a t i o n o f the c r a c k s , n o r m a l i s a t i o n a g a i n s e t s i n by i n t e r n a l micro-adjustments ( s l i p p i n g o f r e i n f o r c e m e n t , e t c e t e r a ) and the f o r c e s i n the p i p e are r e g u l a r i s e d . The cracked s e c t i o n i s shown i n F i g u r e 14. FIGURE 14 "The J o i n t showing the l o c a t i o n o f c r a c k s . Numerals i n d i c a t e t h e i r o r d e r o f f o r m a t i o n . " The j o i n t was then u n l o a d e d , and a l l the v e r t i c a l rods l o o s e n e d , and then r e l o a d e d u n t i l h o r i z o n t a l c r a c k i n g was complete , up t o the i n n e r end o f the p r e c a s t member, on the i n s t r u m e n t e d h a l f . 44. /2 • J o 8 I, V ! NT O Nl MAX.MOAf./fV/C.f?: L-3.8Z . it-20 AT CORNERSJ l—S-SO CRACKS 4.97 CZACK-4- (3/&C£5T) /•22 4.46 c/ZACKS 2,3 GAUGE - L OCAT/OA/J % LOAD/A/6 TO CRACK/A/6 ~ LOCA 7/OA/ Of CRAC/XS AND LOADS AT ITY///CH THEY OCCUR ARE MARKED F/&. A3 4 5 . The rods were a g a i n t e n s i o n e d t o about a 1000 l b s . e a c h , and the j o i n t r e l o a d e d . F i n a l l y a l l but the l a s t two rods were u n t e n s i o n e d , and r e l o a d i n g showed t h a t the j o i n t c o u l d s t i l l c a r r y a major p o r t i o n o f the moment. ( F i g u r e 15) Observat ions o f the changes i n the f o r c e s i n the v e r t i c a l rods d u r i n g these l o a d i n g s showed t h a t a t h i g h l o a d s moment e q u i l i b r i u m o f the c a s t - i n - s i t u p o r t i o n was m a i n t a i n e d by a s h i f t i n g l e v e r arm. That i s , when a l l v e r t i c a l rods were i n o p e r a t i o n , they c a r r i e d a t o t a l l o a d g r e a t e r t h a n when the two end rods were a c t i n g such t h a t the moments p r o v i d e d by them, about a v e r t i c a l s e c t i o n i n the c a s t - i n - s i t u p o r t i o n , were s i m i l a r . ( F i g u r e 16) 46. MAX.MOM 'INK FT. GAGE - L O C A T I O N S LOAD/NG A F T E R ' HORIZ. C R A C K I N G C O M P L E T E F/G. /5 Ll. vi ^0 k j CQ ^ vl k k Uj •< o *0 IOO0-/000~ MOM. /N K.FT ALL RODS ACT/NG . ROD -LOCATIONS /ooo-I * *0 k k Lu ^ k <3 k N ^ k i LOADING TO CRACK MO /060-LOADING AFTER HORIZONTAL CRA CK/NG •4--P.S /•6\6 4" GAGE-LOLA T/QN A'/G /6 48. Concrete stresses recorded during the various loading cycles were found to be unreliable quantitatively possibly on account of micro-adjustments and l o c a l surface behaviour but certain trends were observed which confirm the idea of the lowering of the neutral axis on loading concrete members on account of cracking etcetera, and also the maintenance of the neutral axis at fixed l e v e l when only horizontal s l i p s take place at any layer,- i n t h i s case, the layer between the precast and cast-i n - s i t u member. Thus i n the "loading to cracking" the following table gives the depth of the neutral axis on the basis of concrete s t r a i n gauge readings at Section AA at approximately quarter point of c a s t - i n - s i t u member. Moment i n kip f t . 2.31 4.46 9.13 11.20 12.30 Depth of N.A. ,• from top i n ins. 8.05 8.25 8.-66 8.86 8.92 On the other hand, a f t e r horizontal cracking was complete, and s l i p was v i s i b l e at the interface, re-loading with tensioned v e r t i c a l bars showed l i t t l e , v a r i a t i o n i n the depth of the neutral axis, thus, Moment i n kip f t . 4.97 8.23 12.12 17.31 Depth of N.A. from top i n i n s . 9.05 9.10 9.10 9.20 Also observed during the surface s t r a i n measurements was the prounced effect of cracks across the gauge locations. These cracks i n the prestressed member (see Fig.22) tended to form at the foot of the A9. c r a c k s i n the c a s t - i n - s i t u member, on account o f l o c a l s t r e s s c o n c e n t r a -t i o n s . As c o n c r e t e s t r a i n s are s m a l l , the micro-adjustments w h i c h are seen t o take p l a c e i n concrete even a t low l o a d s would tend t o v i t i a t e the d e t e r m i n a t i o n o f s t r e s s e s i n concrete on the b a s i s o f the measurements. ( F i g u r e 16) D e f l e c t i o n r e a d i n g s t a k e n w i t h the h e l p o f D i a l - g a u g e s d u r i n g the t e s t s show t h a t even a f t e r complete s l i p between p r e c a s t and c a s t - i n - s i t u c o n c r e t e , the d e f l e c t i o n c h a r a c t e r i s t i c s are u n a l t e r e d q u a l i t a t i v e l y as l o n g as the two p o r t i o n s a c t t o g e t h e r on subsequent l o a d i n g . S m a l l q u a n t i t a t i v e i n c r e a s e s i n t h e i r v a l u e s are however n o t i c e d on account o f the g r a d u a l r e d u c t i o n i n s t i f f n e s s o f the j o i n t . ( F i g u r e 17) F/G. /7 CHAPTER L CONCLUSIONS The technique developed for strain measurement i n concrete reinforcement, i n the form of a hollow tube, i s quite simple as compared to previous methods, on account of the use of Eastman 910 cement for bonding gauges, and a room temperature epoxy adhesive for joining the s l i t pipe, and would be quite useful i n fundamental studies of reinforced concrete behavior. However, close attention to the details of the tech-nique, and extreme care i n handling the gauges and leads are necessary to ensure accurate strain measurements. It i s perfectly reliable for instantaneous measurements at least up toa one and a half month period after the casting of concrete, and reasonably so for long term strain measurements extending over this period. If greater accuracy i n long term strain measurements i s 52. desired i t may be obtained by use of an elevated-temperature-curing epoxy adhesive l ike EPY-400, for bonding the gauges which is known to have better long term s tabi l i ty than the Eastman 910 cement. The formation of cracks in concrete affect the strain measurements greatly but indications are that the strains are regularised on higher or cyclic loading, on account of micro-adjustments in the concrete. Also, i t is noticed that transference of stress from the steel to the concrete i s affected by the quantity of concrete surrounding the steel; and in tensile specimen, causes major cracks at regular intervals. In a cast- in-situ joint between precast and prestressed members, composite action is found to take place even after complete horizontal s l ip at the interface, provided the cast- in-situ and precast syrfaces are prevented from further sl ipping. However at high loads, when slipping is allowed to occur, a different moment mechanism is formed. The forces in the stirrups necessary for this mechanism depend on the location of the active stirrups. Further studies in these directions is called for. BIBLIOGRAPHY 1. Sherlock, R.H. and Adil Belgin, "Protection of E l e c t r i c a l Strain Gauges i n Concrete," Journal of the American Concrete Institute. Proc. Vol. 44, Nov..'47, pp. 189 - 192. 2. Mchenry, Douglas and Walker, W.T., "Laboratory Measurements of Stress Distribution i n Reinforcing Steel," Journal of the American  Concrete Institute. Proc. Vol. 44» June '48, pp. 1041 - 1054' 3. Hondros, G., "The Protection and Manipulation of E l e c t r i c a l Resis-tance Strain-Gauges of the Bonded Wire Type for use i n Concrete, Particularly for Internal Strain Measurement," Magazine of Concrete Research. Vol 9, No. 27, Nov. '57, pp. 173 - 180. Discussion Vol. 10, No. 29, Aug. '58, pp. 98 -99. 4.. Mains, R.M., "Measurement of the Distribution of Tensile and Bond Stresses Along Reinforcing Bars," Journal of the American Concrete  Institute. Proc. Vol. 4-8, Nov. '51, pp. 225 - 252. 5. Thompson, J.N., "Techniques Used i n the Experimental Stress Analysis of Reinforced Concrete Structures," Society for Experimental  Stress Analysis. Proc. Vol. 8, No. 2, 1951, pp. I l l - 116. 6. Brice, L.P., "Liaison du Beton et du metal," Travaux. Paris. June, •49, pp. 260 - 264. 7. Wilkins, R.J., "Some Experiments on the Load Distribution i n Bond Tests," Magazine of Concrete Research. No. 5, Jan. 1951, pp. 65 - 72. 8. "Instructions for the use of Tatnall GA-1 Contact Cement Kit," Instruction Manual, BG-3100, Instruments Division, The Budd Company, P.O. Box 245, Phoenixville, Pa. 9. "Data Sheet - 3M Adhesive, EC-1751 Base, EC-1752 Hardener," Issue #2, Oct. 7, 1959, Minnesota Mining and Manufacturing Company. 10. Mylrea, T.D., "Bond and Anchorage," Journal of the American Concrete Institute. Proc. Vol. 44, Mar. '48, Discussion pp. 552 - 1, 552 - 4. ' 11. Guyon, Y., "Prestressed Concrete," John Wiley and Sons, Inc., New York, pp. 178 - 180. 12. Mathey, Robert G. and Watstein, David, "Investigation of Bond i n Beam and Pull-Out Specimens with High Yield Strength Deformed Bars." Journal of the American Concrete Institute. Proc. Vol. 57, March, '61, pp. 1071 - 1090. APPENDIX I DATA ON MATERIALS AND EQUIPMENT USED 55. T e s t s on 2 - p a r t Room Temperature C u r i n g  S c o t c h Weld Adhes ive - (EC 1751 / EC 1752) A b u t t i n g and shear j o i n t s were made u s i n g 3/4 i n . nominal d iameter s t a n d a r d p i p e , and t h e i r s t r e n g t h s t e s t e d , a p p l y i n g the adhes ive a f t e r c h e m i c a l c l e a n i n g as p e r the m a n u f a c t u r e r ' s Data sheet^, and a l s o a f t e r c l e a n i n g s i m p l y by " G h l o r o t h e n e . " Tes ts f o r w a t e r - p r o o f n e s s were a l s o p e r f o r m e d , by pumping a i r a t 25 p s i i n one o f the p i p e s , under w a t e r , but no leakage was observed. The t e s t s i n d i c a t e d t h a t adhesive a p p l i c a -t i o n a f t e r the s i m p l e s o l v e n t c l e a n i n g o f the s u r f a c e s gave adequate shear s t r e n g t h and w a t e r - p r o o f n e s s , e q u a l t o as t h a t a f t e r the r i g o r o u s c h e m i c a l c leaning.recommended. The s i m p l e r procedure was t h e r e f o r e adopted. (Table 7) The t e s t specimens were c u r e d a t room temperature and h u m i d i t y ( a p p r o x i m a t e l y 70° and 60$) f o r 92 h o u r s . 56. TABLE 7 Scotch Weld Adhesive - Test Results ABUTTING JOINT Ult.' Load lbs. Ult. Stress psi  Gleaning B area of ! j contact = .333 sq. i n . 140 area of contact = 1.03 sq. i n . 2465 420 2400 • C H E M I G A L SHEAR JOINT A B r IZ" 3500 area of contact := 2,71 sq. i n . immersed i n water 44 hours 2970 1290 1100 C H E M I C A L D E II immersed i n water 24 hrs. 3000 2780 3240 1110 1027 1190 C H L 0 R 0 T H E N E 57. /OO JOO soo A7AC A / / F/£Z> •SCALE FO R. 3T£>. PB O GOO 12 00 STRAIN IN MICRO-IM PER IN-STRESS-STRAIN CUR YE FOR 6TD. P/P£ AND SHEL&Y TUBING f / G . 18 200 ULTIMATE . L 0 M/XI CEMENT AGGREGATE WATER I 5 0.55 BY WT 400 800 'zoo STRAIN IN MICRO-IN PER IN. M/XI- STRESS-STRAIN. CUR YE ' USING C'CYL F/G. 2 0 60. /20-\ MIX JLT CEMENT AGGREGATE WATER I ' G,Z5 0.£S> BY WT. ULTMATE' LOAD = ///.S K/P6 4-00 800 ST RAM IN MICRO-IN. PER IN. R?/X H STRESS-STRAIN CURVE . USING G" CYL. FAG. 2/ 6 1 . Equipment Used S t r a i n Gauges and A c c e s s o r i e s : 1. SR-4. E t c h e d F o i l Gauges FA-50-12 f o r p i p e , # i n . gauge l e n g t h . 2 . T a t n a l l Gauges C6-141-B f o r R o d s , # i n . gauge l e n g t h . 3. SR-4 c o n s t a n t a n Wire G r i d Gauges A-9-4 f o r c o n c r e t e s u r f a c e . 2# i n . g . l t . 4-. P h i l l i p s TM S t y l e 19 C a b l e s made up o f 19G s o l i d p l a i n c o p p e r , each conductor p o l y e t h y l e n e i n s u l a t e d and p . v . c . j a c k e t e d - f o r l e a d s . 5 . " C h l o r o t h e n e " - s o l v e n t f o r c l e a n i n g . 6 . Transparent Adhesive Tape, B l a c k I n s u l a t i o n Tape, Emery P a p e r , D i j e l l - w a x , e t c e t e r a . S t r a i n Measur ing Equipment: 1. B a l d w i n Type K, and L , S t r a i n - I n d i c a t o r s . 2 . B a l d w i n 20 Channel S w i t c h i n g U n i t Model PSBA-20. 3 . SR-4 C a l i b r a t i o n U n i t , Gauge F a c t o r 2 .00 4. Leeds and Northrup 31-3 s e r i e s s i n g l e p o l e 1 2 - p o s i t i o n r o t a r y s w i t c h e s . H y d r a u l i c T e s t i n g Maahines: 1. B . T . E . 60 k i p s and 400 k i p s U n i v e r s a l T e s t i n g Machine . 2 . B a l d w i n S t r e s s S t r a i n R e c o r d e r . 3. O l s o n 200 k i p s U n i v e r s a l T e s t i n g Machine . APPENDIX I I 62; A d d i t i o n a l d e t a i l s o f J o i n t Test INSTRUMENTED HALF 2 J , si T3~ s1 • 8 \ { AO: 7"/7~r 4* 16 3' ' 26* 3 M £ 5 A/'£"£T EXT EH OS PARTLY TOP VIEW JOINT TEST . DIAGRAM SHOWING POSITION OF CRACKS AND StauENCE OF FORMAT/ON FIG 22 63. v.. 1 8 PAJXS STEEL H E 5"l 7@ J £ G/*6/6ifJ | 4-4-4-1—I—I—4 _f"~ ~ -fL L. "-fi 2" "4--f <i> 5" JOINT TEST i DIAGRAM SHOWING LOCATION OR GAUGES IN P/PE AND CONG. F/&. 23 

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