1996_Push-Out Tests on Studs in High Strength

8/9/2019 1996_Push-Out Tests on Studs in High Strength

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ELSEVIER

J. Construct. Steel Res. Vo l. 36, No. 1, pp. 15-2 9, 1996Copyright 1996 Elsevier Science L tdPrinted in Great Britain. All rights reserved0 1 4 3 - 9 7 4 X ( 9 4 ) 0 0 0 3 6 - 0 0 14 3-9 74 X/9 6 $ 15 .0 0 + 0 .0 0

P u s h - o u t T e s t s o n S t u d s i n H i g h S t r e n g t ha n d N o r m a l S t re n g th C o n c r et e

L i A n & K r i s t e r C e d e r w a l lD i v i s io n o f C o n c r e t e S t r u ct u r es , C h a l m e r s U n i v e r s i t y o f T e c h n o l o g y ,

4 1 2 9 6 G o t h e n b u r g , S w e d e n( R e c e i v e d 4 M a r c h 1 9 94 ; r e v i s e d v e r s i o n r e c e i v e d 29 J u n e 1 9 9 4; a c c e p t e d 1 2 A u g u s t 1 9 94 )

ABSTRACT

Som e te s t r e su l t s f ro m push-ou t t e s t s o f s tuds in normal and h igh s t r e ng th c on c re teare pre se n te d . I t i s fou nd tha t the c onc re te c ompre s s iv e s t r e ng th s ign i f i c an t ly a f fe c t sthe s t r e ng th o f the s tud c onne c t ions . Inc re ase o f the t ransv e r se r ein forc e me nt in thec onc re te s labs has a ne g l ig ib le e f f e c t whe n h igh s t r e ng th c o nc re te i s use d and someeffec t when normal concre te is used. The present des ign code is not adequate toe s t imate th e she ar s t r e ng th o f s tuds e mbe dde d in h igh s t r e ng th c o nc re te and i t i ssugge s te d tha t a de s ign form ula tha t tak e s ac c oun t o f the in te rac t ion be twe e n thes tuds and the sur round ing c onc re te shou ld be use d .

AsdEcEsfc,cubforefckfotfuhPPRdPu

N O T A T I O NC r o s s - se c t io n a l a r e a o f c o n n e c t o r sD i a m e t e r o f s tu d s h a n kM o d u l u s o f e la s ti c it y o f c o n c r e t eM o d u l u s o f e la s t ic i ty o f s t u d s te e lM e a n v a l u e o f c u b e c o m p r e s s i o n s t r e n g th o f c o n c r e t eM e a n v a l u e o f c y l i n d e r c o m p r e s s i o n s t r e n g t h o f c o n c r e t eC h a r a c t e r i s ti c c y l i n d e r s tr e n g t h o f c o n c r e t eM e a n v a l u e o f s p li tt in g t e n s i le s t r e n g t h o f c o n c r e t e c u b eT e n s i l e s t r e n g t h o f s t u d m a t e r i a lO v e r a l l h e i g h t o f st u dS h e a r l o a d o f s t u dS h e a r r e s i s ta n c e o f h e a d e d s t u dM e a s u r e d m a x i m u m l o a d p er s tu d

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16 Li An, K. Cederwall

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Push-out tests on studs in concrete 17I , k o lI I I I I I I I o t'

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Fig. 1. Details of specimens with tw o layers of the reinforcement mesh.w e l d c o l la r o f a ll 6 4 s tu d s w e r e m e a s u r e d . T h e m e a n v a l ue s o f th e h e i g h ta n d t h e d i a m e t e r o f t he w e ld c ol l ar s w er e 4 . 5 4 m m ( > 0 . 2 d = 3 . 8 m m ,i.e . m i n i m u m h e i g h t i n R e f. 2) a n d 2 3 .8 6 m m ( > 1 .2 5 d = 2 3 .7 5 m m , i .e . m i n i -m u m d i a m e t e r i n R e f . 2 ) , r e s p e c t i v e l y .P r o p e r t y o f m a t e r ia l sT h e t en :~ ile t e st s w e r e c a r r i e d o u t o n s t u d s o f t h e s a m e d i a m e t e r , b u t w i t hl e n g t h o f 2 0 0 m m . B o t h 7 5 a n d 2 0 0 m m s t u d s w e r e p r o d u c e d a t t h e s a m et i m e a n d w i t h t h e s a m e m a t e r ia l . T h e o u t s i d e o f t h e h e a d o f t h e s t u d w a st h r e a d e d , s o a s te el b a r c o u l d b e s c r e w e d t o t h e h e a d , a s s h o w n i nF i g . 2 (a). T w o s t r a i n g a u g e s w e r e p l a c e d o n t h e s h a n k o f t h e s tu d . T h em e a s u r e d r e s u l t i s s h o w n a s c u r v e A i n F i g . 2 ( b ) , w h i c h g a v e t h e y i e l ds t r e n g th a n d m o d u l u s o f e l as t ic i ty o f t h e s t u d . A t r a n s d u c e r w a s f ix e db e t w e e n t h e u p p e r a n d t h e lo w e r p la t es o f a t e st in g m a c h i n e t o m e a s u r et h e e l o n g a t i o n o f t h e s t u d. T h e m e a s u r e d r e s u l t is s h o w n a s c u r v e B i nF i g . 2(b ). T h e y i e l d s t r e n g t h o f t h e s t u d w a s d e f i n e d a s t h e s t re s s a t t h e0 . 2 % p e r m a n e n t s tr a in . T h e m e a n v a lu e s o f th e y i e ld s tr e n g t h , te n s il es t r en g t h , m o d u l u s o f e l as t ic i ty a n d t h e e l o n g a t i o n a t f r a c t u r e o f t h e s t u dw e r e d e t e r m i n e d t o b e 4 1 8 M P a , 5 19 M P a , 2 0 7 G P a a n d 1 0- 9% , r e sp e c t-iv e ly . I t s h o u l d b e n o t e d t h a t t h e o r ig i n a l g a u g e le n g t h f o r m e a s u r e m e n t o fe l o n g a t i o n is l o n g e r t h a n t h a t r e q u i r e d b y t h e S w e d i sh S t a n d a r d , 3 w h e r et h e g a u g e l e n g t h i s 5d ( = 9 5 m m ) . T h e r e f o r e , t h e e l o n g a t i o n o b t a i n e d i nt h i s t e s t w a s s o m e w h a t s m a l l e r t h a n t h e v a l u e m e a s u r e d a c c o r d i n g t o t h eS t a n d a r d .


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F i g . 2. M eas u r em en t o f t h e p r o p e r t y o f t h e s t u d . (a ) T es t s e t - u p an d m eas u r em en t .(b) S t r es s - s t r a in d iagra ms of the s tud in tens ion .

T h e c o n c r e t e u s ed i n th e N S C s p e c i m e n s w a s p r o v i d e d b y a r e a d y - m i xf a c to r y . F o r H S C s p e c i m e n s , t h r e e b a t c h e s o f c o n c r e t e o f t h e s a m e r e c i p ew e r e m a d e . S t a n d a r d c y l in d e r s ( d ia m e t e r = 1 5 0 m m a n d l e n g t h = 3 0 0 m m )a n d c u b e s ( l e n g t h = 15 0 m m ) w e r e c a s t a t t h e s a m e t i m e a s t h e p u s h - o u ts p e c i m e n s . T h e t e n s i le s t re n g t h o f c o n c r e t e w a s o b t a i n e d f r o m t h e c u b es p l i t t i n g t e s t . T h e c o m p r e s s i o n s t r e n g t h w a s o b t a i n e d f r o m b o t h t h ec y l in d e r a n d t h e c u b e c o m p r e s s i o n te sts . O n e c y l in d e r f r o m e a c h b a t c h o ft h e H S C s p e c i m e n s w a s u s e d t o d e t e r m i n e th e m o d u l u s o f e l as ti c it y o f t h ec o n c re t e . T h e t es t p r o c e d u r e w a s m a i n l y a c c o r d i n g t o t h e r e q u i r e m e n t s o ft h e S w e d i s h S t a n d a r d . 4 T h e m e a n v a l u e o f th e m o d u l u s o f e la s ti ci ty o f t h eH S C w a s m e a s u r e d t o b e 3 4.0 8 G P a .

L o a d i n g p r o c e d u re an d m e a s u r e m e n tT h e p u s h - o u t s p e c i m e n s w e r e te s t e d in a h y d r a u l i c t e st in g m a c h i n e w i th ac a p a c i t y o f 1 00 0 t o n s . T h e l o a d w a s f ir st a p p l i e d t o 4 0 % o f t h e e x p e c t e df a il u re l o a d w i t h a n i n c r e m e n t o f 5 0 k N , a n d t h e n c y c l e d 25 t im e s b e t w e e n5 a n d 4 0 % o f t h e e x p e c t e d fa i lu r e l o a d . A s u b s e q u e n t lo a d w a s t h e na p p l i e d a n d t h e f a il ur e o f th e s p e c i m e n o c c u r r e d i n a b o u t 3 0 m i n .

T h e l o n g i t u d i n a l r e l a t i v e s l i p b e t w e e n t h e s t e e l b e a m a n d t h e c o n c r e t es la b , t h e s e p a r a t i o n o f t h e c o n c r e t e sl a b s f r o m t h e s te e l b e a m a t t h ep o s i t i o n o f t h e s t u d s a n d t h e s t r a in s i n t h e r e i n fo r c e m e n t w e r e m e a s u r e d .P r o p e r t i e s o f t h e c o n c r e t e a t t h e t e s t in g d a y a n d t h e c y c li c l o a d a r e l i st e di n T a b l e 1. M o r e d e t a i ls a b o u t t h e t e st s c a n b e f o u n d i n R e f . 5.


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Push-out tes ts on s tuds in concrete

T A B L E 1

19

Tes t fc ,cub fc t f~m Ec De nsi ty Cycl ic loadn o . ( M P a ) ( M P a ) ( M P a ) ( G P a ) ( kg / m 3 ) ( kN )N S C 11 38"07 3"22 30 -77 27 .1 b 2354 50 - 40 0N S C 1 2 3 8" 73 - - 3 0- 77 a 2 7 . 0 b 2 3 4 7 4 5 - 3 6 0N S C 2 1 3 8" 73 - - 3 0- 77 a 2 7 . 0 b 2 3 4 7 4 5 - 3 6 0N S C 2 2 4 0 - 34 3 -3 1 3 1- 79 2 7 -4 b 2 3 4 4 4 5 - 3 6 0H S C l l 1 00 .1 1 5 . 20 8 6.1 1 3 4" 08 2 3 8 8 6 0 - 4 8 0H S C 1 2 9 5 .8 5 5- 66 8 1- 26 3 4 .0 8 2 3 8 6 5 0 - 4 0 0H S C 2 1 9 5" 85 5 .6 6 8 1 . 2 6 3 4- 08 2 3 8 6 6 0 - 4 8 0H S C 2 2 1 09 .3 3 6 ' 0 9 1 ' 2 4 3 4- 08 2 4 0 1 6 0 - 4 8 0

a T h e s a m e c y l i n d e r s t r e n g t h i s a s s u m e d f o r s p e c i m e n s N S C 1 2 a n d N S C 2 1 a s t h a t i ns p e c im e n N S C l l , b e c au s e t h ey w e r e t e st ed o n e d a y a f te r N S C l l .b E c w a s e s t i m a t e d f r o m t h e A C I f o r m u l a .

T E S T R E S U L T SC r a c k s

F o r N S C s p e ci m e n s , t h e m a x i m u m l o a d w a s o b t a i n e d w h e n c r a c ks w e reobse rve d [ a t t h e to p su r f a c e o f t he s l a b . Th e r e w a s a s l i gh t d i f f e r e nc e in thec r a c k d i s t r i b u t i o n b e t w e e n t h e s p e c i m e n s w i t h o n e l a y e r a n d w i t h t w ol a y e rs o f re i n f o r c e m e n t m e s h . T h e c r a c k a t t h e t o p s u r fa c e o f t h e s p e c i m e n sw i t h t w o l a y e rs o f r e i n f o r c e m e n t m e s h h a d a t e n d e n c y t o r u n p a r a l l el t ot h e l o n g e d g e o f t h e t o p s u rf a ce o f t h e s la b . T h e c r a c k s a l s o p r o p a g a t e d a tt h e s i d e s ur fa c e. F o r s p e c i m e n s w i t h o n e l a y e r o f re i n f o r c e m e n t m e s h , t h ec r a c k s a t t h e t o p s u r fa c e h a d a t e n d e n c y t o d e v e l o p a r o u n d t h e st u d s .D a m a g e o f t h e c o n c re t e w a s c o n c e n t r a t e d m a i n l y t o t h e ar e a a r o u n d t h es t u d s .I n t h e t e st o f H S C s p e c im e n s , t h e l o a d i n g e n d e d w h e n o n e o f t h e t w os l ab s s e p a r a t e d f r o m t h e s t ee l b e a m . F r a c t u r e o f t h e s t u d s o c c u r r e d a f t e rt h e m a x i m u m l o a d w a s r e a c he d . N o c r ac k s o n t h e o u t s id e s u rf ac e o f t h ec o n c r e t e s l a b f o r m e d d u r i n g l o a d i n g . A f t e r t h e t e s t , s e v e r a l v e r y s m a l lc r a c k s ( w i d t h ~


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2 0 Li An, K. Cederwall

Strain m easurement in reinforcementS t r a i n s i n t h e r e i n f o r c e m e n t w e r e m e a s u r e d d u r i n g t h e t e st . F i g u r e 3 g i ve st h e m e a s u r e d s t r a i n s f o r t h e s p e c i m e n H S C 2 1 , w h e r e t w o l a y e r s o fr e i n f o r c e m e n t m e s h w e r e u s ed . T h e r e su l ts s h o w e d t h a t t h e s t r a in o f t h eb o t t o m r e i n f o r c e m e n t w a s g r e a t e r t h a n t h a t o f t h e to p r e i n f o r c e m e n t a t t h ec o r r e s p o n d i n g p o s i ti o n s; t hi s in d i c a t e d t h a t t h e b o t t o m r e i n f o r c e m e n tt o o k m o r e l o a d t h a n t h e t o p r e i n f o r c e m e n t . T h e r e s u l ts a l so s h o w e d t h a tt h e s t r a i n a t p o s i t i o n 1 w a s v e r y s m a ll . G e n e r a l l y , t h e s t r a i n s i n th er e i n f o r c e m e n t w e r e a t a r a t h e r l o w le v el b e f o r e t h e m a x i m u m l o a d , w h i c hi n d i c a t e d t h a t t h e e ff e ct o f t h e r e i n f o r c e m e n t w a s m a i n l y t o c o n f i n e t h ec o n c r e te . T h e s a m e o b s e r v a t io n s w e r e o b t a i n e d f r o m t h e N S C s p e c im e n s .Load-sl ip diagrams and separationA s lip b e t w e e n t h e s te el b e a m a n d t h e c o n c r e t e s la b s o c c u r r e d w h e n t h el o a d w a s a p p l i ed . T h e m a x i m u m i n c r e a se o f s lip d u e t o 2 5 l o a d c y c le s w a s0-13 m m f o r N S C a n d 0 .0 5 m m f o r H S C s p ec im e n s . T h e m e a s u r e d l o a d -s li p c u r v e s a r e s h o w n i n F i g . 4 . I t c a n b e s e e n t h a t t h e s li p a t th e m a x i m u m

Load [kN]

~8p f8 0 ~ J ~ 2 ~ - ~ ~ >/ / / - ~ ~ t ~oa:on/ " '

I ~ j ~ ~) * Position , bo,40 ~ / ~ Position , o p

-0,2 0 0,2 0,4 0,6 0,8 1 1,2 1,4Strain% o ]Fig. 3. Load-strain curves of the specimen HS C21; to p= measurem ent from the top layerof the reinforcement mesh and bot---measurement from the bottom layer of the reinforce-ment mesh.


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Push-out tests on studs in concrete 21

L o a d [ k N ]'160

'120

8 0 .

4 0 . ~ o I -I S C 1 1~ H S C 1 2

00 2 4 6 8 10 12 14

Average Sl ip [mml( a )

Load [ k N l'180

"135

45H S C 2 2

0 I I I I I I I I I

0 2 4 6 8 1 0 1 2 1 4 1 6 1 8Average S l i p [ m m ]

( b )Fig. 4 . Lo ad-s l ip d iagrams of the specimens . (a) Specimens wi th on e layer of re inforcementmesh. (b) Specimens with tw o layers of reinforcem ent mesh.load was of the same order of magnitude for both NSC and HSCspecimens, ranging from 3.5 to 6"0 mm. The NSC specimens were subjec-ted to additional loading and deformation after the maximum load wasreached. Very ductile behaviour of the studs was observed. In the HSCspecimens, however, the studs were sheared-off from the steel beam afterthe max imum load and the descending branch of load-slip curve was steepand short.

The separation of the slabs from the steel beam was measured. Theamount of separation at the maximum load was also on the same level forboth NSC and HSC specimens, ranging from 0"4 to 1.3 mm.


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F a i lu r e m o d e s o f s tu d sS o m e o f t h e s t u d b r o k e d u r i n g t h e t es t i n b o t h N S C a n d H S C s p e ci m e n s.I n N S C s p e c i m e n s , 11 f r a c t u r e d s t u d s w e r e e x a m i n e d . E i g h t o f t h e mf r a c t u r e d i n th e s h a n k o f t h e s t u d a n d t h r e e o f t h e m f r a c t u r e d i n th ew e l d i n g z o n e . I n H S C s p e c i m e n s , six o f t h e e i g h t c o n c r e t e s la b s w e r es e p a r a t e d f r o m t h e s t e el b e a m i n th e t e st . N i n e t e e n o u t o f 24 s t u d sf r a c t u r e d i n t h e s h a n k , m o s t l y a t t h e fa c e b e t w e e n t h e s h a n k o f t h e s t u da n d t h e w e l d c o l la r . F i v e s t u d s f r a c t u r e d a t t h e w e l d i n g z o n e . F i g u r e 5s h o w s t h e d e f o r m a t i o n o f t h e s t u d s i n t h e c o n c r e t e s la b . M u c h s m a l l e rd e f o r m a t i o n o f t h e s tu d w a s o b s e r v e d i n th e H S C s p e c im e n t h a n i n th eN S C s p e c i m e n .

M a x i m u m l o a dT h e c o n c r e t e s t re n g t h h a d g r e a t e ff ec t o n t h e l o a d - b e a r i n g c a p a c i t y o f t h es pe c im e n s. T h e m a x i m u m l o a d o f H S C s p e ci m e n s w a s a b o u t 3 4 % h i g h e rt h a n t h a t o f N S C s p e c im e n s , as i n d i c a te d i n T a b l e 2 . T h e s p e c im e n s w i t ht w o l a ye r s o f r e i n f o r c e m e n t m e s h h a d s li g ht ly h i g h e r c a p a c i t y t h a n t h o s ew i t h o n e l a y e r i n N S C s p e c i m e n s . T h e i n c r e a s e w a s a b o u t 6 % . H o w e v e r ,

H S C 2 2

(a) (b)F i g . 5 . D e f o r m a t i o n a n d f r a c t u re o f s t u d s i n t h e c o n c r e te . (a ) S t u d i n t h e N S C s p e c im e n . (b )

S t u d i n t h e H S C s p e c i m e n .


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Push-out tes ts on s tuds in concrete

T A B L E 2

23

Test Pu P R d l P R d 2 P~ P 61 a ~2 g3 ano. (kN ) eqn (1) eqn (2) (kN ) eqn (3)( k N ) ( k N ) ( k N )

N S C l l 1 1 5 " 0 1 0 3 " 0 9 4" 6 1 31 '1 1 30 '7 0 ' 1 0 4 0 " 1 7 7 0 " 00 3N S C 1 2 1 11 '5 1 0 3 " 0 9 4 ' 4 1 27 '1 1 3 1 " 3 0 "0 7 6 0 " 1 5 3 - 0 - 0 3 3NS C2 1 120'8 103'0 94 '4 137'7 131'3 0-147 0 '219 0-047NS C2 2 119'1 10 3"0 96"7 135 '8 134 '0 0 -135 0" 18 8 0 '013HS C 11 156 "8 103 '0 117 '7 178'8 201-0 0 " 3 4 3 0" 24 9 - 0" 124H S C 1 2 1 5 8 " 6 1 0 3'0 1 17 -7 1 80 -8 1 9 8 " 0 0 " 3 5 1 0 '2 5 8 - 0 " 0 9 5HSC 21 151 "9 10 3"0 117-7 173"2 198 "0 0 '322 0-225 -0" 14 3H S C 2 2 1 6 1 " 0 1 0 3 " 0 1 17 -7 1 83 '5 2 07 "3 0" 36 0 -2 69 - 0 " 1 3 0

a 61 = (Pu - PR dl)/Pu, 6 2 = ( P u - - P R d 2 ) / P u , ~3 = ( P " -- P ) / P ' .n o o b v i o u s d i ff e re n c e i n th e c a p a c i t y d u e t o t h e a m o u n t o f r e i n f o r c e m e n ti n t h e s l a b s w a s f o u n d i n t h e H S C s p e c i m e n s .

E V A L U A T I O N O F T E S T R E S U L T SS h e a r r e s i s t a n c e o f s tu d s

I n t h e 1 98 5 d r a f t o f E u r o c o d e 4 , 6 t h e s h e a r r e s i s t a n c e o f a h e a d e d s t u d isd e t e rm i n e d b y

( l a )

PR O =0 "36 ctd 2 f~x/f~kE~ 1 (l b )])vcw h i c h e v e r i s s m a l l e r . T h e p a r t i a l s a f e t y f a c t o r 7va s h o u l d b e t a k e n a s 1 .2 5a n d 7v a s 1 .5 f o r t h e u l t i m a t e l i m i t s t a t e .

I n t h e l a t es t p r o p o s a l o f E u r o c o d e 4 , 2 t h e s h e a r r e s i s ta n c e o f a h e a d e ds t u d i n a s o li d s l a b is d e t e r m i n e d b y

C z d 2 ) 1P R d = 0 " 8 f u T 7v (2a )

P , a = 0 " 2 9 ~ d z f ~ c k E i (2b)7v


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2 4 Li An, K. Cederwall

w h i c h e v e r i s s m a l l e r . T h e p a r t i a l s a f e ty f a c t o r 7v s h o u l d b e t a k e n a s1 .25 .

O e h l e r s a n d J o h n s o n p r o p o s e d o n e f o r m u l a to i n c lu d e c o n t r i b u t i o n sf r o m b o t h s t u d s a n d c o n c re t e. 7 T h e m e a n s t r e n g th o f s t u d c o n n e c t o r s i nt h e p u s h - o u t s p e c i m e n s c o u l d b e d e t e r m i n e d b y

P = 5"O A s f " \ K , / \ f u ,] (3 )

w h e r e f c u i s t h e c u b e s t r e n g th .T o t h e w r i t e r s ' k n o w l e d g e , t h e r e i s, a s y e t, n o f o r m u l a t h a t i s s p e c i a l ly

u s e d f o r s t u d s i n h i g h s t r e n g t h c o n c r e t e . W e u s e d t h e a b o v e e q u a t i o n s t oe s t i m a t e t h e s h e a r r e s i st a n c e o f s t u d s , a l t h o u g h t h e y w e r e b a s e d o n t e st s o fs p e c i m e n s w i t h n o r m a l s t r e n g t h c o n c r e t e . T h e p a r t i a l s a f e ty f a c t o rs w e r et a k e n a s 1 .0 i n t h e c a l cu l a ti o n . T h e m e a s u r e d s t r e n g t h a n d t h e m o d u l u s o fe l a s t i c it y o f t h e m a t e r i a l s w e r e u s e d ; 6i d e n o t e s t h e r e l a t iv e d e v i a t i o nb e t w e e n m e a s u r e d a n d c a l c u la t e d s t re n g th s . T h e r e s u lt s a re s u m m a r i s e d i nT a b l e 2. B e c au s e t h e m o d u l u s o f e la s ti ci ty o f t h e N S C w a s n o t m e a s u r e d , i tc a n b e e s t i m a t e d f r o m t h e A C I f o r m u l a : E c = 3 3 o9 15 x / ~ , w h e r e co i s t h e u n i tw e i g h t o f t h e c o n c r e t e i n p c f a n d f~ is t h e c y l i n d e r s t r e n g t h i n p s i. a T h em e a s u r e m e n t o f t h e m o d u l u s o f e la s ti ci ty w a s c a r r ie d o u t i n o u r l a b o r a t o r yf o r c o n c r e t e o f g r a d e K 4 0 . T h e m e a s u r e d E c w a s 2 9 .2 G P a w h e n t h e c y l i n d e rc o m p r e s s i o n s t r e n g t h a n d t h e d e n s i ty o f c o n c re t e w e r e e q u a l t o 3 6.9 M P aa n d 2 3 4 0 k g / m 3, r e s p e c t iv e l y . 9 I f t h e A C I f o r m u l a w a s u s e d i n t h i s c a s e, i tg a v e t h e e s t im a t i o n , E = 2 9.4 G P a . R a t h e r g o o d a g r e e m e n t b e t w e e n t h ee s t i m a t e d a n d t h e m e a s u r e d v a l u e w a s o b t a i n e d . T h e r e f o re , t h e A C I f o r m u l aw a s u s e d f o r t h e N S C s p e c i m e n s . T h e e s t i m a t e d E is li s te d in T a b l e 1.

A s s h o w n i n F i g . 6 , t h e e x p r e s s i o n s i n e q n s ( 1 ) a n d ( 2 ) d e f i n e t h e u p p e rl im i t f or t h e s h e a r r e s i s t a n c e o f s t u d c o n n e c t o r s . T h e e s t i m a t i o n f r o me q n (1 ) u n d e r e s t i m a t e d t h e s h e a r r e s i s ta n c e o f s t u d s b y a b o u t 1 1 % f o rN S C s p e c i m e n s a n d b y a b o u t 3 4 % f o r H S C s p e c im e n s . E q u a t i o n ( 2), f r o mt h e l at e st p r o p o s a l o f E C 4, u n d e r e s t i m a t e d t h e s h e a r r e s is ta n c e b y a b o u t1 8 % f o r N S C s p e c i m e n s a n d b y a b o u t 2 5 % f or H S C s p e c im e n s . T h ed if fe re n c e b e t w e e n H S C a n d N S C s p e c i m e n s o n t h e s af et y m a r g i n h a sb e e n i m p r o v e d i n t h e l a t t e r ca s e. T h e m a i n s h o r t c o m i n g o f e q n s (1 ) a n d (2 )is t h a t t h e s h e a r r e s i s t a n c e o f t h e s t u d i s d e t e r m i n e d s e p a r a t e l y b y t h ec o n c r e t e o r b y t h e s t u d. T h e i n t e r a c t io n b e t w e e n t h e t w o m a t e r i a ls h a s n o tb e e n t a k e n i n t o a c c o u n t i n t h e se e q u a t i o n s .

E q u a t i o n (3 ) w a s d e r i v e d f r o m t e st s o f 1 00 m m s t u d s. T h e s t r e n g t h o f1 00 m m s t u d s w a s a b o u t 1 4 % h i g h e r t h a n t h a t o f 7 5 m m s tu d s , a s s h o w ni n t h e B r i ti sh S t a n d a r d f o r C o m p o s i t e S t r u c t u r e s } T h e r e fo r e , to m a k e it


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1 5 0

1 0 0

5 0

@@@

0 5 0 0 1 0 0 0

NS C specimens H S C specimens

. . . . Eq . {11Eq . 12 )

i i i1 5 0 0 2 0 0 0 2 5 0 0

Fig. 6. Test results and EC 4 formulae.c o m p a r a b l e w i th c a l c u l a t e d r es u lt s f ro m e q n ( 3 ), t h e m e a s u r e d l o a d p e rs t u d , P u , w a s i n c r e a s e d b y 1 4 % , d e n o t e d a s P 'u i n T a b l e 2 . T h e c o m p a r i s o ns h o w e d t h a t a n e s t i m a t i o n b a s e d o n e q n ( 3 ) a g r e e d w e l l w i t h t h e t e s tr e s u lt s f o r N S C s p e c i m e n s , b u t o v e r e s t i m a t e d t h e s t r e n g t h o f t h e s t u d s b ya b o u t 1 2 % f o r H S C s p e c im e n s . T h i s f o r m u l a c o m b i n e s c o n t r i b u t i o n s f ro mb o t h s tu d s a n d c o n c r e te , c o u l d t a k e i n t o a c c o u n t t h e i n c r ea s e o f c o n c r e t es t r e n g t h a n d o b t a i n r e a s o n a b l e r e s u l t s f o r b o t h N S C a n d H S C s p e c i m e n s .I t i s a l s o o b v i o u s t h a t t h e e s t i m a t i o n c a n b e i m p r o v e d b y c h a n g i n g t h ep a r a m e t e r s i n t h e f o r m u l a , w h i c h c a n b e a c h i e v e d b y r e g r e s s io n o f th e t es tr e s u l t s f r o m h i g h s t r e n g t h c o n c r e t e .L o a d - s l i p r e l a t i o n s h i p s

T h e m e a s u r e d l o a d - s l i p c u r v e s h a d s im i l a r sh a p e s f o r th e s a m e t y p e o f t h ec o n c r e t e . T h e c u r v es a f te r t h e c y c l ic l o a d w e r e n o n - d i m e n s i o n a l l y d r a w n i nF i g . 7. A n e m p i r i c a l f o r m u l a f o r th e l o a d - s l i p r e l a t i o n s h i p o f c o n t i n u o u s l yl o a d e d : sp ec im en s wa s p ro p o s ed i n R ef. 1 1 .

P- - = ( 1 - e - 1 8 s ) 0 . 4 ( 4 )PuT h e l o a d - s l i p r e l a t i o n s h i p f o r t h e r e l o a d i n g c o n d i t i o n w a s p r o p o s e d i n

R ef . 1 2 an d a l s o c i t ed i n R ef . 1 1 . Th e ex p res s i o n i sP 80sPu - 1 + 80s (5)


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2 6 Li An, K. Cede rwa l l

P/Pu

1 .~...~.-..-7~..

' x . s c 2 2o,,/,;,? . . . .

0 v i ~ I0 2 4 6S l i p [ m i n i(a )

P/Pu1 ~ ~ ~ . . - - - - . . -

I" " H S C 2 20 , 4. . . . E q . ( 4 )

0 , 2 . . . . . . . E q . ( 5 )- - E q . ( 6 b )0 p ~ t

0 2 4 6S l i p [ m m ]( I , )

F i g . 7 . T e s t r e s u lt s a n d r e g r e s s i o n c u r v e s. ( a ) N S C s p e c i m e n s . (b ) H S C s p e c i m e n s .I n e q n s ( 4) a n d (5 ), s i s th e a v e r a g e s l ip i n in c h e s . T w o f u n c t i o n s a r ec o m p a r e d w i t h t h e m e a s u r e d r e su l ts in F ig . 7(a ) f or N S C s p e c i m e n s a n d i nF i g . 7( b) f o r H S C s p e c i m e n s .

I n o u r t e st s , t h e c y c li c l o a d i n g p r o d u c e d s l ip b e t w e e n t h e c o n c r e t e s l a b sa n d t h e st ee l b e a m . T h e a m o u n t o f s l i p w a s g r ea te r in N S C s p e c i m e n st h a n i n H S C s p e c i m e n s . T h i s r es u l te d i n d i f fe r e n ce s i n t h e b e g i n n i n gb r a n c h b e t w e e n t h e m e a s u r e d a n d e s t i m a t e d c u r v e s f r o m e q n s (4 ) a n d(5 ). T h e e s t i m a t i o n b a s e d o n e q n (5 ) u n d e r e s t i m a t e d t h e sh e a r c a p a c i t yf or b o t h H S C a n d N S C s p e c i m e n s . B a s e d o n o u r te s t re s u l ts , a n o n - l i n e a r


13/15


r e g r e s s i o n w a s c a r r i e d o u t . T h e m e a s u r e d v a l u e s b e f o r e a n d a t t h em a x i m u m l o a d w e r e u s ed i n t h e a n a l y si s. T h e e x p re s si o ns o f t h e l o a d - s l i pr e l a t i o n s h i p a f t e r t h e c y c l i c l o a d a r e g i v e n b y

P 2 "2 4 ( s - 0 "0 58 )P---~ = 1 + 1"98(s-0 "05 8) for N S C s pe cim en s (6a)

P 4.44(s - 0.031)P u 1 + 4 . 2 4 ( s - 0 . 0 3 1 ) f o r H S C s p e c i m e n s (6b)

w h e r e s i s t h e s l i p i n m m . T h e e x p r e s s i o n s a r e s h o w n i n F i g . 7 w i t h s o l i dl in es . I t ca n b e s een t h a t eq n (6a ) s l i g h t ly u n d e res t i m a t e d t h e s l ip d u e t o t h ec y c l ic l o a d i n g a n d o v e r e s t i m a t e d s l i g h tl y th e c a p a c i t y o f t h e s t u d s a f te r t h es li p o f 4 m m . I t g iv e s b e t t e r e s t i m a t i o n o f l o a d - s l i p r e l a t i o n s h i p s t h a n e q n s(4 ) a n d ( 5) . F o r t h e h i g h s t r e n g t h c o n c r e t e , e q n ( 6 b) g iv e s g o o d a g r e e m e n twi th t es t resu l t s .

S U M M A R YT h e c o n c r e t e s t r e n g t h s i g n if i c a n tl y a f f ec t e d th e s h e a r r e s i st a n c e o f s t u dc o n n e c to r s . T h e i n c re a s e o f t h e m a x i m u m s h e a r lo a d w a s a b o u t 3 4 % w h e nt h e c y l i n d e r c o m p r e s s i v e s t r e n g t h o f t h e c o n c r e t e i n c r e a s e d f r o m 3 0 to81 M P a . T h e t es t s h o w e d t h a t t h e a m o u n t o f s li p a t t h e m a x i m u m l o a dw a s o n tlh e s a m e l e v el f o r b o t h N S C a n d H S C s p e ci m e n s. H o w e v e r , d u c ti leb e h a v i o u r o f t h e s t u d s w a s o b s e r v e d f o r th e N S C s p e c im e n s a f te r t h em a x i m u m l o a d . T h e d e s c e n d i n g b r a n c h o f t h e l o a d - s l ip c u r v e s fo r t h e h i g hs t r e n g t h c o n c r e t e w a s s h o r t a n d s te e p.

T h e r e i n f o r c e m e n t in c o n c r e t e s la b s d i d n o t t a k e v e r y m u c h l o a d , b u tc o n f i n e d t h e c o n c r e t e s u r r o u n d i n g t h e s tu d s. T h e a m o u n t o f r e i n f o r c e m e n ti n th e c o n c r e t e s l a b h a d a s li g h t i n f lu e n c e o n t h e l o a d c a p a c i t y o f t h e N S Cs p e c im e n s . T h e i n c r e a s e w a s a b o u t 6 % . N o o b v i o u s i n f lu e n c e o f r e in f o rc e -m e n t o n t h e c a p a c i t y w a s o b s e r v e d i n t h e H S C s p e c i m e n s .

E v a l u a t i o n o f s h e a r r e s is t a n c e o f t h e s t u d s a c c o r d i n g t o d i f f e r e n tf o r m u l a s s h o w e d t h a t t h e f o r m u l a w h i c h c o m b i n e d c o n t r i b u t i o n s f r o mb o t h c o n c r e t e a n d s t u d s c o u l d t a k e v a r i a t i o n o f th e c o n c r e t e s t re n g t h i n t oa c c o u n t a n d g i v e a b e t t e r e s t i m a t i o n o f t h e s h e a r r e s i s t a n c e o f s t u d s.

T h e l o a d - s l i p r e l a t i o n s h i p a f t e r th e c y c l ic l o a d i n g c a n b e e x p r e s s e d a sP 2 . 2 4 ( s - 0 .0 58 )P , 1 + 1 . 9 8 ( s -0 . 0 5 8 ) f o r N S C s p ec im e n s a n d


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28 Li An, K. CederwallP 4-44(s - - 0 .031)

P u 1 + 4 . 2 4 ( s - - 0 - 0 3 1 ) f or H S C s p e c im e n s ,

w h e r e P i s t h e l o a d a n d s i s t h e s l i p i n m m .M o r e t e s t s a r e n e e d e d t o e s t a b l i s h a p r o p e r d e s i g n e q u a t i o n f o r s t u d se m b e d d e d i n h ig h s tr e n g t h c o n c re t e a n d t o u n d e r s t a n d t h e i r b e h a v i o u rb e t t e r .

A C K N O W L E D G E M E N T ST h e r e se a r ch r e p o r t e d h e r e w a s s p o n s o r e d b y t h e F o u n d a t i o n f o r S w e d is hC o n c r e t e R e s e a r c h a n d t h e S w e d i s h C o u n c i l f o r B u i l d i n g R e s e a r c h . W ew o u l d a l s o li k e t o e x p re s s o u r t h a n k s t o M r J. H e d i n a t S S A B , t o M r B .J ~ ig e n st ed t a t B u l t s v e t s t e k n i k A B a n d t o M r H . L i n d b l a d a t T i b n o r A B fo rt h e i r a ss i s ta n c e d u r i n g t h e p r e p a r a t i o n o f t h e s p e c i m e n s . V a l u a b l e c o m -m e n t s f ro m P r o f e s so r R . P . J o h n s o n a t t h e U n i v e r s it y o f W a r w i c k i nE n g l a n d , D r D . J . O e h l e r s a t t h e U n i v e r s i t y o f A d e l a i d e i n A u s t ra l i a ,P r o f e s s o r B . J o h a n s s o n a t L ule ~t U n i v e r s i t y o f T e c h n o l o g y i n S w e d e n a n dP r o f e s s o r B . E d l u n d a t C h a l m e r s U n i v e r si t y o f T e c h n o l o g y ar e a p p r e -c i a t e d .

R E F E R E N C E S1. Editor ia l Panel for EC 4, 1990.2. EECS, Compos i te Beams and Columns to Eurocode 4 . E CCS- T e c h n ic a l Co m -mi t tee 11, Co m pos i te Con s t ruc t ion , 1993.3 . Svensk Standa rd SS -EN 10002-1 , M arch 1990 .4 . Sv e n s k S ta n d a r d SS 1 3 7 2 3 2, Be to n g p r o v n in g me d Sv e n s k S t a n d a r d , BST H b

12, April 1987.5. An, L. & Cederwall, K. Push Tes t s on S tud Connec tor in Normal and HighStrength Concrete . Divis ion o f Concre te S t ruc tu res , Cha lmers Unive r s i ty o fTechn ology , Sweden , Re por t 91 :6 , N ove m ber 1991 .6 . E u r o c o d e 4 . Co mmo n U n i f i e d Ru le s f o r Co mp o s i t e S t e e l a n d Co n c r e t eStructures , 1985.7 . Oehle rs , D . J . & Joh nson , R. P . Th e s t r eng th o f s tud shea r conne c t ions inc o mp o s i t e b ea ms . Struct. Engr, 6511(2) (Jun e 1987) 44-48.8. ACI, A C I M anu al o f Concre te Prac t ice 1993 . Par t 1 : Ma ter ia l and GeneralProper t ies o f Concrete, 1993.9. Claeson, C. , Re in forced H igh S t rength and No rma l S t rength Concre te Columns:An Exper imenta l S tudy . Divis ion o f Co ncre te S t ruc tu res , Cha lmers Unive r s i tyof Tech nology , Sweden , M arch 1994 .


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Push-out tests on studs in concrete 2910. BSI, St ruc tura l U se o f S t ee lw ork in B u i ld in ff . P a r t 3 : D es ign in C om p os i t eC ons t ruc t ion . Bri t ish S tan da rd Ins t i t u t ion , BS 5900 , Sec t ion 3 .1 , 1990.11. Ol lgaard , J . G. , Slutter , R. G. & Fisher , J . W., Sh ear s t ren gth o f s tudsc o n n e c t o r s i n l i g h t we i g h t a n d n o r m a l - we i g h t c o n c r e t e . A I S C E n o n g J . , 8

(April 1971) 55-64.12. Bu t t ry , K. E . , Beh av iour o f s tud con nec to r s i n l igh twe igh t and norm a l -we igh t conc re t e . M.S . Thes i s (unpub l i shed) , Unive rs i ty o f Missour i , USA,Augus t 1965 .

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