verification of load deflection

8/11/2019 verification of Load deflection

1/15

V e r i fi c a t io n o f lo a d

d i s t r i b u t i o n a n d s t r e n g t h o f

s e g m e n t a l p o s t t e n s io n e d

c o n c r e t e b r i d g e s

J E B r e e n

Department of C ivil Engineering, U niversity of Texas at Austin, USA

S K a s h i m a

Honshu-Shikoku Bridge Authority , Japan

Th is paper ou t l i nes t he us e o f s ev era l c ompute r p rog rams o r i g i na l l y

dev e loped by P ro fes s or A . C . Sc orde l i s f o r p red i c t i on o f l oad d i s tr i bu -

t i on de f l ec t i ons and k ey i n t e rna l s t res s es i n s egm enta l l y c on-

s t ruc ted pos t - t ens ioned box g i rde r b r i dges . C ompar i s on w i t h ex per i -

men ta l res u l t s s ho w s genera l l y ex c e l l en t ag reem ent ev en fo r h i gh l y

non-s y mmet r i c a l l i v e l oad p lac ement . I n add i t i on p roc edures f o r

e s t im a t i n g t h e s tr e n g t h o f s u ch s t ru c t u r e s i n c lu d i n g m o m e n t

red i s t r i bu t i on a re i nc l uded .

Keywords pos t - t ens ion ed box g i rde r b r i dges l oad d i s t r i bu t i on

s t r e n g t h

Ove r t he l a s t 20 ye a r s , c ons ide r a b l e r e se a r c h on pos t -

t e ns ione d se gm e nta l l y c ons t r uc t e d box g i r de r b r idge s

ha s be e n c a r r i e d ou t a t T he Unive r s i t y o f T e xa s a t

Aus t i n . D ur ing t h i s pe riod e x t e ns ive use ha s be e n m a de

of se ve r a l box g i r de r a na lys is p r ogr a m s o r ig ina l l y de ve -

lope d a t t he Un ive r s i ty o f Ca l i f o r n i a a t B e r ke l e y by P r o-

fessor A. C. S corde l i s and severa l of his s tudents . W hi le

som e of t h i s m a te r i a l ha s be e n p r e v ious ly r e por t e d i n

l imi ted c i rcula t ion repor ts *'z and unpu bl ished disser ta -

t ions 3 4, the auth ors fe l t it w ould be e xt rem ely useful to

the de s ign p r of e ss ion t o p r e se n t a b r i e f sum m a r y i n a

m or e w ide ly a c c e ss ib l e j our na l . I n a dd i t ion , t he a u thor s

fee l it i s a f i tt ing t r ibute to Profe ssor Sco rde l i s wh o has

a lwa ys be e n m os t w i l l i ng t o sha r e h i s knowle dge a nd

ass is t other invest iga tors in any way poss ible .

T he m a jor phys i c a l i nve s t i ga t i on r e por t e d he r e t ook

place in the ear ly 1970s and has been a corners tone in

subse que n t use o f c a n t i le ve r se gm e nta l c ons t r uc t i on f o r

box girder br idges . The PrOtotype s t ruc ture which was

model led in the physica l tes t s was recent ly inspec ted by

the Cons t r uc t ion T e c hn ology L a bor a to r ie s a nd f ound to

be i n e xc e l l e n t sha pe 5 w i th no e v ide nc e o f j o in t ope n-

ings o r c or r os ion . T h i s a ga in i s a ve r y f a vour a b l e r e f l e c -

t i on on t he ove r a l l de s ign whic h be ne f i t t e d f r om the

c o m p r e h e n s i v e c o m p u t e r a n a l y s i s ( S I M P L A 2 ) d e v e l -

ope d by Br own 4 ( us ing a s a ba s i s P r of e s sor Sc or de l i s '

S I M P L A pr og r a m ) . T h i s p r ogr a m wa s use d to c he c k t he

or ig ina l de s ign be f or e c ons t r uc t i on . T he c ons t r uc t i on

0141 0296191/020113 15

1 9 91 B u t t e r w o r t h H e i n e m a n n L id

a nd the b e ha v iour o f t he b r idge g r e a t ly be ne f i t t ed f r om

the e xc e l l e n t m ode l s t udy by Ka sh im a 3 whic h ve r i f i e d

the a de qua c y o f t he de s ign unde r c ons t r uc t i on l oa ds ,

se r v i c e l oa ds , m o de r a t e ove r loa ds , a nd u l t im a te . T h i s

e xpe r im e nta l s t udy wa s he a v i ly de pe nd e n t on P r of e s sor

Sc or de l i s ' p r ogr a m M UPDI f o r t he i n t e r p r e t a t i on o f

be ha v iour .

I n t he pa s t two de c a de s , subs t a n ti a l use ha s be e n m a de

of p r e c a s t a nd c a s t - i n - p l a c e box g i r de r b r idge s e r e c t e d

us ing c a n t i l e ve r ing t e c hn ique s . I n t h i s c ons t r uc t i on

m e thod , p r e c a s t s e gm e nt s Figur e ] a) ) a r e c a s t a nd

t r a nspor t e d t o t he b r idge s i t e . Af t e r a pp l i ca t ion o f e poxy

jointin g ma terial the precast segments are erected as

shown in

F i g u r e l b ) ,

as balanced cantilevers from the

pier segment wh ich is rigidly connected o the pier either

temp orarily or perma nently. As ea ch pair o f segments is

positioned at the ends o f the balanced cantilever nega-

tive mo me nt tendon s are inserted and tensioned. These

tendons must provide moment capacity for the ful l

cant ilever m oment. E rect ion continues unt il the last

cantilevered sections are p laced at the ce ntre of the span

a nd a t t he e nd suppor t s , a s shown in Figure 1 c ) . T h e

pos i t ive m om e nt t endons i n t he e nd spa n a r e p r e s t r e s se d

a nd the e nd se gm e nt s a r e se a t e d on t he i r support s p r io r

to o r du r ing s t r e s s ing o f p r e s tr e s s ing c a b l e s i n t he m a in

spa n pos i t i ve m om e nt r e g ion . A t m idspa n , t he ga p

be twe e n the two c a n t i l e ve r a rm s i s c lose d w i th c a s t -i n -

place concre te . Pres t ress ing cables to res is t l ive load in

Eng. Struct . 199 1 Vol . 13 Apri l 113


2/15

S e g m e n t a l p o s t t e n s i o n e d c o n c r e t e b r i d g e s : J . E . B r e e n a n d S . K a s h i m a

-_ - - . .+ -- ++ ~, ~ . . . . . . . . . ~:~-++=+.::Tr+ .u

a oint

P r e s t r e s s i n g c a b le

t o b a la n c e t h e w e i g h t

o f t h e s e g m e n t a n d

r e s i s t n e g a t i v e m o m e n t

I I

1 I \ e g o a r s

I I P i e r s e g m e n t

/ v

b M a i n p i e r - - I I B o l t s o r s t r e s s i n c c a b l e s

I I

m e r i t

C l o ad i n p o s i t i v e m o m e n t r e g i o n

F i g u r e

T y p i c a l b a l a n c e d c a n t i l e v e r c o n s t r u c t i o n . ( a) , t y p i c a l c r o s s s e c t i o n o f b o x g i r d e r; ( b ) , c a n t i le v e r e r e c t i o n o f p r e c e s t s e g m e n t s ;

( c) , c o m p l e t i o n o f c a n t i le v e r c o n s t r u c t i o n

t he c e n t r e span p os i ti ve m o m e n t r e g ion a r c i nse r t e d a nd

st ressed. Reac t ions in the end spans a re adjus ted as

r e qu i r e d .

Be c a use t h is t ype o f b r idge ha d ne ve r be e n bu i l t i n the

Uni t e d S t a te s a c oope r a t i ve r e se a r c h p r o j e c t w i th t he

T e x a s H i g h w a y D e p a r t m e n t a n d t h e F e d e r a l H i g h w a y

Adm in i s t r a t i on t o i nve s t i ga t e t he va r ious p r ob l e m s

a ssoc i a t e d w i th de s ign a nd c ons t r uc t i on p r oc e dur e s f o r

long spa n p r e c a s t p r e s t r e s se d c onc r e t e box g i r de r

br idge s o f s e gm e nta l c ons t r uc t i on we r e unde r t a ke n by

T h e U n i v e r s it y o f T e x a s a t A u s ti n C e n t e r f o r H i g h w a y

Re search in 1968.

T he T e xa s H ighwa y De pa r tm e nt u t i l i z e d a p r e l im in-

a r y de s ign de ve lope d a s pa r t o f t he p r o j e c t by t he

Un ivers i t y -o f Texas-at Aus tin- researchers in deve lop ing

p lans for a long spa n br idge o n the John F . Kennedy

Memor ia l Causeway , Corpus Chr i s t i , T exas . T he re -

qu i rem ent to main ta in nav igat iona l c learance dur in g

cons truc tion as we l l as the h igh ly cor ros ive env i ronm ent

on the Texas coa s t led to the cho ice o f a precast

pres t ressed concrete box g i rder br idge bu i l t in

cant i lever .

In orde r to s tudy the app l icab i l i t y and accuracy o f the

design cr i ter ia , analytical m ethods, construct ion tech-

n iques , and shear per formance of the epoxy res in jo in ts ,

an accurate one-s ixth scale mod el o f the three-span con-

t inuous br idge was bu i l t and tes ted a t the P . M.

Ferguson St ruc tura l Eng ineer ing Re search Lab oratory

o f T h e Un ive rs i t y o f T exas a t Aus t i n ' s Ba lcones

Resea rch Ce nter u '3.

This model of the three-span precast prest ressed con-

c re te segmenta l tw in box g i rder br idge was a or .c -s ix th

sca le d i r ec t ' mode l , and was bu i l t in f u l l con f o~ an ce

wi th pro to type cons t ruc t ion procedures . I t c lose ly

s im ula t e d t he be ha v iour o f t he p r o to type bo th i n t he

e las t ic and ine las t ic range .

T he ob j e c t i ve s o f t he m ode l s t udy i nc lude d t he

f o l l owing

De terminat ion o f s t ra in d is t r ibut ion due to pres tress-

ing and o f def lec t ions dur ing cant i lever cons t ruc t ion

and dur ing c losure operat ions

Documentat ion o f br idge I tmhav iour unde r service

leve l load ing for the var ious des ign load ing condi -

t ions

Com par ison o f ana ly t ica l resu lt s f rom beam theo ry

and fo lded p la te theory w i th the cons t ruc t ion and ser -

v ice level load ing exper imental resul ts

De t e rm ina t i on o f b r i dge bchav iou r under u lt ima t e

p r o o f l o a di n g ( 1 . 3 5 D L + 2 . 2 5 ( L L + I t , ) ) f o r th e

var ious des ign load ing condi t ions

Determinat ion o f f ina l fa i lu re mechanisms wi th

spec ia l a t tent ion to any adverse e f fec t o f the epoxy

res in on the shear or f lexura l capac it y o f thebr~dge.

De terminat ion o f the punc h ing shear capac it y o f the

top s lab and eva luation o f any adverse e f fec t o f the

epoxy res in o n suc h capac it y

Asses sme nt o f the app l icab i l i t y o f the u l t imate

s t rength des ign c r i te r ia proposed for th is t ype o f

br idge

D e t e r m i n a ti o n o f a n y i m p r o v e m e n t s o f d e s i g n d et a il s

whic h m igh t m in im iz e f i e ld c ons t r uc t i on p r ob l e m s

pr io r t o t he p r o to type b r idge c ons t r uc t i on

P r ov i s ion o f a m e a n ing f u l de m o ns t r a t i on t o p r ospe c -

t i ve c on t r a c to r s t o a s s i st t h e m in t he v i sua l i z at i on o f

the c ons t r uc t ion t e c hn ique so a s t o r e d uc e unc e r t a in ty

a n d e n c o u r a g e b i d d in g f o r t h e p r o t o ty p e c o n s t r u c t io n

1 1 4 E n g . S t r u c t . 1 9 9 1 , V o l . 1 3 , A p r i l


3/15

Seg me ntal post tensione d con crete br idges: J. E. Bree n and S. Kashima

o d e l

T he 200 f t m a in spa n a nd ba l a nc ing 100 f t s i de spa ns o f

the p r o to type b r idge we r e m ode l l e d i n one - s ix th sc a l e .

De ta i ls a r e sho wn in Figure 2 . A m ic r o- c on c r e t e whic h

c lose ly e m ula t e d t he p r ope r t i e s o f t he p r o to type c onc r e t e

wa s use d . Conc r e t e c om pr e ss ive s t r e ng th a ve r a ge d

7100 ps i . T e ndon s a nd r e in f o r c ing ba r s we r e sc a l e d to

m a tc h t he p r o to type de s ign s . S t r a nd u l t im a te s t r e ng th

wa s a ppr ox im a te ly 260 ks i w hi l e r e in f o r c ing y i e ld

va r i e d f r om 71 ks i t o 79 ks i . E poxy r e s in j o in t ing

mater ia l had a f lexura l tens ion s t reng th of 733 ps i as

m e a su r e d w i th c on c r e t e spe c im e ns j o in t e d w i th the

e poxy . A l l s e gm e nt s ha d t he sa m e t r a nsve r se a nd

long i tud ina l m id s t e e l r e in f o r c e m e nt pa tt e r n a s d id t he

pr o to type s t r uc tu r e . A typ i c a l c a ge i s shown in Figure 3

Since i t was impossible to exac t ly model the mul t iple

s t rand commerc ia l tendons and anchor~Iges used in the

pr o to type , p r e s t r e s s ing c a b l e s w e r e m od e l l e d by se l e c t-

i ng f o r e a c h t e ndon a n e qu iva l e n t s i ng l e c a b l e whic h

c ou ld p r od uc e t he c or r e c t l y sc a l e d te ndon f o r c e . D ur ing

pre l im inary tes ts 6 , a tend ency for spl i t ting a long the

t e ndon wa s ob se r ve d , w hic h wa s r e s tr i c te d by use o f a

Figure 3 C a g e f o r a s e g m e n t

spi ra l in the model . Figures 4 a nd 5 show the p r o f i l e o f

the t e ndon duc t s i n t he m a in a nd s ide spa ns .

T o sa t i s f y s im i l i t ude r e qu i r e m e nt s a nd t o ob t a in t he

sa m e de a d l oa d s t re s s c ond i t i ons a s t he p r o to type b r idge ,

i t would be ne c e ssa r y t ha t t he de ns i t y o f a one - s ix th sc a l e

mod el mater ia l be s ix t imes tha t of the prototype br idge .

A B C D

S p a n A B B C C D

P r o t o t y p e 100' 200' 100 ~

M ode l 16 . 67 ' 33 . 33 ' 16 . 67 '

T 6

4

B I

B2

- I T

T 2

B 3

g

B

B5 t

v j C a s t i n p l a c e s t r i p

- - - . 2 v 2 / / /

T 3 ' : a t m a x. s e c t i o n ~

F i l l e t de t a i l

1

B B I B 2 B 3 B 5 B 7 T T 2 T 3 T 3 ' T q T 6 D H I V l H2 V 2 H3 V 3 Hq v 4

P r o t o t y p e 671 " 71 . 5 " 14 " 156" 80 " 24 " 8 " 7 " 6 " 10 " 12 " 6 " 96 " 8 " 6 " 8 " 6 " 8 " 6 " 4 " 4 "

M o d e l 1 1 2 " 1 1 . 9 " 2 . 3 " 2 6 " 1 3 . 3 " 4 " 1 . 3 3 " 1 . 1 7 " I " 1 . 6 7 " 2 " I " 1 6 " 1 . 3 3 " I " 1 . 3 3 " I " 1 . 3 3 " I " 0 . 6 7 " 0 . 6 7 "

F i gu re

B r i dge m ode l d i m ens i ons . ( a ) , l ong i t ud i na l d i m ens i ons o f b r i dge ; ( b ) , c r os s s ec t i on o f b r i dge

Eng. Struct . 199 1 Vol . 13 Apr i l 115


4/15

S e g m e n t a l p o s t t e n s i o n e d c o n c r e t e b r id g e s : J . E. B r e e n a n d S . K a s h i m a

A i I

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G r a d u a l t r a n s i t i o n o f c u r v a t u r e

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I _ 1 A s l o o ~ l

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F i g u r e T e n d o n d u c t p r o f i le s i n m a i n s p a n

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F i g u r e 5 T e n d o n d u c t p r o f i l e s i n s i d e s p a n

This i s impract ica l to implement . Compensat ing dead

loads have been added in various wa ys for mod el s truc-

tures . In th is case , f ive t im es the weight o f the mod el

segm ent w as added to the segments us ing concrete

blocks . A l l dead load blocks were dis tr ibuted to repre-

sent the weigh t o f each port ion and to g ive reasonable

transverse as well as longitudinal d istribution. Loa d

cel l s , pressure gauges , s tra in gauges , surveyor s l eve l ,

and dia l gauges comprised the ins trumentat ion used for

the model study I .

C o n s t r u c t i o n m e a s u r e m e n t s

T h e fo l l o w i n g s t ep s w ere fo l l o w ed i n th e mo d e l b r i d g e

erec t i o n a n d c l o s u re

1 1 6 E n g . S t r u c t . 1 9 9 1 , V o l . 1 3 , A p r il


5/15

Segmental post-tensioned conc rete bridges: J. E. Been and S. Kashima

1)

2)

3)

4)

5)

6)

7)

8)

9)

Pier segments were temporarily fixed to the piers

AII but the outer and the closure precast segments

were sequentially erected using the cantilever con-

struction method for epoxy joints

The bolts at the pier were temporarily slackened and

the vertical and horizontal alignment was adjusted.

The bolts were then re-torqued

The outer pier segments (SlO) were erected and the

positive moment tendons in the side spans were

prestressed

The half segments (MIO) in the main span were

erected. The longitudinal reinforcement extending

across the midspan gap from each of the half seg-

ments was jointed and the concrete closure seg-

ments were cast

The positive tendons in the main span were inserted

and tensioned after seven days of curing of the

closure segment. The bolts temporarily fixing the

segments to the main piers were released during the

positive tendon stressing operation

The bridge was lowered to final position on

neoprene pads on the piers

The correct reactions were jacked into the outer

piers

All tends were grouted

Friction test results indicated that tendon forces after

stressing were 94 to 97 of those predicted by

SIMPLA2 which considered friction losses assuming a

friction coefficient (w) of 0.23radian and a wobble coef-

ficient (A) of 0.000017 in-.

It was difficult to accurately measure the vertical

deflection during construction because the deflection

was so small in comparison to the span (L/1800).

Deflections were measured only to see the general trend

of cantilever section behaviour. Theoretical deflec-

tions were calculated using the computer program

SIMPLA2 which provides an analysis at each stage of

erection using the finite segment technique. The theore-

tical and experimental deflection profiles are shown in

Figures 6u

and

6b,

respectively, for all stages of erec-

tion. Relative deflections for one typical case are com-

pared in

Figure 7.

There are many factors which affect

the vertical deflections such as pier rotation, joint

thickness and casting soffit errors. Therefore, it is very

hard to determine the cause of errors in deflection. This

is especially difticult since the component of deflection

due to dead load is almost completely balanced by the

deflection due to the prestressing.

Figure 6

indicates that

the overall trend of the theoretical and experimental

results agreed fairly well except that the measured

results show a pronounced upward skew.

Experimental deflection measurements shown in

Figure 6 b)

are averages at each corresponding point to

eliminate the effect of load unbalance or bolt bending.

This figure readily indicates the jointing errors in the

initial stages of cantilever erection when temporary

tensile stresses at the bottom of initial joints were not

controlled and joints widened at the base, causing

upward deflections. During the positive tendon opera-

tions in the main span, Figure 8 indicates that the

experimental and theoretical deflections agreed well. An

additional theoretical procedure was used to calculate

these deflections using an elastic analysis program

BMCOLSO. Superimposing results from

Figures 6.

~~.S~ M~.S~~M~,S~M~.S~~MS,SS M~,S~,S~M~,S~M~,S~

0.10

m

t

a

I

o.oov

1

1

1 I I I

I

1

I

b

Figure 6 Cantilever deflections. a). deflection predicted by

SIMPLAZ for cantilever erection; lb), typical measured deflection

during cantilever erection

f igure 7 Deflection relative to the centre of 6th segment.

Assumes that the centre of the 6th segment is zero when 6th

segments are erected

-C- Experiment

--- BMCOL 50

-..- SIMPLA 2

A6 Raise 261100at

both end supports

Figure 6 Deflection at the centre in main span during positive

tendon operations

and 8 indicates that the relative displacement at the

centre in the main span should be almost zero upon

prestressing of all positive tendons (Al-A6). The centre

of the main span was subsequently lowered 0.08 in.

(0.48 in. in the prototype) by the jacking at the outer

supports.

Eng. Struct. 1991, Vol. 13, April 117


6/15

Se gm enta l pos t tens ion ed c onc re te b r i dges : J . E . B reen and S . Kash ima

B ~ q F ~ A

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F i g u r e S t r a in in M 1 a n d 1 s e g m e n t s d u ri ng b a l a n c e d c a n t il e v e r c o n s t r u c t io n

1 1 8 E n g . S t r u c t. 1 9 9 1 V o l . 1 3 A p r i l


7/15

Seg me ntal post ten sioned cOncrete bridges: J. E. Breen and S. K ashima

Figure 9 show s tha t the exper im enta l s t ra ins in the top

s l ab o f t he M 1 and S 1 se gm e nt s va r i e d w ide ly a c r oss t he

c r oss se c t i on dur ing e r e c t i on o f s e ve r a l s e gm e nt s . T he

m e a sur e d r e su l t s a r e i n good a gr e e m e nt w i th t he

the or e ti c a l c a lc u l a ti ons f o r s t a ge 1 a nd a f t e r e r e c t i on o f

the 5 th se gm e nt . E xpe r im e nta l s t r a ins we r e un i f o r m

a c r oss t he c r oss se c t i on a nd c lose t o t he be a m a na lys i s

va lue s f o r t he e r e c t i on o f t he 6 th a nd subse que n t

segments . Al though the longi tudina l s t ra ins in the top

s l ab o f t he M I a nd S 1 se gm e nt s va r i e d a c r oss t he c r oss

sec t ions in ear ly e rec t ion s tages , i t is not a se r ious pro -

blem. Al l s t ra ins a re in compress ion across the c ross

se c t i on a nd a r e we l l be low the s t r a ins whic h would

a c c om pa ny the m a xim um a l lowa ble c om pr e ss ive s tr e s s.

T he non- un i f o r m i ty o f s t ra in i n t he t op s l a b ov e r t he we b

wa s p r oba b ly g r e a t l y i n f lue nc e d by t he l oc a l c on-

c e n t r a t e d t e ndon f o r c e s . As a dd i t i ona l t e ndons we r e

s t r e s se d dur ing t he e r e c t i on o f t he se c ond to f i f t h

se gm e n t s , t he se loca l e f f e c t s d i e d ou t . M e a su r e m e nt s

showe d m uc h be t t e r a g r e e m e nt dur ing c losur e ope r a -

t ions.

In genera l , both theore t ica l solut ions and the exper i -

m e nta l r e su l t s we r e i n r e a sona b le a gr e e m e nt whe n the

c ha nge o f s t r a in i n e a c h s t a ge wa s r e a sona b ly l a r ge ,

except for the local strains in the top slab during init ial

s t a ge s whe n the l a r ge l oca l c om pr e ss ive f o r c e s f r om the

tends seemed to a f fec t the s t ra in dis t r ibut ions .

Pr ior to posi t ive tendon pres t ress ing opera t ions in the

m a in spa n , t he end suppor t s we r e a d jus t e d t o j us t b e a r

on t he unde r s ide o f e ac h w e b a t t he e dge o f t he e nd p i e r

se gm e nt s . Re a c t ions at t he e nd suppor t s w e r e m e a sur e d

by ,sensi t ive load ce l l s dur ing each s tage . Compar ison

betw een theore t ica l and exp er imen ta l r esul t s i s show n in

Table .

A s im pl if i e d p r oc e dur e wa s use d t o c a l c u l a te t he e nd

reac t ion. Pres t ress ing forces were replaced by the ver -

t i c a l f o r c e s whic h would p r oduc e t he sa m e m om e nt

d i a gr a m a s t ha t p r oduc e d by p r e s t r e s s ing . T he se r e a c -

t ions w e r e c a l c u la t e d us ing t he BM COL 50 pr ogr a m 7.

E xpe r im e nta l r e a c t i ons a gr e e d ve r y we l l w i th t he

theore t ica l va lues for la rge va lues such as A I and A2

te ndons . A s t he r e a c t ion i nc r e m e n t be c a m e sm a l l e r , t he

e xpe r im e nta l r e a d ings be c a m e m uc h sm a l l e r t ha n t he

theore t ica l va lues . However , the tota l exper imenta l

reac t ion ( .69 8 kip) agreed very wel l wi th the tota l

theore t ica l va lue (1 .610 kip) .

e r v i c e l o a d t e s t s

The completed three-span four- lane box girder model

wa s loa d t e s t e d f o r t he gove r n ing AASHT O de s ign

loa d ing c ond i t ions show n in Figure I0. T r uc k loa d ings

u t il i ze d 1 /6 -sc a le m ode l s o f t he AAS HT O H S20- S16

trucks w i th tyre pressures assum ed a t 80 ps i in s iz ing

loa d ing pa ds . Uni f o r m l a ne l oa ds we r e s im ula t e d by a

ser ies of con cent ra te d loads a t 4 f t in te rva ls appl ied

a bove e a c h we b in t he m a in t e s t s e r i e s hu t va r i e d i n

t ransverse dis t r ibut ion ser ies . Comple te de ta i l s of

loa d ing a nd i ns t rum e nta t i on a r e p r e se n t e d e l se whe r e i j .

The resul t s of def lec t ion, s t ra in , and reac t ion

m e a sur e m e nt s we r e c om pa r e d w i th so lu t i ons o f

B M C O L 5 0 7 a n d M U P D I s p r o g ra m s .

BM COL 50 i s a be a m - type a na lys i s p r ogr a m whic h

so lve s t he l i ne a rly e la s t ic be a m or c o lu m n by a d i sc r e t e

e l e m e nt a na lys i s p r oc e dur e . T h i s p r ogr a m t a ke s i n to

a c c oun t va r i a b l e l oa ds a nd non l ine a r suppor t s . L oa d-

de f l e c t i on r e l a t i ons f o r e a c h ne opr e ne pa d we r e

m e a sur e d a nd t he se va lue s we r e i npu t t o BM COL 50 a s

the spr ing a t the suppor ts .

M UPDI i s a ve r sa t i l e ge ne r a l i z e d e l a s t i c p r ogr a m

whic h c a n a na lyse f o lde d p l a t e o r box s t r uc tu r e s w i th

inte r ior r igid diaphragms or suppor ts us ing folded pla te

the or ie s w hic h c ons ide r c r oss se c t ion w a r p ing .

A l though BM COL 50 c a n t r e a t va r i a b l e se c t i ons , t he

s e c t i o n f o r M U P D I h a s t o b e u n i f o r m . T h i s M U P D I

l imi ta t ion was not se r ious in this case because of the

smal l var ia t ions in the c ross sec t ions ( thickened bot tom

s la bs on ly a t m a in p i e r a nd a d j a c e n t s e gm e nt s ) .

BM COL 50 wa s use d t o a na lyse un i f o r m t r a nsve r se

ioa d ings ( f our l a ne l oa d ings ) whi l e M UPDI wa s use d

pr im a r i l y f o r non- un i f o r m t r a nsve r se l oa d ing a s i n t he

two- l a ne l oa d ing o r i n t he tr a nsve r se m om e nt s t udy . Fo r

a c h e c k a n d d i r e c t c o m p a r i s o n o f M U P D I a n d

BM CO L 50, bo th we r e r un f o r one un i f o r m loa d ing c a se .

A l l e x t e r na l a nd t h i c kne ss d im e ns ions f o r e a c h m e m be r

of t yp i c a l box se c t i ons we r e m e a sur e d f o r s e ve r a l

se gm e n t s a nd a ve r a ge d se c t ion p r ope r t i e s we r e use d i n

the pro gra m s *'3.

Only sa m ple t yp i c a l r e su l t s a r e p r ov ide d he r e . E x-

c e l l e n t a g r e e m e nt be twe e n c a l c u l a t e d a nd m e a sur e d

de f l e c t ions a nd r e a c ti ons we r e ob t a ine d f o r sym m e t r i c a l

lane loading as shown in Figure 11. The ful l usefulness

a n d a c c u r a c y o f M U P D I w a s s h o w n w i t h u n s y m m e t r i c a l

Ta b le I

Reaction at outer support during prestressing in main

span

Tendon Experimen t (kip) BMCOL 50 (kip)

A1 0.24 5 0.251

A2 0 .200 0 .213

A3 0 .115 0 .169

A4 0 .074 0 .131

A5 0 .012 0 .091

A6 0 .012 0 .055

a i s e

0.26 in at 1.04 0.70 0

o u t e r

supports

Total 1.698 1.610

Case Crit ical condition Loading condit ion

1 Maximum posi tiv e Lane loading .LP

moment

at the centre . ; . . . . . . r , - Jw

of the main span /x A A

SE SMI*= 0.15q NM NE

2 Maximum positiv e Tru ck loading

moment in tt t

the side span ~, A ~ A

SE SM NM NE

I = 0.222

3 Maximum negative Lane loading w /p /p

moment

at ...... J .... .... .... .... .

the main pie r ~, A A A

SE SM NM NE

1=0.182

q Maximum shear Lane loading IP ..

adjustment to

the main pier ,O, A ,x A

SE SM NM NE

I = 0.182

*1 = impact facto r

F i g u r e I Critical loading conditions in longitudinal direction

Eng. St ruct . 199 1 V ol . 13 Apr i l 11 9


8/15

S e g m e n t a l p o s t t e n s i o n e d c o n c r e t e b r i d g e s : J. E . B r e e n a n d S . K a s h i m a

I w l

t t l

I

i w

F i g u r e

S E C ) O T o t a l

E x p e r i m e n t K ) - 0 . 5 8 3 - 0 . 6 7 0 - 1 . 2 5 3

B M C O L 5 0 - - - 1 . 2 4 0

E x p e r i m e n t / B M C O L 5 0 ~ ,} 1 01

N E T o ta l ]

x p e r i m e n t K ) - 0 , 6 5 8 - 0 . 67 2 - I . 3 3 0

B M C O L 5 0 - 1 . 2 4 0

E x p e r i m e n t I B M C O L 5 0 ~ ,) 1 07 I

R e a c t i o n s a t o u t e r s u p p o r t s f o r l a n e Io a d i n g s f o u r l an e s ) i n m a i n s p a n

l o a d i n g p a t t e r n s f o r w h i c h t h e b o x g i r d e r a n a l y s i s w a s

essen t i a l .

Figure 12

shows tha t t he exper imen ta l resu l t s

a n d MU PD I a n a l y s i s a g r e e d e x t r e me l y w e l l .

U l t i m a t e d e s i g n l o a d t e s t s

At the t ime o f th i s tes t , u l t imate load c r i te r i a we re no t

i n c l u d e d i n t h e A A SH T O s p e c i f i c a t i o n s . T h e Bu r e a u o f

Pub l i c R oads c r i t e r i a 9 we re used . Th i s requ i red 1 .35

d e a d l o a d s o e x t r a c o mp e n s a t i n g b l o c k s w e r e a d d e d t o

the model to b r ing i t t o tha t l eve l . L ive load ing was

i n c r e a se d t o t h e s p e c i f i e d 2 . 2 5 ( L i v e L o a d + I mp a c t

Load) l eve l i n s t ages . Crack ing was no ted a t [ 1 .35DL +

1 . 7 5 ( L L + I L ) ] ( s e e

Figure 13) .

Mi d s p a n d e f l e c t i o n s

b e c a m e m u c h l a r g e r th a n t h e e l a s t ic a n a l y s i s p r e d i c t io n s

o f p r o g r a m BM CO L 5 0 . A t d e s i g n ul ti ma t e , t h e s e g -

me n t s a t t h e o u t e r s u p p o r t s s u d d e n l y r a i s e d u p ( s e e

Figure 14) .

Cr a c k s e x t e n d e d t o t h e w e b mi d - h e i g h t a n d

w e r e i n o r n e a r t h e mi d s p a n c l o s u r e s e g me n t . C r a c k i n g

mo me n t s c a l c u l a t e d u s i n g t h e A CI b u i l d i n g c o d e i n -

d i c a t e d e x p e c t e d c r a c k i n g a t 1 . 3 5 D L + 1 . 9 0 ( L L + I L ) .

T h i s i s a v e r y g o o d p r e d i c t io n o f th e c r a c k i n g w h i c h w a s

a t a L L + I L f a c t o r o f 1 . 75 f o r o n e w e b a n d 1 . 8 8 f o r th e

o t h e r w e b . T h e c r a c k i n g mo m e n t i s v e r y s en s i ti v e t o t h e

ad jus t ing fo rce a t t he end suppor t s .

f - t h e r e a c t io n f o r c e p r o v i d e d a t t h e e n d s u p p o r t s i s

l a r g e , m i d s p a n c r a c k s w i l l a p p e a r a t l o w e r i n c r e me n t s o f

(LL + IL) . I f t he ad jus t ing fo rce p rov ided a t t he end i s

smal l , t he end segment s wi l l ra i se up f rom the neoprene

p a d s u n d e r v e r y s ma l l i n c r e me n t s o f ( L L + I L ) . T h e r e -

f o r e , w h e r e p o s s i b l e t h e e n d r e a c t i o n s f o r t h e b r i d g e

s h o u l d b e s e l e c t e d a t a n o p t i mu m p o i n t w h i c h b a l a n c e s

these two fac to rs .

S i mi l a r te s t s w e r e r u n f o r ma x i mu m n e g a t i v e mo me n t

a t t he main p ie r which opened up add i t iona l c racks near

the p ie r a long nega t ive moment t endon t ra j ec to r i es ,

p a r t ly b e c a u s e o f t h e l o w c o v e r s o v e r t h e l a r g e t e n d o n s .

Ma x i mu m s h e a r l o a d i n g a d j a c e n t t o t h e ma i n p i e r w a s

t h e n a p p l i e d . N o s l i p b e t w e e n s e g me n t s w a s f o u n d a n d

no add i t iona l f l exura l o r d i agonal t ens ion c racks were

o b s e r v e d . I n ma x i mu m p o s i t i v e mo me n t t e s t i n g i n t h e

s i d e s p a n , g e n e r a l l y l i n e a r b e h a v i o u r w a s n o t e d a n d n o

c r a c k in g w a s o b s e rv e d . M U P D I r e s u lt s s h o w e d

e x c e l l e n t a g r e e me n t w i t h me a s u r e d v a l u e s ( s e e

Figure

15 .

ai lure load te s t s

Si n c e t h e b r id g e mo d e l r e a d i ly c a r r i e d t h e B PR d e s i g n

u l t imate load fo r a l l c r i t i ca l f l exura l and shear load ing

cond i t ions , s evera l fa i lu re load t es t s were p l anned to

de te rmine u l t imate capac i ty . In the f i r s t t es t t o fa i lu re ,

f a c t o r e d A A SH T O t r u c k l o a d s w e r e a p p l i e d i n o n e s i d e

s p a n t o p r o d u c e a b e n d i n g f a i l u r e . T h i s l o a d i n g w a s

se lec ted even though the ca l cu la t ed fa i lu re l i ve load

fac to r fo r th i s case was l a rger than tha t wh ich was

c a l c u la t e d f o r ma x i mu m mo me n t l o ad i n g i n t h e ma i n

s p a n . S i n c e b o t h o f t h e s e t y p e f a i l u r e s w o u l d b e f l e x u r a l,

i t was fe l t t ha t a fa i lu re t es t i n the s ide span co u ld ver i fy

f l exura l u l t imate ca l cu la t ions . Such a t es t wou ld l eave

t h e s t r u c t u r e w i t h t w o r e l a t i v e l y u n d a ma g e d s p a n s s o

tha t a shear t es t t o fa i lu re cou ld a l so be run by app ly ing

lane load ings to the main and oppos i t e s ide span . Th i s

l o a d i n g w o u l d p r o d u c e ma x i mu m s h e a r a t t h e ma i n p i e r

a n d b e a n e f f e c t i v e t e st o f e p o x y j o i n t p e r f o r ma n c e .

Truck load ing on the s ide span was s topped af t e r d i s t inc t

y i e l d i n g h a d o c c u r r e d i n t h e s i d e s p a n a n d a t s u p p o r t

SM , a s j u d g e d b y t h e d e f le c t i o n ( s e e

Figure 16)

and

s tr a in r e a d i n g s , b u t b e f o r e c o m p l e t e c o l l a p s e o f t h e s id e

span . Al thoug h load s we re app l i ed in th i s tes t a f t e r fo r -

mat ion o f a p l as t i c h inge , t he e f fe c t o f th i s load ing on the

u l t imate ben d ing and shea r s t reng th o f the o ther spans

a n d d u r i n g t h e s e c o n d ( o r ma x i mu m s h e a r ) f a i l u r e

l o a d in g t e s t w a s j u d g e d n e g l i g ib l e . N o l iv e l o a d w o u l d

b e a p p l i e d o n t h e d a ma g e d s p a n a n d t h e e n d s e g me n t a t

SE w o u l d d e f l e c t u p w a r d .

T h e s c a l e d A A S H T O H S 2 0 - S 1 6 l o a d s w e r e ap p l ie d t o

a l l f o u r l a n e s o f t h e s i d e s p a n t o p r o d u c e ma x i mu m

mo me n t . T h e a l l o w a b l e l o a d r e d u c t i o n f o r a f o u r l a n e

br idge wa s ignored . The l ive loads app li ed" we re in

add i t ion to the a l ready app l i ed 1 .35 dead load . L ive and

impact loads were increased to the 5 .25 (LL + IL) l eve l .

A t t h e 2 . 8 8 ( L L + I L ) i n c r e me n t , a p p r e c i a b l e d e v i a -

t ions f rom the genera l ly l i near load vs def l ec t ion

d i a g r a m

Figure 16)

w e r e n o t e d . I t a p p e a r s a s t h o u g h

c r a c k i n g m a y h a v e s t a r t e d t o d e v e l o p in t h e i n n e r w e b s ,

a l t h o u g h n o c r a c k i n g w a s v i s i b l e i n t h e o u t e r w e b s . A t

the 3 .25 (LL + IL) increm ent , a f l exura l c rack on the

o u t e r w e b a r o u n d t h e c e n t r e o f t he S S 7 R s e g m e n t w a s

v i s ib l e a lmos t up to mid-he igh t and the s t ra in gauges in

the bo t tom s l ab showed a l a rge increase in s t ra in .

1 2 0 E n g . S t r u c t . 1 9 9 1 V o l . 1 3 A p r i l


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~

o

Q

@

T

a

.

=

E

x

m

e

(

K

)

-

0

3

-

0

4

-

0

2

-

0

2

-

1

2

.

(

2

9

3

8

1

7

1

6

0

.

1

T

a

E

m

e

K

)

-

0

3

-

0

q

-

0

2

-

0

2

-

1

3

(

~

2

5

3

2

2

1

2

2

1


10/15


Figure 3

~ 2 . 0 0

j . - ' ~

~

-~ 1.50 BMCOL 50 i

1.00

E

5

. ~ S E S I S M I O

1 . 3 5 D L 0 . 0 0 . / I I I I

0 . 0 . I 0 . 2 0 . 3 0 , 4

D e f l e c t i o n ( i n ]

D e f l e c t i o n s a t S M I O f o r l a n e l o a d i n g s ( f o u r l a n e s ) in m a i n s p a n ( d e s i g n u l t i m a t e

At the 4 .25 LL + IL) increment , a w id e crack mo re

than I /8 in v i sua l ly ) developed suddenly a t the SS6-7

jo int in the outer web o f the west s ide . At the 4 .38

LL + IL) increment a major crack form ed near the

S S 6 -7 jo in t i n th e o u ter w eb o f th e ea s t s id e . A f ter th e~

cra ck s d ev e l o p ed , d e fo rma t i o n s w ere co n cen tra ted i n

the v ic in i ty o f these large cracks . Stra ins w ere seen to

increase rapidly at the 4.8 LL + IL) increme nt and to

7 0 . 1 0 -

0 . 0 0 -

0 .10 -

0 . 2 0

0.30

0 . 4 0 -

2 . 0 0 ( L L + I L )

L o a d i n g c o n d i t io r ~ ( + 1 . 3 5 D L i

~ l l l l l l ~ l f i l l I I

/(~ SM NM ~'

1 . 0 0 ( L L + I L )

1 , 5 0 ( L L + I L )

- ' 0 - E x p e r i m e n t

2 . 1 2 5 ( L L + I L ]

r

. 2 5 ( L L + I L )

1 2 2 . 5

1 2 2 . 7

Figure 4

( L L + I L I SE SS4 SM SM5 SM I0 N M5

1 . 0 0 [ - 0 . 0 0 4 1 - 0 . 0 2 2 9 + 0 . 0 0 1 3 + 0 . 0 8 6 + 0 . 1 3 7 + 0 . 0 8 3

1 . 5 0 [ - 0 . 0 0 7 9 - 0 , 0 3 6 7 + 0 . 0 0 25 + 0 . 1 3 6 + 0 . 2 2 4 + 0 . 1 3 4

2 . 0 0 I - 0 . 0 1 5 5 - 0 , 0 5 5 3 + 0 . 0 0 q 8 + 0 . 2 0 3 + 0 . 3 4 8 + 0 . 2 0 2

2 . 1 2 5 I - 0 . 0 2 2 9 - 0 . 0 6 1 7 + 0 . 0 0 5 2 + 0 . 2 2 1 + 0 . 3 8 2 + 0 . 2 2 1

2 . 2 5 I - 0 . 1 0 1 0 - 0 . 0 9 4 8 + 0 . 0 0 5 9 + 0 . 2 7 1 + 0 . 4 6 9 + 0 . 2 7 2

D e f l e c t i o n s f o r la n e I o a d i n g s ( f o u r l a n e s ) in m a i n s p a n ( d e s i g n u l t i m a t e

N M N S4 N E

+ 0 . 0 0 1 4 - 0 . 0 2 3 9 - 0 . 0 0 4 9

+ 0 . 0 0 2 0 - 0 . 0 3 8 1 - 0 . 0 0 9 0

+ 0 . 0 0 32 - 0 . 0 5 6 3 - 0 . 0 1 7 5

+ 0 . 0 0 38 - 0 . 0 6 3 7 - 0 . 0 3 2 1

+ 0 . 0 0 4 0 - 0 . 1 0 3 8 - 0 . 1 2 8 0

1 2 2 E n g . S t r u c t . 1 9 9 1 V o l . 1 3 A p r i l


11/15

Seg me ntal post tensioned concrete br idges: d. E. Bree n and S. Kashima

J

2 . 2 5

2 . 0 0

1 7 5

1 5 0

I 2 5

1 0 0

0 7 5

0 . 5 0

0 . 2 5

0 00

L o a d i n g c o n d i t i o n ( + 1 .3 S D L )

h lwl

S E S M NM NE

- 1 0 0

C o m p r e s s i o n

/ ' ~ O ~ O P o s i ti o n o f w h e e l s

. / ~ = ~ l q ' ~ l 2 i = ,1 2 = I / C B r i d g e

y ii ii

/ Y ~ 2 7. 5 ,J P o si ti on o t p a p er

s ~ i~ ~ I g a u g e ( t r a n s v e r s e l y )

~ / ~ ' X E x p e r i m e n t S S7

S E M _ _ _ INE

'~ 2 0 0 " - ' - L I0 0" " ' " 2 0 0 " " '

I I

- 2 0 0 - 3 0 0

S t r a i t . ( u i n / i n )

Figure 5 T r a n s v e r s e s t r a i n a t S S 7 R f o r t r u c k I o a d i n g s ( f o u r l a n e s ) in s i d e s p a n ( d e s i g n u l t i m a t e )

increas e l e s s rapidly a f ter that increm ent indicat ing that

a p l a st i c h i n g e w a s f o r m e d a t t h e S S 6 - 7 j o i n t . A f t e r

form ing the p las t i c h ing e the load s we re redis tr ibuted

a n d m o r e l o a d w a s c a r r i e d a t t h e S M p i e r r e g i o n . S i n c e

t he b r idge i s a th ree-span con t inuous beam, p las t i c

h inges have to be fo rmed a t A) and B) in Figure 7 to

have a comple te fa i lu re mechan i sm fo r load ing in the

s i d e s p a n . D u e t o t h e e x t r e m e w i d e n i n g o f t h e c r a c k a t

t h e S S 6 - 7 j o i n t a n u n e x p e c t e d h o r i z io n t a l f o r c e o c c u r -

r ed o n t h e t o p o f t h e S E p i e r . I t c o u l d b e v i s u a l l y

o b s e r v e d a t h i g h l o a d l e v e l s t h a t t h e S E p i e r w a s t i l t i n g

a n d i n c l i n i n g a f t e r t h e l a r g e c r a c k s o p e n e d a r o u n d t h e

S S 6 - 7 j o i n t . A p p a r e n t l y a si g n i f i c a n t h o r i z o n t a l f o r c e

d u e t o t h e d e f o r m a t i o n o f t h e b r i d g e w a s i n d u c e d a t t h e

t o p o f t h e S E p i e r. T h e m o m e n t c o n n e c t i o n b e t w e e n t h e

e n d p i e r a n d th e t es t f l o o r w a s n o t s t r o n g e n o u g h t o k e e p

the p ier from t i l t ing under th i s force .

Beca use i t was obv ious tha t a p l as t ic h inge had fo rm ed

n e a r th e 4 . 3 8 L L + IL ) i n c re me n t a n d b e c a u s e o f th e

inc lina tion o f the end p ie r , i t was dec ided m s top load ing

and rc l casc a ll l i ve load a t t he 5 .25 LL + IL) incremen t .

Th i s re p resen ted p rac t ica l fa i lu re o f the s ide span ,

a l though to t a l co l l apse d id no t occur . In th i s way fu r ther

load t es t ing cou ld be comple ted in the o ther two spans .

A l t e r c o mp l e t i o n o f th e s i d e sp a n t e s ts , f o u r A A S H T O

lane loads were app l i ed to the main span and one ad ja -

cen t s ide span to p roduce the c r i t i ca l shear cond i t ion a t

the f i rs t jo in t in the main span. I t wa s ant icipated fr om

com puta t ions that wi th fu ll deve lopm ent o f shear

s t reng th the b r idge would fa i l i n f l exure even though

u n d e r a ma x i mu m s h e a r l o a d i n g . H o w e v e r , i t w a s

dec ided to check the shear capac i ty s ince bas i c in fo rma-

t ion abou t f l exura l capac i ty w as ob ta ined by app ly ing the

t ruck loads to the s ide span . Lack o f pub l i shed in fo rma-

Figure 6

L o a d i n g c o n d i t i o n ( + 1 . 3 5 D L )

i n

s E ~ l , s M . M

N~

o ~

I E I

5.0 SS7

4 0

+ 3 .0

I I

_= ~ z= t =o 8

o

/ i.r

D f l e c t i o n : a v e r a g e o f 4 r e a d i n g s o n w e b s

1 0

0 0 I I I

0 .0 0 .1 0 .2 0 .3

D e f l e c t i o n ( i n )

D e f l e c t i o n s a t th e c e n t r e o f t h e S S 7 s e g m e n t i n s id e s p a n

I

0 . 4

E n g . S t ru c t . 1 9 9 1 V o l . 1 3 A p r il 1 2 3


12/15

S e g m e n t a l p o s t t e n s i o n e d c o n c r e t e b r i d g e s : J . E . B r e e n a n d S . K a s h i m a

S E ( B } N M H E

S M

= s t p l a s t i c h i n g e

I_

'~ A I

( A ] ( B ]

M 0 1 ~ ( B )

Mo1,M02: plastic moment

2 n d p la s t i c h i n g e

( A ] _ I

U}

C

F i gu re 7

F a i lu r e m e c h a n i s m f o r t r u c k I o a d i n g s i n t h e s i d e s p a n

( a ), l o a d i n g c o n d i t i o n ( + 1 . 3 5 D L ) ; ( h i . f i r s t p l a s t i c h i n g e a n d

m o m e n t d i a g r a m ; ( c ), s e c o n d p la s t ic h i n g e a n d m o m e n t d i a g r a m

a t c o l l a D s e

tion made it very desirable to check the performance of

the epoxy joints under realistic high shear Ioadings.

In addition to the 1.35 dead load, AASHTO live and

impact lane loadings were applied by rams and increased

until failure. The position of the heavy concentrated load

could greatly affect the shear strength of the bridge. It

was considered that a direct shear failure might occur as

the effective depth decreased due to flexural cracks, so

concentrated loads were applied 10 in. outside but adja-

cent to the first joint in the main span.

After the load reached 2.25 LL + IL), the reaction at

the north end started to decrease and at higher loads the

north reaction was unloading the dead load effects. At

the 2.63 LL + IL) increment, the south end segment

SE) raised completely from the neoprene pad support.

At this load level the crack which had previously

developed at the joint of the main span closure segment

during the positive moment ultimate design load test

started to reopen. Strains in segments SS7, SS6, SS1 and

SM I increased almost linearly up to 2.63 LL + IL), but

remained constant after that increment because the south

end reaction became zero and no load was applied to the

unloaded side span. Strains at NS6 were very low until

the 2.5 LL + IL) increment, then increased steadily

until failure. This change was caused by the alteration in

structural configuration when the south side span

became a free cantilever.

At the 3.25 LL + IL) increment, the strain increase

at the NM6 segment stopped. This was due to the con-

centration of deformation in the crack around the centre

of the main span. The rate of deflection increase

changed substantially at 3.25 LL + IL) as shown in

Figure 18

Also, a diagonal tension crack started to

develop at the first segment in the main span outer web

on the west side). At the 3.75 LL + IL) increment, a

flexural crack at the joint of the closure segment

extended to near the top of the web and many cracks

started to develop in the region of segments SM6 to

SM9, as shown in Figu re 19

At the 4.25 LL + IL) increment, the diagonal tension

crack and the flexural crack around the NM pier joined

and a wide flexural crack developed about 1 in, away

from the first joint in the main span. At this stage, the

flexural crack on the top slab was only in the outer can-

tilever portion. At this loading the south end segment

raised up about I in. from the surface of the neoprene

pad support.

At the 4.25 LL + IL) increment in the east side and

the 4.75 LL + IL) increment in the west side, very wide

flexural cracks developed at the SM6-7, SM7-8 and

SM8-9 joints, as shown in

Figure 19

These cracks

F i gu re 8

7 . 0

6 . 0

0

~ 3 . 0 L o a d i n ~ c o n d i t i o n ( + 1 . 3 5 D L )

2 . 0 T S E S M N M N E

1 . 0

0. 0 I I I I I I I

0 . 0 I .0 2 . 0 3 . 0

D e f l e c ti o n a t c e n t r e o f m a i n s p a n i n)

D e f l e c t i o n s a t S M 1 0 d u r in g l o a d i n g t o f a i l u re

I

t l . 0

1 2 4 E n g . S t r u c t . 1 9 9 1 , V o l . 13 , A p r i l


13/15

a

Segmental post-tensioned conc rete bridges: J. E. Breen and S. Kashima

A

0

C D

Lt

A

A

A

Span

AB

BC

CD

Prototype

100

200

100

Model

16.67

33.33

16.67

T3:

Fillet detail

B

B1 B2 83

05 87

Tl

T2 T3 T3' T4 T6 D Hl

Vl HZ V2 H3 V3 H4 V4

Prototype 671 71.5 14 156 80 24

8

7

6

10 12 6 96

8

6 8

6 8

6

4

4

Model

112 11 9 2 3.

26 13.3

4 1.33 1.17 1 1.67 2 1 16 1.33

1 1. 33 1 1.33 1 0.67 0.67

Figure 19 Development of cracks around the centre of main span during loading to failure

developed near the epoxy joints in the web portion in

the flexural tension zone) and about 1 in. away from the

joint in the bottom slab in the pure tension zone). The

cracks at these joints went nearly to the top of the web

with an increase of one increment of loading. The in-

crease of strain around the 4.09 to 4.75 (LL + IL)

increment range at NM9, NM I and NSI stopped

because of concentration of deformations at these joints

and at the first joints from the main pier. At the 5.0

LL + IL) increment. the crack on the top slab of seg-

ment NSI and the NM pier segment extended the full

width of the slab on the east side of the box).

At the 5.75 LL + IL) increment, the bridge looked

straight from the SE pier to the SM6-7 joint and all

major deformation was concentrated at the SM6-7 joint.

The NM pier segment on the neoprene pad support

started to crush on the east side. due to the high com-

pression force.

After taking the instrument readings at the 6.25

LL + IL) increment, the loads were being increased to

the 6.50 LL + IL) increment when a sudden rupture of

the positive moment prestressing cables occured at joint

SM6-7 on the west side. This failure occurred before

applying less than half of the planned increment and the

load dropped immediately after the failure. The load was

then brought back to the 6.25 LL + IL) increment and

rupture of the positive moment prestressed cables in the

east side box occurred after a small increase in load.

Even after rupture of the positive moment cables, the

bridge exhibited great toughness and continued to carry

1.35 DL as balanced cantilevers.

Ultimate capacity was computed recognizing that only

downward restraints existed at the piers. Under high

overload levels the bridge began to act as a two-span

continuous beam with an overhang. Ultimate moments

were computed for the various support conditions.3

and the redistribution of moments was followed through

the loading sequence.

The LF or level of LL + IL) which would form the

first plastic hinge for this loading was calculated for

each type structure. The first plastic hinge would form

at the joint of the closure segment at an increment of

1.35 DL + 5.21 LL + IL)) if the structure was ideally

supported by pins and there was no uplift possible at the

Eng. Struct. 1991, Vol. 13, April 125


14/15


end supports. However, it is not proper to calculate the

LF for a three-span continuous beam since the SE sup-

port raised off its support pad at the (1.35 DL + 2.63

(LL + IL)) increment. Since the south end support

raised completely from the neoprene pad supports, all

forces applied at the time of construction (such as end

reaction due to positive tendon prestressing in the main

span or the jacking force at the end supports to adjust the

reaction) were erased and the structure became a two-

span continuous beam with an overhang. If the structure

were an ideal two-span continuous beam with an over-

hang, the reaction at the NE support would have to

increase as the load increased. But the reaction at the NE

support decreased after the (1.35 DL + 2.25 (LL + IL))

increment due to the appearance of cracks and concen-

tration of deformation around the centre of the main

span. Observations indicated that a plastic hinge was not

formed at the closure segment at (1.35 DL + 2.25

(LL + IL)) as would be indicated for a two-span con-

tinuous beam with an overhang. Since the calculation for

case (3) indicated that the minimum LF of 6,33

(LL + IL) for the first plastic hinge was at the SM6-7

joint for a simple beam with overhangs, it will be proper

to calculate the LF of (LL + IL) for the case and then

take into account the reaction left at the NE support. If

the structure is an ideal simple beam with overhangs, the

first plastic hinge would form at the 6.33 (LL + IL)

increment. The effect of the reaction left at the NE sup-

port was small _and 5.88 (LL + IL) is the calculated

increment to form the first plastic hinge when taking into

account the end reaction at the NE support. This value

agreed well with the 6.25 (LL + IL) experimental value.

I1" the AASHTO allowance for reduction on a four lane

bridge was considered, the bridge would withstand

(I.35 DL + 8.33 (LL + IL)) in this load configuration.

Alter demolishing the bridge, the joints where failure

occurred were carefully examined and it was found that

the five positive tendons in each web were completely

broken through. Although the side span positive tendons

were adequately proportioned by the design procedure

which assumed ideal three-span continuous beam action,

the positive moment reserve was reduced in the main

span because the design did not consider the upward

unrestrained end support condition. A check of the

loading condition which would produce maximum

moment at the centre of the main span indicated that the

main span maximum positive moment flexural capacity

is reduced to (1.35 D L+ 3. 13 (L L+ IL )) if the

AASHTO load reduction for multiple lanes is ignored.

This would be (1.35 DL + 4.17 (LL + IL)) if the nor-

nml design specifications are used for a four-lane bridge.

While this load case was not tested to failure, the good

agreement of other flexural test results and calculations

indicated that this value would undoubtedly have been

attained.

In order to match the test loading conditions, the

model's external dead load moment was computed with

1.0 DL acting on a balanced cantilever and 0.35 DL

acting on the_completed continuous structure. Becau~

of the construction sequence it is not logical to base the

analysis of the completed structure on fully continuous

beam load moments for 1.35 DL. A more rational load

factor procedure for computation of the ultimate design

moments in the completed structure should consider

possible uncertainty in the dead load at various stages of

construction. Based on experience in this program, the

following factors are suggested for analysis of the com-

pleted structure to check the negative moment and shear

capacity.

Load factors are chosen to conform to the BPR

general factor philosophy

U = 1.35 DL + 2.25 (LL + IL)

For a segmental bridge erected in cantilever, during

the construc tion phase M, - M,~ based on

U~ = .35 DL~ + 2.25 (LL~ + IL0 to be

computed for a balanced cantilever

Also, upon completion M, >-. M,_, + M, 3, where

U2 = .35 DLI to be computed for a balanced

cantilever

U3 = 1.35 DL3 +

2 25

(LL3 + IL0 + SL to be

computed for the completed continuous

structure

where

DL~ = dead load during cantilevering

DL~ = dead load applied after completion of

closure (topping, railing, etc.)

LLI = live load due to construction operations

LL3 = design live load

IL I = impact load o f construct ion operations

IL3 = design impact load

SL = resultant reactions due to prestressing of

of tendons and seating forces at outer

supports

Negative tendons can be designed by WSD or USD to

balance the dead load segments and the weight of con-

struction equipment on the segments during the balanced

cantilever stages. However, the ultimate negative

moment capacity of the cantilever structure should be

checked for Ui. The ultimate negative moment capacity

of the completed structure should be cheeked for

U=U,. U~.

In determining positive moment tendons it will be

unconservative to use U,, = i.35 DL~. A highly conser-

vative approach would be to use U, = 0.90 DL~ com-

puted for the balanced cantilever and the preceding

equations.

o n c l u s i o n s

Based on the experimental and analytical results

reported, the following conclusions were drawn.

The segmental bridge model safely carried the

ultimate design loads for all critical moment and shear

loading configurations on which its design had been

based.

The deflection under design live load in four lanes

(only three lanes required by live load reduction factors)

was approximately L/3200 in the main span. This is

much smaller than L/300 which is generally considered

as acceptable.

2 6

En g. Struct . 199 1 Vol . 13 Ap r i l


15/15

Seg me ntal post tensione d conc rete br idges: J. E. Bre en and S. Kashima

Pos i t ive t e ndons i n t he m a in spa n we r e de s igne d a s i f

a n i de a l t h r e e - spa n c on t inuous be a m . S inc e t he c om -

p le t e d b r idge wa s suppor t e d on ne opr e ne pa ds whic h

have no ver t ica l r es t ra int aga ins t upl i f t , the outer ends

we re able to r i se of f the i r suppo r ts so tha t the s t ruc ture

d id no t a c t c on t inuous ly a t u l t im a te c ond i t i ons unde r

m a in spa n pos i t ive m om e nt loa d ing . E v e n so , t he r e wa s

suf f i c i e n t r e se r ve s t r e ng th i n t he m a in spa n t o c a r r y

design ul t imate load.

U n d e r v e r y h i g h c o m b i n e d m o m e n t a nd s h e a r l o a d in g ,

f l e xur al c r a c ks a ppe a r e d n e a r t he e pox y jo in t s i n t he t op

s l a b ne a r t he m a in p ie r . H ow e ve r , t he y j o ine d t he

d i a gona l t e ns ion c r a c ks a nd d id no t e x t e nd a long the

jo in t s . T he r e wa s no s ign o f a ny d i r e c t she a r f a il u r e at

the joints . In tes ts of the ful l br idge mo del , approx i -

m a te ly 75 o f t he t he or e ti c a l u l t im a te she a r l oa d wa s

a pp l i e d i n t he m a xim um she a r l oa d ing t e s t p r i o r t o

f a i lu r e o f t he b r idge dur ing t he t e s t by f l e xur e . N o s ign

of she a r d i s t r e s s wa s e v ide n t . ( Subse que n t t e s t s o f a

th r e e - se gm e nt m ode l unde r se ve r e she a r l oa d ing a s a

cant i lev er sec t ion indica ted tha t full shea r s t rength of the

uni t was deve loped~'3. Hen ce , the epoxy joint tech niqu e

use d d id no t r e duc e the de s ign sh e a r s t r e ng th ) .

Dur ing e r e c t i on o f t he f i r s t f e w se gm e nt s , t e ns i l e

s t ress occur red in the bot tom s lab as predic ted in the

de s ign . T e m por a r y p r e s t r e s s de v i c e s suc c e ss f u l l y c on-

t rol led the e f fec ts of these s t resses .

Theore t ica l ca lcula t ion of the load fac tor for l ive and

impact loads requi red to form the f i r s t p las t ic hinge

a gr e e d ve r y we l l w i th t he e xpe r im e nta l r e su l t s . T he se

tes ts provide the accuracy and appl icabi l i ty of the

ul t imate hind ca lcula t ion procedure consider ing redis t r i -

bu t ion o f m om e nt s .

Most of the theore t ica l ca lcula t ions were in good

a gr e e m e nt w i th t he e xpe r im e nta l r e su lt s , a l t hough the r e

we r e som e a ppr e c i a b l e de v i a t i ons be twe e n the e xpe r i -

menta l and theore t ica l va lues of s t ra in in the top s lab in

som e s t a ge s o f c a n t i l e ve r c ons t r uc ti on .

T he B M C OL 50 pr ogr a m wa s ve r y use f u l i n p r e d i c t i ng

the be ha v iou r o f t he b r idge d ur ing c on s t r uc ti on a nd f i~ r

un i f o r m loa d ing t e s t s . T he BM COL 50 r e su l t s a g r e e d

very wel l wi th the exper imenta l r esul t s for longi tudina l

s t ra ins and def lec t ions . The re la t ive ly s imple da ta input

f o r BM COL S0 i s a no the r a dva n ta ge whe n c om pa r e d t o

the f o lde d p l a te t he or y p r ogr a m s .

T he S I M PL A2 pr ogr a m r e a sona b ly p r e d i c t e d t he

var ia t ion of the longi tudina l s tra in un der very high s t ress

l e ve l s a c r oss t he t op s l a bs o f t he ne wly e r e c t e d se g-

ments .

T he M UPDI p r ogr a m , whic h c a n be use d on ly f o r a

constant c ross sec t ion, agreed very wel l wi th the exper i -

menta l r esul t s a t the se rvice load leve l . The var ia t ion of

c r oss se c t ion a long th is b r idge wa s ve r y sm a l l . M UP Di

c a n be use d t o de t e r m ine t he t r a nsve r se m om e nt s a nd

she a r s unde r unsym m e t r i c a l l oa d ing a nd c a n be use d

e f f e c t ive ly i n de s ign ing t he t r a nsve r se r e in f o r c e m e n t .

How e ve r , t he e f f e c ts o f c r e e p a nd sh r inka ge w e r e

minimal in this s tudy. M ul le r m points out for this c lass

of s t r uc tu r e .

T he e f f e c t o f s t e e l a nd c onc r e t e c r e e p m us t be c on-

s ide r e d w i th r e ga r d t o m om e nt d is t ri bu t ion , t oge the r

w i th t he poss ib l e e f f e c t o f m om e nt r e ve r sa l . F ina l

a d jus tm e nt a nd c om pe nsa t i on f o r sh r inka ge a nd c on-

c r e t e c r e e p m a y he lp t he s t r uc tu r e t o r e a c h t he

op t im um e qu i l i b r ium .

A c k n o w l e d g e m e n t s

This s tudy was par t of Research Projec t 3-5-69-121

sponsor e d by t he T e xa s S t a t e De pa r tm e nt o f H ighwa ys

a nd Pub l i c T r a nspor t a t i on a nd t he Fe de r a l H ighwa y

Adm in i s t ra t i on . T he op in ions e xpr e s se d a r e t hose o f t he

a u thor s a nd d o no t ne c e ssa r i l y r e f le c t those o f t he spon-

sor s . T he a u thor s a r e g r e a t l y i nde b t e d t o m a ny who

played key roles in this ambi t ious sca le model tes t .

L i a i son w i th t he T SDHPT wa s m a in t a ine d t h r ough the

c on ta c t r e pr e se n t a t i ve , M r . Robe r t L . Re e d , a nd t he

S ta t e Br idge E ngine e r , M r . Wa yne He nne be r ge r ; M r .

D . E . Ha r t l e y a nd M r . Robe r t E . S t a ndf or d we r e t he

c on ta c t r e pr e se n t a t i ve s f o r FHWA. Spe c i a l t ha nks a r e

due t o M e ss r s . T hom a s Ga l l a wa y , L a w r e nc e G . G r i f fi s

and John T . Wal l , a l l ass i s tant research engineers a t the

Fe r guson S t r uc tu r a l E ng ine e r ing Re se a r c h L a bor a to r y

a t T he Unive r s i t y o f T e xa s a t Aus t i n ' s Ba l c one s

Re se a r c h Ce n te r . T h e y p l a ye d ke y r o l e s i n t he de ve lop-

m e nt o f m o de l t e chn ique s , f a br i c a t ion p r oc e d ur e s , e r e c -

t i on m e thods , a nd i ns t r um e nta t i on sys t e m s , a nd we r e

r e spons ib l e f o r va r ious s t a ge s o f c ons t r uc t i on ope r a -

t i ons . T he L a bor a to r y s t a f f und e r t he i r supe r v i so r M r .

Ge o r ge M ode n , a l l c on t ri bu t e d s ign i f ic a n t ly to t h i s p r o -

j e c t w i th t he i r un t i r i ng w i l l i ngne ss t o wor k l ong hour s

a nd m a ke a n e x t r a e f f o r t t h r oughout t h i s p r o j e c t . D r .

Ne d H . Bur ns , P r of e s sor o f C iv il E ng ine e r ing a c te d a s

a n a dv i sor on m a ny que s t i ons c onc e r n ing p r e s t r e s s ing

sys t e m s .

Our l as t a c know le dge m e nt is t o t he t i n fe t te r e d ge ne r o-

s i t y o f P r of e s sor A . C . Sc or de l i s o f t he Unive r s i t y o f

Cal i fornia , Berke ley. Alex Scorde l i s wi l l ingly provided

c o m p u t e r p ro g r a m s M U P D I a n d S I M P L A f o r us e w i th

th i s p r o j e c t . He a nswe r e d ' dum b ' que s t i ons w i th h i s

c ha r a c t e ri s t ic g r a c e a nd p r ov ide d e nc o ur a ge m e nt a nd

advice to the authors . Without his he lp the ana lyt ica l

inte rpre ta t ions would have been very l imi ted.

R e f e r e n c e s

10

Kashima. S. and J. E. Breen. Const ruct ion and load tests o f segmen-

ta l p recas t box g i rde r b r idge mode l ' .

R e s . R e p . 1 2 1 - 5 .

Center fo r

H ighway Resea rch , The Un ive rs i t y o f Texas a t Aus t in , Feb rua ry

1975

Brown, R. C. , Burns, N. H. and Breen. J . E. C o m p u t e r analys is o f

segmenta l ly erec ted precast pres t ressed box g i rde r b r idges ' . Res .

Rep . 121 -4 . Cen ter I b r H ighw ay R esea rch . The U n ive rs i t y o f Texas

a t Aus l in , November , 1974

Kash ima. S. Const ruct ion and load tests o f a segmenta l p recast box

g i r d e r b r i d g e m o d e l ' . Ph.D . d i s s , . The Un ive rs i t y o f Texas at Aus t in ,

January 1974

Bro wn , R. C. 'C om pulc r ana lys is o f segmenta lly constructed

prest ressed bo x g i rders . PhD. d iss . . The Un ive rs i t y o f Texas a t

Aust in . 1972

V. Novokshchenov. Sa l t penet ra tion and corros ion in prest ressed

concre te members ' , Fede ra l H ighway Admin is t ra t ion Repo r t

RD-88-269. Ju ly 1989

Ga l lawa y . T .M . ' l ndus t ra l i za t ion and mo de l ing o f segmen ta ll y

p recas t box g i rde r b r idges ' . Ma s te r ' s t hes i s . The Un ive rs i t y o f Texas

at Aust in . 1971

Ma t tock . A . H . S t ruc tu ra l mode l t e~ t ing - - tbeo ry and app l i ca t ions ' ,

J PCA Res. Dev. I .~h. 1962 .4 (3 ) . 12 -22

Scordelis . A. C . 'Analysis of simply supported box girder brid ges ' .

Re p No

SESM 66-77. Depart .ment of Civil Engineering. Un ive~ ity

of Califiwnia. Berkeley, October 19(36

Bureau of Public Roads. Strength and serv iceabi/ iO. criteria rein-

forc e d c onc re te br idge me ntbe rs uhimate de s ign (2nd edn). Bureau

of Public Roads. U.S. Department of Transportation. Washington.

D.C. 1969

Muller. J. Long spa n precast prestressed

concrete

bridge built in

can t i leve r ' . Concrete Bridge Design. ACt Publication SP-23. 1969.

p p . 7 0 5 - 7 4 0

verification of load deflection

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