member connection

8/12/2019 Member Connection

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Basis for Tubular Joint Design

Design criteria of the codes that govern construction ofoffshore drilling platforms are analyzed and evaluated

B Y P. W . MARSHALL A N D A . A . T O P R A C

I n t r o d u c t i o n

Recen t ly pub l i shed codes (Refs .1 ,2 ) inc lude c r i t e r i a fo r the des ign

a n d c o n s t r u c t i o n of w e l d e d c o n n e ct ions fo r c i rcu la r tubes , w h i ch havebeen in use for a number of years ino f f s h o r e d r i l l i n g p l a t f o r ms . T h epurpose o f th i s paper i s to do cum en tthe backg round da ta under ly ing thesecr i t e r i a , in t e r ms o f s t a t i c and fa t igu es t r e n g t h .

:z^x.

40(^0 .50CHORD ~

Fig. 1 Simple joint

20^.0.50BRANCH MEMBERS

P. W. MARSH ALL is Staff Civil E ngineer,Offshore Construction, Shell Oil Company, New Orleans, La. A. A. TOPRA C is

Professor of Civil Engineering, The University of Texas a t A ustin.Paper is based on a survey sponsored by

the WRC Subcommittee on Welded Tubular Structures.

S t a t i c S t r e n g t h

Simple and Punching Shear Jo in ts

Curren t ly the mos t popu la r s ty le o fw e l d e d c o n n e c t i o n f o r i n t e r s e c t i n gcircular tubes as used in f ixed offs h o r e s t r u c t u r e s is t h e " s i m p l e " j o i n ti l lu s t ra ted in F ig . 1. T h e t u b u l a r m e mbers a re s imp ly welded toge ther, anda l l load i s t ran s fe r red f r om oneb ranch to the o ther v ia the cho rd ,w i t h o u t a n y h e lp f r o m s t i f f e n i n g r i n g so r gusse t p la tes . To p reven t excess ive ly h igh loca l i zed s t res se s in th ec h o r d , a sho r t l en g th o f heav ie rsec t ion ( jo in t can) is ofte n used in t heconnec t ion a rea . In such cases , thep rob le m o f jo in t des ig n reduces to

tha t o f s i z ing the jo in t can , pa r t i c

u l a r ly w h e r e c o mp l e t e j o i n t p e n e t r at ion g roove we lds (as def in ed fo rtubular s t ructures (Ref. 2) are used atthe ends o f the b ranch members .

A l t h o u g h t h e c o mp l e t e s t r e s sp ic tu re i s mu ch mo re complex , thec o n c e p t o f p u n c h i n g sffear, Fig . 2 , hasbeen qu i t e u se fu l in co r re la t ing t es td a t a a n d f o r mu l a t i n g d e s i g n c r i t e r i a .The average (o r nom ina l ) pun ch in gshear s t res s , v p , a c t i n g o n t h e p o t e nt i a l fa i lu re su r face i s ca lcu la ted as :

v B = r

rV-r V*y

V

*g TO R 0 0 0.5 I.O

I . I . I . I . I . I . I

(D

6 0 * 3 0 0*BRACE INTERSECTION ANGLE S

Fig. 2 Punching shear Fig. 3 Intersection line effects

1 9 2 - s I M A Y 1 9 7 4


2/11

LINE LOADQ K / i n CLOSED RING Jo

t t

UNIT WIDTHSTRIP BEAM

KELLOGG


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PUNCHING SHEARAT FIRST YIELD

f lY.fi)AXIALLY LOADEDTEE JOINT T =l .0

Fig. 5 Theoretical elastic stresses axially loaded T-joint

as i l lus trated in Fig . 7 . If a s ec t ionth rough the cho rd a t i t s in te rsec t ionw i th the b race i s cons id ered fo r s mal lloads in the e las t i c range , the d i s t r ib ut ion o f c i rc um feren t i a l s t res ses o nthe outs ide surface are shown asS tage 1 in the f igu re . Beyond y ie ld ,the connec t ion defo rms (S tage 2 )wh i le the app l i ed load con t in ues toincrease. Final ly, a t loads 2 .5 to 8t imes tha t a t f i r s t y i e ld , t he jo in t fa i l s by pu l lou t fa i lu re as sh ow n fo rtens ion loads o r by loca l i zed co l l apseo f the cho rd fo r compress ion loads(Stage 3).

T h e a v e r a g e p u n c h i n g s h e a r stressa t fa i lu re* , v p , has been p lo t ted in Fig .8 re la t ive to spec i f i ed m in i m um y ie lds t r e n g t h , F y , and as a fun ct ion ofc h o r d t h i n n e s s rat io .Y; 38 s tat ic tes tswh ic h fa i l ed in the pun ch in g shearmo d e a r e re p r e s e n t e d , a l o n g w i t ht w o s p e c i me n s w h i c h f a i l e d a f t e ron ly a few cyc les o f fa t igue load ing .The so l id c i rc les rep resen t K- jo in t s ;the res t are T and cross jo in ts . D ataare from Toprac (Refs . 4 , 7) and o thersourc es (Refs . 8 , 9) .

Fo r re la t ive ly s tocky cho rd members th ickn ess g rea te r th an 7% o fd iamete r o r 7 l es s than 7 the jo in t smay be said to have a 1 0 0 % p u n c h i n gshear e ff i c iency , in the sense tha t t heshear s t reng th o f the mate r i a l i s fu l lymob i l i zed on the po ten t i a l fa i lu re s u r

face . Th i s c r i t e r ion i s met by AS TM A-53 s tand ard wei gh t p ipe under 2 in .

CHORD ,_THINNESS ' t o

RATIO

Fig. 6 Parameter study

d i a m , by extra s t ro ng p ipe under 5 in .d i a m , and by doub le extra s t r ong p ipe

t h r o u g h 1 2 in . d iam .L a rg e r a n d / o r t h i n n e r c h o r d s

should be t reated on the basis of areduced punch ing shear capac i ty asgiven by the curve in Fig . 8 and

F ( 2 ) "U l t i ma t e v n

Allowable v

0.5 x yc

0.9 x y(2a)

Here , the des ig n a l lowab le p unc h ingshear s t res s inco rpo ra tes a sa fe tyfactor of 1 .8 with respect to theemp i r i ca l cu rve fo r u l t imate punc h ingshear. I t s in tended range o f app l i cat ion i s fo r the m id - ran ge o f d iam ete rra t io s fo r wh ich v P is more or lessi n d e p e n d e n t o f /3 .

S i n c e t h e p r o p os e d e m p i r i c a ldes ign cu rve makes u se o f the pos t -y ie ld rese rve s t reng th o f s imp letubu la r conne c t ion s , i t wi l l be in s t ruct ive to rev iew the sou rces o f th i s ex t racapac i ty. These a re :

I . T h e d i ffe rence be tween e las t i cand p las t i c bend ing s t reng th ( loca l

ized) of the c yl in dric al s he l l , afactor of 1.5.

* Failure was defined as first crack fortension loads. This would functionallyimpair the joint for subsequen t fatigueservice.*'*The ultimate s trength criteria developed by Reber (Ref. 9) reduces to:

Ultimate v p = f (f )-0 55x y c

All simple T Y and K connections are tested on a common basis. Although K connectionshave lower elastic stresses than the correspond ing T and Y connections, they also haveless reserve strength, so that the ultimate capacities come out similar. The chief differencebetween Reber's results and equation (2) is in the degree of conservatism with respect tothe scatter band shown by the test results. Reber provides a good average fit whereas thecurve for equation (2 ) falls on the safe side of most o f the data. Reber's f(/S) shows relatively little influence of diameter ratio: i. e., f (R - R 1

2. Res t ra in t to p las t i c f lo w caused bytriaxial s t resses at the hot spot , a

factor of 1 .6 for the s i tuat ion ofFig. 5.

3 . S t ra in hard en ing fo r the mi lds tee l s rep resen ted in the t es t da ta ,t h e u l t i ma t e t e n s i l e s t r e n g t h(w hic h is at leas t local ly u t i l izedw he n a jo in t fa i l s by sepa ra t ion o fthe mate r i a l ) is g rea te r tha n thes p e c i f i e d mi n i mu m y i e l d s t r e n g t h ,F y , (wh ich i s u sed fo r the e mp i r i ca lco r re la t ion and des ign fo rmu la) byfac to rs f rom 1 .6 to 2 .4 . Correspond ing ly, i t i s sugges ted tha t F yused in ca lcu la t ing the a l low ab lev p shou ld no t exceed two- th i rd s

( 2 / 3 ) t h e t e n s i l e s t r e n g t h .4 . Fu r ther inc reases in capac i ty re

su l t f rom the red i s t r ibu t ion o f load,w h i c h o c c u r s as t h e c o n n e c t i o ny ie ld s and app roac hes i t s l imi tload. I f the cy l ind r ica l s he l l i s v i sual ized as a netw ork of r ing s an ds t r ing ers , the sequ ence o f eve n t smay occur as i l lus trated in Fig . 9 .

P las t i c behav io r, t r i ax ia l s t res ses ,s t r a i n h a r d e n i n g , l o a d r e d i s t r i b u t i o nand la rge defo rm at ion beha v io r p lacee x t r a o r d i n a r y d e ma n d s o n t h e d u c t i li ty o f the cho rd mate r i a l . Some loca lized y ield ing wi l l occur at des ign loadleve l s . These cons idera t io ns shou ldbe kep t in mi nd wh en se le c t ing s t ee l sfor tubular s t ructures (Ref. 8) .

Further Refinements

By and l a rge , des ign codes rep resen t a conse nsus o f eng ineer ing p ract i ces in a par t i cu la r f i e l d . T h e r e w a s agenera l fee l ing tha t , wh i le the da ta o fFig. 8 (as replo t ted in terms of/? in Fig.10 ) d id no t ju s t i f y t ak ing d iam ete rrat io /? in to accoun t , exper ie nce i n d ica ted a bene f ic ia l e ffec t as the d ia mete r ra t io app roaches un i ty, a s i n d i

cated by the heavy dashed l ine in Fig .10.

Square Tubes. Cons iderab le in s igh tin to the effect of /? o n the u l t im ate

194-s I M A Y 1 9 7 4


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FAILURE

S TA G E 1 S TA G E 2

DEFLECTION

Fig. 7 Reserve streng th of a tubular connection

I.Or

MATERIAL LIMITV P F y / y j

U LT IM ATE P U N C H I N G S H E A R

2 0 3 0 4 0 5 0 6 0

R / t y CHORD THINN ESS RATIO

Fig. 8 Emp irical design curve static strength

^

Fig. 9 Load redistribution. First yielding occurs a t hot spot A. Cross hatched yield line isanalogous to plastic hinge in a continuous frame. Full strength of ring AB is reached whenyielding a lso occurs at B, after considerable angle change at hot spot. Ring AB continues todeform at constant load while rest of joint catches up, resulting in more uniform load distribution. Limit load of joint is reached when ring CD and stringer CE also yield. Deforme dshape is indicated by dashed lines

p u n c h i n g s h e a r c a p a c i t y o f t u b u l a rc o n n e c t i o n s w a s g a i n e d f r o m c o n s i dera t ion o f a l imi t ana ly s i s o f squaretubes . Us ing the y ie ld l ine pa t t e rn o fFig. 11 a n d t h e u p p e r b o u n d t h e o r e m

o f p l a s t ic d e s i g n , t h e u l t i ma t e p u n c hing shear s t res s v p i s ob ta ined as :

0 .25

/?( -/?) o.5*y

0.2 0.4 0.6 0.6DIAMETER RATI0-/3

Fig. 10 Static strength /3 effects

w he re / ? and Y a re def in ed in amanner ana logous to the u sage fo rc i rcu la r tubes .

The second t e rm on the r igh t o fequa t ion (3 ) i s qu i t e s im i la r to thee mp i r i c a l p u n c h i n g s h e a r, e q u a t i o n

(2 ); on ly the expone n t o f Y i s d i ffe ren t . The l ead ing t e rm co rresp onds tothe /? e ffec t and has the fo l low ingproper t i es :

1. M i n i m u m v a l u e of 1 .0 , w h i c hoccu rs a t /? = 0 .5 .

2 . I n c r e a s i n g p u n c h i n g s h e a r e ff ic iency a t l a rger and smal le r / ? -ra t io s ; th i s i s comparab le to thetheo re t i ca l resu l t s fo r c i rcu la r T-jo in ts , Fig . 6 .

3 . Where/?approaches i t s l imits (0and 1 .0 ) , punch ing shear i s l imi tedby the shear s t re ng t h o f the ma ter i a l (o r by o ther con s ide ra t ion ssuch as w eb c r ipp l ing ) .

Test data (Ref. 10) for the spe cificcase of 5 x 5 x 0 .187 cho rd a re a l soplot ted in Fig . 1 1 . Fa i lu re wa s d ef ineda s w h e n j o i n t d e f o r ma t i o n r e a c h e d3 % of c h o r d w i d t h . T h e s t r e n g t h i ncrease fo r /? - ra t io s over 0 .5 appearst o b e c o n f i r m e d , w i t h t h e t e s t d a t as h o w i n g s t r e n g t h s r a n g i n g f r o m 1 .5to 1.8 t imes the com pu te d "u ppe rb o u n d " l i m i t load . This rese rves t r e n g t h u n d o u b t e d l y c o me s f r o ms o me o f t h e s a me s o u r c e s d i s c u s s e dabove fo r c i rcu la r tube con nec t ions .

Fo r /? - ra t io s under 0 .5 , how eve r,the t es t da ta show equa t ion (3 ) to beincre as ing ly l es s con serv a t ive as / ?decreas es . The do t t e d l ine (F ig . 11)rep res en t s a punc h ing shear c r i t e r i aw h i c h i s i n d e p e n d e n t o f t h e j3 - ra t io ,given by:

v = f o r / ? < 0 .50 .5 Y

(3a)

i o (3)

No te tha t th i s s t ra igh t s lop ing l inegoes th ro ugh the o r ig in ; to ta l jo in tcapac i ty goes to ze ro as the b racep e r i me t e r a n d / 3 - r a t i o a l s o a p p r o a c hzero . The com bina t ion o f equ a t ions(3 ) and (3a) resu l t s in c r i t e r i a w i t hmore o r l es s cons i s t en t s a fe ty fac to rsth roughou t the range o f /? .

W E L D I N G R E S E A R C H S U P P L E M E N T 195-s


5/11

60

5 0 -

40

in

_-*.I_

3 0

2 0

SPECIFIC RESULTSFOR 5X5X.I87 CHORD

MATERIAL LIMITv p = 0 . 4 Fy^

/

LIMIT ANALYSIS

0.25 Fy

/3(l-/3) 0.5 y-

P 0 . 5 y

FOR /3 < 0 . 5

YIELDLINES

0 0.2

Fig. 11 Ultimate strength analys is square tubes

0.4 0.6 0.8/9 - RATIO I.O

HINGELINES

SIMPLIFIEDLIMIT

ANALYSIS

. 0.5 II/3


6/11

_ 0.4cr

0.3

0 . 2 -

0.1 -

CHORDAREA Ac

Pmax

-1.0 -0.8 -0.6

COMPRESSION

-0. 4 -0.2 0.2 0.4 0.6

CHORD UTILIZATION RATIO

U = FyTc"

0.8 1.0

TENSION

and Q=1.0 for /? 0 . 4 4Q f = 1 . 0 f o r | U | < 0 . 4 4

and |U|= cho r d u t i l i za t ion ra t io a t thec o n n e c t i o n .

Fig. 13 Interaction effects of stress in chord

NEGATIVE ECCENTRICITY ZERO ECCENTRICITY POSITIVE ECCENTRICITY

^ H E A R ON 6'OVERLAP WELD

SHEAR ON 2.5OVERLAP WELD

SHEAR ON 9"VERT. WELD

BEARING ON LEG

COMFARISON OF JOINT EFFICIENCIES

TYPE OFJOINT

POSITIVEECCENTRICITY

ZEROECCENTRICITY

NEGATIVEECCENTRICITY

CALCULATEDBASED ONNOM. YIELDI37* IN 6^8

5 4 %

8 2 %

108%

Fig. 14 Joints o f various eccentricities

W E L D I N G R E S E A R C H S U P P L E M E N T 197-s


7/11

* , )

Fig. 15 Components of resistance foroverlapping joints

In d e s i g n |Ujwould be taken a s theAISC ra tio for the chord a t the tubularconnec t ion (wi th r e spec t to c r i te r iabased on yie ld) . Equation (6) includessa fe ty f ac tor s and cor re sponds to asymmetr ica l f a i lu re enve lope , a s

sh ow n by the solid l in e (Fig. 13) .Where heavy wa l l jo in t cans a re useda t tubu la r conne c t ion s , the u t i l iza t ionra t io wi l l o f ten be le ss than 0 .44 forthe jo in t ca n , cor re s pond ing to noreduc t ions due to in te rac t ion . Forh igh ly s t r e ssed K and X- jo in tsw i t h o u t j o i n t c a n s , b u t w i t h e q u a l d iame te r s , the inc rease in jo in t e ff iciency over equation (2a) wil l bel i m i t e d t o a b o u t 3 0 % , w h e n b o t h Q jand Q f a r e cons ide red .

Overlapping Joints

In ove r lapp ing jo in ts , the b racesin te r sec t each o the r a s we l l a s thec h o r d , and pa r t o f the load i s t r ans

fe r red d i r ec t ly f rom one brace to ano t h e r t h r o u g h t h e i r c o m m o n w e l d .One advantage of such jo in ts i s tha t ,s ince the chord no longe r mus t t r ansfe r the en t i r e load , i t s th ic kne ss ca nb e r e d u c e d a n d " j o i n t c a n s " e l i mina ted . The amount o f ove r lap can becont ro l led by ad jus t ing the eccen t r ici ty of brace ce nte r l ine s, as indica tedin Fig. 14. Neg ative ecc en tr ic i t y (Ref .12) can be used to increase the

amount o f ove r lap and the s ta t ic loadt ransfe r capac i ty o f the connec t ion .

A c rude u l t ima te s t r eng th ana lys isis proposed (see Fig. 1 5 ) , in w hi ch thepun chin g shea r capac i ty fo r tha t port ion of the b race r each in g the ma inm e m b e r a n d t h e m e m b r a n e s h e a rc a p a c i t y o f t h e c o m m o n w e l d b etw ee n braces a re a ssum ed to ac ts imul taneous ly. Thus , the to ta l capac i ty o f the conn ec t io n for t r an sfe r r ingloads pe rpe ndicu la r to the chord bec o m e s

P s in 9

w h e r e

(7)

v = a l lowa ble pun ching shea rstress equ ation (6) for th em a i n m e m b e r

t = ma in mem ber wa l l th ickness

I = c i r cu mfe re n t ia l l eng th fo rthat por t ion of the bracew h i c h c o n t a c t s t h e m a i nm e m b e r

andv = a l lowa ble shea r s t r e ss fo r

wt h e c o m m o n w e l d b e t w e e n

q 10,000

5,000

CYCLES OF LOAD

Fig. 16 Family of fatigue design curves (see Table 1)

198-s I M A Y 1 9 7 4

the braces*t w = th roa t th ickness fo r the

c o m m o n w e l d b e t w e e nb r a c e s *

1 2 = the p ro jec ted chord leng th(one side) of the over lapp ing w e l d , measured in theplane of the braces and perpendicu la r to the ma inm e m b e r * *

A compar ison of computed capac i t i es , in terms of brace axia l l oad , P,us ing u l t ima te v p and y ie ld v w x t w ,versus test results is given in Fig. 14.Equa t ion (6) appea r s to be conse rvat ive in p red ic t ing s ta t ic jo in t capac i t i es , p rov ided the re i s suff ic ien t ducti l i ty that the st iffer e lement ( the overlap) does not fa i l befo re the rest of th ejoi nt ca tche s up. A t e las t ic load levelsthe over lap is so much st iffer that i tt r ie s to ca r ry the en t i r e l oad ; thus ,w h e r e o v e r l a p p i n g j o i n t s a r e i n t e nt iona l ly used , som e des ign e r s l ike toproportion the over lap to carry a tlea s t 50% of the ac t ing t r ansve r seload.

W h e r e e x t r e m e a m o u n t s o f o v e r l a pare used, i t may become necessary tocheck the capac i ty o f the connec t ionfor t r an sfe r r ing loads pa ra l le l to thema in me mbe r as we l l a s t ransv e r seloads . Both may be accompl ishedwi th vec tor combina t ion of thev a ri o us s t r e n g t h e l e m e n t s , assugg ested in Figs. 14 and 15.

F a t i g u e

Few memb ers or con nec t io ns in

convent iona l bu i ld ings need to be des igned for f a t igue , s ince m os t loadchanges occur in f requent ly o r p roduce on ly minor cyc l ic s t r e sses . Thefu l l des ign win d or ea r thqu ake loadsa re suff ic ien t ly r a re tha t f a t igue neednot be cons ide red .

H o w e v e r , c r a n e r u n w a y s a n d s u ppor t ing s t ruc ture s fo r mac hine ry a reof ten sub jec t to f a t igue load ing condit i o n s . Off shore s t ruc ture s a re sub jec tto a con tinuo us sp ectru m of cyclicw a v e l o a d i n g s , w h i c h r e q u i r e c o n s i de ra t ion of cumula t ive f a t igue damage(Ref. 13).

We lde d tubula r conne c t ions , in pa rt icu la r, r equ i re spec ia l a t ten t ion to f at igue , s ince s ta t ica l ly accep tab le designs may be subject to localizedpla s t ic s t r a ins , even a t nomina l lya l lowable s t r e ss leve ls .

Fa t igue may be de f ined a s damagethat results in f rac ture af ter a su ff i -

*Except that the line load capacity v w x wshould not exceed the shearing capacity of

the thinner adjoining base metal.Projected chord length is proportiona l tothe resultant of membrane shear, actingat peak value along the full length of theoverlapping weld.


8/11

Table 2 Fatigue Categories

, b)

- . (b)

S t r e s sc a t e g o r y S i t u a t i o n

A P l a i n u n w e l d e d t u b e .

A But t sp l ices , no cha nge in sec t ion , fu l l pen e t ra t ion groovewelds , g round f lush , and inspec ted by x- ray or UT.

B Tu b e w i t h l o n g i t u d i n a l s e a m .

B B u t t s p l i c e s , f u l l p e n e t r a t i o n g r o o v e w e l d s , g r o u n d f l u s h .

B M e m b e r s w i t h c o n t i n u o u s l y w e l d e d l o n g i t u d i n a l s t i f f e n e r s .

C B u t t s p l i c e s , f u l l p e n e t r a t i o n g r o o v e w e l d s , a s w e l d e d .D M e m b e r s w i t h t r a n s v e r s e ( r i n g ) s t i f f e n e r s , o r m i s c e l l a n e o u s

a t t a c h m e n t s s u c h a s c l i p s , b r a c k e t s , e t c .

D Te e a n d c r u c i f o r m j o i n t s w i t h f u l l p e n e t r a t i o n w e l d s(except a t tubula r connec t ions) .

S i m p l e T, Y, o r K c o n n e c t i o n s w i t h f u l l p e n e t r a t i o nt u b u l a r g r o o v e w e l d s .

B a l a n c e d T a n d c r u c i f o r m j o i n t s w i t h p a r t i a l p e n e t r a t i o ngroove welds or f i l l e t welds (except a t tubula rc o n n e c t i o n s ) .

M e m b e r s w h e r e d o u b l e r w r a p , c o v e r p l a t e s , l o n g i t u d i n a ls t i ffeners , gusse t p la tes , e tc . , t e rmina te (except a tt u b u l a r c o n n e c t i o n s ) .

S i m p l e T, Y, a n d K t y p e t u b u l a r c o n n e c t i o n s w i t hp a r t i a l p e n e t r a t i o n g r o o v e w e l d s o r f i l l e t w e l d s ; a l s oc o m p l e x t u b u l a r c o n n e c t i o n s i n w h i c h l o a d t r a n s f e r i sa c c o m p l i s h e d b y o v e r l a p ( n e g a t i v e eccentricity,)gussetp la tes , r ing s t i ffeners , e tc .

F End we ld of cover p la te or doub ler wr ap ; we lds ongusse t p la tes , s t i ffeners , e tc .

G T and c ruc i form jo in ts , loaded in ten s io n orb e n d i n g , hav ing f i l l e t o r par t ia l pene t ra t iong r o o v e w e l d s .

G ' S im ple T, Y, or K co nne c t ion s hav ing f i l l e t o r par t ia lp e n e t r a t i o n g r o o v e w e l d s .

X M a i n m e m b e r a t s i m p l e T, Y, a n d K c o n n e c t i o n .

X U n r e i n f o r c e d c o n e - c y l i n d e r i n t e r s e c t i o n .

X C o n n e c t i o n s w h o s e a d e q u a c y i s d e t e r m i n e d b y t e s t i n gan accura te ly sca led s tee l model .

K (c | S i m p l e K t y p e t u b u l a r c o n n e c t i o n s i n w h i c h g a m m ara t io R/T of main member does no t exceed 24 .

S i m p l e T a n d Y t u b u l a r c o n n e c t i o n s i n w h i c h g a m m a r a t i oR/T of main member does no t exceed 24 .

(c)

K i n d s o f s t r e s s '3 '

TCBR

TCBR

TC R

TC R

TC R

TC R

TC R

TC R

TCBR in branch member (main member must be checkedseparately per Category K or T).TCBR in member (weld must also be checked per Category G).

TCBR in member.

TCBR in branch member (main member in simple T, Y, orK connections must be checked separately per CategoryK or T; weld must also be checked per Category G').

Shear in weld.

Shear in weld (regardless of directio n of loading).

Nominal shear in weld (P/A + M/S)

Hot spot, stress or strain on the outsidesurface of the main member, at the toe of weldjoining branch member measured in model of

prototype connection, or calculated with bestavailable theory.Hot spot stress at angle change.

Worst measured hot spot strain, after shake down.

Punching shear on shear area (d> of main membe r.

Punching shear on shear area


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c 2 \o3 a* c 5 o 6 io7 io 8CYCLES

Fig. 17 Fatigue curve C nominal stress adjacent to weld

102 103 IO 4 105 106 107 |08CYCLES

Fig. 18 Fatigue curves C and X hot spot strain adjacent toweld

o 7 w *CYCLES, N

Fig. 19 Punching shear fatigue strength of 7 -connections

ate u s e d b e c a u s e t h e y a r e m o r e a pp r o p r i a t e t o t u b u l a r s t r u c t u r e s e xp o s e d t o a c o n t i n u o u s s p e c t r u m o fc y c l i c l o a d s . I n t h e s e s i m p l e s i t u at i o n s t h e n o m i n a l m e m b e r s t r e s s ( f a +f b ) f a i r l y w e l l r e p r e s e n t s t h e a c t u a ls t r e s s a s w o u l d b e m e a s u r e d a d j ac e n t to t h e w e l d . S e e F i g . 1 7 .

C u r v e X is b a s e d o n c u r r e n t d e s i g np r a c t i c e s f o r o f f s h o r e s t r u c t u r e s ( R e f .8 ) . T h e r e l e v a n t s t r e s s fo r f a t i g u e f a i lu r e o f t u b u l a r c o n n e c t i o n s i s t h e h o ts p o t s t r e s s m e a s u r e d a d j a c e n t t o t h ew e l d , a s s h o w n i n F i g . 1 8 . T h i s i su s u a l l y c o n s i d e r a b l y h i g h e r t h a n t h en o m i n a l m e m b e r s t re s s , a n d w o u l dn o r m a l l y be d e t e r m i n e d f r o m a d et a i l e d t h e o r e t i c a l ( R e f s . 5 , 6 ) , o r e x -

10* IO3 K)4 io5 io6 o 7 o 8

CYCLES, N

Fig. 20 Punching shear fatigue streng th of K-connections

Fig. 21 Fatigue curves D and D' nominal member stress atfull penetration T welds and simple joints

100

E' .

T

TEE

LAP

' | 0 2 C 3 IO4 IO5 IO6 O 7 IO 8

CYCLES

GUSSET

Fig. 22 Fatigue curves E and E 'let welds and complex joints

OVERLAP

nominal m ember stress at fil-

p e r i m e n t a l ( R e f s . 4 , 7) , a n a l y s i s o f t h ec o n n e c t i o n . C a t e g o r y X is c o n s i s t e n tw i t h c a t e g o r y C s i n c e t h e l o c a lt r a n s v e r s e s t r e s s a d j a c e n t to t h ew e l d is c o n s i d e r e d i n b o t h c a s e s . I nt h e r a n g e o f i n e l a s t i c s t r e s s e s a n d

l o w c y c l e f a t i g u e ( R e f . 1 7 ) i t i s m o r er e a l i s t i c t o d e a l i n t e r m s o f h o t s p o ts t r a i n r a t h e r t h a n s t r e s s .

T h e d a t a p l o t t e d i n F i g . 18 r e p r es e n t h o t s p o t s t r e s s ( o r s t r a i n ) f r o m

a c t u a l a s - w e l d e d h a r d w a r e t u b u l a rc o n n e c t i o n s , p r e s s u r e v e s s e l s , la bo r a t o r y m o d e l s a n d p r o t o t y p e f a i l u r e s f r o m a v a r i e t y o f s o u r c e s ( R e f s . 1 3 ,1 4 , 1 6 , 1 8 , 1 9 , 2 0 , 2 1 ) . I n t h e l o wc y c l e r a n g e , t h e d e s i g n c u r v e c o r r es p o n d s t o r o u g h l y 9 5 % s u r v i v a l ( 5 %f a i l u r e p r o b a b i l i t y ) b a s e d o n t e s t d a t aw h i c h a r e s p r e a d o u t o v e r a s c a t t e rb a n d m o r e t h a n o n e l o g c y c l e w i d e .W i t h i n t h i s r a n g e , a ll s t r u c t u r a l q u a l -

2 0 0 - s I M A Y 1 9 7 4


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11/11

1 9 7 4 R e v i s io n s t o S t r u c t u r a l W e l d i n g C o d e

T he 1974 R evisions to Structu ral Welding Code (AWS D l . l - R e v 2-74)contains the second set of authorized revisions to the Structural WeldingCode, Dl .1-72. For convenience an d overal l economy in u pda t ing exis t ingcopies of the Code, 88 pages of the Code have been reprinted, 59 of whichhave been revised to incorporate changes. (The remaining pages are notchanged but appear on the reverse side of revised pages.)

To fulfil l the needs of all Code purchasers, the 1974 revisions are available as a bound book and as individual looseleaf sheets. The boundcopies are intended primarily for l ibraries and others who wish to keeptheir original copies of the Code, as well as the subsequent revisions,intact. The looseleaf version will be ideal, however, for those Code users

who plan to update their present Codes by insert ing the revis ion pagesinto them.With the looseleaf pages, the t ime-consuming process of cutting,

pasting, or tearing out will be avoided. To update the Code, old pages aresimply removed and the new revised pages inserted in their place. Allpages are 8V in . 11 in. and are p unch ed for three-hole looseleaf or postbinders .

All pages revised for 1974 are l isted on the contents page, and allchanges in f igures and tables are enumerated and described immediatelyfollowing the contents page. Changes in text material are denoted in bolditalics; deleted material is crossed through with double l ines. (The 1974revisions can thu s be dis t inguishe d from the 1973 revis ions wh ich aredes ignate d by reg ula r i talics an d single cross-throu gh lines.) Th e newpages are printed on blue stock, and pages containing 1974 (and/or 1973)revisions are clearly labeled.

These are the principal changes in Code requirements: SMAW fillet welding of stud s is now perm itted. Th e prequalified sta tus of join ts welded by short-circuiting tran sfer

GMAW has been removed. Cam ber tolerances of welded me mb ers hav e been revised. SN T qualification of all ND T ope rator s is now required. Ad ditions and deletions ha ve been m ad e to the l ists of prequalified

steels for buildings, bridges, and tubular structures. Bridge design criteria rel atin g to fatigue stress ha ve been elim inated .

P r i c e s

D l . 1 - 7 2 Stru ctura l W elding Code 16.00D l . l - R e v 1 - 7 3 1973 R evisions to Stru ctura l W elding Code 6.00D l . l - R e v 2 - 7 4 1974 R evisions to Stru ctur al W elding Code 6.00

Discounts: 25 to A and B members; 20 to bookstores, public libraries a nd schools;15 to C and D members. Send your orders to the American Welding Society, 2501 NW 7thStreet, Miami, FL 33125. Florida residents add 4 sales tax. Be sure to specify whetheryou want a looseleaf or a bound copy.

202-s I MA Y 19 7 4

member connection

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