Residual Stresses in Heavy Welded Shapes

Transcription

1 Residual Stresses in Heavy Welded Shapes Gemetry f plates and shapes is an imprtant variable affecting residual stress magnitude and distributin, and initial residual stresses due t rlling can be a higher magnitude than thse due t welding BY G. A. ALPSTEN AND L TALL ABSTRACT. Residual stresses can have a significant influence n the lad-carrying behavir f structural steel members subjected t cmpressive lads. Previus experimental research n residual stresses and the strength f clumns was related t small and medium-size shapes. In tday's large structures, increasingly heavy shapes are emplyed. While heavy clumn shapes are being used extensively, very little infrmatin has been available n the residual stresses and strength f such members. This paper presents the results f the first phase f a majr investigatin int the residual stresses in, and the behavir f, thick plates and heavy shapes used in cmpressin members. The shapes cnsidered in this initial study are a 5H290 shape and a 23H68 shape, as well as tw lse cmpnent plates, PL 6x2 and PL24x3V.,. Fr the smaller shape, cmparative tests were carried ut fr different manufacturing cnditins f the cmpnent plates (universal-mill and flamecut plates), different weld type (penetratin) and different yield strengths f the material. The results f residual stress measurements carried ut in this first phase f the study indicate the fllwing fr heavy fabricated members:. All phases f the manufacture and fabricatin prcedure generally affect the frmatin f residual stresses. 2. The weld type (penetratin) and the yield strength f the steel are nt majr factrs in the frmatin f residual stresses. 3. The gemetry f the plates and shapes is ne f the imprtant variables affecting the residual stress magnitude and distributin. 4. The variatin f residual stress acrss the thickness f plates mre than G. A. ALPSTEN is Assciate Directr. Swedish Institute tr Steel Cnstructin and was frmerly with Lehigh University: L. TALL is Directr, Divisin fr Fatigue and Fracture. Fritz Engineering Labratry. Lehigh University, Bethlehem, Pa. Paper presented at the AWS 50th Annual Meeting held in Philadelphia, Pa., during April 28 t May 2, 969. in. thick can be cnsiderable. 5. The welding residual stresses in prtins f the crss sectin ther than the weld area tend t decrease with increasing size f the member, prbably because the weld area, and cnsequently, the heat input, is relatively smaller in heavy plates and shapes as cmpared t light members. 6. The initial stresses can be f a higher magnitude than the welding residual stresses. The relatinship between initial residual stresses in ccmpnent plates and welding residual stresses implies that effrts t limit the magnitude f residual stresses in heavy welded shapes shuld be directed twards the manufacture f the cmpnent plates. Thus, by using flamecut plates in heavy welded shapes, there is a prspect fr an increase in strength when cmpared with lighter members at the same slenderness rati. There is even a pssibility that such welded shapes may be strnger than their rlled cunterparts. Intrductin Only in the past tw decades was it experimentally and theretically verified that residual stresses are a majr influence n the strength f steel members in cmpressin. It was shwn that they have a significant effect n clumn strength '- 2 and n the buckling f plates. 3-4 It is als knwn that residual stresses can be f great imprtance in fatigue, brittle fracture, and stress crrsin. The previus experimental research n residual stress and the strength f welded steel members was related t small and medium-size shapes that is, shapes f cmpnents with a thickness equal t r less than in. ~ rl In tday's large structures, increasingly heavy shapes are used. Very little infrmatin has been available n the residual stresses and strength f heavy clumns, yet they are used extensively in Nrth America and elsewhere. Applicatins include the lwer stries f multi-stry buildings, majr bridges, and launching gantries fr rckets and space vehicles. Similar structural elements are used in ship and submarine hulls, and in vessels fr atmic reactrs. Sme heavy clumn shapes used in existing structures are shwn in Fig., which als illustrates the different ways f designing a heavy clumn shape. Rlled shapes can be used and are available in sizes up t the 4WF730 "jumb" shape f Fig. la. If the strength f the available rlled shape is insufficient fr a particular applicatin, plates can be welded t a rlled shape as shwn in Figs, lb and c. A heavy shape can als be built up frm welding tgether three plates t frm an H-shape, as illustrated in Fig. ld. Finally, a bx-shape can be made frm welding tgether fur plates Fig. le. The plates used in a welded shape can be manufactured either as universal-mill plates (that is, rlled t exact width and used with as-rlled edges) r as flame-cut * plates (that is, flame-cut frm a larger base plate). At present, the design f heavy clumns des nt differ frm that f small and medium-size clumns. The design criteria previusly develped fr small and medium-size rlled clumns 2 have been extraplated t include heavy members. While experience has indicated that this leads t safe design, it may nt be a cmpletely ratinal design methd. An extensive research prgram is currently underway at Lehigh University t study residual stresses in heavy welded plates and shapes. (Heavy plates and shapes are defined here as members with a thickness exceeding in.). The specific bjectives f the * Or xygen-cut (frm xygen cutting as defined by AWS in Terms and Definitins, AWS A3.0-69). WELDING RESEARCH SUPPLEMENT 93-s

2 X" I 8W (a) IIH66 (b) I4H2 (O I5H290 (d) 730 lb/ft (a) 30 lb/ft (b) 2690 lb/ft (C) 3 Scale (inches): 23H68I (e) 24D774 (f) 24HII22 (g) 60 Ib/ff 90 lb/ft (d) (e) Fig. Heavy clumn shapes in existing structures 0 30 Scale (inches): i i Fig. 2 Test clumns study are t determine the magnitude and distributin f residual stresses in thick welded plates by bth experimental and theretical means, and t relate this t the stability under cmpressive lads f structural members. Prir t the initiatin f the current study, critical infrmatin was lacking n the behavir f heavy clumns. The present status is illustrated in Fig. 2 (a-d) which shws: a. The largest test shape s far used in a multi-stry frame test. b. The largest welded shape in a beam-clumn test. c. The largest clumn shape. d. The largest stub clumn shape. The shapes in Figs. 2e thrugh 2g are examples f the specimens in the current research prgram. These shapes cmpare t the heavy clumn shapes used in cnstructin (see Fig. ). The paper presents sme experimental results btained in the first phase f the investigatin. While the specimens in the verall prgram cver the cmplete range f dimensins which are practical in cnstructin, that is, plates ranging in size frm 9 x V 2 up t 24 x 6 in. and welded H-shapes and a bx-shape ranging frm a 7H28 t a 24H22 shape, the specimens cnsidered in this paper are the 5H290 and 23H68 shapes (see Figs. 2d and e) as well as tw as-manufactured plates, 6x2 and 24 x 3 /? in. Figure 3 shws a cmparisn between the 23H68 shape and the 7H28 shape, crrespnding t the heaviest and lightest welded specimens tested s far in the Lehigh prgram. The results f the verall study will allw the predictin f residual stresses in any plate and any welded shape used in cnstructin. The plates and shapes in the investigatin will serve as reference data, and by knwing the dimensins f cmpnents and the manufacturing and fabricatin details f a practical clumn, the distributin f residual stress can be predicted. The clumn strength can then be determined, including the effect f residual stresses. The study is f a fundamental nature and f cnsiderable imprtance in many areas; hwever, the present Fig. 3 Largest (23H68) and smallest (7H28) clumn shapes tested s far in the research prgram Fig. 4 Fabricatin f the welded H- shape 23H68 (curtesy Bethlehem Steel Crp.) applicatin is the develpment f infrmatin which will be useful in preparing design criteria fr heavy clumn members as are used in cnstructin. The findings btained fr the basic welded plates will be applicable als t ther types f structures fr instance, ship and submarine hulls, and atmic reactr vessels. Fabricatin f Test Specimens The test specimens were fabricated by steel fabricatrs accrding t nrmal practices and prcedures. AWS specificatins were fllwed in the fabricatin. Submerged-arc welding methd was used fr all specimens. Pertinent welding data have been summarized in Table. The first fur specimens were fabricated frm universal-mill plates that is, the cmpnent plates in the welded shapes were used with as-rlled edges. The remaining specimens were fabricated frm flame-cut plates, btained by flame-cutting the cmpnent plates frm larger base metal plates. Specimens f the 5H290 shape were fabricated in bth ASTM and A44 steel fr cmparative tests. In additin, bth a fillet weld (partial penetratin) and a grve weld (full penetratin) were used. Fr the heavy shape 23H68, nly ne specimen f steel with fillet welds was fabricated. The welds in the 5H290 shapes were depsited in a symmetrical pattern as indicated in Table, t minimize the distrtin f the members. Tw passes were used fr the 5H290 shapes with fillet welds, but seven passes were required fr the grve welds. 94-s MARCH 970

3 Table --Welding Data fr Fab ricatin f Test Specimens Test specime n Shape n. designatin Materia H290 5H290 5H290 5H290 5H290 5H290 5H290 5H290 PL6 X 2 PL24 X 3Vs 23H68 A44 A44 A44 A44 Static yield stress, ksi Manufacture f plates UM UM UM UM b Size f flange plate, in. 4 X 2>A 4 X 2»/a 4 X 2>/, 4 X 2 /., 4 X 27, 4 X X 2'/., 4 X 27, 24 X 37, Size f web plate, in. 0 x 72 0 x 72 0 X iy* 0 x 72 0 X 7-j 0 x iy s 0 x 72 0 x 72 6 X2 Type submergedarc weld Fillet Grve Fillet Grve Fillet Grve Fillet Grve Fillet Detail f weld'' A- B" 2 D« E" See test specimen n. See test specimen n. 2 See test specimen n. See test specimen n. 2 See test specimen n. See test specimen n. 2 F= st DC FI. AC 2nd DC FI. AC c<- N. f passes Se-. Welding fr quence Vltage, each f weld Pass weld passes 0 n. V data- Cur- ' rent, amp Speed ipm Weighted average. ' UM universal milled; flame cut. See sketch ppsite letter designatin belw: A SAW>"f>/ Ft t SAW> l II TS 60*^" The 23H68 shape was welded using an autmatic beam welding machine with tw tandem electrdes. Thus, it was pssible t weld simultaneusly n bth the left and the right side f the shape, each weld being depsited in ne pass frm ne d-c electrde and ne a-c electrde spaced 4 / 2 in. apart. After the first flange and the web were jined tgether, the T-shape was turned ver and the secnd flange was welded t the T t frm the final H-shape. Figure 4 shws the 23H68 specimen and the beam welding machine used fr the fabricatin. A mre detailed accunt f the fabricatin f the 23H68 shape can be fund in the literature. s It was specified that n straightening peratins in any frm shuld be used after the welding. In practice, such peratins may becme necessary t fulfill straightness requirements. The cmmn methds used fr straightening heavy welded shapes that is, gagging r lcal heating by a flame will change the residual stress distributin lcally at the straightened sectin. The residual stresses in the unstraightened parts f the clumn will remain unchanged. Prcedure fr Measurement f Residual Stress The residual stress distributin in a thick plate is generally three-diu SAW> J rl 8, ,7 mensinal with stresses in the lngitudinal as well as the transverse directins. While the transverse stresses will affect the yielding behavir f the different fibers f the crss sectin, the lngitudinal stresses are f primary interest fr clumn strength. Thus, the theretical methds nrmally emplyed fr the predictin f clumn behavir and maximum strength f clumns cnsider the lngitudinal re- SECTIQNING -Tp Surface Reading 6,9,8,2, 25,24,7 27,22,9, 4,.6,3 4.5.I2A,2,28 8,23,26,.7,0,5 sidual stresses nly. When nly lngitudinal stresses are taken int accunt in the theries fr clumn strength predictin, it is in fact mre relevant in the residual stress measurement t cnsider the apparent lngitudinal stresses as btained directly frm the measured released strain in the lngitudinal directin, rather than t separate the influence f the stresses in all three direc- Straight Line Apprximatin Bttm Surface Reading SLICING Additinal Stress Frm Slicing Straight Line Apprximatin Frm Sectining -Shaded Area Equals Final Residual Stress Distributin Fig. 5 Principle f the sectining methd fr residual stress measurements WELDING RESEARCH SUPPLEMENT! 95-s

4 - 0 - \ \ 60 k f, \ \ rr*>^/ / \ t I i I i I ' I i I ' I 60 ~ - J \ \ \ 0 ^ / V - Fig. 6 Residual stresses in a welded shape 5H290 universal-mill plates, Steel, y, in. fillet welds Fig. 7 Residual stresses in a welded shape 5H290- -Univer- sal-mill plates, Steel, "/m in. grve welds tins. 0 This is because the effect f transverse stresses n the measured released strain in a sectining prcedure is smewhat similar t that n the yielding behavir f a clumn under lad. Thus, there are tw apprximatins, the errr f which tend t cancel each ther." With this prcedure f treating the measurements as ne-dimensinal, and when the transverse stresses are reasnably small that is, less than 50% f the lngitudinal stress the relative errr in the applied stress t cause yield in a fiber is less than %. Fr the behavir f the cmplete crss sectin, the relative errr will be cnsiderably less. Anther imprtant feature f the residual stress distributin in thick cmpnents is that the lngitudinal stresses can be expected t vary significantly thrugh the thickness f the cmpnents. The methd fr measurement f residual stresses must take int accunt this variatin. The prcedure used fr the measurements was a sectining methd, invlving lngitudinal saw cuts bth acrss the width and thrugh the thickness f the cmpnents. The methd is basically similar t the sectining methd used by Kalakutsky in 888 fr the measurement f residual stresses in steel cylinders. 0 The technique f the sectining methd as applied t heavy welded shapes was develped in the Lehigh research prgram. Gage pints were first laid ut arund the specimen (Fig. 5), and readings were btained using a 0 in. Whittemre mechanical extensmeter. The specimen was then cut int elements cntaining ne r mre gage pints n each surface ("sectining"), and new measurements were made. The released strains at bth surfaces f the elements culd be evaluated frm these measurements. If the rati f width t length and width t thickness f the elements is such that beam-type actin will ccur, the thrugh-thickness variatin f strains released in the sectining ( s(,,. t.) will apprximate a straight line ging thrugh the data pints btained n the surfaces. Measurements have indicated that the straight-line assumptin is reasnable fr the gemetry f elements used, and this assumptin is the basis fr the evaluatin prcedure. The sectining was then cntinued t btain the actual variatin f residual stress thrugh thickness. After the first set f saw cuts were made ("sectining"), additinal gage pints were laid ut alng the sides f the elements. New readings were taken by the extensmeter, fllwed by sawing the elements int strips acrss the thickness ("slicing"). Frm extensmeter readings befre and after the slicing, additinal strains, e sli(., were btained. These strains are superimpsed upn the strains frm the sectining t furnish the ttal strain variatin (see Fig. 5). Assuming that all residual strains have been released, the residual stress may be btained frm the relatinship: E (**, < (. + Eslic.) () The residual stresses released in the slicing prcedure must be in equilibrium fr each sectinal element. Thus, there is n cntributin t the average stress thrugh thickness frm these stresses. Cnsequently, the average residual stress btained as the mean value f readings frm bth surfaces in the sectining prcedure is equal t the actual average stress thrugh the thickness. The accuracy in the stress measurement is f the rder f ± ksi. An extensive study f the accuracy and 9B-s I MARCH 970

5 60 0 I ' I fl u Fig. 8 Residual stresses in a welded shape 5H290 universal-mill plates, A44 Steel, */, in. fillet welds -- Fig. 9 Residual stresses in a welded shape 5H290 universal-mill plates, A44 Steel, U / M in. grve welds the errr surces in the measurements was carried ut in cnnectin with the investigatin. 2 The experimental wrk invlved in the methd is enrmus, bth with respect t the required number f gage pint readings and the necessary sawing peratins. Fr example, the number f gage readings invlved in the measurements n a 24 x 3 /:; in. plate (see Figs. 7 and 9) is mre than 5000; the sawing was dne n a band saw and required a net machine time f the rder f 00 hr. Test Results The residual stress distributins btained frm sectining f the fur 5H290 specimens fabricated frm universal-mill plates are given in Figs. 6 thrugh 9. The curves shwn refer t the results btained n bth surfaces f the shape cmpnents in the sectining that is, befre slicing. The Fig. 0 Tw-dimensinal variatin f residual stress in a welded shape 5H290 universal-mill plates, Steel, Va in. fillet welds WELDING RESEARCH SUPPLEMENT 97-s

6 - - yv^~x 0< Hr*-*> r - w 60 X n n TT I ' I ' I ' I ' I ' i Fig. Residual stresses in a welded shape 5H290- cut plates, Steel, 7» in. fillet welds shapes in Figs. 6 and 7 are f steel, differing nly in the type f weld. Figures 8 and 9 shw a similar cmparisn fr A44 steel. The results f a cmplete sectining and slicing prcedure frm ne f the specimens is given in Fig. 0. The residual stress distributin is represented in the frm f an is-stress diagram, that is, cntur lines fr cnstant stress. Fr all fur shapes f universal-mill plates, the stresses at the flange tips are in cmpressin, and f a relatively high magnitude. The average stress at the flange tip varies between 6 and 24 ksi fr the fur shapes. Figures thrugh 4 shw the residual stresses as measured in the fur 5H290 specimens fabricated frm flame-cut plates. Again, the curves in the diagrams crrespnd t the measurements btained n bth surfaces f the cmpnents in the sectining test. Each specimen made f flame-cut plates in Figs. thrugh 4 crrespnds t a similar specimen made f universal-mill plates (Figs. 6 thrugh 9) s the distributins may be cmpared directly. Instead f relatively high cmpressive stresses as in the -flame- - L universal-mill plates, there are very high tensile stresses at the flange tips f the shapes made f flame-cut plates. Figure 5 gives the results btained frm sectining and slicing f the 5H290 specimen made f steel, and with fillet welds. As may be seen frm the cntur lines, there are steep gradients in the weld regin and at the flame-cut edges. As will be discussed further in the next sectin, it is bvius frm the results n the 5H290 specimens that the initial stresses existing in the cmpnent plates prir t welding are f great imprtance. Therefre, measurements n the cmpnent plates, befre welding, were included in the study f the 23H68 shape. Figures 6 and 7 give the average residual stress thrugh the thickness fr a 6 x 2 in. plate, taken frm the same base metal as the web plate f the shape, and a 24 x 3 /., in. plate, crrespnding t the flange plates f the shape. The stresses at the plate edges are in tensin with a maximum f apprximately 50 ksi at the flame-cut surface. The tensile stresses are balanced by cmpressive stresses in the center Fig. 2 Residual stresses in a welded shape 5H290 flamecut plates, Steel, "/,«in. grve welds f the plates. A cmplete picture f the actual distributin f lngitudinal residual stresses in the thick plates can be btained nly frm a study f the tw-dimensinal variatin f residual stresses ver the crss sectin. Figures 8 and 9 shw is-stress diagrams as btained frm sectining and slicing f the 6x2 in. and the 24 x 3 /,, in. plates, respectively. The variatin thrugh the thickness amunts t apprximately 2 ksi fr the 6 x 2 in. plate and 5 ksi fr the 24 x 3V 2 in. plate. Thus, althugh the average stress in the center part f the plates is cmpressive (see Figs. 6 and 7), the actual stress in the interir is tensile. Similarly, while the maximum cmpressive stress in the average diagram f the 24 x 3 /., in. plate is ksi, and true maximum cmpressin at any measured pint thrugh the crss sectin is actually 22 ksi. Figure shws schematically the additin f stresses during welding f the 23H68 shape. The distributins shwn are thse measured in separate specimens f lse plates and shapes, s there is n true algebraic additin in the diagrams. The additinal residual stresses resulting frm the welding 98-s MARCH 970

7 - 0 r / I S* r\ *J \ ~l rn / i / r h TT 4-4- Fig. 3 Residual stresses in a welded shape 5H290- cut plates, A44 Steel, Va in. fillet welds -flame i r \ \ / \j \i y~-sjj Fig. 4 Residual stresses in a welded shape 5H290- flamecut plates, A44 Steel, "/ v. in. grve welds were btained frm gage readings n the plates befre and after welding. These welding residual stresses add t the initial stresses existing prir t welding. It shuld be nted that the welding stresses culd be measured nly in the regins which remain elastic thrughut the welding and cling after welding. In the parts f the crss sectin where plastic defrmatins ccurred at any stage f the prcess, the measured strain will cntain a plastic cmpnent and cannt directly be cverted t stress. While the initial stresses in the flange plates vary between apprximately ksi and 50 ksi, the additinal stresses as measured in the elastic part f the flanges nwhere exceed 2 ksi (Fig. b). Fr the web the cmparisn between initial stresses and welding stresses is similar, althugh the welding stresses are f a smewhat larger magnitude than encuntered in the flanges that is, up t 3 ksi. Measured welding stresses in mst pints were in cmpressin. Naturally, the stress in the weld regin must be in high tensin, but this culd nt be meastired directly as explained abve. Because f the small residual stresses due t welding f this heavy shape, the distributin f the initial stresses is retained in the welded shape, nly with sme mdificatins in the magnitude f stress. Figure 2 shws the stresses as measured n bth surfaces f the cmpnents f the welded shape 23H68. The diagram can be cmpared directly with thse in Figs. 6-9 and -4 fr the 5H290 shape. A full understanding f the distributin f the residual stresses in the 23H68 shape can be gained nly frm the results f cmplete sectining and slicing, shwn in Fig. 22. The diagram indicates that nt nly is the variatin f stress acrss the width retained in the welded shape but als the variatin acrss the thickness is similar t that in the lse cmpnent plates. (Cmpare the diagram in Fig. 22 with thse in Figs. 8 and 9). Majr changes have ccurred nly in the weld area. Discussin f Results Frm the results btained n thickplates and heavy shapes in the investigatin it is clear that the welding residual stresses in areas f the crss sectin away frm the weld are far smaller in heavy welded shapes than fund in the earlier investigatins 3 -" fr small plates and shapes. Figure 23 shws a cmparisn between the initial residual stresses in a universal-mill plate 0 x V 2 in. and the residual stresses after applying welds in the center f the plate."' While the maximum cmpressive stress in the asrlled plate is 6 ksi, the maximum cmpressive stress in the welded plate is 26 ksi, indicating a cntributin frm the welding f ksi at this pint. Thus, fr this plate, which is representative f small and mediumsized plates, the residual stresses frm welding cnstitute the majr part f the residual stress distributin. Cmparing these results with thse summarized in Fig., it is nted that the situatin in the heavy material is quite different; the majr prtin f the residual stresses in the 23H68 shape are thse riginating frm the initial plates. The maximum cmpressive welding stress in the flange plate is 2 ksi. The flange plate is basically a center-welded plate and may, therefre, be cmpared directly with the center-welded plate in Fig. 23. The cmparisn exemplifies the bservatin that the welding residual stresses WELDING RESEARCH SUPPLEMENT 99-s

8 0 PLI6x2() Fig. 6 Residual stresses in a 6 x 2 in. flame-cut plate Fig. 5 Tw-dimensinal variatin, f residual stress in a welded shape 5H290 flame-cut plates, Steel,»/, in. fillet welds are f a smaller abslute and relative magnitude in heavy plates and shapes. This culd als be predicted since the rati f weld area t that f base metal is smaller fr heavy practical shapes. Thus, prprtinately, there is a smaller heat input fr shapes f 0 thick plates than there is fr light plates, and s heavy shapes wuld be expected t cntain cmpressive welding residual stresses f a smaller magnitude. The abve finding als means that the initial residual stresses existing in PL 24x3^ () Fig. 7 Residual stresses in a 24 x 3, in. flame-cut plate the cmpnent plates befre welding are f greater imprtance fr heavy shapes. This cnclusin is bvius frm the results btained n the 5H290 when cmparing the residual stresses in the shapes made frm universal-mill plates (Figs. 6-9) and frm flame-cut plates (Figs. -4). The nly difference between the tw sets f specimens is in the manufacturing prcedure fr the plates, s the cmparisn reflects the effect f this variable nly. All flanges f the 5H290 shapes made f universal-mill plates shw a similar kind f distributin with high cmpressive stresses at the flange tips. As can be seen in Fig. 0, the cmpressive stresses are at the yield pint level in the flange tip crners. This is in accrdance with theretical predictins f residual stresses in universalmill plates based upn the heat flw in cling.,:t Accrding t the predictins, the residual stresses tend t increase with increasing size f the member. Fr heavy plates subjected t free cling, the cling residual stresses as predicted are in high cmpressin at the plate edges and may apprach the yield pint fr sme plates. Flame-cut plates shw a reversed distributin with high tensile stresses at the flame-cut edge, balanced by cmpressive stresses in the center f the plate. The stress at the flame-cut surface is larger than the yield pint f the parent material. This is pssible because the mechanical prperties f the material clse t the flame-cut surface have been increased frm the rapid cling after cutting. Anther factr which influences the cnditins is the three-dimensinal stress state. Since the lcal stresses in the heated material nrmally are in high tensin 00-s MARCH 970

9 that is, f equal sign in all three directins the material can sustain a higher stress than the yield pint in a uni-axial tensin test. Basically, these cnditins prevail als in the weld regins in the welded shapes; this can explain the high tensin stresses invariably experienced in the welds. Fr the weld, hwever, the weld area cntains a mixture f electrde and base metal. The mechanical prperties f electrdes used fr welding structural carbn steels nrmally have a higher strength than the base metal. Thus, there are three effects tn c r. c < c UJ a: CO 60 OJ OJ 0 l > O <* CM i ' CO OJ CO UI 8 UJ CO CD z a ui i S i < >- t- Q n < CO c UI cc OJ c CM O * CD l l LU ID O O CM t O j < CO UJ a' (/> (/) <D -t-». OO UD i 75 CM / Ql Q. r -Sj!" =? r il.e WELDING RESEARCH SUPPLEMENT 0-s

10 which explain the ccurrance f high stresses in the weld areas:. Increased strength f material due t the electrde material. 2. Increased strength due t the cling rate. 3. Three-dimensinal stresses. Tensin tests f specimens cntaining weld metal have indicated a yield strength f ksi fr A7 steel that is, abut 50% higher than the yield strength f the base metal."' The residual stresses measured in the weld area f the heavy shapes are all f this rder f magnitude. The weld type is nt a majr factr in the frmatin f residual stresses in thick plates and shapes. A cmparisn f the distributins in Figs. 6 and 3. fr fillet welds, and the crrespnding diagrams in Figs. 7, 9, 2, and 4 fr grve welds, indicates n significant difference. This is prbably because the heat input in each weld pass is f the same rder f magnitude fr the fillet weld and the grve weld (see Table ). Similar results were btained previusly fr small and medi- -hum-size plates."' The residual stress distributins as measured in the shapes f steel and f A44 steel are similar, indicating that the type f steel has n great influence n residual stress. Since the effect f residual stress n clumn strength is dependent n the rati f residual stress t yield stress while at the same time the magnitude f the residual stresses are nt much affected by the type f material, it can be expected that clumns made f highstrength steels are strnger than thse made f steel, als when cmpared n a nn-dimensinal basis. This has been cnfirmed previusly by residual stress measurements and clumn tests n small and mediumsize welded shapes. 4 The gemetry f the plates and shapes is ne f the majr variables affecting the residual stress distributin. As discussed abve, the cntributin f residual stress due t welding is greatly dependent n the size f the cmpnents that is, whether the shape is light, medium-size, r heavy Fig. 2 Residual stresses in a welded shape 23H68 flame-cut plates, Steel, ' s in. fillet welds Figure 24 summarizes the results f residual stress measurements made n a number f welded shapes using flame-cut plates, ranging frm the 7H28 shape t the 23H68 shape. Generally, the residual stresses due t welding decrease with increasing size f the member. Anther feature f residual stresses in thick plates is the variatin thrugh the thickness f the cmpnents. Results f measurements including bth sectining and slicing have shwn that the variatin in thick plates is cnsideiable. Fr instance, the nnsymmetrical applicatin f welds n a flange plate results in high tensile stresses n the welded side, whereas the stress at the ppsite side ften is cmpressive. It is believed that the large variatin f stress acrss the thickness fr the cmpnent plates 24 x 3 /., in. and 6 x 2 in. (Figs. 8 and 9) remains frm the cling after rlling f the base metal. Theretical predictins f cling stresses in rlled plates f a similar size shw a distributin f stress thrugh thickness f the plate very clse t that measured in the center f these flame-cut plates. :i Als, the variatin acrss the width fr the center prtin f the plates appears t be influenced by the initial stresses frm the cling after rlling f the base metal plates. If there were n initial stresses befre flame-cutting f the plates, the stress distributin in the center prtins f the plates wuld apprximate a plane, except fr the heated and yielded regins at the flame-cut edges, where tensile stresses are intrduced. The measured distributins, hwever, shw a variatin acrss the plate width f 0 ksi and 3 ksi fr the center prtins f the 6 x 2 in. and 24 x V/., in. plates, respectively. The actual type f distributin in the center f the plates, with higher cmpressive stresses twards the edges, is cnsistent with predictins f cling stresses in similar rlled plates. VA This means that the stresses in thick flamecut plates result frm bth the cling after rlling f the base metal and the lcal heat input in the flame-cutting prcess. Thus, the residual stress distributin in a fabricated member f thick cmpnent plates generally is a cmplex superimpsed pattern resulting frm the different stages f manufacture and fabricatin prcedures. This is t say that cling residual stresses after rlling, residual stresses frm flamecutting as well as the welding residual stress and any ther prcedure emplyed in the manufacture and fabricatin will influence the final residual stress distributin in a heavy welded.shape. Hwever, since the welding 02-s MARCH 970

11 residual stresses in heavy welded shapes are small, except in the weld regin, residual stresses in such shapes may be predicted by determining the initial stresses in the cmpnent plates frm existing data r frm measurements and estimating the additinal residual stresses due t welding. This is a further simplificatin f the finding btained previusly fr smaller shapes that the residual stresses in a welded shape can be predicted frm a knwledge f the residual stress distributin in the separate cmpnent plates with simulated weld beads. 7 The relatinship between initial residual stresses in cmpnent plates and welding residual stresses implies that effrts t limit residual stresses in heavy welded shapes shuld be directed twards the manufacture f the cmpnent plates. Thus, by using flame-cut plates in heavy welded shapes, there is a prspect fr an increase in strength when cmpared with lighter members at the same slenderness rati. On the ther hand, the clumn strength f heavy clumns made f universal-mill plates with asrlled edges may be lwer, in particular fr steel and at higher slenderness ratis. 6 Fr heavy welded clumns made f flame-cut plates, there is even a pssibility that such welded shapes may be strnger than their rlled cunterparts. Figure 25 shws the measured distributin f residual stress in a rlled shape 4W r The nminal strength characteristics f this shape fall in between thse f the tw welded shapes 5H290 and 23H68 studied here. The stresses are very high, f a similar distributin and rder f magnitude as in the welded shape 5H290 made f universal-mill plates. The favrable indicatins fr the strength f heavy welded clumns made f flame-cut plates is in cntrast with previusly published results fr small and medium-size welded shapes f universal-mill plates which prved t be weaker than their rlled cunterparts. 6 Hwever, since the present basis fr the implicatins n heavy clumn strength is limited t the few specimens studied, the statements are preliminary; the general cnclusins will be develped further when the current research prgram is cmpleted. Cnclusins The purpse f this study was t investigate experimentally the magnitude and distributin f residual stress in heavy clumn shapes built up by welding plates with thickness in the range f V 2 t 3V 2 in. Tw shapes were investigated a 5H290 shape and a 23H68 shape. Fr the smaller shape cmparative tests were cnducted t study the influence f the manufacture f plates, weld type, and yield strength f the material. The specimens referred t in this paper cnstitute the first phase f a majr research prgram cncerning residual stresses in thick welded plates. Based n the results f this first phase f the prgram, the fllwing cnclusins can be stated: Fig. 22 Tw-dimensinal variatin f residual stress in a welded shape 23H68 flame-cut plates, Steel, Va in. fillet welds WELDING RESEARCH SUPPLEMENT' 03-s

12 0- - 7H28 I0H62 PLI0x'/2 (UM) - - ' ^^^^5^ M*^ ^D 0-60 \ / I2H79 I4H2 I5H290 23H68I Stress Scale(ksi): H68I I5H290 I4H2 I2H79 I0H62 7H28 60 Grve Weld Duble V Weld Fig. 23 Residual stresses in a 0 x /, in. universal-mill plate. The residual stress distributin in a fabricated member f thick cmpnent plates generally is a cmplex superimpsed pattern resulting frm the different stages f manufacture and fabricatin prcedures that is, cling residual stresses frm the rlling f the base plates, residual stresses frm flame-cutting the plates, as well as the residual stresses frm the welding prcess, all influence the final residual stress distributin in a welded shape. 2. The welding residual stresses in prtins f the crss sectin ther than the weld area tend t decrease with increasing size f the member, prbably because the weld area, and cnsequently, the heat input, is relatively smaller in heavy plates and shapes as cmpared t lighter members. 3. The results f cmparative meassurements n 5H290 shapes indicate that the weld type (penetratin) is nt a majr factr in the frmatin f residual stresses in heavy plates and shapes, as lng as the heat input is nt drastically changed. 4. The residual stress distributins as measured in shapes f ASTM steel and f A44 steel are similar, indicating that the yield strength f Fig. 24 Residual stresses in welded H-shapes f different gemetry. Flame-cut plates, Steel, fillet welds. (Results fr 2H79 and 4H2 shapes frm McFalls and Tall ") the steel has n great influence n residual stresses in heavy shapes. 5. The magnitude and distributin f initial residual stresses depends greatly n the manufacturing prcedure that is, universal-mill plates r flame-cut plates. 6. The gemetry f the plates and shapes is ne f the majr variables affecting the residual stress distributin. Mre specifically, the residual stresses will depend upn whether the shape is light, medium-sized r heavy (effect f size f crss sectin) r whether the plates are narrw, medium r wide (effect f width t thickness rati). 7. Residual stresses due t cling after rlling f a plate nrmally are cmpressive at the edges, balanced by tensin stresses in the center prtin f the plate. Measurements n fur welded H-shapes, 5H290, cntaining universal-mill plates indicate that the initial stresses in the flange plates are very high. This cnfrms t the bservatin made previusly frm the results f theretical predictins that the cling residual stresses in rlled plates tend t increase with increasing size f the plate. 8. Residual stresses due t flamecutting are in high tensin at the flame-cut edge due t the lcal heat input. Fr the flame-cut plates studied, the stress at the burned surface is abut 50% abve the yield pint f the base metal. The tensile stresses are balanced by cmpressin in the center part f the plate; the distributin f residual stresses in the center f a heavy flame-cut plate is dependent als n the initial stresses due t rlling. 9. The variatin f residual stress acrss the thickness f plates mre than in. thick can be cnsiderable. Such variatin will result in a plate with welds depsited n ne side f the plate; als, a significant difference can be expected between stresses in the surface and the interir f heavy rlled plate cmpnents. 0. The relatinship between the initial residual stresses in cmpnent plates and the welding residual stresses implies that the welding stresses in thick welded plates and shapes are f less imprtance than the initial stresses existing prir t welding. Effrts t limit residual stresses in heavy welded shapes shuld be directed twards the manufacture f the cmpnent plates.. Since the welding residual stresses in heavy welded shapes are small, except in the weld regin, residual stresses in such shapes may be predicted by determining the initial stresses in the cmpnent plates frm existing data r frm measurements, and estimating the additinal residual stresses due t welding. This is a further simplificatin f the finding btained previusly fr smaller shapes that the residual stresses in a welded shape can be predicted frm a knwledge f the residual stress distributin in the separate cmpnent plates with simulated weld beads. 7 The effect f residual stresses n the 04-s MARCH 9 70

13 lad-carrying behavir and strength f heavy clumns will be discussed further in the future paper. 6 Briefly, by using flame-cut plates in heavy welded shapes, there is a prspect fr an increase in strength when cmpared with lighter members at the same slenderness rati. Under certain circumstances, there is even a pssibility that such welded shapes may be strnger than their rlled cunterparts; this is the ppsite relatinship as cmpared t the situatin fr small and medium-sized shapes. On the ther hand, heavy welded clumns f universal-mill plates and steel are expected t shw a lwer clumn strength, especially fr clumns f a medium t high slenderness rati. l4w r T T Acknwledgments This paper presents the results f an experimental study f residual stresses in heavy welded shapes. The investigatin is the first phase f a majr research prgram designed t determine the residual stresses in thick welded plates and shapes and t relate this t the stability under lad f cmpressin members. The investigatin was cnducted at Fritz Engineering Labratry, Lehigh University, Bethlehem, Pa. The Natinal Science Fundatin spnsrs the current research prgram. A pilt study, included in this paper, was part f a prject spnsred jintly by the Pennsylvania Department f Highways, the Bureau f Public Rads f the U. S. Department f Cmmerce, the Clumn Research Cuncil, the American Institute f Steel Cnstructin, and the American Irn and Steel Institute. The specimens were fabricated by the Bethlehem Steel Crp., and thanks are due t that crpratin and its persnnel wh assisted in the design and fabricatin f the specimens. The guidance f Task Grup f the Clumn Research Cuncil, under the chairmanship f Jhn A. Gilligan, is gratefully acknwledged. Special thanks are due t Lynn S. Beedle, Directr f Fritz Engineering Labratry, fr his advice and encuragement thrughut the prgram. Firell R. Estuar and William C. Cranstn carried ut the experiments n the 5H290 shape and Charles R. Nrdquist assisted in the measurements n the 23H68 shape and its cmpnent plates. Their assistance is sincerely appreciated. Thanks are als due t Kenneth R. Harpel, labratry freman, and his staff fr the preparatin f the test specimens, t Mrs. Sharn Balgh fr the preparatin f the drawings, and ) V Fig. 25 Residual stresses in a ht-rlled shape 4\AF426, A7 steel t Miss Janne Mies and Mrs. Linda Welsch fr their care in typing the manuscript. References. Huber. A. W.. and Beedle, L. S.. "Residual Stresses and the Cmpressive Prperties f Steel," WELDING JOURNAL, 33 (2), Research Suppl s t 64-s, (954). 2. Beedle. L. S., and Tall. L.. "Basic Clumn Strength," Trans. ASCE, Vl. 27, Part II, pp. 38 t 79, Nishin, F., Ueda. Y., and Tall. L., Experimental Investigatin f the Buckling f Plates with Residual Stresses, ASTM STP N. 49. "Test Methds fr Cmpressin Testing," August Ueda, Y., and Tall, L., "Inelastic Buckling f Plates with Residual Stresses," Publicatins, Internatinal Assciatin fr Bridge and Structural Engineering, Vl NagarajaRa. N. R.. and Tall. L.. "Residual Stresses in Welded Plates." WELDING JOURNAL, (0), Research Suppl., 468-s t 480-s (96). 6. Estuar, F. R.. and Tall. L.. "Experimental Investigatin f Built-Up Clumns." WELDING JOURNAL. 42 (4), Ibid., 64-s t 76-s (963). 7. NagarajaRa, N. R., Estuar, F. R., and Tall, L., "Residual Stresses in Welded Shapes. WELDING JOURNAL, 43 (7), Ibid., 295-s t 396-s (964). 8. Alpsten, G. A., "Residual Stresses in a Heavy Welded Shape 23H68," Fritz Labratry Reprt N , in preparatin. 9. Alpsten. G. A.. "Three-Dimensinal Residual Stresses and Clumn Strength," Fritz Labratry Reprt N. 337., in preparatin. 0. Kalakutsky, N., The Study f Internal Stresses in Cast Irn and Steel, Lndn Estuar, F. R.. "Welding Residual Stresses and the Strength f Heavy Clumn Shapes," Ph.D. Dissertatin. Lehigh University, Aug (University Micrfilms, Inc.. Ann Arbr, Michigan). 2. Brzzetti. J.. and Alpsten. G. A.. "Accuracy f the Sectining Methd fr Residual Stress Measurements," Fritz Labratry Reprt N in preparatin. 3. Alpsten, G. A.. "Thermal Residual Stresses in Ht-Rlled Steel Members." Fritz Labratry Reprt N , December, Kishima. Y.. Alpsten, G. A., and Tall, L., "Clumn Strength f Welded Shapes Using Flame-Cut Plates." Fritz Labratry Reprt N in preparatin. 5. McFalls, R. K., and Tall, L., "A Studv f Welded Clumns Manufactured frm" Flame-Cut Plates." WELDING JOURNAL, 48 (4), Research Suppl., 4-s t 5-s (969). 6. Alpsten. G. A., and Tall, L., "Clumn Strength f Heavy Shapes-A Prgress Reprt," Fritz Labratry Reprt N in preparatin. 7. Fujita, Y., "The Magnitude and Distributin f Residual Stresses," Fritz Labratry Reprt N. 2A., May, 955. WELDING RESEARCH SUPPLEMENT 05-s