Mat Chapter 31

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Mat Chapter 31
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  WELDS-STATIC AND FATIGUE STRENGTH-II  WELDS- STATIC AND FATIGUE STRENGTH – II 1.0 INTRODUCTION In the previous chapter, a etai!e account o various #e!in$ processes, t%pes o #e!s,avanta$es o #e!e connections etc& #ere presente& It #as seen that #e!econnections are continuous an 'ore ri$i #hen co'pare to (o!te connections& It #asa!so pointe out that i!!et #e!s an (utt #e!s constitute respective!% )*+ an + o  a!! #e!s in the construction inustr%. the (a!ance + is 'ae up (% p!u$, s!ot an spotresistance #e!s&In this chapter, the (ehaviour an esi$n o #e!e connections uner various static!oain$ conitions is consiere& A t%pica! connection esi$n process is initiate #ith theesi$n, #hich is o!!o#e (% the #e!in$ operation an, conc!ues #ith inspection& 2.0 CONNECTION DESIGN In the esi$n o connections, ue attention 'ust (e pai to the !o# o the orce throu$hthe connection& The trans er o orces shou! occur s'ooth!%, #ithout causin$ an% stressconcentration or crac/s& The connections can (e either concentric or eccentric& Inconcentric connections, the orces actin$ on the connections #i!! essentia!!% (e a0ia! innature, #hereas in eccentric connections, the a0ia! orces #i!! (e coup!e #ith (enin$ or torsion& These t%pes o connections are escri(e in the o!!o#in$& 2.1 Concentric connections  Static stren$th o a #e!e 1oint epens upon the o!!o#in$ actors ã T%pe an si2e o the #e! ã 3anner o #e!in$, an ã T%pe o e!ectroe use&A pri'ar% responsi(i!it% o a esi$ner is to se!ect the t%pe an si2e o the #e!& A nu'(er o varieties o #e!s are avai!a(!e& When it is proper!% chosen #ith the correct e!ectroe,it eve!ops u!! stren$th o the parent 'ateria!& The chosen t%pe o #e! shou! eve!op'ini'a! resiua! stresses an istortions& As state in the introuction, (utt an i!!et #e!s are the usua! or's o #e!s in practica! (ui!in$ construction& 4utt #e!s are use at an e$e-to-e$e 1unction or a tee 1unction& A (utt #e! connection is 'ae (% (rin$in$ the p!ates to (e 1oine ace to acee$e#ise an then i!!in$ the cavit% or'e (% e$e preparation or (% 1ust penetratin$ theunprepare 1unction& 4utt #e!s can (e either u!! penetration or partia! penetration& 5 Cop%ri$ht reserve ersion II!1-1 !1  WELDS-STATIC AND FATIGUE STRENGTH-II 6artia! penetration (utt #e!s 'a% (e use or static !oain$, i reuce stren$th isaccepta(!e& 7n the other han, a i!!et #e! is 'ae a#a% ro' the e$es o the a(uttin$ p!ates& The 1oint is or'e (% #e!in$ the 'e'(ers in an over!appe position or (% usin$a seconar% 1oinin$ 'ateria!& The 'ain avanta$e o a i!!et #e! is that the re8uire'entso a!i$n'ent an to!erance are !ess ri$orous #hen co'pare to (utt #e!s& Fi!!et #e!in$cou! (e app!ie or !ap 1oints, tee 1oints an corner 1oints& A etai!e escription o theset#o t%pes o #e!s an their esi$n re8uire'ents are presente in the o!!o#in$&  2.2 #tt $e%&s Fu!! penetration (utt #e!s are or'e #hen the parts are connecte to$ether #ithin thethic/ness o the parent 'eta!& For thin parts, it is possi(!e to achieve u!! penetration o  the #e!& For thic/er parts, e$e preparation 'a% have to (e one to achieve the #e!in$,#hich has (een iscusse in the previous chapter& There are nine i erent t%pes o (utt 1oints9 s8uare, sin$!e :, ou(!e :, sin$!e U, ou(!eU, sin$!e ;, ou(!e ;, sin$!e (eve! an ou(!e (eve!& The% are sho#n in Fi$& & In orer to8ua!i % or a u!! penetration #e!, there are certain conitions to (e satis ie #hi!e'a/in$ the #e!s& The 'ore i'portant ones are $iven (e!o#9 2.2.1Static behaviour of butt welds For (utt #e!s the 'ost critica! or' o !oain$ is tension app!ie in the transverseirection <Fi$& =>& It has (een o(serve ro' tests conucte on tensi!e couponscontainin$ a u!! penetration (utt #e! nor'a! to the app!ie !oa that the #e!e 1ointha hi$her stren$th than the parent 'eta! itse! & Durin$ the app!ication o the !oa, the#e!e portion an the HA? <Heat A ecte ?one o the parent 'eta!> have !esstransverse contraction co'pare to the parent 'eta!& The %ie! stress o the #e! 'eta!an the parent 'eta! in the HA? re$ion #as oun to (e 'uch hi$her than the parent'eta!& The increase in %ie! stress in the HA? is ue to the 8uenchin$ e ect associate#ith rapi coo!in$ a ter eposition o the #e!& ersion II!1-2 (a) Square(b) Single V (c) Double V (d)Single Bevel (e)Double Bevel (f) Single U (g) Double U (h) Single J (i)Double J  Fig. 1Different types of butt joints (j) Double V – finished flush on both sides  WELDS-STATIC AND FATIGUE STRENGTH-II The %ie! stress o the #e! 'eta! is a!so raise ue to the 8uenchin$ e ect& The 'eta!a!!o%s constitutin$ the e!ectroe contri(ute to the increase in %ie! stress& These a!!o%s penetrate the parent 'eta! in !uencin$ its 'echanica! properties& Due to the !o#er %ie! stress an hi$her transverse contraction in the parent 'eta!, ite0periences a hi$her true stress& As a conse8uence, the ai!ure o the coupon a!#a%soccurs a#a% ro' the #e!& The hi$her stren$th achieve (% the #e!e 1oint averse!%a ects its tou$hness an ucti!it% properties& These ne$ative e ects can (e 'ini'ise (%choosin$ proper e!ectroes& 6artia! penetration #e!s, sho#n in Fi$& @, i er in t#o #a%s ro' the u!! penetration#e!s9 the reuction in cross section an the uncertaint% o the #e! root 8ua!it%& First!%,there is a reuction in the cross section at the 1oint resu!tin$ in over!oain$ an severe p!astic strainin$& Further, the #e! root 8ua!it% cannot (e inspecte an the% cannot (erepaire as 'a% (e one or u!! penetration #e!s& 2.2.2Design The (utt #e! is nor'a!!% esi$ne or irect tension or co'pression& Ho#ever, a provision is 'ae to protect it ro' shear& Desi$n stren$th va!ue is o ten ta/en the sa'eas the parent 'eta! stren$th& For esi$n purposes, the e ective area o the (utt-#e!econnection is ta/en as the e ective !en$th o the #e! ti'es the throat si2e& E ective!en$th o the (utt #e! is ta/en as the !en$th o the continuous u!! si2e #e!& The throatsi2e is speci ie (% the e ective throat thic/ness& For a u!! penetration (utt #e!, thethroat i'ension is usua!!% assu'e as the thic/ness o the thinner part o the connection&Even thou$h a (utt #e! 'a% (e rein orce on (oth sies to ensure u!! cross-sectiona!areas, its e ect is ne$!ecte #hi!e esti'atin$ the throat i'ensions& Such rein orce'entso ten have a ne$ative e ect, proucin$ stress concentration, especia!!% uner c%c!ic!oas& ersion II!1-!  Fig.3 Partial penetration weld   Longitudinal directionTransverse direction   (a)(b) Fig.2 (a !oad applied in transverse direction (b longitudinal shrin age restraint   WELDS-STATIC AND FATIGUE STRENGTH-II Genera!!% spea/in$, partia! penetration #e!s 'ust (e avoie& 6artia! penetration $roove#e!s are use in non-critica! etai!s, so as to avoi (ac/-$ou$in$& I the% are consiereessentia!, the% shou! (e esi$ne #ith care& So'e coes o practice o not reco''entheir use in tension& 7thers speci % that the% (e esi$ne in the sa'e #a% as i!!et #e!s&This is (ecause the !oa trans er is not s'ooth an e icient #ith partia! penetration#e!s& The e ective throat thic/ness o a partia! penetration #e! is ta/en as the'ini'u' thic/ness o the #e! 'eta! co''on to the parts 1oine, e0c!uin$rein orce'ent& For stress ca!cu!ation, a 'a0i'u' va!ue o reuce e ective throatthic/ness e8ua! to ) o the thic/ness o the thinner part 1oine 'ust (e use& Theun#e!e portion in partia! penetration (utt #e!s, #e!e ro' (oth sies, sha!! not (e$reater than B thic/ness o the thinner part 1oine, an shou! (e in the centra! portion& I the stresses are uni or' across the throat thic/ness, the avera$e stress concept 'a% (eapp!ie to eter'ine its stren$th& Connections #ith partia! penetration #e!s #ith#e!in$ on on!% one sie is $enera!!% avoie uner tensi!e !oa ue to the eccentric!oain$ invo!ve& 7ther#ise, the eccentricit% e ects shou! (e consiere in the esi$n&Unsea!e (utt #e!s o :, U, ; an (eve! t%pes an inco'p!ete penetration (utt #e!sshou! not (e use or hi$h!% stresse 1oints an 1oints su(1ecte to %na'ic ana!ternatin$ !oas& Inter'ittent (utt #e!s are use to resist shear on!% an the e ective!en$th shou! not (e !ess than our ti'es the !on$ituina! space (et#een the e ective!en$th o #e!s nor 'ore than  ti'es the thinner part& The% are not to (e use in!ocations su(1ecte to %na'ic or a!ternatin$ stresses& So'e 'oern coes o not a!!o#inter'ittent #e!s in (ri$e structures& For (utt #e!in$ parts #ith une8ua! cross sections, sa% une8ua! #ith, or thic/ness, thei'ensions o the #ier or thic/er part shou! (e reuce at the (utt 1oint to those o thes'a!!er part& This is app!ica(!e in cases #here the i erence in thic/ness e0cees = + o  the thic/ness o the thinner part or @&* '', #hichever is $reater& The s!ope provie atthe 1oint or the thic/er part shou! not (e steeper than one in ive Fi$s& <a> <(>& Ininstances, #here this is not practica(!e, the #e! 'eta! is (ui!t up at the 1unction e8ua! toa thic/ness #hich is at !east = + $reater than the thinner part or e8ua! to the i'ensiono the thic/er part Fi$& < c >& Where reuction o the #ier part is not possi(!e, the enso the #e! sha!! (e returne to ensure u!! throat thic/ness& ersion II!1-' (a)Ta!er not e ceeding # in $%eld Ta!er not e ceeding # in $ (b) t  (c)  &ot less than t'  u! to the di*ension of thic+er *aterial  Fig. # $utt welding of %e%bers with (a&(b une'ual thic ness (c une'ual width
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