** Daim ntawv ceeb toom tseem ceeb: ** Qhov no yog cov ntawv sau cia, tsis yog cov qauv tsim tam sim no, suav nrog cov ntaub ntawv pov thawj, cov ntaub ntawv pov thawj ntawm lub peev xwm thauj khoom lossis kev tsim khoom thiab cov lus qhia sib dhos. Kev tsim cov qauv steel yuav tsum suav nrog cov kev ua haujlwm tiag tiag, kev sib txuas, kev ruaj ntseg, qaug zog, hluav taws kub, corrosion thiab tag nrho lwm yam cuam tshuam raws li cov cai thiab cov qauv siv tau, nrog rau lub luag haujlwm ntawm tus tsim qauv tsim.
Kev tsim thiab kev tsim cov qauv hlau tsis yog ib feem ntawm kev muab pej xeem tam sim no ntawm Savo Kusić. Niaj hnub no lub hom phiaj tsim khoom muaj xws li ntoo qhov rais, ntoo-aluminium Qhov rais thiab kev cai qhov rooj.
Cov qauv hlau muaj qhov sib txawv hauv qhov uas lawv feem ntau yog ua los ntawm cov hlau kub kub. Kev sib koom ua ke yog ua tiav siv rivets, screws lossis vuam. Qhov no suav nrog cov qauv hlau rau cov txuas hniav, cov tsev, kev lag luam thiab mining, hydraulic engineering, pillars, towers, tanks, nyob rau hauv ib tug dav dav kev txiav txim siab thiab rau cranes, shipbuilding, boilers, thiab lwm yam. Lub hom phiaj ntawm kev nthuav qhia hauv qab no yog kev kho cov ntsiab lus yooj yim.
Cov ntaub ntawv
Cov khoom siv tseem ceeb ntawm kev tsim steel yog dov profiles los ntawm kev tsim kho zoo steel S235, S275, S355, S420, S450. Nyob ntawm tus qauv, muaj ntau ntau hom kev tsim steel, qhov twg tus lej hauv kev faib tawm feem ntau qhia txog lub zog tensile ntawm cov hlau. Muaj ob peb tsab ntawv cim, qhov twg hauv qhov no S sawv cev rau cov qauv hlau. Cov ntaub ntawv siv ntau tshaj plaws yog S, B (paj steels, reinforcement) thiab Y (prestressing steel).
Steel dov kev txhawb nqa
Muaj ntau yam kev txhawb nqa steel profiled thiab txhua tus muaj nws lub hom phiaj, qhov zoo thiab qhov tsis zoo.
- Ua-profiles
- I-profiles nrog ob txhais ceg nqaim (IPE, IPN)
- I-profiles nrog ob txhais ceg dav (HEA, HEB, HEM, HD)
- Hollow profiles / thawv (round, square, rectangular)
- Cov ntawv
- Cov khoom txias tsim (tau los ntawm txias dov ib lub tiaj tiaj thiab twisting ib lub tiaj tiaj)
Txhua yam ntawm cov profiles no txawv ntawm cov duab, qhov ntev, lub hom phiaj, thiab lwm yam. Piv txwv li, muaj ntau tshaj 20 txawv IPN profiles, uas txawv qhov ntev; loj profiles tuaj yeem tiv taus buckling (flexural thiab lateral-torsional), deflections, thiab lwm yam.
Muaj plaub chav kawm ntawm cov hlau nyob ntawm seb lawv mus txog qhov taw tes tawm thaum muaj kev ntxhov siab ntxiv, seb qhov kev tsom xam yog cov yas los yog elastic, dab tsi yog qhov muaj peev xwm ntawm cov ntoo khaub lig, thiab lwm yam. qhov twg thawj chav kawm yog qhov zoo tshaj plaws thiab qhov thib plaub yog qhov phem tshaj. Xav paub ntxiv txog cov qauv thiab lub zog ntawm cov hlau tuaj yeem nyeem ntawm no.
Voltage equalization thiab nqa lub peev xwm ntawm cov khoom ruaj khov
Bearing muaj peev xwm. Qhov ntev ntawm cov qauv steel raug txiav txim siab kom tsis txhob muaj qhov cuam tshuam loj heev. Cov kabmob muaj peev xwm, ntawm qhov tod tes, nyob rau hauv ntau qhov xwm txheej tsis yog sab hauv txhua txoj kev thaum qhov kev sib piv siab tshaj plaws mus txog qhov taw tes tawm los - tom qab ntawd cov deformations loj hlob sai dua qhov kev ntxhov siab. Rau cov qauv hlau, tib qhov kev cia siab ib yam li thaum yielding tuaj yeem ua raws li qhov txwv ntawm Hooke txoj cai rau cov xeev kev ntxhov siab. Nyob rau hauv cov ntaub ntawv ntawm homogeneous kev nyuaj siab xeev, uas sib npaug ntawm txhua qhov chaw, tsis muaj kev hloov pauv tshwm sim thaum qhov kev txwv ntawm proportionality yog tshaj, tshwj tsis yog tias tag nrho cov deformations loj hlob sai dua qhov kev ntxhov siab.
Kev sib npaug ntawm kev ntxhov siab thaum khoov. Nyob rau hauv rooj plaub ntawm dabtsi yog khoov ntawm lub nqaj, lub rectilinear kev ntxhov siab faib raws li Navier hypothesis siv, kom txog rau thaum ntug kev ntxhov siab σ = M / W tsis tshaj qhov txwv ntawm proportionality. Longitudinal expansions ε = ε(σ). Qhov no muaj tseeb tsawg kawg yog rau cov khoov me me. Cov kev ntxhov siab uas siab tshaj qhov sib npaug ntawm qhov kev ntxhov siab tuaj yeem loj hlob qeeb dua li qhov nthuav dav ε. Hauv daim duab. 1 qhia txog kev khoov kev ntxhov siab rau daim duab qhia kev ua haujlwm thiab rau ntau yam txiaj ntsig ntawm ntug kev nthuav dav. Lub cheeb tsam ntawm qhov sib npaug (cim nrog lub voj voog ntawm tag nrho cov kab hluav taws xob) yog li ua me thiab me me nrog nce ntug dilatation. Lub ntug voltage yog thawj zaug txwv los ntawm σF. Tsuas yog tom qab cov deformations tseem ceeb heev ua rau qhov siab tshaj plaws kev ntxhov siab nce siab tshaj σF, kom lub zog ntawm cov txheej txheem steel qhov cuab lub zog yuav pom (cov ntaub ntawv 5).
Daim duab. 1 - Khoov voltage vaj huam sib luag
Kev sib npaug ntawm kev ntxhov siab peaks. Kev faib tawm ntawm qhov kev ntxhov siab ntev thoob plaws ntu los ntawm nruab nrab ntawm lub qhov hauv ib qho tensioned drilled pas nrig kwv yees li ntawm kab 2 hauv daim duab. 2. Qhov voltage ncov σmax nyob ntawm qhov sib piv d/b. Nws yog feem ntau nyob ib ncig ntawm σmax = 2-3 σm, qhov twg σm = S / FM qhia qhov nruab nrab tus nqi ntawm tensile kev nyuaj siab nyob rau hauv seem tsis muaj zog los ntawm lub qhov ntawm FM. Sl. 2 siv tau kom txog rau thaum lub xeev voltage tshaj qhov P-limit. Ntawm cov loads siab dua, txhawm rau ua tiav qee qhov dilation, qhov voltages qis dua raws li txoj cai ncaj nraim tsuas yog yuav tsum tau nyob ze ntawm lub qhov. Ntawm cov ntsiab lus kev ntxhov siab tshaj plaws, cov kev ntxhov siab yuav tsis nce ntxiv nrog S, tab sis qeeb dua. Ntawm tus ciam teb, kwv yees li kev faib tawm ntawm qhov kev ntxhov siab longitudinal σm = σf yuav tau txais tag nrho seem 2-2. Shear thiab transverse stresses tau neglected. Qhov tshwm sim ntawm kev sib npaug ntawm kev ntxhov siab thaum lub sij hawm qeeb qeeb ntawm lub zog S hauv tus pas nrig ua pov thawj tias txoj kev niaj hnub rau cov qauv steel nyob rau hauv cov nyhuv ntawm cov khoom zoo li qub yog tsim nyog, tsis quav ntsej cov kev ntxhov siab peaks thaum lub sij hawm qhov ntev thiab sib piv tsuas yog qhov nruab nrab ntawm kev ntxhov siab σm \ = S / Fm hauv seem tsis muaj zog Fm nrog tus nqi tso cai.
Daim duab. 2
Dimensioning txheej txheem raws li lub peev xwm thauj khoom
Raws li lub load nce, voltage equalization tshwm sim nyob rau hauv seem. Hauv kev ua li ntawd, cov kev ntxhov siab tau muab rov qab los ntawm qhov kev ntxhov siab tshaj plaws ntawm ntu mus rau qhov tsis tshua muaj kev ntxhov siab. Ntev npaum li qhov deformations tsis loj heev uas lawv yuav tsum tau coj mus rau hauv tus account thaum teeb tsa qhov sib npaug, cov txheej txheem no tsis tuaj yeem hloov pauv ib yam dab tsi ntawm qhov loj ntawm lub zog ntawm S, M, thiab lwm yam nrog cov qauv txiav txim siab.
Kev txhawb nqa tsis tu ncua thiab thav duab: raws li qhov kev xav ntawm Hooke txoj cai, nws tau txais rau ib qho kev txhawb nqa tas mus li ntawm ntu (daim duab.3) lub sijhawm kab qhia hauv qab a. Cov kev ntxhov siab khoov yog proportional rau lub sijhawm khoov M. Yog tias ob qho tib si loads sib npaug, P-limit thawj zaug yuav dhau los ntawm kev txhawb nqa nruab nrab B. Cov kabmob txwv tau mus txog thaum lub sijhawm txwv MDF tau mus txog hauv thaj chaw ib yam. Nyob rau hauv cov ntaub ntawv ntawm ib tug beam clamped rau ob sab ntawm ib tug tas li symmetrical seem nrog ib tug concentrated quab yuam (fig.4) lub sij hawm equalization tshwm sim los ntawm qhov pib. Thaum P-limit ntau tshaj, tsis muaj kev hloov pauv hauv lub sijhawm faib khoom. Ntawm qhov tsis sib xws, nyob rau hauv cov ntaub ntawv ntawm ib tug sib npaug faib load (Fig.5) qhov sib npaug ntawm lub sijhawm ua rau txo qis ntawm lub sijhawm pinching nrog -2/3 Mtxog ntawm -1/2 Mo.
Sl.4
Sl.3lwm.5, ntsig txog: khoov lub sij hawm: a) ua ntej, b) txwv lub xeev tom qab quab yuam regrouping; a) ua ntej, b) tom qab sib npaug ntawm lub zog
Lattice kev tsim kho: nrog rau sab hauv statically indeterminate trusses, muaj xws li dependencies zoo li nrog thav duab tsim. Cov kev ntxhov siab thib ob, uas muaj feem xyuam nrog cov nodes uas nruj hauv kev khoov, tuaj yeem tsis saib xyuas hauv thawj qhov kev kwv yees thaum ntsuas lub peev xwm thauj khoom. Plasticized seem ua zoo ib yam li cov pob qij txha, yog li ntawd qhov kev ua haujlwm zoo li qub ntawm lub girder nyob rau hauv qhov kawg load nws tseem tuaj yeem nqa tau ze rau qhov zoo tshaj plaws truss nrog cov pob qij txha hauv cov pob qij txha. Nyob rau hauv cov ntaub ntawv ntawm kev tsim kho nrog nquag rov ua haujlwm, nyob rau hauv uas qaug zog lub zog tshwm sim yuav tsum tau coj mus rau hauv tus account, yog li ntawd muaj kev xav tsis thoob txog kev sib npaug ntawm cov rog rau hauv tus account thaum lub sij hawm dimension. Ntawm qhov tsis sib xws, nws yog qhov tseem ceeb tshaj plaws los xaus rau kev cuam tshuam ntawm kev hloov pauv ntawm kev txhawb nqa. Txij li thaum lub zog ua hauj lwm ntawm tus kheej cov txheej txheem nyob ntawm tsuas yog nyob rau hauv cov kev txwv ntawm kev nyuaj siab, thiab tsis nyob ntawm qhov luaj li cas ntawm tag nrho cov deformations, lub displacements ntawm cov kev them nyiaj yug tsis muaj feem xyuam rau lub bearing muaj peev xwm.
Alternating load: qhov kev xav ntawm cov ntaub ntawv load tas li tsis tshua paub. Nrog tus choj girders, muaj qhov sib txawv load xeev. Cov kev xav txog kev quab yuam thiab kev ntxhov siab nyob rau hauv tus kheej cov txheej txheem, uas ua kom yooj yim, muaj ntau yam hauv kev ua haujlwm nrog cov qauv hlau, raws li yav dhau los, lawv raug tsim nyog raws li qhov xwm txheej. Qhov no yog qhov tseeb tshwj xeeb tshaj yog rau kev tsis saib xyuas hauv zos voltage peaks. Nws tsis tuaj yeem raug pom zoo kom siv cov txheej txheem ntawm qhov loj me raws li lub peev xwm thauj khoom hauv qab (dynamic) qaug zog loading. Yog li, cov txheej txheem dimensioning raws li lub peev xwm load yog txwv rau cov ntaub ntawv ntawm feem ntau zoo li qub loads, tshwj xeeb tshaj yog rau kev tsim kho hauv kev lag luam hauv tsev. Nyob rau hauv lwm yam mob, nyob rau hauv uas yuav tsum tau them nyiaj mloog mus rau cov tsos ntawm qaug zog, loj deformations yuav tsum tau muab tshem tawm thiab txoj kev xav ntawm elasticity coj raws li lub hauv paus. Nyob rau hauv tas li ntawd, ib tug yuav tsum siv zog rau ib tug txaus loj nyob deb ntawm lub yield point. Lub toughness ntawm kev tsim steel ces muab ib co ntxiv kev ruaj ntseg.
Alternating stress
Cold stretching and aging: In fig. 6 txoj kab kev ntxhov siab-dilation ntawm ib puag ncig pas nrig, uas tau raug rau kev hloov tensile thiab compressive stresses, tau siv. Cov txheej txheem thauj tus kheej raug cim nrog cov lej raws li lawv qhov kev txiav txim. Elastic dilatations uas rov qab thaum unloading kuj tshwm sim tom qab loj stretches nyob rau hauv feem rau cov kev ntxhov siab. Thaum hloov qhov hluav taws xob kos npe, P-limit yuav luag tag. Yog li ntawd, cov khoom elastic ntawm kev tsim kho steel kos nyob rau hauv lub xeev txias tsis pom zoo nrog tus nqi qub. Nyob ntawm kev ua haujlwm dhau los, qhov sib txawv tseem ceeb tuaj yeem pom.
Daim duab. 6
Nrog rau qhov ntawd los ntau cov cim ntawm kev laus. Lo lus no suav nrog tag nrho cov kev hloov pauv hauv cov khoom uas tshwm sim dhau sijhawm yam tsis muaj kev cuam tshuam sab nraud. Stretch aging tuaj yeem pom tom qab deformation tas li los ntawm kev ncab txias. Yog tias cov khoom kuaj tau mus tas li raug tso tseg rau qee lub sijhawm yam tsis muaj kev thauj khoom ntawm chav tsev kub, lub zog tensile thiab, kom tsawg dua, lub zog tearing nce siab tshaj tus nqi qub, thaum lub elongation ntawm kev tawg txo qis (Fig. 7). Cov txheej txheem kev laus yuav siv sij hawm ntau hnub, tab sis txo qis rau ob peb teev lossis tsuas yog feeb xwb, yog tias cov qauv hlau tau rhuab mus txog 300 oC. Nws yuav tsum tau hais tias stretching aging tshwm sim ib txhij nrog stretching, yog hais tias qhov no tshwm sim ntawm temp. 200 – 400 oC, i.e. nyob rau thaj tsam xiav ci.
Daim duab. 7 - a) expansion kab ntawm ib tug pas nrig loaded ob npaug; b) dilation kab ntawm ib tug pas nrig stretched nyob rau hauv ib tug txias xeev
Kev ua tom ntej thiab hysteresis: Hauv cov khoom siv elastic tag, muaj kev sib koom ua ke tsis sib haum xeeb ntawm lub xeev kev ntxhov siab thiab deformation, yog li qee qhov kev ntxhov siab ib txwm sib haum mus rau tib yam deformations thiab vice versa. Nrog rau txoj cai ntawm elasticity, lub deformations tsis nyob ntawm lub sij hawm dhau mus txij li thaum lub load tau thov, thiab kuj tsis yog nyob rau hauv txoj kev uas lub load yog thov. Kev sib txawv ntawm tus cwj pwm tsis zoo elastic tuaj yeem piav qhia nyob rau hauv ob theem ntawm kwv yees: hauv thaj tsam elastic muaj qhov sib txawv me me; lawv tuaj yeem raug ignored nyob rau hauv thawj approximation. Lawv tuaj yeem txiav txim siab los ntawm kev ntsuas qhov tseeb, tshwj xeeb tshaj yog thaum sib piv cov kev ntxhov siab ze rau qhov txwv elastic. Namely, dilatation tsis yog tsuas yog ib tug muaj nuj nqi ntawm voltage, tab sis nrog ib tug kaw load voj voog thiab tib voltage, nws yog ib txwm me ntsis me ntsis thaum lub sij hawm unloading tshaj lub sij hawm loading. Deviation los ntawm tiav elasticity, ie. Qhov sib txawv ntawm cov kev nthuav dav ntawm tib qhov kev ntxhov siab yog hu ua elastic hysteresis. Yog tias lub voj voog thauj khoom rov qab ntau dua, qhov no tau txais ntawm qhov tsis muaj hluav taws xob ntau dhau - lub voj kaw ntawm hysteresis lossis damping. Sl. 8 qhia cov damping loops rau ntau yam AC load qhov tseem ceeb. Qhov dav ntawm lub voj voog nce siab nrog qhov siab ntawm qhov voltage. Cov cheeb tsam ntawm lub voj yog proportional rau lub deformation ua hauj lwm, uas yog poob ntawm txhua lub voj voog thiab hloov mus rau hauv tshav kub. Tsis tas li ntawd, cov deformations yog qhov sib txawv tsis tsuas yog nrog qhov siab ntawm qhov voltage, tab sis kuj nrog lub sijhawm, lawv nyob ntawm qhov ceev thiab txoj kev thauj khoom. Ib feem ntawm qhov deformation, uas nyob ntawm lub sijhawm, yog hu ua aftereffect. Hysteresis thiab aftereffect tshwm sim ib txhij. Raws li txoj cai, lawv tsis muaj qhov tseem ceeb rau cov hom kev tsim kho steel uas tshwm sim hauv cov qauv steel ntawm chav tsev kub.
Sl. 8
** Daim Ntawv Ceeb Toom: ** Cov khoom siv keeb kwm tsim, kev xav, daim duab kos thiab cov txheej txheem hauv cov ntawv yuav tsum tsis txhob siv los hloov cov qauv tam sim no, cov khoom tshwj xeeb, cov qauv kev suav thiab cov kws tshaj lij ntawm kev tsim kho tag nrho.