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LessonLesson#Newwordscolloidal 膠狀的，膠體的，'colloid膠體sieven,v.篩，過篩，過濾sample .樣品，取樣specimenmesh網(wǎng)孔，網(wǎng)格，分網(wǎng)格'cumulativea.積累的；cumulate,cumulationgradingn.級配，等級；gradesedimentationn.沉淀;sedimentsuspensionn.懸??；suspend~bridgecable-stayedbridgeagitatev.攪動，混合；disturbhydrometern.（液體）比重計(jì)viscosityn.黏性；viscoidalflaky n.薄片狀的，offlakepipette n.吸液管irrecoverablea.不可恢復(fù)的irretrievableconcavea.凹的；convex凸的permeabilityn.滲透性;permeate,permeableseepseepagePhrasesandexpressionsfrostsusceptibility霜凍敏感性sievingmethod 篩分法semi-logarithmiccurve半對數(shù)曲線gradingcurve 級配曲線wetsieving 濕法篩分dispersingagent 分散劑Stoke’slaw 斯托克定律unitweight 重度coefficientofgrading級配系數(shù)sedimentationmethod沉降法particle-sizedistribution粒徑分布TextParticleSizeAnalysis粒徑分析Therangeofparticlesizesencounteredinsoilsisverywide:fromaround200mmdowntothecolloidalsizeofsomeclaysoflessthan.在各種土中所遇到的粒徑范圍很大，大到200mm小到小于的一些粘土膠粒。Althoughnaturalsoilsaremixturesofvarious-sizedparticles,itiscommontofindapredominanceoccurringwithinarelativelynarrowbandofsizes.盡管天然土都是由各種粒徑的顆粒組成，但通?？砂l(fā)現(xiàn)其主要組成顆粒出現(xiàn)在一個(gè)比較小的粒徑范圍內(nèi)。Whenthewidthofthissizebandisverynarrowthesoilwillbetermedpoorly-graded,ifitiswidethesoilissaidtobewell-graded.當(dāng)這一粒徑范圍非常小時(shí)，稱這種土級配較差，而當(dāng)其較大時(shí)，稱這種土級配良好。Anumberofengineeringproperties,.permeability,frostsusceptibility,compressibility,arerelateddirectlyorindirectlytoparticle-sizecharacteristics.土的許多工程特性，如滲透性、霜凍敏感性、可壓縮性等都直接或間接的與土的級配特性有關(guān)。showstheBritishStandardrangeofpercentageofparticlesizes.圖為粒徑百分?jǐn)?shù)的英國標(biāo)準(zhǔn)范圍。Theparticle-sizeanalysisofasoiliscarriedoutbydeterminingtheweightpercentagefallingwithinbandsofsizerepresentedbythesedivisionsandsub-divisions.通過確定落入由這些粒徑分組和子組所代表的粒徑范圍的重量百分比，對土進(jìn)行粒徑分析。Inthecaseofacoarsesoil,fromwhichfine-grainedparticleshavebeenremovedorwereabsent,theusualprocessisasieveanalysis.對于粗粒土，它里面的細(xì)粒土被除去或本身就無細(xì)顆粒，常用的方法就是篩分法。Arepresentativesampleofthesoilissplitsystematicallydowntoaconvenientsub-samplesizeandthenoven-dried.此法是將要分析土的一代表樣本系統(tǒng)地分為方便的子樣本，然后烘干。Thissampleisthenpassedthroughanestofstandardtestsievesarrangedindescendingorderofmeshsize.再使烘干的土樣通過一組篩孔尺寸由大至小放置的標(biāo)準(zhǔn)試驗(yàn)篩。細(xì)粒粗粒非常粗大顆粒粘土膠粒粉土砂礫石石塊細(xì)中粗細(xì)中粗細(xì)中粗卵石塊石Wherethesoilsamplecontainsfine-grainedparticles,awetsievingprocedureisfirstcarriedouttoremovetheseandtodeterminethecombinedclay/siltfractionpercentage.在土樣中含有細(xì)土粒的場合，首先用濕篩分法將其除去，并確定粘粒/粉粒總共所占的分?jǐn)?shù)。Asuitable-sizedsub-sampleisfirstoven-driedandthensievedtoseparatethecoarsestparticles(>20mm).將一適量的分土樣烘干，并過篩分開最粗的顆粒(>20mm的顆粒)Thesub-sampleisthenimmersedinwatercontainingadispersingagentandallowedtostandbeforebeingwashedthrougha63m(micron)meshsieve.然后將土樣浸入含有分散劑的水中，并在將其用63微米篩過篩前擱置起來(并將其擱置一會，再用63micron的篩子過篩)。Theretainedfractionisagainoven-driedandpassedthroughanestofsieves.將篩中保留的部分烘干，并用一組篩子過篩。Afterweighingthefractionsretainedoneachsieveandcalculatingthecumulativepercentagepassingeachsieve,thegradingcurveisdrawn.稱量落在每個(gè)篩中土重，并計(jì)算出通過每個(gè)的累計(jì)百分?jǐn)?shù)后，就可描出級配曲線。Thecombinedclay/siltfractionisdeterminedfromtheweightdifferenceandexpressedasapercentageofthetotalsub-sampleweight.Thecoarsestfraction(>20mm)canalsobesievedandtheresultsusedtocompletethegradingcurve.由重量差確定粘粒/粉粒的總重，并將其表示為子土樣總重的百分?jǐn)?shù)。最粗的部分(即粒徑>20mm的部分)也可被過篩，并用其結(jié)果完成級配曲線的繪制。Afurthersub-divisionofparticle-sizedistributioninthefine-grainedfractionisnotpossiblebythesievingmethod.不能用篩分法對細(xì)粒部分的粒徑分布作進(jìn)一步分組。Aprocessofsedimentationisnormallycarriedoutforthispurpose.通常必須用沉降法實(shí)現(xiàn)此目的。Asmallsub-sampleofsoilisfirsttreatedwithadispersingagentandthenwashedthrougha63msieve.首先將一小子土樣用分散劑進(jìn)行處理，然后洗過63的篩子。Thesoil/watersuspensionisthenmadeupto500ml,agitatedvigorouslyforashortwhileandthenallowedtosettle.再從中取出500ml的土/水懸浮液，充分?jǐn)嚢枰粫笞屍涑两怠heprocedureisbasedonStoke'slaw,whichstatesthatthevelocityatwhichasphericalparticlewillsinkduetogravityinasuspensionisgivenby:此方法是基于斯托克思定律，即在重力作用下球形顆粒在某一懸浮液中下降的速度為Whered=diameterofparticle顆粒直徑=unitweightofthegrainofparticle顆粒重度sw=unitweightofthesuspensionfluid（usuallywater）懸浮液的重度（通過為水的重度）=vescosityofthesuspensionfluid（懸浮液的黏度）Usuallyh=100mm,通常h=100mm,giving由此給出Samplestakenatadepthof100mm,atanelapsedtimeoft,willnot,therefore,includeparticlesofgreatersizethanthediameterdgivenby因此在，在深度100mm處，t時(shí)間后所取的懸浮液中將不會有粒徑大于式所給出的土粒;buttheproportionsofparticlessmallerthandinthesuspensionwillremainunchanged,但懸浮液中小于d的顆粒所占的比例仍保持不變。Theprocedureusingahydrometerconsistsofmeasuringthesuspensiondensityatadepthof100mmataseriesofelapsed-timeintervals,用液體比重計(jì)的方法包括以一系列時(shí)間間隔在深度100mm處測定懸浮液的比重。Thepercentage-finervaluescorrespondingtoparticulardiameter,particlesizes)areobtainedfromthedensityreadings,andthusagradingcurveforthefine-grainedfractionmaybedrawn,通過比重讀數(shù)得到小于某一特定粒徑的顆粒的百分?jǐn)?shù)，從而可畫出細(xì)粒部分的級配曲線。GradingCharacteristicsThegradingcurveisagraphicalrepresentationoftheparticle-sizedistributionandisthereforeusefulinitselfasameansofdescribingthesoil,級配曲線是粒徑分布的一種圖形表達(dá)，因而可用來作為描述土的手段。Forthisreasonitisalwaysagoodideatoincludecopiesofgradingcurvesinlaboratoryandothersimilarreports,因此，人們總是認(rèn)為在實(shí)驗(yàn)室報(bào)告或其它報(bào)告里附上幾份級配曲線是一種好做法。Itshouldalsoberememberedthattheprimaryobjectistoprovideadescriptivetermforthetypeofsoil.還應(yīng)牢記的是我們的主要目的是提供對土的類型的描述性術(shù)語。Thisiseasilydoneusingthetypeofchartbyestimatingtherangeofsizesincludedinthemostrepresentativefractionofthesoil.這可容易地通過采用這種級配曲線做到，因?yàn)橛盟芄烙?jì)出土中最有代表性的成分的粒徑范圍。Forexample,thesteepcurvemaybetakentorepresentapoorly-gradedmediumsand,indicatinganarrowrangeofsizes.例如，陡峭的曲線可用來表示級配差的中砂，并表示其粒徑范圍比較小。Afurtherquantitativeanalysisofgradingcurvesmaybecarriedoutusingcertaingeometricvaluesknownasgradingcharacteristics.通過采用某些稱為級配特征的幾何值，可進(jìn)一步對級配曲線進(jìn)行定量的分析。Firstofall,threepointsarelocatedonthegradingcurvetogivethefollowingcharacteristicsizes:首先，定出級配曲線上的三個(gè)點(diǎn)以給出以下特征粒徑：D10=maximumsizeofthesmallest10percentofthesample;只有10%土樣通過的最大粒徑；D30=maximumsizeofthesmallest30percentofthesample;只有30%土樣通過的最大粒徑；D60=maximumsizeofthesmallest60percentofthesampl；e只有60%土樣通過的最大粒徑；Fromthesecharacteristicsizes,thefollowinggradingcharacteristicsaredefined:根據(jù)這些特征粒徑，定義出如下級配特征：Effectivesize有效粒徑Uniformitycoefficient均勻系數(shù)CoefficientofgradationLesson4NewWordsundergo[ndu]vt.經(jīng)歷,遭受,忍受;experienceevaporation[ivprein]n.蒸發(fā)（作用）evaporatevaporattribute[tribju（:）t]vt.把…歸因于,把…歸咎于，加于,歸結(jié)于;ascribe，impute，級配系數(shù)distribution[distribju:n]n.分配,分發(fā)distributedistributorupwind[pwind]adj.逆風(fēng)的adv. 逆風(fēng)地windward;leeward12.diminish[dimini]v.（使）減少,（使）變小diminishment;credit，assign，refershrinkageshrink[rinkid]口,收縮shrinkcapillary [kpilri]adj.毛細(xì)作用的tensioncapillarityevaporate[ivpreit]v.（使）蒸發(fā),消失paste[peist]n.糊,粘土團(tuán)cementpasteambient[mbint]adj.周圍的,包圍著的surroundingambientairspecimen[spesimin]n.標(biāo)本,樣品,樣本,待試decreasecreep[kri:p]n.徐變;slippageslip[slipid]n.滑動，滑移,滑程sliphumidity[hju:miditi]n.濕氣,潮濕,濕度;humidrelativehumidityaug'ment[:ment]v.增力口，增大n.增力口；increase,enlargeaugmentationsustained[ssteind]adj.持續(xù)不變的,相同的;sustainabledevelopmentfatigue[fti:]n.疲

驗(yàn)物;samplePhrasesandExpressions驗(yàn)物;samplePhrasesandExpressions1.moisturecontent含cementpaste水泥漿mortarcapillarytension毛細(xì)管張力，微張力gradation ofaggregate骨料級配coarsefine(crushedstone,gravel)TheBritishCodePC100英國混凝土規(guī)范PC100;nowadayBS8110coefficientofthermalexpansion乏,疲勞,vt.使疲勞，vi.疲勞strength8.sustainedload永久荷載，長期荷載permanent plasticstrain永久的塑性應(yīng)變stresscrystallattice晶格,晶格cementgel水泥凝膠體water-cementratio水灰比expansionjoint伸縮縫stabilityofthestructure結(jié)構(gòu)的穩(wěn)定性structuralstabilityfatiguestrengthofofconcrete混凝土熱膨脹系數(shù)7.TheCode英國標(biāo)準(zhǔn)規(guī)范concrete混凝土的疲勞強(qiáng)度TextVolumeChangesofConcreteConcreteundergoesvolumechangesduringhardening.混凝土在硬結(jié)過程中會經(jīng)歷體積變化。Ifitlosesmoisturebyevaporation,itshrinks,butiftheconcretehardensinwater,itexpands.如果蒸發(fā)失去水分，混凝土?xí)湛s；但如果在水中硬結(jié)，它便膨脹。Thecausesofthevolumechangesinconcretecanbeattributedtochangesinmoisturecontent,chemicalreactionofthecementwithwater,variationintemperature,andappliedloads.混凝土體積變化的原因可歸結(jié)為含水量的變化、水泥與水的水化反應(yīng)、溫度變化和所施加的荷載。ShrinkageThechangeinthevolumeofdryingconcreteisnotequaltothevolumeofwaterremoved.Theevaporationoffreewatercauseslittleornoshrinkage.混凝土干燥時(shí)的體積變化量不等于它所失去的水的體積。自由水的蒸發(fā)基本不產(chǎn)生收縮。Asconcretecontinuestodry,waterevaporatesandthevolumeoftherestrainedcementpastechanges,causingconcretetoshrink,probablyduetothecapillarytensionthatdevelopsinthewaterremaininginconcrete.隨著混凝土的不斷變干，水分蒸發(fā)，受約束水泥漿的體積也變化，導(dǎo)致了混凝土的收縮，這多半是由于殘留在混凝土中的水的毛細(xì)張力所致。Emptyingofthecapillariescausesalossofwaterwithoutshrinkage.Butoncetheabsorbedwaterisremoved,shrinkageoccurs.毛細(xì)管變空導(dǎo)致無收縮的水分丟失，但一旦失去吸收的水分，收縮便發(fā)生。Manyfactorsinfluencetheshrinkageofconcretecausedbythevariationsinmoistureconditions.許多因素都會影響因水分環(huán)境發(fā)生變化而產(chǎn)生的混凝土收縮。andwatercontent.Themorecementorwatercontentintheconcretemix,thegreatertheshrinkage.水灰比：水灰比越大，收縮越大；andfinenessofcement.High-early-strengthandlow-heatcementsshowmoreshrinkagethannormalportlandcement.Thefinerthecement,thegreateristheexpansionundermoistconditions.水泥的成分和細(xì)度：早強(qiáng)和低熱水泥的收縮大于普通水泥，水泥越細(xì)，其在潮濕環(huán)境中的膨脹越大。,amount,andgradationofaggregate.Thesmallerthesizeofaggregateparticles,thegreateristheshrinkage.Thegreatertheaggregatecontent,thesmalleristheshrinkage.骨料的類型、含量及其級配：骨料的粒徑越小，收縮越大；骨料含量越大，收縮則越小。conditions,moisture,andtemperature.Concretespecimenssubjectedtomoistconditionsundergoanexpansionof200to300x10-6,butiftheyarelefttodryinair,theyshrink.Hightemperaturespeedstheevaporationofwaterand,consequently,increasesshrinkage.外部條件，水分與溫度：潮濕環(huán)境下的混凝土試件的膨脹量為200to300x10-6，但如果讓其在空氣中干燥，它們將收縮。高溫加速了水分的蒸發(fā)，因此也加快了收縮。Admixturesthatincreasethewaterrequirementofconcreteincreasetheshrinkagevalue.添加劑：使用水量增加的外加劑也增加了收縮值。andshapeofspecimen.Asshrinkagetakesplaceinareinforcedconcretemember,tensionstressesdevelopintheconcrete,andequalcompressivedevelopinthesteel.Thesestressesareaddedtothosedevelopedbytheloadingaction.Therefore,cracksmaydevelopinconcretewhenahighpercentageofsteelisused.Properdistributionofreinforcement,byproducingbetterdistributionoftensilestressesinconcrete,canreducedifferentialinternalstresses.試件的尺寸和形狀：當(dāng)收縮在鋼筋混凝土構(gòu)件中發(fā)生時(shí)，混凝土中產(chǎn)生拉應(yīng)力，同樣大小的壓力產(chǎn)生于鋼筋中，這些力與荷載引起的力相迭加。因此，當(dāng)鋼筋的配筋率高時(shí)，可能會使混凝土開裂。鋼筋的合理分布、會使混凝土中的拉應(yīng)力分布更有利，可減小內(nèi)部應(yīng)力差。Thevaluesoffinalshrinkageforordinaryconcretevarybetween200and700x10-6.普通混凝土的收縮應(yīng)變終值在200and700x10-6之間。Fornormal-weightconcrete,avalueof300x10-6maybeused.對常重混凝土，收縮應(yīng)變終值可取為300x10-6TheBritishCodeCP100givesavalueof500x10-6,whichrepresentsanunrestrainedshrinkageofmmin3mlengthinthin,plainconcretesections.英國CP100規(guī)范不出的收縮應(yīng)變終值為500x10-6,這表示3m長素混凝土薄截面構(gòu)件的非約束收縮為.Ifthememberisrestrained,atensilestressofabout10N/mm2(1400psi)arises.如果此構(gòu)件受到約束，便產(chǎn)生了大約10N/mm2(1400psi)的拉應(yīng)力。Ifconcreteiskeptmoistforacertainperiodaftersetting,shrinkageisreduced;如果凝結(jié)后將混凝土保持在潮濕環(huán)境中，可減小其收縮。therefore,itisimportanttocuretheconcreteforaperiodofnofewerthan7days.因此，將混凝土至少在潮濕環(huán)境中養(yǎng)護(hù)7天非常重要。Exposureofconcretetowindincreasestheshrinkagerateontheupwindside.將混凝土置于風(fēng)中將增加其在迎風(fēng)一側(cè)的收縮速率。Shrinkagecausesanincreaseinthedeflectionofstructuralmembers,whichinturnincreaseswithtime.收縮引起結(jié)構(gòu)構(gòu)件的撓度增大，而撓度也隨時(shí)間而增長。Symmetricalreinforcementintheconcretesectionmaypreventcurvatureanddeflectionduetoshrinkage.混凝土截面的對稱配筋可防止因收縮而產(chǎn)生的曲率和撓度。Generally,concreteshrinksatahighrateduringtheinitialperiodofhardening,butatlaterstagestheratediminishesgradually.通常，在硬結(jié)初期，混凝土收縮較快，但在后期，收縮速度會慢慢變小。Itcanbesaidthat15%to30%oftheshrinkagevalueoccursin2weeks,40%to80%occursin1month,and70%to85%occursin1year.可以說15%to30%收縮量的發(fā)生在前兩周，40%to80%發(fā)生在前一個(gè)月，70%to85%發(fā)生在第一年。ExpansionDuetoRiseinTemperature升溫膨脹Concreteexpandswithincreasingtemperatureandcontractswithdecreasingtemperature.Thecoefficientofthermalexpansionofconcretevariesbetween4and7x10-6perdegreeFahrenheit.7混凝土受溫膨脹，變冷時(shí)收縮。Anaveragevalueofx10-6perdegreeFahrenheit(12義10-6perdegreeCelsius)canbeusedforordinaryconcrete.一般混凝土的平均收縮值為每華氏度X10-6(或每攝氏度12x10-6)。10-5perdegreeCelsius.英國標(biāo)準(zhǔn)規(guī)范的建議值為每攝氏10-5Thisvaluerepresentsachangeoflengthof10mmina30-mmembersubjectedtoachangeintemperatureof33℃.Ifthememberisrestrainedandunreinforced,astressofabout7N/mm2(1000psi)maydevelop.這一值表示如果30m長的構(gòu)件溫度變化33度，其長度變化為10mm.如果該構(gòu)件受到約束但并未配筋，由此產(chǎn)生的應(yīng)力可能約為7N/mm2(1000psi)。Inlongreinforcedconcretestructures,expansionjointsmustbeprovidedatlengthsof100to200ft(30to60m).在較長的鋼筋混凝土結(jié)構(gòu)中，每隔100英尺到200英尺630m至30m)必須留伸縮縫。Thewidthoftheexpansionjointisabout1in.(25mm).伸縮縫寬度約為1英寸625mm)Concreteisnotagoodconductorofheat,whereassteelisagoodone.Theabilityofconcretetocarryloadisnotmuchaffectedbytemperature.混凝土并非好的熱導(dǎo)體，但鋼材卻是。因此混凝土的承載能力并不太受溫度的影響。Greep徐變Concreteisanelastoplasticmaterial,andbeginningwithsmallstresses,plasticstrainsdevelopinadditiontoelasticones.混凝土是一種彈塑性材料，即使受低應(yīng)力作用，它就產(chǎn)生伴有彈性應(yīng)變的塑性應(yīng)變。Undersustainedload,plasticdeformationcontinuestodevelopoveraperiodthatmaylastforyears.在持續(xù)荷載作用下，在很長時(shí)間內(nèi)其塑性變形連續(xù)增長，甚至可達(dá)數(shù)年。Suchdeformationincreasesatahighrateduringthefirst4monthsafterapplicationoftheload.Thisslowplasticdeformationunderconstantstressiscalledcreep.此變形在加載后的前4個(gè)月最快。這種在持續(xù)應(yīng)力作用下的緩慢變形稱為徐變。Figureshowsaconcretecylinderthatisloaded.圖表示受荷載作用的一混凝土圓柱體。Theinstantaneousdeformationis￡1,whichisequaltothestressdividedbythemodulusofelasticity.其瞬時(shí)變形為乙,它等于應(yīng)力除以彈性模量。Ifthesamestressiskeptforaperiodoftime,anadditionalstraine2,duetocreepeffect,canberecorded.如果將此應(yīng)力保持一段時(shí)間，便可測出另一由徐變所產(chǎn)生的應(yīng)變增量￡2,Ifloadisthenreleased,theelasticstrain,￡1,willberecovered,inadditiontosomecreepstrain.如果卸去荷載，彈性應(yīng)變便得到恢復(fù)，同時(shí)還產(chǎn)生一些徐變應(yīng)變。Thefinalpermanentplasticstrain,￡3,willbeleft,asshowninFigure.最終會剩下永久塑性應(yīng)變￡3，如圖所示。Inthiscase￡3=(1—a)￡2,whereaistheratiooftherecoveredcreepstraintothetotalcreepstrain.在此情況下，￡3=(1—a)￡2,a是恢復(fù)徐變應(yīng)變與總徐變的比值。Theratioarangesbetweenand.其值在至之間。Themagnitudeofcreeprecoveryvarieswiththepreviouscreepanddependsappreciablyupontheperiodofthesustainedload.徐變后效的大小隨先前徐變的大小而變化，且在很大程度上取決于荷載的持續(xù)時(shí)間。Creeprecoveryratewillbelessiftheloadingperiodisincreased,probablyduetothehardeningofconcretewhileinadeformedcondition.如果持荷時(shí)間增加，徐變恢復(fù)率將變小，這大概是由于混凝土在變形硬化所致。FigureDeformationinaloadedconcrete

cylinder:(a)specimenunloaded,(b)

elasticdeformation,

(c)elasticpluscreepdeformation,(d)

permanentdeformationafterreleaseofload.Theultimatemagnitudeofcreepvariesbetweenx10-6and2x10-6perunitstress(1b/perunitlength.Avalueof1x10-6canbeusedinpractice.Theratioofcreepstraintoelasticstrainmaybeashighas4.Creeptakesplaceinthehardenedcementmatrixaroundthestrongaggregate.Itmaybeattributedtoslippagealongplaneswithinthecrystallattice,internalstressescausedbychangesinthecrystallattice,andgraduallossofwaterfromthecementgelintheconcrete.徐變在強(qiáng)度更高的骨料周圍的硬結(jié)的水泥基中產(chǎn)生，這可能是由于沿晶格中一些平面發(fā)生滑移、晶格變化所產(chǎn)生的內(nèi)部應(yīng)力、及混凝土凝膠體中水分不斷丟失的結(jié)果。Thedifferentfactorsthataffectthecreepofconcretecanbesummarizedasfollows.影響徐變的各種不同因素可概括如下：Thelevelofstress.Creepincreaseswithanincreaseofstressinspecimensmadefromconcreteofthesamestrengthandwiththesamedurationofload.應(yīng)力大?。篋urationofloading.Creepincreaseswiththeloadingperiod.About80%ofthecreepoccurswithinthefirst4months;90%occursafterabout2years.持荷時(shí)間：Strengthandageofconcrete.Creeptendstobesmallerifconcreteisloadedatalateage.Also,creepof2000psi-(14N/mm2-)strengthconcreteisaboutx10-6whereasthatof4000psi-(28N/mm2-)strengthconcreteisaboutx10-6perunitstressandlengthoftime.混凝土強(qiáng)度和齡期：conditions.Creepisreducedwithanincreaseinthehumidityoftheambientair.周圍環(huán)境條件：ofloading.Creepincreaseswithanincreaseintherateofloadingwhenfollowedbyprolongedloading.加載速率：anddistributionofsteelreinforcementinareinforcedconcretemember.Creeptendstobesmallerforhigherproportionorbetterdistributionofsteel.鋼筋混凝土結(jié)構(gòu)中鋼筋的配筋率及其分布：oftheconcretemass.Creepdecreaseswithanincreaseinthesizeofthetestedspecimen.混凝土尺寸：,fineness,andcontentofcement.Theamountofcementgreatlyaffectsthefinalcreepofconcrete,ascementcreepsabout15timesasmuchasconcrete.水泥的類型、細(xì)度和含量：ratio.Creepincreaseswithanincreaseinthewater-cementratio.水灰比：andgradingofaggregate.Well-gradedaggregatewillproducedenseconcreteandconsequentlyareductionincreep.骨料的類型和級配：ofcuring.High-temperaturesteamcuringofconcreteaswellastheproperuseofaplasticizerwillreducetheamountofcreep.養(yǎng)護(hù)方式：Creepdevelopsnotonlyincompression,butalsointension,bending,andtorsion.徐變不僅產(chǎn)

生于受壓，它也產(chǎn)生于受拉，受彎和受扭。Theratiooftherateofcreepintensiontothatincompressionwillbegreaterthan1inthefirst2weeks,butthisratiodecreasesoverlongerperiods.受拉徐變的速率與受壓徐變的速率之比在前兩周將大于1，但會在長時(shí)間內(nèi)減小。Creepinconcreteundercompressionhasbeentestedbymanyinvestigators.Troxell,Davis,andRaphaelmeasuredcreepstrainsperiodicallyforupto20yearsandestimatedthatofthetotalcreepafter20years,18%to35%occurredin2weeks,30%to70%occurredin3months,and64%to83%occurredin1year.許多研究者都對混凝土的受壓徐變進(jìn)行了試驗(yàn)研究。二0.1337，二0.1337，where=creepstrainperunitstressperCunitlength.對28天齡期加載的普通混凝土，「?！币?，=單位應(yīng)力下單位時(shí)間內(nèi)的徐變。CreepC=0.1337Cr raugmentsthedeflectionofreinforcedconcretebeamsappreciablywithtime.Inthedesignofreinforcedconcretemembers,long-termdeflectionmaybecriticalandhastobeconsideredinproperdesign.隨時(shí)間的增加，徐變會大大增加鋼筋混凝土梁的撓度。Extensivedeformationmayinfluencethestabilityofthestructure.過大的變形會影響結(jié)構(gòu)的穩(wěn)定性。Sustainedloadsaffectthestrengthaswellasthedeformationofconcrete.持續(xù)加載會影響混凝土的強(qiáng)度和變形。Areductionofupto30%ofthestrengthofunreinforcedconcretemaybeexpectedwhenconcreteissubjectedtoaconcentricsustainedloadfor1year.當(dāng)混凝土在持續(xù)集中荷載作用下長達(dá)一年時(shí)，其鋼筋混凝土的強(qiáng)度可能要降低30%.Thefatiguestrengthofconcreteismuchsmallerthanitsstaticstrength.混凝土的疲勞強(qiáng)度大大低于其靜力強(qiáng)度。Repeatedloadingandunloadingcyclesincompressionleadtoagradualaccumulationofplasticdeformations.受壓的重復(fù)加載和卸載會導(dǎo)致混凝土塑性變形的逐漸積累。Ifconcreteincompressionissubjectedtoabout2millioncycles,itsfatiguelimitisabout50%to60%ofthestaticcompressionstrength.Inbeams,thefatiguelimitofconcreteisabout55%ofitsstatic

strength.如果混凝土不斷受壓加載2百萬次，其疲勞強(qiáng)度容許值會降為其靜態(tài)抗壓強(qiáng)度的50%至60%.在梁中，混凝土的疲勞強(qiáng)度約為其靜態(tài)強(qiáng)度的55%.Lesson5LoadsNewwords1.prescribev.指示，規(guī)定;specify2.criterionn.標(biāo)準(zhǔn)，規(guī)范，準(zhǔn)則；standard3.dictatev.規(guī)定，指示，命令；dominate4.survey.調(diào)查，測量；investigation5.variationn.變更，變化，差異；vary,variable,various6.deterministica.確定性的，nondeterministic,probabilistic7.rationala.合理的，理性的；reasonable,logical8.stochastica.隨機(jī)的；stochasticprocess,butrandomvariable9.pertainv.適合，屬于;pertaining10.cumbersomea.討厭的，麻煩的；troublesome11.landscapen.地形，風(fēng)景，景觀12.endeavor.盡力，努力；strive，puteffortto13.deviationn.背離；deviate,14.constancyn.恒定性，不變性，constant15.occupantn.居住者16.fluctuationn.波動，起伏；fluctuate17.'tenantn.房客，承租人；18.transienta.瞬時(shí)的；instantaneous19.sustainvt.維持，支撐，持續(xù)；sustainable20.premisen.前提；vt.假定；PhrasesandExpressionsnominalvalueinpracticeatbestnominalvalueinpracticeatbestbuildingcodeseismicactionreference(return)period標(biāo)準(zhǔn)值，名義值實(shí)際上，在實(shí)踐上充其量，最好也只不過地震作用，earthquakeload重現(xiàn)期semiempiricalequationwindtunneltestingsemiempiricalequationwindtunneltestingmeanvaluecode-prescribeddatatransientliveloadsustainedliveloadTextLoads（1）Introduction半經(jīng)驗(yàn)公式empirical風(fēng)洞試驗(yàn)均值；平均規(guī)范規(guī)定數(shù)值瞬時(shí)活荷載持續(xù)活荷載Normally,adesignspecificationdoesnotprescribethemagnitudesoftheloadsthataretobeusedasthebasicinputtothestructuralanalysis,withtheexceptionofspecialcasessuchascranedesignspecifications.除特殊情況設(shè)計(jì)規(guī)程外（如起重機(jī)設(shè)計(jì)規(guī)程），一般設(shè)計(jì)規(guī)程并不規(guī)定荷載的大小，盡管它是作為結(jié)構(gòu)分析所輸入的基本變量。Itistheroleofthespecificationtodetailthemethodsandcriteriatobeusedinarrivingatsatisfactorymemberandconnectionsizesforthestructuralmaterialinquestion,giventhemagnitudesoftheloadsandtheireffects.設(shè)計(jì)規(guī)程的作用就是對于給定的荷載值及其效應(yīng)，詳細(xì)說明用設(shè)計(jì)材料能得到滿意構(gòu)件及其連接尺寸的方法和準(zhǔn)則。Thespecificationthereforereflectstherequirementsthatmustbesatisfiedbythestructureinorderthatitwillhavearesponsethatallowsittoachievetheperformancethatisneeded.因此，規(guī)程反映了結(jié)構(gòu)必須滿足的各種要求，從而使其具有這樣一種結(jié)構(gòu)反應(yīng)，它能使其達(dá)到所要求的性能。Loads,ontheotherhand,aregovernedbythetypeofoccupancyofthebuilding,whichinturnisdictatedbytheapplicablelocal,regional,andnationallawsthataremorecommonlyknownatbuildingcodes.另一方面，荷載取決于建筑物的使用類型，這反過來取決于相應(yīng)的地區(qū)，地方和國家法規(guī)，即常說的建筑規(guī)范。Thebuildingcodeloadshavetraditionallybeengivenasnominalvalues,determinedonthebasisofmaterialproperties.,deadload）orloadsurveys.,liveloadandsnowload）.建筑規(guī)范的荷載傳統(tǒng)上都是作為標(biāo)準(zhǔn)值給出，它們是根據(jù)材料特性確定（如恒載）或荷載調(diào)查所確定（如活荷載及雪荷載）Tobereasonablycertainthattheloadsarenotexceededinagivenstructure,thecodevalueshavetendedtobehigherthantheloadsonarandomstructureatanarbitrarypointintime.為了適當(dāng)?shù)卮_保作用在任一結(jié)構(gòu)上的荷載不超過規(guī)范值，后者往往都要比任一時(shí)刻作用任一結(jié)構(gòu)上的荷載值大些。Thismay,iffact,beoneofthereasonswhyexcessivegravityloadsarerarelytheobviouscauseofstructuralfailures.事實(shí)上，這可能就是過大的重力荷載大都不會導(dǎo)致結(jié)構(gòu)破壞的原因所在。Bethatatitmay,thefactofthematteristhatallofthevarioustypesofstructuralloadsexhibitrandomvariationsthatarefunctionsoftime,andthemannerofvariationalsodependsonthetypeofload.盡管可能如此，實(shí)際上結(jié)構(gòu)上的各種荷載都具有隨時(shí)間而變化的隨機(jī)變化特性，且這種變化也取決于荷載類型。Ratherthandealingwithnominalloadsthatappeartobedeterministicanature,arealisticdesignprocedureshouldtakeloadvariabilityintoaccountalongwiththatofthestrength,inorderthatadequatestructuralsafetycanbeachievedthroughrationalmeans.不是去處理看上去具有定值特征的標(biāo)準(zhǔn)荷載，現(xiàn)實(shí)的設(shè)計(jì)方法應(yīng)同時(shí)考慮荷載和強(qiáng)度的變異性，以便以合理的手段得到足夠的結(jié)構(gòu)安全度。Sincetherandomvariationoftheloadsisafunctionoftimeaswellasanumberofotherfactors,themodeling,strictlyspeaking,shouldtakethisintoaccountbyusingstochasticanalysestoreflectthetimeandspaceinterdependence.由于荷載的隨機(jī)變化是時(shí)間以及許多因素的函數(shù)，嚴(yán)格地講，通過采用隨機(jī)分析方法以反映時(shí)間與空間的相互影響，應(yīng)使建模對此加以考慮。Manystudieshavedealtwiththishighlycomplexphenomenon,especiallyasitpertainstoliveloadinbuildings.許多研究工作都涉及了這一高度復(fù)雜的現(xiàn)象，特別是當(dāng)其屬于活荷載時(shí)。Inpractice,however,theuseoftime-dependentloadsiscumbersomeatbest,althoughtherelationshipmustbeaccountedforincertaincases.,seismicaction）.然而，實(shí)踐中采用時(shí)間相關(guān)荷載至少半是麻煩的，盡管在一些情況下必須考慮其相關(guān)性（即在有地震作用時(shí)）。Formostdesignsituationsthecodewillspecifythemagnitudeoftheloadsasiftheywerestatic.對于大多數(shù)設(shè)計(jì)，規(guī)范將規(guī)定荷載的大小，就象它們是靜載似的。Theirtimeandspacevariationarecoveredthroughtheuseofthemaximumloadoccurringoveracertainreference（return）period,anditsstatistics.通過采用出現(xiàn)在某一參照期（重現(xiàn)周期）內(nèi)的最大荷載及其統(tǒng)計(jì)特性，將它們的時(shí)間和空間的變異加以考慮。Forexample,Americanliveloadcriteriaarebasedonareferenceperiodof50years,whileCanadiancriteriausea30-yearinterval.例如，美國活荷載準(zhǔn)則基于50年重現(xiàn)周期，而加拿大準(zhǔn)則是30年。Thegeographicallocationofthestructureplaysanimportantroleforcertainloads.結(jié)構(gòu)的地理位置對某些荷載起很重要的作用。Itisparticularlyapplicabletosnow,windandseismicaction,thefirstbeingofspecialimportanceinnorth-centralandnorth-easternareasoftheUnitedStates,thesecondinhighwindcoastalandmountainareas,andthelastinareashavingearthquakefaultlines.特別是對于雪、風(fēng)和地震作用更是如此。第一種荷載對美國中北部和東北部地區(qū)非常重要，第二種對具有大風(fēng)的沿海地區(qū)和山嶺地區(qū)特別重要，第三種對具有地震斷裂帶的地區(qū)則特別重要。Deignforwindeffectsiscomplicatedbyanumberofphenomena.由于數(shù)個(gè)現(xiàn)象使風(fēng)作用效果的設(shè)計(jì)復(fù)雜化。Likesnowloadsandearthquakeaction,windloadsaregivenmoreattentionincertainpartsofthecountry,類似于雪荷載和地震作用，在本國的一些地區(qū)，對風(fēng)荷載更加重視。Atthesametimewindloadsareneitherstaticnoruniformlyvarying,andareheavilyinfluencedbythegeometryofthestructureaswellsthesurroundingstructuresandlandscape.同時(shí)，風(fēng)載不但非靜態(tài)，而且也非均勻變化，同時(shí)還受結(jié)構(gòu)幾何形式和周圍結(jié)構(gòu)物及地形的影響。Toacertaindegreethisalsoappliestothemagnitudeofthesnowload.在一定程度上，這也適用于雪荷載。Buildingcodestreattheseeffectsasstaticphenomenaandrelatethemtotheactualconditionsthroughsemiempiricalequations.建筑規(guī)范將這些作用作為靜力荷載并用半經(jīng)驗(yàn)公式將其與實(shí)際情況相聯(lián)系。Thisgivesthedesignerabetterhandleonadifficultproblem,butcanleadtodifficultieswhentherealstructuredepartssignificantlyfromthebasesofthecode.這使設(shè)計(jì)者能更好地處理復(fù)雜問題，但當(dāng)實(shí)際結(jié)構(gòu)與設(shè)計(jì)規(guī)范出入太大時(shí)，便導(dǎo)致了一些困難。Forthatreasonwindloads,andsometimesearthquakeandsnowloads,aredeterminedonthebasisofmodeltest.為此，風(fēng)荷載、有時(shí)地震荷載和雪荷載都要用模型試驗(yàn)來確定。Inparticular,windtunneltestinghasbecomeausefulandpracticaltoolintheseendeavors.特別是風(fēng)洞試驗(yàn)，它已經(jīng)成為這些努力中一個(gè)有用且實(shí)用工具。Theloadsonthestructurearenormallyassumedtobeindependentofthetypeofstructureandstructuralmaterial,withtheexceptionofdeadloads.除恒載外，通常都假定結(jié)構(gòu)上的荷載與結(jié)構(gòu)類型及其材料無關(guān)。Theresponseofabuilding,however,willbedifferentfordifferentmaterials,dependingonthetypeofload.然而，一建筑物的反應(yīng)將隨其建材的不同而不同，這取決于荷載的類型。Forexample,thebehaviorofamoment-resistantsteelframewillbequiteunlikethatofabracedframe,whensubjectedtolateralloads,especiallythoseduetoanearthquake.例如，在側(cè)向荷載作用下，特別是當(dāng)其由地震所引起時(shí)，抗彎鋼框架的工作性能將全然不同于有支撐框架的性能。Ontheotherhand,theresponseofthesetwoframestogravityloadswillnotbeallthatdifferent.另一方面，這兩種框架對重力荷載反應(yīng)的差別卻并沒有那么大。Thesizeofastructure（height,floorarea）hasasignificantimpactonthemagnitudesofmostloads.一個(gè)結(jié)構(gòu)物的大?。ㄈ缙涓叨?，樓層面積）對大多數(shù)荷載的量值影響很大。Allloadsareinfluencedbytheincreasingheightofamultistorybuilding,forexample.例如，所有的荷載都受多層建筑高度增加的影響。Similarly,thegreaterthefloorareathatistobesupportedbyasinglemember,thesmallerwillbetheprobabilitythatthecodeliveloadwillappearwithitsfullintensityovertheentirearea.與這類似，單個(gè)構(gòu)件所支承的樓層面積越大，整個(gè)樓層上滿載規(guī)范規(guī)定的活荷載的可能性將越小。Insuchcasesaliveloadreductionmethodisusedtoarriveatmorerealisticdesigndata.在此情況下，將采用活荷載折減法以得到更真實(shí)的設(shè)計(jì)值。LessonLesson6NewWmptvt.促使，鼓動，spur;incite:2.serviceablea.適用的；service,serviceable,s