Unit21asystemofforcesissaidtobeinequilibriumwhentheresultantoftheforcesandtheresultantofallthemomentatonepointareequaltozero2iftherearemorethanthreeunknowns,theequationscannotbecompletelysolvedandthesystemwillbestaticallyindeterminateorredundant.3thethereactionmustbecapableofresistinganydisplacementorrotationthatisappliedtothestructure4however，forthepurposeofcalculationitwillbesufficientlyaccuratetoassumethattheloadisactingatthepoint5itcanbeseenthatthequestionofstabilityanddeterminacyofthereactionsmustbeindependentoftheactualloadingthatisappliedtothestructure6当所有力的合力和某一点所有弯矩等于零时，力系处于平衡状态。7如果未知量超过三个就不能完全求解平衡方程系统给静不定8反力必须能够抵抗施加在结构上任何很小的位移和转动9为了计算假设荷载作用在一点是足够精确地10可以看出稳定问题和反力问题的确定必须独立于施加在结构上的实际荷载Unit511formostdesignsituationsthecodewillspecifythemagnitudeoftheloads12designforwindeffectsiscomplicatedbyanumberofphenomena13thegreatthefloorareathatistobesupportedbyasinglemember，thesmallerwillbetheprobabilitythatthecodeliveloadwillappearwithitsfullintensity14howevercomparedtotheotherstructuralloads，thedeadloadvariationsarerelativelysmall，andtheactualmeanvaluesarequiteclosetothecode-prescribeddata15intheory，atleast，thedeadloadonastructureissupposedtoremainconstant16对于大多数设计情况规范规定的是静力荷载的大小17对于风作用许多现象使设计复杂化18类似的，单个构件承担的楼板面积越大，在整个面积上，规范活荷载已全部强度出现的概率就越小19然而，与其他结构荷载相比，横在变化是相对较小的，实际平均值于规范规定的值很接近10.至少在理论上，结构上恒荷载被认为是保持不变的Unit620acrackinthetensionzoneofconcreteimpliesthatsomesliphasoccurredbetweenthesteelreinforcementandthesurroundingconcrete21however,iftheconcretestainismeasuredoveragaugelengththatincludesseveralcracks,itisfoundthatbernoulli’sprincipleappliestothisaveragetensilestrain22somedeviationfromlinearitymustbeexpectedbecauseofsmallinaccuraciesinindividualstrainmeasurementsandsmallerrorsinthelocationofgaugelines23stress-straincurvesfortheconcretewerealsodeterminedfromaxiallyloadedcylindersandwerefoundtobesimilartothestress-staincurvesfortheconcreteinthespecimens24anytensilestressthatexistsintheconcretejustbelowtheneutralaxisissmallandhasasmallleverarm25混凝土受拉区出现裂缝就意味着混凝土与钢筋之间已经出现滑移26如果测量混凝土应变的标距包括数个裂缝，则帕努利原理可适用于平均拉应变27由于每个应变的测量误差和测量线位置的误差，计算结果可能会偏离线性假定28中性轴下方混凝土中的拉应力很低，而且其内力壁也很小Unit929probablythemostdifficultofproblemsthatsoilsengineerisaskedtosolveistheaccuratepredictionofthesettlementofaloadedfoundation30verticaldeformationduetothechangeinshapeistheimmediatesettlement31bytheprincipleofsuperpositionitispossibletodeterminetheimmediatesettlementunderanypointofthebaseofafoundation32theporewaterinasaturatedwillcommencetodrainawayroomafterimmediatesettlementhastakenplace,theremovalofthiswaterleadingtothevolumechangeisknownasconsolidation33theapparatusgenerallyusedinthelaboratorytodeterminetheprimarycompressioncharacteristicsofasoilisknownasconsolidationtestapparatus34岩土工程师需要解决的最困难的问题可就是准确预测地基在荷载作用下的沉降35由于形状的改变而引起的竖向变相就是瞬时沉降36根据叠加理论可以确定基地任意一点的瞬时沉降37在瞬时变形发生后不久，饱和粘土中的空隙土压力就会开始消散10.通常在实验室中...
