《土木工程专业英语》PPT课件

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1、4StressLimitsinDesign第4课设计中的应力极限Howlargecanwepermitthestressestobe?Orconversely:Howlargemustapartbetowithstandagivensetofloads?Whataretheoverallconditionsorlimitsthatwilldeterminethesizeandmaterialforapart?我们可以允许多大应力？或者反过来说，构件尺寸该多大才能抵抗给定的一组荷载？决定构件尺寸和材料的总体条件和限值是什么？Designlimit

2、sarebasedonavoidingfailureoftheparttoperformitsdesiredfunction.设计限值是以构件不发生破坏而执行其要求的功能为基础的。Becausedifferentpartsmustsatisfydifferentfunctionalrequirements,theconditionswhichlimitload-carryingabilitymaybequitedifferentfordifferentelements.因为不同构件必须满足不同的功能要求，不同构件界定承载能力的条件可能差别很大。

3、Asanexample,comparethedesignlimitsforthefloorofahousewiththoseforthewingofanairplane.举例来说，可以将住宅楼板和机翼的设计限值比较一下。Ifweweretodeterminethesizeofthewoodenbeamsinahomesuchthattheysimplydidnotbreak,wewouldnotbeveryhappywiththem;theywouldbetoo“springy”.Walkingacrosstheroomwouldbelikew

4、alkingoutonadivingboard.如果我们要这样来确定木梁的尺寸，只要它不断裂就行，那我们可能就不会很喜欢这些木梁了，这些木梁可能弹性变形太大了。人们穿过房间就会像从跳水板下来一样。Obviously,weshouldbeconcernedwiththemaximum“deflection”thatwe,asindividuals,findacceptable.Thislevelwillberathersubjective,anddifferentpeoplewillgivedifferentanswers.显然，我们应该关心我们

5、作为个体能够接受的最大挠度，这个水平的主观性相当大，不同人将给出不同的答案。Infact,thesamepeoplemaygivedifferentanswersdependingonwhethertheyarepayingforthefloorornot!事实上，同一群人也会给出不同的回答，这取决于他们是否支付楼板的费用。Anairplanewingstructureisclearlydifferent.Ifyoulookoutanairplanewindowandwatchthewingduringturbulentweather,youw

6、illseelargedeflections;infactyoumaywishthattheyweresmaller.However,youknowthattheimportantissueisthatof“structuralintegrity”,notdeflection.一个机翼结构显然不同，你如从机窗向外观看恶劣天气中的机翼，你就会看到很大的变形，而事实上你会希望这种变形更小些才好。然而，你知道重要的是结构的完整性，而不是变形。Wewanttobeassuredthatthewingwillremainintact.Wewanttobe

7、assuredthatnomatterwhatthepilotandtheweatherdo,thatwingwillcontinuetoactlikeagoodandproperwing.我们要确保机翼完好无损，我们要确保机翼一直处于良好的工作状态，而不管飞行员做什么或者天气怎么样。Infact,wereallywanttobeassuredthatthewingwillneverfailunderanyconditions.Nowthatisaprettytallorder;whoknowswhatthe“worst”conditionsm

8、ightbe?事实上，我们确实想要确保机翼在任何条件下都不会失效。现在这是不可能实现的事，谁又知道最恶劣的条件是什么呢？Engineerswhoare