广播电视大学《混凝土结构设计原理》作业参考答案小抄.doc

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电大混凝土结构设计原理作业1、2、3、4参考答案作业1说明:本次作业对应于文字教材1至3章,应按相应教学进度完成。一、选择题1下列关于钢筋混凝土结构的说法错误的是( A )。A钢筋混凝土结构自重大,有利于大跨度结构、高层建筑结构及抗震B取材较方便、承载力高、耐久性佳、整体性强C施工需要大量模板、工序复杂、周期较长、受季节气候影响大D耐火性优、可模性好、节约钢材、抗裂性差2我国混凝土结构设计规范规定:混凝土强度等级依据( D )确定。A圆柱体抗压强度标准 B轴心抗压强度标准值C棱柱体抗压强度标准值D立方体抗压强度标准值3混凝土的弹性系数反映了混凝土的弹塑性性质,定义( A )为弹性系数。A弹性应变与总应变的比值B塑性应变与总应变的比值C弹性应变与塑性应变的比值D塑性应变与弹应变的比值4混凝土的变形模量等于(D )。A应力与弹性应变的比值B应力应变曲线原点切线的曲率C应力应变曲线切线的斜率D弹性系数与弹性模量之乘积5我国混凝土结构设计规范规定:对无明显流幅的钢筋,在构件承载力设计时,取极限抗拉强度的( C )作为条件屈服点。A75%B80%C85%D70%6结构的功能要求不包括( D )A 安全性B 适用性C 耐久性D 经济性7结构上的作用可分为直接作用和间接作用两种,下列不属于间接作用的是( B )。A 地震B 风荷载C 地基不均匀沉降D 温度变化8( A )是结构按极限状态设计时采用的荷载基本代表值,是现行国家标准建筑结构荷载规范(GB 50009-2001)中对各类荷载规定的设计取值。A 荷载标准值B 组合值C 频遇值D 准永久值二、判断题1通常所说的混凝土结构是指素混凝土结构,而不是指钢筋混凝土结构。( )2混凝土结构是以混凝土为主要材料,并根据需要配置钢筋、预应力筋、型钢等,组成承力构件的结构。( )3 我国混凝土规范规定:钢筋混凝土构件的混凝土强度等级不应低于C10。( )4 钢筋的伸长率越小,表明钢筋的塑性和变形能力越好。( )5钢筋的疲劳破坏不属于脆性破坏。( )6粘结和锚固是钢筋和混凝土形成整体、共同工作的基础。( )7只存在结构承载能力的极限状态,结构的正常使用不存在极限状态。( )8一般来说,设计使用年限长,设计基准期可能短一些;设计使用年限短,设计基准期可能长一些。( )9钢筋和混凝土的强度标准值是钢筋混凝土结构按极限状态设计时采用的材料强度基本代表值。( )10荷载设计值等于荷载标准值乘以荷载分项系数,材料强度设计值等于材料强度标准值乘以材料分项系数。( )三、简答题1钢筋和混凝土这两种物理和力学性能不同的材料,之所以能够有效地结合在一起而共同工作,其主要原因是什么?答:3提示答案:1)钢筋和混凝土之间良好的黏结力;2)接近的温度线膨胀系数;3)混凝土对钢筋的保护作用。2试分析素混凝土梁与钢筋混凝土梁在承载力和受力性能方面的差异。答:提示答案:素混凝土梁承载力很低,受拉区混凝土一开裂,裂缝迅速发展,梁在瞬间骤然脆裂断开,变形发展不充分,属脆性破坏,梁中混凝土的抗压能力未能充分利用。钢筋混凝土梁承载力比素混凝土梁有很大提高,受拉区混凝土开裂后,钢筋可以代替受拉区混凝土承受拉力,裂缝不会迅速发展,直到钢筋应力达到屈服强度,随后荷载略有增加,致使受压区混凝土被压碎。梁破坏前,其裂缝充分发展,变形明显增大,有明显的破坏预兆,结构的受力特性得到明显改善。同时,混凝土的抗压能力和钢筋的抗拉能力得到充分利用。3钢筋混凝土结构设计中选用钢筋的原则是什么?答:提示答案:1)较高的强度和合适的屈强比;2)足够的塑性;3)可焊性;4)耐久性和耐火性5)与混凝土具有良好的黏结力。4什么是结构的极限状态?结构的极限状态分为几类,其含义是什么?答:提示答案:整个结构或结构的一部分超过某一特定状态就不能满足设计指定的某一功能要求,这个特定状态称为该功能的极限状态。结构的极限状态可分为承载能力极限状态和正常使用极限状态两类。结构或构件达到最大承载能力、疲劳破坏或者达到不适于继续承载的变形时的状态,称为承载能力极限状态。结构或构件达到正常使用或耐久性能的某项规定限值的状态,称为正常使用极限状态。5什么是结构上的作用?结构上的作用分为哪两种?荷载属于哪种作用?答:提示答案:答:结构上的作用是指施加在结构或构件上的力,以及引起结构变形和产生内力的原因。结构上的作用又分为直接作用和间接作用。荷载属于直接作用。6什么叫做作用效应?什么叫做结构抗力?答:提示答案:直接作用和间接作用施加在结构构件上,由此在结构内产生内力和变形,称为作用效应。结构抗力R是指整个结构或构件承受作用效应(即内力和变形)的能力,如构件的承载力和刚度等。作业2说明:本次作业对应于文字教材4至5章,应按相应教学进度完成。一、选择题1受弯构件抗裂度计算的依据是适筋梁正截面( A )的截面受力状态。A第I阶段末B第II阶段末C第III阶段末2受弯构件正截面极限状态承载力计算的依据是适筋梁正截面( C )的截面受力状态。A第I阶段末B第II阶段末C第III阶段末3梁的破坏形式为受拉钢筋的屈服与受压区混凝土破坏同时发生,则这种梁称为( C )。A少筋梁B适筋梁C平衡配筋梁D超筋梁4双筋矩形截面梁正截面承载力计算基本公式的第二个适用条件的物理意义是( C )。A防止出现超筋破坏 B防止出现少筋破坏C保证受压钢筋屈服 D保证受拉钢筋屈服5受弯构件斜截面承载力计算公式是以( D )为依据的。A斜拉破坏B斜弯破坏C斜压破坏D剪压破坏二、判断题1混凝土强度等级的选用须注意与钢筋强度的匹配,当采用HRB335、HRB400钢筋时,为了保证必要的粘结力,混凝土强度等级不应低于C25;当采用新HRB400钢筋时,混凝土强度等级不应低于C30。( )2一般现浇梁板常用的钢筋强度等级为HPB235、HRB335钢筋。( )3混凝土保护层应从受力纵筋的内边缘起算。( )4钢筋混凝土受弯构件正截面承载力计算公式中考虑了受拉区混凝土的抗拉强度。( )5钢筋混凝土梁斜截面破坏的三种形式是斜压破坏、剪压破坏和斜拉破坏。( )6钢筋混凝土无腹筋梁发生斜拉破坏时,梁的抗剪强度取决于混凝土的抗拉强度,剪压破坏也基本取决于混凝土的抗拉强度,而发生斜压破坏时,梁的抗剪强度取决于混凝土的抗压强度。( )7剪跨比不是影响集中荷载作用下无腹筋梁受剪承载力的主要因素。( )8钢筋混凝土梁沿斜截面的破坏形态均属于脆性破坏。( )三、简答题1钢筋混凝土受弯构件正截面的有效高度是指什么?答:计算梁、板承载力时,因为混凝土开裂后,拉力完全由钢筋承担,力偶力臂的形成只与受压混凝土边缘至受拉钢筋截面重心的距离有关,这一距离称为截面有效高度。2根据配筋率不同,简述钢筋混凝土梁的三种破坏形式及其破坏特点? 答:1)适筋破坏;适筋梁的破坏特点是:受拉钢筋首先达到屈服强度,经过一定的塑性变形,受压区混凝土被压碎,属延性破坏。2)超筋破坏;超筋梁的破坏特点是:受拉钢筋屈服前,受压区混凝土已先被压碎,致使结构破坏,属脆性破坏。3)少筋破坏;少筋梁的破坏特点是:一裂即坏,即混凝土一旦开裂受拉钢筋马上屈服,形成临界斜裂缝,属脆性破坏。3在受弯构件正截面承载力计算中,的含义及其在计算中的作用是什么?答:是超筋梁和适筋梁的界限,表示当发生界限破坏即受拉区钢筋屈服与受压区砼外边缘达到极限压应变同时发生时,受压区高度与梁截面的有效高度之比。其作用是,在计算中,用来判定梁是否为超筋梁。4什么情况下采用双筋截面梁?答:对于给定截面弯矩当按单筋截面梁设计时,若给定弯矩设计值过大,截面设计不能满足适筋梁的适用条件(),且由于使用要求截面高度受到限制又不能增大,同时混凝土强度等级因条件限制不能再提高时,可采用双筋截面。即在截面的受压区配置纵向钢筋以补充混凝土受压能力的不足。5有腹筋梁斜截面剪切破坏形态有哪几种?各在什么情况下产生? 答:受弯构件斜截面剪切破坏的主要形态有斜压、剪压和斜拉三种。当剪力相比弯矩较大时,主压应力起主导作用易发生斜压破坏,其特点是混凝土被斜向压坏,箍筋应力达不到屈服强度。当弯剪区弯矩相比剪力较大时,主拉应力起主导作用易发生斜拉破坏,破坏时箍筋应力在混凝土开裂后急剧增加并被拉断,梁被斜向拉裂成两部分,破坏过程快速突然。剪压破坏时箍筋在混凝土开裂后首先达到屈服,然后剪压区混凝土被压坏,破坏时钢筋和混凝土的强度均有较充分利用。6影响有腹筋梁斜截面受剪承载力的主要因素有哪些?答:配有腹筋的混凝土梁,其斜截面受剪承载力的影响因素有剪跨比、混凝土强度、纵向钢筋的销栓作用、箍筋的配筋率及其强度、弯起钢筋的配置数量等。四、计算题1已知钢筋混凝土矩形梁,一类环境,其截面尺寸,承受弯矩设计值,采用C30 混凝土和HRB335 级钢筋。试配置截面钢筋。解:解:, 满足要求,取选配钢筋3 25(2已知矩形截面梁,已配纵向受拉钢筋4根22mm 的HRB400级钢筋,按下列条件计算此梁所能承受的弯矩设计值。 混凝土强度等级为C25; 若由于施工原因,混凝土强度等级仅达到C20级。解: 查教材附录知:对于一类环境,可取梁的保护层厚度mm,HRB400级钢筋,C25级混凝土,。 当混凝土强度等级为C25,梁所能承受的弯矩设计值为。 若由于施工原因,混凝土强度等级仅达到C20级,C20级混凝土。 若由于施工原因,混凝土强度等级仅达到C20级,梁所能承受的弯矩设计值为。3一钢筋混凝土矩形截面简支梁,处于一类环境,安全等级二级,混凝土强度等级为C25,梁的截面尺寸为,纵向钢筋采用HRB335级钢筋,箍筋采用HPB235级钢筋,均布荷载在梁支座边缘产生的最大剪力设计值为250kN。正截面强度计算已配置425 的纵筋,求所需的箍筋。解:(1)确定计算参数 , (2)验算截面尺寸,属一般梁 截面符合要求。(3)验算是否需要计算配置箍筋 故需进行计算配置箍筋。 (4)求箍筋数量并验算最小配筋率选双肢箍8(,)代入上式可得:取,可得:满足要求4. 承受均布荷载设计值作用下的矩形截面简支梁,安全等级二级,处于一类环境,截面尺寸,混凝土为C30级,箍筋采用HPB235级钢筋。梁净跨度。梁中已配有双肢 200箍筋,试求:梁在正常使用期间按斜截面承载力要求所能承担的荷载设计值。解:(1)确定计算参数, (1)求荷载设计值 作业3说明:本次作业对应于文字教材6至9章,应按相应教学进度完成。一、选择题1螺旋箍筋柱较普通箍筋柱承载力提高的原因是( C )。A螺旋筋使纵筋难以被压屈B螺旋筋的存在增加了总的配筋率C螺旋筋约束了混凝土的横向变形D螺旋筋的弹簧作用2大偏心和小偏心受压破坏的本质区别在于( B )。A受拉区的混凝土是否破坏B受拉区的钢筋是否屈服C受压区的钢筋是否屈服D受压区的混凝土是否破坏3偏心受压构件界限破坏时,( D )。A远离轴向力一侧的钢筋屈服比受压区混凝土压碎早发生B远离轴向力一侧的钢筋屈服比受压区混凝土压碎晚发生C远离轴向力一侧的钢筋屈服与另一侧钢筋屈服同时发生D远离轴向力一侧的钢筋屈服与受压区混凝土压碎同时发生4进行构件的裂缝宽度和变形验算的目的是( A )。A使构件满足正常使用极限状态要求 B使构件能够在弹性阶段工作C使构件满足承载能力极限状态要求 D使构件能够带裂缝工作5轴心受拉构件破坏时,拉力( C )承担。A由钢筋和混凝土共同B由钢筋和部分混凝土共同C仅由钢筋D仅由混凝土6其它条件相同时,钢筋的保护层厚度与平均裂缝间距、裂缝宽度的关系是( A )。A保护层越厚,平均裂缝间距越大,裂缝宽度也越大B保护层越厚,平均裂缝间距越小,裂缝宽度越大C保护层厚度对平均裂缝间距没有影响,但保护层越厚,裂缝宽度越大7通过对轴心受拉构件裂缝宽度公式的分析可知,在其它条件不变的情况下,要想减小裂缝宽度,就只有( A )。A减小钢筋直径或增大截面配筋率B增大钢筋直径或减小截面配筋率C增大截面尺寸和减小钢筋截面面积二、判断题1钢筋混凝土受压构件中的纵向钢筋一般采用HRB400级、HRB335级和RRB400级,不宜采用高强度钢筋。( )2在轴心受压短柱中,不论受压钢筋在构件破坏时是否屈服,构件的最终承载力都是由混凝土被压碎来控制的。( )3. 钢筋混凝土长柱的稳定系数随着长细比的增大而增大。( )4两种偏心受压破坏的分界条件为:为大偏心受压破坏;为小偏心受压破坏。( )5大偏心受拉构件为全截面受拉,小偏心受拉构件截面上为部分受压部分受拉。( )6钢筋混凝土轴心受拉构件破坏时,混凝土的拉裂与钢筋的受拉屈服同时发生。( )7静定的受扭构件,由荷载产生的扭矩是由构件的静力平衡条件确定的,与受扭构件的扭转刚度无关,此时称为平衡扭转。( )8对于超静定结构体系,构件上产生的扭矩除了静力平衡条件以外,还必须由相邻构件的变形协调条件才能确定,此时称为协调扭转。( )9受扭的素混凝土构件,一旦出现斜裂缝即完全破坏。若配置适量的受扭纵筋和受扭箍筋,则不但其承载力有较显著的提高,且构件破坏时会具有较好的延性。( )10在弯剪扭构件中,弯曲受拉边纵向受拉钢筋的最小配筋量,不应小于按弯曲受拉钢筋最小配筋率计算出的钢筋截面面积,与按受扭纵向受力钢筋最小配筋率计算并分配到弯曲受拉边钢筋截面面积之和。( )11钢筋混凝土构件裂缝的开展是由于混凝土的回缩和钢筋伸长所造成的。( )12荷载长期作用下钢筋混凝土受弯构件挠度增长的主要原因是混凝土的徐变和收缩。( )三、简答题1钢筋混凝土柱中箍筋应当采用封闭式,其原因在于?答:钢筋混凝土柱中箍筋应当采用封闭式箍筋是为了保证钢筋骨架的整体刚度,并保证构件在破坏阶段箍筋对混凝土和纵向钢筋的侧向约束作用。2钢筋混凝土偏心受压破坏通常分为哪两种情况?它们的发生条件和破坏特点是怎样的?答:钢筋混凝土偏心受压破坏可分为两种情况:大偏心受压破坏与小偏心受压破坏。大偏心受压破坏的发生条件是:偏心距较大,且受拉钢筋配置得不太多时。破坏特点是:受拉区的钢筋能达到屈服,受压区的混凝土也能达到极限压应变。小偏心受压破坏的发生条件是:偏心距较小或很小,或者虽然相对偏心距较大,但配置了很多的受拉钢筋。破坏特点是:靠近纵向力一端的钢筋能达到受压屈服,混凝土被压碎,而远离纵向力一端的钢筋无论是受拉还是受压,一般情况下都达不到屈服。3简述矩形截面大偏心受压构件正截面承载力计算公式的使用条件?答:矩形截面大偏心受压构件正截面承载力计算公式的适用条件如下:1)为了保证构件破坏时受拉区钢筋的应力先达到屈服强度,要求满足:2)为了保证构件破坏时,受压钢筋应力能达到抗压屈服强度设计值,与双筋受弯构件相同,要求满足:4实际工程中,哪些受拉构件可以按轴心受拉构件计算,哪些受拉构件可以按偏心受拉构件计算?答:在钢筋混凝土结构中,真正的轴心受拉构件是罕见的。近似按轴心受拉构件计算的有承受节点荷载的屋架或托架受拉弦杆和腹杆,刚架、拱的拉杆,承受内压力的环形管壁及圆形储液池的壁筒等;可按偏心受拉计算的构件有矩形水池的池壁、工业厂房双肢柱的受拉肢杆、受地震作用的框架边柱和承受节间荷载的屋架下弦拉杆等。5轴心受拉构件从加载开始到破坏为止可分为哪三个受力阶段?其承载力计算以哪个阶段为依据?答:轴心受拉构件从加载开始到破坏为止可分为三个受力阶段:第一阶段为从加载到混凝土受拉开裂前,第二阶段为混凝土开裂至钢筋即将屈服,第三阶段为受拉钢筋开始屈服到全部受拉钢筋达到屈服。承载力计算以第三阶段末为依据。6大、小偏心受拉构件的破坏特征有什么不同?如何划分大、小偏心受拉构件?答:大偏心受拉构件破坏时,混凝土虽开裂,但还有受压区。当数量适当时,受拉钢筋首先屈服,然后受压钢筋的应力达到屈服强度,混凝土受压边缘达到极限应变而破坏。小偏心受拉构件破坏时,一般情况下,全截面均为拉应力,其中一侧的拉应力较大。随着荷载的增加,一侧的混凝土首先开裂,而且裂缝很快就贯穿整个截面,所以混凝土将退出工作,拉力完全由钢筋承担,构件破坏时,及都达到屈服强度。偏心受拉构件正截面承载力计算,按纵向拉力N的作用位置不同,可以分为大偏心受拉与小偏心受拉两种情况:当纵向拉力N作用在钢筋合力点和合力点范围之间时,为小偏心受拉。7钢筋混凝土纯扭构件有哪几种破坏形式?各有何特点?答:钢筋混凝土纯扭构件的破坏形态可分为适筋破坏、部分超筋破坏、完全超筋破坏和少筋破坏4类。适筋破坏的特点:纵筋和箍筋先到达屈服强度,然后混凝土被压碎而破坏,属于延性破坏。部分超筋破坏的特点:破坏时仅纵筋屈服,而箍筋不屈服;或箍筋屈服,纵筋不屈服,破坏时具有一定的延性,但较适筋破坏时的截面延性小。完全超筋破坏的特点:纵筋和箍筋都没有达到屈服强度,而混凝土先行压坏,属于脆性破坏。少筋破坏的特点:裂缝一旦出现,构件就会立即发生破坏,此时,纵筋和箍筋不仅达到屈服强度而且可能进入强化阶段,属于脆性破坏。8. 钢筋混凝土弯剪扭构件的钢筋配置有哪些构造要求?答: 1)纵筋的构造要求对于弯剪扭构件,受扭纵向受力钢筋的间距不应大于200mm和梁的截面宽度;在截面四角必须设置受扭纵向受力钢筋,其余纵向钢筋沿截面周边均匀对称布置。当支座边作用有较大扭矩时,受扭纵向钢筋应按受拉钢筋锚固在支座内。当受扭纵筋按计算确定时,纵筋的接头及锚固均应按受拉钢筋的构造要求处理。在弯剪扭构件中,弯曲受拉边纵向受拉钢筋的最小配筋量,不应小于按弯曲受拉钢筋最小配筋率计算出的钢筋截面面积,与按受扭纵向受力钢筋最小配筋率计算并分配到弯曲受拉边钢筋截面面积之和。2)箍筋的构造要求箍筋的间距及直径应符合受剪的相关要求。箍筋应做成封闭式,且应沿截面周边布置;当采用复合箍筋时,位于截面内部的箍筋不应计入受扭所需的箍筋面积;受扭所需箍筋的末端应做成135 弯钩,弯钩端头平直段长度不应小于10d(d为箍筋直径)。9钢筋混凝土裂缝控制的目的是什么?答:裂缝控制的目的一方面是为了保证结构的耐久性,因为裂缝过宽时,气体和水分、化学介质会侵入裂缝,引起钢筋锈蚀,这不仅削弱了钢筋的面积,而且还会因钢筋体积的膨胀而引起保护层剥落,产生长期危害,影响结构的使用寿命。另一方面是考虑建筑物观瞻、人的心理感受和使用者不安全程度的影响。四、计算题1已知某柱两端为不动铰支座,柱高H=5.6m,截面尺寸为400mm400mm,采用C20混凝土、HRB335钢筋,柱顶截面承受轴心压力设计值N=1692kN,试确定该柱所需的纵向钢筋截面面积。解: (1)确定稳定系数,查附表3-3,得(2)计算纵向钢筋截面面积(3)验算配筋率而,满足。2已知某钢筋混凝土屋架下弦,截面尺寸,承受的轴心拉力设计值,混凝土强度等级C30,钢筋为HRB335。求截面配筋。解:首先,确定计算参数,查教材附录知,HRB335钢筋。选用416()能够满足要求。作业4说明:本次作业对应于文字教材10至11章,应按相应教学进度完成。一、选择题1混凝土极限拉应变约为( C )。A(1.001.80)10-3B(0.200.40)10-3C(0.100.15)10-3D(1.001.50)10-32钢筋HPB235、HRB335、HRB400和RRB400屈服时,其应变约为( D )。A(1.501.80)10-3B(0.200.40)10-3C(0.100.15)10-3D(1.001.80)10-33条件相同的钢筋混凝土轴拉构件和预应力混凝土轴拉构件相比较,( B )。A后者的刚度低于前者 B后者的抗裂度比前者好C前者与后者的抗裂度相同 D. 前者与后者的刚度相同4下列各项预应力损失类型中,不属于后张法预应力损失的是( C )。A锚固回缩损失B摩擦损失C温差损失D应力松弛损失5公路桥涵现浇梁、板的混凝土强度等级不应低于( A ),当用HRB400、KL400级钢筋配筋时,不应低于( B )。AC20BC25CC30DC15二、判断题1普通钢筋混凝土结构中采用高强度钢筋是不能充分发挥其作用的,而采用高强混凝土可以很好发挥其作用。( )2无粘结预应力混凝土结构通常与先张预应力工艺相结合。( )3后张法预应力混凝土构件,预应力是靠钢筋与混凝土之间的粘结力来传递的。( )4对先张法预应力构件,预应力是依靠钢筋端部的锚具来传递的。( )5我国混凝土结构设计规范规定,预应力混凝土构件的混凝土强度等级不应低于C30。对采用钢绞线、钢丝、热处理钢筋作预应力钢筋的构件,特别是大跨度结构,混凝土强度等级不宜低于C40。( )6张拉控制应力是指预应力钢筋在进行张拉时所控制达到的最大应力值。()7为保证钢筋与混凝土的粘结强度,防止放松预应力钢筋时出现纵向劈裂裂缝,必须有一定的混凝土保护层厚度。( )8我国公路桥规采用以概率论为基础的极限状态设计法,按分项系数的设计表达式进行设计,对桥梁结构采用的设计基准期为50年。( )9与房建规范不同,公路桥规在抗剪承载力计算中,其混凝土和箍筋的抗剪能力没有采用两项相加的方法,而是采用破坏斜截面内箍筋与混凝土的共同承载力。()10公路桥规规定受压构件纵向钢筋面积不应小于构件截面面积的0.5%。( )11我国公路桥规关于裂缝宽度的计算与混凝土结构设计规范是相同的。( )12. 我国公路桥规中指出裂缝宽度主要与受拉钢筋应力、钢筋直径、受拉钢筋配筋率、钢筋表面形状、混凝土标号和保护层厚度有关,而挠度的计算则根据给定的构件刚度用结构力学的方法计算。( )三、简答题1与普通混凝土相比,预应力混凝土具有哪些优势和劣势?答:与普通混凝土相比,预应力混凝土具有优势是:1)构件的抗裂度和刚度提高;2)构件的耐久性增加;3)自重减轻;4)节约材料。与普通混凝土相比,预应力混凝土具有劣势是:预应力混凝土施工需要专门的材料和设备、特殊的工艺、造价较高。2简述有粘结预应力与无粘结预应力的区别?答:有粘结预应力,是指沿预应力筋全长其周围均与混凝土粘接、握裹在一起的预应力。先张预应力结构及预留孔道穿筋压浆的后张预应力结构均属此类。无粘结预应力,是指预应力筋伸缩、滑动自由,不与周围混凝土粘接的预应力。无粘结预应力混凝土结构通常与后张预应力工艺相结合。3列举三种建筑工程中常用的预应力锚具?答:螺丝端杆锚具、锥形锚具、镦头锚具、夹具式锚具。4预应力混凝土结构及构件所用的混凝土,需满足哪些要求?答:预应力混凝土结构构件所用的混凝土,需满足下列要求:1)强度高。与普通钢筋混凝土不同,预应力混凝土必须采用强度高的混凝土。因为强度高的混凝土对采用先张法的构件可提高钢筋与混凝土之间的粘结力,对采用后张法的构件,可提高锚固端的局部承压承载力。2)收缩、徐变小。以减少因收缩、徐变引起的预应力损失。3)快硬、早强。可尽早施加预应力,加快台座、锚具、夹具的周转率,以利加快施工进度。5引起预应力损失的因素有哪些?如何减少各项预应力损失?答:引起预应力损失的因素主要有锚固回缩损失、摩擦损失、温差损失、应力松弛损失、收缩徐变损失等。 见教材P216-2206公路桥涵按承载力极限状态和正常使用极限状态进行结构设计,在设计中应考虑哪三种设计状况?分别需做哪种设计?答:公路桥涵按承载力极限状态和正常使用极限状态进行结构设计,在设计中应考虑以下三种设计状况:1)持久状态。该状态需要作承载力极限状态和正常使用极限状态设计。2)短暂状态。该状态主要做承载力极限状态设计,必要时才作正常使用极限状态设计。3)偶然状态。该状态仅作承载力极限状态设计。四、计算题1已知一矩形截面简支梁,截面尺寸bh=200mm550mm,混凝土强度等级为C25,纵向钢筋采用HRB335级,安全等级为二级,梁跨中截面承受的最大弯矩设计值为M=160kNm。若上述设计条件不能改变,试进行配筋计算。若由于施工质量原因,实测混凝土强度仅达到C20,试问按问所得钢筋面积的梁是否安全?,假设mm,则有效高度。(1)计算受压区高度 (2)计算钢筋数量 (3)选择并布置钢筋选用3 25(,钢筋布置如图所示。(4)验算配筋率实际配筋率 。 请您删除一下内容,O(_)O谢谢!2016年中央电大期末复习考试小抄大全,电大期末考试必备小抄,电大考试必过小抄Basketball can make a true claim to being the only major sport that is an American invention. From high school to the professional level, basketball attracts a large following for live games as well as television coverage of events like the National Collegiate Athletic Association (NCAA) annual tournament and the National Basketball Association (NBA) and Womens National Basketball Association (WNBA) playoffs. And it has also made American heroes out of its player and coach legends like Michael Jordan, Larry Bird, Earvin Magic Johnson, Sheryl Swoopes, and other great players. At the heart of the game is the playing space and the equipment. The space is a rectangular, indoor court. The principal pieces of equipment are the two elevated baskets, one at each end (in the long direction) of the court, and the basketball itself. The ball is spherical in shape and is inflated. Basket-balls range in size from 28.5-30 in (72-76 cm) in circumference, and in weight from 18-22 oz (510-624 g). For players below the high school level, a smaller ball is used, but the ball in mens games measures 29.5-30 in (75-76 cm) in circumference, and a womens ball is 28.5-29 in (72-74 cm) in circumference. The covering of the ball is leather, rubber, composition, or synthetic, although leather covers only are dictated by rules for college play, unless the teams agree otherwise. Orange is the regulation color. At all levels of play, the home team provides the ball. Inflation of the ball is based on the height of the balls bounce. Inside the covering or casing, a rubber bladder holds air. The ball must be inflated to a pressure sufficient to make it rebound to a height (measured to the top of the ball) of 49-54 in (1.2-1.4 m) when it is dropped on a solid wooden floor from a starting height of 6 ft (1.80 m) measured from the bottom of the ball. The factory must test the balls, and the air pressure that makes the ball legal in keeping with the bounce test is stamped on the ball. During the intensity of high school and college tourneys and the professional playoffs, this inflated sphere commands considerable attention. Basketball is one of few sports with a known date of birth. On December 1, 1891, in Springfield, Massachusetts, James Naismith hung two half-bushel peach baskets at the opposite ends of a gymnasium and out-lined 13 rules based on five principles to his students at the International Training School of the Young Mens Christian Association (YMCA), which later became Springfield College. Naismith (1861-1939) was a physical education teacher who was seeking a team sport with limited physical contact but a lot of running, jumping, shooting, and the hand-eye coordination required in handling a ball. The peach baskets he hung as goals gave the sport the name of basketball. His students were excited about the game, and Christmas vacation gave them the chance to tell their friends and people at their local YMCAs about the game. The association leaders wrote to Naismith asking for copies of the rules, and they were published in the Triangle, the school newspaper, on January 15,1892. Naismiths five basic principles center on the ball, which was described as large, light, and handled with the hands. Players could not move the ball by running alone, and none of the players was restricted against handling the ball. The playing area was also open to all players, but there was to be no physical contact between players; the ball was the objective. To score, the ball had to be shot through a horizontal, elevated goal. The team with the most points at the end of an allotted time period wins. Early in the history of basketball, the local YMCAs provided the gymnasiums, and membership in the organization grew rapidly. The size of the local gym dictated the number of players; smaller gyms used five players on a side, and the larger gyms allowed seven to nine. The team size became generally established as five in 1895, and, in 1897, this was made formal in the rules. The YMCA lost interest in supporting the game because 10-20 basketball players monopolized a gymnasium previously used by many more in a variety of activities. YMCA membership dropped, and basketball enthusiasts played in local halls. This led to the building of basketball gymnasiums at schools and colleges and also to the formation of professional leagues. Although basketball was born in the United States, five of Naismiths original players were Canadians, and the game spread to Canada immediately. It was played in France by 1893; England in 1894; Australia, China, and India between 1895 and 1900; and Japan in 1900. From 1891 through 1893, a soccer ball was used to play basketball. The first basketball was manufactured in 1894. It was 32 in (81 cm) in circumference, or about 4 in (10 cm) larger than a soccer ball. The dedicated basketball was made of laced leather and weighed less than 20 oz (567 g). The first molded ball that eliminated the need for laces was introduced in 1948; its construction and size of 30 in (76 cm) were ruled official in 1949. The rule-setters came from several groups early in the 1900s. Colleges and universities established their rules committees in 1905, the YMCA and the Amateur Athletic Union (AAU) created a set of rules jointly, state militia groups abided by a shared set of rules, and there were two professional sets of rules. A Joint Rules Committee for colleges, the AAU, and the YMCA was created in 1915, and, under the name the National Basketball Committee (NBC) made rules for amateur play until 1979. In that year, the National Federation of State High School Associations began governing the sport at the high school level, and the NCAA Rules Committee assumed rule-making responsibilities for junior colleges, colleges, and the Armed Forces, with a similar committee holding jurisdiction over womens basketball. Until World War II, basketball became increasingly popular in the United States especially at the high school and college levels. After World War II, its popularity grew around the world. In the 1980s, interest in the game truly exploded because of television exposure. Broadcast of the NCAA Championship Games began in 1963, and, by the 1980s, cable television was carrying regular season college games and even high school championships in some states. Players like Bill Russell, Wilt Chamberlain, and Lew Alcindor (Kareem Abdul-Jabbar) became nationally famous at the college level and carried their fans along in their professional basketball careers. The womens game changed radically in 1971 when separate rules for women were modified to more closely resemble the mens game. Television interest followed the women as well with broadcast of NCAA championship tourneys beginning in the early 1980s and the formation of the WNBA in 1997. Internationally, Italy has probably become the leading basketball nation outside of the United States, with national, corporate, and professional teams. The Olympics boosts basketball internationally and has also spurred the womens game by recognizing it as an Olympic event in 1976. Again, television coverage of the Olympics has been exceptionally important in drawing attention to international teams. The first professional mens basketball league in the United States was the National Basketball League (NBL), which debuted in 1898. Players were paid on a per-game basis, and this league and others were hurt by the poor quality of games and the ever-changing players on a team. After the Great Depression, a new NBL was organized in 1937, and the Basketball Association of America was organized in 1946. The two leagues came to agree that players had to be assigned to teams on a contract basis and that high standards had to govern the game; under these premises, the two joined to form the National Basketball Association (NBA) in 1949. A rival American Basketball Association (ABA) was inaugurated in 1967 and challenged the NBA for college talent and market share for almost ten years. In 1976, this league disbanded, but four of its teams remained as NBA teams. Unification came just in time for major television support. Several womens professional leagues were attempted and failed, including the Womens Professional Basketball League (WBL) and the Womens World Basketball Association, before the WNBA debuted in 1997 with the support of the NBA. James Naismith, originally from Al-monte, Ontario, invented basketball at the International YMCA Training School in Springfield, Massachusetts, in 1891. The game was first played with pea
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