推荐回答(2个)

表中了w为预应力俐筋强度标准值.可由本教材附录2表8查得.从表10一I石
到.〔‘」是以预应力俐筋的强度标准值给出的。这是因为张拉预应力锅筋时仅诊及
材料本身.与构件设什无关,故〔氏一」可不受预应力钢筋的强度设计俄的限制.而
直接与标准流相联系。
规范还规定.符介下列情况之一时,表中的〔‘」值可提高0.05 f,,, .0妥求
提离构件在施工阶段的杭裂性能而在使用阶段受压区内设盆的顶应力俐筋。0要求部
分抵消由于应力松弛、康摊、俐筋分批张拉以及顶应力钢筋与张拉台座之间的沮趋等
因素产生的预应力扭失。
张拉控侧应力允许值〔‘」不宜取得过低.否则会因各种应力损失使预应力俐
筋的回弹力减小,不能充分利用钢筋的强度。因此,预应力钢筋的氏.应不小
于0.4几.。
从表10一1可见.对同一钢种.先张法的俐筋张拉控翻应力‘较后张法大一些.
这是由于在先张法中.张拉钢筋达到控制应力时.构件混凝土尚未浇筑.当从台座t
故松俐筋使滋挂土受到预压时,钢筋己随粉混凝土的压缩而回缩.因此在混凝土受到
顶压应力时.俐筋的预拉应力已经小于控制应力氏.了。而对后张法来说,在张拉钢
筋的同时.混凝土即受挤压。当钢筋张拉达到控制应力时.混凝土的弹性压编也已经
完成.不必考盛由于混凝土的弹性压缩而引起钢筋应力值的降低。所以.哟控制应力
口r.相等时.后张法钩件所建立的预应力俄比先张法为大。这就是在后张法.卜所采用
的控侧应力伏规定得比先张法为小的原因。
10.3. 2预应力损失
实侧表明,在没有外荷峨的作用情况下,预应力炯筋在构件内各部分的实际顶拉应
力会变得比张拉时的控侧应力小不少,其减小的那一部分应力称为顶应力很失。预应力
损失与张拉工艺、构件制作、配筋方式和材料特性等因求有关。由于各形响因索之间相
互制约且有的因素还是时间的函数.因此确切侧定顶应力捆失比较困难.规范则是以各
个主要因东单独造成的顶应力搜失之和近似作为总横失来进行计算的。顶应力报失的计
算是分析构件在受荷前应力状态和进行预应力构件设计的旅要内容及前提。
在设计和施工预应力构件时。应尽甘正确地预计预应力创失.并设法减少顶应力
损失。
顶应力投失可以分为下列几种.:
10.3.2.1张拉.枯其交形和钥筋内编引起的贾应力栩失On
不论先张法还是后张法,张拉端锚具、夹具对构件或台座施加挤压力是通过钢筋
回缩带动锚具、夹几来实现的。山于预应力钥筋回弹方向与张拉时拉伸方向相反。因
此.只要一卸去千斤顶后.就会因预应力俐筋在锚具、夹具中的清移‘内绪)和锚
几、央具受挤If后的压编变形(包括接触面间的空晾)以及采用垫板时垫板间缝晾的
挤紧.使得原来拉吸的顶应力钥筋发生内缩。俐筋内编.应力就会有所降低.由此遗
混凝土路面修补材料:
1.表面薄层(麻面、骨料外露等)修复:
可将表面清除干净,露出坚实的混凝土部分,再在表面涂刮JN-X混凝土修补胶或JN-F封口胶即可。为保证更好的修补效果及美观,修补区域的边缘应向老混凝土中切入约10mm并切成规则形状。修补后JN胶的颜色接近混凝土本色,若对颜色有更高要求,可在现场添加适量颜料。
2. 坑洞(接缝及边角处)局部修复:
混凝土路面坑洞(接缝及边角处)局部快速修复采用以有机环氧树脂作为胶结材料的JN-X混凝土修补胶。JN-X混凝土修补胶系A、B两组分改性环氧树脂类胶粘剂,由多种有机及无机改性材料复合而成,其主要特点为:
(1)常温固化,固化速度较快,且可应用户要求进行调整;
(2)本身强度及与混凝土的粘结强度高;
(3)不含挥发性溶剂,硬化时基本不收缩;
(4)与混凝土颜色接近;
(5)抗老化性及耐介质(酸、碱及水等)性好;
(6)两组分配胶比例较宽,便于现场操作;
( 7)可操作时间较长,使用方便、无毒。
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