预应力课程设计终结.docx
反摩擦影响长度/lf = J /EJAb",Atz 二 "。""式中：限张拉端锚下控制应力；Z/锚具变形值，OVM夹片锚有顶压时取4mm；I张拉端到锚固端之间的距离，本例中=15980mm0当O时，离张拉端x处由锚具变形、钢筋回缩和接缝压缩引起的、考虑/ 一 Y反摩擦后的预拉力损失为区二八。上一， = 2dlf入/a Jlf当X时，表示该截面不受反摩擦影响。反摩阻影响长度计算表如下：表11反摩阻影响长度计算表反摩阻影响长度计算钢束号12341395139513951395l1321.41326.11331.21331.2d0.0046050.0043120.0039910.003991lf13014.413449.113979.913979.9锚具变形损失计算见下表:表12截面钢束1钢束2钢束3钢束4总计1X400.0400.0400.0400.0119.87115.99111.59111.59l2116.18112.54108.40108.40445.522X5100.05100.05100.05100.0119.87115.99111.59111.59l272.8972.0170.8870.88286.6633X8190.08190.08190.08190.0续上表12119.87115.99111.59111.59!244.4345.3646.2246.22182.224X15980.015980.015980.015980.0119.87115.99111.59111.59l20.000.000.000.000.003、分批张拉损失b/4LE*ypc,p式中：八巴一一在计算截面先张拉的截面重心处，由后张拉的各批钢筋产生的混凝土法向应力；功一一预应力钢筋与混凝土弹性模量之比，a 后 E E=1.95×105 3.45 ×104= 5.65t c本例中预应力筋束的张拉顺序为：4321,有效张拉力N作为张拉控制力减去摩擦损失和锚具变形损失后的张拉力。预应力分批张拉损失的计算见下表。表13÷截面张拉顺序张拉力Np张拉钢束的偏心矩ep计算钢束的偏心矩叩4号损失钢钢束钢束钢 钢 钢钢钢钢支束234束2束3束4束2束3束4点3号束1424.7200381.600381.60.000.0014.322号束1424.130-198.4-198.40381.6381.60.004.884.881号束1419.94-458-458.4-458.4-198381.6381.611.950.650.65总计11.955.5419.85变截面3号束1434.2900697.000697.00.000.0039.432号束1446.290308308.0697.0697.00.0025.4725.471号束1443.58108.0108108.308.0697.0697.015.8818.0918.09总计15.8843.5682.99L/43号束1446.3300711.00711.00.000.0041.472号束1461.0407117110711.0711.00.0041.8941.891号束1459.33564.0564564711.0711.0711.036.1536.1536.15总计36.1578.04119.5跨中3号束1480.320071900718.80.000.0043.192号束1474.6107197190718.8718.80.0043.0243.021号束1469.4638.63639718.8718.718.39.739.739.718988000总计39.782.72126.4、钢筋应力松弛损失b/5/WG(O52%0.26).J pk式中：超张拉系数，本例中 = 1.0；q钢筋松弛系数，本例采用低松弛钢绞线，取4 = 0.3；pe传力锚冏时钢筋应力，pe = con - z - l2 - l4。钢筋应力松弛损失的计算见下表表14钢束松弛损失截面spe (MPa)s L5 (MPa)钢束I钢束2钢束3钢束4钢束1钢束2钢束3钢束4支点1276.91268.71275.71261.437.1536.0536.9935.06变截面1298.21284.71246.31206.840.0938.2233.0628.02L/41312.41277.71222.61181.142.0837.2730.0124.88跨中1321.41286.41248.51205.343.3838.4533.3527.835、混凝土收缩徐变损失1 + 15 磔 psN N p MGk1ePps = 1+M = ia式中：构件受拉区全部纵向钢筋截面重心处，由预加力(扣除相应阶段应力损失)和结构自重产生的混凝土法向应力；久Sd )预应力筋传力锚固龄期为小，计算龄期为t时的混凝土收缩应变；j)加载龄期为，计算龄期为t时的混凝土徐变系数；p构件受拉区全部纵向钢筋配筋率，p = (Ap + A,)4 o设混凝土传力锚固龄期和加载龄期均为28天，计算时间1 = 8,桥梁所处环境的年平均湿度为75%,以跨中截面计算其理论厚度h：z = 2×0.63× 1000/6.6 = 191m查表得：入t)=0.26x10-3，尢 =2.15，但是考虑到所用混凝土强度等级为C50,Com U()' S'O f上述数值应该乘以系数J26.8u =0.732,结果%(0=0.19x10-3,叫“=1.57。混凝土收缩、徐变损失的计算见下表表15混凝土收缩、徐变损失截面epsrpsNpMGKspc预spc自spcsl6支点107.50.004761.0595652.00.04.940.004.9467.65变截面505.10.007581.9635600.11608.314.45-4.1110.3594.82L/4700.80.007582.8165553.22269.520.82-7.8812.94103.54跨中722.50.007582.9255628.53026.121.95-10.8011.1491.816、预应力损失组合上述各项预应力损失汇总情况组合列于下表16表16截面sl,Isl,II钢束1钢束2钢束3钢束4平均钢束1钢束2钢束3钢束4平均支卢X118.07126.26119.31133.63124.32104.81103.70104.64102.71103.96变截面96.82110.26148.73188.16135.99134.91133.04127.88122.84129.67L/482.65117.26172.38213.85146.54145.63140.81133.55128.42137.10跨中73.59108.61146.50189.69129.60135.19130.27125.17119.65127.57七、正常使用极限状态计算1、全预应力混凝土构件抗裂性验算(1)正截面抗裂性验算正截面抗裂性验算以跨中截面受拉边的正应力控制。在荷载短期效应组合下应满足： -0.85z, <0外为在荷载短期效应组合下，截面受拉边的应力:g%÷ J2÷"gC5小汽/1/心 为、心、先2、/。、分别为阶段1、阶段2、阶段3、的截面惯性矩和截面重心至受拉边缘的距离，查表得：L/4700.80.007582.8165553.22269.520.82-7.8812.94103.54跨中722.50.007582.9255628.53026.121.95-10.8011.1491.816、预应力损失组合上述各项预应力损失汇总情况组合列于下表16表16截面sl,Isl,II钢束1钢束2钢束3钢束4平均钢束1钢束2钢束3钢束4平均支卢X118.07126.26119.31133.63124.32104.81103.70104.64102.71103.96变截面96.82110.26148.73188.16135.99134.91133.04127.88122.84129.67L/482.65117.26172.38213.85146.54145.63140.81133.55128.42137.10跨中73.59108.61146.50189.69129.60135.19130.27125.17119.65127.57七、正常使用极限状态计算1、全预应力混凝土构件
