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先张法空心板梁预应力施工作业指导书

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先张法空心板梁预应力施工作业指导书
一、张拉前的准备工作
先张法梁的预应力筋是在底模整理后，在台座上进行张拉已加工好的预应力筋。对于长线台座，预应力筋或者预应力筋与拉杆、力筋的连接，必须先用连接器串连好后才能张拉。先张采用一端张拉，另一端在张拉前要设置好固定装置或安放好预应力筋的放松装置。
张拉前，应先安装定位板，检查定位板的力筋孔位置和孔径大小是否符合设计要求，然后将定位板固定在横梁上。在检查预应力筋数量、位置、张拉设备和锚具后，方可进行张拉。
二、张拉程序
0&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp初应力（0.1δk）&nbsp&nbsp&nbsp&nbsp&nbsp0.2δk&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp0.5δk&nbsp&nbsp&nbsp&nbsp&nbsp&nbspδk（持荷2分钟锚固）
三、张拉控制数据计算
钢绞线张拉采用张拉力和伸长值双重控制。
&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp根据设计要求采用美国标准ASTM&nbspA416-90a270级φj15.24高强度低松弛钢绞线,选用秦皇岛预应力钢绞线联营公司提供的该规格的钢绞线，公称直径φj=15.24mm,截面积Ag=140mm2,强度等级Ryb=1860MPa,弹性模量Eg=1.95×105MPa。
&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp张拉控制应力δkb=0.75Ryb=1395MPa,单根钢绞线控制张拉力Ng=δkb×&nbspAg=195.3KN，整体控制张拉力为:
&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp13m板梁:&nbspNy=10根×&nbsp&nbspNg=1953KN；
&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp16m板梁:&nbspNy=11根×&nbsp&nbspNg=2148.3KN；
&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp20m板梁中梁:&nbspNy=15根×&nbsp&nbspNg=2929.5KN；
&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp20m板梁边梁:&nbspNy=16根×&nbsp&nbspNg=3124.8KN；
&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp1、张拉设备的选用
&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbspA&nbsp整体张拉选用YDT1960型千顶，2台公称张拉力为4000KN＞&nbsp3124.8KN;单根张拉选用QYC230型千斤顶，公称张拉力为200KN＞195.3KN,可以保证张拉工作的可靠性、准确性。
&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp2、张拉伸长值估算:
&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp△L&nbsp&nbsp=δK÷Eg×L=1395÷1.95×105×7600=54.4cm
&nbsp&nbsp&nbsp&nbsp&nbsp&nbspYDT1960型千斤顶的行程为80cm＞54.4cm,可以满足要求。&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp
&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbspC压力表的选用：
&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbspPu=Ny/Au=1562400/41526.5=37.6MPa
选用鉴定证书压力表最小量程为100MPa可以满足使用要求。
&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp3、油泵选用YBZ&nbsp2×2/50型电动油泵,与YDT1960型千斤顶、QYC230型千斤顶配套使用。
&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp4、选用开封预应力锚具厂XM系列锚具及配套夹片。
&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp5、伸长值控制
&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp钢绞线调整到初应力后，对张拉端的钢绞线和固定端的砂箱活塞长度进行标定记录，在测量各级钢绞线伸长值时要扣除砂箱活塞的回缩量，以保证伸长值准确无误。
&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp钢绞线张拉时的控制应力，应以伸长值进行校核，实测伸长值与理论伸长值误差控制在±6%之内，若超出此范围应停止张拉，待查明原因，纠正后方可继续张拉。
&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp（1）理论伸长值的计算
&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp△L&nbsp&nbsp=δK÷Eg×L=1395÷1.95×105×7600=54.4cm
&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp（2）实际伸长值的量测及计算方法
&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp在整体张拉前,先将钢绞线都调整到初应力0.1δK,再开始整体张拉和计测伸长量,&nbsp最后再加上初应力时的估算伸长值。即：
&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp△L=△L1&nbsp+△L2
&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp△L2——张拉至0.1&nbsp5δk时的估算伸长值，按理论伸长值的15%。
&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp△L1&nbsp——为0.15&nbspδk至δk时的实测伸长值。
具体施工控制数据及校定结果附后。
四、张拉操作&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp
1、调整预应力筋长度
采用螺丝杆锚具，拧动端头螺帽，调整预应力筋长度，使每根预应力筋受力均匀。
2、初始张拉
一般施加10%的张拉应力，将预应力筋拉直，锚固端和连接器处拉紧，在预应力筋上选定适当的位置刻画标记，作为测量延伸量的基点。
3、正式张拉
一端固定，一端整体张拉。千斤顶必须同步顶进，保持横梁平行移动，预应力筋均匀受力，分级加载拉至张拉应力。
4、持荷
按预应力筋的类型选定持荷时间2min-5min，使预应力筋完成部分徐舒，完成量约为全部量的20%-25%，以减少钢丝锚固后的应力损失。
5、锚固
补足或放松预应力筋的拉力至控制应力。测量、记录预应力筋的延伸量，并核对实测值与理论计算值，其误差应在±6%范围内，如不符合规定，则应找出原因及时处理。张拉满足要求后，锚固预应力筋，千斤顶回油至零。
五、预应力筋放张
当混凝土达到设计规定的放松强度之后，可在台座上放松受拉预应力筋，对预制梁施加预应力。当设计无规定时，一般应大于混凝土设计强度标准值的75%时进行。放张采用砂箱法，放松的装置设在预应力筋和拉前放置在非张拉端。放张时打开出砂口，让砂慢慢流出，活塞缩回，放砂速度均匀一致，分四次完成，每次间隔20min。
砂箱放松后，采用手持砂轮机切割，切割时从放张端开始，分根交错，逐次切向另一端。切割后的外露端头应用砂浆封闭或涂刷防蚀材料，防止生锈。