竖向预应力筋预应力损失的试验研究

1、竖向预应力筋预应力损失的试验研究朱浩1；芶洁 2（1成都合众桥梁科技有限公司 四川成都 610031； 2贵州交通职业技术学院 贵州贵阳 550008）摘要：预应力混凝土梁式桥竖向预应力钢筋因其长度较短，即使出现很微小的松弛或锚头回缩也会出现较大的预应力损失，以至于危及结构安全。因此本文主要对竖向预应力钢筋预应力损失展开研究，并为以后同类桥梁设计提供参考数据。关键词：竖向 钢筋 预应力 预应力损失 试验1. 概述桥梁结构的竖向预应力筋通常采用精轧螺纹钢筋（高强钢筋）。由于竖向预应力筋通常长度较短，因此精轧螺纹钢筋即使出现很微小的松弛或锚头回缩也将引起竖向预应力筋出现较大的预应力损失，以至于危及

2、结构安全。 本次试验主要围绕如何降低竖向预应力筋的预应力损失展开，通过试验达到：（1）获得竖向预应力筋损失的影响因素及控制要素；（2）获得竖向预应力永存应力的实测资料，为今后桥梁的病害分析及同类桥梁的设计提供第一手资料；2. 试验方法和设备预应力损失分为两部分：瞬时预应力损失和长期预应力损失两部分。瞬时预应力损失主要包括锚具变形和接缝压缩，以及混凝土支架的管道摩阻损失。长期预应力损失主要由钢筋松弛和混凝土的收缩徐变以及温度变化引起。对于大跨径混凝土梁式桥竖向预应力控制技术研究主要采用试验研究，通过在特别设计的试件上对预应力筋进行加载，测试预应力筋中的有效预应力随时间的变化，通过对试验数据的各种

3、分析得出相应地研究结论。本试验共选用3根5m长的32国产高强精轧螺纹钢，编号分别是C5,C6,C7。依次在钢支架上张拉，然后放张并连续测量10d的预应力损失。1.1.1 回缩量对比及松弛试验方案利用A类试件形式，取L4000mm，选用Error! Reference source not found.中的高强钢筋类型，每种类型进行3组试验，在常温环境进行试验。试验流程为：（1）将高强钢筋张拉至0.8倍屈服强度，记录各传感器读数；（2）用手旋紧锚具，千斤顶卸压锚固，记录各传感器读数；（3）持荷10天，每隔2小时记录各传感器读数。（4）分析获得各厂家高强钢筋的锚具回缩量及松弛值。为加快试验进度，本

4、试验采用4套试件同步进行。1.1.2 疲劳试验方案利用C类试件形式，取L4000mm,选用Error! Reference source not found.的高强钢筋类型，每种类型进行1组(含两根高强钢筋)试验，在常温环境进行试验。试验流程为：（1） 对试件进行张拉，张拉吨位为0.8倍高强钢筋屈服强度，锚固后记录传感器读数；（2） 对预应力孔道进行压浆，并每隔24h记录传感器读数；（3） 压浆材料强度满足要求后利用MTS试验机对试件进行疲劳加载，传感器采样周期为1h，根据计算分析确定加载吨位及加载循环次数。（4） 分析获得各厂家高强钢筋的永存应力和加载次数的关系。1.1.3 锚固区混凝土影响

5、试验方案利用B类试件形式，取L4000mm，选用国产32高强精轧螺纹钢，试件数量为3组，同时利用Error! Reference source not found.中的A类试件进行对比试验，在常温环境进行试验。试验流程为：（1）将高强钢筋张拉至0.8倍屈服强度，记录各传感器读数；（2）用手旋紧锚具，千斤顶卸压锚固，记录各传感器读数；（3）持荷10天，每隔12小时记录各传感器读数。（4）分析获得锚固区混凝土对高强钢筋锚固效果的影响。（5）另外，从对比A类构件的结果可以得到10天的松弛结果。试验方法：第节、第节、第节；试验设备： 第5.2节 。3、将和8.4节的内容合并成文章的主体。将1.1.4

6、国产高强精轧螺纹钢松弛回缩试验该组实验一共选了3根表 1.21 国产高强精轧螺纹钢C5预应力损失（单位：KN）C5总损失时间效应损失二次张拉600600.617回油稳定575.85324.7641h574.42826.1891.4262h573.80826.8092.0463h572.9427.6772.9134h572.50628.1113.3475h572.19628.4213.6576h571.79328.8244.067h571.728.9174.1538h571.4929.1274.3639h571.28529.3324.56810h571.08829.5294.76511h570.

7、89129.7264.96212h570.69429.9235.15913h570.49930.1185.35414h570.30930.3085.54415h570.27530.3425.57916h569.961 30.656 5.892 17h568.748 31.869 7.105 18h567.846 32.771 8.007 19h566.478 34.139 9.375 20h564.798 35.819 11.055 22h564.923 35.694 10.930 24h563.959 36.658 11.894 26h561.937 38.680 13.916 28h561

8、.657 38.960 14.196 40h561.595 39.022 14.258 46h561.004 39.613 14.849 52h559.884 40.733 15.969 64h559.293 41.324 16.560 70h557.458 43.159 18.395 76h557.303 43.314 18.550 88h557.707 42.910 18.146 96h555.250 45.367 20.603 102h555.343 45.274 20.510 114h555.592 45.025 20.261 120h553.508 47.109 22.345 126

9、h554.037 46.580 21.816 138h554.472 46.145 21.381 144h551.766 48.851 24.087 150h552.637 47.980 23.216 162h553.570 47.047 22.283 168h551.424 49.193 24.429 174h552.450 48.167 23.403 186h552.077 48.540 23.776 192h550.615 50.002 25.238 198h551.424 49.193 24.429 210h550.895 49.722 24.958 216h550.087 50.53

10、0 25.766 222h550.824 49.793 25.029 234h550.095 50.522 25.758 240h549.487 51.130 26.366 表 1.22 32国产高强精轧螺纹钢C6预应力损失（单位：KN）C6总损失时间效应损失二次张拉600603.875回油稳定560.04743.8281h559.12944.7460.9192h558.57745.2981.473h557.90445.9722.1444h557.50546.372.5425h557.19946.6762.8486h556.92346.9523.1247h556.7447.1353.3088h

11、556.55647.3193.4929h556.37547.53.67310h556.20247.6733.84611h556.0347.8454.01812h555.86348.0124.18513h555.70348.1724.34514h555.60348.2724.44515h555.57648.2994.47216h555.155 48.720 4.892 17h553.942 49.933 6.105 18h553.040 50.835 7.007 19h551.672 52.203 8.375 20h549.992 53.883 10.055 22h550.117 53.758

12、9.930 24h549.153 54.722 10.894 26h547.131 56.744 12.916 28h546.851 57.024 13.196 40h546.789 57.086 13.258 46h546.198 57.677 13.849 52h545.078 58.797 14.969 64h544.487 59.388 15.560 70h542.652 61.223 17.395 76h542.497 61.378 17.550 88h542.901 60.974 17.146 96h540.444 63.431 19.603 102h540.537 63.338

13、19.510 114h540.786 63.089 19.261 120h538.702 65.173 21.345 126h539.231 64.644 20.816 138h539.666 64.209 20.381 144h536.960 66.915 23.087 150h537.831 66.044 22.216 162h538.764 65.111 21.283 168h536.618 67.257 23.429 174h537.644 66.231 22.403 186h537.271 66.604 22.776 192h535.809 68.066 24.238 198h536

14、.618 67.257 23.429 210h536.089 67.786 23.958 216h535.281 68.594 24.766 222h536.018 67.857 24.029 234h535.289 68.586 24.758 240h534.681 69.194 25.366 表 1.23 32国产高强精轧螺纹钢C7预应力损失（单位：KN）C7总损失时间效应损失二次张拉600602.999 回油稳定569.744 33.255 1h567.843 35.156 1.901 2h567.322 35.677 2.422 3h566.955 36.044 2.789 4h566

15、.525 36.474 3.219 5h566.525 36.474 3.219 6h566.206 36.793 3.538 7h565.915 37.084 3.829 8h565.664 37.335 4.080 9h565.444 37.555 4.300 10h565.250 37.749 4.494 11h565.059 37.940 4.685 12h564.867 38.132 4.877 13h564.748 38.251 4.996 14h564.588 38.411 5.156 15h564.468 38.531 5.276 16h564.152 38.847 5.592

16、 17h562.939 40.060 6.805 18h562.037 40.962 7.707 19h560.669 42.330 9.075 20h558.989 44.010 10.755 22h559.114 43.885 10.630 24h558.150 44.849 11.594 26h556.128 46.871 13.616 28h555.848 47.151 13.896 40h555.786 47.213 13.958 46h555.195 47.804 14.549 52h554.075 48.924 15.669 64h553.484 49.515 16.260 70

17、h551.649 51.350 18.095 76h551.494 51.505 18.250 88h551.898 51.101 17.846 96h549.441 53.558 20.303 102h549.534 53.465 20.210 114h549.783 53.216 19.961 120h547.699 55.300 22.045 126h548.228 54.771 21.516 138h548.663 54.336 21.081 144h545.957 57.042 23.787 150h546.828 56.171 22.916 162h547.761 55.238 2

18、1.983 168h545.615 57.384 24.129 174h546.641 56.358 23.103 186h546.268 56.731 23.476 192h544.806 58.193 24.938 198h545.615 57.384 24.129 210h545.086 57.913 24.658 216h544.278 58.721 25.466 222h545.015 57.984 24.729 234h544.286 58.713 25.458 240h543.678 59.321 26.066 图 1.21 国产高强钢筋松弛引起的预应力损失将预应力筋总的预应力损

19、失分为瞬时损失和长期损失，下面将分别分析这两种预应力损失。 根据公路钢筋混凝土及预应力混凝土桥涵设计规范（JTG D62-2004）（以下简称规范）中表的规定，锚具变形和接缝压缩按照1mm计算，则这两项引起的钢筋预应力损失为38.5kN。而根据试验结果，三根32国产高强精轧螺纹钢的瞬时预应力损失分别为24 kN、43kN和33 kN，平均值为33 kN，在规范规定的范围内；而最大值43kN，比按规范得出的计算值略大。长期预应力损失主要由钢筋松弛引起。根据规范中的规定，采用超张拉的精轧螺纹钢筋，由于钢筋松弛引起的预应力损失极值按照0.035倍的张拉应力计算。根据规范中F.3的规定，钢筋松弛引起的

20、10d预应力损失值按照0.61倍的损失极值计算，则钢支架上的32国产高强精轧螺纹钢的10d的预应力损失的理论值为13kN。根据试验结果，三根32国产高强精轧螺纹钢的10d的平均预应力损失为26kN，这与规范规定的理论值相比大约超出了13kN。假设施工操作不规范，没有到达规范对于超张拉的要求，改为按照一次张拉计算，松弛引起的预应力损失极值为0.05倍的张拉应力，则32国产高强精轧螺纹钢的10d的预应力损失的理论值为18.3kN，与实测值相比仍小8kN左右。1.2 混凝土对锚固效果的影响试验本组试验将分别对一组5m长32国产高强精轧螺纹钢和一组9m长32国产高强精轧螺纹钢进行张拉，然后放张并连续观

21、测10d，试验的目的是通过对比混凝土支架和钢支架上钢筋的预应力损失，获得锚固区混凝土对高强钢筋锚固效果的影响。 图 1.21 混凝土支架与钢支架对比试验1.2.1 5m国产高强精轧螺纹钢对比试验该组实验一共选了4根5m长的32国产高强精轧螺纹钢，编号分别是C7,C8,C9,C10，其中C7在钢支架上张拉，其余3根在混凝土支架上张拉。表 1.21 钢支架预应力长期损失（钢筋C7长5m）C7（钢支架）温度总损失时间效应损失二次张拉600605.435 14.0 回油稳定577.628 14.0 27.806 1h576.384 13.5 29.050 1.244 2h575.233 13.0 30

22、.201 2.395 3h574.922 13.0 30.512 2.706 4h574.269 13.0 31.165 3.359 5h573.927 13.0 31.507 3.701 6h573.678 13.0 31.756 3.950 7h573.274 13.0 32.161 4.354 8h572.994 12.5 32.441 4.634 9h572.745 12.5 32.689 4.883 10h572.621 12.5 32.814 5.008 11h572.434 12.5 33.000 5.194 12h572.434 12.5 33.000 5.194 13h572

23、.310 12.5 33.125 5.319 14h572.154 13.0 33.280 5.474 15h572.061 13.0 33.374 5.567 16h570.537 16.0 34.898 7.092 17h569.324 13.5 36.111 8.305 18h568.422 13.0 37.013 9.207 19h567.053 20.0 38.381 10.575 20h565.374 16.5 40.061 12.255 22h565.498 15.5 39.936 12.130 24h564.534 19.0 40.901 13.094 26h562.512 1

24、8.5 42.922 15.116 28h562.232 16.5 43.202 15.396 40h562.170 22.0 43.264 15.458 46h561.579 20.0 43.855 16.049 52h560.459 18.0 44.975 17.169 64h559.868 22.0 45.566 17.760 70h558.033 21.0 47.401 19.595 76h557.878 19.0 47.557 19.750 88h558.282 24.0 47.152 19.346 96h555.825 22.0 49.609 21.803 102h555.918

25、20.0 49.516 21.710 114h556.167 24.0 49.267 21.461 120h554.083 22.5 51.351 23.545 126h554.612 21.0 50.822 23.016 138h555.048 24.0 50.387 22.581 144h552.342 24.0 53.093 25.287 150h553.212 19.0 52.222 24.416 162h554.146 22.0 51.289 23.483 168h551.999 21.0 53.435 25.629 174h553.026 19.0 52.409 24.603 18

26、6h552.653 24.0 52.782 24.976 192h551.191 23.0 54.244 26.438 198h551.999 20.0 53.435 25.629 210h551.471 26.0 53.964 26.158 216h550.662 24.0 54.773 26.966 222h551.399 19.0 54.035 26.229 234h550.671 24.0 54.764 26.958 240h550.062 23.0 55.373 27.566 表 1.22 混凝土支架预应力长期损失（钢筋C8长5m）C8（混凝土支架）温度总损失时间效应损失二次张拉60

27、0609.808 13.5 回油稳定593.539 13.5 16.270 1h591.745 13.0 18.063 1.794 2h590.958 13.0 18.850 2.580 3h590.234 13.0 19.574 3.304 4h589.637 13.0 20.172 3.902 5h588.850 13.0 20.959 4.689 6h588.472 13.5 21.336 5.067 7h588.126 13.5 21.682 5.413 8h587.623 13.0 22.186 5.916 9h587.276 13.0 22.532 6.262 10h586.804

28、 13.0 23.004 6.734 11h586.521 13.0 23.287 7.018 12h586.143 13.0 23.665 7.395 13h585.892 13.0 23.917 7.647 14h585.514 12.5 24.294 8.025 15h585.420 12.5 24.389 8.119 16h585.199 12.5 24.609 8.339 17h585.042 12.5 24.766 8.497 18h584.916 12.5 24.892 8.623 19h584.979 12.5 24.829 8.560 20h584.948 13.0 24.8

29、61 8.591 22h585.073 13.0 24.735 8.465 24h584.224 16.0 25.585 9.315 26h581.580 13.5 28.228 11.958 28h579.629 13.0 30.179 13.909 40h580.605 20.0 29.204 12.934 46h577.804 16.5 32.004 15.735 52h576.042 15.5 33.767 17.497 64h577.301 19.0 32.508 16.238 70h574.217 18.5 35.592 19.322 76h572.454 16.5 37.354

30、21.084 88h573.996 22.0 35.812 19.542 96h571.196 20.0 38.613 22.343 102h569.056 18.0 40.753 24.483 114h570.503 22.0 39.305 23.036 120h567.797 21.0 42.012 25.742 126h565.783 19.0 44.026 27.756 138h567.797 24.0 42.012 25.742 144h564.587 22.0 45.221 28.952 150h562.856 20.0 46.952 30.683 162h564.461 24.0

31、 45.347 29.078 168h561.786 22.5 48.022 31.753 174h560.055 21.0 49.753 33.483 186h562.227 24.0 47.582 31.312 192h559.206 24.0 50.603 34.333 198h558.545 19.0 51.263 34.994 210h560.307 22.0 49.501 33.232 216h557.538 21.0 52.271 36.001 222h556.594 19.0 53.215 36.945 234h559.930 24.0 49.879 33.609 240h55

32、6.908 23.0 52.900 36.630 表 1.23 混凝土支架预应力长期损失（钢筋C9长5m）C9（混凝土支架）温度总损失时间效应损失二次张拉600609.667 14.0 回油稳定584.315 13.0 25.353 1h580.193 13.0 29.475 4.122 2h578.209 13.0 31.458 6.106 3h576.877 13.0 32.791 7.438 4h575.296 13.0 34.372 9.019 5h574.645 13.5 35.022 9.670 6h574.025 13.5 35.642 10.290 7h573.219 13.0

33、 36.448 11.096 8h572.630 13.0 37.037 11.684 9h572.104 13.0 37.564 12.211 10h571.670 13.0 37.998 12.645 11h571.174 13.0 38.494 13.141 12h570.802 13.0 38.866 13.513 13h570.461 12.5 39.207 13.854 14h570.151 12.5 39.516 14.164 15h569.872 12.5 39.795 14.443 16h569.624 12.5 40.043 14.691 17h569.500 12.5 4

34、0.167 14.815 18h569.438 12.5 40.229 14.877 19h569.283 13.0 40.384 15.032 20h569.128 13.0 40.539 15.187 22h567.765 16.0 41.903 16.550 24h565.037 13.5 44.630 19.278 26h563.054 13.0 46.614 21.261 28h563.333 20.0 46.335 20.982 40h560.543 16.5 49.124 23.772 46h559.055 15.5 50.612 25.260 52h559.737 19.0 4

35、9.930 24.578 64h556.886 18.5 52.782 27.429 70h555.460 16.5 54.207 28.855 76h556.576 22.0 53.092 27.739 88h554.189 20.0 55.478 30.125 96h552.423 18.0 57.245 31.892 102h553.167 22.0 56.501 31.148 114h550.749 21.0 58.918 33.566 120h549.200 19.0 60.468 35.115 126h550.966 24.0 58.701 33.349 138h547.371 2

36、2.0 62.297 36.944 144h546.472 20.0 63.195 37.843 150h547.960 24.0 61.708 36.355 162h544.799 22.5 64.869 39.516 168h543.466 21.0 66.202 40.849 174h545.418 24.0 64.249 38.897 186h542.536 24.0 67.131 41.779 192h542.102 19.0 67.565 42.213 198h543.869 22.0 65.799 40.446 210h540.924 21.0 68.743 43.391 216

37、h540.397 19.0 69.270 43.918 222h543.745 24.0 65.923 40.570 234h540.119 23.0 69.549 44.196 240h539.127 20.0 70.541 45.188 表 1.24 混凝土支架预应力长期损失（钢筋C10长5m）C10（混凝土支架）温度总损失时间效应损失二次张拉600610.721 14.0 回油稳定575.730 14.0 34.991 1h572.135 13.0 38.587 3.595 2h570.616 13.0 40.105 5.114 3h569.066 13.0 41.655 6.664 4

38、h568.477 13.5 42.244 7.252 5h567.982 13.5 42.740 7.748 6h567.207 13.0 43.515 8.523 7h566.742 13.0 43.979 8.988 8h566.277 13.0 44.444 9.453 9h565.843 13.0 44.878 9.887 10h565.409 13.0 45.312 10.321 11h565.161 13.0 45.560 10.569 12h564.851 12.5 45.870 10.879 13h564.634 12.5 46.087 11.096 14h564.417 12

39、.5 46.304 11.313 15h564.262 12.5 46.459 11.468 16h564.169 12.5 46.552 11.561 17h564.293 12.5 46.428 11.437 18h564.293 13.0 46.428 11.437 19h564.386 13.0 46.335 11.344 20h563.271 16.0 47.451 12.459 22h560.264 13.5 50.457 15.466 24h558.622 13.0 52.100 17.108 26h559.861 20.0 50.860 15.869 28h556.514 16

40、.5 54.207 19.216 40h555.274 15.5 55.447 20.456 46h556.607 19.0 54.114 19.123 52h553.260 18.5 57.462 22.470 64h552.051 16.5 58.670 23.679 70h553.756 22.0 56.966 21.974 76h550.780 20.0 59.941 24.950 88h549.169 18.0 61.553 26.561 96h550.532 22.0 60.189 25.198 102h547.681 21.0 63.040 28.049 114h546.286

41、19.0 64.435 29.444 120h548.642 24.0 62.080 27.088 126h544.582 22.0 66.140 31.148 138h543.590 20.0 67.131 32.140 144h545.697 24.0 65.024 30.033 150h542.040 22.5 68.681 33.690 162h540.924 21.0 69.797 34.805 168h543.311 24.0 67.410 32.419 174h539.871 24.0 70.851 35.859 186h539.809 19.0 70.913 35.921 19

42、2h541.792 22.0 68.929 33.938 198h538.383 21.0 72.338 37.347 210h537.794 19.0 72.927 37.936 216h541.947 24.0 68.774 33.783 222h537.887 23.0 72.834 37.843 234h536.616 20.0 74.105 39.114 240h536.523 24.0 74.198 39.207 图 1.22 混凝土支架上三根钢筋(5m)的长期预应力损失曲线图 1.23 混凝土支架与钢支架上钢筋(5m)的长期预应力损失对比通过前面的研究可知，总的预应力损失分为瞬时

43、损失和长期损失。下面将分别分析这两种预应力损失，并对比钢支架和混凝土支架上钢筋长期预应力损失的区别。根据规范，锚具变形和接缝压缩按照1mm计算，引起的钢筋预应力损失为38.5kN。混凝土支架的管道摩阻损失为3.5kN。所以混凝土支架的瞬时预应力损失的理论值应为42kN，钢支架的瞬时预应力损失的理论值为38.5kN。根据试验结果，混凝土支架上的32国产高强精轧螺纹钢的瞬时预应力损失分别为16 kN、26 kN和36 kN，其中最大值36 kN，在规范规定的42kN以内；钢支架上的32国产高强精轧螺纹钢的瞬时预应力损失为28kN，也在规范规定的38.5kN以内。长期预应力损失主要由钢筋松弛和混凝土

44、的收缩徐变以及温度变化引起。根据规范，松弛引起的预应力损失极值按照0.05倍的张拉应力计算，松弛引起的10d预应力损失值按照0.61倍的损失极值计算，则钢支架上的32国产高强精轧螺纹钢的10d的预应力损失的理论值为18.3kN。而对于混凝土支架来说，还要考虑收缩徐变和温度引起的预应力损失：10d内收缩徐变引起的预应力损失为6kN，温度升高了约10度，引起的预应力损失为4.5kN，则混凝土支架上的32国产高强精轧螺纹钢的10d的预应力损失的理论值为28.8kN。根据试验结果，混凝土支架上的32国产高强精轧螺纹钢的10d的平均预应力损失为39kN；钢支架上的32国产高强精轧螺纹钢的10d的预应力损

45、失为27.5kN。两者的差值为11.5 kN,这与理论计算得出的10.5 kN（收缩徐变与温度变化之和）是一致的，这说明扣去收缩徐变与温度变化的影响，混凝土支架和钢支架上的32国产高强精轧螺纹钢的10d的预应力损失是一致的，均为28kN左右。但是，预应力长期损失的实测值与规范规定的理论值相比大约超出了10kN。实测值（28kN）与规范规定的40d松弛引起的预应力损失终值（30kN）的比为91%，大约相当于34d时由于松弛引起的预应力损失值。1.2.2 9m国产高强精轧螺纹钢对比试验该组实验一共选了4根9m长的32国产高强精轧螺纹钢，编号分别是C3,C11,C12,C13，其中C3在钢支架上张拉

46、，其余3根在混凝土支架上张拉。表 1.25 钢支架预应力长期损失（钢筋C3长9m）C3温度总损失时间效应损失二次张拉600605.329 13.5 回油稳定592.517 13.5 12.813 1h590.241 13.0 15.088 2.276 2h588.694 13.0 16.636 3.823 3h587.270 13.0 18.059 5.247 4h586.466 13.0 18.864 6.051 5h585.754 13.0 19.576 6.763 6h585.042 13.0 20.287 7.475 7h584.392 12.5 20.937 8.125 8h583.

47、866 12.5 21.463 8.651 9h583.525 12.5 21.804 8.991 10h583.185 12.5 22.144 9.332 11h582.845 12.5 22.485 9.672 12h582.845 12.5 22.485 9.672 13h582.226 13.0 23.104 10.291 14h581.792 13.0 23.537 10.724 15h580.528 16.0 24.801 11.989 16h579.507 13.5 25.822 13.010 17h578.919 13.0 26.410 13.598 18h576.536 20.0 28.793 15.981 19h575.422 16.5 29.907 17