拉力型锚索各锚筋受力不均匀现象试验研究

采用同步张拉、单拉及整体张拉法,在3个场地的基坑工程进行了65组土层拉力型锚索试验,结果表明,锚索整拉时:(1)锚筋数量较少或黏结长度较短时,锚筋实际抗拉力或浆筋极限黏结力偏低是受力不均匀的重要原因;(2)锚索在正常使用及承载能力极限状态下,均普遍存在着受力严重不均匀现象,明显降低了锚筋极限承载能力。锚筋受力变异系数0.15,或相对极差30%且偏离度20%,可作为判断严重不均匀程度的定量指标;(3)锚筋刚度系数具有很大的随机性及不确定性,大体上随着筋体自由长度的减短或受力的增加而增加;(4)锚筋随着受力增加,受力不均匀程度普遍增加,但严重程度下降;(5)锚筋数量越多,受力越均匀;(6)锚筋极限抗拉力可取标准值的0.8倍;(7)预张拉及提高预紧力不能改善锚筋受力不均匀程度,同步张拉是最佳改善方法。

Experimental study on uneven load phenomenon of tendons of tensile anchors

Under integral tensioning of anchors, the results of 65 tensile anchor tests in 3 foundation pit projects with different tensile methods such as synchronous tension, separate tension and integral tension show that: (1) The real tensile resistance or ultimate bonding resistance is low if the number of tendons is less or the bonding length between tendon and grouting is short, and they are the important reasons for uneven loads on tendons. (2) The serious uneven load phenomenon of tendons is general under the serviceability limit state and ultimate limit state, and the ultimate load capacity of the anchor is reduced obviously. The variable coefficient 0.15, relative range 30% and deviation degree 20% can be used as the quantitative indice for estimating the severity. (3) The stiffness coefficient of tendons has much randomness and uncertainty, and it decreases along with the free length of tendons and increases along with the loads on tendons in general. (4) The degree of uneven load increases but serious degree decreases along with the loads on tendons in general. (5) The more the number of anchors, the more the uniform loads. (6) The ultimate tensile resistance of tendons can get 0.8 times the characteristic value. (7) Pretensioning and high pretension loads can not improve the unevenness degree of the tendons, while the synchronous tension method can improve it.