盾构隧道原型管片接头抗弯性能试验

Experiment study on flexural performance of prototype segment joint of shield tunnel

盾构隧道原型管片弧形接头试验在研究管片接头抗弯性能、尤其是破坏的发展过程时更接近实际,但由于加载力系复杂,试验难度较大。文章依托某输气盾构隧道工程,开展了原型管片弧形接头抗弯试验,首先进行弧形管片接头受力分析,考虑了弧形接头接缝变形对其内力的影响,确定了弧形管片接头抗弯试验的等轴力加载方法并推导了荷载计算公式。分析了接缝面应变、螺栓应力、张开量、张开高度以及抗弯刚度随接头内力的变化规律,讨论了弧形管片接头破坏的发生发展与接头变形的关系。结果表明,弧形管片接头接缝面轴力和弯矩的相对大小、螺栓受力状态对接头抗弯性能影响较大,轴力抑制接缝张开,对接头的抗弯能力有保持作用;弯矩使得接头发生张开变形,接头抗弯刚度随其增大而减小。压弯条件下,随着弯矩的增大,接缝变形呈近似线性发展;当接头张开至螺栓附近时,螺栓受力明显增大,此时接缝变形受到一定的限制;随着弯矩进一步增长,弯矩对于接缝张开变形的控制强于轴力和螺栓对于接缝面变形的控制,接缝变形基本由弯矩控制。故随着弯矩的增长,接缝变形呈非线性变化。接头破坏过程与接缝变形的关系可分为稳定变化阶段和失稳阶段,两者的破坏特征区别明显。前者表现为出现首条裂缝和螺栓屈服,后者表现为裂缝的持续发展以及接缝面混凝土压溃。对于弧形接头,两阶段分界点为弯矩与破坏弯矩比值达到0.75~0.85,或管片直径变化率为0.35%~0.45%;对于直接头,分界点一般出现在破坏弯矩比值达到0.35~0.45,故弧形接头和直接头的抗弯性能存在明显差异。轴压比为0.0902时,弧形接头压弯破坏属于延性破坏,破坏前裂缝的发展可以分为数量增长和宽度长度扩展两个阶段。当观察到大量宽度大于0.5mm的裂缝时,弯矩与破坏弯矩比值已达到0.95~0.97。研究结果可为盾构隧道管片接头的设计和类似试验提供重要参考。

In the study of segment joint flexural performance,especially the development process of destruction,the arc joint load test of shield tunnel prototype segment has the advantages that its results are closer to reality,but due to the complex loading force and loading system,it is difficult to carry out such experiment. In this paper,based on a shield tunnel project,the prototype segment joint test is carried out. The force analysis model of joint is established firstly,the influence of the joint deformation is considered in the calculation,the process and loading mode of equal axial force method and the force calculation equations are obtained. The change laws of joint surface strain,bolt stress,joint openings,joint open height and bending stiffness with internal force of joint are analyzed,and the relationship between failure process of segment joint and joint deformation is discussed. The results show that the relative magnitude of the axial force and bending moment,the stress state of the bolt have great influence on the bending resistance of joint. The axial force of joint inhibits joint from opening and has a bearing effect on the bending performance of the joint,bending moment causes opening and deformation of the joint and the bending performance of the joint decreases with the increaseof the joint bending moment. Under the condition of compression and bending,the joint deformation developments approximately linear with the increase of bending moment; when the joint opens to the height of the bolt,the bolt force increases obviously,at the same time,the joint deformation is limited; with the increase of bending moment,the control of bending moment for joint deformation is stronger than that of axial force and bolt,and the joint deformation is controlled by bending moment basically. Therefore,with the increase of bending moment,the joint deformation is nonlinear. The joint failure process can be divided into two stages: stable stage and unstable stage,the damage characteristics of which are distinct. The former is characterized by the occurrence of the first crack and bolt yielding while the latter is mainly characterized by the continuous development of cracks and the collapse of concrete. For arc joint,the demarcation point of the two stage is the point that ratio of bending moment to the damage moment reaches0. 75 ~ 0. 85,or the segment diameter change rate reaches 0. 35% ~ 0. 45%; but as for straight joint,the dividing point usually appears when the ratio of bending moment to damage moment reaches 0. 35 ~ 0. 45,so the bending performance of the arc joint and the straight joint are obviously different. When the axial compression ratio is 0. 0902,the bending failure of the arc joint belongs to ductile failure,and the development of crack before damage can be divided into two stages: quantity increase stage,width and length extension stage,when many cracks whose width is greater than 0. 5 mm are observed,ratio of bending moment to the damage moment has already reached 0. 95 ~ 0. 97. The research results can provide important reference for the design of segment joint and similar test.