重载铁路隧道底部结构疲劳性能及累积损伤试验研究

Experimental Study on Fatigue Performance and Cumulative Damage of Bottom Structure of Heavy Haul Railway Tunnel

根据重载铁路隧道底部疲劳关键部位的力学特性,开展双侧限高静载低动载波动疲劳试验,得到重载铁路隧道底部结构试件的最大拉应变及电导的演化规律,通过分析试验数据研究结构的疲劳性能和累积损伤。结果表明:当最大应力水平不高于0.60时,试件最大拉应变呈2阶段发展,未产生疲劳破坏,其最大拉应变幅值、增速始终保持恒定;当最大应力水平超过0.70时,试件最大拉应变呈“倒S”型3阶段发展,产生疲劳破坏,试件的最大拉应变及其增量、幅值、增速在第Ⅰ和第Ⅲ阶段增长较快,在第Ⅱ阶段呈缓慢线性增长;试件的疲劳寿命随静载、动载的增大而缩短,采用多元线性函数对试验数据进行拟合,得到双参数疲劳寿命(S—N)计算公式;同时,基于试件最大拉应变及电导的时变特性,得到隧道底部结构的非线性累积损伤演化曲线及计算公式。

According to the mechanical characteristics of fatigue vulnerable positions at the bottom of heavy haul railway tunnel,a series of fatigue tests were conducted in the condition of high static load and low dynamic load with bilateral confinements to obtain the evolution laws for the maximum tensile strain and conductance of the bottom structure of heavy haul railway tunnel.Then the fatigue performance and cumulative damage of the structure were studied through analyzing test data.Results show that when the maximum stress level is not higher than 0.60,the maximum tensile strain of the specimen develops in 2 stages with no occurrence of fatigue failure,and the maximum tensile strain amplitude and growth rate always keep constant.When the maximum stress level exceeds 0.70,the maximum tensile strain of the specimen develops in 3 stages of“inverted S”type,resulting in fatigue failure.The maximum tensile strain and its increment,amplitude,growth rate increase quickly in stage-Ⅰand stage-Ⅲ,and slow linear in stage-Ⅱ.The fatigue life of specimens decreases with the increase of static load and dynamic load.The formula of two-parameter fatigue life(S—N)is obtained by fitting the test data with multivariate linear function.At the same time,based on the time-varying characteristics of the maximum tensile strain and the conductance of the specimen,the nonlinear cumulative damage evolution curve and calculation formula of the tunnel bottom structure is obtained.