【作者】 陈玮；

【导师】 张小飞； 张伟；

【作者基本信息】 广西大学 ， 工程硕士（水利工程）（专业学位）， 2019， 硕士

【摘要】 水电站埋藏式压力钢管(简称埋管)最主要的失效形式是在外压作用下失稳,目前研究认为埋管在外包混凝土中受外压失稳是受约束稳定失效问题,其临界外压公式建立在稳定失效模式和强度失效准则上。然而,埋管仍有可能发生强度失效或者纯稳定失效。鉴于此,本文系统剖析了计算埋管临界外压的强度失效理论、受约束稳定失效理论和纯稳定失效理论及各自的代表方法——锅炉公式、Jacobsen法和Boot法,并利用埋管临界外压的主要力学影响因素分析了三种临界外压计算公式的关联性,利用埋管设计参数径厚比r/t、缝隙率△/r和屈服强度σs量化了锅炉公式、Jacobsen法和Boot法的适用范围。为方便应用,给出了三种公式适用范围的快速查询图,汇总了三种公式计算临界外压的结果查询图。主要结论如下:(1)锅炉公式建立在强度失效模式和强度失效准则上;Jacobsen法建立在稳定失效模式与强度失效准则上;Boot法建立在稳定失效模式与稳定失效准则上。锅炉公式和Jacobsen法的失效准则均为最大应力微元达到屈服强度受压屈曲,故为强度失效准则;Boot法使用失稳区应变能最大的驻值条件作为失效准则,不涉及管材屈服强度σs,是稳定失效准则。Jacobsen法和Boot法的失效模式类似,认为管壁横截面上只存在一个失稳区,内含屈曲波,是典型的稳定失效模式。锅炉公式的失效模式没有考虑失稳区和屈曲波,是强度失效模式。(2)径厚比r/t是影响埋管在外压作用下发生何种失效模式的关键因素。径厚比r/t减小时,屈曲波振幅减小,最大应力微元靠近外包混凝土,管壁约束增强,埋管从受约束稳定失效向强度失效过渡;径厚比r/t增大时,屈曲波振幅增大,最大应力微元远离外包混凝土,管壁约束减弱,埋管从受约束稳定失效向纯稳定失效过渡。(3)受缝隙率△/r和屈服强度σs影响,径厚比r/t大致在30以下时,埋管发生强度失效,推荐使用锅炉公式;径厚比r/t在30～120之间,埋管发生受约束稳定失效,推荐使用Jacobsen法;径厚比r/t大致在120以上时,埋管发生纯稳定失效,推荐使用Boot法。为提供更详细的临界外压计算公式适用范围并且方便应用,给出了以上3种公式适用范围的快速查询图。更多还原

【Abstract】 The main failure type of buried pressure tubes(buried tubes for short)in hydropower station is buckling under external pressure.At present,it is considered that buckling of buried tubes encased in concrete under external pressure is a constrained stability failure problem.However,strength failure or pure stability failure may still occur.In view of this,this article analyzed the failure theories of calculating the critical external pressure of buried tubes,i.e.the strength failure theory,the constrained stability failure theory and the pure stability failure theory.Their representative methods,i.e.the boiler formula,the Jacobsen method and the Boot method were formulated too.The relevance among three formulas was illuminated by using the main mechanical factors of the critical external pressure of buried tubes.The application scopes of three formulas were qutified by the design parameters of buried tubes,i.e.the radius-thickness ratio(r/t),the gap rate(e/r)and the yield strength(σs).For the convenience of application,the quick query graphs of the application scopes of three formulas were given and the result query graphs of the critical external pressure by three formulas were summarized.The main conclusions are as follows:(1)The boiler formula is based on the strength failure mode and strength failure criterion.The Jacobsen method is based on stability failure mode and strength failure criterion.The Boot method is based on stability failure mode and stability failure criterion.The failure criterion of the Jacobsen method and boiler formula is that the maximum stress of elements reaches the yield strength,so it is a strength failure criterion.The Boot method bases on the stationary value condition of the maximum strain energy in the buckling area.The Jacobsen method and Boot method have similar failure mode,and it is considered that there is only one buckling area with buckling waves on the cross section of tube.This failure mode is a typical stability failure mode.The failure mode of the boiler formula does not consider the buckling area and waves.(2)The radius-thickness ratio(r/t)is a key factor influencing the failure type of buried tubes under external pressure.When the radius-thickness ratio(r/t)decreases,the amplitude of buckling waves decreases.At the same time,the element with the maximum stress is closer to the concrete and the constraint on the tube wall is strengthened.The failure type of buried tubes thus trasitions from the constrained stability failure to the strength failure.When the radius-thickness ratio(r/t)increases,the amplitude of buckling waves increases.At the same time,the element with the maximum stress is far away from the concrete and the constraint on the tube wall is weakened.The failure type of buried tubes thus trasitions from the constrained stability failure to the pure stability failure.(3)With the influence of the gap rate(△/r)and the yield strength(σs),the strength failure of buried tubes will happen when the radius-thickness ratio(r/t)is approximately below 30 and the boiler formula is recommended.When the radius-thickness ratio(r/t)is between 30 and 120,the constrained stability failure will happen and the Jacobsen method is recommended.When the radius-thickness ratio(r/t)is approximately above 120,the pure stability failure of buried tubes will occur and the Boot method is recommended.In order to provide a more detailed formula for calculating the critical external pressure and convenient application,quick query diagrams are given.更多还原