【作者】 王致富；

【导师】 于志强；

【作者基本信息】 西南交通大学 ， 岩土工程， 2010， 硕士

【摘要】 基桩低应变反射波法测试中激振力特性,如脉冲宽度、入射波幅值等,对检测结果的可靠性有重要影响,本文利用有限元软件ANSYS/LS-DYNA对力脉冲宽度影响因素及其对测试效果的影响进行数值模拟。论文首先简单的阐述了低应变反射波法的基本理论及运用ANSYS/LS-DYNA的建模过程,其次定义了钟形力脉冲宽度,并运用数值模拟得出了钢、铝、尼龙和聚乙烯塑料四种材料手锤的脉冲宽度。重点探讨了接触面积、敲击速度、锤重以及垫片厚度对脉冲宽度的影响规律,得出了以下主要结论：(1)接触面积越大,激励的力脉冲宽度越小,入射波幅值也越小；(2)敲击速度对脉冲宽度基本没有影响,但入射波幅值随敲击速度的增大按线性规律增大：(3)脉冲宽度随激振锤重量的增大按幂函数的关系增大；(4)锤头材料越厚(垫片厚度越大),力脉冲宽度越大,并且力脉冲宽度随垫片厚度的增大按线性规律增大。最后应用不同脉冲宽度的激振锤,来验证对测试效果的影响。研究发现钢锤敲击的窄脉冲波对识别桩头附近的缺陷比较有利,而长大桩使用钢锤激振会引起波速下降、波形振荡,但是聚乙烯塑料锤敲击的宽脉冲波能克服上述问题。因此应根据桩的几何尺寸及测试目的,合理调节锤头材质、接触面积、敲击速度、锤重以及垫片厚度来激发合适脉冲宽度的入射波以满足测试的需要。在能够获得桩底反射的前提下,脉冲宽度和敲击速度尽量小。更多还原

【Abstract】 The impact force character of reflected wave test for low strain, such as pulse width, the incident wave amplitude,have important influence to the reliablity of the test results. Using the finite element program ANSYS/LS-DYNA, this thesis simulated the influence factors of the force pulse width and its effect to the test results.Firstly,the basic theory of reflected wave test for low strain and the modeling process by applied ANSYS/LS-DYNA are simple described, followed by the definition of a bell-shaped force pulse width. The pulse width of four materials, such as steel, aluminum, nylon and polyethylene plastic are calculated by the numerical simulation. The most important investigation is the Influence of pulse width of contact area, impact velocity, weight of hammer and shim thickness, reached the following conclusions:(1) the greater the contact area, the smaller the pulse width of impact force, the incident wave amplitude is also smaller;(2) impact velocity had no effect on the pulse width, but the incident wave amplitude increases with the impact velocity increased by a linear law;(3) Pulse width increases with the impact vibration hammer weight increases by a power function relationship(4) Thicker shim, the greater the pulse width,and impact force pulse width with shim thickness increased by a linear law.Lastly apply a impact hammer with different pulse width to verify the effect of the test. It found that narrow pulse wave which produced by the steel hammer is propitious to identify defects in the vicinity of pile top, whereas steel hammer impact large diameter pile may cause wave speed decreased and wave graph oscillated.At the same time,wide pulse wave which produced by the polyethylene plastic hammer can overcome these problem.So the appropriate pulse width of the incident wave which are adjusted by hammer material,contact area,impact velocity, weight of hammer and shim thickness should be determined according to the geometry size of pile and testing purposes to meet the test requirements.The pulse width and impact velocity as small as possible on the premise that can obtain reflection from the pile toe.更多还原