【作者】 晏露超；

【导师】 李建中； 黎超群；

【作者基本信息】 中南大学 ， 地质工程， 2010， 硕士

【摘要】 混凝土和钢筋混凝土结构物,有时因施工管理不善或受使用环境及自然灾害的影响,其表面和内部容易出现裂缝,不少结构的破坏都是从裂缝开始的,如何采用较有效的方法查明混凝土裂缝的性质、范围及尺寸,以便进行技术处理,乃是工程建设中的一个重要课题。本文综合论述了混凝土结构裂缝的超声波无损检测发展概况、现状及基本原理,指出了超声波检测中单面平测法的优点和适用范围,在已有的理论基础上对超声波平测法进行了深入研究：(1)强调了斜裂缝的概念。现有的超声波平测法只考虑混凝土裂缝与检测平面相垂直,即垂直裂缝模型,并以此来计算裂缝深度。但实际工程中,大部分混凝土结构的裂缝是与检测面相斜交的,即为斜裂缝,垂直裂缝只是裂缝倾角为90°的一种特殊情况。仅以垂直裂缝模型来检测计算实际裂缝深度是不完善的,这样会给混凝土结构裂缝的评价造成较大的偏差。因此,有必要研究斜裂缝的检测方法和计算公式,以提高单面平测法的精确性。(2)研究了平测法中的声速问题。通过对实验混凝土模型进行声速检测实验,说明在超声波平测法中,不能用不跨缝测得的声速值进行裂缝参数的计算,而应用对测法测得的声速值。从性质上说,不跨缝测得的首波为横波,跨缝和对测时测得的首波为纵波。因此不跨缝测得的声速值根本不能代替跨缝检测时的声速值。(3)设计了一种检测斜裂缝的新方法—三角余弦方程法,该方法操作便捷,计算简单。并先后使用三角余弦方程法和传统的双椭圆定位法对同一混凝土斜裂缝模型进行了检测实验,结果表明三角余弦方程法所测得的裂缝倾角和延伸长度误差都很小,且明显小于双椭圆定位法的误差。该斜裂缝平测新方法准确度很高,能够较精确的检测单条斜裂缝的倾角和延伸长度,相比传统的斜裂缝检测方法有一定优势。(4)阐述了平测法中尚存的问题和未来的可研究方向。如结构中钢筋对混凝土声速的影响,多条裂缝存在时平测法复合波形的分解问题,利用表面波检测深度大于500mm长裂缝的可能性。更多还原

【Abstract】 Sometimes, because of the omission in working management, environment and natural disasters, there are cracks come out of the concrete and ferroconcrete. The destruction of many structures begin with the cracks, so how to detect the character, extent and size of the cracks? This is an important issue in constructional engineering.This paper discourses on the development, existing conditions and basic theory of the ultrasonic nondestructive testing, and points out the advantage and application of single plane detecting. On the existing theory basis, this paper does some profound research in the ultrasonic nondestructive testing:(1)Brought up the concept of inclined crack. The existing ultrasonic single plane detecting only consider the vertical cracks, but in actual construction, the inclined cracks are usual, and vertical cracks are just the special cases. Therefore, it is necessary to research the detecting method and computing formula for the inclined crack, so that the ultrasonic single plane detecting can be more accurate.(2)Researched the velocity of ultrasonic in single plane detecting. By the ultrasonic velocity experiment on a concrete model, found out that it is accurate to use the velocity tested through the concrete rather than on the surface of the concrete in calculation. In essence, the first wave detected when testing on the surface is transverse wave, but when testing through the concrete, the first wave is longitudinal wave.(3)Designed a new detecting method for the inclined crack—trigonal cosine equation method. Using this new method and a traditional method to detect the same concrete model with inclined crack respectively, the result validated the rationality of this new method,and its error rate is much lower than the traditional method. So this new method has high accuracy, it can be used to detect the obliquity and length of single inclined crack.(4)Discussed the problems in single plane detecting and looked forward to the future research direction. Such as the effect of reinforcing steel when testing the ferroconcrete, the problem of testing more inclined cracks, and the possibility of using rayleigh wave to detect long cracks(≥500mm).更多还原