Application Study Of Ultrasonic Nondestructive Testing Technique In Bridge Health Condition Assessment

Pile foundation belongs to underground construction structure, there are some difficulties on detection to it, and some special test equipments are needed. Integrity testing to pile body is usually essential. Generally speaking, pile foundation should satisfy two requests. First, each pile constituted pile foundation must have enough strength, namely quality of pile foundation must achieve the design standard; Second, the soil layer (rock layer) around the pile foundation and at the tip of pile must have the enough loading capacity. Therefore, the pile foundation testing work is carrying on the test to pile foundation's quality and loading capacity. In the past, the static test method is usually adopted to examine the quality of pile foundation and determine the loading capacity of single pile, but this kind of method's work load is big, usually only can extract a few several type pile, cannot satisfy the request of engineering technology and engineering security by far. Dynamical testing is simple and quick, its preparation work and operation is simple and convenient, and in addition, computer technology's swift development strengthened the function of dynamical testing. There are a lot of dynamical testing methods, like hydroelectric effect method, stable mechanical impedance method, reflected wave method and so on. In these methods, because the ultrasonic wave testing method is facile, flexible, and has advantages like high test result precision, big effective detection range, low cost compared to core-drilling test, enables this technology obtain a widespread application in pile foundation engineering of water conservation, mining industry, transportation, municipal administration and so on.The reinforced concrete commonly used as building material in concrete bridge structure is a kind of composite material which takes cement mortar as main body and take the aggregate as reinforced material. During the formation process of concretes material, internal micro crevice and micro crack are always exist, it presents one kind of sparse hole and micro crack dissemination structure condition.. The bridge structure is in the presence of environmental factor and external load, particularly in the presence of dynamic load for a long time, so the concretes interior original flaw expands, and forms a certain size macroscopic crack. This will cause the drop of strength and rigidity of concrete, even destroy it and reduces the service life of structure, harms safe operation of building. For this reason, it is necessary to make judgment to the quality condition of concrete; the key question is to seek for a effective examination method to fast and accurately discover the hidden danger and disease in the concretes, namely carry on fast and effective examine to the concrete's damage, forecasts its safe condition effectively, provides reliable method for bridge structure's safety evaluation, this has a great importance to the safe operation of engineering. There are a lot of methods for concrete quality detection, among them the ultrasonic wave law is one important method.The quality of concrete relates the structure security, strengthens the quality detection and controls to concrete has been an important topic of the bridge engineering technology. The main qualitative index of concrete is always taking the standard test sample compressive strength as the basis. However, because the formation condition, the curing condition and the stressful condition of test sample are impossible to be completely consistent with the structure concrete, the test value of test sample cannot represent the real condition of structure. Therefore the research of direct examination of structure concrete strength in the structure, and does not harm the structure becomes an important issue what we have to face. The examination of bridge structure concrete strength by ultrasonic-rebound combined method is a current development trend. The ultrasonic-rebound combined method used in bridge structure concrete strength testing has been taken gradually by people as an important symbol to evaluate a nation's construction testing level. It is a real and accurate important tool to reflect the quality of structure concrete; it is a need to quality detection and identification of old building. It can feed back the concrete quality information in the process of structure (component) construction.In aspect of pile foundation integrity examination of bridge structure, crack depth survey of bridge member and strength determination of structure concrete, ultrasonic wave non-destructive inspection technology has been a current development trend, therefore launches application research of the ultrasonic wave non-destructive inspection technology in the evaluation of bridge health state is very essential.This paper has mainly done the following several aspects research work. (1) Has thoroughly analyzed the basic principle of ultrasonic wave transmission method used in pile foundation integrity detection, then set the request to this method's general specification, and carries on the exhaustive introduction to the examination method; Then deep researched the data processing method and flaw decision method of ultrasonic wave transmission method; Finally combining a engineering example of pile foundation integrity detection, introduced the application of ultrasonic wave transmission method in the pile foundation integrity detection.(2) The method which can be used in the bridge structure concretes component crack depth examination at present based on the ultrasonic wave non-destructive inspection technology mainly are:â‘ One-sided plane testing method,â‘¡Two-sided testing method,â‘¢initial wave phrase reverse method,â‘£hole-drilling testing method. Mainly elaborated the basic principle of these crack measuring techniques, the specification and the crack depth computation and decision method.(3) Introduced the crack depth surveying and computation method by one-sided plane testing method with emphasis. Based on the least squares method principle, used the linear regression method to carry on the linear regression to measured data not crossing the crack, and calculated the spreading velocity of sound wave in the non-crack concrete, and introduced the process of crack depth computation by the mathematical method. Finally combining a web plate's crack depth measuring engineering of a simple support reinforced concrete beam in Songyuan, confirmed the usability and validity of this method.(4)Conducted a deep research on the basic principle of the compressive strength determination of concretes component with rebound method, supersonic method and ultrasonic-rebound combined method, in this foundation, proposed the general requirement of the ultrasonic-rebound combined method, and elaborated the test procedure and estimation method of concretes compressive strength of the ultrasonic-rebound combined method. Based on above research and combining a real engineering, confirmed the validity and reliability of the method elaborated in this paper.