Advanced Materials Research Vols. 639-640

Abstract: Using the static and dynamic test data simultaneously to update the finite element model can increase the available information for updating. It can overcome the disadvantages of updating based on static or dynamic test data only. In this paper, the response surface method is adopted to update the finite element model of the structure based on the static and dynamic test. Using the reasonable experiment design and regression techniques, a response surface model is formulated to approximate the relationships between the parameters and response values instead of the initial finite element model for further updating. First, a numerical example of a reinforced concrete simply supported beam is used to demonstrate the feasibility of this approach. Then, this approach is applied to update the finite element model of a prestressed reinforced concrete rigid frame-continuous girders bridge based on in-situ static and dynamic test data. Results show that this approach works well and achieve reasonable physical explanations for the updated parameters. The results from the updated model are in good agreement with the results from the in-situ measurement. The updated finite element model can accurately represent mechanical properties of the bridge and it can serve as a benchmark model for further damage detection and condition assessment of the bridge.

Abstract: Yiyang rubber machinery group cargo terminal is a vertical frame wharf established in the early 1970’s. A certain degree of deterioration and damage has occurred to the structure because of the long service time and long-term exposure of some parts of the structure. Taken the subsequent use of safety into account, the structure was completely detected. The detection content included array of structure, apparent damage and rebar corrosion situation, carbonation depth and compressive strength of concrete, distributions of reinforcement and cover thickness, verticality of the overall structure and so on. The bearing capacity of the main structure was checked according to the corresponding detection results and standards. Then the safety of the wharf structure was comprehensively assessed and some suggestion about repairing and reinforcement was also made which could provide the reference for the follow-up repair and reinforcement or other similar engineering.

Abstract: In this paper, a new solution method is proposed for determining the natural frequency of a given mode for a finite-length circular cylindrical thin shell with a circumferential part-through crack. The governing equation of the cracked cylindrical shell is derived by integrating the line-spring model with the classical thin shell theory. The proposed method calculates the natural frequency from an initial trial to satisfy both the governing equations and appropriate boundary conditions through an optimization process. The initial trial is proposed to satisfy the governing equations by using the beam modal function to determine the modal wavenumbers and mode shapes of cylindrical shells in the axial direction, assuming the flexural mode shapes of cylindrical shells in the axial direction to be of the same form as that of a flexural vibration beam with the same boundary conditions. Four representative sets of boundary conditions are considered: simply supported (SS-SS), clamped-clamped (C-C), clamped-simply supported (C-SS), and clamped-free (C-F). Compared with the finite element (FE) method, the proposed solution method is verified to provide an accurate and efficient way to calculate the dynamic characteristics of both intact and cracked cylindrical shells.

Abstract: The damage detection method based on wavelet multi-scale analysis is presented in the paper. The damage location can be identified by analyzing the multi-scale wavelet transform coefficients of curvatures of mode shapes. The extreme value of wavelet transform coefficients indicates the damage location. But it is difficult to detect the location of defect if the defect is near to the equilibrium position of vibration. In order to solve this problem, we put forward a method which is to add the wavelet transform coefficients of multi modals together. The method can effectively overcome the above problem. Three damage situations of simply supported beam bridge are discussed in the paper. The results show that the peaks of wavelet transform coefficients indicate the damage location of structural. It is possible to pinpoint the damage location based on wavelet multi-scale analysis on curvatures of mode shapes.

Abstract: The tendon ducts in post-tensioned bridge girders must be grouted fully so as to prevent water and oil stain from entering the ducts, which will decrease the durability and load-carrying capacity of post-tensioned bridges badly. This paper describes the motivations for and recent history of Impact-Echo (IE) scanning applications to internal grout condition evaluation of tendon ducts in post-tensioned girders. The tendon ducts’ internal injection quality of a railway bridge in Yichang city was evaluated using IE technology. During the in-situ testing, the IE signals were collected firstly, then the transformation from the time to the frequency domain was carried out using the principles of the fast Fourier transform, data interpretation was much simpler and quicker in the frequency domain. The grout condition of tendon ducts could be determined according to the frequency analysis, poorly grouted sections can be differentiated from the well-grouted sections within the tendon ducts. Results show that the IE method can be employed to detect voids in the grouted tendon ducts of many types of post-tensioned structures.

Abstract: The concrete residual compressive strength after different burning temperature and time by water cooling was experimentally studied. A detailed review of experimental phenomena in fire and the concrete failure characteristics in compressive test were given, and the relationship between the compressive strength and temperature, time were discussed. It is found that with the exposure of temperature and time increasing, the concrete residual compressive strength tends to decrease generally, but when the temperature is low or time is short, the concrete residual compressive strength tends to increase on the contrary. According to analysis of the experiment results, the formula for concrete residual compressive strength and temperature-time relationship after the fire was built.

Abstract: Concrete Filled Steel Tube(CFST) is widely used in civil engineering structures because of its superior mechanical performance. Yet the mechanical behavior of CFST is highly depended on the construction quality of the filled concrete. Hence it is very important for the inspection of the construction quality of the filled concrete in CFST structures. In this paper, the ultrasonic testing technique was used to detect the defect of the filled concrete of a CFST arch bridge. During the inspection, the ultrasonic transducer was moved along the circumference of the cross-section of the arch, and the defect of the concrete was comprehensively judged by detecting the change of sonic time, sonic amplitude and sonic frequency. Based on the analysis of the ultrasonic transmission path, the influences of different defects on the sonic time, sonic amplitude and sonic frequency were discussed. The detecting results were verified by core-drilling method. The verification showed that different kinds of defects defected by ultrasonic testing was in good accordance with the drilling samples, which demonstrates the adaptability of the ultrasonic detection technique in the construction quality inspection of CFST structures.

Abstract: The design point method is a commonly-used method on fatigue reliability analysis. It is put forward, based on Palmgren-Miner linear fatigue damage accumulation rule, that the evaluation method of fatigue reliability for orthotropic plate in this article. It is analyzed the random variables of limit state equation of single component, established the three parameters of stress amplitude , fatigue life and constant , and derived the calculation method on reliability index of design point method, which would provide evidence for consequent design of Orthotropic Plate.

Abstract: The research to identify and locate the damage to the engineering structure mainly aimed at some simple structure forms before, such as beam and framework. Damage shows changes of local characteristics of the signal, while wavelet analysis can reflect local damage traits of the signal in time domain and frequency domain. For confirming the validity and applicability of structural damage identification methods, wavelet analysis is used to spatial structural damage detection. The wavelet analysis technique provides new ideas and methods of spatial steel structural damage detection. Based on the theory of wavelet singularity detection，with the injury signal of modal strain energy as structural damage index，the mixing of the modal strain energy and wavelet method to identify and locate the damage to the spatial structure is considered. The multiplicity of the bars and nodes can be taken into account, and take the destructive and nondestructive modal strain energy of Kiewitt-type reticulated shell with 40m span as an example of numerical simulation，the original damage signal and the damage signal after wavelet transformation is compared. The location of the declining stiffness identified by the maximum of wavelet coefficients，analyzed as signal by db1 wavelet，and calculate the graph relation between coefficients of the wavelets and the damage to the structure by discrete or continuous wavelet transform, and also check the accuracy degree of this method with every damage case. Finally，the conclusion is drawn that the modal strain energy and wavelet method to identify and locate the damage to the long span reticulated shell is practical, effective and accurate, that the present method as a reliable and practical way can be adopted to detect the single and several locations of damage in structures.

Abstract: Based on the finite element theory, a method is proposed for crack identification of simple beam via the wavelet analysis of vibration modal parameters. A cracked simple beam is simulated using finite element method, and its modal parameters, including first three-order vibration modes, are obtained. Then, these modal parameters are analyzed via mexh and db wavelets. The crack location of the simple beam is identified by the maximum of wavelet coefficients, which validates the proposed method. This research may be useful in crack identification of simple beam structures.