Damage Assessment of Structures VII

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Authors: Dariusz Szwedowicz, Jorge Bedolla
Abstract: Conical rings are used to joint a shaft with other mechanical parts through frictional forces induced by clamping of the inner ring into the outer one. In design, their coupling strength and the allowable torque are determined with the well known analytical formulas. However, the assumption of rigid and smooth contacts considered in the analytical solution generates technical uncertainties for reliability of conical joints especially for their small dimensions. The coupling strength of the conical rings is investigated at a set-up and by using Finite Element (FE) Method. A FE model of the analytically analysed conical joint is created with friction contact conditions on all interfaces of the joint. For a very fine mesh with the smooth interfaces, the FE contact forces differ remarkably from the analytical solution. This confirms that the elasticity of parts has to be taken into account in the design process. To assess an influence of real contact profiles on the coupling performance, contours of contact surfaces are measured at a Mitutoyo coordinate measuring machine. Based on the measured height variation in the normal to the contact plane, the surface profiles are extrapolated by approximation functions. Then, the FE mesh is modified locally on the contact with respect to the extrapolated profile functions and coupling strength of the conical joint is computed with friction sliding. According to the obtained results, the implementation of the real profile of the contact is needed in the design process to avoid failures under real operation conditions of conical joints. According to the obtained FE static results, the contour irregularities induces local separations in the contact, which can be monitored by measuring electrical resistance between the outer and inner conical rings.
Authors: Byoung Han Choi
Abstract: A modeling technique to generate good design alternatives from optimal design of steel moment resisting frames is proposed. First presented is the development of Genetic Algorithm(GA)-based approaches that enable designers to identify the best locations for rigid connections in a frame. This GA uses a unique cost function that enables the trade-off study between the number of rigid connections and total cost. Second, the optimization formulation is modified to generate alternatives with a cost comparable to that of the optimal solution. It enables engineers to compare different solutions on the basis of the structure’s lateral load resistance capacity along with incidental factors like the location of the rigid connections, number of different section types, column splices etc. An example of a 5-story and 5-bay steel moment resisting frame is provided to illustrate the effectiveness of the proposed study.
Authors: Wen Ying Chen, Fu Lei Chu, Shao Ze Yan, Ke Yun Wang
Abstract: The upper and lower bound estimation of natural frequencies for intelligent truss structure with uncertain-but-bounded parameters is studied in this paper. Firstly, following the finite element method, the expressions of the interval stiffness and interval mass matrix of piezoelectric intelligent truss structures are derived directly from the interval parameters. Then, based on the matrix perturbation and interval extension theory, an interval parameter perturbation method is proposed for solving the upper and lower bound of natural frequencies. Finally, a 16-bar planar intelligent truss structure is used as an example to illustrate the applicability and validity of the presented method, and some useful conclusions are obtained.
Authors: Alberto Carpinteri, Giuseppe Lacidogna, Amedeo Manuello
Abstract: Acoustic emissions (AE) are ultrasonic waves generated by the rapid release of energy from discontinuities or cracks spreading in materials subject to a stress and strain field. By identifying the complete shape of the signals and taking into account a larger quantity of data, it becomes possible to ascertain the three-dimensional location of damage sources from AE sensor records. In this connection, the authors have fine-tuned an original procedure that uses seismic analysis techniques, such as the moment-tensor solution. The experimental program consisted of tests conducted in situ on masonry walls of historical buildings.
Authors: Simon P. Shone, Brian R. Mace, Tim P. Waters
Abstract: A method is presented for locating discontinuities in a uniform waveguide from two or more point frequency response functions (FRFs). The phase of the FRF exhibits modulation when plotted against wavenumber because of interference of waves reflected from the discontinuity, and this is related to the distance of the excitation point from the discontinuity. Such discontinuities might be known boundaries or unknown damage sites. An inverse Fourier transform is used to transform from the wavenumber domain to the spatial domain in order to extract the locations of the discontinuities. The use of the transform relies upon knowledge of the dispersion relation for the waveguide. Experimental results are presented for several uniform isotropic beams which were damaged to differing extents by sawing transverse slots in them. The results show the method to be successful in locating the slots.
Authors: Sheng En Fang, Ricardo Perera, Maria Consuelo Huerta
Abstract: An environmental excitation having random characteristics may be more effective and cost-efficient than other excitation means for non-destructive damage identification purpose on most of the large-scale engineering structures under operation. In general, many existing damage indexes are constructed based on the modal properties derived firstly from the power spectral density (PSD) analysis of the structures under random excitation. However, the derivation procedures for the modal parameters usually introduce some extra errors into the indexes. This paper aims to propose a simple and feasible damage location index (DLI) constructed directly derived from the analysis results of the structural response PSD. The performance of DLI was verified using an aluminum beam with fixed ends and an experimental reinforced concrete (RC) beam under free boundary condition. Our results show that the damage location of the aluminum beam can be determined via the plot of DLI value by selecting the peaks with the amplitudes exceeding a predefined threshold value in both single- and multi-damaged scenarios. And the index may also predict the possible damage zones in the RC beam experimentally tested.
Authors: Yu Xiang Liu, Wei Wei Zhang, Hong Wei Ma
Abstract: Damage detection by the wavelet transform of the fundamental vibration mode receives much attention recently. However, the higher vibration modes were hardly discussed in past literatures. As we know they are more sensitive to the crack comparing with the fundamental mode, which bring abundant damage information. The objective of this study is to show that the first four modes are available using wavelet transform for crack parameter identification. Specially, using the higher mode could result in an excellent quality of crack identification when the mode data was contaminated by noise. But too higher modes have possibly adverse effects on the quality of crack detection.
Authors: Dan Sheng Wang, Hong Ping Zhu, Bo He
Abstract: Crack damage brings a serious threat to the safety of mechanical and civil structures, and the problem of incipient damage identification of structures has been paying attention as a puzzle by many researchers in recent years. To seek for an alternative solution of the problem, a method for incipient crack localization using the slope of the anti-resonance curve is proposed in this paper. The method makes use of the driving-point mechanical impedance characteristics of cracked beams stimulated by harmonic force. To characterize the local discontinuity due to the presence of crack, a simplified rotational spring model is presented to model the crack. Subsequently, the proposed method is verified by a numerical example of cracked beam under simple support or cantilever boundary conditions.
Authors: M. Taghvaei, S.B.M. Beck, W.J. Staszewski, J.B. Boxall
Authors: Nicolae Constantin, Alexandrina Mihai, Mircea Găvan, Ştefan Sorohan, Constantin Dumitraşcu, Viorel Anghel
Abstract: Composite pipes enjoy increasing interest in the sector of petroleum and gas transportation, due to a number of qualities, concerning especially the corrosion resistance and light weight, face to the traditional steel pipes. As composite materials are prone to a various range of defects and damages which can seriously affect their service ability, reliable inspection methods have to be tested in order to assure the required in service reliability. The paper presents progress made in applying complementary global/local non-destructive inspection (NDI) methods, such as Lamb wave method and infrared thermography (IRT) method, to effective structural health (SHM) monitoring of composite pipes.

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