Advanced Materials Research Vols. 163-167

Abstract: Dynamic loading test is exerted on a railway continuous beam bridge with a main span of 100m and a pier of 99m high, and dynamic responses are tested under natural excitation. Chebyshev digital filter is used to signal for low-pass filter according to the frequency distribution in FFT spectrum. A series of IMFs are obtained from the Hilbert-Huang Transform of a measured lateral displacement response, which shows: EMD is a self-adaptive signal analysis method that can effectively process non-stationary signal; IMFs can clearly show local features of complicated signal. Modal parameters of the bridge are identified based on HHT and Random Decrement Technique (RDT), the comparison of the identified results obtained from FFT, HHT-RDT and Finite Element Method is made, which show that HHT-RDT is an effective method to identify modal parameters of large bridge structures.

Abstract: A prototype of sensored bridge bearing was developed, fabricated, tested and planned to be applied in two bridge structures for sensing and monitoring of construction process and service condition. Besides, numerical modeling of the prototype was performed using the finite element method with ABAQUS, and meanwhile the testing results were calibrated. Numerical simulation results of the selected two bridge structures show that certain bearing reactions are sensitive to the interested behaviors and performances. This kind of sensored bearing is considered feasible for monitoring construction, damage scenario, and applied loads.

Abstract: A kind of SMA material with the chemical composition of Ti-51% at Ni (made in china) which is austenitic at room temperature is tested to find out the influences of adding/unloading frequency, loading amplitude and adding/unloading cycles on the superelasitc properties of it. Then the conclusions were made according to the experimental results given in the paper. Finally, some suggestions to improve the performance of the SMA material were offered.

Abstract: The elastic stress and strain fields in a circular cross-section bar with semielliptic groove subjected to uniaxial tension are systematically investigated using the finite element method. It is found that the stress and strain concentrations are different even if the material is in the elastic state. The relation between the stress and the strain concentration factors depends on Poisson’s ratio and the groove’s geometric configuration. The coupled influences of the shape factor of the semielliptic groove and the relative depth of the groove on the stress and strain concentrations are examined. The equations that describe the stress and strain concentration factors for different groove’s geometric configurations and Poisson’s ratios are obtained based on finite element results.

Abstract: Based on the theoretical analysis of the dynamic parameters of multi-DOF complex structures, it is shown that the optimum TMD parameters under the harmonic base excitation are not the exact optimization for seismic protection, whose main reason is that the optimum damping ratio of TMD for seismic protection is obviously lower than that under the harmonic base excitation. In this paper, an effective TMD design method is developed to control the seismic responses of many-degree-of-freedom complex structures. The EI-Centro seismic wave is introduced as the excitations and the approach to determining the optimum TMD parameters for seismic protection is effectively solved. Then with the case to design the TMD of a series reactor, the optimum TMD parameters for seismic protection are obtained. Its result proves that the designed TMD is able to reduce the seismic responses of the series reactor significantly, and this approach can provide a reference for the TMD design for seismic protection of other multi-DOF structures.

Abstract: The subharmonic resonance response of the strongly nonlinear delay differential equation is solved using the incremental harmonic balance method. The value of the exciting frequency when the subharmonic resonance occurs is discussed. The influences of the time delay and the feedback gain on the system subharmonic resonance response are studied. The variation of the subharmonic resonance response with the system parameters is obtained. The results show that the value of the exciting frequency when the subharmonic resonance occurs is affected by the system parameters. The proportion of the one third harmonic in the amplitude increases rapidly with the increase of the exciting frequency. The variation of the amplitude ratio of the one third harmonic and the first harmonic is wavy type. The proportion of the one third harmonic in the amplitude decreases with increasing the displacement feedback gain and increases with increasing the velocity feedback gain. The proportion of the one third harmonic in the amplitude occupies a dominant position in the subharmonic resonance response.

Abstract: Preparation of repeatable cement compacts may contribute to quantitively research of processing, structure and properties of cement materials. Capillary absorption of liquid by powder compact was briefly reviewed. Deviation degree of absorption coefficient (Dac) was designed for evaluation on repeatable preparation of cement compacts. Dry cement was compacted in special moulds. A group of orthogonal experiments were designed to investigate repeatable preparation of the compacts. Results show the most important factor influencing on repeatable preparation is the cavity size of mould. The influence of force and specific surface area of cement is generally below 1.41%. According to optimum scheme for preparation, Dac is 0.00%. Repeatable preparation of cement compacts may provide a new method for quantitatively research of cement materials.

Abstract: This paper presents a damage detection method using a combination of global (changes in natural frequencies) and local (displacement mode shapes) vibration-based analysis data as input in neural networks for location and severity prediction of structural damage. The necessary features for damage detection have been selected by performing sensitivity analyses. In order to check the robustness of the input used in the analysis and to simulate the numberical errors, artificial random noise has been generated numerically and added to noise-free data during the training of the neural networks. Furthermore, a modified back-propagation neural networks with the dynamic steepest descent (DSD) algorithm as training algorithm is used to improve the training efficiency. With those as basis, the neural networks can assess damage condition (locaiton and severity) with very good accuracy.

Abstract: Ultrasonic inspection is a key method of inspecting wall thickness flaw of seabed oil pipelines. How to lay out ultrasonic probes to fit for three inner diameter pipelines of Φ195mm, Φ247mm and Φ297mm was analyzed detailed. Diameter changing principle feasibility of ultrasonic inspection adopting 10 parallelogram mechanisms was discussed, and the key parts of structure of equidirection umbrella diameter changing mechanism were analyzed. In the end model machine experiment verified that equidirection umbrella diameter changing technology is feasible.

Abstract: In order to evaluate the identification precision and the computational efficiency of identification indices on damage detection and provide a reasonable basis to choose identification indices for deeply developing structural damage identification, a fuzzy analytical hierarchy process is used to comprehensive analyse and assess nine kinds of identification indices. By establishing the mathematical relationship between the precedence relation matrix and the fuzzy judgement matrix, the consistency of the judgement matrix in analytical hierarchy process is effectively improved. Using above methods and based on three evaluation standards that include mean error, network scale and measuring difficulty , a fuzzy hierarchy to assess identification indices is set up. On the basis of the fuzzy judgement matrix, the performance of nine kinds of identification indices is ranked. Empirical results show that deflection, first modal shape and fundamental frequency are more suitable for identification indices than other indices. And a fuzzy judgement matrix can be established only using the relative relationship between identification indices in the fuzzy analytical hierarchy process. Thus, the fuzzy analytical hierarchy process can be convenient extended to evaluate other identification indices and effectively improve the identification precision and the computational efficiency on damage detection.