关键词：
impact of attenuation;ground penetrating;effectively improve GPR
摘要：
To reduce the impact of attenuation and dispersion in ground penetrating radar (GPR) detection and to effectively improve GPR profile recording and to identify a weak detection target, a high-resolution processing method based on orthogonal matching pursuit and wavelet spectrum whitening (the OMWS method) is presented. First, according to the matching pursuit algorithm and the strong reflection-forming mechanism and based on sparse representation theory, a sparse dictionary suitable for the characteristics of a strong reflection signal was selected, and the signal was decomposed, which displayed the weak target signal well. Second, wavelet analysis was used to decompose the processed GPR signal into time-domain subsignals in different frequency bands, and each subsignal was whitened by a whitening filter. Then, the processed subsignals were reconstructed. The final results were compared with the results of conventional spectrum whitening method and showed that the OMWS method can accurately weaken the effect of the strong impedance interface and effectively enhance the local information of microcrack-reflected signals in both the time and frequency domains. The resolution of the processed GPR image is greatly improved, and the reflected signal of the hidden microcrack is easily visible. The method is clearer and more intuitive in the expression of the weak signals of hidden microcrack than the conventional spectrum whitening method, and the compensation for the high-frequency of the signals is more obvious.
通讯机构：
[Wen Xiaolong] H;Hunan City Univ, Coll Civil Engn, Yiyang 413000, Hunan, Peoples R China.
关键词：
Piezoelectric effect;sensing modeling;lump mass method;numerical analysis;experimental validation
摘要：
This paper proposes the modified mechanical and mathematical modeling of lead zirconium titanate (PZT) sensor based on the PZT constitutive relation in order to solve the complicated boundary condition and stress situation of PZT sensor due to the effect of adhesive-layer damping. The experimental study on the surface-bonded PZT sensor is chosen to carry out the correctness of the proposed models. The results show that the PZT sensor modeling is simplified to three types. When the amplitude of harmonic force is constant, the greater the excitation frequency, the more sensitive the output voltage is, the easier the signal acquisition is. At a certain frequency, the voltage output is proportional to the force amplitude. The larger the area or thickness of PZT, the greater the output voltage is, the more sensitive the signal output is. The output voltage is in quadratic relation to the bonding thickness. Furthermore, the smaller the output voltage, the greater the damping is. The signal loss is about 25.82%. The signal acquisition effect of the PZT square wafer is better than that of circular wafer under the same area of PZT sensor. The research achievements reveal the sensing mechanisms and validate the efficiency of the developed model and effectively simulate and detect direct piezoelectric rule of PZT sensor.
作者：
Cao, Guohui*;Zhang, Wang;Hu, Jiaxing;Zhang, Kai
期刊：
International Journal of Civil Engineering,2018年16(8):887-895 ISSN：1735-0522
通讯作者：
Cao, Guohui
作者机构：
[Cao, Guohui; Zhang, Kai] Hunan City Univ, Coll Civil Engn, 518 Yingbin East RD, Yiyang 413000, Hunan, Peoples R China.;[Zhang, Wang] Changsha Univ Sci & Technol, Coll Civil Engn & Architecture, 960,2nd Sect,Wanjiali South RD, Changsha 410114, Hunan, Peoples R China.;[Hu, Jiaxing] Hunan Univ, Coll Civil Engn, Lushan South RD, Changsha 410082, Hunan, Peoples R China.
通讯机构：
[Cao, Guohui] H;Hunan City Univ, Coll Civil Engn, 518 Yingbin East RD, Yiyang 413000, Hunan, Peoples R China.
关键词：
Retard-bonded;Prestressed concrete;Beams and girders;Deflection;Creep
摘要：
This study compares the mechanical properties of the retard-bonded and conventionally bonded prestressed concrete (RBPC and BPC, respectively) under uniform loads. Results show that the prestressed strands and concrete of the RBPC T-beams are firmly bonded with harden of retard-bonded materials, thereby exhibiting the same mechanical properties as that of the BPC beams. The growth rate of the long-term deflections of the RBPC T-beam is slightly lower than that of the BPC T-beam. Given the effect of concrete shrinkage, creep and time variation of prestress loss, the regular patterns of deflection growth of the RBPC T-beam mid-spans are analysed based on the age-adjusted effective modulus method, method of equivalent prestress load and calculation model of prestress loss. Accordingly, the long-term deflection development curves of the RBPC T-beam mid-spans under self-weight, prestressing force and external loads are obtained. Calculation results are in good agreement with the test results. This method has immense applicability for the computation of the RBPC T-beams, and can be used to estimate the long-term deflection growth of regular patterns of the RBPC components.
摘要：
A long-term deflection test is performed for 470 days on two simply supported prestressed concrete box beams under sustained uniform load. The deflection growth rules of the box beams under both cracked and uncracked states are studied. The measured longterm deflection of the cracked beam is 18.4% larger than that of the uncracked beam, whereas the deflection growth coefficient of the cracked beam is 65.3% that of the uncracked beam. The larger long-term deflection of the cracked beam is mainly attributed to the huge value of the instantaneous deflection caused by the crack. Then, the cracks lead to the release of concrete stress, thereby reducing the creep effect. For the uncracked beam, the influences of concrete shrinkage, creep, and prestress loss on the long-term mechanical behavior of components are considered, and then deflection is predicted using the blended method based on the age-adjusted modulus method, the prestressed equivalent load method, and the calculation method for prestress loss. Results show that the theoretical and measured values are in good agreement. For the cracked beam, the crack influence coefficient is introduced to revise its effective elastic modulus by considering the influence of cracks on the long-term deflection of the cracked beam. Then, a formula for calculating the long-term deflection of cracked beams that considers stiffness reduction for instantaneous deflection correction is proposed. The formula exhibits high precision in calculating and analyzing the long-term deflection of the cracked beam. The deviation between the calculated and measured values is within 10%.
关键词：
sandstone and mudstone particles;rheological deformation;segmented rheological model;rheological limit strain;rheological test
摘要：
A mixture of sandstone and mudstone particles is often used as the main filling material for many agriculture-related and civil engineering projects, including rock-fill dams and foundations. The long-term rheological deformation experienced by rock-fill dams and foundations filled with this mixture is much bigger than that of coarse-grained and cohesive soils, due to the deterioration and softening of the mudstone particles. This study focuses on the rheological deformation of a sandstone-mudstone particle mixture, prepared by mixing sandstone and mudstone particles, based on the content by weight of four mudstone particle types. Confined uniaxial compression tests were performed to test the rheological deformation of 24 samples of the mixture, and a stress-strain curve was obtained for each test. On the basis of compression curves, the rheological process of the mixture was divided into four phases: linear, attenuation rheological, secondary attenuation rheological and stable phases. The three defining features of the curve, namely the rheological attenuation factors, attenuation rheology critical strain and limited rheological strain, were then determined and modeled. A segmented rheological model was then proposed, based on a modified attenuation rheological constitutive model for coarse-grained soil. The modelled results compared well with the experimental data, and the modelled compression-curve prediction was able to describe the two-stage attenuation rheology features (attenuation rheological and secondary attenuation rheological phases) of the sandstone-mudstone particle mixture.
摘要：
The classical theory of heat conduction (Fourier theory) predicts an infinite speed for thermal disturbance propagation, which is physically unrealistic. By extending the classical Fourier heat conduction and Fick's diffusion, this paper presents a hyperbolic diffusion law with different phase lags of thermal and moisture fluxes to simulate coupled heat-moisture diffusion-propagation behavior. Transient hygrothermal and elastic response of an infinitely long cylinder subjected to sudden hygrothermal loadings at the surface is studied. By using Laplace transform and decoupling technique, a closed form solution of temperature, moisture, displacements and stresses is determined. The analytical results show that the thermal and moisture relaxation times or phase lags of heat and moisture fluxes play a significant role in the early stage of transient response after heat/moisture shock. The classical results corresponding to vanishing phase lags can be recovered from the present ones. For non-vanishing phase lags, hygrothermal waves have finite propagation speeds. Numerical results are calculated and displayed graphically to show the influence of the phase lags of heat and moisture fluxes on transient hygrothermoelastic fields. A comparison between classic model and hyperbolic hygrothermal coupling model is given. Based on the non Fourier heat conduction and non-Fick diffusion, some shortcomings induced by the classical Fourier's and Fick's laws can be effectively avoided. (C) 2018 Elsevier Ltd. All rights reserved.
通讯机构：
[Cao Guo-hui] H;Hunan City Univ, Coll Civil Engn, Yiyang 413000, Peoples R China.
关键词：
PC box girders;long-term load experiment;flexural behaviors;cracks;static performance
摘要：
Long-term load and flexural failure experiments are carried out on two prestressed concrete (PC) simply supported box girders. In the long-term load experiment, girder-1 (G1) is in an elastic state, while girder-2 (G2) is in a cracking state. To investigate the influence of cracking on the flexural behaviors of PC simply supported box beams, the experiment results are analyzed from many aspects, such as load–deflection, load–strain, and failure mode. Experiment results show the following: 1) the shrinkage and creep of concrete have considerable influences on the long-term deflection and strain of the two girders; 2) in the flexural failure experiment, the cracks and ultimate loads of the two girders are close. The rigidity degeneration of G2 is significantly faster than that of G1, and thus G2 shows nonlinear characteristics earlier; 3) to prove the validity and rationality of the current code, the cracking load and ultimate load of the two girders are calculated according to the current code.
摘要：
Due to the complexity of components and damage mechanism of reinforced concrete, the wave propagation characteristics in reinforced concrete are always complicated and difficult to determine. The objective of this article is to study the failure process of reinforced concrete structure under the damage caused by pencil-broken. A new method on the basis of the acoustic emission technique and the Hilbert-Huang transform theory is proposed in this work. By using acoustic emission technique, the acoustic emission wave signal is generating while the real-time damage information and the strain field of the reinforced concrete structure is receiving simultaneously. Based on the Hilbert-Huang transform (HHT) theory, the peak frequency characteristics of the acoustic emission signals were extracted to identify the damage modes of the reinforced concrete structure. The results demonstrate that this method can quantitatively investigate the acoustic emission wave propagation characteristic in reinforced concrete structures and might also be promising in other civil constructions.
