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Experimental investigation on dynamic mechanical characteristics and microstructure of steam-cured concrete

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Science China(Technological Sciences) 2014年第10期57卷 1902-1908页

作者： LONG GuangCheng WANG Meng XIE YouJun MA KunLin School of Civil Engineering Central South University National Laboratory for High Speed Railway Construction Technology

Steam-cured concrete is widely used to manufacture prefabricated units of high-speed railway foundation structure such as girder and track *** dynamic mechanical property of steam-cured concrete is one of the key properties affecting service performance of high-speed railway foundation *** the present paper,serial macro/micro-experiments were carried out to investigate the dynamic elastic modulus,shear modulus,damping ratio,and microstructure of steam-cured *** relationships between compositions,curing regime,microstructure,and dynamic properties of steam-cured concrete as well as the corresponding mechanisms were *** results indicate that steam-cured concrete in early age has a larger dynamic elastic modulus and shear modulus as well as a smaller damping ratio compared with standard-cured *** the contrary,at a later age a slightly smaller dynamic elastic modulus and a larger damping ratio of steam-cured concrete are *** of mineral admixture results in a bit lower dynamic elastic modulus and damping ratio of concrete than that of the control specimen without mineral *** achievements can provide some fundamental suggestions for materials parameters selection during structural design of steam-cured concrete precast element.

关键词： steam-cured concrete dynamic elastic modulus shear modulus damping ratio microstructure

Test and Analysis of the Sound Insulation Performance of Four Types of Timber Structure Floors under Jumping Excitation

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Journal of Renewable Materials 2021年第4期9卷 829-840页

作者： Yujie Huang Hao Zhu Dauletbek Assima Zheng Wang Minmin Li Xinyue Zhao College of Materials Science and Engineering Nanjing Forestry UniversityNanjing210037China College of Mechanical and Electronic Engineering Nanjing Forestry UniversityNanjing210037China College of Civil Engineering Tongji UniversityShanghai200092China College of Civil Engineering Nanjing Forestry UniversityNanjing210037China

To improve the impact sound insulation performance of building floors and meet the objective requirements for living comfort of residents,in this article,three kinds of elastic cushion materials,Portuguese cork board,BGL insulation sound insulation foam board,and EPP polypropylene plastic foam board,are applied to the sound insulation of a light frame wood floor structure of the same bedroom and compared to the ordinary *** study uses the transfer function method and transient excitation method to measure the sound insulation,damping ratio,and elastic modulus of materials,as well as the sound insulation of the floor under the jumping excitation method of daily *** comparative analysis,the results and factors of improving the sound insulation performance of the floor are obtained,according to which three types of elastic cushion materials and the floor covering composed of them have higher vibration and noise reduction *** them,the overall sound insulation performance of BGL board floor is the highest,followed by EPP board and cork board floor,and ordinary OSB floor is the *** the jumping excitation method,three floating floors can improve the impact sound insulation performance of the middle and low-frequency bands.

关键词： Timber floor structure elastic cushion material damping ratio elastic modulus jumping excitation method of daily behavior testing and comparative analysis

Cyclic behavior of reinforced sand under principal stress rotation

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Journal of Rock Mechanics and Geotechnical Engineering 2017年第4期9卷 585-598页

作者： Alaa H.J. Al-rkaby A. Chegenizadeh H.R. Nikraz Department of Civil Engineering School of Civil and Mechanical Engineering Curtin University Perth Australia

Although the cyclic rotation of the principal stress direction is important,its effect on the deformation behavior and dynamic properties of the reinforced soil has not been reported to *** carried out on large-scale hollow cylinder samples reveal that the cyclic rotation of the principal stress direction results in significant variations of strain components(ε,ε,εand γ) with periodic characteristics despite the deviatoric stress being constant during *** oscillation can be related to the corresponding variations in the stress components and the anisotropic fabric that rotate continuously along the principal stress *** under rotation appears to develop a plastic *** trends are observed for reinforced sand,but the shear interaction,the interlocking between particles and reinforcement layer,and the confinement result in significant reductions in the induced strains and associated irrecoverable plastic *** of the strains occur in the first cycle,and as the number of cycles increases,the presence of strains becomes very small,which is almost *** indicates that the soil has reached anisotropic critical state(ACS),where a stable structure is formed after continuous orientation,realignment and rearrangement of the particles accompanied with increasing cyclic *** in the range of 60°-135° produces more induced strains even in the presence of the reinforcement,when compared with other *** relates to the extension mode of the test in this range in which σ>σand to the relative approach between the mobilized plane and the weakest horizontal *** results in an increase in shear modulus while it appears to have no effect on the damping *** cycles of rotation result in an increase in shear modulus and lower damping ratio due to the densification that causes a decrease in shear strain and less dissipation of energy.

关键词： Cyclic rotation Principal stress direction Reinforced sand Strain components damping ratio Shear modulus

A novel dual-feed low-dropout regulator

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Journal of Semiconductors 2015年第6期36卷 110-114页

作者：段志奎胡建国丁一路崇丁颜玉王德明谭洪舟 School of Information Science and Technology Sun Yat-Sen University

A novel dual-feed （DF） low-dropout （LDO） is presented. The DF-LDO adopts dual control loops to maintain the output voltage. The dual control loops include a feedback loop and a feedforward loop. There is an equilibrium point in dual control loops, and the equilibrium point is the output voltage of the DF-LDO. In addition, the transient performance is optimized by adjusting the damping ratio and natural frequency. With a 1 #F decoupling capacitor, the proposed DF-LDO is fabricated in a 0.18 μm CMOS process and its output voltage is 1.5 V. When the workload changes from 100 μA to 100 mA in 100 ns, load regulation of 7 mV for a 100 mA step is achieved, the settling time is 997 ns and the undershoot is 12.8 mV; when the workload changes from 100 mA to 100 μA in 100 ns, the settling time is 249 ns with an imperceptible overshoot.

关键词： dual-feed fast transient response DF-LDO damping ratio natural frequency

Constitutive Model of Saturated Soft Clay with Cyclic Loads under Unconsolidated Undrained Condition

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Transactions of Tianjin University 2013年第4期19卷 260-266页

作者：李书兆王建华 State Key Laboratory of Hydraulic Engineering Simulation and Safety Tianjin University Geotechnique Engineering Institute Tianjin University

An equivalent visco-elastic model of saturated soft clay was studied under unconsolidated undrained (UU) condition, which can be used to evaluate the stability of ocean foundation. Cyclic triaxial compression and extension tests were conducted to study the parameters of the model. Results showed that the relationships of the damping ratio and the octahedral shear modulus with the octahedral cyclic shear strain were nearly unique, when the initial octahedral shear stress ratios of specimens were equal to 0.3, 0.5 and 0.7. The relationships of the damping ratio and the octahedral shear modulus with the octahedral cyclic shear strain determined from the cyclic triaxial compression tests were basically the same as those determined from the cyclic triaxial extension tests. Furthermore, the relationships were not related to the initial stress condition, the test stress state and the octahedral cyclic shear stress ratio. The relationships determined from the cyclic triaxial tests under no deviatoric stress were basically the same as those determined from the cyclic triaxial tests under deviatoric stress. The change of the octahedral cyclic accumulative strain with the number of cycles was unique under different tests stress states. An equivalent visco-elastic constitutive model of saturated soft clay under UU condition was initially established.

关键词： visco-elastic constitutive model damping ratio octahedral cyclic shear modulus octahedral cyclic shear strain octahedral cyclic accumulative strain cyclic triaxial test

Experimental Study on Mechanical Properties of Weathered Rock Covered by Loess

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Journal of Shanghai Jiaotong university(Science) 2013年第6期18卷 719-723页

作者：王平吴志坚王峻张泽忠王谦 Key Laboratory of Loess Earthquake Engineering Gansu Earthquake AdministrationChina Earthquake Administration Lanzhou Institute of Seismology China Earthquake Administration Geotechnical Disaster Prevention Engineering Technology Research Center of Gansu Province

Based on dynamic triaxial test, the mechanical properties of the weathered rock covered by loess were studied. The cohesion value of weathered mudstone is far below that of the weathered sandstone, while the internal friction angle values are basically equivalent, about 30. Compared with the undisturbed sample, the cohesion value of remodeling weathered rock sample decreases significantly. With the increase of moisture content, the strength of weathered mudstone is obviously decreased due to the influence of the water softening efect. This results illustrate that the bearing stratum is not easily afected by external disturbance in comparison to weathered mudstone. In the engineering, in order to ensure the good mechanical properties of the soil, more attention should be paid to keeping the water content constant, even to reducing the water content. The experiments show that the relations between shear stress and strain of weathered rock were nonlinear and the behavior of weathered rock can be expressed by the hyperbolic model. The initial modulus of undisturbed weathered rock, under the same consolidation conditions, is much greater than that of remodeling samples. Meanwhile, the initial dynamic elastic modulus of sandstone is also greater than that of the mudstone. The dynamic shear modulus ratios of the undisturbed sandstone, the undisturbed mudstone, as well as the remodeling mudstone have the normalization characteristics with the increase of dynamic shear strain. The damping ratio of mudstone is larger than that of the sandstone, and the damping ratio of remolding sample is also greater than that of the undisturbed mudstone. The mudstone has the bad mechanical properties as bearing stratum.

关键词： weathered rock mechanical characteristics dynamic elasticity modulus damping ratio cohesion

Inversion of waveforms from Xiangtang borehole seismic array for soil dynamic property

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Acta Seismologica Sinica(English Edition) 2007年第4期20卷 425-434页

作者：陈学良金星陶夏新韦永祥 Institute of Engineering Mechanics China Earthquake Administration

In order to understand the site soil response of the Xiangtang borehole seismic array under real strong ground motion, reveal the site response, verify the technique of borehole exploration, and improve the precision of in-situ test and laboratory test, this paper presents a new approach, which is composed of two methods. One is the layered site seismic response method, whose layer transform matrix is always real. The other is a global-local optimization technique, which uses genetic algorithm （GA）-simplex method. An inversion of multi-component waveforms of P, SV and SH wave is carried out simultaneously. By inverting the records of three moderate and small earthquakes obtained from the Xiangtang borehole array （2^#） site, the soil dynamic characteristic parameters, including P velocity, damping ratio and frequency-dependent coefficient b, which has not been given in previous literatures, are calculated. The results show that the soil S wave velocity of the Xiangtang 2^# borehole is generally greater than that obtained from the 1994 in-situ test, and is close to the velocity of the 3^# borehole, which is more than 200 m away from the 2^# borehole. Meanwhile, perceptible soil nonlinear behavior under peak ground motion of about 60×10^-2 m/s^2 is detected by the inversion analysis. The presented method can be used for studying the soil response of other borehole array sites.

关键词： Xiangtang borehole array inversion analysis soil response P and S wave velocity damping ratio

Dynamic constitutive model for soils considering asymmetry of skeleton curve

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Journal of Rock Mechanics and Geotechnical Engineering 2013年第5期5卷 400-405页

作者： Guoxing Chen Hua Pan Hui Long Xiaojun Li Institute of Geotechnical Engineering Nanjing University of Technology Geotechnical Research Institute Hohai University Institute of Geophysics China Earthquake Administration

Based on the asymmetric characteristic of skeleton curve obtained from dynamic tests on soils,a function with double asymptotes is proposed for describing the dynamic constitutive relations of *** hysteresis loops observed during unloading and reloading show the same form as the skeleton curve and are constructed by taking the ultimate stress as the corresponding *** coeffcient of initial unloading modulus is used to ensure that the constructed hysteresis loop fts well with the experimental ***,a new dynamic constitutive model considering the asymmetry of skeleton curve is *** verifcation tests on saturated Nanjing fne sand are performed using a hollow cylinder apparatus to verify the applicability of the UD *** is found that the predicted curves by the UD model agree well with the test data.

关键词： Function with double asymptotes Dynamic constitutive model Shear modulus damping ratio Complex initial stress state

Dynamic Analysis of a Single-Column Platform

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China Ocean Engineering 1991年第4期6卷 385-394页

作者： Lian Gan , Ni Kan, Hu Kai and Guo Dawei Prof., Senior Engineer, Marine Design and Research Institute of China, Shanghai Senior Engineer, Marine Design and Research Institute of China, Shanghai Engineer, Marine Design and Research Institute of China, Shanghai

In this paper, a single-column structure used as well-head platform is studied. The loads of wave and current exerted on the single-column will be greatly reduced, therefore the cost of the structure will be decreased. The advantages of the single-column structure compared with ordinary jacket structure are explained. A dynamic analysis of this type of structure is made and some problems related to dynamic analysis are solved. In order to check the reliability of computation theory and programme, model tests have been carried out. However, as space is limited, the conclusion of tests will be introduced in another paper. Therefore, this type of structure is applicable for proctical engineering.

关键词： single-column structure dynamic analysis diffraction wave theory natural period,resonant dynamic strength damping ratio fictitious stiffness of pile top fatigue analysis