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Intermediate HSS bracing members during seismic excitations: modeling, design, and behavior

Madhar HADDAD

《结构与土木工程前沿（英文）》 2018年第12卷第1期页码 148-162 doi: 10.1007/s11709-016-0375-5

摘要： Concentric hollow structural section (HSS) bracing members are used frequently in steel framed structural systems to resist seismic excitations. Finite element modeling of the HSS braces that utilizes the true stress-strain curves produces hysteresis responses that are reasonable matches to the experimental response. True stress-strain curves are obtained from coupon tests or stub-column tests while utilizing an exponential function or strain hardening rule with a trial and error procedure to obtain the hysteresis behavior. In the current study, the true stress-strain curves are directly obtained from tests on stub-columns extracted from the full scale HSS bracing members away from the mid-length plastic hinge after cyclic testing. Two experimental tests (Shaback 2001 and Haddad 2004) were used to validate the model. Results indicate that the stress-strain curves for these braces are not unique. A refined damage accumulation model for ultra-low-cycle fatigue is implemented to predict fracture of the brace tests. The refined damage model is then used in the finite element modeling to predict fracture of braces in a chevron braced frame of an eight-storey building subjected to selected ground motions analyzed using OpenSees program. Results indicate that all braces could sustain the selected earthquake records without fracture.

关键词： HSS FEM stress-strain curves damage model

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Kinematic Model Building and Servo Parameter Identification of 3-HSS Parallel Mechanism

YANG Zhi-yong, WU Jiang, HUANG Tian, NI Yan-bing

《机械工程前沿（英文）》 2006年第1卷第1期页码 60-66 doi: 10.1007/s11465-005-0019-2

摘要：

Aiming at a parallel mechanism with three degrees of freedom, a method for dynamic model building and the parameter identification of its servosystem is presented. First, the reverse solution models of position, velocity, and acceleration of parallelogram branch structure are deduced, and then, its dynamic model of a rigid body is set up by using the virtual work principle. Based on the above model, a method to identify the servo parameter of the parallel mechanism is put up. In this method, the triangle-shaped input with variable frequency is adopted to offset the disadvantages of pseudorandom number sequence in parameter identification, such as dramatically changing the vibration amplitude of the motor, easily impacting the motor that results in its velocity loop to easily open, and so on. Moreover, the rotary inertia can also be identified by the additive mass. The abovementioned data will lay a solid foundation for the optimum performance of the system in the whole workspace.

关键词： building acceleration additive workspace optimum performance

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Evolution of humic substances in polymerization of polyphenol and amino acid based on non-destructive characterization

Jianmei Zou, Jianzhi Huang, Huichun Zhang, Dongbei Yue

《环境科学与工程前沿（英文）》 2021年第15卷第1期 doi: 10.1007/s11783-020-1297-y

摘要： Abstract • Humification evolution was identified with non-destructive characterization method. • Humification process from precursors to fulvic and humic acid was confirmed. • MnO2 alone had limited oxidation ability to form HA. • MnO2 played a key role as a catalyst to transform FA to HA in the presence of O2. • MnO2 could affect the structure of the humification products. Abiotic humification is important in the formation and evolution of organic matter in soil and compost maturing processes. However, the roles of metal oxides in abiotic humification reactions under micro-aerobic remain ambiguous. The aim of this study was to use non-destructive measurement methods to investigate the role of MnO2 in the evolution of humic substances (HSs) during oxidative polymerization of polyphenol-amino acid. Our results suggested a synergistic effect between MnO2 and O2 in promoting the polymerization reaction and identified that MnO2 alone had a limited ability in accelerating the transformation of fulvic acid (FA) to humic acid (HA), whereas O2 was the key factor in the process. Two-dimensional correlation spectroscopy (2D-COS) showed that the evolution in the UV-vis spectra followed the order of 475–525 nm>300–400 nm>240–280 nm in the humification process, indicating the formation of simple organic matter followed by FA and then HA. 13C nuclear magnetic resonance (13C NMR) analysis revealed that the products under both air and N2 conditions in the presence of MnO2 had greater amounts of aromatic-C than in the absence of MnO2, demonstrating that MnO2 affected the structure of the humification products. The results of this study provided new insights into the theory of abiotic humification.

关键词： Two-dimensional correlation spectroscopy (2D-COS) Humic substances (HSs) Humification Manganese dioxide Polyphenol