Table of Content

25 June 2009, Volume 37 Issue 6

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Chemistry & Chemical Engineering

Preparation and Photo-Cathodic Protection Properties of Nano-Sized TiO₂/SnO₂ Coatings

Zeng Zhen-ou Zhou Min-jie Zhong Li Zhao Guo-peng

2009, 37(6):  1-6. 

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Nano-sized double-layer TiO₂/SnO₂coatings were prepared on Type 304 stainless steel substrate via the sol-gel method. The ＂photo-electrochemical effect and photo-cathodic protection properties of the coatings were then investigated by measuring the stable potential. Moreover, the surface morphology, structure and composition of the prepared coatings were characterized by means of SEM, XRD and XPS. The results show that  the nano-sized double-layer TiO₂/SnO₂ coatings prepared by dipping TiO₂ and SnO₂ coatings respectively for 4 times are of the best photo-electrochemical effect, charge-storage capability and photo-cathodic protection properties, which provides the coated Type 304 stainless steel with a cathodic protection lasting 7 h after the irradiation by UV illumination for 1 h ;  the coatings are uniform and compact, with continuous surface, anatase TiO₂ and rutile SnO₂; and  both the outer and the inner layers of the coatings are composed of Ti, Sn, C and O. The mechanism of photo-cathodic protection of the nano-sized TiO₂/SnO₂ coatings is also discussed in the paper.

Synthesis and Application of Zircoaluminate Coupling Agent as Surface Modifier of Nano-Sized Titanium Dioxide

Li Bin Li You-ming Yang Wen-liang

2009, 37(6):  7-12. 

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Zircoaluminate coupling agent with carboxy groups was synthesized, with polyaluminium chloride, zirconium oxychloride and adipic acid, etc. , as the materials. The product and the nano-sized TiO2 before and after the surface modification were then characterized by means of FT-IR, TG-DTG, XRD, TEM and by measuring the size distribution. It is found that one carboxy group in adipic acid forms a complex bridge between the aluminum and the zirconium centers, while the other remains unchanged as the functional group of the coupling agent; and that the proportion of inorganic parts in the coupling agent is up to 71%. Moreover, as for the nano-sized ZiO2 surface-modified with the coupling agent, there exists a chemical adsorption of the coupling agent on TiO2 surface, which has no effect on the crystalline form of nano-sized TiO2, and, the dispersion of the modified nano-sized TiO2 in water improves remarkably.

Intrinsic Reaction Kinetics CO on Cu-Mn of Catalytic Oxidation of Catalyst Bed

Zhang Hui-ping Peng Guan-lan Yan Ying Guan Jian-yu Xiao Xin-yan

2009, 37(6):  13-16. 

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Cu-Mn catalyst suitable for the CO removal from gas via low-temperature catalytic oxidation was prepared by means of coprecipitation. The product was then characterized using XRD and SEM. It is found that the amorphous catalyst is of high catalytic activity for CO oxidation at room temperature. Moreover, the catalytic isotherm of CO oxidation on the Cu-Mn catalyst bed at 50 - 80℃ was obtained, and the corresponding intrinsic reaction kinetics was investigated. Experimental results show that the surface reaction on the catalyst bed plays the most important role in the control of reaction rate, and that, when eliminating the internal and external diffusion, the catalytic oxidation of CO on the Cu-Mn catalyst bed is a first-order reaction with an activation energy of 43.0 kJ/mol.

XPS Analysis of Cellulose Treated with Two Ionic Liquids

Zhang Jing-qiang Lin Lu He Bei-hai Liu Shi-jie Ouyang Ping-kai

2009, 37(6):  17-21. 

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Two kinds of ionic liquids, namely, 1 -allyl-3-methylimidazolium chloride （ [ Amim ] C1） and 1 -butyl-3- methylimidazolium chloride （ [ Bmim ] C1）, were respectively used to decrystallize microcrystalline cellulose （MCC） for 20, 40 and 60 rain. XRD spectra show that, after the treatment with [ Amim ] C1 or [ Bmim ] C1, the crystalline index of MCC decreases from 90.2% to 72. 4% or to 66.8%. Moreover, XPS spectra indicate that, different from the relative content of chemical bonds, the chemical-bond type of cellulose macromolecules shows no obvious change after the decrystallization; and that the relative content changes of C--OH and C--OH…O are highly related to the variation of crystalline index, with the conelation coefficients being 0. 9990 and 0. 9846, respectively.

Thermogravimetric Characteristics and Kinetic Analysis of Lignin Hydrolyzed by Dilute Acid

Tan Yang Wu Shu-bin Lou Rui Yang Qing

2009, 37(6):  22-26. 

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The pyrolysis characteristics of lignin hydrolyzed by dilute acid at different heating rates were investigated by means of thermogravimetry, and the effect of heating rate on the pyrolysis was analyzed. Afterwards, a dynamic model describing the pyrolysis process was established according to the differential thermogravimetric curves, and the corresponding kinetic parameters were calculated. The results show that   the pyrolysis mainly occurs at 200 - 450 ℃ ;   with the increase of heating rate, the thermogravimetric curve shifts to the high-temperature range;   at the heating rates of 10, 20 and 30 ℃/min, the mass loss reaches the peak value at 311.9, 323.8 and 338.1℃, respectively, with only one obvious mass loss peak occurring at the differential thermogravimetric curves;   according to the Coats-Redfern method, the pyrolysis can be described by two first-order reactions; and   the activation energy, 18.27 - 18.47 kJ/mol at low-temperature range and 74. 45 - 84.37 kJ/mol at high- temperature range, slightly decreases with the increase of heating rate.

Microwave-Irradiated Preparation Modified Chitosan and Adsorption Property of Microsphere

Ge Hua-cai Huang Shi-ying Liang Kai

2009, 37(6):  27-30，36. 

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Crosslinked chitosan salicylaldehyde Schiff base microspheres were firstly prepared under microwave irradiation, with glutaraldehyde as the crosslinking agent. The structure and morphology of the product were then characterized by means of FT-IR, XRD and TG, etc. Moreover, the adsorption capacities of the product for some metal ions were investigated, and the results were compared with those of the microspheres produced by the traditional water-bath heating method. It is indicated that  microwave irradiation remarkably accelerates the reaction and improves the yield ;   as illustrated by FT-IR, XRD and TG results, the structure of the product accords well with the expectation due to a successful graft crosslinking of chitosan; and   the microsphere adsorbent prepared by means of microwave irradiation is uniform in size and is of an increased specific surface area and an remarkably-increased adsorption capacity for Pb^2＋ and Cd^2＋

Influence and Removal of Water on In-Situ DRIFTS Characterization

He Yun-bing Ji Hong-bing Xu Jian-chang Wang Le-fu

2009, 37(6):  31-36. 

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In the investigation of the catalytic oxidation of volatile organic compounds （VOCs） using in-situ diffuse reflectance infrared Fourier transform spectroscopy （DRIFTS） , the existence of water greatly influences the recognition of surface species and restrains the catalytic behavior of catalysts. In order to solve this problem, the dehydration effects of concentrated H2SO4, anhydrous CaC1₂ and anhydrous CuSO₄, silica gel, and 5A molecular sieves were compared, and the influence of vacuuming on the removal of gaseous water in the in-situ cell was analyzed. The results show that   temperature and the chosen drier greatly affect the removal of gaseous water;   the dehydration becomes easier at a higher temperature;   different from other driers, 5A molecular sieves exhibit the most excellent dehydration effect and improves the catalytic oxidation to a certain degree; and   vacuuming is feasible in the removal or reduction of gaseous water.

Finite Element Analysis of Large Autoclave Based on Hybrid Modeling Technology

Qu Jie Jiang Nan

2009, 37(6):  37-42. 

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The hybrid modeling technology of coupling shell element with solid element is used to perform the finite element analysis and strength analysis of an autoclave for refining. In the investigation, first, the components of the autoclave are reasonably simplified based on the geometric characteristics, and a 3-D finite element model of the autoclave is built using the professional pre-processing software Hypermesh and the large finite element software Abaqus. Then, the stress intensity of the autoclave under the complex loads including the bending moment, the torque moment, the deadweight, and the concentrated force, ete. , is analyzed. Based on the analysis results, the safety of the autoclave is finally assessed according to JB 4732-1995 ＂Steel Pressure Vessels--Design by Analysis＂. The results show that the designed autoclave fully meets the safety requirements for such components as the support, the head, the web plate and the bolt, etc.

Synthesis of p-Substituted Phenolic O-Glycoside via Improved Tietze＇s Method

Lin Dong-en Huang Xiao-long Zhang Yi-wei

2009, 37(6):  43-46. 

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Proposed in this paper is an improved Tietze＇s method to synthesize phenolic O-glycoside. In this method, anhydrousSnCl₄instead of trimethylsilyl trifluromethanesulfonate was used as the reaction accelerator, and peracetyl glycoside instead of 1-O-trimethylsilyl acetyl glycoside was used as the starting material to react with three phenolic trimethylsilyl ethers （ Ⅰ a- Ⅰ c）. Thus, three kinds of products, namely 1-O-（4-nitrophenyl）-2,3,5-tri- O-acetyl-β-D-ribofuranoside, 1-O-（ 4-acetylphenyl ） -2,3,5-tri-O-acetyl-β-D-ribofuranoside, and 1-O-（ 4-benzoyloxyphenyl）-2,3,5-tri-O-acetyl-β-D-ribofuranoside, were synthesized, with a shortened synthesis route and at low cost. Moreover, the effects of different Lewis acids, the proportion of the starting materials, the anhydrous SnCl₄dosage, and the solvents on the reaction were investigated. The results show that   anhydrous SnCl₄proves to be an optimal reaction accelerator to the synthesis when the dosage is more than the stoichiometric amount;   the suitable molar ratios of the starting materials are respectively nⅠa：nⅡ：nSnCl₄=1.0：1.4：1.5,nⅠb：nⅡ：nSnCl₄=1.0：1.1：1.4,nIc：nⅡ：nSnCl₄=1.0：1.0：1.5; and   dried diehloromethane is a suitable solvent for the reaction, while aeeto- nitrile or un-dried diehlorolnethane as solvent may produce the by-product 4-nitrophenyl acetate.

Synthesis of Waterborne Epoxy Acrylate

Xiao Xin-yan Hao Cai-cheng

2009, 37(6):  47-52. 

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By using bisphenol-A epoxy resin （E-44） as the basic resin and acrylic acid （AA） as the modifier, solvent-based epoxy acrylate （EA） was synthesized, and the effects of reaction temperature, reaction time, catalyst content and inhibitor content on the AA conversion were discussed. Afterwards, waterborne epoxy acrylate （EB） was synthesized via the reaction of hydrophilic carboxy groups in maleic anhydride （MA） with the hydroxyl groups in EA. The results indicate that, when the mass ratios of the catalyst and the inhibitor to E-44 are respectively 1.5% and 0. 075% , the polymerization results in a AA conversion up to 98.27% at 95℃ for 4. 5h; and that the optimal temperature and time for EB synthesis are respectively 80℃ and 1.5 h. It is also demonstrated by the FT-IR spectra of EA and EB that the formation of EA is due to the ring-opening esterification of AA with E-44, while that of EB is due to the esterification of MA with the hydroxyl groups in EA.

Crosslinking Modification and Film Properties of Waterbrone Polyurethane-Acrylate

Qu Jin-qing Luo Chun-hui Chen Huan-qin

2009, 37(6):  53-57. 

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Polyurethane-acrylate （PUA） hybrid emulsions were crosslinked by aziridine （AZ） derivatives and polycarbodiimide （ PCDI）, respectively. FT-IR spectra of the emulsions show that the carboxyls （--COO-） in PUA react with AZ and PCDI in the crosslinking process. Test results of PUA film properties indicate that AZ greatly improves the water-, solvent- and pollution- resistance due to the increase of the gel content and its hardness, especially at a AZ-to-carboxyl mass ratio of 6. 60 ; and that PCDI remarkably improves the flexibility and freezing-thawing resistance, especially at a PCDI-to-carboxyl mass ratio of 16.67. Moreover, the TG curves show that both AZ and PCDI improve the thermal stability of PUA films.

Vacuum Pyrolysis of Flame-Retardant HIPS Plastic

Chen Yuan Chen Lie-qiang

2009, 37(6):  58-62,68. 

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The vacuum pyrolysis of waste TV housings （high impact polystyrene, HIPS） containing decabromodipheny） ether was carried out, and the pyrolysis characteristics of flame retardant and plastics in different heating conditions were investigated. Experimental results indicate that   as compared with the flash pyrolysis, the controlled two-step slow pyrolysis is beneficial to the selective distribution of brominated compounds, thus making a large amount of highly-brominated compounds accumulate in Step 1 but relatively fewer lowly-brominated compounds in Step 2;   the controlled pyrolysis significantly influences the products yield and distribution; and   more products with single-benzene ring can be obtained due to the slow heating, thus avoiding the occurrence of any polyreaction at high temperature.

Biological Engineering

Analysis and Identification of rDNA ITS Sequences of Alpinia officinarum Hance and Its Adulterants

Pang Qi-hua Yan Ping Zhao Shu-jin

2009, 37(6):  63-68. 

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In order to provide molecular data for the germplasm resource study on Alpinia officinarum （A officina rum） Hance and to identify A. officinarum Hance from its adulterants, the rDNA internal transcribed spacer （ITS） sequences of A. officinarum Hance and its adulterants were determined and analyzed by means of polymerase chain reaction （PCR）. Wild and cultivated A. officinarum Hance collected in different areas, and three adulterants including A. japonica （Thunb.）, A. chinensis （ Retz. ） Rosc. and A. galanga （ L. ）, were used as samples. The results of sequence analysis indicate that   the intraspecies sequence homology of A. officinarum Hance is up to 100% ;   there exist heterotic sites in all samples of A. officinarum Hance, and the proportion of the two bases in heterotic sites in the sample from Guangxi is different from that in other samples;   there are 61 variable sites （including 60 informative sites） in the 812bp sequences among A. officinarum Hance and its adulterants, with a homology of 96.32% ;   11 sites in the ITS1 and ITS2 regions can be used to identify A. officinarum Hance and its adulterants due to the great difference of the sites in different samples; and   some further researches should be performed because the classification results of A. officinarum Hance and its adulterants based on DNA sequences do not totally accord with those based on morphologic characteristics.

Submerged Fermentation of Trichoderma Koningii for High-Yield Cellulase and Xylanase

Zou Shui-yang Xiao Kai-jun Guo Si-yuan

2009, 37(6):  69-73. 

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In this paper, strain Trichoderma Koningii QF-02 was cultivated in submerged state to produce cellulases and xylanase, and the effects of carbon source, initial pH value and cultivation time for the production of enzymes were investigated by single-factor and orthogonal experiments. The results show that   the variety and nature of carbon sources play an important role in the enzyme production;   rice straw is a good carbon source due to its high performance and low cost;   the optimal shake-flask culture conditions are： 4 g of straw powder; （40 meshes）, 100mL of Mandels solution and an initial pH value of 4. 5; and   after the cultivation in the optimal conditions for 144 h, the enzymatic activities of filter paper cellulase, β-glucosidase, and xylanase respectively reach 1.49FPU/mL, 0. 39U/mL, and 174. 10U/mL. Moreover, by comparing the saccharification ability of the compos- ite enzyme produced by Trichoderma Koningii with that of a commercial cellulase, it is found that, when using the produced enzyme to treat alkali-pretreated straw and natural straw, the yields of total reducing sugar respectively increase by 55% and 40% , and the yields of glucose respectively increase by 33% and 12%.

Molecular Identification of Fallopia multiflora by PCR-RFLP Based on rDNA ITS Sequence

Zheng Chuan-jin Zhao Shu-jin Zhao Zhen-hua Guo Jun

2009, 37(6):  74-78，83. 

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The rDNA internal transcribed spacers （ITS） of Fallopia multiflora （F. multiflora） and its frequent adulterants, such as Fallopia multiflora var. cilliinerve, Pteroxygonum giraldiiwere and Cynanchum auriculatum, were sequenced and analyzed. The results show that in the ITS1 region, the divergences between F. multiflora and the three adulterants are respectively 6.91%, 18.10% and 42. 20%, while in the ITS2 region, the divergences are respectively 10. 00%, 19.40% and 43.90% ; and that the intraspecies ITS1 and ITS2 divergences of F. multi- flora are 0. 00% -2. 13% and 0. 00% -1.03% , respectively. Based on the divergences, a endonuclease Nsb I restriction site specific for F. multiflora was detected in the ITS2 region and was used for PCR-RFLP （Polymerase Chain Reaction and Restriction Fragment-Length Polymorphism） analysis. It is found that the PCR product from F. multiflora rDNA ITS can be cleaved by Nsb I into two fragments of about 531 bp and 109bp, while that from the adulterants cannot be cleaved, and that the PCR-RFLP map still retains the undigested original rDNA ITS pattern. It is thus concluded that the proposed PCR-RFLP method is effective in discriminating F. multiflora from its adulterants.

Rational Design of Site-Directed Mutagenesis of Lysine270 in Pichia sfipitis Xylose Reductase

Zeng Qi-kai Lin Ying Zhai Zhi-chen Lin Xiao-qiong Du Hong-li

2009, 37(6):  79-83. 

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Lysine270 has been found to be a key amino acid that forms the binding pocket of PsXR （Piehia stipitis xylose reduetase） with nieotinamide adenine dinucleo,Lide phosphate （NADPH） or with nieotinamide adenine dinucleotide （NADH）. In order to investigate the effect of Lysine270 on the PsXR coenzyme specificity, 19 XR mu- tants were produced by substituting 19 amino acids tot Lysine270, and the interaction between XR mutants and NAD^＋ or NADP ~ was assessed by means of homology modeling and molecular docking. Then, K270R and K270N mutants were chosen to perform the bioinformatic analysis. After being induced by isopropyhhio-β-d-galactoside （IPTG） in Escherichia coli （E. coli）, the xylose reduetases of wild type and mutagenesis were purified and finally used to investigate the enzymatic properties. The results show that   K270R mutagenesis reduces the binding capability of XR with NADP^＋ and results in an increase of Michaelis constant from 0. 025 mmol/L to 0. 050 mmol/L;   K270N mutagenesis makes XR bind with NAD^＋ only; and   the coenzyme dependence of rationally-designed K270N completely reverses from NADPH to NADH.

Construction of Heterologous Gene Expression System for Filamentous Aspergillus oryzae

Wang Bin Pan Li Guo Yong

2009, 37(6):  84-90. 

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The expression elements such as promoter, terminator and selectable marker gene were obtained by means of polymerase chain reaction （PCR）, with the genome DNA of Aspergillus oryzae （A. oryzae） RIB40 as the template. The elements were then cloned one by one into the plasmid pUC119 to construct a recombinant expression vector pNMA. Moreover, Rhizomucor miehei lipase （RML） was cloned into pNMA vector by following its promoter, with a pNMA-RML vector being obtained. For the transformation of A. oryzae niaD300, the pNMA-RML vector was linearized by Apa Ⅰ digestion, and an integrative positive transformant A. oryzae ONL1 was obtained. The supernatant of 7-day fermentation broth of A. oryzae ONL1 could hydrolyze to form a transparent clear zone on the tributyrin plate, and the enzyme activity measured by the base titration method reached 2.5 U/mL. It is demonstrated by the SDS-PAGE electrophoretogram of the superuatant that there is a typical RML band at 32 500, which represents a successful expression of RML in A. oryzae niaD300 and verifies the feasibility of the constructed heterologous gene expression system of A. oryzae.

Cloning of Cellobiohydrolase Ⅱ and Its Expression Encoding Gene from Trichoderma in Saccharomyces cerevisiae

Liu Ze-huan Quan Yan-cai Tang Gen-yun Gong Ying-xue Xiao Wen-juan Wang Jun-mei

2009, 37(6):  91-95. 

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Cellobiohydrolase Ⅱ （ CBH Ⅱ ） encoding gene cbh2 was obtained from Trichoderma viride by using the reverse transcription polymerase chain reaction （RT-PCR） method, and was then cloned into the integrative expression vector pSclKP of Saccharomyces cerevisiae to generate a recombinant plasmid pScIKP-cbh2. Afterwards, the plasmid was transformed by electroporation into Saccharomyces cerevisiae, and the transformants were screened and selected via G418 concentration gradient. Moreover, the protein expression of CBHⅡ was tested by means of SDSPAGE, and the enzyme activity of recombinant CBH Ⅱ was measured via CMC （ Carboxymethylcellulose Sodium） saccharification. Experimental results indicate that cbh2 gene coding 472 amino acid residues is composed of 1416 nucleotides, and that it submits the sequence to GenBank with an accession number of DQ864992. SDS-PAGE results show that the transformants result in a successful exocytosis of the recombinant CBHⅡ with a relative molecular mass of 70000. According to the CMC saccharification results, it is also found that the recombinant CBHⅡ with excellent thermal stability is of an activity up to 7.71 U/mL, and that it exhibits optimum catalytic activity at pH 5.0 and 65 ℃.

Mechanics

Investigation into Permissible Tensional Prestress of Prestressed Carbon Fiber-Reinforced Polymer

Guo Xin-yan Huang Pei-yan Zheng Xiao-hong

2009, 37(6):  96-100. 

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Bonding prestressed carbon fiber-reinforced polymer （carbon FRP, CFRP） plates to reinforced concrete （RC） beams can improve the working efficiency and force conditions of structures. However, larger tension prestress is not always better. In this paper, the permissible tensional prestress of the RC beams strengthened with pre- stressed CFRP is discussed in terms of the tensile strength of concrete, the shear strength of interface between concrete and CFRP, and the tensile strength of CFRP. Moreover, the permissible tensional prestresses in the concrete tensile-cracking, interface debonding and CFRP fracture before steel bar are respectively calculated. It is found that the permissible tensional prestress in interface debonding is the lowest.

Thermal Buckling of Functionally Graded Cylindrical Shells Subjected to Temperature Gradient

Huang Huai-wei Han Qiang Feng Neng-wen Fan Xue-jun

2009, 37(6):  101-106. 

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The thermal buckling behaviors of functionally graded cylindrical shells subjected to temperature gradients are investigated by using the energy method. The critical buckling condition is given by employing the Ritz method. Due to the coupling effect between material properties and temperature field, the critical temperature rise is obtained via an iterative algorithm. Moreover, the effects of two kinds of temperature gradients and temperature-dependent material properties on the critical temperature inhomogeneous parameter of functionally graded materials rise are discussed. Numerical results show that   the affects the critical temperature rise significantly only in a small scope ;   the effect of structure dimension on the critical temperature rise is greater than that of the inhomogeneous parameter;   the temperature-dependent properties must be considered in the thermal buckling analysis of functionally graded cylindrical shells, otherwise the critical temperature rise would be overestimated; and   if an assumed quadratic distribution is used to approximate the actual steady one-dimension thermal conduction, the critical temperature rise is likely to be underestimated in the condition of ceramic-rich thin shell, while being over- estimated in the condition of metal-rich thick one.

Analysis of Debonding Load-Carrying Capacity for RC Beams Strengthened with Prestressed FPR Under Bending Load

Xie Jian-he Huang Pei-yan Guo Xin-yan

2009, 37(6):  107-112. 

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Based on the bilinear bond-slip model of the interface between fiber-reinforced polymer （FRP） and concrete, the interfacial bonding shear stress in the intermediate cracking zone of the reinforced concrete （RC） beam strengthened with prestressed FRP laminates under bending load was analyzed, and the effects of the prestress level and the crack spacing on the debonding load-carrying capacity were discussed. Moreover, some theoretical models to predict the initial debonding and the debonding failure were established, with the critical slip corresponding to the interfacial fracture energy as the debonding criterion. Some experiments were finally performed to verify the models. It is indicated that the proposed models effectively predict the debonding and the corresponding load-carrying capacity of RC beams strengthened with prestressed FRP laminates under bending load, and that the debonding load-carrying capacity improves with the increase of the prestress level of FRP and with the decrease of the crack spacing.

Simulation of Freak Waves Based on Benjamin-Feir Instability

Hu Jin-peng Zhang Yun-qiu Zhu Liang-sheng

2009, 37(6):  113-116，123. 

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In this paper, the four-order nonlinear Schrodinger equations and the pseudo-spectral method are introduced to develop a 2-D numerical water flume based on the Benjamin-Feir instability of random wave trains, which is adopted to simulate the freak waves in deep water. In order to verify the efficiency of the numerical water flume, the propagation distortion of random wave trains with sideband disturbances in a 2-D water flume is then simulated. The numerical results are finally compared with the test ones, showing that the proposed model simulates freak waves well.

Analysis of a Nonlinear Generation Mechanism of Freak Waves

Zhang Yun-qiu Hu Jin-peng

2009, 37(6):  117-123. 

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According to the nonlinearity of freak waves and the sideband instability existing in the evolution of slowly-modulated periodic wave trains, the modified four-order nonlinear Schrodinger equation is employed to investigate the generation of freak waves and the variation of the corresponding complex wave-envelope spectra in the condition of sideband disturbances. Then, with the sideband instability being satisfied, the influences of the disturbance fre- quency bandwidth, the initial disturbance amplitude, the wave steepness and the nonlinear order on the develop- ment of sideband instability and on the occurrence of freak waves are analyzed. The results show that the occurrence of freak waves is due to the local exponential growth of the wave train because the carrier wave energy rapidly transfers to the neighbourly-unstable sideband components. Thus, energy transfer is a main reason for the occurrence of freak waves in the condition of sideband disturbances. It is also indicated that narrow frequency bandwidth, high disturbance amplitude, large wave steepness and strong nonlinearity all contribute favorably to the development of sideband instability and to the occurrence of freak waves.

Architecture & Civil Engineering

Experimental Study on RC Space Frames with Specially-Shaped Columns Subjected to Elevated Temperature

Wu Bo Jing Ya-tao

2009, 37(6):  129-135. 

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Three full-scale reinforced concrete space frames with specially-shaped columns were tested following the ISO834 standard heating process, and the influences of loading level and beam-to-column stiffness ratio on the failure mode, displacement-time curve and fire resistance of the specimens were investigated. Experimental results show that   the frame beams in the failure stage reveal a force pattern similar to catenary action;   the horizontal linear displacement of the frame joints in different directions are closely related to the axial expansion of the adjacent frame beam in the same direction;   when the frame beam keeps unchanged, the rotation of beam-tocolumn joints obviously decreases and even becomes opposite with the increase of column stiffness ratio in the middle and later stages of the test ; and   high loading levels make the specimen reach its fire resistance more easily, but the beam-to-column stiffness ratio has no obvious ,effect on fire resistance. It is thus concluded that the research on the fire resistance of a total structure is more convenient to the investigation of fire performance of the structure and its components.

Curvature Ductility of Reinforced Concrete Column with L-Shaped Crosse Section

Cai Jian Xu Xue-feng

2009, 37(6):  136-141，146. 

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By fully considering the influence of load angle on the curvature ductility of reinforced concrete （RC） columns with L-shaped cross sections, two kinds of curvature ductilities are defined. Then, the curvature ductilities of 10800 L-shaped columns are calculated by simulation, and the influences of different parameters on the curvature ductility are revealed. The results indicate that   both the neutral axis angle and the axial compression ratio have great effect on the curvature ductility;   the increase of volumetric percentage of stirrups generally improves the curvature ductility;   at a constant axial compression ratio, concrete strength and longitudinal steel strength only have slight influence on the curvature ductility; and   the curve of curvature ductility tends to be smooth when the L-shaped ratio decreases. The formulas to calculate the curvature ductilities of neutral axis angle and load angle are also presented in the paper.

Optimization of Cable Force for Cable-Stayed Bridges with Ultra Kilometer Span Under Dead Loads

Zhang Yang-yong Sun Bin Xiao Ru-cheng

2009, 37(6):  142-146. 

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In this paper, the cable force optimization of cable-stayed bridges with ultra kilometer span is equated as a nonlinear implicit optimization model. Then, by taking the minimum bending strain energy as the optimization object and by determining the nonlinear constraints according to the reasonable finished dead state, the model is solved via the projection gradient method, with all kinds of geometric nonlinearity being fully considered. Moreover, a finite element model of a cable-stayed bridge with the span of 1400 m is established based on ANSYS and is used to establish a mathematical optimization model of cable force. Calculated resuhs show that, after the optimiza- tion, the cable force slightly changes, yet the internal force state under dead load remarkably improves, the bending moment of girder and pylon as well as the deflection of girder significantly decreases, and the deformation of pylon migrates towards the shore side. All these variations contribute favorably to the concrete pylon under longterm loads.

Spatial Distribution Estimation of Wind Loads on Transmission Tower Based on High-Frequency Force Balance Tests

Xiao Zheng-zhi Li Zheng-liang Wang Zhi-song Yan Zhi-tao

2009, 37(6):  147-152. 

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Based on the basic principle of high-frequency force balance assumption of pulse wind loads, the spatial distribution of wind loads on numerical analysis is conducted on the crossing tower ZVK of the （HFFB） technique and the quasi-steady the transmission tower is estimated. Then, Xiangjiaba--Shanghai , Jinping--Sunan ＋ 800 kV ultra-high voltage （UHV） transmission project now being constructed, and the effectiveness of this proposed method is verified. Calculated results show that the proposed method extends the HFFB test reliably and feasibly because it well reveals the spatial distribution of wind loads on the transmission tower.