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Table of Content

    25 March 2008, Volume 36 Issue 3
    Chemistry & Chemical Engineering
    Li Jing Lei Xiao-yu Kang Zhong-xian Xia Qi-bin Li Zhong
    2008, 36(3):  1-5. 
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    Polymethylmethacrylate-butylmethacrylate (PMMA-BMA) resin was prepared by means of microwave irradiation. The morphologies and textural properties of the product were then characterized using SEM. Moreover, the effects of monomer proportion, the initiator dosage, the dispersant dosage, the cross-linking agent dosage and the microwave power on the oil fume-adsorbing capacity of the resin were investigated. The results show that the adsorption ratio is up to 0. 191 at 60℃ when the mass ratio of MMA to BMA is 0.8:1 and when the dosages of the initiator, the dispersant and the cross-linking agent are respectively 0. 4%, 0. 3% and 0.35%. As compared with the traditional water-bath heating, microwave irradiation shortens the reaction time from 6 h to 2 h and results in a greater adsorption capacity even than those of the activated carbon and the commercial high-capacity G-1651 resin.

    Zhao Zhen-xia Li Zhong Xia Qi-bin Xu Jin-fang
    2008, 36(3):  6-11. 
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    In this paper, thermo-sensitive poly (N-isopropylacrylamide) (PNIPAAm) hydrogels were first synthe-sized in the presence of microwave irradiation. The structure of the product and its effect on the swelling properties were next investigated. Then, the morphologies of the hydrogels in swollen and dry conditions were respectively characterized using SEM. Finally, the swelling properties and the corresponding kinetics of the hydrogels were revealed. The results show that, as compared with the hydrogels produced by means of water-bath heating, the hydrogels produced by microwave irradiation possess more and larger pores, which may result in higher swelling ratio below the lower critical solution temperature (LCST, tc) , lower swelling ratio above the LCST, faster swelling and all-swelling rates.

    Hu Xiao-yong Guo Si-yuan Chen Huan-qin
    2008, 36(3):  12-15. 
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    The free toluene diisocyanate (TDI) in the curing agent TDI-TMP (Trimethylol Propane) of polyure-thane was separated in laboratory by means of high-vacuum two-stage thin-film evaporation. The corresponding pi lot-scale investigation was then performed to analyze the effects of feeding flow and evaporation temperature on the separation efficiency. The results show that, when the separation is performed with a feeding flow of 25 kg/h, a first-stage evaporation pressure of 5000 Pa at 130 ℃ and a second-stage evaporation pressure of 80 Pa at 180 ℃, the content of free TDI in the separated curing agent is less than 0.5%, and the solid and NCO contents are respectively more than 75% and 11.8%, meaning that the free TDI is effectively separated.

    Hong Meng-na Deng Xian-he Huang Kuo Li Zhi-wu
    2008, 36(3):  16-19,25. 
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    In order to enhance the heat transfer, a method that combines the converging-diverging tube and the spaced twisted tape was presented, and the heat transfer characteristics and flow resistances of four converging-diverging tubes with spaced twisted tapes being inserted in four different spaces were experimentally investigated. The results were then compared with those of the smooth circular tube with or without the twisted tape and the converging-diverging tube without twisted tape. Experimental results indicate that the heat transfer is more greatly enhanced with the Reynolds number increasing in the range of 3400 to 20000, and that, when the twisted tapes with a length of 68 mm and a rotation angle of 180 are inserted in the converging-diverging tube with a space of 700 mm, the tube possesses the best heat transfer performance and the valuation factor of heat transfer respectively increases by 21% , 15% and 16%, as compared with those of the three other above-mentioned tubes. It is thus concluded that the inserting of spaced twisted tapes may greatly enhance the heat transfer performance of the converging-diverging tube.

    Xiong Yong-qiang Li Ya-jun Hua Ben
    2008, 36(3):  20-25. 
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    In this paper, the exergy loss and saved energy in the cold energy utilization of liquefied natural gas (LNG) by means of such technologies as air separation, cryogenic comminution and cold warehouse are calculated and analyzed. Then, a principle of "parallel temperature and gradient utilization" is presented to integrate and optimize the cold energy utilization of LNG. The results show that, with the integration of the three above-mentioned technologies, the exergy lost of cold energy utilization of LNG decreases by more than 55.7%, as compared with that only with a single technology, and that the largest amount of energy saved in the cold energy utilization with the integrated system for per ton LNG reaches 349.0 kW·h, which is 1.56 times that only with the air separation equipment. It is thus concluded that the integration of the three above-mentioned technologies may greatly improve the utilization efficiency of LNG cold energy.

    Yang Dong-jie Qiu Xue-qing Pang Yu-xia LouHong-ming
    2008, 36(3):  26-31. 
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    In order to improve the compressive strength and seepage resistance of cement mortar, the modified lig-nosulfonate additive GCL1-M was prepared, with the calcium lignosulfonate (CLS) from the black liquor of paper-making as the main material. The physical and mechanical properties as well as the microstructure of the mortar were then investigated. The results indicate that, with the addition of GCL1-M, the water-reducing ratio of the mortar reaches 30%, and the 28-day compressive strength and seepage pressure of the mortar with 0. 30% of GCL1-M are respectively raised by 20% and 230%. The nitrogen adsorption and SEM measurements show that the addition of GCL1-M decreases the heat-releasing rate of cement hydration and the pore size of the mortar, but increases the seepage resistance of the mortar. Moreover, the results of adsorption performance test and environmental scanning electron microscopy reveal that the GCL1-M may be absorbed on the cement surface in a network form. Thus, the static repelling force between cement particles increases and the dispersive and water-retention performances of GCL1-M on the mortar improve, which may result in the improvement of the seepage resistance and the compressive strength of the mortar.

    Zou Hua-sheng Chen Jiang-fan Chen Wen-biao
    2008, 36(3):  32-36. 
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    In this paper, highly dispersed water-in-oil (W/O) microemulsion with uniform drop size was prepared by using the composite surfactant Tween80-Span80 and by taking cyclohexane as the oil phase. Then, for the purpose of obtaining the maximum solved water, the influences of such factors as the surfactant composition, four alcohol cosurfacants, the temperature and the salinity on the microemulsion stability were investigated by means of visual inspection and conductivity measurement. The optimum conditions for preparing the microemulsion were finally obtained. Experimental results show that, when the mass fraction of Tween80 in the composite surfactant is 60% and the mass ratio of the consurfactant ethanol to the composite surfactant (Km) is 1.0, the best W/O microemulsion system as an ideal microreactor can be prepared, and that, with the increase in temperature, the stable region of the microemulsion in phase diagram decreases and the influence of salinity on the region becomes slight.

    Wu Yue-huan Liu Shu-mei Zhao Jian-qing
    2008, 36(3):  37-40. 
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    Acrylate micro-latex containing 1.5% (mass fraction, below the same) emulsifier and 50% polymer with a particle size of 35.6nm and a polydispersity index of 0. 133 was prepared by means of seed emulsion poly- merization. The particle size and its distribution of the micro-latex affected by the feeding modes of the monomer, the emulsifier and the initiator were then investigated. The results indicate that the dropwise addition may result in a large quantity of micelles, a high nucleation rate and a small particle size, and that the particle size decreases with the content increment of the emulsifier and the initiator pre-added before the polymerization.

    Zhang Teng-yun Zhong Li Fan Hong-bo Chuang Karl
    2008, 36(3):  41-44,49. 
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    Nonaqueous peracetic acid was synthesized in a tubular packed reactor by means of acetaldehyde liquid-phase oxidation in acetone, and was used for the homogeneous oxidative desulfurization of hydrogenized diesel fuel. Then, the oxidative desulfurization efficiency, which was influenced by the desulfurization temperature and time and by the dosages of the extractant(acetic acid solution with 5% water) and peracetic acid, was studied. Experi- mental results show that, when the ratio of the extractant to the oxidized diesel fuel is 2:1 and the dosage of peracetic acid product is two times that of the theoretical one, after the oxidative desulfurization for 30 min at 50 ℃ , the sulfur content in the hydrogenized diesel fuel reduces from 295.8 mg/kg to 13.4 mg/kg, the desulfurization efficiency rises to 95.5% , and the diesel fuel yield reaches 93.8%. It is thus concluded that the sulfur content of the des-ulfurized diesel fuel with homogeneous oxidation by peracetic acid can meet the requirements of the new international standard because it is less than the limitation of 15 mg/kg.

    Luo Fa-xing Huang Qiang Zhang Le-xing Li Lin
    2008, 36(3):  45-49. 
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    The rheological and viscosity properties as well as the acid and salt tolerances of acetylated distarch adipate (ADA) waxy potato starch paste were investigated by using the Brabender viscographer and the rotary visco- simeter. The results show that, after the acetylated distarch adipate modification, the setout gelatinization temperature of ADA waxy potato starch paste increases from 64.7 ℃ to 67.3 ℃, while the peak viscosity and the relative breakdown strength decrease respectively from 919BU to 652BU and from 76.4% to 27.6%. Moreover, it is found that the viscosity stability, shear tolerance, retrogradation property and acid and salt tolerances of the paste are all improved in varying degrees.

    Li Hao Song Hui-yu Liao Shi-jun
    2008, 36(3):  50-54. 
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    Nano-sized cobalt particles with the diameter of 2 nm were prepared via an organic colloidal process, with sodium formate, ethylene glycol and sodium citrate respectively as the reducing agent, the solvent and the complexing agent. The effects of sodium citrate addition on the yield, crystal structure, particle size and size distribution of the prepared nano-sized cobalt particles were then investigated. The results show that the average particle diameter decreases from 200 nm to 2 nm when the molar ratio of sodium citrate to cobalt chloride changes from 0 to 6, that the sodium citrate plays a crucial role in the controlling of size distribution of the nano-sized particles, and that the size distribution of the particles without sodium citrate addition ranges from tens of nanometers to 300 or 400 nm, while that with sodium citrate addition is limited in the range of (2±0.25) nm. Moreover, it is found that the addition of sodium citrate as a complexing agent may decrease the yield of the nano-sized cobalt particles.

    Li Hai-long Chen Jia-chuan Zhan Huai-yu Fu Shi-yu Yang Gui-hua Liu Meng-ru
    2008, 36(3):  55-59. 
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    In this paper, the influence of xylanase treatment on wheat straw pulp was investigated. The results indicate that the the surface morphology and chemical composition of xylanase treatment may change the surface morphology and chemical composition of wheat straw pulp, soften the pulp fiber and roughen the fiber surface with obvious crackles and flakes. Moreover, the ESCA and SEM results show that the lignin coverage on the pulp surface increases after the xylanase treatment, and that the coverage also increases with the dosage of xylanase.

    He Dao-hang Ma Ying-qi Hu Ai-xi Xia Lin Ou Xiao-ming
    2008, 36(3):  60-63. 
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    4-arylthiazol-2-amines were synthesized by the reaction of a-bromoarylalkyl ketone with thiourea, and further reacted with salicylal to give nine 4-aryl-2-benzyliminothiazoles. The structures of all new compounds were confirmed by 1 NMR spectra. The results of preliminary bioassay show that the title compound (E)-2-((4-(3-(triiquoromethyl) phenyl) thiazol-2-ylimino)methyl) phenol exhibits an inhibition rate of 60.0 % against Rhizoctonia solani at a concentration of 500 mg/L and that the inhibition rates of compounds (E)-1-(2-chloro-4-(4-chlorophe-noxy)phenyl)-2-(2-(2-hydroxybenzylideneamino) thiazol-4-yl) ethanone and (E)-2-((4-(3-chlorophenyl) thiazol-2-ylimino) methyl) phenol against Sclerotinia sclerotiorum are 65.4% and 56.1%, respectively.

    Wang Hai-yan Cui Chun Zhao Mou-ming Shen Guang-lin Rao Cuo-hua
    2008, 36(3):  64-68. 
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    In this paper, tobacco polyphenols were extracted through microwave-assisted technology, and their main components were identified by the combination of hgh-performance liquid chromatography, photodiode array detector and mass spectrography. Moreover, the effects of microwave power, methanol content, extraction time and material-to-liquid ratio on the polyphenols yield were investigated. It is seen from the response surface analysis (RSA) that, in the optimum extraction conditions for tobacco polyphenols, that is, With 53 % methanol as the solvent, a material-to-solvent ratio of 1:11, a microwave power of 560 W and an extraction time of 70 s, the yield of total to- bacco polyphenols reaches 22.38 mg/g (dry weight). HPLC-PDA-MS results demonstrate that the main components in tobacco polyphenols are chlorogenic acid and rutin.

    Wan Xiao-fang Wang Xiao-jun
    2008, 36(3):  69-72,94. 
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    The co-monomers of ethyl methylacrylate-trimethylammonium chloride ( DMC ) and acrylamide (AM) were grafted onto carboxymethyl guar gum (CMGG) to synthesize amphoteric guar gum (AC-GG), with potassium permanganate/sulfuric acid as the initiator. The effects of the concentrations of the initiator, the monomer and CMGG as well as the degree of substitution (DS) of CMGG on the grafting copolymerization were then investigated. The results show that, in the optimal conditions, the polymerization conversion ratio, the grafting ratio and the grafting efficiency are respectively 92.9%, 797%and 84.7%. Moreover, it is found that potassium permanganate is a high-efficiency initiator because the apparent activation energy calculated by Arrhenius equation is up to 13.28 kJ/mol. The grafting is further characterized by means of 13C-NMR.

    Environment Science & Technology
    Zhou Shao-qi Zhang Hong-guo
    2008, 36(3):  73-76. 
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    A set of 4.5-L upflow anaerobic sludge blanket (UASB) bioreactor was used to perform the anaerobic ammonium oxidation (ANAMMOX) and denitrification of leachate generated from a landfill site in Guangdong, China. The results show that there exists a synergistic effect of ANAMMOX and denitrification in the UASB bioreactor, that the average removals of NH4^+ -N and NO2-N from the 120th day on are respectively 94.79% and 98.17%, that the maximum and average CODcr removals are respectively 51.68% and 23.51% , and that the average removal of volumetric loading reaches 84.53 mg/(L·d).

    Xiao Jun-xia Wei Chao-hai Hu Ji-jie Ren Yuan Wu Chao-fei
    2008, 36(3):  77-82. 
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    Ten dyes with different structures were used to investigate the rules of photocatalytic oxidation degradation of dyes in TiO2/UV system. The concentration, total organic carbon (TOC) and well as the concentration variations of NO2-,NO3-,SO42 and Cl-in the solution were that most dyes have the similar degrees of degradation and mineralization, except the pH value of the solution as all tested. The results show cationic blue FGL with the strongest adsorption capability, the highest degradation rate and the lowest mineralization rate, that the pH values of most dyes at first decrease and then increase with the exception that the pH value of the reactive brilliant blue X-BR with the lowest degradation velocity continuously decreases, that less than 5 % of N in the solution turns into NO2-andNO3-and 15%-60% of--SO3Na and  Cl-respectively turn into SO42 and Cl-after the reaction, that both the naphthalene ring and the striazine structure are more stable than the benzene ring, that the naphthalene ring joined to one azo bond is more stable than that joined to two symmetrical azo bonds, and that the benzene ring joined to the azo bond is more stable than that being far from the azo bond.

    Wu Hai-zhen He Qin-cong Wei Chao-hai Wang Ju-fang Liang Shi-zhong
    2008, 36(3):  83-88. 
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    A bacterial strain OCNB-1 was isolated from the activated sludge in the wastewater treatment plant of a chemical factory, with o-chloronitrobenzene as the sole carbon, nitrogen and energy sources. The strain was then identified as Pseudomonas putida by the automatic biometrical system WSVTK-R07.02 and the 16S rDNA sequence analysis. Afterwards, the strain was applied to the degradation of 1.07 mmol/L o-chloronitrobenzene at a rotation speed of 120r/rain, a pH value of 8.0 and a temperature of 32℃ , finding that about 80% of o-chloronitrobenzene is degraded by the strain after 42 h. The results of plasmid detection indicate that there exists a plasmid strip in OCNB-1 strain, the plasmid size of which is proved to be about 32kbp according to the single cutting results by using 7 kinds of restriction enzymes. The results of antibiotic resistance reveal that the resistances of the strain to erythromycin, ampicillin and benzylpenicillin sodium have nothing to do with the plasmid, while those to rifampicin and chloramphenicol are related to the plasmid. Moreover, as the obtained plasmid can be transferred to Pseudomonas. stutzeri through bacterial conjugation and the conjugant can grow by using o-chloronitrobenzene as the sole carbon, nitrogen and energy sources, it is concluded that the plasmid carries the gene for o-chloronitrobenzene degradation.

    Li Wei-guo Ma Fang Wei Li Zhang Da-wei Liu Feng Wang Guang-yu Su Jun-feng
    2008, 36(3):  89-94. 
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    In order to investigate the application of moderately halophilic bacterium to the treatment of hypersaline organic tanning wastewater, a halophilic bacterium YS-1 was isolated from the salt water of a salina. The atomic force microscopy (AFM) observation, the physiologic-biochemical index measurement, the whole-cell fatty acid analysis and the 16S rDNA sequence homology identification for the bacterium were then carried out. The results show that the closest relative of YS-1 strain is Halomonas sp. (AB167061), meaning that YS-1 strain is a novel moderately halophilic species of Halomonas sp.. Moreover, according to the results of hypersaline tanning wastewater treatment by the identified bacterium combined with the biological activated carbon (BAC) technology in a sequencing batch reactor (SBR), it is found that, for the wastewater with an initial salt content of 9.3% and an initial CODer of 1378mg,/L, the CODcr removal reaches 86% after the treatment for 168h, and rises to 98% after 216h. It is thus concluded that YS-1 strain can enhance the treatment of hypersaline tanning wastewater, and that a "halophilic-BAC technology" combining the screened bacterium and the BAC technology is feasible in the treatment of hypersaline tanning wastewater.

    Hou Yi Li You-ming Zheng Zhen-shan
    2008, 36(3):  95-98. 
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    In this paper, the pollutants in the wastewater from the manufacture of papermaking-reconstituted tobacco slice were analyzed via common chemical assays, FTIR and gas chromatography-mass spectrography (GC-MS). The results show that the wastewater is of complicated pollutants, high suspended sediment concentration, acidity pH and good biodegradation property, that the pollutants mainly include the hydrolysates of cellulose, hemicellulose and liglin, and that there exist some matters with low molecular mass, some non-volatile organic acids, nicotine, tar and phenols in the wastewater, which darkens the wastewater. The complete biodegradation of the above-mentioned components is the key to the successful wastewater treatment during the manufacture of papermaking-reconstituted tobacco slice.

    Architecture & Civil Engineering
    Zhang Yu Meng Qing-lin Chen Yuan-rui
    2008, 36(3):  99-103. 
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    A simulated experimental environment of small-step periodically-controlled climatic parameters, such as air velocity, temperature, humidity and heat radiation, is important to the repeated experiments of thermal performance for building envelope structures, and is effective in the investigation of passive evaporative cooling effect of porous materials in natural climate. This paper develops a dynamic laboratory of hot-humid climatic wind tunnel, in which the low-speed air flow is adjustable and the infrared light, the humidifier as well as the heating/cooling facility are set up, thus primarily implementing the simulation and control of such natural environmental elements as solar radiation, air velocity, temperature and humidity. The PC-based measurement and control system of the hot-humid climatic wind tunnel uses a data collector block to manage the data collection, the data feedback and the control instruction output. Thus, the environmental elements can be real-timely examined, numerically displayed and effectively saved. It is shown from special mechanism calibration that the control precisions of solar radiation, air velocity, temperature and humidity in the developed dynamic laboratory are respectively ±10 W/m2,±0.2 m/s, ±0.5℃ and ±5%.

    Su Cheng Xu Rui Fan Xue-ming
    2008, 36(3):  104-107,120. 
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    An arbitrary 8-node element with curved sides is proposed for the discretization of 2D random fields, and the formulations of second-order stochastic characteristics are presented for the local averages of the random field based on the proposed element. Explicit matrix expressions of the relation between the covariance matrix of the local averages and the covariance matrix of the random variables at Gaussian points are then established by means of coordinate transformation and Gaussian numerical integral. The proposed element is found suitable for the discretization of random fields with curved edges, with straightforward and practical calculation of the stochastic characteristics for local averages. Moreover, the thin-plate bending, the plane stress and the plane strain problems are taken as examples to reveal the effects of correlation structure and correlation length on the displacement deviation via the proposed discretization method and the Monte-Carlo method, the choice of Gaussian points being finally considered.

    Pan Jian Chen Hong-bing
    2008, 36(3):  108-113. 
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    The conventional numerical simulation applied to the excavation of foundation pit may result in inaccurate excavation deformation because it does not fully integrate the case history with the observed performance data. The self-learning method for engineering simulation is a neural network-based inverse analysis technique that combines the finite element analysis and the artificial intelligence. The excavation simulation process includes three steps : (1) obtaining the case observation data, (2) calculating the soil stress and measuring the soil deformation, and (3) performing the finite element analysis using the obtained data and predicting the deformation in the following excavation stage. This method possesses the self-adaptability and the self-organization, learning, association, fault tolerance and anti-interference abilities of neural network and can reveal the nonlinear correlation between the historical information and the field observed data. The application of the self-learning method to a simulated case and three historical cases indicates that the method is feasible in the excavation simulation of foundation pit.

    Ji ring Wu Ai-ming Wang Yan-jun Han Xiao-lei
    2008, 36(3):  114-120. 
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    This paper presents a new kind of concrete-filled steel tube (CFST) connection with steel ring and steel brackets through tubular core, which is of the shape similar to the common reinforced concrete beam-column joint and meets the demand of architectural design well. The interior and the side connections are then experimentally investigated. The results prove that the ring steel bar and radial steel bar in slab can well control the crack development of connection, and that the working behavior of the longitudinal bar connected with screwed cannula in the beam under reciprocating load meets the demand of seismic design well. The deformation, strain, crack development, failure mechanism and ultimate bearing capacity of the presented CFST connection are also analyzed in this paper, and a nonlinear FEA simulation is finally carried out, the results further revealing the mechanics of the connection.

    Hou Jia-jian Han Xiao-lei Xie Zhuang-ning
    2008, 36(3):  121-127. 
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    In this paper, first, a wind tunnel test was carried out to investigate the characteristics of wind load on the surface of a twin-tower corridor-connected tall building with complex geometric plan. Next, a single-tower test was performed for comparison. Then, the total wind force along the coordinate axis was calculated by integrating the wind pressure along the plan circumference. The results were finally inversly calculated to obtain the global shape coefficient. It is found that the wind pressure slightly increases with the elevation and the global shape coefficient continuously decreases, that the wind angle of single tower corresponding to the maximum shape coefficient is 15 away from the coordinate axis, that the x-direction shape coefficient of the upstream tower in the twin towers is slightly less than that of the single tower and that of the downstream tower is 50% less than that of the single tower, that the y-direction shape coefficient is slightly less than that of the single tower, and that the shape coefficient of space corridor is about 2. 0 in y direction and zero in x direction. The analyses demonstrate that the block of wind by the upstream tower may decrease the global shape coefficient of the downstream tower and the downstream tower may slow down the wake flow and decrease the negative pressure on the back of the upstream tower, thus slightly redu- cing the corresponding shape coefficient. However, the local wind pressures of the upstream and the downstream towers both increase due to the complicated wake flow. The authors also present some design values of wind load for similar projects based on the analyzed and tested results.

    Yang Chun Cai Jian Chen Guo-dong Luo Qi-zhi Zuo Zhi-liang
    2008, 36(3):  128-133. 
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    Concrete-filled rectangular steel tubular (CFRST) truss is suitable for long-span structures because it possesses excellent mechanical properties due to the concrete-filled steel tube. In this paper, the experiments of two large specimens were performed to make a comparison between the CFRST truss with cantilever and the rectangular steel tubular (RST) truss. The destruction mode, deformation and ultimate strength of the CFRST truss were then investigated. Experimental results show that, as compared with the RST truss, the CFRST truss is of higher stiffness, ultimate strength and smaller deformation. The filled concrete can effectively prevent the steel tube from locally buckling, and the destruction mode of the specimens is controlled by material strength. The moments of the chord members and the web members at the joints where the members are connected by direct welding are quite large, so that the effect of the moments on the ultimate strength of the joints cannot be ignored in engineering design.

    Shao Jian-tao Liu Jing Zhao Jia-ning Fu Zhi-peng Zhang Wen-wu
    2008, 36(3):  134-139. 
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    In this paper, some problems in the current researches on external convective heat transfer of buildings are analyzed, and a new naphthalene sublimation method is developed for the field measurement of external convective heat-transfer coefficient (CHTC) of building roof. Experimental results show that the CHTC of the roof is in a positive linear relation with the representive velocity of wind flowing on the roof, and that the CHTC ranges from 5 to 50 W/(m2·K) at a representive wind velocity of less than 5.6 m/s. Analytical results also indicate that the fluctuation of the temperature on the surface of naphthalene test specimens and the temperature difference between the air and the roof sligthly affect the measurement resluts. Moreover, by considering the influence of building dimensions and by choosing the distance from the roof edge to the measurement point as the representive length, a dimensionless corelation about the external convective heat-transfer characteristics is obtained. The effectiveness of the proposed naphthalene sublimation method is finally validated by a heat balance experiment.

    Du Jiang Han Da-jian
    2008, 36(3):  140-146. 
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    With the rapid development of demands for transportation, highway bridges are under much heavy operating load that overruns the design standards, which results in fast degradation of the highway bridges completed in 1990's. In order to make the best use of the limited funds for bridge maintenance, an improved model is represented to optimize the maintenance strategy of bridges. This model uses the "expected life" as the optimization objective instead of various performance indices, and combines the optimization objective with the conventional objective "cost" to construct a bi-objective optimization problem. In this model, the difference in the performance and the degradation rate at the end of the horizon period in different strategies is considered, and the demands for various performance indices are unified as the objective "expected life". The authors also introduce two efficiency indices, namely the "life per cost" and the "cost per year" for the decision of maintenance strategy. Several examples are finally presented based on the data of highway bridge components.

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