Study on Heat Transfer at Steel-Concrete Interface of Shield Tunnel Composite Segment under Fire

Wenjun Zhang,Chi Zhang,Gaole Zhang 대한토목학회 2022 KSCE Journal of Civil Engineering Vol.26 No.8

During the actual construction process and operation period of the tunnel project, due to improper construction operation techniques, long-term load effects, concrete shrinkage and creep, etc., it is difficult for the steel plate and concrete to be in close contact, and there is a void between the two. This results in discontinuous heat transfer. In order to seek the real heat transfer state between steel plate and concrete under high temperature of fire, this paper mainly adopts the methods of model test, theoretical analysis and numerical simulation to study the heat transfer of composite segment steel plate and concrete contact interface under high temperature of fire. The heat transfer process between steel plates and concrete with different thicknesses at different void heights is studied, the temperature time history curve is obtained, and the temperature at the interface and the transition heat transfer coefficient are calculated. The results show that within 5 minutes of the fire, the heat is basically absorbed by the steel plate, the temperature of the concrete is basically unchanged, and the transition heat transfer coefficient rapidly decreases from 1.0 to about 0.2 − 0.3. When the fire continues to develop, the concrete temperature increases rapidly and the transition heat transfer coefficient increases. With the increase of the void height, the temperature difference between the concrete interface and the steel plate interface gradually increases. According to the data fitting, the relationship between the concrete interface temperature T and the time x and the void height t is obtained. It can be used to calculate the temperature of the concrete interface at a certain moment when the composite segments with different clearance heights are on fire, which has important engineering application value for reducing the adverse consequences of shield tunnel fire.

Numerical and Experimental Studies on the Effects of the TBM Cutter Profile on Rock Cutting

Wenjun Duan,Longguan Zhang,Mengqi Zhang,Yemao Su,Jiliang Mo,Zhongrong Zhou 대한토목학회 2022 KSCE JOURNAL OF CIVIL ENGINEERING Vol.26 No.1

This paper explores the effect of the profile of tunnel boring machine (TBM) cutters on the rock cutting performance via the use of a particle flow discrete element model. Two of the most commonly used cutters, namely a flat-tip cutter and a circular-tip cutter, are considered in the study. Reduced-scale rotary rock cutting experiments are performed to verify the key conclusions obtained by the numerical analysis. The results from both the simulations and experiments indicate that, at the same penetration depth, the volumes of rock chips produced by the two cutters are similar, but the normal force of the circular-tip cutter is much smaller than that of the flat-tip cutter, leading to a lower specific energy. Contact analysis implemented by a finite element model further reveals that the stress field caused by the circular-tip cutter has a higher magnitude and is concentrated in a smaller area, indicating that the circular-tip cutter could penetrate the rock with lower normal force and produce less rock powder, which could avoid excessive rock broken.

DNA-functionalized single-walled carbon nanotube-based sensor array for gas monitoring

Wenjun Zhang,Yu Liu,Ming. L Wang 국제구조공학회 2013 Smart Structures and Systems, An International Jou Vol.12 No.1

Nine deoxyribonucleic acid (DNA) sequences were used to functionalize single-walled carbon nanotube (SWNT) sensors to detect the trace amount of methanol, acetone, and HCl in vapor. DNA 24 Ma (24 randomly arranged nitrogenous bases with one amine at each end of it) decorated SWNT sensor and DNA 24 A (only adenine (A) base with a length of 24) decorated SWNT sensor have demonstrated the largest sensing responses towards acetone and HCl, respectively. On the other hand, for the DNA GT decorated SWNT sensors with different sequence lengths, the optimum DNA sequence length for acetone and HCl sensing is 32 and 8, separately. The detection of methanol, acetone, and HCl have identified that DNA functionalized SWNT sensors exhibit great selectivity, sensitivity, and repeatability with an accuracy of more than 90%. Further, a sensor array composed of SWNT functionalized with various DNA sequences was utilized to identify acetone and HCl through pattern recognition. The sensor array is a combination of four different DNA functionalized SWNT sensors and two bare SWNT sensors (work as reference). This wireless sensing system has enabled real-time gas monitoring and air quality assurance for safety and security.

Tillage and Overseeding Pasture for Winter Forages Production in Lowland Areas of South-west China

Zhang Wenjun,Yang Chunhua,Zhang Xinquan,Cheng Lingzhi,Su Shiming 한국초지조사료학회 2009 한국초지조사료학회 학술대회논문집 Vol.2009 No.08

In lowland areas of south-west China, especially in late winter and early spring, animal nutrition is so poor t㏊t some animals die because of shortages of forage. Farmers in these areas are finding it difficult to conserve sufficient forage. It is a big challenge to find a new strategy to solve the problem, so tillage systems and overseeding of a perennial pasture can influence the performance of winter annual forage production in the future.

Intercalation of Europium Inclusion Complex of β-Cyclodextrin into Layered Double Hydroxides Through Layer-By-Layer Assembly and Its Luminescent Properties

Wenjun Zhang,Yi Chen,Yanlin Li,Sumin Guan,Yan Chen,Qian-Qian Yang,Lu Liu,Qing-Chen Xue,Yu-Cui Guang 성균관대학교(자연과학캠퍼스) 성균나노과학기술원 2017 NANO Vol.12 No.10

"In this work, organic–inorganic hybrid ultrathin transparent films (UTFs), produced by layer-by-layer (LBL) assembly of the europium inclusion complex of β-cyclodextrin ( β-CD) and Mg–Al layered double hydroxide (MgAl–NO3–LDHs) nanosheets, are reported. UV-visible (UV-Vis) absorption and fluorescence spectroscopy show orderly growth of the europium inclusion complex of β-CD/layered double hydroxide (EICC/LDH) films with an increasing number of deposition cycles. X-ray diffraction and scanning electron microscopy measurements indicate that the films feature periodic layered structures with uniform surface morphology. Moreover, when EICC is assembled with inorganic rigid LDH nanosheets, the lifetimes are prolonged due to the isolation effect, and the UTFs are transparent with high brightness, which indicate that these films could serve as new optical materials."

Study on Stress and Deformation of Bolt Joints of Shield Tunnel under Static and Seismic Action

Wenjun Zhang,Qi Zhang,Wenzhen Cao 대한토목학회 2021 KSCE Journal of Civil Engineering Vol.25 No.8

In this paper, three dimensional numerical models for shield tunnel lining bolted joints, which are suitable for seismic excitation and static pressure of surrounding rocks, are established respectively. The influence of different seismic directions on the stress and deformation characteristics of bolted joints is studied in detail. Based on the existing tests, the numerical model of double segment bolted joint was verified. Then, the mechanical properties of the lining joint with different bolted forms were explored, and the applicability analysis of connecting bolted under seismic excitation and surrounding rock static pressure was improved. The results showed that: Compared with the deformation of the circumferential joint under the earthquake transverse excitation, the deformation of the circumferential joint under the longitudinal earthquake excitation is relatively more significant, and the deformation of the inclined bolted joint is the largest. Under the static pressure of surrounding rocks, the opening of the inclined bolted joint is the smallest, but the dislocation is the largest. The opening of the bent bolted joint is the largest, while the dislocation is the smallest. The stress value of the inclined bolted is the largest, whereas the stress value of the bending bolted is the lowest.

Synthesis, Characterization and Photocatalytic Activity of Reduced Graphene Oxide-Ce/ZnO Composites

( Wenjun Zhang ),( Jinfeng Zhao ),( Xuefeng Zou ) 한국화학공학회 2016 Korean Chemical Engineering Research(HWAHAK KONGHA Vol.54 No.1

A series of Ce-doped ZnO (Ce/ZnO) nanostructures were fabricated using the co-precipitation method, then a simply nontoxic hydrothermal approach was proposed for preparation of reduced graphene oxide (rGO)-Ce/ZnO composites. The synthesized composites were investigated by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR), photoluminescence spectroscopy (PL), electrochemical impedance spectroscopy (EIS), UV-vis diffuse reflectance spectroscopy (DRS) techniques and Raman pattern. The as-synthesized rGO-Ce/ZnO composites showed high photodecomposition efficiency in comparison with the rGO-ZnO, Ce/ZnO, pure ZnO under UV, visible-light and sunlight irradiation. The degradation of methylene blue (MB) (10 mg/L, 100ml) by 95.8% within 60 min by using rGO-2 (10 mg) under sunlight irradiation was observed. The repeated use of the rGO-2 was investigated, and the results showed almost no decay in the catalytic activity.

DNA-functionalized single-walled carbon nanotube-based sensor array for gas monitoring

Zhang, Wenjun,Liu, Yu,Wang, Ming. L Techno-Press 2013 Smart Structures and Systems, An International Jou Vol.12 No.1

Nine deoxyribonucleic acid (DNA) sequences were used to functionalize single-walled carbon nanotube (SWNT) sensors to detect the trace amount of methanol, acetone, and HCl in vapor. DNA 24 Ma (24 randomly arranged nitrogenous bases with one amine at each end of it) decorated SWNT sensor and DNA 24 A (only adenine (A) base with a length of 24) decorated SWNT sensor have demonstrated the largest sensing responses towards acetone and HCl, respectively. On the other hand, for the DNA GT decorated SWNT sensors with different sequence lengths, the optimum DNA sequence length for acetone and HCl sensing is 32 and 8, separately. The detection of methanol, acetone, and HCl have identified that DNA functionalized SWNT sensors exhibit great selectivity, sensitivity, and repeatability with an accuracy of more than 90%. Further, a sensor array composed of SWNT functionalized with various DNA sequences was utilized to identify acetone and HCl through pattern recognition. The sensor array is a combination of four different DNA functionalized SWNT sensors and two bare SWNT sensors (work as reference). This wireless sensing system has enabled real-time gas monitoring and air quality assurance for safety and security.

Biosynthesis of Isoprenoids: Characterization of a Functionally Active Recombinant 2-C-methyl-D-erythritol 4-phosphate Cytidyltransferase (IspD) from Mycobacterium tuberculosis H37Rv

Shi, Wenjun,Feng, Jianfang,Zhang, Min,Lai, Xuhui,Xu, Shengfeng,Zhang, Xuelian,Wang, Honghai Korean Society for Biochemistry and Molecular Biol 2007 Journal of biochemistry and molecular biology Vol.40 No.6

Tuberculosis, caused by Mycobacterium tuberculosis, continues to be one of the leading infectious diseases to humans. It is urgent to discover novel drug targets for the development of antitubercular agents. The 2-C-methyl-Derythritol-4-phosphate (MEP) pathway for isoprenoid biosynthesis has been considered as an attractive target for the discovery of novel antibiotics for its essentiality in bacteria and absence in mammals. MEP cytidyltransferase (IspD), the third-step enzyme of the pathway, catalyzes MEP and CTP to form 4-diphosphocytidyl-2-C-methylerythritol (CDP-ME) and PPi. In the work, ispD gene from M. tuberculosis H37Rv (MtIspD) was cloned and expressed. With N-terminal fusion of a histidine-tagged sequence, MtIspD could be purified to homogeneity by one-step nickel affinity chromatography. MtIspD exists as a homodimer with an apparent molecular mass of 52 kDa. Enzyme property analysis revealed that MtIspD has high specificity for pyrimidine bases and narrow divalent cation requirements, with maximal activity found in the presence of CTP and $Mg^{2+}$. The turnover number of MtIspD is $3.4 s^{-1}$. The Km for MEP and CTP are 43 and $92{\mu}M$, respectively. Furthermore, MtIspD shows thermal instable above $50^{\circ}C$. Circular dichroism spectra revealed that the alteration of tertiary conformation is closely related with sharp loss of enzyme activity at higher temperature. This study is expected to help better understand the features of IspD and provide useful information for the development of novel antibiotics to treat M. tuberculosis.

Preparation of Nano-Fe3O4/Nylon Composite Fabric with Magnetic Properties by Post Finishing Method

Ruquan Zhang,Boya Zhang,Wenjun Dou,Ying Wu,Lei Luo 한국섬유공학회 2019 Fibers and polymers Vol.20 No.7

In this paper, the functional nano-Fe3O4 composite fabrics with good magnetic properties were fabricated througha combined chemical co-precipitation and finishing method. The particle size and magnetic properties of Fe3O4 weremeasured using Malvern Laser Particle Size Analyzer and vibrating sample magnetometer (VSM), respectivily. Thestructure, magnetic flux and mechanical property of the composite fabric were characterized by Fourier infrared spectrometry(FT-IR), X-ray diffraction (XRD), Tesla meter and Instron electronic tensile machine. The particle-size of prepared Fe3O4 isnano-scale and has excellent magnetic properties. The nano-Fe3O4/nylon composite fabrics have good magnetism,mechanical property and water repellency. The maximum magnetic flux of nano-Fe3O4 composite fabric is 2.4 mT.