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Half-Grouted Sleeve Connection (HGSC) is extensively applied in the Prefabricated Concrete (PC) structures. The performance of the PC structures after fire has become an interesting research topic. However, the post-fire mechanical behaviors of the HGSC are still an issue that needs to be studied in depth. The experimental results of twelve HGSC specimens with concrete cover under static tension after 25 °C to 600 °C are presented in this paper. In the experiments, the post-fire HGSCs' failure mode is just rebar tension fracture, not bonding failure. The properties, such as strength, elongation, ductility, and elastic modulus were analyzed, and the failure mechanism, elongation and bonding slip, influence of concrete cover, bonding behaviour of HGSC after high temperature were discussed. It was found that some post-fire tensile properties of the HGSC were obviously affected by the peak temperature and the concrete cover.

Half grouted sleeve connection is widely used in joining rebars in precast concrete structures. However, its mechanical behaviors at elevated temperatures remain to be a topic with little research. This paper presents experimental results of 12 half grouted specimens and 12 single rebars under static tension at different temperatures. The tensile properties of half grouted sleeve connection were found to be directly affected by the temperature, and some characteristics are different from that of the rebar. The results showed that the half grout sleeves exhibited two types of failure, namely rebar fracture and rebar pullout due to bonding failure. The mechanical properties of specimens were similar to that of single rebars. When the temperature elevated, the failure mode and rebar breakpoint location may change. The bonding length that would be sufficient at room or low temperature, becomes insufficient at 600 °C. Suggestions about the bond length are given to avoid rebar pull out from the grout due to bond failure at elevated temperature.

In this paper, a mechanics based analytical truss model is proposed to predict the shear strength and deformation of conventionally reinforced coupling beams with span-to-height ratios less than 1.75 (referred to as short coupling beams). The model considers the yield of only parts of stirrups, and its load path is composed of a direct main strut connecting the compression zones at both ends of the beam and secondary struts balancing with stirrups. By satisfying the compatibility condition at the intersection node of the struts, the assignment of the applied shear load in the main and secondary struts, as well as the shear load-transverse displacement relationship of the beam, are determined. The shear strength predictions by the truss model are compared with test results of 37 conventional reinforced short coupling beams, which shows that it can accurately predict the shear strength with a coefficient of variation (COV) of 0.052, while the predictions provided by ACI 318-19 and GB 50010-2010 are relatively inaccurate (the COVs are 0.19 and 0.21, respectively). In addition, the skeleton curves of 27 short coupling beams are calculated by the truss model, and the results show that the predictions are in good agreement with the test results. In order to simplify the calculation, a simplified model is proposed based on the refined truss model. Although the accuracy of the simplified model is slightly reduced (the COV is 0.071), it is still significantly higher than those of the design codes. Based on the simplified model, a standardized design method, which indirectly considers the beam deformation capacity, is provided for practical shear design.

Pushover and nonlinear dynamic analysis method are applied to analyze the seismic performance of RC frame structure with or without slabs under the action of multiple factors in this thesis. Meanwhile, the structural response exerted by oblique seismic action is summarized from the theoretical formula derivation. By analyzing and comparing two kinds of established models, the results demonstrate that with various axial compression ratio and moment magnifying factors of columns, the seismic performance of the structure will be degraded when the influence of the floor is taken into account. And the increment of the values of axial compression ratio μ and moment magnifying factor of column η c with the floor exceeds that without the floor. Moreover, Earthquakes input along the principal axis can realize the “strong column weak beam” of the structure. Considering the influence of floor, when the value of axial compression ratio is higher than 0.56 or moment magnifying factors with the floor increases above 2.0, frame structure under oblique seismic action can form “strong column weak beam” yield mechanism.

Knowledge of the nonlinear elastic response and anharmonic properties of MgO single crystal is important for interpreting the seismically observed velocity variations in the Earth’s mantle and constructing reliable mineralogical modes of the Earth’s interior. However, investigations on these properties of it have not been performed sufficiently to date. So the nonlinear elastic response of the MgO is first studied by calculating the second-, third-, and fourth-order elastic constants. Results show that our predications on the high-order elastic constants exhibit excellent agreement with the available experimental ones and other theoretical values, which indicates that the present computational approach is suitable for the calculations of the high-order elastic constants and it can be expanded into other complex systems. Then on the basis of the elastic constants, the related anharmonic properties such as the first-order pressure derivatives of the second- and third-order elastic constants, Gruneisen constants of the long-wavelength acoustic modes, and ultrasonic nonlinear parameters are also investigated. The predications on the anharmonic properties first given in the present work are hoped to serve as a valuable guidance or reference for further related investigations.

An efficient method for reliability assessment of structural dynamic systems is proposed. In the proposed method, the reliability is evaluated by the equivalent extreme value distribution of structural dynamic systems, where an estimator-corrector scheme based on the principle of maximum entropy with fractional moments as constraints is adopted to derive such distribution. The fractional moments, which are of paramount importance to the efficiency and accuracy of reliability assessment, can be obtained by a multidimensional integral. To calculate such an integral, a new approach named unequal weighted quasi-Monte Carlo Simulation is put forward. In this approach, different strategies for the construction of unequal positive weights, the rearrangement of sampling points to be integration points and the determination of required number of points are explored. The integral for the evaluation of fractional moments is then determined efficiently based on the obtained integration points and the weights straightforwardly. Numerical example is studied to verify the proposed method. The investigations indicate that the proposed method is of accuracy and efficiency for reliability assessment of structural dynamic systems, with only a few hundreds of deterministic dynamic response analysis for a practical problem involving multiple random parameters.

ZnO nanometer materials were synthesized by microwave reaction from ZnO micrometer powders with different C aids. Effect of C style on the morphology of ZnO products was studied. The result show that ZnO nanometer materials can not be formed by using directly high temperature evaporation from ZnO micrometer powders without C aids. Fine ZnO nanometer crystals can be obtained by using carbon black as aids. In this sample, most ZnO grains were nanometer particles with a size of about 100nm. And a small amount of ZnO grains were short rods with a length of 1~2μm and a average diameter of 100nm. Amounts of short columnar and long zigzag ZnO crystals can be obtained by using graphite as aids. One effect mechanism of ZnO crystalline was proposed. ZnO reacted C to form CO and CO2 gas. Concentration of CO/CO2 directly effects the morphology of ZnO in the products.

Two-parameter elastic foundation models have great potential for approximate soil-foundation-structure interaction analysis. A hurdle to the wide application of this model has been the difficulty of calibrating the two soil coefficients: the compression coefficient k and shear coefficient G. This paper presents a novel parameter calibration method for k and G based on a number of rigid plate loading tests. Empirical k and G values are also recommended. Experiments showed the validity of the proposed method. Two case studies verified the significance of the two-parameter model in the prediction of footing settlement when interactions among neighboring footings exist.

Half grouted sleeve connection (HGSC) is widely used in joining rebars in precast concrete structures. Construction defects and fires are inevitable in practical projects. However, the mechanical behaviors of post-fire HGSC with construction defect remain to be a topic with little research. The present work presents experimental results of 66 post-fire HGSC specimens with construction defect under static tension at room temperatures. Results show that the tensile properties of post-fire HGSC are directly affected by the peak temperature and the construction defect, and some properties are different from that of the rebar. Post-fire HGSC exhibited two main types of failure mode: rebar fracture and bonding failure. The protruded rebar in some post-fire specimens obviously slides before the rebar fractured and the ultimate elongation becomes larger. Different type of construction defect has a different effect on the behavior of the specimens, and the effect depends on the weakening of the effective bond area between rebar and grout. The peak temperature and construction defect may make reliable HGSC be unreliable and not acceptable, once the corresponding peak temperature is near 600 °C. Results also show that the proposed method to simulate the construction defects of HGSC is feasible and the X-ray method is an effective way to detect the defects in HGSC.

The performance of the prefabricated concrete (PC) structures at elevated temperature becomes an important focus, once a fire occurs. The failure in fire of fully-grouted sleeve connection (FGSC) that extensively used in PC members will cause serious consequences. To fill this knowledge gap, the present work presents the experimental results of 15 FGSC specimens and 15 single rebar (SR) specimens by static tension. The results show that the mechanical behavior of FGSC specimens at high temperature is affected by the temperature and similar to that of SR. Two types of failure modes appear in the FGSC specimens, namely, rebar tension fracture and bond failure. The bond failure was observed at 600 °C. Based on the test results, the tension constitutive relation curves was established, and the bond strength design of FGSC at elevated temperatures were put forward to avoid the bond failure. A new prediction method for calculating mechanical property of prefabricated rebar connection at elevated temperature is proposed.

In reinforced concrete (RC) column footings, the soil stiffness can significantly affects the punching shear strength of the foundation slab. The present study conducted eccentric compression tests on three RC column footings considering the complex interaction between the soil and structure, and investigated the load-carrying capacity, displacement distribution, reaction distribution, failure mode, crack development, and strain distribution. The test parameter was flexural reinforcement ratio in the foundation slab. The test results showed that the footing specimen with lower reinforcement ratio was susceptible to brittle punching shear failure, and the flexural reinforcement ratio affected the crack distribution and the spalling of concrete cover. Since only one specimen was used in each flexural reinforcement ratio, however, the test results should be carefully considered. On the basis of the test results including existing studies, the effect of design parameters on the punching shear strength was evaluated. As a result, a new method was developed to predict the punching shear strength by addressing the eccentric compression force.

Half-grouted sleeve connections (HGSCs), which are extensively used in prefabricated concrete (PC) structures, have attracted considerable research interest, including their mechanical properties under fire. However, research on the post-fire behaviors of this type of connection under different cooling methods and paths is limited. To fill this knowledge gap, the present work presents the experimental results of 33 HGSC specimens subjected to various peak temperatures and different cooling methods. Results show post-fire tensile properties are significantly affected by the exposed peak temperature and subsequent cooling method. Two types of failure modes are observed on the basis of the exposed peak temperature and cooling method, namely, rebar tension fracture and bond failure. The bond length of HGSC designed for room temperature is sufficient after a fire if the connection is naturally or air-cooled after peak temperature; whereas the bond length must be increased if water cooling is applied. Finally, a set of stress–strain relationships of HGSC and rebar is suggested for the post-fire performance evaluation and numerical simulation of PC structures with HGSCs.

An oxide-alumina-silicacoating which would to improve the oxidation resistance of carbon fibers was prepared by sol-gel method. XRD and SEM were used to characterize the surface appearance and phase transition about the carbon fibers with oxide-alumina-silica coating. The oxidation resistance of carbon fibers was also analyzed with the DSC-TG and the isothermal oxidation experiment. It was shown that the antioxidant properties of the carbon fibers with oxide-alumina-silica coating improved significantly. The concentration of precursor sol had an influence on the coating of carbon fibers and the antioxidant properties of the carbon fibers with oxide alumina silica coating increased 300°C compared to uncoated ones.

Over the last two decades, the electromagnetic radiation is becoming the fourth public pollution in addition to the noise, water and air pollution. Here, we had studied the structure and the electromagnetic properties of machine-knitted fabric coated with silver by means of microscopy and shielding effectiveness in the open space. The silver-plated polyester fabric showed a different shielding effectiveness of electromagnetic wave in the open space compared with enclosed space. The value of SE had closed relation with transmitting and receiving distance except the theory factor. When the frequency dropped below 900 MHz, the value SE usually became negative.

Laser processing ceramic materials is a new application of laser technique. This paper presents the study of making cracked glaze surface by laser processing. Proposed the applicable the composition of glaze, the main processing parameters of laser processing, and discussed the factors which may affect the quality of cracked glazing surface. It indicates that laser processing could be a new and easy processing method to produce the cracked glazing on the ceramic surface.

A visible-light-driven photocatalyst Ag3PO4 was prepared by a novel precipitation- replacement process. The synthesized sample was cubic crystals with the bandgap of 2.16 eV. And most of the particles size was among 0.5~2 mm. The Ag3PO4 shows high photocatalytic activity for the degradation of methyl orange (MO) solution under the visible light (l>420 nm). The apparent ratio constant (kapp) value of Ag3PO4 was about 239 and 50 times that of P25 and C-TiO2, respectively.

A novel visible-light-active C-N-Cl-codoped TiO2 photocatalyst was prepared by a simple process. The as-prepared sample was characterized by XRD, XPS, and UV-Vis. The analysis results showed that the as-synthesized sample was anatase and possessed a narrow bad gap of 2.4 eV after the doping of carbon, nitrogen and chlorine. An obvious absorption for visible light was observed in the range of 400~700 nm for C-N-Cl-codoped TiO2. By degrading of methyl orange (MO) solution under the visible light (l>420 nm) irradiation, the synthesized photocatalyst showed 5 times photocatalytic activity than that of P25.

Mechanical properties have close relation with microstructure. Based on orientation of the molecule chain in fiber, they show a rapid increase in tensile properties. Nevertheless, block materials mainly gain rise of mechanical properties by blend or composite, it is hardly proposed on the self-reinforced materials by optimizing the microstructure. In this work, the structure and tensile properties of polypropylene (PP), treated at 105°C for 5min under different pressure, were studied with microscopy, differential scanning calorimetry (DSC). The variety of supra-structure that the spherulite deforms into ellipse even fractures piece in the pressure field adds to the mechanical properties. The orderliness of crystal increases with the pressure, and Tm is increased slightly from the original level.

An approach which formed sheet structure through plane compression processing in the bulk of polymer (polypropylene (PP)) was suggested and the strengthening mechanism was presented based on a series of experiment. The variety of super-molecular structure that the spherulite deformed into ellipse even fractures piece in the pressure field helped to increase the tensile performance. In the polar reign of spherulite, the lamellae underwent a slight deformation, and the lamellae broke into fraction and then slid each other along the flow direction in the equatorial region. Finally, the lamellae in the sample aligned along the flow direction, and the sheet structure which was packed each other by lamellae was built up by plane compression processing.

Mechanical properties have close relation with microstructure. Based on orientation of the molecule chain in fiber, they show a rapid increase in tensile properties. Nevertheless, block materials mainly gain rise of mechanical properties by blend or composite, it is hardly proposed on the self-reinforced materials by optimizing the microstructure. In this paper, a strengthening of PP was gained by uniaxial compression through small deformation of spherulite. A series of measurements were applied, including tensile test, polarizing optical microscope (POM) and differential scanning calorimeter (DSC). The results show that the tensile properties of polypropylene (PP) have a rapid rise. POM suggestes that the spherulite has deformed into ellipsoid even belt along the orientation of sample of PP, which plays an important role in self-reinforcing of PP. And the initial melt point displayed by DSC slightly decreases because of the partial ruptures of crystal phase.

In this study a solution-blend method is adopted to prepare conductive polyvinyl alcohol (PVA) and polyaniline doped with dodecyl benzene sulfonic acid (PVA/PANI-DBSA) blend films. Emeraldine base (EB)-type polyaniline (PANI) is dissolved in N-methyl-2-pyrrolidinone (NMP) and then blended with PVA/dodecyl benzene sulfonic acid (DBSA) solution by various amounts. The morphological structures and characterized of the films were observed via scanning electronic microscopy (SEM), thermogravimetric analysis (TGA) and X-ray powder diffraction (XRD). Electrical properties of the blends were characterized by means of electrical conductivity measurements. It is found that the electrical conductivity and the thermal degradation onset temperature of the PVA/PANI-DBSA blend film are increased as the amount of PANI-DBSA is increased.

Concrete filled tubular (CFT) columns are being more and more utilized in construction of tall buildings and bridges. Xiao recently developed a new CFT column system, named as confined concrete filled tubes (CCFT), and validated its excellent load carrying capacity and ductility, by static and simulated seismic loading tests. This paper reports the impact behavior of CFT and CCFT stub columns. The impact responses of concrete filled steel tubes (CFT) and the confined concrete filled steel tubes (CCFT) were investigated using a high-speed gas gun. Experimental parameters included the confinement details and impact speed. Dynamic strains and the failure patterns are discussed. The test results demonstrate the effectiveness of lateral confinement to improve the dynamic impact behavior of CFT columns. Comparisons were also made between the test results and the analytical results using LS-DYNA. The trend of the stress wave propagation in the CFT specimen was reasonably well predicted.

The effects of the copolymerization system on the monomer reactivity ratios for a copolymer of acrylonitrile with N-vinylpyrrolidone was studied for contrast. The values of the monomer reactivity ratios were calculated by the Kelen–Tudos method. The reactivity ratios in the aqueous suspension polymerization system were similar to those in the solution polymerization system at polymerization conversions of less than 6% [reactivity ratio of acrylonitrile (rAN) = 0.438 ± 0.015, reactivity ratio of N-vinylpyrrolidone (rN-VP) = 2.28 ± 0.02]. As conversion of more than 12%, the changes in the monomer reactivity ratios became less prominent (rAN = 0.651, rN-VP = 1.98). In the water-rich reaction medium [H2O/dimethylsulfoxide (DMSO) > 60/40], the monomer reactivity ratios were approximately equivalent to those in the aqueous suspension polymerization system. In the DMSO-rich reaction medium (DMSO/H2O > 60/40), the reactivity ratios were similar to those in the solution polymerization system. With an increase in the polarity of the solvent, the values of the reaction ratios both decreased. The values of the reaction ratios gradually tended toward 1 with increasing copolymerization temperature. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 422–425, 2003

Free-radical solution copolymerization of itaconic acid and acrylonitrile was carried out in DMSO using azodiisobutyronitrile as an initiator, changing the feed rate of itaconic acid. The resulting polymerization solution was spun to form polyacrylonitrile (PAN) precursors of carbon fibers. The precursors were treated with a CoSO 4 aqueous solution on-line. The structure and properties of untreated and treated PAN precursors and the resultant carbon fibers were characterized by SEM and TEM, a stabilization process, etc. It is suggested that CoSO 4 acts as a catalyst in the formation of a ladder structure and reduces the temperature of cyclization, and the carbon fibers developed from treated PAN fibers showed improvement in the tensile strength and the Young's modulus.

Since knowledge of the structure and elastic properties of Ta at high pressures is critical for addressing the recent controversies regarding the high-pressure stable phase and elastic properties, we perform a systematical study on the high-pressure structure and elastic properties of the cubic Ta by using the first-principles method. Results show that the initial body-centered cubic phase of Ta remains stable even up to 500 GPa and the high-pressure elastic properties are excellently consistent with the available experimental results. Besides, the high-pressure sound velocities of the single- and poly-crystals Ta are also calculated based on the elastic constants, and the predications exhibit good agreement with the existing experimental data.

Direct melt/solid polycondensation of lactic acid (LA) was carried out to obtain high molecular weight poly(lactic acid) (PLA) by a process using various catalysts in the first-step melt polycondensation, and followed solid polycondensation by using p-toulenesulfonic acid monohydrate (TSA) as the catalyst in the second step. Effects of various catalysts and reaction temperature on the molecular weight and crystallinity of resulting PLA polymers were examined. It was shown that SnCl2·2H2O/TSA, SnCl2·2H2O/succinic anhydride, and SnCl2·2H2O/maleic anhydride binary catalysts should be effective binary catalysts to obtain high molecular weight PLA of more than 1.2 × 105. A conventional melt spinning method was used to spin PLA fibers, which displayed tensile strength of (382.76 ± 1.41) MPa and tensile modulus of (4.36 ± 0.07) GPa.