Abstract:

Abstract:The Brilliouin optical time domain analysis (BOTDA) is a newly developed technique adopted to measure and monitor the strain and temperature generated along optical fibers. The BOTDA has the characteristics of distributed measurement, long distance, high precision and durability, so it is suitable to structural health monitoring. Then a new optical fiber sensor embedded method based on air-blowing and vacuum grouting is introduced. It can lay the long distance distributed optical fiber into the concrete easily in short time. An experiment has been set up to study the validity of the new method, which shows that the embedded optical fiber can measure the concrete strain accurately, and it can realize the comprehensive, long-term, stable and real-time health monitoring to the civil structure.

Abstract:The influence of shrinkage crack on chloride ion penetration and carbonation of concrete is investigated. The concrete samples with shrinkage crack of 0.07 mm，0.1 mm，0.2 mm，0.4 mm and 0.62 mm are prepared, and both an accelerated carbonation test and Qingdao sea water corrosion test are conducted on sound concrete and cracked concretes. The depths of carbonation, the content of free chloride and total chloride in crack zone and perimeter zone of concrete are analyzed. The enperimental result shows that both free chloride and total chloride content in cracked concrete increase with the rise of the shrinkage crack width, and they are related in quadratic function. The chloride penetration velocity in crack zone is higher than that in perimeter zone of concrete. However, the increased specific surface in shrinkage crack tip improves chloride binding capacity and decreases the free chloride content in this zone. When the shrinkage crack is less than 0.07mm, the carbonation depth in crack zone is same as that of sound concrete. The chloride diffusion coefficient and the carbonation depth of cracked concrete increase limited as the shrinkage crack is less than 0.1mm, and then increase significantly with the increasing of shrinkage cracked width. Moreover, the carbonation depth in crack zone is increased by 3mm in comparison with that in perimeter zone of cracked concrete.

Abstract:Based on the analysis of chloride ion-induced erosion mechanism of reinforced concrete and the Fick’s second law, a multi-factor model of the chloride ion erosion is established. In this model, the influences of water-cement ratio, humidity, time, temperature, and chloride ion binding capacity of concrete are taken into consideration, and the mathematic solution to the new model is provided by considering the boundary conditions. The new model is verified by analyzing the long-term exposed experiment data. Compared with the traditional model of Fick's second law, the model can indicate the development trend of the structure eroded by chloride and the chloride ion concentration in different depth, and at the same time, it can predicate the chlorine ion concentration on rebar surface in different corrosion periods and the initiation corrosion time of reinforcement.

Abstract:The accurate calculation of the deformation capacity of structures is very important to performance-based seismic design, which satisfies the explicit deformation demands. The method to evaluate drift capacity of fiber reinforced polymer (FRP) confined reinforced concrete circular columns under simulated seismic loading is focused. Firstly, the moment-curvature relationship of FRP confined sections of reinforced concrete (RC) circular columns is simulated by numerical analysis. It is found that the calculated ultimate curvature is significantly less than the test result, and the difference is controlled by the axial load ratio of the tested columns. According to the numerical and the test results, an equation is proposed to modify the calculated ultimate curvature. Based on this, the drift capacity can be predicted with the equivalent plastic hinge method. The calculated result agrees well with the test result when FRP amount is low, but it is significantly larger when FRP amount increases. Finally, the main parameters exerting influences on the drift capacity of the FRP-confined RC circular column are analyzed.

Abstract:The finite element software ABAQUS is used to calculate the deformation of reinforced concrete walls under fire. The calculated results agree well with previous experimental results. Based on the finite element model, the influences of such parameters as axial load level, lateral load level, height-to-thickness ratio, wall thickness, concrete compressive strength, steel reinforcement yield strength, steel reinforcement ratio and concrete protection thickness on deformation and fire resistance of walls are analyzed systematically. It is found that, under the conditions of big axial load level or wall thickness without lateral load and small height-to-thickness ratio, the reverse deflection of reinforced concrete walls in fire is apt to occur. Within the work range of parameters in common use, the fire resistance of walls decreases with the increase of axial load level, lateral load level, height-to-thickness ratio, steel reinforcement yield strength or steel reinforcement ratio, and increases with the increase of wall thickness or concrete compressive strength.

Abstract:In order to effectively assess the damage of concrete in freeze-thaw condition, prediction model for concrete frost damage is presented based on damage mechanical theory and the experimental test. The degeneration of tension strength of air-entraining concrete is tested after freezing and thawing. Provided with the fact that the degeneration of concrete is an interior damage evolving process, freezing and thawing damage accumulation of concrete is analyzed based on the discrete grid with probability of stochastic method. And Three-dimensional multi-parameters Weibull distribution model about concrete damage evolutions is presented. Parameters are estimated based on gradient method, and the mathematical model is verified according to the tested data. Corresponding algorithm is designed and programming is completed by C + + programming language to establish concrete durability prediction model under freeze-thaw conditions. It is indicated that the damage of concrete develops in nonlinear way as the freezing and thawing increases.

Abstract:Taking a two-lane extra large bridge as sample,it is to analyze the real time thermal field and thermal effect on a long-span prestressed concrete box girder. The obtained data is compared with the simulation which is based on a balancing theory of temperature distributions and exchange in box girder exterior surfaces. The results show that the proposed method can emulate the actual boundary conditions precisely, it can satisfy the design analysis requirement of the practice engineering. Based on the emulation of the temperature field, with the ANSYS secondary development technology, FEM modules are developed to analyze the thermal field of the prestressed concrete box girder bridges. The present examples show that the developed modules are effective and useful.

Abstract:The static load test and the finite element analysis of the multi-tower cable-stayed bridge with tie-down cables are carried out. The test and analysis model of the bridge is created by referencing to the actual structure of a Changjiang River bridge. The static mechanical behaviors of such bridge with tie-down cables and the normal multi-tower cable-stayed bridge are comparatively analyzed by the static load test and the finite element analysis. It is shown that the structural system of the cable-stayed bridge with tie-down cables can effectively improve the structural rigidity and reduce the bending moment of the main beams, pylons and piers. According to the results, the best scheme about the location and number of tie-down cables is proposed.

Abstract:The basic structure of Variable Curvature Friction Pendulum Isolation Bearing (VCFP) is introduced. Based on the principle of mechanical equilibrium, theoretical analysis on two types of VCFP which are Variable Frequency Pendulum Isolation Bearing (VFPI) and Conical Friction Pendulum Bearing (CFPI) are conducted. The stiffness of each VCFP is derived, and the recovery characteristics were discussed and the computing formula of maximum residual displacement was deduced as well. Moreover, with the use of ABAQUS software, the models with solid element of each VCFP are built, and the hysteresis property under low cyclic loading and recovery characteristic are simulated. The comparative analysis of VCFP and Friction Pendulum Bearing (FPB) are also conducted. The results show that: 1) the numerical simulation results are identical to the theoretical analysis; 2) according to its plump hysteresis loops, the hysteresis property of VCFP is favorable, further more, its effective viscous damping ratio and coefficient of energy dissipation are higher than FPB, which indicates its greater ability in energy dissipation; 3) the stiffness of the VCFP is determined by curvature radius, that is, sliding surface function. And its stiffness decreases with the increase of bearing displacement through rational design. And then its isolation period increases as the displacement increases and the low frequency resonance problem of isolated structures can be well solved; 4) compared with FPB, the softening mechanism of stiffness can make the shear force transferred to superstructure decrease; 5) the maximum stress of bearing appears when the bearing reaches its designed displacement, and in general it may situate in the edge of ball joint surface of slider or bearing plate 6) the maximum residual displacement of VCFP depends on both friction coefficient and the parameters of sliding surface function, therefore, parametric design based on analysis or simulation is necessary so as to control the maximum value in an acceptable range in engineering.

Abstract:Negative shear property of soil-concrete interface is one critical issue in civil engineering. According to negative simple shear tests of soil-concrete interfaces with various water content, quantitative analysis on changes of shear strength, friction angle and cohesion force of negative sheared interface against positive shear experience were conducted. Several empirical formulae were proposed for above changes, and critical positive shear ratio was put forward. Based on improved stress-strain equation, mathematical model for tangent modulus of negative sheared soil-concrete interface was established. This new model consists ten parameters which can be determined by simple shear test. Process for determining these ten parameters was presented, and empirical values of them were obtained. Simulations for stress-strain curves of soil-concrete interface were carried out, and good ability of the model was found.

Abstract:Confined by the condition of static loading test, the ultimate load of pile group is modified by the ultimate load of static loading test of a pile, so the estimated ultimate value lacks objectivity. The variables of universal function of bearing capacity of pile group are put up. First, based on one another matching parameters of strength for geotechnical material according to simultaneity relation in the forced pile foundation, and induced the strength reduction factor, the safety storage factor (SSF) is put up, which is denoted the ratio of real ultimate load to the load on pile foundation. Second, the plastic deformation is happen at the soils around pile tie at the condition of ultimately loading, and the steady state of pile-soil system rapidly changes into a unstable state (rapid changing relation), the phenomenon of loading-settlement shows that the vertical line lies at the inflexion after the ultimate load point. Hereby, the criterion of ultimate load, which is computed by the strength reduction method of no-linear FEM limit analysis for pile group, is build. Finally, used the ANSYS softer, the screw pile group of the practical foundation engineering is analyzed by 3-d FEM strength method. At P=207 800 N, the SSF is equal to 1.16, and the ultimate load (Q) is 241 048 N, which it is small 3.35% than the estimated ultimately loading of state loading test (249 400 N). This result validated the feasibility of strength reduction method used to decide the ultimate load of pile group.

Abstract:Aiming at evaluating the effects of vibration history on dynamic characteristics of normally consolidated clay, a series of multi-cycled cyclic shear tests were conducted on 16 soil samples under consolidation pressure of 50 kPa, 100 kPa, 300 kPa and 500 kPa respectively. The experimental results reveal that, on the stage of drainage and consolidation, with the development of duration shear modulus curve ascends while damping curve descends; this trend became significant as consolidation pressure increased. The variation tends to be stable in 25 hours. When subjected to cyclic loading controlled by constant strain amplitude, both the modulus and damping of soil samples change significantly during the first 50 cycles, and then the differences become moderate afterwards, in which the damping curve acts in hyperbolical type. It is also found that there exists a clear sign of pre-straining that affects damping more significantly than modulus.

Abstract:Based on fuzzy self-adapting stochastic damage model, the characteristics of generalized damage stress field on material crack tip are studied. The results express that the numerical algorithm is reliable. Sensitivity of rolled-concrete gravity dam under fuzzy-stochastic damage gaining is implemented by considering the spatial variation of material parameters. It is found that the compression strength of rolled-concrete is the governing index on gravity dam reliability. The activation simulations on fuzzy self-adapting stochastic damage model were carried by adopting different fuzzy distributions, which indicated the governing characteristics of the distribution on generalized damage evolution of rock-like material.

Abstract:For the duct-ventilated highway embankments in permafrost regions of the Qinghai-Tibet Plateau, the cooling capability of duct-ventilated embankment enhanced by a self-windward vent is focused. Based on the intake-air volume in the ventilation pipe, the factors influencing the cooling capability in duct-ventilated embankment enhanced by a self-windward vent are analyzed. The analysis results indicate that the enhancement of the cooling capability in the duct-ventilated embankment with a self-windward vent is significant during winter months. For the self-windward vent equipped on the top of the vertical pipe, the cooling capability during winter months in the embankment increases with the increase of vertical pipe height. Convective heat transfer is a dominant mode of heat exchange between the ventilation pipe wall and the ambient air in the duct-ventilated embankment. From a convective heat transfer point of view, the height of self-windward vent installed ought to be as high as possible. However, due to disturbance of the wind field near both sides of the duct-ventilated highway embankment caused by the running vehicles, the height of self-windward vent shouldn’t exceed the embankment height.

Abstract:In the analysis of rock burst criterion prediction at home and abroad, the prediction standards of rock burst are selected including the conditions of mechanics、integrity、energy and brittle. The concept of relative membership degree on the rock burst prediction was introduced. The weight of standards and fuzzy matrix of relative membership degree are calculated. Uncertainty in rock burst prediction is described and compared according to the information entropy. Generalized weighted distance is also defined to characterize the differences in rock burst based on the maximum entropy principle, the establishment of a rock burst prediction fuzzy optimization model. The results from the application to practical example and comparisons with other methods are fairly good. Finally, the prediction model is applied in Putaoshan tunnel and the predictions are consistent with the actual rock burst.

Abstract:Buffer zone set between aisle and anteroom is proposed to improve the traditional mode of pressurizes mechanic smoke extraction. Fire Dynamic Simulation is used to simulate the model of high-rise fire. Eight models are set and analyzed, in which the smoke temperature distribution and concentration distribution are compared, and the best parameters is worked out. The result shows, when exhaust smoke volume is constant, the velocity of air curtain is as low as possible; when the volume of air curtain is constant, the smoke volume is as low as better. Based on the comparison, it is found that the smoke removal efficiency of mode 4 is the best one, which is about 74.06%. The evacuating buffer not only can let smoke out timely, but also can guarantee safe personnel evacuation.

Abstract:In order to study the influence on water temperature raise of river water source heat pump tail water discharged in different methods, the real sensor network is established by using digital temperature sensors. The simulation experiments of different discharging methods of river water source heat pump are carried out, including submerged-type discharge, surface-type discharge and jet-type discharge with 12 effluent ways. By using weighted average method, the preferred values of such factors as the average temperature raise，the temperature raise variance, the biggest temperature raise value, and the number of temperature measure points above the temperature raise average value are calculated. Moreover, the experiment results are analyzed by the three-dimensional figures of water temperature raise, which shows that jet-type discharge is better than submerged-type discharge and surface-type discharge，and the double-port way is better than single-port way. In addition, the double-port way along with the current in surface-type discharge method is the one that exerts least influence on river water temperature raise.

Abstract:The energy consumption of the air-conditioning system in the Internet Data Center (IDC) occupies about 40% of the total energy consumption. The thermosyphon heat exchanger using ambient energy is applied in the IDC to reduce energy consumption. By taking one IDC in Beijing as reference, the testing model is set up to experimentally analyze the heat dissipation characteristics and the energy consumption of thermosyphon heat exchanger and air-conditioning system respectively. The result indicates that the heat dissipation capacity of the building envelope takes about 19.5% of the total IDC heat load in Beijing winter conditions. The average energy consumption of the air conditioner is 3.5 kW h ~ 4 kW h per day. And the energy consumption of the thermosyphon heat exchanger takes only 41% of the air conditioner. The annual energy consumption reduces by nearly 40%. Besides, the effect of the outdoor temperature on the air conditioner energy consumption is remarkable compared with the indoor set temperature. And the air conditioner energy consumption increases by 5% ~ 6% on average when the outdoor temperature raises by 1℃.

Abstract:To study the velocity distribution rule, the sludge deposition and the energy-optimized distribution of the oxidation ditch, the experiment was processed in a WWTP with A/A/O Oxidation Ditch technology. The study individually focused on the velocity distribution of curved sections in out-ditch by testing three operation conditions of the Oxidation Ditch. The result shows: firstly, the velocity of the first ditch is too large; easily lead to waste of energy, intermittent on/off submerged flow drivers can optimize the energy distribution of the system. Secondly, in the second ditch, the flow pattern in crook ditches were very complex, there existed high velocity outside and low inside. For such situation, it is easy to cause sludge deposit in the inside of the ditch. Finally, in order to improve the problem of sludge deposition, the measures were put forward as follows: installing off-center training in curved sections of the second ditch, adjusting the position of submerged flow driver.

Abstract:The patterns and characteristics of radial oxygen loss（ROL）under natural, aerobiotic and anoxic conditions were investigated respectively by the standard oxidized dye (methylene blue agar)method. And the characteristics of pore and oxygen loss barriers were observed by using the front stand fluorescence microscope. Based on these experiments, the effects of oxygenation conditions on treatment of swine waste water controlled by canna floating bed technology were analyzed. ROL is very low in any pot in aerobiotic conditions, and it reaches its peak in root apex zone and declines dramatically along the rhizel in anoxic condition. ROL is high in every pot under natural conditions. Corresponding to the higher ROL, the pore is bigger and the oxygen loss barrier is thicker. ROL makes water aerobiotic. The removal rates of NH3-N and TN were 62.36% and 47.9% respectively by taking canna floating bed technology, and NO3+-N accumulated and increased under aerobiotic condition.

Abstract:CuO/TiO2 is modified by anionic, nonionic and cationic surfactant respectively in the preparation process. XRD, BET, UV-Vis, FTIR, 3D fluorescence and SEM are used to characterize the structure and photocatalytic activity of catalysts, which shows that crystal and UV-visible absorption characteristics of photocatalysts do not change with surfactant modification. All photocatalysts contain anatase TiO2 and CuO crystal, and their UV-visible absorption edges reach 900 nm. Whilse different kinds of surfactant lead to different amount of organic groups in photocatalytic surface, oxygen vacancies and the particle size of photocatalysts. Photocatalyst modified by anionic surfactant has the highest photocatalytic activity, because it has the richest organic groups and oxygen vacancies, and its particle size is the smallest. In contrast, photocatalyst modified by cationic surfactant has the lowest photocatalytic activity. In addition, degradation of dibutyl phthalate photocatalyzed by sodium dodecyl sulfate modified photocatalysts reaches at 93%.

Abstract:Advanced oxidation processes with O3/UV are applied to treat the acrylic fiber wastewater which is biorefractory and has high microbial toxicity. Effects of reacting time, pH value and feed concentration of contamination on the treatment efficiency are systematically investigated. The results show that, with remarkable synergistic effect, the treatment of acrylic fiber wastewater with combination of O3/UV is more efficient than the simple fold of ozone and UV treatment. The B/C of the wastewater increased from 0.08 to 0.3 after treatment, which improved the biodegradability of fiber wastewater and benefits the followed-up biotreatment. The optimum treatment efficiency was achieved after 30 minutes when pH reaches 6. The COD value decreased from 1 120 mg/L to 850 mg/L, with the removd rate of 25%, and the B/C ratio of wastewater is increased to 0.34.

Abstract:To realize the purpose of enhanced nitrogen removal (TN<5 mg·L-1) in step feed process treating urban wastewater, by using SBR reactor, the nitrite accumulation, variation of pH and ORP as well as dynamic properties during denitrification with methanol and glucose as the sole carbon sources are investigated in details. The results show that for both carbon sources, serious nitrite accumulations are observed during denitrification under different ratios of nitrogen and carbon (C/N). With identical C/N, when glucose is used as carbon source there is more maximum NO2--N accumulation concentration. However, NO3--N reduction rate is faster than NO2--N reduction rate for both carbon sources. Furthermore, with the increase of C/N, the maximum NO2--N concentration increases and the time in which the NO2--N achieves the highest concentration is accordingly shortened. For glucose, however, under high C/N ratio (C/N=29.3) both the denitrification rate and NO2--N accumulation concentration decrease. Besides, the changes of pH and ORP reflect the variation of NO2--N accumulation concentration well because pH and ORP have the significant relationship with NO2--N concentration. The second inflexion on curves indicates the real end of denitrification process.

Abstract:Based on the sewage treatment device of Two-phase Integrated Sludge Thickening and Digestion reactor (TISTD), microbial community structure in stable operation and its ecological variation when load changes are investigated. During a stable operation with 30% sludge dosage rate, 20 dominant bacterial strains are individually isolated from acid-phase and methane-phase of the reactor. Sequence analysis of 16S rDNA reveals that six of the achieved strains belong to Bacillus, Methanospirillum and Methanococcus respectively. Ten sludge samples are collected separately in 5 periods when the reactor operates with 10%, 20% and 30% sludge dosage rate and in the state of started-up and disordered, and followed by DNA extraction, purification, 16S rDNA PCR amplification and temperature gradient gel electrophoresis (TGGE). The good quality of DNA extraction and amplification demonstrates that there is an abundant biomass in the sludge under mid-temperature condition. The results show that TISTD reactor has a high biodiversity in microbial communities and is complex and stable in ecosystem structure, which effectively supports the good digestion in sludge thickening.