Abstract:In order to study the influence of slope on the vertical bearing characteristics of pile foundation, combined with model test and numerical simulation method, multiple groups of slope conditions and horizontal ground condition were designed to study the vertical bearing characteristics of single pile. The vertical bearing capacity, axial force, side friction and load transfer mechanisms during load-bearing of pile was compared and analyzed in unilateral slope and continuous slope with the same pile length. The results show that:1.Under the same slope condition, the single-pile bearing capacity of unilateral slope is less than that of continuous slope, and the vertical ultimate bearing capacity of pile decreases with the increase of slope gradient, and the slope influence degree increases non-linearly; 2.The slope type mainly affects the peak value of the pile side resistance, and the pile tip resistance is close when the pile side resistance peaks. 3.In the slope, there is a difference in the stress distribution between the front and back of the pile body. The vertical stress and shear stress at the front of the pile body are larger than that at the position back of the pile body, but the difference in shear stress only exists in the area around 0~4 times the pile diameter.

Abstract:Ultimate bearing capacity analysis of shallow foundations has been extensively studied by geotechnical scholars. Since different hypotheses exist in the slip surface and relationship between bearing capacity factors, the value of bearing capacity factors is not same depending on the theory used. Based on the classical analytical model, a limit equilibrium method of moment equilibrium is used to deduce the bearing capacity formula of strip footing on sand, and the equations of bearing capacity factors N_q and N_γ are given. Compared to commonly used theoretical models, the equations of factors N_q and N_γ are independent thus avoid the interplay of two factors and reduce the uncertainty in calculation. In order to verify the accuracy of the equations, the calculation is compared with the theory solution of limit analysis and laboratory test results in literature. Results indicate that the N_γ values calculated by the proposed equations of different internal friction angle are closer to solution of limit analysis than other theoretical models. Furthermore, the bearing capacity calculated by equations in this paper shows good agreement with the data of laboratory test.

Abstract:More and more attention has been paid to the results of quantitative assessment of slope failure risk by using uncertainty analysis method. In view of the problem that only stationary random field was used to simulate the distribution characteristics of shear strength parameters in the existing risk assessment of slope failure, in this paper, taking an undrained saturated clay slope as an example, combined with finite element limit analysis, strength reduction method and Monte Carlo simulation, the influence of shear strength parameters of soil simulated by non-stationary random field model and stable random field model on Calculation of slope instability risk assessment results were discussed.The results show that the traditional method of calculating the risk of slope failure by using stationary random field will overestimate the risk of slope failure, which will increase the project cost.The slip surface of slope with high safety factor is not necessarily a shallow slip surface. The vertical correlation distance of slope has little influence on the calculation of its failure risk by using non-stationary random field, while the vertical correlation distance of slope has significant influence on the calculation of its failure risk by using stationary random field. The influence of vertical correlation distance on position and shape of sliding surface is weak.The research results can provide guidance for the accurate evaluation of slope stability.

Abstract:Lime treatment is an economical and useful soil improvement method. However, lime-treated soils in site always present a serious degradation in strength, since they are exposed to the long-term changes in climate and environment. Water retention curve is essential to study the pore water movement inside soils and their hydro-mechanical behavior. This paper investigates the influences of temperature and curing time on the water retention curve of lime-treated soil. In this test, untreated samples and lime-treated samples(28, 90 d)were statically compacted. The water retention curves of untreated and lime-treated samples were measured at different temperatures (0~40℃). The results indicate that the water retention capacity of loess is effected by lime treatment, curing time and temperature changes. The effect decreased with the moisture content dropping. The temperature effect gradually weakens with the temperature increases. Besides, the VG model was applied to model the water retention curve of loess. And the effects of temperature and curing time on the parameters of a, n, θ_s, θ_r are analyzed. The research results can provide useful information for engineering construction.

Abstract:When the liquefied water-saturated sand is regarded as a fluid, it can be idealized as a kind of shear thinning non-Newtonian fluid. Based on non-Newtonian fluid mechanics, the theoretical analysis was conducted on the liquefied water-saturated sand. According to this, the relationship between the shear strain rate and the viscosity under zero effective stress state can be properly described by pure viscous flow constitutive model. The Gross model of liquefied water-saturated sand is established by fitting the flow curve of the dynamic torsional shear test results on the basis of predictions obtained from several commonly used pure viscous flow constitutive models. The representative model parameters include the relative density, the consolidation stress and the impact of stress history. The functional relationships among time dimension K, zero shear apparent viscosity η₀ and limit shear apparent viscosity η_∞ are fitted based on the dynamic torsional shear test results, and the physical meanings of the parameters are introduced in the composed function. The research landmarks a theoretical foundation for further analysis of large deformation of liquefied flows based on fluid mechanics theory.

Abstract:The underground silos can take full advantages of the underground space, which is of better fireproof, anti-toxicity, explosion-proof and other merits. In the meantime, the underground silos can use the shallow geothermal energy to realize quasi-low temperature storage. With the advantages of energy-saving, low-consumption and grain quality-ensuring, it plays a significant role in ensuring the grain safety and sustainable development of China. The mechanical properties of the silo wall before completion acceptance of large underground concrete silos were studied by the combination of engineering full-scale test and numerical analysis. By comparing the test results with the engineering-scale testing results,, the rationality and effectiveness of the numerical analysis method were verified. Furthermore, the mechanical properties of the silo wall under the most unfavorable load conditions were numerically analyzed. The results show that the internal forces of the numerical simulation results of the silo wall were in good agreement with that of experimental results. Due to the relatively large thickness of the silo wall, and the rigidity of the contact part between the silo wall and the silo bottom and the silo roof, the radial stress on the inside and outside of the silo wall shows the opposite law. The radial stress of the silo wall is highest at the bottom of the silo wall, and the hoop stress is highest at about 2/3 of the position from the top of the silo wall. Under the most unfavorable load conditions, the radial stress and hoop stress of the silo wall show similar changes with the burial depth as in the actual working condition, and the stress is greater at the same depth.

Abstract:In order to study the mechanical properties of Magnetorheological Damper (MRD) under quasi-static action, a four-coil shear valve MRD was fabricated. A quasi-static test was carried on the MRD by using the triangular displacement loading system under different currents and displacements. In the test, the variation of the mechanical properties of MRD with the changes of current and displacement was studied, and the causes of the damping force fluctuation phenomenon were analyzed. Based on the test results, a modified mechanical model under quasi-static loading was proposed, the parameters of the model were identified, and the mechanical model was verified. The results show that the damping force of MRD fluctuates remarkably during the quasi-static test process. The damping force decreases slightly with the increase of displacement amplitude when there is no current, and increases slightly with the increase of displacement amplitude when there is current. The damping force increases obviously with the increase of current, and when the current exceeds 1.5A, MRD reaches magnetic saturation and the increase of damping force decreases obviously. The mechanical model proposed in this paper can well describe the variation of damping force with the change of current and displacement under quasi-static force.

Abstract:To study the effect of shear reinforcement and installation of concealed beam on seismic behavior of slab-column connections, five slab-column connections were tested under low-cycle reversed load. The control specimen had no shear reinforcement, while the other four specimens were equipped with spiral stirrups, four-leg stirrups, eight-leg stirrups and studs, respectively. Crack development characteristics, failure modes, hysteretic behaviour, unbalanced moment capacity and ductility of each specimen were analyzed. The results show that compared with the specimen without shear reinforcement, unbalanced moment capacity and ductility of specimens with shear reinforcement are increased by 13%~48% and 68%~198%, respectively. The general seismic performance of specimens is significantly improved by properly designing the concealed beam. The specimen with four-leg stirrups can meet the requirement of seismic performance in Chinese code and is more economical than the that with eight-leg stirrups. By summarizing and analyzing existing test data, it is found that for slab-column connections with shear reinforcement, the calculated results with Chinese code are in good agreement with test results, but the dispersion of calculated results is relatively high.

Abstract:Based on the design principle of "strong transformation", a multi-lines defense seismic fortification method has been proposed for the frames with prestressed steel reinforced concrete (PSRC) vierendeel truss transfer story. In this method,the transfers columns and lower chord of transfer truss are designed as the last defense line. The second line includes the frame columns joined with transfer story, the upper chord and the middle web members of the transfer truss. Finally, the other columns and beams upon transfer story are the first line. In this study, firstly, the OpenSEES software was used to set up a series finite element models. Then the elastic-plastic time history analysis was finished under the horizontal and vertical earthquakes to study the basic seismic performance and the influence of the difference vertical motion (V/H=0, 0.65, 1.2). Results show that the structure can avoid the overall and partial damage under rare and very rare earthquake level (V/H=0.65). And a "beam-column mixed hinge mechanism" can be formed to dissipate energy mainly relying on the beams upon transfer story. The target of multi-lines defense seismic fortification has been realized. On the other hand, with the increase of the vertical component of the ground motion, its influence is focus on the increase of the lower chord deflection.

Abstract:The optimization criterion of evolutionary topology optimization algorithms is one of the key factors affecting the structural optimization results. In this paper, some deep beam models under different load and boundary conditions are taken as a numerical examples, and comparing the difference between the optimization solution and the computational efficiency of the three algorithms based on different optimization criteria. The results show that the evolutionary topology optimization algorithms based on one-way optimization criteria and deterministic optimization criteria can efficiently obtain the optimal topology for components with simple conditions such as load and boundary, and the evolutionary topology optimization algorithms based on probabilistic optimization criterion or bidirectional optimization criterion have a stronger scope of application, and it also shows a strong ability to avoid optimized distortion and conduct global optimization on components with complicated conditions such as load and boundary. At the end of this paper, a flow chart is established for the genetic bidirectional evolutionary structural optimization algorithm combining probabilistic optimization criterion and bidirectional optimization criterion. The preliminary discussion is carried out to further improve the practicability and optimization ability of evolutionary structural optimization algorithm.

Abstract:Aluminum alloy plate has the advantages of light weight, high strength, corrosion resistance and good extensibility. It is an ideal material for strengthening concrete structure in complex and harsh environment. In this paper, the study of bond-slip behavior of aluminum alloy-contrete interface was carried out by conducting double-sided pure shear tests on 45 members. The failure form, load-strain relationship curve, bond interface shear stress distribution curve, load-slip relationship curve and interfacial ultimate bearing capacity were obtained. The evolution of interfacial bond-slip behavior under different concrete strength grades, surface roughness of aluminum alloy plate, bond length and bond width of aluminum alloy plate were analyzed. The results show that the interfacial stress is gradually transferred from the loading end to the free end during loading. With the increase of the strength grade of concrete, and the length/width of bonding interface, the peeling capacity of the specimen is improved. But there is an effective bond length value for the aluminum alloy, beyond which the peeling bearing capacity of the specimen will not increase. Meanwhile, the surface roughness of the aluminum alloy has no substantial effect on the peeling bearing capacity of the specimen. By measuring the strain of aluminum alloy plate, the bond slip test curve of aluminum alloy plate and concrete under different parameters was obtained. The results show that the curve is of obvious interfacial softening characteristics and nonlinear behavior, which can be used to guide the actual engineering design of aluminum alloy plate reinforced concrete.

Abstract:For the seperation problem of bridge deflection monitoring, it presents a single channel blind source separation algorithm based on EEMD-JADE. First, the single channel signal of bridge deflection is decomposed into a series of linear and stationary intrinsic mode function (intrinsic mode function, IMF) by traditional ensemble empirical mode decomposition (EEMD), and then using the discriminant method based on the energy entropy increment to identify and eliminate the false IMF component. The IMF component with larger energy entropy increment compose the input signal of the blind source separation model. Finally, the Joint Approximate Diagonalization of Eigen-matrices (JADE) algorithm is used for blind source separation of the input signal. JADE can also separate the source signal well under the condition that the frequency difference of the source signal is small and the frequency is mixed, but the number of observed signals must be greater than or equal to the number of source signals. The Ensemble Empirical Mode Decomposition (EEMD) has good adaptability, which can decompose the mixed signals of single channel into multi-scale and form multi-channel signal, but the decomposition result has the endpoint effect and the modal aliasing. JADE algorithm can solve the end-point effect and modal aliasing problem in the decomposition result of EEMD, while EEMD also solves the prerequisite of JADE separation algorithm. The two algorithms have complementary advantages and can better separate the deflection components. With the model of background bridge established by the finite element software Midas/civil, the response of the bridge structure under the action of each single factor is obtained by the simulation analysis, and it is superimposed together as a mixed deflection signal to be separated. The correlation coefficient between the result of the simulation signal separation and the source signal is above 0.98, and the separation effect is better. Finally, the measured deflection signals are collected for separation. The correlation coefficients of the deflection components separated at the symmetric position are above 0.9, which proves the applicability of the algorithm.

Abstract:Width to height ratio Π shaped girder of cable stayed bridge is very big, and the shear lag problem is very outstanding. For considering the variation of load and boundary conditions in construction process, a beam element with two shear-lag degrees of freedom at each node is established to take the coupling effect of shear lag and bending deformation of composite girder into account, which is suitable for the complex load and boundary conditions. In the formula derivation, it is assumed that the longitudinal displacements of the concrete slab are described by a third-power parabolic function, and the steel flanges share the same displacements with concrete slab at the same abscissa. The shear-lag effects of Πshaped composite girder in a cable-stayed bridge during the construction process is analyzed by using the proposed method. The dead weight of decks, tensioning loads and secondary dead load are considered in analysis according to the dynamic shear-lag boundary conditions during the construction process. The numerical analysis results were compared with measured ones. It was shown that the shear lag of main girder alternates with positive and negative effect along with the changes of load increments and boundary conditions in different construction stages. Comparing with the vertical loads such as the dead weight of decks, the cable-tensioning loads have a much more obvious effect on the shear lag of the main beam. The shear lag effect at the sections near the towers is more obvious than that at the other sections. As the construction continuing of the bridge, the shear lag coefficients of the Πshaped composite beam are gradually decreasing. In addition, it should pay more attention to the shear lag effect in the cantilever construction stages than that in the final structure.

Abstract:The factors such as maximum temperature, duration, diffusion condition and concrete bursting at high temperature increase the difficulty of obtaining material properties by using temperature. In order to quickly obtain the real performance parameters of the materials of the pre-stressed concrete beam bridge in the post-disaster bridge evaluation, the appearance classification and material test of 32 hollow slabs demolished after the fire of the existing beam bridge in a highway were carried out. The relationship between the commonly used testing indexes and the properties of materials is obtained by measuring the properties of materials after fire. The applicability of these indexes is verified by the ultimate bearing capacity test and finite element simulation. The results show cracking and spalling of concrete at high temperature not only results in significant loss of section, but also significantly reduces the strength of concrete and prestressing steel strand in this area, which leads to the reduction of bearing capacity. When the spalling depth of concrete exceeds 2/3 of the net protective layer of steel strand after overfire, the reduction coefficient of compressive strength and tensile strength of pre-stressed steel wire reaches 0.7, which will seriously affect the ultimate bearing capacity. Fire action will change the ultimate failure form of hollow slab from ductility to brittleness. The ultimate bearing capacity of the prestressed hollow beam after fire is analyzed by using the reduction relationship between the conventional inspection indexes and the material properties, and the finite element simulation, so as to meet the engineering precision.

Abstract:The apparent characteristics, mass loss and mechanical properties of ultra-high performance concrete after exposure to high temperature were studied through the high temperature heating test and the cubic compressive strength test. The effects of steel fiber, polypropylene fiber, steel fiber and polypropylene fiber on cracking suppression of ultra-high performance concrete were compared. The effects of temperature, fiber type and content, aggregate (quartz sand and steel slag) on the strength of ultra-high performance concrete were investigated. The test results show that 1% steel fibers and 2% polypropylene fibers can effectively restrain high temperature explosion behavior, and the specimen remains intact after high temperature. Ultra-high performance concrete with steel slag aggregate and hybrid fiber has excellent high temperature mechanical properties, the residual strength of 67% can still be maintained after being exposed to high temperature at 1 000℃. With the increase of temperature, the cubic compressive strength of ultra-high performance concrete increases first and then decreases. High temperature enhances the compressive ductility of ultra-high performance concrete when the target temperature is more than 600℃.

Abstract:Early shrinkage cracking is one of the important factors leading to the deterioration of concrete, the elongation and extension of cracks can be slowed down or even reduced by adding fibers. The objective of this article was to study the influence rules of regenerated cellulose fibers (RCFs) on the early cracking and the self-shrinkage of cement mortar under the sealed curing. The recycled cellulose fiber, UF500 cellulose fiber and non-absorbent polypropylene staple fiber were compared. The strength, the ratio of flexural strength to compressive strength and the self-shrinkage strains of cement mortar with fibers mixed at 1% or 2% by mass were analyzed. The results showed that the crack-resistance and self-shrinkage could not be improved by adding RCFs when the cement mortar at 0.3 water-cement ratio. When water-cement ratio was higher than 0.35, the ratio of flexural strength to compressive strength of mortar increased by adding 1% RCFs although it decreased the flexural strength and the compressive strength. Then under the quantity, the crack-resistance and shrinkage-reducing effect of cement mortar were enforced, too.

Abstract:The service structure in the complex salt etch environment of sulfate and chloride may be affected by the coupling effect of them. In this paper, the chloride penetration resistance (CPR) of the concrete half immersion in sodium sulfate solution (SSS) under capillary action is studied. The capillary rising test of mortar with different water-cement ratio and different concentration of SSS was designed. Scanning electron microscopy(SEM), X-ray diffraction (XRD) and electric flux of chloride ion are applied to the concrete half immersion in SSS. The results show that the CPRs of concrete samples half immersion in SSS deteriorates, and have obvious degradations at early stage, but recover a bit at later stage. Combined with the results from microscopic tests, the degradations are attributed to the SSSs filled in the pores of concrete samples. The SSS impairs the ability of bound chloride ion and releases more free chloride ions, which increases the electric flux of chloride ion. With the extension of soaking time and the change of the relative humidity of environment, supersaturate SSS comes into being Na₂SO₄ and Na₂SO₄·10H₂O crystals. The admixtures of crystals deposit on the walls of pores, and partially hinder the diffusions of chloride ions, hence increase the CPRs. When the concentration of SSS is higher than 5 percent, the velocity of capillary suction (VCS) slows down and the CPR of concrete is accordingly enhanced with the increase of the concentration of SSS. The VCS can be used to predict the CPR of concrete. The mixed solutions with sodium sulfate and sodium chloride can retard the VCS and then improve the CPR for concrete.

Abstract:The photodegradation process of ofloxacin in ultrapure water at different pH (3,7 and 11) and dissolved oxygen concentration (DO=9 and 0 mg/L) was investigated under UVA-LED irradiation. The results showed that the photodegradation follows first-order-kinetics, mainly direct photolysis. When dissolved oxygen exists, the self-sensitized photolysis could significantly promote the photodegradation. Under different DO conditions, the photodegradation efficiency and rate were the fastest at pH=7, followed by pH=11 and the slowest at pH=3. The main reason for the difference is that the photonic yield of ofloxacin varies with pH value. The analysis of degradation products and their formation process showed that the degradation pathways of ofloxacin was mainly demethylation, piperazinyl ring cleavage/oxidation, hydroxylation and decarboxylation. The degradation pathways and products of ofloxacin under different pH and DO conditions were slightly different, but have a significant influence on the process of products generation and further degradation over time. The above research results clarified the effects of pH and DO on the photodegradation of ofloxacin.

Abstract:The nano-zinc titanate (ZnTiO₃) photocatalyst was prepared by hydrothermal-assisted sol-gel method. Rhodamine B was taken as the target degradant. The effect of initial concentration of Rhodamine B (RhB) on the degradation was analyzed by kinetic model. ZnTiO₃ was characterized by SEM, XRD, XPS and UV-Vis DRS. The degradation mechanism was analyzed by free radical trapping experiments. The results show that ZnTiO₃ is a pure hexagonal phase with a spherical shape and a particle size of about 50 nm. Under the condition of catalyst dosage of 1 g·L^-1, initial concentration of RhB of 5 mg/L and pH of 3, the degradation rate of RhB was 93.2% after photocatalytic reaction for 150 min. Its kinetic equation is k=0.132C₀^-1.253. In the degradation process of ZnTiO₃ photocatalyst, ·OH, h⁺, ·O₂^- all play a catalytic role, and the amount of ·OH and h⁺ is similar and more than ·O₂^-, indicating that ·OH and h⁺ play a major role in the catalytic reaction.

Abstract:Aiming at the possible biological and ecological hazards caused by endocrine disrupting chemicals (EDCs) in domestic sewage, this study took steroid endocrine disruptors as the treatment object, and applied bio-ecological coupling technology to carry out a multi-stage AO+ subsurface flow constructed wetland treatment experiment. The effects of hydraulic residence time (HRT) on the removal of COD_Cr, ammonia nitrogen (NH₄⁺-N), total phosphorus (TP) and total nitrogen (TN) were investigated. At the same time solid phase extraction (SPE) and GC-MS were used to detect the concentration changes of four endocrine disruptors, including estrone (E1), 17β-estrogen (E2), estriol (E3) and 17α-ethynylestradiol (EE2), in the effluent and inlet of each reactor. The results showed that when the HRT of multi-stage AO is 9.5h and that of wetland is about 10.3d, the removal rates of COD_Cr, NH₄⁺-N, TP and TN could reach 78.64%, 97.16%, 91.84% and 90.55% respectively. The concentration is lower than the limit of discharge standard of main water pollutants for municipal wastewater treatment plant and key industries of Taihu area (DB32/1072-2017). The total removal rates of endocrine disruptors E1, E2, E3 and EE2 by multi-stage AO + constructed wetlands were 96.04%, 92.45%, 85.09% and 88.38% respectively. And the removal rates of E1, E2, E3 and EE2 by multi-stage AO system were 75.50%, 72.00%, 65.08% and 63.35% respectively. The first-stage aerobic tank in multi-stage AO contributed the most to the removal of four EDCs, all of which could reach more than 27%. The removal rate of the first three EDCs by wetland system were about 20%, and EE2 was 25%. Alpha diversity index analysis showed that the number and diversity of species in aerobic pond were more than those before EDCs were added. Species and abundance analysis of microbial communities in phylum and genus classifications showed that relative abundance of phylum and genus levels changed, and the increased dominant bacteria might play a role in promoting the removal of EDCs in the system.

Abstract:The energy consumption of air conditioning in residential buildings is determined mainly by the occupants. The key to predict the energy consumption of room air conditioning is to understand how occupants control their room air conditioners. Although the American Society of Heating, Refrigerating, and Air-Conditioning Engineers recommends a uniform occupancy schedule, occupants' behavior patterns vary by region and time. Based on actual monitoring data obtained during 2016-06-01-2016-08-31, factors affecting the energy consumption of the room air conditioner such as the temperature setting and the daily/hourly usage rate were statistically analyzed, as well as the behavioral pattern of air conditioning usage in relation to the daily mean outdoor temperature. The result showed that occupants have a low tolerance to heat indoors and are likely to use the air conditioner even when the outdoor temperature is low. Then the results of the optimized energy consumption simulation model based on the traditional simulation model and the energy consumption prediction model were compared with the measured energy consumption. The results of the optimized energy consumption simulation model that adopted the daily usage rate and the energy consumption prediction model based on the temperature setting of the air conditioner, the outdoor daily mean temperature, and the length of daily operating time was closer to the measured value than the traditional energy consumption simulation model.

Abstract:To reveal the thermal comfort characteristics and thermal environment requirements of outdoor pedestrians and cyclists in hot and humid areas in summer, the methods of environmental parameters testing and questionnaire survey was used to investigated the thermal environment status, thermal comfort, thermal environment preference and thermal environment acceptability of pedestrians and riders, then correlation analysis was carried out. The results show that with the change of shading rate, thermal sensation of pedestrians are more sensitive than that of cyclists, and the comfort level is lower than that of cyclists. The main uncomfortable factors are excessive solar radiation and temperature. The lower the SET* value, the more comfortable pedestrians and cyclists feel. The thermal requirement for pedestrians is that SET* ≤ 30.2℃,TSV ≤ 1.4, for cyclists SET* ≤ 32.9℃,TSV ≤ 1.5, Pedestrians have higher requirements for thermal environment.