Abstract:Four-dimensional Lattice Spring Model (4D-LSM) is a newly developed discrete numerical method considering the extra-dimensional interaction. The method needs large amounts of computing resources in three-dimensional rock failure analysis and therefore is not suitable for the conventional personal computer (PC). In this work, based on the multi-core parallel technology, the computational performance and bottleneck of 4D-LSM were analyzed in details. A variety of hardware environments, such as Alibaba cloud, multi-core PC, and multi-core workstation, were selected to investigate effects of the model size, problem type, thread number and hardware configuration on the parallel computing performance. It is found that the memory capacity determines the limit size of the computable model, and the computational time of the elastic problem is proportional to the model size. The parallel computing efficiency is affected by both the CPU performance and memory bandwidth. The flexibility of cloud computing in multi-core matching and memory allocation is especially suitable for parallel computing of 4D-LSM without considering the economic factor. Through analysis, it is found that the maximum size of 4D-LSM based on Alibaba cloud can reach 1 billion particles. However, due to the bottleneck lies on the pre-processing and post-processing, the current maximum capacity of 4D-LSM is still limited to 20 million particles. Finally, as an example, 4D-LSM was used to solve a three-dimensional coin-shaped crack propagation problem.

Abstract:Concrete face rockfill dams vary in structural dimensions. Efficient and refined analysis methods are important tools in seismic research of the face-slab dams. In this paper, via combining the non-linear scaled boundary polygon element method with efficient quadtree discretization technology, the application of high-performance refined analysis of the concrete face dam is investigated. Firstly, the static and dynamic analysis and permanent deformation calculation of the same face-slab dam model are carried out by using the scaled boundary polygon element method and the traditional finite element method. Subsequently, combined with the quadtree discretization technology, the high-efficiency cross-scale fine analysis of typical face-slab dam structures is applied. The computation results indicate that:(1)the two methods are in good agreement, indicating that the scaled boundary polygon finite element method is an effective tool in the analysis of the dam. (2)The scaled boundary finite element method can be seamlessly coupled with quadtree technology for efficient cross-scale fine analysis applications, and is efficiently in the reconstruction of analysis model, which greatly improve the analysis efficiency. Thus it is concluded that this method can provide technical support for study of local damage evolution and progressive damage of structures.

Abstract:The classical Coulomb and Rankine earth pressure theories are based on the assumption that the soil near a retaining wall are semi-infinite. It is obvious that these theories are no longer suitable for the narrow backfill behind a retaining wall. A series of numerical simulations are conducted by DEM to study the active failure process of limited cohesionless soil with finite width behind a rough and smooth walls. The development of the failure surface, the displacement field of the soils and the distribution of active earth pressure are analyzed. The results show that multiple slip surfaces occur in the backfill if the region behind the smooth wall is narrow enough. The slip surface angle is close to the Coulomb's theoretical solution, which shows no relation with the width height ratio. This ratio also has little influence on the active earth pressure in this case. In another case, when the wall is rough, the actual shape of failure surface is a curve rather than a straight line. The rougher the wall, the weaker the reflection. The angle of failure surface decreases along with the width height ratio of soils increases. And the failure surface is finally located inside the Coulomb's failure surface. There exists a critical width height ratio of soils behind the rough wall. The active earth pressure decreases with increases of the ratio if it is smaller than the critical value, but the active earth pressure is independent from the ratio if it is larger than the critical ratio. The smaller the width height ratio is, the smaller displacement of the ultimate equilibrium state will be, regardless of roughness of the retaining wall.

Abstract:A series of one-dimensional consolidation tests were performed on two types of clays dredged from Xiangmiao-Fushan section of Huaihe River with measured pore pressure at specimen base. Based on the experimental data, the difference between the degree of consolidation determined by settlement-time curve fitting method (the Casagrande method) and excess pore pressure dissipation method is investigated. The results show that excess pore pressure is not completely dissipated when the degree of consolidation determined by the Casagrande method reaches 100% and the remaining undissipated is about 10%~20% of the staged loading. Besides, the difference in settlement determined by the two different methods has a semi-logarithmic relationship with the vertical effective stress. In the end, the vacuum drainage preloading is taken as example to investigate the differential magnitude in settlement determined by the two different methods.

Abstract:Double cut-off walls have been widely used in deep overburden foundation with alternating interloyered soils in Southwest China. However, how to determine the spacing and the layout of double cut-off walls, and the effect of seepage control need to be further investigated. In this paper, based on the unsaturated seepage theory, taking the deep overburden dam foundation with alternating interlayered soils as an example, double cut-off walls are experimentaly studied. The seepage discharge and exit gradient were obtained, and seepage control effect of cut-off walls under different layouts was discussed. Results show that the total seepage discharge and the exit gradient decrease with the distance. The seepage discharge of dam body is divided by the spacing of 13.2 and 16.5 cm, which increases at first and then decreases. Seepage discharge of dam foundation is divided by the spacing of 13.5 and 17.5 cm, which decreases at first and then increases. The wall with deeper penetration depth reduces the head of water more. The front and back walls reduce 37.5 percent and 50 percent, respectively, when the depth of two cut-off walls are same. It is found that given the same total penetration depth of two cut-off walls, the arrangement form with short in front and long in back decreases seepage discharge and controls exit gradient more effectively, which is therefore recommended for priority.

Abstract:Cushion is the core of composite foundation, which can coordinate the differential deformation between piles and soils. The working characteristics of the cushion may change when the pile penetrated into the cushion, which is lack of inrestigation at present. In this paper, by means of model tests, the working characteristics of the cushion during the penetrating of pile were analyzed by measuring the pile top's pressure, displacement and deformation of cushion. Besides, the effects of the pressure between piles and soil, and the pile diameter on the cushion were analyzed. The results show that, during penetraton process, there are three different deformation stages, i.e., compaction deformation, shear deformation and crush deformation. The pressure between piles and soils affects the whole process of the cushion's deformation, and the bearing capacity and the bearing thickness of the cushion are increased with the pressure. The effect of the pile diameter on the cushion is signigicant in the crushing deformation stage. The bearing thickness of the cushion increased linearly with the pile diameter.

Abstract:This study aims to explore the bearing characteristics of rigid pile-net composite foundation with multi-layer reinforced cushion. Firstly, the reinforced cushion layer with multi-layer geogrids is regarded as a large deflection plate for simplification. The interaction characteristics between multi-layer geogrids and gravel cushions were analyzed based on laminating theory. The stiffness matrix of reinforced cushion was then derived. Considering the actual three-dimensional stress and displacement boundary of the rigid pile-net composite foundation, the stress function and the deflection differential control equations were deduced through the static equilibrium. Subsequently, Galerkin method was used to solve the equations. Based on the deformation of the reinforced cushion layer, the pile-soil stress ratio of rigid pile-net composite foundation was calculated through Winkler foundation beam method and the tension force of geogrids was derived via large deflection plate theory. Finally, the calculation method was validated by practical engineering. The factors that affect pile-soil stress ratio and tension force, such as total number of geogrids, geogrids spacing and location of the geogrids, were systematically analyzed. It is shown that the analytical solutions agree well with the measured data. With increase of the total number of geogrid layers, the pile-soil stress ratio increases and the geogrid tensile force decreases. The most efficient number of geogrid layers is 2 or 3. With the increase of vertical spacing between geogrids and the spacing from the bottom geogrid to pile cap, pile-soil stress ratio decreases and tension force increases. More importantly, these findings may provide guidance on optimal design of geogrid in engineering practice.

Abstract:To study the bond anchoring performance of full-thread high strength bolts, pull-out tests were carried out on forty-eight specimens in twenty-four groups, where the influential factors on bond anchorage capacity were considered, including the bolt type, bolt diameter d, the anchorage length l_a and the thickness of concrete cover c. The results show that the anchorage performance of straight high strength anchor bolts was lower than that of with head ones. The bond stress of straight high strength anchor bolt was mainly concentrated on the contact area within the anchorage length 10d. Its bonding performance increases with the thickness of concrete cover. However, increasing the anchorage length will reduce the influence of the thickness of concrete cover on the bonding property. The energy translation and dissipation of high strength anchor bolt under tension are influenced by the concrete failure pattern and anchorage length. Moreover, the calculation formula in the design codes provide over-conservative estimation for the critical anchorage length of anchor bolts.

Abstract:To investigate the influence of CFRP and fine aggregate type on strengthened seismic performance of corroded reinforced concrete short columns(RCSCs), the pseudo-static tests of one un-corroded reinforced concrete short column reinforceel concrete short column(RCSC), two corroded RCSCs and four corroded RCSCs strengthened with CFRP were carried out in this study. Besides, a practical method to calculate the shear strength of corroded reinforced concrete columns strengthened with CFRP was suggested. Experimental results show that the corrosion of steel bars will weaken the seismic performance of short columns. The shear bearing capacity, ultimate deformation capacity and cumulative hysteretic energy dissipation of corroded RCSCs are reduced by 7.8%, 35.5% and 42.2%, respectively. CFRP wrapping can enhance the shear strength of corroded RCSCs to a level of 107.1%~109.1% of that un-corroded RCSC, and can significantly improve the ductility and energy dissipation capacity of corroded RCSCs. When CFRP layer is increased from one to two, the shear capacity of the reinforced specimen is marginally improved, and the maximum strain of CFRP decreases when the specimen reaches the peak load. Moreover, the hysteretic rules for the dimensionless hysteresis loops of RCSCs closed to limit state for cases with un-corrosion and with corrosion, without CFRP strengthening and with CFRP strengthening are similar.

Abstract:This paper aims to study the mechanical performances of reinforced concrete two-way slab with different stud parameters. The experimental study on seven reinforced concrete two-way slab-column connections with punching shear studs was conducted. The main parameters investigated were spacing of stud, the diameter of the stud, the height of the stud, the strength of the stud and the arrangement of the stud. The whole process of damage of slab-column connections with studs was simulated using static loading method. The results show that increasing the diameter of the stud, the height of the stud or the strength of the stud can improve the anti-punching shear performance of the specimen. The increase in diameter is the most obvious, and the decrease in deformation is up to 36%. Increasing stud spacing and reducing stud height weaken the load-bearing capacity and thus the deformation are increased. By comparing three different stud layouts, it is found that using radiation type contributes better to the improvement of the specimen anti-punching shear capacity, and the former was more economical. Then, the accuracy of the test results was verified by comparing the calculated results of relevant specifications with the test results. The results show that the safety reserve of specification calculation results of slab-column structure with studs is sufficient. However, it is not enough to reflect the nature of test results, especially contributions of the stud to anti-punching shear performance of slabs are underestimated.

Abstract:Vertical vibration would be incurred easily under the pedestrian-elevator load in the cantilevered floor with erecting escalators. The cantilevered floor in a commercial interlayer is used as an example to study the vertical vibration response considering the influence from the escalator operation, the number of pedestrians and the walking direction.Based on the test data, we evaluate the comfort of the cantilevered floor and the perception of personnel. Results show that the pedestrian frequency is the primary factor affecting the vibration of the cantilevered floor, while the operation of escalator is a secondary factor. It is also found that compared with the unidirectional walking, the vibration response of the cantilevered floor becomes to be weakened obviously when people are walking on the escalator in two-way by the same step. The peak acceleration is used to evaluate the comfort of the cantilevered floor. It is revealed that when the pedestrian runs on the escalator, the vibration response of the cantilevered floor is easy to exceed the comfort limit. And we use the KB (Konstant Beurteilungswerte) value to evaluate the comfort of cantilevered floor. When the pedestrian is stationary relative to the escalator, the vibration of the cantilevered floor does not exceed the perceptibility allowable value. However, when the pedestrian walks or moves relative to the escalator, the vibration of the cantilevered floor will exceed the threshold value.

Abstract:This paper studies the heat conduction limit of fire protection for isolated rubber, and provides theoretical evidence and experimental data for fire protection. Based on one-dimensional unsteady heat conduction, formula under ISO834 standard fire is derived. According to the GB 9978.1-2008 fire test, three kinds of components, LNR500, LNR1500 support board fire protection, LNR500 support board with flexible fireproof material fire protection, are tested.Modeling and finite element thermal analysis are carried out via ABAQUS. The numerical analysis and fire test results verified the proposed theory. Based on the derivation and experimented data, when the temperature of the support surface reaches the critical temperature of 150℃, the table of the limit thermal conductivity of fireproofing board with different thickness can be referred in engineering applications.

Abstract:The effect of transverse diaphragms on the temperature field of concrete bridge with T-girders under fire was investigated based on the character of pool fire flame spread in this study. Firstly, the dimensionless relation ship between the total flame extension length and the heat release rate was studied theoretically. Then the fire models of the T-girders bridge with 4 fire scenarios were built in the FDS to analyze thespatio-temporal distribution of the boundary temperature. Boundary temperature and heat flux were subsequently translated to the finite element model of T-girder after surface fitting in order to analyze numerically the temperature field inside the T-girders. The simulation result shows that:the proportional coefficient of 2/5 power of dimensionless heat release rate to the dimensionless total flame extension length is greater than 2.58. The diaphragm effectively reduces the boundary temperature of the indirect influence area of the fire source, and divides the boundary temperature along T-girders into four step sections with 9.7%, 41%, and 56.8% respectively in boundary temperature reduction compared to the case of no diaphragm. Besides, diaphragm reatrains the heat transmitting along the girders. In the section above fire source, the temperature girders of the T-girder are 33% and 13.3% higher in the center and bottom of the rib and 5% higher in the bottom of flange than the similar case without diaphragms.

Abstract:The aluminum alloy material is of advantages, including as high strength, good deformation performance and corrosion resistance. And it is an ideal strengthen engineering material for reinforced concrete structures in coastal erosion environment. The bonding performance of the aluminum alloy plate and the concrete is the key issue for cooperative work of RC beam strengthened with aluminum alloy plate. Therefore, the bonding behaviors between aluminum alloy plate and concrete are studied theoretically and experimentally. In order to take into account the effects of concrete strength, width and thickness of aluminum alloy plate, bonding length and interfacial treatment on bonding performance between aluminum alloy plate and concrete block, a set of fixture device was designed. In-plane simple shear tests of 105 aluminum alloy plates adhering on concrete prism were carried out by universal testing machine. Combined with experimental results and theoretical analyses, the typical bond failure characteristics, the distribution of shear stress and the bond-slip curve were obtained. Results show that there are two types of failure modes on specimen:failure caused by debonding of interfacial and by stripping of concrete layer. Interfacial treatment has important influence on the bonding properties. Failure caused by interfacial debonding appeared on specimen with no rough treatment. Failure of the other specimens is stripped by concrete layer. The bonding performance is improved with the increase of concrete strength, and decrease of width and thickness of the aluminum alloy plate. The bonding ultimate load cannot be increased when the bonding length is greater than that of the effective bonding length.

Abstract:The foamed concrete (FC) was produced by using the main materials including Portland cement and foaming agent of animal protein. The effects of water-cement ratio, dry density, fiber lengths and fiber types on strengths, complete stress-strain curves under uniaxial compression, distributions of pore size and water absorption capability were investigated. Test results indicate that the compressive strength decreases exponentially with increasing porosity for both FC and fiber-reinforced foamed concrete (FRFC). The compressive strength has its different changing patterns with water-cement ratio for different fiber contents and porosities. In addition, the compressive and tensile strengths can be apparently raised by shorter fiber filament and change variously with different fiber contents. A greater improvement of compressive and tensile strengths is obtained by adding fiber meshes compared with fiber filaments under the same conditions. Three segments are discovered in the complete stress-strain curve, which include ascend, decend and fluctuant processes. The peak strain of FRFC reduces, however, the modulus of elasticity and residual strength of FRFC increases. For FRFC, the percentage of pore with larger radius decreases with increasing fiber content. Thus, the water absorption capability can be enhanced by fiber.

Abstract:The solution with ZnSO₄ was chosen to repair the crack of concrete by electro-migration. To explore the influence of current density on electrodeposition repairing performance, mineral composition and microstructure of the sediments, the electrical resistance and crack filling depth were used in this study. Results show that the resistance of concrete specimens increased significantly after the electrodeposition repair for 36 days, and the growth rate of resistance decreased with increase of energization days. The early rate of the resistance increase was faster, and the depth of crack filling was more shallow with increase of current density. Besides, X-ray diffraction results showed that ZnO was the main mineral component of the sediments. Scanning electron microscopy results showed that the size of sediment particles increased with increase of current density. The rank of sediments was more ordered and the microstructure was more compacted as the current density decreased.

Abstract:The properties such as surface hardness, compressive strength, freeze-thaw resistance and other properties of the prepared glutinous rice mortar were determined by mortar performance. The influence of the species of aggregate, the size of the particle and the amount of the aggregate on the properties of glutinous rice mortar are discussed and its action mechanism is explored by means of SEM and XRD. Results show that the addition of silica sand, river sand and brick grain improve the shrinkage and freeze-thaw resistance. Among the three aggregates, brick grain make the freeze-thaw resistance of sticky rice-lime mortar increased by 125% compared to blank sample. However, with increase of aggregate particle size and bone ash ratio, the compressive strength, freezing-thawing resistance and shrinkage of aggregates decreased. Therefore, for the protection practice of brick cultural relic, it is suggested that the brick grain is added as the aggregate, the grain size is controlled to be within 3 mm, and the aggregate to lime ratio below 2:1, which is the optimal way to improve the performance of glutinous rice mortar.

Abstract:Multi-walled carbon nanotubes/cuprous oxide (MWCNTs/Cu₂O) composite microspheres were fabricated by liquid phase reducing method. The analycis of the functional group, phase and morphology on the samples were characterized by fourier transform infrared spectrometer (FTIR), scanning electron microscope (SEM) and x-ray diffractometer (XRD), which indicated that MWCNTs were combined with Cu₂O to form composite microspheres by vertical and horizontal interspersing. The results showed that compared with the photocatalytic activity of the Cu₂O, the MWCNTs/Cu₂O composite catalyst has more excellent catalytic effect on target organic compound N-formylmorpholine.

Abstract:In this study, a complex UV initiation system was established by utilizing low light intensity and then high light intensity with redox initiator and azo initiator compound. Acrylamide (AM) and diallyldimethylammonium chloride (DMDAAC) were used as monomers to copolymerize P (DMDAAC-AM) (PDA). Initiators with different activation energies were injected to the system, and UV light with were different intensities is controlled to generate radicals at different times. Therefore, high intrinsic viscosity PDA could be prepared as a consequence of even and thorough polymerization. Effect of factors on the intrinsic viscosity of PDA was investigated, and the optimal synthesis condition was obtained. The results indicated that the highest intrinsic viscosity of 19.60 dL/g was reached at V-50 concentration of 0.3‰, (NH₄)₂S₂O₈-NaHSO₃ concentration of 0.4‰, low light intensity of 8.5 mW/cm² then increased to 13 mW/cm², mass ratio between AM and DMDAAC of 8:2 and total monomer mass percentage of 20%. It was confirmed that PDA was the copolymer of AM and DMDAAC through proton nuclear magnetic resonance spectroscopy and Fourier-transform infrared spectroscopy. In addition, the prepared PDA possessed an acceptable thermostability and favorable flocculation performance which can be confirmed through thermos gravimetric analysis and the flocculation experiment.

Abstract:Because of the complexity of the internal space structure and function diversity, personnel behavior in commercial complex, the load characteristics,plants operation and indoor environment are complex. Therefore, the chiller plants design and energy optimization need to combine their own characteristics. Firstly, through indoor thermal environment test to analyze the air conditioning demand of commercial complex, it is found that the indoor environment fluctuates more greatly compared with traditional commercial buildings, and there are significant differences among different commercial types. Secondly, the refrigeration system operation is analyzed through chiller plants operation records. It is indicated that the cooling load of commercial complex is relatively stable with the refrigeration system running for a long time, and the design capacity of the plants is generally too large. Finally, the load characteristics is analyzed through DeST modelling, and different chiller plants design optimization is compared. The result shows that the refrigeration system design method according to the commercial type load distribution is beneficial for energy efficiency, especially in the commercial complex with scattered commercial type layout and large difference in cooling load of different commercial type.

Abstract:In order to investigate the heat transfer process in the closed-type heat source tower under the non-frosting condition in winter, the finite difference method was adopted to develop the dynamic heat and mass transfer model. Comparing the calculated results with the experimental findings, the root mean square error of the outlet solution temperature turns out to be 0.201℃ and the validity of the model is verified. The dynamic heat transfer characteristics of the closed-type heat source tower on variable load operation are analyzed through experiments and simulations, which show that the closed-type heat source tower, as a heat extraction device, can provide a relatively stable heat source for the evaporator when the heat pump unit working under changing operating mode. Besides, compared with the traditional air source heat pump, the closed-type heat source tower has lower frost formation risk and higher energy saving potential under low temperature and high humidity environment.

Abstract:Bathing was tewater contains a large amount of neaste heat, a double heat pump unit in series with large temperature difference was proposed to maximize the recovery of waste heat energy from bathing wastewater. The rated design conditions of the unit are as follows, the inlet and outlet temperatures of the bathing wastewater on the evaporator side are 30℃ and 6℃、respectively and the inlet temperature of tap water on the condenser side is 10℃ with hot water outlet temperature at 45℃. In this study, the effects of inlet temperature of tap water, outlet temperature of hot water and inlet temperature of bath wastewater on thermal performance of heat pump unit were studied experimentally. The experimental results showed that the COP reduced from 5.0 to 3.85 as the inlet temperature of tap water increased from 5℃ to 15℃. When the outlet temperature of the hot water changed from 40℃ to 50℃, the COP reduced by 7.5%. And when the inlet temperature of bathing wastewater rose from 30℃ to 35℃, the COP increased by 3.1%. In the absence of an auxiliary heat source, if the bathing wastewater temperature reduces from 30℃ to 6℃, the tap water temperature must be higher than 12℃ to ensure that the hot water outlet temperature is 45℃. Besides, when the inlet temperature of bathing wastewater reaches 35℃, the hot water outlet temperature can also reach 45℃ even if the tap water temperature is 6℃.