In this paper, the prediction of the energy transmission spectrum for layered periodic structures is studied. By considering three cases of geometric parameters and physical parameters changing individually or simultaneously, a deep back propagation (BP) neural network is constructed to realize accurate prediction of the energy transmission spectrum of layered periodic structure. A comparison of the predicted results with those obtained by the radial basis function (RBF) neural network verifies the effectiveness of the proposed method.
Aimed at the nonlinearity and uncertainty of building energy consumption, a forecasting approach based on the support vector machine is proposed in this paper for the prediction of hourly energy consumption of an office building. The univariate model test is used to determine the input parameters. Superior model hyper-parameters are found by grid search optimization. The confidence interval of the model fitting error is applied to describe the uncertainty of building energy consumption. A case study is conducted using the data collected from an actual office building to verify the proposed approach. The results show that the overall mean absolute percentage error (MAPE) of the model after grid search optimization is reduced by 31.3%, and a higher model precision is achieved. After combining the prediction with the confidence interval, MAPE is found to be lower than 1.5% in different seasons and the building operation fluctuations are embodied. This approach can be used in the diagnosis and optimization of building operation.
Aimed at the wind-induced response and vibration reduction of an H-rotor type three-bladed vertical axis wind turbine (VAWT), and based on computational fluid dynamics (CFD) method, a numerical simulation is conducted to obtain the blade wind pressure distribution during the rotation period. Then, the wind pressure obtained is applied to the surface of the blades to analyze the wind vibration response of the VAWT. Dampers are arranged at different positions of the VAWT to simulate the vibration reduction capacity. The results show that applying the damper at the connection between the main shaft and the support rod of VAWT could reduce the displacement response of the structure to a certain extent and the maximum drop would reach 44%. Furthermore, the displacement reduction rate of the structure is related to the position of the damper. If a damper is arranged near the top end of the blade, the maximum displacement of the structure would occur at the bottom of the blade. However, if a damper is arranged near the bottom end of the blade, the maximum displacement of the structure would occur at the top of the blade and the maximum drop would reach 40.7%. The results would provide technical reference for research on the vibration reduction of VAWT structures.
The infill wall has a significant influence on the progressive collapse resistance of the precast concrete (PC) frame, and there is no corresponding design method at present. In order to obtain a reliable calculation method for progressive collapse, a numerical and analytical analysis of progressive collapse resistance of PC frames with infill walls was conducted. According to the 3∶1 scale test of PC frames with and without infill walls after removing middle column, and considering the displacement of middle column under the asymmetric distribution of infill walls, a mechanical model based on equivalent strut was established by introducing asymmetry coefficient. Based on the finite element (FE), numerical models of the sub frames with the asymmetric infill walls were established, and displacement-load curves of the middle column were obtained, based on which, the analytical solutions were compared with the test results of bare, double, and single infill wall PC frames, and the results were found in good agreement. A comparison of the calculation results with the recommended values in current codes indicates that the displacement of PC frames under the peak load of catenary is increased when considering the infill wall. The recommended value of the displacement, whose middle column is 0.2 times of the span, is suitable for the bare PC frames, but conservative for the PC frames with infill walls. The results provide a basis for the calculation of the progressive collapse resistance of PC frames with infill walls.
For the foundation of the monopile in the shallow water environment,a scale model of sand-monopile-wave was adopted in the wave flume simulation experiment, and the static load test of the monopile under wave action was explored. The pore water pressure of the soil around the monopile and the settlement of the monopile at different wave loads were examined. Based on the static load test results, the interaction mechanism between sand and the monopile subjected to wave load, the characteristics of load settlement curve,and the influence of excess pore water pressure (ps) on the vertical bearing capacity of the monopile with various pile diameters were analyzed. The results show that due to the presence of the monopile, the ps of the soil around the pile increases whereas the ps at the bottom of the monopile decreases. However, the ps around the pile increases with increasing pile diameter. The bearing capacity of the monopile under the influence of wave load is less than that without wave load. At the same load, the pile settlement increases remarkably and the increase is more obvious in the case of larger pile diameter. The experiment shows that the effect of wave load on the pile foundation bearing capacity should be monitored during the design process.
The high accuracy small strain triaxial apparatus (hereinafter inferred to as the new triaxial apparatus) developed and assembled by Shanghai Jiao Tong University adopts a built-in pressure chamber by integrating the stress and strain loading function automatically controlled by the program and the linear variable differential transformer (LVDT) function of measuring small strain. In this paper, the new triaxial apparatus is further expanded. Now it has the function of measuring K0 coefficient of undisturbed soil sample and performing stress path loading along any direction of q-p (q is the deviatoric stress and p is the average principal stress) stress space. First, the development history of the new triaxial apparatus is briefly introduced and the control program algorithm of K0 coefficient measurement and stress path test for the two new functions are described in detail. Then, the K0 coefficient measurement and stress path test for deep soft clay in Shanghai are conducted, and the results are analyzed to verify the reliability of the new functions. The experience of the new triaxial apparatus can provide reference for the development of geotechnical instruments.
To predict the ultimate bearing capacity of long-term loaded piles, the shortcomings of current empirical formulas of pile bearing capacity considering time effect are discussed. Based on the current research of the bearing capacity of static bearing piles in natural saturated clay, factors for the bearing capacity of long-term loaded old piles are analyzed. Then, based on analysis of the data from pile foundation bearing tests, the formula for calculating the ultimate bearing capacity of jacked piles considering the time effect and the current pile foundation technical code is proposed, in which the pile side resistance aging coefficient of pile side resistance is proposed, and some factors for the aging coefficient are discussed. Based on the experimental data, a method for calculating the parameters in the formula by using soil properties is proposed. The accuracy of the proposed method is verified by a field test. The results show that this pile side resistance aging coefficient can predict the bearing capacity of single pile under current code, increase the design value of the bearing capacity of old piles while ensuring safety. By using the undrained shear strength and plasticity index, the pile side resistance aging coefficient can be predicted.
Uniaxial tensile tests of ethylene-chloro-tri-fluoro-ethylene (ECTFE) foils were conducted at a thickness of 250 μm and various low and high temperatures (-50, -40, -30, -20, -10, 0, 10, 20, 30, 40, 50, 60, 70, and 80 ℃). The specimens were fabricated according to the machine direction (MD). The tensile stress-strain curves of the foils at various temperatures were obtained. According to the variation discipline with temperature, several parameters such as elastic modulus, yield stress, yield strain, cold drawing stress, tensile strength, and tensile strain at break were subsequently analyzed and calculated. The results show that with the elevation of the stress-strain curves, the yield strength, tensile strength, cold drawing stress, and elastic modulus increase, but the strain at break and toughness decrease when the temperature decreases. At a wide range of temperatures from -50 ℃ to 80 ℃, the difference of elastic modulus can increase up to 93%, with a yield stress of 89%, which reflects the great sensitivity of ECTFE to temperatures. The fitting formulas of main mechanical parameters are also obtained, which can be used to predict the mechanical properties of ECTFE foils at various temperatures.
According to the engineering characteristics of pile foundation in soft soil layer, a virtual column structure model was proposed, and a theoretical solution to pile foundation settlement displacement was established. Besides, the load transfer characteristics of pile foundation in soft soil layer, the bearing mode of pile foundation, and its dynamic relationship with the gradual evolution of load and environmental conditions were studied. The results show that there are friction bearing and friction with pile end bearing modes in pile foundation, and they change significantly with pile top load, construction, and environmental factors. Affected by the load transfer law, there is a 0-axis force section in the axial direction of pile foundation. The relationship between the depth and the length of pile foundation affects the type of bearing mode and displacement calculation results. The field results verify the correctness and applicability of the theoretical method.
Based on the Pasternak model of elastic foundation beams, and combining the effective stress principle of soil and Dupuit hypothesis, the analytical solution of adjacent pipeline deformation in sandy soil caused by single well dewatering is derived. The example calculation results are in good agreement with the results of pumping test and numerical simulation, which verifies the applicability. The law of stress and deformation for the pipeline is studied by parameter analysis. The results show that the influence of soil shear stiffness should not be ignored in the study of soil-pipeline interaction and the pipeline deformation range is approximately equal to the influence radius of dewatering. Pipeline deformation and stress are greatly influenced by dewatering depth and the distance between the pipeline and the dewatering well. Before reaching the critical drawdown, the maximum value of pipeline deformation and bending moments are at the center of pipeline, increasing with the increase of dewatering depth. When the dewatering depth exceeds the critical drawdown, the maximum bending moment will shift outward from the center with the increase of the dewatering depth, resulting in two peak bending moments which are at the intersection of the water level line and at the pipeline. The research results can provide reference for pipeline protection in relevant projects.
To solve the fresh water scarce problem in dry regions, a desiccant wheel-assisted atmospheric water harvesting system is designed. Using water production rate as the index, studies are conducted to find the optimized air handling process under typical ambient conditions, considering influencing factors such as air flow rate ratio, stage numbers, and regeneration temperature. Based on a three-stage-desiccant wheel air humidification system, power consumptions are calculated for ideal and actual thermodynamic processes. Besides, using water production efficiency as the index, at the same water production rate, this system is compared with the traditional air-cooling method. The results show that this system has higher performances than the traditional air-cooling method. Under the discussed working conditions, the water production rate of the proposed system is in the range of 15.8—30.9 kg/h and the water production efficiency is in the range of 1.3—2.1 kg/(kW·h). The water production efficiency can be enhanced to 3.3—4.4 kg/(kW·h)when solar heater is used to replace heat pump systems. The proposed method can effectively enrich fresh water sources in dry regions.
A numerical simulation is conducted to investigate the local scour of the seabed around the pile under the actions of both solitary waves and currents. By solving the N-S equations enclosed by the RNG k-ε turbulence model, the change of the flow field around the pile is simulated accurately. The sediment transport model considers all the sediment transport processes including entrainment, suspended load transport, deposition, and bed-load transport. For the slope seabed, the influence of gravity on the sediment particles is considered, and the shields parameter is modified. The accuracy of the model is verified by comparing the numerical results with the experimental data. Besides, the process of scour development at different wave heights is investigated in detail. The effect of pile foundation protection layer on scour is preliminarily studied. The results show that the combined solitary wave-current conditions have a significant effect on the scour depth around the pile than the current-only or wave-only. The scour depth around the pile on the inclined seabed is larger than that of the horizontal seabed. The setting of protection layer can effectively reduce the local scour depth around the pile. In addition, the particle size of the protective layer has a great influence on the protective effect.
The damping matrix of the complex damping model is easy to be constructed, which only depends on the material loss factor and the structural stiffness matrix. However, the complex damping model has some shortcomings, such as time-domain divergence and causality. Structural inherent characteristics are constant, so that the equivalent relationship between material loss factor and structural damping ratio is deduced and the viscous damping model which is equivalent to complex damping model is obtained. The proposed damping model overcomes the shortcoming of the complex damping model. Besides, the convenience that the complex damping model is directly dependent on material loss factor is retained. According to the equivalent relationship between the material loss factor and structural modal damping ratio, the real mode superposition method based on the proposed damping model is suggested for the proportional damping system. For the non-proportional damping system, according to the equivalent relationship between the material loss factor and modal damping ratio of the substructure, the complex mode superposition method based on the proposed damping model is proposed by the aid of Rayleigh damping and the state space method. The example analysis proves the feasibility and correctness of the proposed method.
Overlying excavation will inevitably cause uplift of the existing tunnel due to the stress relief and rebound of soil, and the impact will be more significant when the long-distance is in line. Based on the Timoshenko simplified model of tunnel which considers the shearing dislocation between rings, and combining with the Winkler foundation model, an analytical model for soil-tunnel interaction analysis of overlying excavation was established. Based on the superposition principle, the model proposed was applied to a case study of tunnel deformation induced by overlying long-distance collinear excavation. By comparing the calculated results with the measured data, the accuracy of the proposed model was verified. The analysis results show that after the construction of the upper main structure, the uplift deformation of the tunnel has significantly decreased, but the local differential settlement increases, resulting in a significant increase in the internal force of the tunnel and the deformation of the annular joint. The groundwater leakage generally occurrs not at the location with the maximum uplift of tunnel, but between the location with the maximum opening of joint and the location with the maximum shearing dislocation. As a result, not only the total deformation but also the opening and dislocation deformation of joints caused by differential settlement should be concerned in practice. Although the shear deformation generally accounts for about 21.41% of tunnel deformation, the induced shearing dislocation is significant compared with the opening caused by bending, which can be more important for waterproof in joints. The analytic model should not neglect the shearing deformation of the tunnel.
The pile foundation of offshore wind turbines is not only subjected to the cyclic action of wave load, but also the threat of seismic load. Therefore, the environment of pile in the ocean is complex. However, most theoretical investigations have often focused on the seabed response at water wave load or seismic load respectively. In this paper, a wave-seismic-pile-seabed coupling model is constructed by using the finite element method. The numerical analysis is based on the implicit dynamic analysis in Abaqus. Morison’s equations are used to simulate the effect of water wave on pile foundation. The Mohr-Coulomb model is adopted to simulate the seabed while the pile is considered as an elastic medium. The earthquake is applied on the bottom of the model as acceleration. The dynamic response of the pile embedded in seabed are studied, such as acceleration, displacement, shear force, and bending moment. The results show that seismic load has an important influence on the single pile foundation of offshore wind turbine. Under the action of earthquake load, the acceleration and displacement response of the pile are amplified to a certain extent. The properties of the soil and the parameters of the pile are crucial to the design of the single pile foundation for offshore wind turbines.
This paper conducted a three-point loading experiment and analytical investigations on the shear performance of reinforced concrete (RC) beams with anchor defect at the lower end of stirrups. In the experiment, artificial methods were used to simulate the anchor degradation of the lower end of the stirrup caused by the alkali-aggregate reaction (AAR). The results show that, compared with the sound beams, the anchorage degradation of stirrups reduces the shear capacity of RC beams, and the degree of reduction becomes more pronounced with the increase of the local bond degradation area. The decrease in shear capacity is thought to be attributed to the reduction of the shear contribution by the stirrups and the reduction of the shear resistance by interlock action of coarse aggregate between diagonal cracks. The quantitative evaluation of shear contribution based on the computed stirrup strains confirms that the anchorage defect at the lower end of the stirrup reduces both the shear contribution Vc by concrete and Vs by stirrups, and the reduction of Vs is more significant than Vc.
To study the influence of consolidation on the bearing capacity of the composite foundation in the process of caisson heightening, the consolidation characteristics of the sand pile composite foundation in the process of caisson heightening are discussed based on the sand pile composite foundation engineering of a large-scale onshore caisson foundation. The influence of loading duration and replacement rate of the sand pile are analyzed. Based on the area ratio method of pile-soil and the pile-soil stress ratio method, the formula of the ultimate bearing capacity of the sand pile composite foundation considering the consolidation effect is derived, which is compared with the measured value of the ultimate bearing capacity of the foundation. The results show that the time history curves of the bearing capacity of the composite foundation based on the two methods are close, and the initial bearing capacity is less than the measured value of bearing capacity, while the bearing capacity after consolidation is 68% and 80% higher than the natural strength of the composite foundation. This method considers the influence of consolidation on the bearing capacity of the foundation in the process of caisson heightening. It can avoid the problem of stagnant sinking of open caisson as it underestimates the actual bearing capacity of the foundation, and provides suggestions for calculation of ultimate bearing capacity of the composite foundation considering the influence of consolidation and formulating the reasonable construction scheme of open caisson.
It is generally difficult to consider the fluid dynamic boundary problem in the traditional particle-fluid coupling algorithm, causing calculation errors owing to the mismatching of the fluid-solid boundary and affecting the accuracy of the results in the modeling of large deformation issues. In view of this problem, the dynamic updating method of fluid mesh is introduced and Darcy’s seepage equation and the particle-fluid interaction equation in dynamic mesh are derived. Based on the discrete element commercial software PFC2D, the particle-fluid coupling algorithm considering dynamic fluid mesh is developed. The proposed algorithm is applied to simulate the undrained shear biaxial test of saturated soil. The comparison result with the constant volume method verifies the effectiveness of the developed algorithm. Finally, the algorithm is used to simulate the undrained biaxial tests at different confining pressures. The law of the calculated results agrees well with that of the laboratory tests. By considering the problem of fluid dynamic boundary, the developed algorithm can obtain the fluid-solid boundary matching in the simulation of triaxial compression test and one-dimensional consolidation test or other cases in large deformations, which can help to improve the simulation accuracy and offer a theoretical reference for similar studies.
To investigate the influence of pore size effect on dynamic response of saturated soil foundation, a model for predicting the dynamic response of the ground surface of the saturated soil foundation under incident P wave and SV wave is proposed based on the nonlocal-Biot theory. The analytical solution is obtained using the wave function expansion method. The influence of pore size described by nonlocal parameter, input frequency, and the incident angle on the dynamic response of displacement and stress is discussed in detail. The results show that at low frequencies, the calculation results of the nonlocal-Biot theory are basically the same as those of the classical Biot theory. At high frequencies, the surface displacement and stress change significantly with nonlocal parameters, that is, at high frequencies, the effect of pore size on the surface response cannot be ignored. The influence of incident wave frequency on the ground-surface response is related to pore size, that is, the larger the pore size, the more significant the frequency effect. The influence of SV wave on the dynamic response of ground surface is larger than that of P wave. Besides, the total reflection phenomenon is observed at an incident angle of 45° for the incident of SV wave. The results obtained in this work can provide reference for studying the problem of wave propagation in half-space saturated soil foundation.
Extended finite element method (XFEM) is based on the idea of unit decomposition. The jump function that can reflect the discontinuity of the crack surface and the progressive displacement field function of the crack tip is added to the conventional finite element displacement mode, which avoids the inconvenience of remeshing the crack tip and the heavy calculation. Then the conventional finite element method calculates the fracture problem, and the crack propagation is independent of the mesh. When the standard finite element deals with time integration, the degree of freedom of the overall stiffness matrix will continue to increase in the process of crack propagation, which makes iterative calculation impossible. This paper proposes a novel Newmark implicit time integration scheme based on the XFEM to simulate dynamic crack growth. This method enriches all the nodes with the Heaviside function and the asymptotic displacement field function at the crack tip, that is, each node has 12 degrees of freedom, so that the overall stiffness matrix is consistent without making iterative calculation impossible. At the same time, a sparse matrix technology is proposed to solve the problems of large memory and long calculation time occupied by the matrix.
Based on the principle of mud pressure balance earth pressure, this paper establishes a mechanical model for analyzing the stability of pile hole, and analyzes the applicable conditions and application scopes of the three construction methods, namely, no-support excavation, the hole formation method by mud retaining wall, and the hole formation method by hard support. It also provides reasonable determination methods for maximum depth of pore-creating without support, lower limit value of mud weight of protecting wall, and useful tables. The research results show that the friction angle, the cohesion, and the mud weight of soil are basic factors for maintaining the stability of the pile hole. When the depth of pore-forming is less than the maximum depth of pore-creating without support, no-support excavation can be adopted. Otherwise, hole-forming should be assisted by slurry-support, and mud weight should not be less than the lower limit value of mud weight for the retaining wall determined by the site soil. When the friction angle is greater than 25°, mud weight can be arbitrarily selected. When the lower limit value of mud weight for the retaining wall calculated by look-up table is greater than the maximum mud weight given by specification, casing or other hard support measures should be adopted.
In order to study the dynamic response of a single pile foundation under combined action of wind and wave loads in the marine environment, a three-dimensional unidirectional coupling numerical model of wind wave-seabed-single pile is established. The Reynolds average N-S equation and the Biot dynamic equation are used to control the wave motion and seabed response respectively. Based on the verification of the rationality of the model, the influence of wind and wave parameters (such as wind speed, wind shear coefficient, and wave height) on the response of fluid and pile foundation under combined action of wind and wave loads are explored. The results show that the increase of wind speed, wind shear coefficient, and wave height will aggravate the fluid deformation around the pile, accelerate the wave propagation, and then affect the horizontal displacement and bending moment of the pile. Therefore, when calculating the bearing capacity of offshore pile foundations, the combined effect of wind and wave loads on the pile foundation should be considered comprehensively. The results will provide an important theoretical basis for the study of the bearing performance of pile foundations in harsh marine environments.
A novel test method for analyzing the influence of stress path and roughness of structure on the strength characteristics of saturated sand-structure interface by using triaxial apparatus is presented. By making a triaxial specimen with a slope structure with a certain inclination angle, the soil slides along the preset failure surface during the shearing process, and the slope surface roughness of the structure can be controlled and adjusted. A triaxial instrument is used to control the changes in axial pressure,confining pressure to achieve loading in different stress paths. The soil slides along the structure surface with a certain angle during shearing when preformed failure surface exists. The roughness of the structure can be controlled and adjusted. The triaxial apparatus is used to control the confining pressure change of the sample to realize loading under different drainage conditions and stress paths. To verify the effectiveness of the method, direct shear test and triaxial shear tests are carried out on the specimen composed of Fujian sand and steel structures with different roughness and different stress paths. The results show that at the beginning of sliding, the friction angle of the interface in the interfacial constant normal stress path is smaller than that in the conventional shear path. Under smooth conditions, the interface friction angle obtained by direct shear test is 30% to 40% lower than that obtained by triaxial test. Under rough conditions, the interface friction angle obtained by direct shear test is slightly smaller than that obtained by triaxial test, and closer to the friction angle in normal stress shear paths.
Integral steel platform formwork is widely used in the construction of super high-rise buildings, which brings a high degree of risk uncertainty to construction personnel. Therefore, it is crucial and necessary to establish a risk-based evacuation model for steel platform formwork in skyscraper construction. First, the spatial distribution of hazards sources on the steel platform is considered, hazardous areas are defined, and expert data are collected through survey questionnaires to assess the joint risk probability. Next, the joint risk probability of hazardous areas is coupled into the evacuation process based on the cellular automaton floor field model, and the evacuation process of construction personnel on the steel platform is simulated. Finally, the proposed risk-based evacuation simulation model is applied to an actual construction project. The results show that the influence of the top and lower hazardous areas on the evacuation process is significantly affected by the size of the exit. The model provides a new paradigm for experience-oriented construction safety management, with a theoretical and application value for the maintenance of the integral steel platform formwork system.
