Abstract:In order to reveal more information and understand the behavior and failure mechanisms of high strength steel endplate connections, a full-scale experimental and numerical study is carried out and presented in this paper. Moreover, their experimental behaviors are compared to the numerical results and relative provisions of Eurocode 3. The test results show that the failure mode of high strength steel end plate connections is bolt failure with flange yielding, and the rotation capacity of high strength steel beam-to-column end plate connections is sufficient. Furthermore, the component-based method of Eurocode 3 based on mild steel connections is used to calculate the plastic resistance and to predict the failure mode of high strength steel end plate connections, but it is not suitable to predict their stiffness. Meanwhile, the suggestions on rotation capacity of connections proposed in Eurocode 3 are too conservative for high strength steel end plate connections. The validation of this numerical modelling against all representative experimental results is further verified on moment-rotation relationship and failure mode, which shows good agreements.

Abstract:To study the influence of hidden weld between the overlapped brace and chord on mechanical properties of overlapped CHS-to-SHS N-joints, two partially overlapped specimens with hidden seam weld and two without hidden weld were tested under monotonic loading. The test results showed that when the overlapped brace was in tension, the absence of hidden weld reduced the bearing capacity of joints, and the increased overlapped ratio decreased the joint bearing capacity obviously. Furthermore, weld crack appeared for all specimens without the hidden weld. Based on the experimental results, a finite element model was generated and validated. Using this model, the effects of loading hierarchy reversal of the braces and the hidden seam weld were studied on the response of totally 324 overlapped CHS-to-SHS N-joints with different geometric parameters. It revealed that the absence of hidden weld had less influence on the bearing capacity of the through-brace-in-compression joints than that of through-brace-in-tension joint. In view of the fact that the steel hollow section truss was assembled first and then welded, design suggestions were given.

Abstract:In order to investigate the elevated-temperature mechanical behavior of aluminum alloy, tensile tests of domestic structural aluminum alloy 6082-T6，6N01-T6，6061-T4，6061-T6 under constant elevated temperatures were carried out, and their mechanical properties under various temperatures（20 ~ 300 ℃） were obtained, including the nominal yield strength, ultimate strength and elongation. It was found that the strain of aluminum alloy specimens at elevated temperature could hardly be accurately measured, leading that their elastic modulus was not obtained. The formulae of reduction factors on the mechanical properties of the 4 kinds of aluminum alloy at elevated temperatures were derived through numerical fitting method, laying a solid foundation of the research on fire resistance of aluminum alloy structures. Moreover, the theoretical formulae were compared with the reduction factors suggested by Eurocode and American Standard. The results revealed that the codes inclined to the safe side, and the American Standard was more conservative.

Abstract:To implement the seismic design principle of “strong column and weak beam”，frame structure with local slot in floor slab is designed, where the continuous slot penetrating through the slab along the beam ends was set to separate the longitudinal reinforcement in the slab from the beam ends. Based on the probabilistic seismic demand analysis method, frame structure with local slot in floor slab was investigated. To investigate the accuracy of numerical model, shaking table test data was utilized to verify the calculated data of frame structure with local slot in floor slab modelling by the finite element software, OpenSees. The numerical models of frame structure without slab, conventional frame structure with cast-in-place slab, and frame structure with local slot in floor slab were established subsequently. Seismic performance was studied to explore the effect of the local slot of floor slab in the viewpoint of probability based on the probabilistic seismic demand analysis，which used 22 seismic ground motions. The results showed that the cast-in-place floor slab decreased the seismic performance. Besides，the slot in floor slab weakened the adverse influence of cast-in-place floor slab and increased the seismic performance and collapse-resistant capacity of frame structure.

Abstract:The seismic performance and failure mechanisms of the substation structure system considering dynamic interaction on the main structure and substructure was studied systematically, based on the mechanism of primary-secondary structure dynamic interaction, implicit dynamics numerical simulation analysis and shaking table test. Seismic response of the structure system was analyzed in some aspects such as internal force, displacement and acceleration. This paper obtained the interaction mechanism between the electrical equipment with main structure, the dynamic magnification factor of the electrical equipment and the dynamic property values, and put forward the seismic performance goals of the main structure. Meanwhile, the results based on the displacement revised factor method established the level damage assessment model and the overall damage assessment model, and then proved the correctness of the damage assessment model by shaking table test. These research results have important reference function on seismic design and seismic damage assessment of the similar lifeline engineering and industrial architectures with complex equipment.

Abstract:A grid generation method for complicated multiple surfaces with trimmings and holes is presented. This method is based on the discretization and concentrates on the aim of homogeneity. The multiple surfaces are discretized separately and seamed together to achieve a discrete surface. The points are distributed on the discrete surface according to the density applying improved error-diffusion method. The points are homogenized by particle dynamics method with Euclid distance and then homogenized once more by k-means algorithm with surface distance. The Voronoi diagram with surface distance is delivered on the discrete surface to obtain the grids. The topological and smooth relaxations are applied on the grids. Eventually, the case study indicates that this method can solve the problem of grid generation for complicated multiple surfaces effectively and achieve the homogeneous and smooth grids.

Abstract:Due to the high flexibility, light self-weight and low damping ratio of the power transmission tower, wind loads are the dominant lateral loads at its design stage. This study conducted a series of rigid model tests on the aerodynamic forces of circular steel tubular lattice structures under smoothly uniform flow conditions in the wind tunnel laboratory, and the models were fabricated based on a super high-rise power transmission tower in Huainan-Nanjing-Shanghai UHVAC transmission line. The Large-eddy simulation（LES） of lattice structures were performed to simulate the aerodynamic forces in the longitudinal, transverse and lateral directions, and the results were compared to the corresponding specifications in the available wind codes or standards. In addition, the aerodynamic forces of lattice structures were simulated by using LES under the flow conditions with turbulence intensities of 5%, 10%, 15% and 20%. The results showed that the numerical results were in relatively reasonable agreement with the experimental measurements, and the incoming turbulence intensity had indispensable influences on the fluctuating components of the aerodynamic forces. Moreover, the maximum positive pressures were observed on the windward surface at the junction of the strut and the diagonal member, while the maximum negative pressures were recorded on the lateral surface of the strut. Furthermore, the vorticity analysis showed that the vorticity in the x-direction was more scattered while those in the y- and z- directions were more uniform and continuous. The findings of this study are of great use for evaluating the aerodynamic forces of circular steel tubular lattice structures in the practice constructions.

Abstract:The aerodynamic performances of large wind turbine systems are significantly affected by blade yaw and interference, and then the wind-induced response and stability of the wind turbine system are changed. Taking the 5 MW wind turbine as the example，the flow field and aerodynamic forces of the wind turbine systems considering the six yaw angles (0, 5, 10, 20, 30 and 45 degrees) were simulated by large eddy simulation method, and the numerical simulation results were compared with standard curves to verify the validity of the numerical method. On this basis, the dynamic characteristics, wind-induced response and stability of the wind turbine systems under different yaw angles were analyzed by the finite element method. Main conclusions are as follows: The maximum values of the mean value and the mean square deviation of the radial displacement forthe tower under different yaw angles appearat 0 and 180 degrees, the maximum bending moment at the bottom of the tower appears in the circumferential direction of 20 degrees, and the peak value of three blade tip displacement response under 0 degrees yaw is more than 2.7 m. With the increase of the yaw angle, the mean value and mean square deviation of the radial displacement at the top of the tower, the forward displacement of the blade and the internal force of the blade root are gradually reduced, and the critical wind speed decreases first, then increases and decreases again. The results show that the aerodynamic performance and the wind-induced response of large wind turbine systems is the most unfavorable andthe largest under the 0 degree yaw angle, and the stability performance under 45 degrees yaw angle is the most unfavorable.

Abstract:Based on the measured stress response of 4 kinds of asphalt pavement structures, the relationship between the driving speed and the load response duration under different depths was systematically studied. The results show that the effective length of the impact of the traffic load along the route direction has a peak at the speed of about 20km/h. There is a significant nonlinear relationship between the duration of the stress response in the asphalt structure and the speed and depth of the traffic. Through the nonlinear data fitting, the relationship between the load time and the load velocity and the structural depth when the driving speed is greater than 20km/h was obtained. The formula has clear meaning, and the fitting accuracy is greatly improved compared with the existing theoretical methods. The relationship between the driving speed of more than 20km/h and the road load frequency was analyzed, and the relationship between the driving speed and the load frequency of different pavement depth was established, which provides a basis for the effective simulation of the driving load in the laboratory.

Abstract:The relationship between the deformation and stability of the ancient landslide is studied in this paper. The necessity of considering the stiffness degradation in the process of reducing the mechanical parameters of the landslide is proved by the formula derivation, and a new method that considers the coupling effect of stiffness- and strength- degradation is presented. The deformation curve of the instability in the ancient landslide is drawn by a large number of engineering experiences, and the concepts about the warning displacement value of self-stabilizing ability and the ultimate displacement value of ancient landslide are put forward and defined by a determined method. Comparing with the methods of global strength degradation and slide zone strength degradation and the method in this paper applied to actual engineering example, it is seen that the method in this paper is more realistic to analyze the deformation field of the ancient landslide.

Abstract:The objective of this study is to discuss the plugging effects of open-ended pipe pile. According to the formation process and mechanism of soil plug，the forced state of soil plug is analyzed, and the balance equation of unit plug is established. The expression of the total vertical load is also obtained. Moreover, the plug is regarded as a “pile in the pile”，and then the formula of bearing capacity limit for pile end is reduced, based on the ultimate bearing capacity model theory that was put forward by Terzaghi K. Accordingly, the expression of the soil critical height in the process of driving is derived. Finally, the conclusion is drawn that these expressions are appropriate by comparing and analyzing the results of theoretical calculation and engineering examples, and the influence of the factors such as radius-thickness ratio, cohesion of soil and roughness of the surface between piles and soil are also discussed. It is concluded that the height of the soil increases with the increase of the radius-thickness ratio, and decreases with the increase of the surface roughness between piles and soil, but the cohesion of the soil has little effect on the height of the soil. The rationality of the formula has a certain reference value to predict the height of soil plug of open-ended pipe pile during jacking into soil.

Abstract:An elastic-plastic shakedown solution is established for the shadedown analysis of the structure under moving loads.On the basis of the Melan’s static shakedown theorem，this method is developed by searching for the best residual stress field，and calculating the actual elastic stress field subjected to the moving loads.This method avoids the operation of mathematical programming in traditional method of shakedown analysis，and therefore obstruction due to large scale mathematical programming is overcome. The validity of this method is verified by comparing the results of the previous study. Based on this method，the upper bound type 1 shakedown limit kI and static shakedown limit kSD of railway subgrade are presented. A sensitive analysis is also presented, showing that the shakedown limit remains stable if the distance between the loads L and rails B is longer than 10a，so that the upper bound type 1 shakedown limit kI is shown. Meanwhile, by means of investigation on the influence of Poisson′s ratio and internal friction angle, it is found that the static shakedown limit kSD diminish marginally with the increase of Poisson′s ratio, while both the upper bound type 1 shakedown limit kI and static shakedown limit kSD experience a steadily growth with the increase of internal friction angle. A design method for subgrade is finally proposed based on the envelope diagram of shakedown limits, which can provide guidelines for design and safety assessment of railway subgrade.

Abstract:Taking a case of Changsha Metro Line 4 excavated beneath closely spaced existing Changsha Metro Line 2 twin tunnels as research background, this paper studies the application of the Metro Jet System (MJS) Horizontal Column Reinforcement in Shield Tunneling. The quality of MJS column and the response of stratum and overlying tunnels are studied during the shield tunneling by carrying out in-situ and laboratory tests, installing the additional stress sensors and vertical displacement monitoring points inside Metro Line 2 and setting up monitoring points on ground surface. The result indicates that the diameter is appropriately 2 m and the compressive strength is higher than 3.0 MPa, which satisfy the designed specifications. When the shield excavates beneath the overlying tunnels, the settlement of the overlying tunnel present Gaussian curve distribution, and the maximum settlement is 4.33 mm. Due to the unloading of the shield excavation，the maximum additional stress is 1.4 MPa and the maximum settlement is 1.1 mm. Surface settlement is relatively small in the MJS horizontal pile reinforcement area. Overall，MJS horizontal pile can effectively reduce the settlement of existing tunnel，and can offer reference for the application of similar engineering.

Abstract:In order to study the resistance characteristics of pile supported Ming dig tunnel excavation pile lateral soil, mechanical model and displacement modelare set up considering pile foundation pile lateral soil pressure insoil mass stress state. Secondly, according to the principle of function and displacement mode, the function and formula of velocity fieldfor pile supported Ming dig tunnel excavation pile lateral soil is established. Then, through the introduction of extreme limit method, the coefficient calculation methodis put forward considering the interface roughness coefficient of pile-soil pile horizontal bearing capacity of pile foundation pit supported Ming dig tunnel. At the same time, this method was applied to calculate examples. A comparative analysis between the theoretical calculation method and calculated results demonstrates the rationality and feasibility of this method. Finally, by using the method established in this paper, the influence of pile spacing, pile and soil contact surface coefficient and pile embedment depth of foundation pit on horizontal resistance coefficient is also analyzed. The results show that the horizontal bearing capacity of pile decreases with the decrease of the pile spacing and reaches to a minimum value. The level of the pile bearing capacity coefficient of Np pile soil increases with the increasing interface roughness coefficient alpha. When the pile-soil interface roughness coefficient alpha is unchanged，the horizontal bearing capacity coefficient of Np increases with the increase of buried depth. When the embedment depth ratio Z/D is larger than 7, the horizontal bearing capacity coefficient of Np increases with the increase of embedment depth and reaches a constant value.

Abstract:In order to reveal the pressure arch range of surrounding rock in deep buried unlined circular tunnel, based on the complex variable theory and the classical elastic-plastic theory and the M-C yield criterion, a method for accurately predicting the boundary of pressure arch is proposed. The correctness of the prediction method is verified by numerical calculation. On the basis of the correct prediction results, the sensitivity of the tunnel buried depth and lateral pressure coefficient and surrounding rock grade are discussed. The results show that: 1)The upper part of the deep unlined circular tunnel is the key to the construction of the tunnel, and the proper advance supporting measures should be taken to ensure the safety of the tunnel construction, and its support range should be more than 120°. 2) When the surrounding rock condition is poor, the tunnel construction urges the surrounding rock loose zone to run through, and it is necessary to take the full section ahead of grouting reinforcement measures to prevent the further development of surrounding rock loose zone. The research theory can provide reference to determine whether the loose zone around the tunnel penetrates through and to determine the position and range of the advance support.

Abstract:Based on the engineering construction method，the refreezing process of backfill is investigated by model test method under simulated ambient temperature. The results indicate that the frozen layer thickness increases with the freeze-thaw cycles when the simulated average temperature is -2.71 ℃. The thawing depth is about 6.1 cm at maximum ambient temperature in every freeze-thaw cycle, and the frozen layer thickness increases to 20.0 cm after 13 freeze-thaw cycles. The pile foundation has an effect on the refreezing process of backfill in the horizontal and longitudinal directions, but its scope of influence is limited. The interface temperature between air and pile is close to the air temperature, but the interface temperature between air and soil is very different from air temperature. The air temperature is higher than air-soil interface temperature by 5.0 ℃ at the maximum ambient temperature, and lower than air-soil interface temperature by 6.7 ℃ at the minimum ambient temperature. This experiment results help to further understand the actual refreezing process of backfill, and provide reference for determining the control conditions in model test and the boundary conditions of numerical simulation.

Abstract:A type of fresh air system integrated with shading photovoltaic is researched. In summer, photovoltaic panel is used for shading and electricity generation. In winter, this system can generate power and heat fresh air by extra thermal energy of PV panel. By using class region method, a photovoltaic and photo-thermal conversion model is established to simulate the performance of the fresh air system, and the system model is validated by experimental data. On this basis, the fresh air volume of the fresh air system integrated with shading photovoltaic is optimized. The results show that the photovoltaic power generation efficiency, the heat gain of the fresh air and the heating efficiency increase, while temperature rise of fresh air and outlet temperature of fresh air reduce with the increase of the fresh air volume, and the power generation efficiency and heat collection efficiency grow with the increase of solar radiation intensity. In this paper, the fresh air system integrated with shading photovoltaic has functions of electricity generation, shading and fresh air heating, and provides a new method for building energy saving.

Abstract:This paper proposed a passive composite hygroscopic material to control indoor humidity based on field experiment. A series of aggregates including wood fibre, sepiolite, expanded perlite and diatom ooze were mixed at different ratios to make an optimal composite hygroscopic material for further experiment. Two testing rooms，which were attached with conventional cement mortar（Room 1） and composite hygroscopic material（Room 2），respectively，were built to conduct comparison experiments（mainly testing temperature and humidity） in January and April in 2017 in Changsha, Hunan. The hygroscopic performances were evaluated by the practical Moisture Buffer Value，and performances of indoor environment mold inhibition of two rooms were also analyzed. The results showed that in the two tested seasons，Room 2 outperformed in hygroscopicity than Room 1, where the relative humidity was lower by 6%-14.3% and moisture content was lower by 0.3-3.1g/kg·a. In the cold January， the risk of mold growth in Room 1 was about 4 times higher than that in Room 2，while in humid April，the risk rate of mold growth in Room 2 was only about 2%（6.5 h in monitored 288 h），which was obviously lower than that in Room 1. The newly studied composite hygroscopic material was found to be efficient and practical in controlling indoor humidity.

Abstract:This paper proposed a method for the comprehensive thermal performance assessment （equivalent heat transfer coefficient） of building envelopes in existing buildings. This method is based on the index evaluation and equivalent energy consumption model, which integrates many evaluation indexes into an equivalent index. The thermal performance and energy-saving potentiality of the building envelope are evaluated by calculating and comparing the heat transfer coefficient of the two equivalent energy consumption models. It is shown that only measurement of indoor and outdoor temperature is needed, while measurement of every parameter in the envelope structure is not needed, which can overcome the difficulties in testing the existing buildings with complex structures. The proposed method can assess the total thermal performance of building envelope rapidly and evaluate the necessity of retrofitting before energy-saving renovation.