Abstract:Flow past cylinders is an important issue in ocean engineering. Periodical vortex shedding occurring around the offshore platform in current leads to reciprocating motion of the offshore platform, which may aggravate the fatigue damage and thus cause the reduction of fatigue life of the moorings. In order to study the mechanical characteristics of flow past multi-column floating wind turbine platform and understand the mechanism of wake interference clearly, numerical simulations were performed using Delayed Detached Eddy Simulation (DDES). The effects of headings and current velocities on the mechanical characteristics of the semi-submersible floating wind turbine platform were investigated. The mechanism of wake interference was studied from the level of coherent structures, and spatial correlation between different wakes behind the columns was also investigated. The results demonstrate that: (1) the average drag force coefficient of downstream column has a large fluctuation with the change of current velocity; and streamwise vortex and hairpin vortex are the main coherent structures; (2) the interaction between coherent structures results in wake interference; (3) the upstream wake and the downstream wake have strong spatial correlation, but their coherent structures are different. The research results provide a theoretical reference for understanding the phenomenon of flow past multi-column offshore platform.

Abstract:For the problems of downburst steady wind field simulation, based on Computational Fluid Dynamic (CFD) methods, firstly, 2-dimensional (2-D) and 3-dimensional (3-D) impinging jet models were used to simulate the downburst wind field, and the characteristics of downburst wind field were studied. On this basis, according to the characteristics that the effect of downburst on bridge structures is mainly affected by the horizontal wind speed, the horizontal wind field of downburst in Boundary Layer Wind Tunnel (BLWT) with inclined plate was studied by using 2-D numerical simulation method. Finally, the horizontal wind filed simulation experimental device of the downburst in the BLWT was designed and manufactured, and the horizontal wind field simulation experiment of the downburst was carried out in the BLWT. The numerical simulation results were compared with the experimental results in this study and the results from the existing literature. The comparison results show that the simulation results of the 2-D impinging jet model for the downburst wind field are in good agreement with that of the 3-D impinging jet model, that is, the 2-D impinging jet model is an effective simplified simulation method for the downburst wind field. The numerical simulation results of the horizontal wind speed and wind field of the downburst simulated by setting up the inclined plate in the BLWT are in good agreement with the wind tunnel test results, and are in good agreement with the numerical simulation results of impinging jet model and the field measured results, that is, the characteristics of steady horizontal wind filed of downburst flow can be simulated by setting an inclined plate in BLWT.

Abstract:Based on the wind tunnel test of the second largest-scale airport terminal in China (where the maximum space among the corridors is almost larger than 1,500m), this study investigates the aerodynamic interference effects of surrounding buildings on the wind pressure distribution characteristics of the complex large-scale roof with multiple corridors. Also, the non-Gaussian characteristics of wind pressures on the super large-scale roof structure is investigated by High-order Statistical Moment Method and Kolmogorov-Smirnov Method （K-S method）. The results show that the effect of surrounding buildings on the wind pressure distribution characteristics is generally small, which is featured with slight decrease in the minimum negative pressure. Furthermore, the wind pressure on this roof is generally negative, in particular, the extreme values of negative pressures are observed on the leeward edge and roof corners due to the strong flow separation and vortices. In addition, the non-Gaussian regions distinguished by High-order Statistics Method are inconsistent in the same region, and the results are insensitive to the approaching wind directions. Meanwhile, the results of K-S method are quite consistent and are in good correspondence with the wind pressure distributions. Moreover, the large-scale roof with multiple corridors shows obviously distinguished non-Gaussian characteristics at the windward eave, corners and leeward areas. Therefore, it is of worth to consider the non-Gaussian characteristics in the wind load code of large-scale roof structures, and improve the peak factor estimate method and increase the peak factor in the non-Gaussian regions.

Abstract:In the process of structural dynamic time-history analysis, reasonable ground motion selection is always a difficult point in engineering. By improving the existing harmony search method for ground motion selection, dynamic time-history analysis is performed for two differently periodic prestressed concrete (PC) frame structures designed according to currently Chinese codes. Then, it is compared with the periodic point method, the dual-band method and the area method for calculation results. The results show that the discreteness of structural response parameters of the periodic point method and the improved harmony search method is smaller in frequently earthquake, and the coefficient of variation is about 10%. Compared with the base shear force of mode-superposition response spectrum method, the dual-band method and the improved harmony search method are more in accordance with the standard design. Structural response parameters of the area method and the improved harmony search method are smaller dispersion in rarely earthquake, and the coefficient of variation is about 15%. Furthermore, the results of the periodic point method are the most dispersion. The periodic point method is only applicable to the ground motion selection process of elastic time-history analysis. The improved harmony search method is applicable to both elastic and elastic-plastic time-history analysis, which can meet standard design and engineering requirement.

Abstract:A modal pushover analysis (MPA) method based on the soil-structure interaction（SSI） was proposed through the principle of periodic equivalence, and the feasibility of this method was verified. Taking a 10-story RC frame structure with vertical irregular filling walls as the research object, we adjust the stiffness ratio between stories and the layout position of “weak stories”，and use this method to analyze the seismic response regular pattern of this kind of structure under the condition of different sites and seismic precautionary intensity. The results indicate that: 1）In strong earthquakes, setting up “weak layer” in “the most sensitive layer of weak layer” makes the effect of weak layer more significant, and the greater the ratio of stiffness between layers，the more adverse the displacement angle between layers of RC frame structure. Irregular arrangement of filled walls in the outer floor of "sensitive area of weak layer" makes the structure form the distinct weak layer. 2）With regard to SSI effect, the deformation of RC frame structure with filled wall concentrates more obviously to the bottom floor, and the stiffness ratio between layers decreases when the structure collapses and the site soil becomes soft. Therefore，it is proposed to control the stiffness ratio between stories more strictly to ensure the ductility of such structures under earthquake effect.

Abstract:To research the progressive collapse resistance performance of fully assembled precast concrete frame structure, two half-scale precast concrete（PC） specimens were designed and studied by static tests. The PC specimens were built by high-strength bolt and anchor plate with ductile rod connections in the beam-column joint region, where one specimen（PC1） was designed without corbel component, while the hided corbel was employed in another one（PC2）. In addition，a cast-in-situ reinforced concrete（RC） frame tested by our research team previously was used as a comparison reference. The quasi-static load tests were conducted for the specimens under mid-column loss scenario. The structure responses including ultimate loading capacity，strain response，deformation performance and failure mode were discussed，respectively. Compared with the RC specimen where both compressive arch action（CAA） and catenary action existed, only the CAA was observed in PC specimens，indicating that this type of PC structures has a lower secondary progressive collapse resistance capacity. Meanwhile，the ultimate load of PC1 and PC2 was 95% and 123% of that of RC specimen at CAA stage，respectively，while the ultimate displacement of PC1 and PC2 was 48% and 61% of that of RC specimen, respectively. During testing，the deformation and strain response of PC specimens was mainly concentrated on the joint region. The PC specimens were damaged by the fracture of ductile rod with anchor plate.

Abstract:In order to investigate the progressive collapse capacity of prestressed concrete frame structures, we established a nonlinear finite element model of a bonded-prestressed concrete frame. The experimental data were used to verify the model. On this basis, the differences of mechanical mechanism between bonded prestressed frame and reinforced concrete frame in the process of progressive collapse were studied, and the influencing factors of the first peak bearing capacity of prestressed frame were analyzed. The studies show that the application of prestress enhances the arch compression effect and weakens the failure of the side column, but it aggravates the failure of the middle column. The ratio of reinforcement, depth of beam and span have great influence on the bearing capacity of arch compression（Fa.u）. When the top reinforcement ratio increased from 0.66% to 1.32%，Fa.u increased by 19.6%. When the bottom reinforcement ratio increased from 0.66% to 1.32%, Fa.u increased by 31.5%. When the depth of beam increased from 700 mm to 900 mm，Fa.u increaseds by 220.7%. When the span increased from 9 m to 15 m，Fa.u decreaseds by 64.0%. When the size of column section is small，increasing the size of column section has a great influence on Fa.u. However，when the column section size is large，increasing the column section size has little influence on Fa.u. The initial tensile control stress and tendon area have little effect on Fa.u.

Abstract:In order to solve the tediously calculative problem of deflection and finite element analysis of the pedestrian suspension bridge under vertical load, a simplified calculation method was proposed by considering the flexible structure of pedestrian suspension bridge, neglecting the stiffness of the stiffening beam, and considering the IP displacement of the main cable, the cable sag effect, and the geometric nonlinearity. The stress-free length and midspan deflection of bridge main cables with different spans and different rise-span ratios were calculated, and the application scope and error of the simplified calculation method were analyzed based on the results of the trial calculation. The calculation accuracy and application scope of the method were verified. Taking a pedestrian suspension bridge with a span of 117 m as an example, the mechanical properties of the suspension bridge under completed and vertical load state were analyzed by the calculation method in this paper, and compared with the results of finite element analysis and test. The results show that the simplified calculation method proposed has good practicability and can provide a reference for the rapid solution and verification of finite element analysis result of pedestrian suspension bridges in practical engineering.

Abstract:To obtain the time-dependent reliability of corroded steel beam, accelerated corrosion test and monotonic tensile test were carried out on 9 groups of specimens. 3D data of corrosion depth and the nominal yield strength of corroded steel were measured. Probability model of corrosion depth and nominal yield strength of corroded steels was statistically analyzed, and performance function of the corroded steel beam was established. Then, based on probability density evolution theory, the time-dependent failure probability and reliability index of corroded steel beams were obtained, which were compared with those calculated by Monte Carlo simulation (MCS) method. The results of the study show that the corrosion depth on surface and nominal yield strength of corroded steels obey the normal distribution. With the increase of corrosion time, the mean and standard deviations of the corrosion depth increase. With the increase of weight loss ratio, the mean of nominal yield strength decreases whereas the standard deviation of nominal yield strength increases. Probability density evolution method is closer to calculation results of the MCS, which shows that the method proposed in this paper is effective. The randomness of corrosion depth and strength has great influence on the reliability of corroded steel beams.

Abstract:The damping ratio on aluminum alloy single layer spherical reticulated shells with plate-type joints was studied by field measurement. For an aluminum alloy spherical latticed shell with a planar dimension of 45m×45m and a rise of 2.86m, a total of 11 test cases were planned and 160 acceleration damped free vibration signals were collected on site under human-induced excitations as well as 6 vibration signals under environmental excitations. Using the method of analytical modal decomposition (AMD) combined with the Hilbert transform, natural frequencies and modal damping ratio of the structure were identified. Statistic studies were carried out and an average damping ratio of 4% was suggested for this kind of structures. Finite element (FE) models were established using the suggested damping ratio, and the nodal dynamic responses given by numerical analysis showed good consistency with those given by the tests. The damping ratio given here could give a basis for the revision of the current code and provide a reference for the structural dynamic analysis and engineering design.

Abstract:To investigate the seismic performance of reinforced concrete (RC) piers retrofitted by active confinement of domestic NiTiNb-SMA wires, a pseudo-static test of three column specimens was carried out. Based on the experimental phenomena and lateral force-displacement curves, the skeleton curves, bearing capacity and ductility, strength degradation, cumulative energy dissipation and residual displacement of the specimens were analyzed. The results show that thermal excited NiTiNb-SMA wires can effectively provide active confinement stress for the pier, which reduced the damage and improved the ductility and energy dissipation capacity of piers. Compared with the control specimens, thermal excited SMA wires increased the displacement ductility coefficient and cumulative energy dissipation of the specimen by 27.8% and 10.4%, respectively. What′s more, it effectively reduced the strength degradation and improved the ability of restoring the residual displacement of piers.

Abstract:To investigate the shear behavior of Load-bearing Horizontal-hole Interlock Concrete Block (LB-HHICB），three kinds of blocks were used to fabricate the shearing specimens and each took three mortar strengths as variables. At first, a static shear loading test was carried out to investigate the failure profiles and shear failure loads of the specimens. Then, the main factors affecting the shear strength of the masonry were analyzed and compared with other similar test results and specification values. Finally, a method was proposed to calculate the shear strength of LB-HHICHB considering the effective bonding area. The study showed that the shear failure of LB-HHICB was mainly bond failure of the interface between mortar and concrete block. When calculating the shear strength of masonry, the effective bonding area between mortar and concrete block was employed. Based on it, the calculation method on shear strength of LB-HHICB was put forward. This calculation method can not only accurately calculate the shear strength of this kind of block but also calculate the other types of concrete block based on the shear bond failure.

Abstract:In order to investigate the influence of confining pressure on strength characteristics of cemented soil and establish a damage constitutive model under different confining pressures, triaxial shear tests under different confining pressures at room temperature and freezing state were carried out. The influence of confining pressure on mechanical parameters of cement soil was investigated. A modified Hoek-Brown strength criterion which can reflect the strengthening effect of low confining pressure and the weakening effect of high confining pressure on the strength of frozen cement soil was established. It is assumed that the distribution law of cement soil micro-element strength obeys the two-parameter Weibull function. Based on the Hoek-Brown strength criterion and its modified form, the micro-element strength of cement soil at room temperature and frozen state is determined, respectively, and the statistical damage constitutive model considering the influence of confining pressure is established. The results show that the damage constitutive model based on Hoek-Brown strength criterion and its modified form can describe the stress-strain curves of cement soil at room temperature and freezing state, and can reflect the strain softening phenomenon under low confining pressure and strain hardening phenomenon under high confining pressure. Under different confining pressures at room temperature, the damage variables change with the axial strain in a similar shape, showing a monotonic "S" pattern as the axial strain increases. Low confining pressure inhibits the damage and deterioration of cement soil under freezing condition. High confining pressure increases the degree of damage deterioration, and the damage variable reaches a larger value when the axial strain is very small.

Abstract:The post-construction settlement of road constructed on soft ground is significant and widespread. The current international roughness index（IRI） subjects some limitations. Hence，based on the driving comfortableness, this study proposed an assessment method for driving quality of roads on soft ground. Firstly，the influences of fitting methods and the distance of fitting points on the vehicle vibration acceleration were evaluated by five-degree 1/2 vehicle-road interaction model. The weighted root mean square of vehicle acceleration was thus obtained. Secondly, based upon the standard for vibration comfortableness（ISO2631），the equations for DCI and RQI for assessing the comfortableness of driver and passenger were developed. Finally, on the basis of two scenarios of soft ground and non-soft ground, the evaluation results calculated from the methods in this study and IRI were compared. The results demonstrate that, in the non-soft ground, the results are similar. In contrast, the results in soft ground are quite different, and the methods proposed in this study are more in line with the engineers′ visual sense.

Abstract:In order to solve the problems of bearing capacity and stability for the double-layer slope foundation under the load of the strip foundation，this paper compared and analyzed the previous research results，and judges the rationality of its hypothesis. According to the basic characteristics of the asymmetry of the failure mode of the slope foundation and considering the velocity inequality at the stratified interface of the double-layer foundation, a new multi-slider failure mode was used to build its destruction mode. The compatibility velocity field was determined according to the speed-compatible relation and velocity triangle closure condition. At the same time，the upper limit analysis theory of the limit analysis method was introduced to derive the calculation formula of the upper limit bearing capacity of the asymmetric double-layer slope foundation of the strip foundation. The optimization calculation method of the secondary planning algorithm in MATLAB was used to optimize and solve the upper limit bearing capacity of double-layer slope foundation. Finally，the engineering examples was used to verify the rationality of the proposed method, and compared with the existing research methods and the results of the software calculation，proving the feasibility of the method used in this paper.

Abstract:The main problems in the detection of shield tunnel lining defects are how to obtain high quality images of different defects and how to quickly and accurately detect the defects. A device for mobile tunnel inspection (MTI-100) was designed and manufactured based on CCD line array cameras. Using MTI-100, Shanghai Metro Lines 1, 2, 4, 7, 8, 10 and 12 were tested and a large number of lining images were obtained. These images were manually labeled to form a high quality database of lining defects samples. Based on the Faster R-CNN (Faster Region-based Convolutional Neural Network), a deep learning framework for automatic disease detection was established. Inspired by the existing model VGG16, the CNN detection model of tunnel lining defects was established. Considering the particularity of cracks and leakage defects, statistical analysis and K-means clustering algorithm were used to analyze the geometric features, so as to optimize the related parameters of anchor box in the VGG-16 network model. The results show that the accuracy of the optimizeation is greatly improved（about 7%），and the training time is reduced. It is verified that the method can also improve the accuracy of the defect detection model of crack or leakage singly.

Abstract:DamageAnalysis on Subway Tunnel Structure under Effect of Reverse Fault DislocationAN Shao1，TAO Lianjin1，BIAN Jin2，HAN Xuechuan1，WU Xiaowa1 (1. Beijing Key Laboratory of Earthquake Engineering and Structural Retrofit，Beijing University of Technology，Beijing 100124，China;2. Guang Dong Ocean University，Zhanjiang 524008，China)Abstract:Taking the subway tunnel in Urumqi crossing Xishan reverse active fault as an example，a three- dimensional elastic-plastic finite element model of soil-tunnel structure was established to simulate and analyze plastic strain development process of secondary lining，transverse and longitudinal distribution of tensile damage factor，compressive damage factor and shear strain，calculate the crack width of concrete under the action of reverse fault dislocation. Then the damage law of the tunnel structure with different dislocation displacements,different vertical distances from tunnel bottom to the interface of surrounding rocks and different widths of fault zone was studied. Finally，the disaster reduction effect of the flexible joint was studied. Results show that the damage of secondary lining first appeared in the vault，then the bottom，and finally accumulated at the waist. The shear，tensile and compressive damage all appear at the tunnel waist of the rupture surface. When the tunnel structure is away from rupture surface，the tensile damage appears at the tunnel vault of hanging wall and invert of fault zone，the compressive damage appears at the tunnel invert of hanging wall and vault of fault zone. The severe and slightly tensile-crack damaged length are 10 m and 30 m respectively based on the crack width of concrete. The larger the fault displacement is，the more serious the structural damage is. The larger the vertical distances from tunnel bottom to the interface of surrounding rocks，the thicker the soil is，resulting in that more energy is dissipated and the structural damage is lighter. The damage to tunnel increases with the increase of width of fault zone，but when the width increases to 26 m，the influence of width of fault zone on tunnel damage becomes stable. Setting flexible joints can significantly reduce structural damage and substantially meet the design requirements for fault displacement.