Abstract:The hanger cables of long-span suspension bridges are susceptible to wind-induced vibration as they have low natural frequencies and low mechanical damping. In this paper, the wind-induced vibration problem of the hanger cables of Xihoumen Bridge was investigated to research the vibration control method. Firstly, the dynamic characteristics of the hanger cables were obtained by environmental incentive method. Then, the scheme of installing spacers was determined by theoretical analysis and wind tunnel experiments, in addition, the influence of the number of spacers on vibration-reduction efficiency was investigated in the experiments. Finally, according to the field test of the wind-induced vibration of two hanger cables with and without spacer respectively conducted in strong wind weather, the results indicates that after installation of the spacers, the collision phenomenon between the strands is eliminated. Moreover, the vibration of different modes of the hanger cable is significantly reduced by 55%～95%.

Abstract:The mechanism of wind-induced oscillation of hangers in a long-span suspension bridge was investigated qualitatively on the basis of field observations, and the possibility of wake galloping, or vortex-induced resonance, or wind-rain-induced oscillation was excluded by reasoning. Numerical simulation and theoretical analysis reveal that this is a kind of resonance induced by the buffeting of main cables. Stochastic wind fields excite the stochastic responses of the main cables, which are abundant in a wide range of modal components, and the resonance occurs when the natural frequency of a hanger is adequately close to one of the main cable’s natural frequencies that possess enough energy. Hence, it is not the hangers themselves but the main cables that are responsible for the energy absorbing from the turbulence. Compared with the modal mass of a main cable, the mass of one hanger is too small to pose substantial effects on the oscillation of the main cable, and therefore, a steady supply of energy from the main cable to the hangers can be formed. Furthermore, TMD mounted on the main cables can suppress the wind-induced vibration of cables at the natural frequency of hangers, which results in the significant reduction of the vibration of the hangers.

Abstract:This paper studied the aeroelatic effect on tall buildings. An aeroelastic model was designed and manufactured for wind tunnel tests. With the time-history responses of the structure obtained from the aeroelastic model in the wind tunnel test, we could identify the structural dynamic characteristics by spectral analysis, and get the aerodynamic damping from the natural excitation technique method (NExT), the ARMA method, combined with a change in mode order, and then study the rules of aerodynamic damping changing with wind speeds. In a strong wind situation, filter technique was used to analyze the along-wind time-history acceleration response to eliminate the influence of the across-wind energy transfer. And vortex-excited resonance existed in the process of identifying the aerodynamic damping. The peak acceleration responses of the rigid models by pressure test and high-frequency-force-balance test, which considered the aerodynamic damping ratios, were very close to the results of the aeroelastic model test. The accuracy of the aeroelastic model test was verified. For the rigid models, irrespective of aerodynamic damping ratios, the peak acceleration responses were much larger than the results of the aeroelastic model test. The biggest difference was 41%. However, in some cases, the aerodynamic damping ratios increased the responses, and the necessity of considering the aerodynamic coupling effect on the wind-resistant design of flexible high-rise buildings has been verified.

Abstract:Downbursts are dramatically different from the atmospheric boundary layer. To investigate the wind load characteristics of high-rise building in thunderstorm downbursts, a static impinging jet was used to simulate the thunderstorm downburst. Rigid model manomeric test was carried on a high-rise building. Both local and overall wind load characteristics were discussed in time domain and frequency domain. The results indicate that the position of the maximum mean surface pressure is consistent with the peak radial velocity. Meanwhile, the maximum surface pressure on the windward side is located at the bottom of the building, obviously different from the top part tested in atmospheric boundary layer wind field. The maximum mean radial wind load of each layer is located at the middle of the building. And the mean wind load is 0 at the cross-wind and torsional direction. Wind load spectrums of each layer keep unchanged along the height at the radial and cross-wind direction. But wind load spectrums changes obviously at the twist direction.

Abstract:CFD numerical simulation method was employed to study the wind field characteristics of three-dimensional hills under isolated hill and two adjacent hills condition. The influence of the calculation model surface roughness on the wind field was studied. The wind fields on isolated hill with different slopes were calculated. The wind fields of two adjacent hills in left-right arrangement were also investigated, and the influence of the hill slope, wind azimuth and hill distance on the wind field was studied. The results show that, if the model surface roughness increases, the speedup effect of half hill height above the top of the hill decreases and the height of vortex region increases. The speedup effects on the cross-wind plane of an isolated hill are more significant than those on the along-wind plane, and the most unfavorable position ranges from the half hill height to the top of the hill on the cross-wind plane. When two adjacent hills are in left-right arrangement with zero distance, the speedup ratios on the front hill are larger than those on the rear hill under yawed azimuth, and the speedup ratio, when wind blows perpendicularly to the two hills, is between these two data.

Abstract:The existing studies of ride comfort are based on wind-vehicle-bridge coupled vibration, which seldom consider the effects of both traffic random characters and road surface progressive deterioration, thus they cannot match very well for the real situation of the bridge under the random traffic loads. Based on wind-traffic-bridge system under random traffic loads, this paper studied the ride comforts taking into account the road surface progressive deterioration. We presented a three-dimensional vehicle model with 24 degrees-of-freedoms (DOFs) including a three-dimensional suspension seat model and longitudinal vibration of the vehicle, and then introduced an improved CA model considering the influence of the next-nearest neighbor vehicle and a progressive deterioration model for road-roughness. The wind-traffic-bridge coupled equations were established by combining the motion equations of both the bridge and vehicles using the displacement relationship and interaction force relationship at the patch contact. The numerical simulations show that the proposed method can rationally simulate the vibration of the wind-traffic-bridge coupled system; and the 3-D vibrations of the driver seat model can significantly affect the drive comforts.

Abstract:As an important excitation source, track irregularities have a significant effect on the running safety and riding comfort of the high-speed train and bridge. A three-dimension train-track-bridge coupled dynamic model was established to study the effect of short-wavelength components of track irregularities on the dynamic responses of the train and 32 m simple supported box-girder bridge. Five different wavelength track irregularities were generated from German low interference track spectra in numerical method. The dynamic responses of train-track-bridge coupled system under different track irregularities were calculated. The results have shown that the 1 m short-wavelength component in track irregularities can significantly amplify the wheel-rail force, offload coefficient, derailment coefficient and the mid-span acceleration of the bridge. The mid-span displacement of the bridge, the wheel-rail relative lateral displacement and the car-body acceleration are less affected by the short-wavelength component of track irregularities. The main reason for the offload coefficient exceeding the code limits is 1~2 m short-wavelength components of track irregularities. The reduction of the short wavelength track irregularities component is effective in increasing the running safety.

Abstract:In order to explore the failure process and fragments ejection rule of blast case for masonry walls, the AUTODYN program was used to simulate the dynamic response of masonry walls under close range blast load. The distribution of blast pressure on masonry walls and debris ejection laws were obtained. The results show that the destruction rules of 120 mm, 240 mm masonry walls, and the strengthened 240 mm wall under close range blast load are similar. The debris ejecting speed of 240 mm wall and the strengthened 240 mm wall declines obviously when compared with 120 mm masonry wall. The debris ejecting speed of the strengthened 240 mm wall declines significantly on account of the consolidated film of PU. Moreover, the relationship between ejecting speed and scaled distance is similar to the relationship between scaled distance and peak overpressure.

Abstract:Based on the experimental study of the flexural performance and shear performance of precast hollow-core slabs strengthened with HPFL, the ANSYS was applied to build the spatial finite element model to analyze the precast hollow-core slabs strengthened with HPFL. Further analysis was conducted for the HPFL strengthening surface mortar strength, HPFL reinforcement layer steel bar mesh size, HPFL reinforcement stripe width and the direction of precast hollow slabs and other factors on the precast hollow slabs shear performance strengthened with HPFL. The results demonstrate that finite element analysis results and the experimental results are basically identical and the effectiveness of HPFL as a kind of improved precast hollow slabs flexural resistance and shear resistance. The HPFL stripe width and the strengthening surface mortar strength have the most important influence on the strengthening effects. The ultimate capacity increases with their enlargement. The ultimate capacity increases slightly with the steel bar mesh size. HPFL can also improve the precast hollow slabs' shear bearing capacity of horizontal and vertical directions.

Abstract:This paper took the project of Shandong Zoucheng International Convention Centre, a multi-story frame structure, as the research background. In this project, circular steel tubes and rectangular steel tubes were chosen for sections of columns, and steel truss and H-section steel were used for sections of beams. For instance, at the second floor, sections of the upper and underside chord members of large-span steel truss were made from H-section steel and were connected to circular steel tubes with pin joint. It could be treated as a relatively ideal hinge connection.There is heavy load on floor, and the current structural code does not include the design method of pin joint, therefore, it is necessary to conduct experimental analysis. Through four groups of experiments and finite element analysis, the result has indicated that the pin joint is equipped with good force transmission ability and rotation capacity, and it satisfies the design requirement of bearing capacity. The design method of pin joint in this paper can be used as a reference for similar projects.

Abstract:Based on the engineering background of an island water diversion aqueducts truss, this paper put forward a method using prestressed force and outsourcing cement filling material to strengthen the bottom chord of reinforced concrete truss, used the hierarchical load test method to carry out in-situ static load experiment on the strengthened truss, tests deflection, strain(stress) value and their changes of the main control section of truss at different levels of loads, made a comparative analysis of the test results, calculated the value of finite element method, and obtained the mechanical performance of the truss after reinforcement. The experimental results show that the use of prestressed force and outsourcing cement filling material to strengthen truss can improve the bearing capacity of truss structures to a great extent, and new structural layers can work with the original structural layers and their deformation coordination is good. The reinforcement effect is also ideal.

Abstract:A square concrete-filled steel tube frame column with end ribs was put forward. The end longitudinal rib was used to avoid the premature local buckling of steel tube wall and then to improve the load carrying capacity, ductility and seismic performance of concrete-filled steel tube. Refined nonlinear finite element (FE) models were established by using MSC.Marc to study the existing experiments, and the results from the FE models fit well with the test data. Based on the reasonability of the FE models, parametric analyses were carried out to further explore the behavior of the square concrete-filled steel tube frame column with end ribs. The analyses have shown that the end ribs can delay the local buckling of the steel tube and improve the load carrying capacity, ductility and seismic performance. The length of the end ribs are to be set at 1~2 times the sectional side length from the column end, and the height and thickness of the end ribs should satisfy certain structural requirements. The increase of the thickness of the end ribs or the number of end ribs on each side can improve the load carrying of the column, and the latter is better.

Abstract:Based on the pile-soil soft support model, a simplified interaction finite element analysis model of soil- structure was established, and the nonlinear dynamic time history analysis was conducted for this model under different seismic excitations and different conditions of the pile-soil. The result shows that, under certain ground motion and soil-foundation conditions, the nonlinear effect of the upper structure can be greater than fixed base assumption, and pile-group-soil soft support model also influences the weak layer position on the upper structure. The analysis results and the existing test results are in good agreement. By using structural units to solve complex computational problems in geotechnical engineering, designers can carry out dynamic time history analysis and seismic evaluation for the superstructure quickly, accurately and efficiently.

Abstract:Limit support pressure is a key parameter to keep the stability of the excavation face in shield tunnel excavation, but there has been little research on the limit supporting force of tunnel excavation face for shield machine in upper-hard lower-soft ground． Based on the limit equilibrium method, silo theory and hypothesis of sliding surface being a broken line, the limit supporting force calculation model and formula of excavation face for shield tunnel in upper-hard lower-soft ground were established. To check the rationality of the model and the necessity of considering layers, comparative numerical analyses were conducted. The agreement between the two methods is very good. The effect of buried depth, thickness of upper and lower soil layer, cohesion and internal friction angle on limit support force was analyzed. It shows that the results are different when considering layered or not when the layer is uneven. Therefore, it cannot be equated with homogeneous soil, which should be considered in engineering practice.

Abstract:Combined with the characteristics of the asymmetry failure mode of the two-layer clay foundation near slope and layered properties, the unilateral sliding failure mode of two-layer foundation under strip footing adjacent to slope was built on the basis of the existing relevant researches. The failure mechanism was formed by many sliders. According to speed compatible relationships and triangle closed condition, the corresponding planar kinematically admissible velocity field was constructed. By introducing the upper limit analysis theory, the ultimate bearing capacity calculation model of strip footings over two-layer foundation soil was derived. A new approach for determining the ultimate bearing capacity of two-layer foundation under strip footing adjacent to slope was put forward by using sequential quadratic programming optimization algorithm. By the use of Matlab symbolic operation function and optimization function, the finite element numerical analysis results were analyzed and compared with programmed calculation. The feasibility and rationality of the proposed approach was shown.

Abstract:To learn the fire resistance performance of wood mortise-tenon joints of commonly used wooden species in China, 4 framed mortise-tenon joints commonly used in ancient wooden structures were exposed to fire, and 1 contrast specimen of bearing capacity test was experimentally studied. It is found that, in the capacity test, the vertical displacement of the contrast specimen in the middle of the beam changes linearly with the load. Meanwhile, there is no obvious yield point and the specimen has poor ductility. The value of the constant load of 4 specimen applied in the fire endurance test was identified according to the bearing capacity of the reference specimen and the different load ratio. The fire endurance of specimen with a load ratio of 25%, 37.5% and 50% was 59, 44, 21 minutes respectively, and the fire endurance of the specimen with fire proof coating and a load ratio of 50% was 58 minutes, which indicates that the decrease of load ratio and the fire proof coating can both effectively increase the fire endurance of mortise-tenon connection. Temperature data have shown that the load ratio has little impact on the rate of temperature rise, and the small gaps of 2~4 mm between the tenon and the mortise has little impact on the heat transfer of wood.

Abstract:The mechanical properties of the Ban mortise-tenon joints of the ancient traditional timber buildings in the South Yangtze River Regions were studied with the experimental and theoretical methods. The tested mortise-tenon joints include three Ban mortise-tenon joints. The failure modes, the hysteretic curves, the skeleton curves, the rotation rigidities of this kind of mortise-tenon joint under low cyclic loading were obtained. The results show that the hysteretic curves of the Ban mortise-tenon joints appear to be the Z shape and have the obvious pinch effects. During the process of the test, these mortise-tenon joints orderly pass through the elastic stage, the yield stage and the failure stage. Furthermore, with the consideration of the nonlinear contact influence of the mortise-tenon joint and the nonlinear stress-strain behavior of the timber material, the mechanical properties of the Ban mortise-tenon joints were analyzed by ANSYS software. The theoretical results agree well with the experimental results. The relationship of in-plane rotational rigidity, the out-of-plane rotational rigidity and the tortional rigidity of the Ban mortise-tenon joint is achieved, the ratio of them was 1.4∶1.0∶1.1. The results can provide the theoretical basis for computing analysis and repair design of the traditional timber buildings in the South Yangtze River Regions.

Abstract:Post-earthquake damage state evaluation of ancient wooden buildings involves many impact factors and there are correlations and uncertainty among these factors. In order to improve the damage state assessment accuracy of post-earthquake ancient wooden buildings, fuzzy mathematics theory was employed to investigate this issue. Firstly, ancient wooden buildings were decomposed into three parts: subsoil, foundation and superstructure, and 13 indicators were selected for the evaluation factors based on their damage characteristics. Then, the weight coefficient vector was determined by hierarchy analytical process and the judgment matrix was constructed using membership function and analogy method. Two-phase three-level fuzzy comprehensive evaluation model was built. Finally, taking the Emperor Temple in Qingcheng mountain as an example, the developed model was applied to evaluate its damage state after Wenchuan earthquake. The results show that the evaluation method can reasonably and accurately assess the post-earthquake damage state of ancient wooden buildings, which can provide references to the post-earthquake repair measures of these buildings.

Abstract:According to the ISO and CUREE cyclic test loading protocol, some mechanical performance parameters of wood framed constructions were calculated in Bouc-Wen hysteresis model. Based on analysis of the ultimate strength，ultimate displacement, stiffness, energy dissipation and strength and stiffness degradation of wood framed construction, some basic conclusions on the mechanical performance considering the influence of different loading protocols and reference displacements were obtained. The influence of the loading protocols and reference displacements should be taken into consideration in order to evaluate the mechanical performance parameter based on the test results exactly. Reference displacement equal to 120mm resulted in a 12%~13% and a 66%~68% increasing in ultimate strength and ultimate displacement respectively when compared with reference displacement equal to 60mm under ISO protocol. Reference displacement equal to 100mm resulted in a 4%~6% and a 55%~58% increasing in ultimate strength and ultimate displacement respectively when compared with reference displacement equal to 50mm under CUREE protocol. The loading protocol appeared to have little influence on the scant stiffness of the wood framed construction. It was shown that the ISO protocol with different reference displacements had more effect on the energy dissipation and strength and stiffness degradation when compared with the CUREE protocol.

Abstract:A coupled heat, air and moisture transfer model， which takes into consideration the heat transfer, moisture transfer and air convection and their coupled effect, was developed to predict the distribution of the temperature and humidity and to investigate the rule of the coupled heat, air and moisture transfer in walls. The temperature, relative humidity and air pressure were chosen as the driving potentials. A program based on the finite element method was developed to calculate the governing equations. And the numerical results of this model were compared with the internationally accepted HAMSTAD benchmarks, and the results agree well with each other.