Abstract:A two-degree-of-freedom magnetic levitation vibration energy harvester (TMEH) was designed, which can use the bridge vibration energy to provide continuous power for the sensors. The energy harvesting efficiency of the TMEH is much higher than that of the traditional single-degree-of-freedom magnetic levitation vibration energy harvester (SMEH). Firstly, the motion control equation and the electromechanical coupling equation of TMEH system were deduced. Then, the multi-objective optimization model of TMEH was established, and the design parameters were optimized by using the NSGA2 algorithm. Finally, the response characteristics of TMEH and SMEH under the harmonic excitation and normal vehicle-bridge vibration excitation were compared, respectively. The results show that: 1) After optimization by the NSGA2 method, TMEH can obtain a wider frequency band and higher output power;2) The energy harvesting efficiency of TMEH is significantly higher than that of the SMEH. Under harmonic vibration excitation and normal vehicle-bridge vibration excitation, the output power of TMEH is about two times higher than that of SMEH.

Abstract:To investigate the global and local dynamic response of plate-truss composite structure (i.e.,cable-stayed bridge induced by train-bridge coupling vibration),a numerical approach was presented based on train-bridge coupled dynamics. A coupled train-bridge system model composed of a 3D vehicle model with 31 degrees of freedom,a 3D fine bridge model established by the direct stiffness method,and an assumed wheel-rail spatial contact relationship based on the Hertz nonlinear contact model and nonlinear creep force model were developed. The self-developed software TRBF-DYNA was applied to analyze the dynamic responses,such as acceleration,displacements and stresses. The Dongting Lake three tower cable-stayed bridge with a main span of 406 m in Jingyue railway line was taken as an example. The global and local dynamic response of the bridge,variations of running safety,and ride comfort index were discussed under different routes,speeds and track irregularities conditions. The results show that the local dynamic response of orthotropic steel bridge deck is much larger than the response of steel truss girder. Dynamic coefficient of large-span cable-stayed bridge is small,and the influence of the speeds and track irregularity on dynamic coefficient of large-span cable-stayed bridge is insignificant. The lower chord and web members of steel truss girder are in high cycle fatigue stress state,which should be paid more attention in the study of their fatigue properties. Further,the dynamic response of bridge,running safety indexes and ride comfort index satisfy the code requirements under the designed running speed.

Abstract:A new deployable bridge for relief was developed. The system,component,connection and deploy method of the new deployable bridge were introduced. The deployable bridge is based on universal scissor components which can guarantee swift expansion and fixation by small machinery. The bridge structure is not only stable but also deployable and consists of deployable arch ribs,rigid columns and deployable decks. The finite element software SAP2000 was used to model and optimize the bridge structure. Cross-section optimization and linear and nonlinear buckling analysis were performed. The safety coefficient of linear buckling of optimal scheme is 5.72 and the safety coefficient of nonlinear buckling is 2.95 which evaluate the structural favorable capacity of the deployable bridge. The deployable bridge is light,easy to transport,reliable,and fast to construct. It can efficiently fix traffic interruption.

Abstract:Based on temperature-history data recorded by structural health monitoring system (SHMS) installed on long-span bridge,the characteristics of the temperature in the top deck and bottom deck of the steel box girder was studied. According to the indirect coupling method,temperature was regarded as body load and applied to three-dimensional multi-scale finite element (FE) model. Structural stress induced by temperature can be obtained and the analysis from thermal to the structure was realized. And then,based on the strain data from SHMS,the difference of strain characteristics induced individually by vehicle loads and environment temperature were investigated. Strain histories caused by the above factors were separated and extracted,and they were compared with the results by the FE simulation. Finally,based on the continuum damage mechanics,the cumulative fatigue damage of the bridge was induced by vehicle load separately as well as the interaction of vehicle load and environment temperature. The results show that the analysis flow of fatigue damage proposed in this paper can realize fatigue damage analysis at key locations of bridge under the action of environmental temperature and vehicle load. Fatigue damage caused by the temperature alone is small and can be ignored. But the fatigue damage caused by the interaction of these two loads has significant difference with that caused by the vehicle alone. At the beginning of the service periods,the influence of temperature on damage is not significant,but with the increase of fatigue damage,the influence of the interaction of these two loads becomes more prominent. That indicates that loads induced by temperature change accelerate the rate of fatigue damage accumulation at the mid-late service periods,and have a significant impact on the structure fatigue life.

Abstract:The originally developed horizontal damping support was applied to the high-rise tridimensional parking structure.The plane shear angle of the parking zone and lifting zone under the horizontal excitation was taken as the performance index.A parametric model of a 15-floors tridimensional parking structure was established by APDL language of ANSYS.Based on the dynamic time history analysis，the effects of the supporting bar layout，damping coefficient and energy loss coefficient of the visco-elastic material on response control of horizontal damping support were studied.After comparison and analysis，the optimal level of horizontal damping support parameters was determined.The results showed that when the optimal supporting bar layout was applied，the damping coefficient was 200 kN·s/m，energy loss coefficient was 5.0，and the peak plane shear angle of the parking zone under different two-dimensional seismic waves was decreased by 65.67% ,51.72% and 51.59% respectively，while the peak plane shear angle of the lifting zone was reduced by 73.23% ,72.51% and 75.36%.Meanwhile，the synchronization of the beam and column deformation in the structure plane was enhanced，the working environment stability of the lifting equipment was improved significantly，and the horizontal damping support was in good working condition.The results provide significant guideline for the application of visco-elastic damper to the high-rise parking structure and the design of high-rise tridimensional parking structure.

Abstract:In order to establish an efficient and accurate procedure for the vertical seismic performance evaluation of space truss structures,a modal pushover load pattern,taking the structural mass distribution into consideration,was adopted so as to modify the establishing process of the equivalent single-degree-of-freedom (ESDF) systems based on the overall structural stiffness parameter. The characteristic of the vertical vibration of space truss was investigated,which is influenced by gravity and obviously asymmetric. By assuming the equivalent load-deformation relationship of the ESDF system to be “one-side” elastic,the simplified modal ESDF systems for space truss structures were established. Basic processes for both vertical seismic response analysis and vertical seismic performance evaluation of space trusses were given. It is demonstrated by a numerical example that the proposed equivalent-simplified-model-based procedure can yield accurate vertical displacement response (error of central nodal displacement is less than 5%) and can approximately locate the inelastic members of space truss structures. Meanwhile,the time consuming of the proposed simplified procedure is much less than that of the nonlinear response history analysis. Moreover,for practical engineers,the proposed approach is pretty concise and easy to use.

Abstract:Six bridge column specimens with shear span ratio of λ=1.5 were tested under combined constant axial load and lateral reverse loads. The effectiveness of built-in steel tube in enhancing the seismic behavior of RC stub bridge column was evaluated. Besides, the influence of axial load ratio, longitudinal rebar ratio, stirrup ratio, and steel tube ratio on the shear strength, deformation capacity, strength attenuation, and energy dissipation of STRC stub bridge columns was also discussed. Test results indicate that the failure patterns of RC and STRC stub bridge columns were shear diagonal-tension failure and ductile shear diagonal-compression failure, respectively. The existence of core steel tube alleviated the damage of RC stub bridge column and changed the brittle failure into a ductile fashion, which significantly enhanced the seismic behavior of STRC stub bridge column specimen over the RC counterpart. The shear strength, ductility and energy dissipation of STRC stub bridge column were improved with the increase of steel tube ratio or stirrup ratio. With the increase of the longitudinal rebar ratio or axial load ratio, the shear strength of STRC stub bridge column gained a noticeable increment, while the ductility and energy dissipation tended to deteriorate. Test results in this paper could provide reference for theoretical research and practical application of STRC stub bridge columns.

Abstract:Three kinds of fine-grained concrete matrix with chopped steel fibers of 0%,0.8% and 1.6% volume ratios were used to fabricate the basalt TRC plates,and various prestressing were exerted on basalt textile layers. The stress-strain relationship and cracking patterns of TRC plate were investigated by means of uniaxial tensile tests. The obtained results indicate that,with the increase of the number of textile layers,cracking strength of TRC plate decreases,the peak load and strain capacity tend to increase,and cracking patterns are greatly improved. In addition,the increased cracking strength,reduced strain capacity and undesirable cracking patterns are observed with the increase of prestressing,while no obvious change occurs for peak load. Furthermore,the tensile performance of basalt TRC plate is correlated with volume ratios of chopped steel fibers and prestressing. When chopped steel fibers with 1.6% volume ratio are mixed in the matrix and appropriate prestress force is applied to textile layers,the basalt TRC plate exhibits relatively good tensile performance.

Abstract:In order to investigate the adaptation of ultrasonic test in evaluating the performance of reactive powder concrete (RPC) after high temperature exposure, the high temperature tests under 100 ℃, 200 ℃, 300 ℃, 400 ℃, 500 ℃, 600 ℃, 700 ℃ and 800 ℃ were performed. The relationship between the four parameters (relative wave velocity, damage degree, relative frequency and relative amplitude) and temperature as well as compressive strength loss rate was analyzed. The microstructure of RPC was also studied by scanning electron microscopy (SEM) technique after exposure to high temperature. The results showed that adopting the parameters of damage degree and relative velocity to evaluate the performance of RPC after high temperature was better than adopting the parameters of relative frequency and relative amplitude. The correlation of the fitting value of damage degree with experimental value was the largest, which can accurately reflect the damage degree of RPC. On the contrary, the fitting value of relative frequency and relative amplitude showed little correlation with the experimental value. With the increasing of the elevated temperature, the internal defects of RPC exacerbated, and the cracks at the bonding interface of fiber and the matrix occurred gradually, which illustrated that the micro-structure of RPC deteriorated constantly and the loss rate of compressive strength increased gradually.

Abstract:The interfacial properties between textile reinforced concrete (TRC) and existing concrete were studied by double-side shear tests. Based on the plasticity limit analysis theory and the interface model between new and old concrete,the interface model of TRC and conventional concrete was modified,and the theoretical calculation formula of maximum cohesive force between their interfaces under the conventional environment was derived. Subsequently,according to the experimental results of the interfacial bond strength between their interfaces under the effect of different number of sodium chloride solution wet-dry cycles，the environmental impact coefficient was fitted. The theoretical calculation formula of the bond strength between the TRC and conventional concrete under wet-dry cycle was then derived. By comparing the relative error between theoretical and experimental results,the correctness of the theoretical model and calculation formula were verified.

Abstract:In this study,tapered steel fibers with various angles (0°,2°,5°,and 7°) were designed in the point view of biomimetic. The surfaces of the fibers were classified into chemical bonding and no chemical bonding based on whether their surfaces were treated or not. The fibers were pulled out from cementitious matrix under various loading speeds (2.5 mm/min,25 mm/min,and 250 mm/min) using a MTS load frame. Pullout force and displacement of the fiber were recorded for further calculation of maximum pullout force and work of pullout. The experimental results show that the maximum pullout force increases significantly when the taper angle increases from 0° to 5°,but decreases slightly when the angle is 7°. The maximum pullout force increases by 20.2% and 13.4% with the pullout speed increasing from 2.5mm/min to 250mm/min for 5° and 7° fibers,respectively. The maximum pullout force decreases by 25.9% and 8.2% for 0° and 2° fiber when pullout speed increases from 25 mm/min to 250 mm/min,respectively. The maximum pullout force for untreated fibers are 64.1%,22.2% and 6.7% higher than that for treated fiber when the taper angles are 0°,2° and 5°,respectively. However,for the fibers with 7° taper angle,the maximum pullout force of untreated fiber is 6.2% lower than the treated ones. The work of pullout for 2° fiber is the largest under three various speeds. There is no obvious effect on the work of pullout whether the fiber is treated or not. The tapered fibers designed in this work can effectively enhance equivalent adhesive strength between the fiber and cement mortar matrix.

Abstract:Due to the mechanical characteristics of arched concrete structures, some differences of the penetration effect subjected to high velocity projectile impact exists between arched structures and slab or beam structures. In order to study the dynamic response and damage characteristics of concrete arch structures subjected to high speed penetrating load, the strain rate effect under impact load was taken into consideration for the establishment of the penetration model based on the coupling method of SPH and Lagrange. The reliability of the coupling model was also verified. Based on the coupling model, the perforation and penetration damage process of concrete arch targets subjected to impact load were studied. The results indicated that the arch effect had important influence on the damage process of concrete structures, the dynamic response of concrete arch targets and the length of fracture zone caused by high velocity impact from extrados were smaller than that from intrados, and the residual velocity of projectile from extrados was also smaller than that from intrados.

Abstract:This paper selected threaded rod as the shear connectors of glued bamboo beams. Single-sided shear tests on total 6 groups of shear-slip GluBam-Concrete composite specimens were performed. The major mechanical properties such as the load-slip curves, shear bearing capacity and anti-slip stiffness were measured and then evaluated. The test results indicate that the typical failure modes of composite blocks are the splitting of GluBam due to local compression caused by the connector, and obvious plastic deformation of rod occurs in the glued-in depth. The mechanical performance of the specimens is enhanced with the increasing diameter of dowel, while the improvement efficiency descends. The diameter of rod of 18 mm is a critical value for the shear-slip behavior, and it seems to be a reasonable choice. The quality grade of threaded rod has no substantive effect on the mechanical properties and composite action. Moreover, the action of the waterproof layer at the interface is temporary, and it can be removed for improving the composite effect.

Abstract:Temperature effect is one of the main factors that influence the performance of box girder-track in high speed railway. Through the continuous temperature field monitoring of CRTS I twin-block ballastless track with 32 m simple supported beam bridge for the entire year,the time-dependent temperature variation and the regular distribution of temperature gradient were analyzed. The representative values of temperature differences with a certain return period were ascertained by Higher Moment Method. Based on the 16560 data at each measurement point,the vertical temperature load modes of box girder-track in southeastern China were suggested. The analysis results reveal that the goodness-of-fit is increased by using the first Fourier series to simulate the temperature fluctuation characteristics of sunny day,and the same season fitting parameters a,b,ω and φ decrease from top to bottom and the temperature fluctuation amplitude of a is close to 0℃ as the depth increases. The diurnal variation characteristics of each section on sunny days are basically similar in the different seasons,and the positive and negative temperature gradients approximately appear around 11:00 to 21:00 and 01:00 to 9:00,respectively. The positive and negative representative values of box girder-track vertically are 14.87℃ and -6.3℃ with the exceedance probability of 0.01,respectively. And the positive and negative representative values of the top plate and bottom plate are 13.74℃,-3.54℃ and 2.38℃,-1.12℃ with the exceedance probability of 0.01,respectively. The values of positive and negative temperature difference of top plate are fitted by the exponential form,which is approached to the temperature load modes of the concrete box girder in Chinese railway bridge code. The values of bottom plate are fitted by linear form. The correlation coefficients of the two fitting forms are more than 0.99,which can be used for the engineering application and reference.

Abstract:In order to study the seepage characteristics of rock mass containing periodic fractures with partial filling, an analysis model for the seepage of rock mass was built. Two boundary conditions were given for the interfaces between different medium in the model: 1) equal velocity; and 2) continuous shear stress. According to the given conditions, the velocity distribution in the fractures was deduced by using the Navier-Stokes equation and that in porous medium was deduced by using the Brinkman-extended Darcy equation. The equivalent permeability of rock mass containing periodic fractures without partial filling was also derived. A test equipment was made to carry out the equivalent permeability tests. In the tests, concrete and sandstone were used to simulate rock and filling fractures between two pieces of concrete. The difference of the results measured by tests and the equivalent permeability calculated from the theoretical expression was very small. The test result validates well the derived expression.

Abstract:In order to study the optimal row spacing and supporting structure internal forces of the double-row piles supporting structure of deep foundation pit, indoor model tests were carried out for double-row piles supporting structure with row spacing of 2D, 3D, 4D and 5D (D is the diameter of the pile), respectively. Jacking forces were applied to simulate the load of different excavation depths, and the stress in the pile and the displacements at the top of the piles were measured. The effects of row spacing and excavation depth on bending moment and the displacement of these two rows of piles in the double-row piles supporting system were analyzed, and the optimal row spacing was obtained. This research shows that the change of row spacing causes large influences on both the bending moment of the pile and the displacements at the top of the pile. The change of row spacing affects the internal stress of the back pile much more than that of the front pile. It affects the positive bending moment more than the negative bending moment. The curve of depth-displacement is approximately a quadratic function curve passing the origin. It is positive bending moment in the pile above the foundation pit, and it is negative bending moment in the pile below the foundation pit. The displacement at the top of the pile reaches the smallest value when the row spacing is 3D, and the positive bending moment reaches the maximum value when the row spacing is 4D.

Abstract:In order to overcome two faults of the complicated calibration experiment in present methods for quick testing subgrade compactness and the neglectful effect of initial ground stress on deformation parameters, a new method for quick testing subgrade compactness was established. Firstly, the laws of porosity, deformation modulus and density varying with the deformation of subgrade soils were studied based on porous media theory. Then, the force-settlement analytical relation was established by considering the effect of initial ground stress and subgrade deformation on variational mechanical parameters by using the layer-wise summation method and step-loading idea in the process of static penetration. Besides, on the basis of force-settlement curves observed by static penetration experiments, the parameters of force-settlement analytical relation were obtained by back-analyses with adaptive genetic annealing algorithm, and the determination method for subgrade compactness based on porous media theory was then established. Finally, the engineering cases proved that the accuracy of this method satisfied the engineering requirements, and this method tested the subgrade compactness quickly and accurately without complicated calibration experiments which are essential in present methods. It shows that the proposed method is reasonable and feasible.

Abstract:In order to study the dynamic evolution laws of asphalt oxidative aging process，three binders were aged at different temperatures and aging periods.The master curve of complex modulus and phase angle of each binder were determined through frequency sweep tests by using a dynamic shear rheometer，and crossover modulus can be determined further.The dynamic evolution laws of crossover modulus with aging time and temperature were analyzed.The oxidation dynamic model which can predict the crossover modulus was established.It is found that the growth rates of the inverse of log crossover modulus are fast at the beginning aging time，and then gradually get slow to linear for both of unmodified and modified binders.The model can predict the crossover modulus of binders with aging time and temperature.Each binder has its own aging path with aging conditions.

Abstract:Research on the swelling of gypsiferous rock has practical significance on the stability of tunnel invert arch.The WG consolidation apparatus and TWJ data sampling system were employed for tests，including the free swelling tests with lateral restraint of dehydrated gypsum，anhydrite and gypsum and the swelling pressure tests of dehydrated gypsum and anhydrite.The results indicate that the swelling strain-time curves of dehydrated gypsum and anhydrite behave as “S” curve.The minimum swelling strain of dehydrated gypsum and anhydrite is 9% and 0.4% at 600 min，respectively，while the maximum strain of gypsum is only 0.12% in 40 days，which indicates that the swelling deformation of gypsum is non-significant.The swelling strains of dehydrated gypsum and anhydrite increase with the increase of swelling stresses，and their swelling stress-strains behave as concave shape curve.Based on the test results，the “S” curve model of swelling strain-time was established，which showed a better fitting result than the exponential model.The swelling stress-strain model was also established.Combing with the characteristic-line theory，the characteristic line for anhydrite rock mass was established，which can give guidance to the design of invert arch.

Abstract:In order to study the effect of liquid filling rate and operating parameters on the performance of micro-channel separate heat pipe (MCSHP),the steady state heat transfer model of MCSSHP was established. Compared with experimental data,the maximum relative error of this model is 7.9%. Based on the model,the effects of refrigerant filling rate,airflow rate and height difference between evaporator and condenser on refrigerant side heat transfer coefficient,pressure drop,heat transfer rate and energy efficiency ratio (EER) were analyzed. The results showed that the optimal refrigerant filling rate of this system was about 80.2%~105.6%,and the corresponding maximum heat transfer rate was 3.75~3.90 kW. With the increase of the refrigerant filling rate,the heat transfer coefficient at the refrigerant side increased first and then decreased,and the system pressure increased with the increase of the refrigerant filling rate. Meanwhile,when the airflow rate at the evaporator side increased from 1 500 m3/h to 5 000 m3/h,the heat transfer rate and EER increased by 100.1% and 92.5%,respectively. When the height difference between evaporator and condenser increased from 1.2 m to 2.4 m,the average heat transfer rate of the MCSHP increased by 9.18%. The research results are valuable for the energy-saving design and operation control of MCSHP.