Abstract:The parameter optimization design and damping effect of the single-degree-of-freedom structure under the simple harmonic load by the MTVMD (multiple tuned viscous mass damper) are studied. The robustness of the system is analyzed when the structural parameters are changed. Taking the displacement and acceleration dynamic amplification factor as the optimization targets, the improved mode search method is used to search for the optimal parameters of MTVMD. The analysis shows that the increase of mass ratio and of sub-TVMD number, the damping performance of MTVMD is enhanced, and the structural robustness is enhanced when the structural parameters change. Considering the actual working state of the damper, the parameters may deviate from the optimal parameters. Assuming that the deviation of each sub-TVMD parameter obeys normal distribution, the Monte Carlo test method is used to compare and analyze the damping effectiveness and reliability of STVMD (single tuned viscous mass damper) and MTVMD in the most unfavorable deviation state of their parameters. Numerical results show that the damping effectiveness and reliability of STVMD are positively correlated with the number of sub-TVMD, while MTVMD has an optimal sub-TVMD number to make the damping effectiveness best. The damping performance of STVMD and MTVMD is negatively correlated with the maximum deviation rate of parameters.

Abstract:When the structure identification algorithm was applied to practical engineering, the structure angle information was difficult to accurately measure and the degree of freedom of rotation was often neglected. The method of measuring dynamic signals with gyroscope sensor and the identification of structural physical parameters under the condition of incomplete output information were studied in this paper. Firstly, a commercial Micro Electro Mechanical Systems (MEMS) gyroscope sensor was proposed to measure the angular velocity and angle responses, and the theoretical formulas of structural physical parameters identification method based on the least square recursive method were deduced. Then, taking a four-story frame structure as an example for analysis, two working conditions that the rotation angle reconstructed by the generalized inverse method and the adoption of the true value of rotation angle were set up, and the physical parameters was identified. The correctness of the theoretical derivation was verified. The results of physical parameters identified under two working conditions were compared, which reflected that the effect of physical parameter identification was not very ideal when the angular response was reconstructed, so we can consider measuring the rotational responses. The dynamic accuracy of MEMS gyroscope sensor under impact vibration was verified by experiments firstly. The results demonstrated that the accuracy of dynamic angle measurement was 0.1° when the initial displacement of the structure was less than 10 mm. On this basis, the measured dynamic test data and analysis results of a three-story and two-span steel frame model verified that using MEMS gyroscope sensor to directly measure the rotational response was better than using reconstructed rotational response for the time domain identification of stiffness parameters for the bending-shear structure.

Abstract:In order to study the flexural performance of cold-formed thin-walled steel-fine aggregate concrete composite beams, static tests were carried out on three composite beams with different shear structures. The failure mode and bearing capacity of composite beams were investigated. The failure characteristics of composite beams include shear failure and torsion of joist web, plastic yield of upper flange of the joists, pull-out of part of the shear screws and cracks in concrete, which lead to overall failure of composite beams. The test results show that setting shear connectors has insignificant effect on the ultimate bearing capacity, but can increase the bending stiffness. An ANSYS finite element model is established for numerical simulation as well as parametric analysis based on the calibrated model. The results show that reducing the screw spacing, increasing the strength of steel, increasing the web height of joists or the thickness of concrete can improve the bearing capacity. Bending bearing capacity formulas with a modified coefficient which considers the influence factors of the web height of joists and screw spacing are proposed. The accuracy of the proposed formulas is verified by comparing the theoretical calculation results with the experimental results and finite element analysis results.

Abstract:In order to study the degradation law of residual bearing capacity of steel-concrete composite beams under fatigue loading, the classical steel beam and concrete slab bearing capacity degradation model and the fracture mechanics-based bearing capacity degradation model considering the initial defect of studs were taken to study. By considering the residual ultimate bearing capacity calculation model after degrading into incompletely sheared structures under fatigue loading, a prediction calculation method for the residual bearing capacity of composite beams was established. The validity of the proposed prediction method was verified by comparing the fatigue test data of five typical test beams. On this basis，some parameter analyses of the key influencing factors were carried out. The results show that the calculation method of bearing capacity proposed in this paper has high accuracy and the error is within 8%. Under fatigue loading, the strength of each component of composite beam is degraded at different rates. The stud degrades the fastest, the steel beam is the second, and the concrete slab is the slowest. The degradation degree of the bearing capacity of the composite beam in the early stage of loading stage is dominated by the steel beam, and it is dominated by the studs in the later stage. The degradation rate of the bearing capacity increases with the increase of the loading times. The growth of the bearing capacity in the early stage is slow, basically in a linear distribution, and later it increases rapidly in an exponential manner. The ratio of later bearing capacity attenuation to total attenuation can be more than 70%. The stud spacing（degree of shear connection），initial stud defects, and load amplitude are important factors in controlling the degradation of fatigue capacity. They are necessary to be controlled in engineering design to satisfy the normal operation of the bridges.

Abstract:The bolt slippage of gusset joints can cause structural deformation in aluminum alloy single-layer reticulated shells. The magnitude of deformation depends on the axial displacement of gusset joints, thus, a reasonable axial stiffness of gusset joints can model the bolt slippage to calculate the structural deformation. A stochastic-polylines model is proposed for the distance of bolt slippage influenced by the random error of bolt geometries. It is found that the structural deflection calculated with the stochastic-polylines model can be fitted by that calculated with an ideal four-polylines model. Based on the four-polylines model, a case study is used to research on the structural deflection which varies with bolt pre-tightening force. It is found that if pre-tightening forces are larger than a limit value, the structural deflection ranges with a small amplitude, otherwise it increases distinctly. Further numerical analysis concludes that the maximum deflection approximately linearly varies with the number of grid rings and the gap between bolt and hole. And it is also affected distinctly by the structural span, the ratio of structural height to span and support type, but uncorrelated with the geometry of member section and joint gusset and the scale of loads. Then, a formula to compute the maximum deflection is proposed. And the optimum diameters of holes in gusset joint are lastly suggested for the widely used bolt and rivet connections.

Abstract:In order to study the influence of end plate thickness and node types on seismic behavior of prefabricated eccentrically braced steel frame，pseudo-static tests of two eccentrically braced semi-rigid steel frames with different end plate thickness and one eccentrically supported rigid steel frame were carried out. Based on the testing results, the main characteristics of the failure modes，load-deformation hysteresis curves, skeleton curves, lateral ductility coefficients and equivalent viscous damping coefficients of the specimens are analyzed and discussed. The results show that the prefabricated eccentrically braced steel frame with end plate connections has good seismic performance. The thickness of the end plate is an important factor affecting the energy dissipation capacity of the prefabricated eccentrically braced steel frame, and the energy dissipation capacity of the structure increases by 43.32% with the thickness of the end plate increasing from 16 mm to 24 mm. At the same time, affected by the slip of high-strength bolt-end plate connection, the hysteresis curve of semi-rigid steel frame with eccentric support is“bow”，showing a phenomenon of “pinching”.

Abstract:To expand the application of prefabricated segmental bridge piers in middle and high intensity seismic region, energy dissipating steel plates are set at the outer side of the pier bottom. The performance of the prefabricated bridge piers with external energy-dissipation plates under quasi-static loading was analyzed and compared with that of the cast-in-place piers as well as the prefabricated piers with built-in energy dissipating steel bars. The rationality of the proposed prefabricated piers is studied from the aspects of hysteretic curve, skeleton curve, cumulative energy consumption and recoverability. Based on the three line skeleton curve model, a calculation method for the skeleton curve of prefabricated pier with external energy dissipating steel plates is proposed. The predictions from the proposed method are compared with the numerical simulation results, and both are in good agreement. The seismic performance of the prefabricated piers with externally placed energy consuming steel plates is analyzed by Pushover Method. The results show that increasing the prestressing level can increase the bearing capacity and stiffness, while reduce the ductility. When the prestressed steel strand is arranged around, the bearing capacity, stiffness and energy dissipation capacity of the pier are improved. When the steel strand is arranged in the center, the ductility of the pier is improved and the deformation capacity is strong after yielding. Increasing the amount of energy dissipation steel plate can improve the bearing capacity and stiffness of piers. To a certain extent, increasing the amount of energy dissipation steel plates can compensate for the adverse effect of the increase of slotting rate on the structure.

Abstract:In order to study the bond behavior between the steel bar and the grouting material of the sleeve grouting joint in the precast concrete structure, 30 specimens of grouting sleeve are designed for pull-out tests. The effects of four parameters including steel anchorage length, grouting compressive strength, grouting thickness and steel bar diameter on the bond strength of steel bars were studied. The results show that as the anchor length increases, the bond strength between the steel bar and the grout decreases; with the increase of compressive strength of grouting material, the bond strength between reinforcement and grouting material increases. With the thickness of the grout increasing, the bond strength decreases. For 12 mm steel bars, when the thickness of the slurry is between 9 mm and 11 mm, the thickness of the slurry has little effect on the bond strength. When the thickness of the slurry exceeds 11 mm, the effect is significantly increased. The bond strength increases as the diameter of the bar increases. According to the measured sleeve strain and the balance distribution model of the spacer, the relationship between the bond strength and the restraint stress as well as the compressive strength of the grout is obtained, which can provide a reference for the anchorage length of grouted sleeve connections in the engineering practice.

Abstract:Taking the sand soil in the limited range behind the retaining wall as the object, the relationship between the retaining wall displacement and the internal and external friction angles is established. Assuming that the earth behind the wall is arc-shaped and considering the shear stress between the soil layers, the angle of fracture surface and passive earth pressure coefficient under the hypothesis of multichannel slip surfaces are adopted, and then the theoretical formula of passive earth pressure with limited soil is derived. It can also be degenerated into the solution of passive earth pressure with semi-infinite soil. Compared with the model test, the proposed theoretical solution is in good consistency with the experimental values, which verifies the rationality of the analytical solutions. Parameter analysis shows that: considering the inter-layer shear stress, the total value of passive earth pressure is not influenced, while the position of action point is higher. The passive earth pressure changes little at first and then increases significantly with the decrease of the soil aspect ratio. With the increase of the internal friction angle, the resultant of passive earth pressure increases while the position of action point is lower.

Abstract:To improve the ductile failure mode and seismic performance of concrete hollow block masonry walls, this study proposes techniques for strengthening these walls with high ductile concrete (HDC). Three unreinforced masonry walls (URM) and three confined walls were built, and then both types were strengthened using single-sided and double-sided HDC layers, respectively. Based on the cyclic loading tests, the failure mode, hysteretic behavior, shear strength and deformation capacity were studied to provide a theoretical basis for the design of such structural members. For the URM walls, HDC layer effectively restricted the development of diagonal cracks, improved the ductile failure mode of wall and increased the shear resistance and deformation capacity. For the confined masonry walls, the strengthened specimens had higher bearing capacity and residual strength, and the damage of the internal masonry walls was slighter. Based on relevant theory analysis，the formulas，for the shear capacity of tested specimens，were proposed. The calculated results matched well with the tested results. Therefore, it can be a reference for the calculation of the shear strength of the strengthened concrete block masonry walls.

Abstract:In order to study the seismic performance of corroded steel frame columns in offshore atmospheric environment, an indoor artificial-climate accelerated test on six steel frame columns was implemented firstly. And then, low-cyclic reversed loading tests were conducted on the six corroded steel columns. The influence of corrosion levels and axial compression ratios on the failure modes, hysteretic curves, skeleton curves, stiffness degradation, ductility and energy dissipation capacity of the specimens was analyzed and discussed. The test results indicate that with the increase of corrosion level, the displacement corresponding to the flange local buckling, web local buckling and formation of plastic hinges gradually reduce, and the bearing capacity, deformation capacity and energy dissipation capacity of specimens decrease as well. In addition, with the increase of axial compression ratio, the occurrence of local buckling is advanced, the load bearing capacity and ductility decrease obviously, the strength and stiffness degenerate significantly, and the energy dissipation capacity degrades. Based on the test results, the seismic performance levels and quantitative limits of performance index for the corroded steel frame columns were preliminarily determined. This study can provide experimental support for the seismic performance evaluation of existing steel structures in offshore atmospheric environment.

Abstract:An innovative composite structure, named seawater and sea sand concrete（SWSSC） filled reactive powder concrete（RPC） tube（SFRPCT），was presented in the paper. In the hybrid system, carbon fiber reinforced polymer（CFRP） hoops are arranged in prefabricated RPC tube and then SWSSC is cast in tube. From the material durability point of view, SFRPCT has excellent corrosion resistance and it can be potentially applied in marine construction. A total of 15 large-scale columns were conducted under axial compression test, including 12 SFRPCT specimens and 3 CFRP hoops confined SWSSC（FRPHSC） specimens. Composite effect between RPC tube and internal SWSSC and influence of mechanical properties from lateral confinement level were investigated in test. The results showed that only slight crack on RPC tube of SFRPCT column occurred without any spalling when axial load approached its peak value. Compressive strength and ductility of the SFRPCT columns were significantly higher than those of the corresponding FRPHSC specimen and increased with the increase of the volumetric hoop ratio in RPC tube. Therefore, SFRPCT hybrid system effectively combined the super-high strength of RPC and confinement effect by CFRP hoops. Based on existing test data and model, a calculation method for carrying capacity of SFRPCT was proposed. Contribution ratio of RPC tube for carrying capacity of SFRPCT columns was quantified and its value varied from 0.39 to 0.42.

Abstract:There is divergent phenomenon existing in time-domain calculation results based on complex damping model. Hysteretic damping model has the shortcomings that energy dissipation is not consistent with the practical case and a defect of nonlinearity in linear elastic stage. To overcome the above shortcomings of complex damping model and hysteretic damping model, a frequency dependent viscous damping model is obtained based on the principles of frequency domain transformation in this paper. For the realization of structural time-history calculation method, an improved frequency dependent viscous damping model is obtained based on the assumption of the relationship between acceleration and displacement. The improved frequency dependent viscous damping model has the advantage that energy consumption is independent of external excitation frequencies. At the same time, the energy consumption in the proposed model is consistent with the practical case, and it maintains linear characteristic of single-degree-of-freedom structure with a single vibration frequency. It is assumed that structural response is harmonic vibration response in every time step. It contains the single frequency. By introducing the constant average acceleration method, a time-history calculation method of single degree of freedom system can be put forward. On this basis, combined with the modal superposition method, the time-history calculation formulas of multi-degree of freedom system are obtained. The analysis results of the cases show that improved frequency viscous damping model can overcome the shortcoming of the frequency-domain method based on complex damping model. It can also avoid the divergent phenomenon in calculation results of time-domain method based on the complex damping model.

Abstract:The bottom of wind turbine foundation will cause fatigue damage under wind loads. In order to study the fatigue reliability of wind turbines under wind loads, the random fluctuating wind loads were expanded orthogonally, and the expanded wind load model was used to calculate the fatigue reliability of the wind turbine tower using the number theory selection method and the probability density evolution method. The thrust coefficient method was used to calculate the stress time history of the dangerous part of the wind turbine foundation under the wind load, and then the fatigue damage of the point was calculated by the rain flow counting method, which is substituted into the probability density evolution equation. The probability density function of fatigue damage can be obtained by solving differential equation. By accumulating the probability of fatigue damage less than 1, the fatigue reliability of the dangerous parts can be obtained, that is, the fatigue reliability of the entire foundation. The effectiveness of the proposed method is verified by a 3 MW wind turbine. Using the probability density evolution method, the fatigue reliability of the foundation under wind load can be accurately given. The findings of this paper have reference significance for the calculation of fatigue reliability of wind turbine foundation under similar working conditions.

Abstract:Layout of construction site facilities has great impact on the project objectives, such as project cost. In this paper, the problem of the construction site facilities layout with many facilities, which is an optimization problem with discrete variables, is considered. Firstly, the problem is transformed to a high-dimensional random sampling problem, and then addressed by a novel meta-heuristic algorithm based on transitional Markov chain Monte Carlo (TMCMC). Different from original TMCMC developed for optimization problems with continuous variables, the proposed meta-heuristic algorithm is based on introducing a sequence of probability distribution functions instead of probability density functions, and thus the method for iteratively generating states of Markov chains is modified in the proposed algorithm, in order to meet the specifics of optimization problems with discrete variables. As shown in an illustrative example, compared with the widely used genetic algorithm, the proposed meta-heuristic algorithm can obtain higher improvement in the stability of achieving global optimal solution.

Abstract:In photovoltaic (PV) modules, the solar cells are separated by small gaps and the stress distribution in cells is thus different from that where the cell layer is considered as a continuous one. In this paper, the solutions of the stress and displacement fields in the crystalline solar cells were developed. The stresses of the crystalline solar cells in PV module with a size of 1 580 mm × 808 mm were evaluated and the variation of the wind pressure and the effects of the storage shear modulus of the Ethylene-Vinyl Acetate (EVA) were considered. The results by the present solution were compared with those from Finite Element (FE), and the stresses of 125 mm × 125 mm and 156 mm × 156 mm cells were compared. The comparison shows that the results by present solution are in good agreement with those from the FE. The maximum stress (Von Mises stress) occurs at the middle of the cell and increases nonlinearly with an increase of the storage shear modulus of EVA. The results also show that the stress rises when the larger cells are applied.

Abstract:In order to improve the accuracy of fly ash permeability calculation，firstly，the diameter and number of pores and particles in fly ash specimens are obtained by using microdigital imaging technology and professional image processing technology. Then，the frequency histogram of pore and particle is plotted，and the pore exponential distribution function and particle Rayleigh distribution function are fitted by the least square method. Secondly，the pores and particles are divided into three grades，and their characteristic particle sizes are calculated and arranged in order from small to large. Finally，based on the ball-touch process without dropping back，Matlab programming was used to simulate the random arrangement of pores and particles in a square with a diameter of 5 times the maximum particle equivalent circle，and the connectivity of pores was calculated. On this basis，the formula of fly ash permeability considering the porosity connectivity is derived，which is compared and analyzed with the results of other literatures. The good agreement proves the feasibility of the method in this paper.

Abstract:A new form of composite air carry energy radiant end combined with roof and sidewall is proposed. An office building is taken as the research object and the heating performance of the composite air carry energy radiant end in cold-winter and high-humidity climate zone is studied by an experimental method. The results show that the composite air carry energy radiant air-conditioning system can reach a stable state within 30 minutes after opening. Compared with traditional air-conditioning system, it has faster heating rate and stronger stability, and the indoor temperature change is relatively uniform after stabilization. The system has good heating performance in winter. In the range of human activity (0.2 m to 2.2 m from the ground), the indoor air temperature is 16.5 °C ~ 18.2 °C, and the relative humidity is 33% ~ 36%. The heating requirement in winter can be met when the temperature is set at 16 °C. In addition, the system can effectively improve the situation that floor temperature is too low due to the occlusion of objects, thereby effectively avoiding local discomfort. The composite air carry energy radiant end combined with roof and sidewall can meet the demand of heating in winter and has the characteristics of energy saving and comfort. The results can provide some guidance for the practical application of air carry energy radiant air-conditioning system in cold-winter and high-humidity climate zone in the future.

Abstract:In order to implement the dual-objective optimization of load ratio of the combined ceiling radiant cooling panel and DOAS air-conditioning（CRCP-DOAS） system, BES-CFD co-simulation is introduced. Taking a residential room in Changsha with applications of CRCP-DOAS system as a research case, energy consumption of the system and indoor thermal environment are studied under different load ratio of three supply air temperature difference, and the optimal load ratio range is obtained from the perspective of energy saving, thermal comfort and safety. The results show that when considering the energy saving of the system, the optimal load ratio ranges are 46%~85%， 16%~85%, 3%~85% at the supply air temperature difference of 4 ℃，6 ℃，8 ℃，respectively. And it is more energy efficient when the supply air temperature difference is larger. From the perspective of thermal comfort, the optimal load ratio ranges are：20%~72%（4 ℃），16%~59%（6 ℃），3%~50%（8 ℃），respectively. And the load ratio has a larger adjustment interval when the supply air temperature difference is smaller. Under each load ratio, the surface temperature of ceiling and floor is higher than the air dew-point temperature near the surface, so there is no condensation risk. The optimal load ratio ranges are 46%~72%（4 ℃），16%~59%（6 ℃），3%~50%（8 ℃），respectively，under comprehensive consideration of energy efficiency，thermal comfort and safety.