Abstract:In order to investigate the mechanism of wake-induced vibration of the suspension bridge hangers, and to verify the applicability of quasi-steady assumption in the research of the wake-induced vibration, a series of wind tunnel tests for two parallel circular cylinders were carried out to measure the aerodynamic derivatives of the downstream cylinder. Second, a theoretical analysis model of wake-induced vibration of the downstream cable was developed on the basis of the unsteady theory, and the Runge-Kutta method was adopted to numerically solve the motion equations to obtain the responses of wake-induced vibration. The results show that obvious oscillations of the leeward cable take place in the spatial region of 5.2≤X≤5.6 and 1.1≤Y≤2.1, and the vibration frequency of cable is slightly less than its natural frequency. A positive work within a period is always done by the aerodynamic stiffness force if large amplitude vibration of wake-induced vibration takes place, which indicates that the aerodynamic stiffness force is the key factor to evoke the wake-induced vibration of the leeward cable. Moreover, the results based on the quasi-steady theory show small variation when compared with those based on the unsteady theory, and the wake-induced vibration mechanism obtained by the two theories is consistent.

Abstract:Wind tunnel testing methods were employed to study the interference effect and drag coefficients of multi-bundled conductors under various azimuths. Drag coefficients of isolated conductor and circular cylinder with the same diameter were compared under various wind velocities and turbulence intensities. The drag coefficients of sub-conductor and total drag coefficients of multi-bundled conductor were obtained and their results are compared with those obtained from Codes and other researchers. The results show that the drag coefficient of the isolated conductor is 13% less than that of the circular cylinder under high velocity, indicating that the twisted shape can reduce the drag coefficient of the circular cylinder. When two sub-conductors are in front-back arrangement, the drag coefficient of the back sub-conductor decreases significantly, and the less distance between them, the more the drag coefficient decreases. The total drag coefficient of multi-bundled conductors is small under certain azimuth when the significant interference effect is considered. The enveloped drag coefficients of multi-bundled conductors with 23.94 mm in diameter and 400 mm in distance are recommended as 1.02, 1.00, 0.97 and 0.93 for isolated conductor, two-bundled conductor, four-bundled conductor, six-bundled conductor and eight-bundled conductor, respectively.

Abstract:In this context, based on the analytical methodology of the ship-ship collision, the deformation mechanisms and failure modes of structural members in steel fenders (e.g., outer plate, transverse, and vertical ribs) were investigated. The characteristics of impact forces under different impact locations were carefully discussed. The analysis results indicate that the adjacent members at the impact location could work cooperatively at the same time because of the close arrangement and the small space inside the steel fender, and the differences of impact forces under various impact positions would be not significant. Based on the resistance characteristics of steel fenders under difference bow shapes, the typical collision scenarios were defined. Accordingly, the analytical method was developed to estimate the anti-collision performance of steel fenders, which is suitable for both ship vessels with a bulbous bow and those with a raked bow. The impact force versus crush depth curves of the fixed-type steel fenders were obtained by using the proposed analytical method for different ship impacts. The analytical results were compared with those obtained from the finite element analysis. The results show that the analytical results are in good agreement with the finite element results, indicating the rationality of the analytical method developed in this study.

Abstract:To reduce the computing work and improve the efficiency of vehicle-bridge coupling analysis when using traditional fully coupled method, a high efficiency highway vehicle-bridge interaction analysis system was established based on improved binary search and isoparametric mapping. The finite element model of the bridge was simulated using ANSYS, the multiple refined dynamic vehicles were modeled in MATLAB, and the inter-history iteration method was used to analyze the bridge subsystem and vehicle subsystem separately. The quadrilateral isoparametric mapping and improved binary search method were introduced for quick determination of interpolation coefficient and loading position of vehicle-bridge contact point to realize the quick automatic loading of wheel load. Based on the spring-mass model passing through a simply supported beam and a running test of a long-span suspension bridge, the proposed analysis system was compared with the classical numerical analysis method, measured data and traditional time step iteration method. The results show that the proposed analysis system exhibits a good computing efficiency and accuracy and rapid convergence, which can provide a reference for the bridge spatial response analysis under large and highly random traffic flow.

Abstract:In order to promote the application of Q500GJ high-strength steel in steel structure engineering, five specimens of Q500GJ high-strength steel welded H-section columns were tested under horizontal reciprocating loading. The effects of slenderness ratio and loading conditions around the strong or weak axis on the failure mode, deformation capacity and seismic energy dissipation capacity of specimens were studied. The results show that the load-displacement hysteretic curves of all specimens are rich and the hysteretic performance is good. The skeleton curves are basically symmetrical in both the right and reverse direction with similar trend . From elastic deformation to yield point, after reaching the maximum load, the skeleton curves begin to decline until the plastic failure. The specimens under cyclic loading around the strong axis fail due to local elastic-plastic instability of the plate, and the plasticity develops insufficiently. While the specimens under cyclic loading around weak axis fail due to the whole section into plasticity. The ductility coefficient of specimens under cyclic loading around weak axis is much higher than that under cyclic loading around strong axis. The maximum and minimum inter-story displacement deflection of the specimens are 1/20 and 1/26, respectively, which meet the limit requirements, i.e., 1/50 of elastic-plastic inter-story displacement deflection, for multi-story and high-rise steel structures in GB 50011-2010 Code for Seismic Design of Buildings.

Abstract:Based on the effective width method (EWM) in the Chinese code GB50018-2002 and the EWM and direct strength method (DSM) in the North American code , the local buckling bearing capacity of 66 cold-formed thin-walled steel (CFS) built-up box section short columns composed of C-section and U-section assembles connected by ST4.8 self-tapping screws was calculated by using the available results from experiment and finite element parametric analysis. The comparison between theoretical values and experimental and finite element (FE) values shows that the calculation results obtained from the EWM in GB50018-2002 and American Iron and Steel Institute (AISI) are conservative, while the results calculated by DSM are accurate but unsafe. Based on the above results, a superposition method was presented, and a theoretical calculation model for CFS built-up box-section short columns failed in local buckling under axial compression was proposed. Then，according to the variable parameter results of 48 finite element specimens, the combination coefficient（α） of the theoretical calculation formula was obtained from regression analysis, and the formula for calculating the ultimate bearing capacity of the built-up columns was obtained. Finally, the applicability and accuracy of the proposed design method were verified by comparing with the test data and the calculation results of Chinese and American codes. It also provides a simple method for calculating the bearing capacity of CFS built-up box-section short columns.

Abstract:In order to improve the seismic performance of steel frame welded connections, a new type connection with combined strengthened cover and hole weakened web was presented. Low-cyclic reversed loading tests and finite element analysis were carried out on four steel beam-to-column connections with different structural forms (standard form, cover-plate reinforced form, web-opening weakened form, and new form). The influence of local structural forms at beam end on the failure modes, hysteretic behavior, bearing capacity, stiffness degradation, ductility and energy dissipation capacity of the specimens were compared and discussed. The results show that, compared with the standard connection, the connection with local structural forms realizes the outward movement of plastic hinge from the connection zone, making the failure mode from the brittle failure of the connection weld to the plastic failure of the beam . Plastic deformation capacity and energy dissipation capacity are significantly improved as well. Plastic strain accumulation aggravates the local buckling of plates, resulting in gradual degradation of strength and stiffness, and the seismic performance is superior. In addition, under the premise that the bearing capacity and stiffness basically remain unchanged, the ductility and energy dissipation capacity of the new type connection increase by 20.0% and 27.9%, respectively, which verifies the feasibility of this connection. The finite element model, based on stress triaxiality damage criterion illustrated in this paper, can well predict the mechanical performance of various types of steel-frame-welded connections under cyclic loading.

Abstract:In order to solve the problems that it is difficult to directly measure the damping force provided by the damper of passive energy dissipation structure, and it is difficult to evaluate the performance and state of the damper, in this paper, a structural identification method based on adaptive extended Kalman filter is proposed and the method is applied to the damper characteristic identification of passive energy dissipation structures. Under the condition that the damper model is known, the damper parameters can be identified; under the condition that the damper model is unknown, the additional damping force provided by the damper can be considered as the unknown excitation and can also be identified by the proposed method. A multi-storey shear frame structure and a multi-storey damper controlled structure are used as numerical examples, and a single-storey damper controlled structure is used as experimental example to demonstrate the effectiveness and feasibility of the proposed method. The proposed method can provide more basis for the characteristic identification and performance evaluation of the dampers in the passive energy dissipation structure.

Abstract:In order to get reasonable seismic design for silo structures and obtain the practical calculated value of storage side pressure, the “Shi Weixing” calculation method of storage side pressure under the earthquake is introduced at first. Based on the material parameters which can be obtained in engineering design, the revised parameters needed in the calculation of storage side pressure are determined. Then, the numerical model of silo structure is established with ABAQUS to calculate the side pressure variation curve and the correction values of the corresponding parameters are obtained by curve fitting. Modified formulas of side pressure considering silo-storage interaction are summarized by synthesizing different parameters. Finally, the calculated values obtained from the modified formula of storage side pressure are compared with the existing test data and the design values of the code. The results show that the calculated values are in good agreement with the experimental values and can reflect the real and reasonable storage side pressure. Compared with the results, the storage side pressure under the action of strong earthquake is dangerous according to the design value of the code, which means that the proposed calculation formula in this paper is more economical and reliable.

Abstract:The reinforced concrete slabs using HRB500 rebar and ordinary steel rebar were corroded by artificial accelerated method, and four-point bending test was applied on these corroded slabs. The failure modes, flexural capacity, load-deflection curves of the slabs were analyzed by comparing test specimens under different corrosion degree. This study further investigated the relationship between corrosion ratio and deterioration of tensile capacity and bond behavior of corroded steel. Considering the occurrence of reinforcement yielding and bond-slip due to different corrosion degree, a calculation method of flexural bearing capacity of corroded reinforced concrete slab was proposed. A good agreement between calculated values and tested results of the corroded reinforced concrete slab was achieved. The average ratio of calculated values to test results was 1.019, and the standard deviation was 0.081.

Abstract:In order to achieve the purpose of rapid reinforcement of underwater concrete pier column of bridge without drainage, this paper proposed a strengthening method for underwater concrete pier column with Basalt FRP mould shell without drainage based on the concept of underwater self-stress undispersed concrete and “assembly type”. To study the axial compression performance of concrete pier columns by this strengthening method, eight specimens were made to carry out axial compression tests. The effects of Basalt FRP mould shell reinforcement, filled concrete performance, filling layer thickness and maintenance environment on the axial compression failure mode, bearing capacity and toughness of the specimens were studied. The test results show that Basalt FRP mould shell reinforcement could effectively improve the bearing capacity and toughness of the specimen；using underwater self-stress non-dispersive concrete as filling layer, adding proper amount of expansive agent, and controlling the strengthening thickness of the filling layer were beneficial to obtain better reinforcement effect. In freshwater environment, the ultimate bearing capacity of Basalt FRP mould shell strengthened specimen was better than that of seawater environment. According to the experimental results and some existing formulas of axial compressive bearing capacity of confined concrete columns, the formulas for calculating the axial compressive bearing capacity of concrete pier columns strengthened with Basalt FRP mould shells was proposed, and the theoretical calculation results were in good agreement with the experimental results.

Abstract:Digital image correlation method (DIC) can realize non-contact displacement measurement of member by spraying uniform speckle on member surface and taking pictures before and after deformation. Considering the problems of poor recognition effect and low calculation efficiency in deformation measurement of traditional integral pixel algorithm for ancient building painted beams caused by painted pattern uneven gray scale, an Improve-Adaptive Rood Pattern Search (IARPS) method is proposed to calculate the entire pixel displacement. Firstly, the search radius of the first search point is estimated, and an exhaustive search is performed within the radius. Then, Adaptive Rood Pattern Search was introduced to search the whole pixel displacement through small diamond search. By using simulated speckle pattern displacement and the bending test of common regular painted pattern decorative wood beam, IARPS is compared with the coarse-fine search method commonly used in DIC. Through comparative analysis, the results show that IARPS method can effectively overcome the imprecision of local computation in the coarse-fine search method, and the calculation efficiency can be improved by 71.6%, which provides a new method to apply DIC to non-contact deformation measurement of ancient painted beams.

Abstract:On the basis of Navier’s solution to rectangular plates, the bending problem was studied for the four edges supported thin plates under local uniformly distributed load, where the double Fourier series with additional terms was adopted as the deflection function of the plates. Linear algebraic equations for solving the undetermined coefficients were derived. A unified solution was obtained to the rectangular plates with clamped and simply supported edges. The rate of convergence was discussed on the solution of the series method with additional terms. The proposed method was compared both with superposition series method on accuracy, and with finite element numerical method on computational cost. The results show that 40 terms should be employed for a convergence of the series. The method with additional terms shows the same accuracy of solution as superposition series method does. The solution by finite element method gradually approaches that by the series method as the mesh gets finer and finer. In comparison with finite element method, the computational time by the series method is negligible. This work is applicable for structural analysis of the top plates of underground buildings under truck wheel pressure.

Abstract:Based on the force and deformation characteristics of the double-row pile retaining structure in the layered foundation, the front and rear row piles were regarded as elastic foundation beams inserted vertically into the layered foundation, and the interaction between the front and rear row piles and the layered soil is simulated by a series of horizontal springs with different stiffnesses. Taking the contact surface of each soil layer as the interface, the front and rear row pile support structures are divided into several parts. The active earth pressure acting on the rear row piles is calculated by Rankine earth pressure theory, and the passive earth pressure below the bottom surface of pit foundation of the front row pile is calculated by elastic resistance method, taking into account the linear variation of resistance coefficient of foundation along the depth . Based on the theory of Euler-Bernoulli double-layer foundation beam, the pile-pile and pile-soil interaction are considered to obtain the differential equations and the power series solutions of double-row pile support structure in the layered foundation. Then, according to the continuous conditions of internal force and displacement and the boundary conditions of pile top and bottom, the horizontal displacement, rotation, shear force and the bending moment of any depth of pile can be obtained. Finally, through one engineering example, the calculation results of this method are compared with the reported results，which verifies the feasibility of the proposed method.

Abstract:To solve the frost damage problems of road embankment caused by moisture accumulation in subgrade in seasonal frozen soil area, drainage and freeze-thaw tests were carried out on kaolinite soil samples dealt with the quasi wicking fabric. It’s aimed to study the drainage performance of quasi wicking fabric and its control effect on frost heaving of soils. The test results indicate that the quasi wicking fabric can discharge water from unsaturated soil and reduce the moisture content of soil sample by 20%~30%. The drainage effect of the condition that the soil sample is laterally wrapped by wicking materials is better than that of placing the material in the sample. As the initial water content of the sample increases, the drainage performance of the quasi wicking fabric also becomes more effective. In the freeze-thaw test, frost heave and thaw settlement increases with the increasing initial water content of the soil sample. The quasi wicking fabric can effectively reduce the volume change of the soil sample during freeze-thaw process by 5%~15%, which thereby can inhibit the frost damage of the soil.

Abstract:A comparison and comprehensive verification, including theoretical verification, inter-model verification and experimental verification, was performed on two models, the Künzel model and the Liu & Chen model for the hygrothermal simulation of porous building envelopes, which are driven by relative humidity. The simulations were also carried out by two computation tools, self-programmed Fortran code and COMSOL Multiphysics for the two models. The simulation results were compared with analytical solutions, simulation solutions of other models and experimental data under single/double-sided controlled boundary conditions. The verification showed that the simulation results of the two models agreed well with the comparison values. Through the comparison between the simulation results of the two models, it was found that the two models have slight difference in the low relative humidity section in the hygroscopic range; while in the end of the hygroscopic range (relative humidity gradually increases to nearly 95%), the Künzel model was no longer able to accurately simulate the distributions of moisture. The investigations in this study demonstrate that the two models are fully validated within the hygroscopic range and provide references for the verification of future hygrothermal models.

Abstract:Air-conditioning use behaviors of the people in mixed-mode buildings have a significant impact on building energy. A one-year field investigation was conducted in mixed-mode residential buildings mainly on the elderly in the Hot Summer and Cold Winter Region. Climate parameters, air-conditioning usage rates, turning-on time, and indoor set-point temperatures were continuously monitored and recorded. The results show that the periods of the elderly using air conditioners in the living rooms, dining rooms, and bedrooms were different in summer and winter. In summer, the indoor set-point temperatures of living rooms and dining rooms were both mostly within 26~28°C, and those of bedrooms mainly varied within 25~29°C. The most frequent set-point temperature of the three rooms was 27.5°C. In the winter, the indoor set-point temperatures of all rooms were similar, and the most frequently selected one was 20.5°C. In summer, the outdoor tolerance temperatures of the elderly were about 31°C and 26°C in the daytime and night, respectively. In winter, the outdoor tolerance temperature of the elderly was about 12 °C and 8°C in the daytime and night, respectively. Besides, this study established the logistic regression models between air-conditioning use rates and outdoor temperatures, normal-distributed models of air-conditioning use rates over time, as well as the models of indoor set-point temperature distribution. This study provides a reference for researches on air-conditioning use behaviors in mixed-mode residential buildings.

Abstract:In order to reduce the energy consumption of data center, the micro channel separate heat pipe (MCSHP) would reduce the airflow rate according to the actual heating load, resulting in a reduce of thermal performance. In order to investigate and analyze the thermal performance of MCSHP under low airflow rate and heating load, a one-dimensional steady-state model was established. Compared with the experimental results, the maximum average relative error of the result predicted by the established model was 6.3%. By using the established model, the effect of operation parameters on the thermal performance of MCSHP and thermal safety of data center were investigated. When the server exhaust air temperature increased from 27 ℃ to 39 ℃, the cooling capacity was increased by more than 60% under the various airflow rates. When chilled water supply temperature increased from 6 ℃ to 18 ℃, the cooling capacity was decreased by a maximum of 41.8%. The cooling capacity and refrigerant mass flow rate increased with the increasing height difference between evaporator and condenser under airflow rate ranged from 200 to 1 400 m3/h，and the growth rate of cooling capacity increased with the airflow rate. However, the growth rate of cooling capacity decreased with the height difference under the same airflow rate. Those results give a guidance to improve the design optimization and energy-saving operation of the application of MCSHP in data center.