Abstract:The application of recycled concrete structure is in line with the utilization of construction waste resources and the sustainable development of building materials. It has received attention from academic and engineering circles at home and abroad. The long-term working characteristic of recycled concrete structures is an important aspect in the research of recycled concrete, among which the freezing and thawing resistance, carbonation resistance, chloride-permeation resistance, creep of recycled concrete, steel corrosion and rust cracking in recycled concrete, corroded steel and recycled concrete bonding properties, and long-term performance of recycled concrete components are essential components to determine the long-term working performance of recycled concrete structures. The above-mentioned qualities of recycled concrete structures are studied in this paper, which is summarized as follows: 1) Progress has been made on the long-term working characteristic of recycled concrete structures, and some valuable conclusions have been drawn. However, some of the research conclusions are not completely consistent or even mutually exclusive, which might be attributed to the difference in recycled aggregate, mix design, and test methods. Therefore, further research is still needed. 2) Most of the research is mainly based on medium and low-strength recycled concrete, involving less on high-strength recycled concrete. More research on the long-term working characteristic of high-strength recycled concrete should be conducted along with the promotion of high-strength steel bars, so that recycled concrete and steel bars can fully draw on their respective advantages and waste can be avoided. 3) There are many macro researches yet few micro studies, so research on micro study should be enhanced. 4) Compared with the research results of long-term working characteristic of recycled concrete materials, the research on recycled concrete component and structural parts is relatively scarce, and subsequent research on components or structures should be carried out. 5) Long-term working characteristic of recycled concrete studies are mostly single factor studies, while engineering is mostly multi-factor coupling. Multi-factor coupling research can be carried out in the future in order to combine theory with practice. It is expected that this paper is able to provide ideas and directions for the study of the long-term working characteristic of recycled concrete, and provide statistical and theoretical support for the promotion and application of recycled concrete.

Abstract:Ultra-high performance lightweight concrete (UHPLC) is a new type of cement-based structural material with a density of less than 1 950 kg/m³ and is composed of high-strength cement paste,cenospheres, and fibers.This study investigated the effects of different curing systems and curing ages on the mechanical properties of UHPLC, which includes compressive strength, tensile performance, and flexural performance.Besides, the microscopic morphology of the cenospheres was also observed by scanning electron microscopy (SEM).Results show that, the compressive strength, tensile strength and bending peak strength increased obviously as the curing age increased, and UHPLC exhibited strain-hardening behavior.It indicates that curing age has a significant effect on the strength of UHPLC matrix and the interfacial bond strength between fiber and UHPLC matrix.High-temperature steam curing for 3 days, which can make the compressive strength and bending properties of the UHPLC matrix to the level of standard of curing for 28 days,can promote early strength development and shorten the curing age. However, it contributed less to the bond strength, which is still mainly affected by age.The actual density of UHPLC was 1 815.2 kg/m³ and its cubic compressive strength reached 103.1 MPa. During direct tensile test, its ultimate tensile strength and ultimate tensile strain was 7.60 MPa and 0.431% respectively, and it exhibited strain-hardening behavior. Moreover, its bending strength reached 22.43 MPa, meeting the strength demand of RPC160.The required lightweight and high-strength cement based structural materials has been achieved.

Abstract:Seven coral aggregate reinforced concrete beams (CARCBs) with different types of reinforcement were designed in this study to investigate their shear behavior and calculation model. The shear behavior of CARCB was tested, and the deformation and shear capacity were investigated. The relationships of bending moment-midspan deflection, load-steel strain, and load-crack width were established. A calculation model for the ultimate bearing capacity (V_cs) of CARCB was proposed. Results show that normal section cracking load (V_cr) and V_cs of CARCB followed the rule: 316 stainless steel > common steel > zinc-chromium coated steel > organic new coated steel. The common steel had serious corrosion in the CARCB, which led to the degradation of stiffness. The CARCB crack width increased with the increase of load for different reinforcement types. In the initial loading stage, flexural cracks occurred at the midspan of the beam, which developed slowly. Inclined cracks were formed from the support to the concentrated force point with increasing loads, which widened rapidly, leading to beam failure. Therefore, with comprehensive consideration on the effects of reinforcement corrosion and high-strength concrete on the V_cs of CARCB, a calculation model for the V_cs of CARCB was proposed.

Abstract:To study the bending tensile performance of alkali-activated slag ceramsite concrete hollow block (AASCHB) masonry, tests on 108 masonry specimens with Mb25~Mb90 of alkali-activated slag mortar with pottery sand (AASM) were carried out. The experimental results show that the formula calculation based on Table B.0.1-2 of GB 50003—2011 cannot exactly estimate the bending tensile strength of AASCHB masonry with AASM. When the compressive strength of mortar was lower than 70.3 MPa, the formula calculation of the bending tensile strength along straight joint was higher than the test result.When the compressive strength of mortar was between 70.3 MPa and 91.9 MPa, the formula calculation of the bending tensile strength along straight joint was lower than the test result. The formula calculation of the bending tensile strength along slot joint was higher than the test result as the compressive strength of mortar was lower than 46.2 MPa.When the compressive strength was in the range of 46.2 MPa to 91.9 MPa, the formula calculation of the bending tensile strength along slot joint was lower than the test result. It was found that the bending tensile strength of AASCHB masonry was not only related to the compressive strength of AASM, but also affected by the factors of water to cementitious material ratio, sand to cementitious material ratio, Na₂O content, and silicate modulus.Based on the experimental results, the formulae for the bending tensile strengths of AASCHB masonry along straight joint and slot joint were developed, respectively.

Abstract:To investigate the axial compressive performance of alkali-activated slag ceramsite concrete hollow block (AASCHB) masonry, a total of 36 masonry specimens of the AASCHB at MU7.5, MU10, and MU15 as well as alkali-activated slag mortar with pottery sand (AASM) at Mb20, Mb25, and Mb30 were tested. Results show that the axial compressive strength of the AASCHB masonry increased with that of AASCHB, while the axial compressive strength of the AASM had a complicated impact on that of the masonry.Based on the formula provided in Code for Design of Masonry Structures(GB 50003—2011), the estimated values of the axial compressive strength of the masonry using AASCHB and AASM are generally higher than the experimental results.By introducing the characteristic coefficient of AASM and adjusting the correction coefficient of the axial compressive strength for mortar, a formula for the axial compressive strength of the new type of block masonry with the key parameters of the compressive strength of AASCHB and AASM was proposed, which is in accordance with the codified formula of the masonry axial compressive strength adopted in Code for Design of Masonry Structures.

Abstract:To investigate the mechanical properties of alkali-activated slag ceramsite concrete blocks after exposure to high temperature, compression tests were conducted on 48 alkali-activated slag ceramsite concrete blocks with two strength grades, MU10 and MU20, and all the specimens were exposed to normal temperature and a temperature history of 400 ℃, 600 ℃, 700 ℃, 800 ℃, 900 ℃, 1 000 ℃, and 1 100 ℃. The results show that the compressive strengths of MU10 and MU20 ceramsite concrete blocks exhibited a linear decrease with the increase of the heating temperature from 20 ℃ to 1 100 ℃. Based on the test results, the formulas were constructed to calculate the compressive strengths of the alkali-activated slag ceramsite concrete blocks after exposure to high temperature in term of the heating temperatures.

Abstract:Circular steel tube filled with rigid polyurethane foam (RPUF) with density of 300 kg/m³ was proposed for energy absorbing components according to the requirement of civil engineering. Three groups of empty steel tubes and three groups of RPUF-filled short circular steel tubes were tested under axial compressive load to gain their mechanical properties and ability of energy absorbing. Experimental results show that filling RPUF could effectively transform the plastic bucking behavior of circular steel tube under axial compressive load from asymmetric mode towards symmetric mode. The first peak load and structural crashworthiness indicators of the RPUF-filled steel tube increased significantly. The thinner the wall thickness was, the greater the increased. Moreover, a finite element model of RPUF-filled short circular steel tube was built based on the ABAQUS/Explicit, and simulation results showed good agreement with experimental results, which confirmed the accuracy of the model. Parameters analysis was carried out subsequently, which showed that the energy absorbing ability of the RPUF-filled circular steel tube increased with its wall thickness and tube diameter increase. An effective prediction formula for mean crush load (MCL) was also deduced based on the classical progressive collapse model proposed by Alexander. After comparison with the experimental and simulation results, it is found that this formula can effectively predict the average compressive force of the RPUF-filled short circular steel tube.

Abstract:The use of inorganic adhesive to bond aluminum alloy (AA) plate for strengthening reinforced concrete structure provides an effective solution to meet the requirement of corrosive environmental resistance and high ambient temperature, where the problem of interfacial bond of AA plate, adhesive, and concrete surface is essential to be solved. Taking adhering length as dominate parameter, the dual shear test of concrete-AA plate was conducted using three inorganic adhesives including sulfur aluminate cement, magnesium phosphate cement, and alkali activated slag for adhering two 3 mm-thick AA plate on prismatic concrete samples. Three typical failure modes (AA plate debonding, adhesive failure, and interfacial bonding failure) were observed for different bonding lengths and adhesives. It was found that under the same condition the maximum values of bonding strength between adhesive and AA plate were mainly provided by magnesium phosphate cement, followed by sulfur aluminate cement, and the last was alkali activated slag. The effective bonding length was analyzed on the basis of the data of interfacial bonding force and slip. A model of the relationship between bond strength and slip for three inorganic adhesives was proposed. This study provides reference for optimizing the inorganic adhesives applied to the flexural members strengthened by bonding AA plate.

Abstract:To study the flexural fatigue performance of prestressed reactive powder concrete (RPC)-normal concrete (NC) composite beams, four identical reduced-scale model beams were designed and produced on the basis of a 32 m span T-girder of Chinese railway. One of the beams suffered static load and others were under bending fatigue test. Strain distribution in normal section, strain variation in compressed NC, crack propagation, and the development of fatigue deflection and stiffness were analyzed. Furthermore, flexural property of the composite beams without failure after fatigue loading were compared with the composite beams that did not experience fatigue loading and the NC beams with identical structural size and reinforcement condition. Results show that fatigue failure of prestressed RPC-NC composite beams was caused by the fatigue fracture of non-prestressed longitudinal bars, which was the same as balanced-reinforced NC beam. Strain in normal section was always approximately linear with the height of the section under fatigue load, which means the plane section assumption can be applied to prestressed RPC-NC composite beams. Flexural ductility of the composite beams without failure after fatigue loading declined compared with the composite beam before fatigue loading, while it was still greater than NC beam. Stiffness degradation formula of test beams related to fatigue loading cycles was obtained by fitting experimental data, which can be a reference for the design of prestressed RPC-NC composite beams.

Abstract:To investigate the performance degradation of reinforced concrete bridges under multiple factors, the time-dependent evolution process of its resistance and reliability was studied. The effects of carbonization, chloride accumulation, load, and crack on chloride ion erosion were analyzed. According to Fick’s second law and the path probability model, the unconditional probability density distribution of corrosion rate at different service periods was obtained, and then the probability density distribution of resistance corresponding to different service periods was obtained. The three parameter Burr XII distribution model was used to fit it. The Monte Carlo method was used to calculate the reliability probability of the bridge in different service periods, and the effect of the carbonization and chloride accumulation on the probability of corrosion of steel bar as well as the resistance and the reliability of the bridge was studied. The results show that the resistance and reliability of the bridge gradually decrease with the increase of service time, and the dispersion of resistance increase gradually. The resistance and reliability of the bridge reduce when the effect of carbonization and chloride accumulation is considered. The effect of carbonization and chloride accumulation on bridge reliability is mainly manifested in the later stage of service. The influence of carbonization and chloride accumulation should be considered when evaluating the reliability of a bridge that has been in service for a long time.

Abstract:To study the relationship between brittleness index and elastic strain energy, the lateral strain response method was used to determine the crack initiation stress of hard rock. By using the crack initiation stress and peak stress of rock, the relationship between brittleness index and elastic strain energy was explained based on fracture mechanics theory and energy theory, and a functional relationships were constructed between brittleness index and elastic strain energy from uniaxial compression test for two types of rock. Results show that the brittleness indexes B₁₃, B₁₄are in power function relationship with the crack initiation elastic strain energy (single variable), and the brittleness indexes B₁₅, B₁₆are in power or linear function relationships with the crack initiation elastic strain energy (single variable). However, no apparent functional relationship was discovered between the brittleness indexes B₁₃, B₁₄, B₁₅, B₁₆and the peak elastic strain energy (single variable). The new brittleness index could be either obtained from both the crack initiation strain energy and the peak elastic strain energy (two variables), or the crack initiation elastic strain energy (single variable). The relationship between brittleness index and the peak elastic strain energy is of great significance for studying rock burst proneness. The calculation method for brittleness index was redefined. Besides, the verifications of two examples show that this method, using the crack initiation elastic strain energy, demonstrates certain credibility. This study provides a new method determining the relationship between brittleness index and the crack initiation elastic strain energy of rock.

Abstract:In order to analyze the effect of external sulfate attack on the durability of concrete cast-in-situ piles, the diffusion-reaction behavior of sulfate ion for concrete cast-in-situ piles was studied and the factors that affect the degradation of pile structure were analyzed. Based on the Fick’s second law, the non-steady diffusion-reaction equation of sulfate ion under column coordinates was established. The finite difference scheme for solving the diffusion equation was obtained by the numerical method. The accuracy of the theoretical model and the calculation method was verified by related experimental results. Expansion strain was obtained according to the expansion product produced by chemical reaction. The damage and bearing capacity of pile were calculated by damage evolution equation. The correlation between damage degree and bearing capacity was established. Influences of different corrosion factors and corrosion time on the damage and bearing capacity of pile were compared and analyzed. Results indicate that the internal expansion strain and damage developed more rapidly on the surface than in the interior layers. The increase of pile radius could significantly improve the durability and bearing capacity of the pile. When the water-cement ratio was larger than 0.4, the damage degree of the pile experienced the biggest growth. Therefore, the reasonable increase of pile radius and the use of smaller water-cement ratio can effectively reduce concrete damage, improve pile durability, and reduce the loss of bearing capacity of pile.

Abstract:To investigate the ground vibration of unsaturated ground subjected to moving loads caused by high-speed train,a two-and-a-half-dimensional finite element method (2.5D FEM) was deduced. The foundation was considered as three-phase medium, and the Euler beam model was used to simulate the track system. The 2.5D FEM equations were derived by using the Galerkin method and the Fourier transform with respect to time and load moving direction. The solution in the frequency-wave number domain was transformed to the time-space domain through the Fast Fourier Transform (FFT). The influences of train speed and water saturation on ground vibration and excess pore water pressure were analyzed. Results show that at the track center, ground vibration displacement amplitude increased significantly as the soil varied from near saturated (S_r=99%) to fully saturated state.At a given speed, the unsaturated ground acceleration amplitude was larger than that of the saturated ground,and it decreased more rapidly over time than the saturated ground. At 8 m away from the track center, the unsaturated ground acceleration amplitude was far greater than that of the saturated ground at the same speed. but, when the train speed was beyond 300 km/h, their displacement amplitudes tended to be equal. The ground vibration amplitude attenuated rapidly near the track center, while it attenuated slowly beyond 5 m. The excess pore water pressure of the unsaturated ground under the track center was mainly distributed in shallow depth (0~4.5 m beneath the ground surface) and the peak value appeared at about 1.8 m, which decreased sharply as the ground saturation decreases.

Abstract:To study the convection diffusion in fractured porous media, the Smooth Particle Hydrodynamics (SPH) method was applied to simulate the flow process of water at the pore scale level. The real migration process of solute penetrating fractured porous media was realized by simulation, and a simplified Two-Region Model was proposed to describe the penetrating process. In the calculation, the SPH method was first used to discretize the Navier-Stokes equation, and a two-dimensional hydrodynamic field model considering complex porous particle boundary was established. Based on the constructed model, simulation experiments of solute penetration of porous media with three different fracture widths were carried out. As the fracture width in the medium increased, the flow velocity difference between the fracture region and the matrix region increased, and the early penetration and tailing phenomenon became more obvious. The Two-Region Model could well describe this phenomenon, while the traditional convection diffusion equation could not, though it is difficult to obtain accurate analytical solutions from the generalized model. Therefore, a simplified method was proposed and its corresponding analytical solution was provided. Results show that the proposed model can fit to the breakthrough curves accurately in fractured porous media, and the parameters of convection dispersion can be obtained by inversion.

Abstract:To better reveal the inner fatigue deterioration mechanism of steel industrial plants and effectively protect the plants from brittle fractures, a fatigue prognosis analysis method was proposed. Multi-scale fatigue damage models were established based on the power balance principle at the cross-scale interface. The damage of the structures caused by existing defects was quantified. Fatigue damage evolution and mixed mode crack propagation of the vulnerable positions were analyzed. Fatigue prognosis results illustrated that the fatigue damage of the steel crane runway girder evolved slowly at the initial phase and accelerated rapidly at the final phase, which proved that the assessment results based on Miner’s law are too conservative. Fatigue failure more likely occurred at the weld joint between the spile and the end sealing plate of the steel crane runway girder. The studied fatigue crack grew rapidly when the length a reached 5 mm, in which some actions should be taken. The crack in the serious position had great influence on the fatigue performance of other vulnerable parts.

Abstract:To identify the damage member location for space steel structures after earthquake, a single-layer reticulated shell structure test model was designed with a single damaged member to study the location identification method. In consideration of the characteristics of spatial steel structure, such as multi-degree of freedom and dense modal, the acceleration responses of two monitoring stages(i.e., before and after structural damage)were used to establish the damage identification index based on wavelet packet energy analysis. The numerical analysis data of 17 different damage locations of members were established as the damage sample base using the finite element software ANSYS. The acceleration response data of the test structure with single member damage were processed and clustered with the damage sample base data to identify possible damage location of the actual structural members. The method can quickly identify the possible damage location of the damaged member in the actual structure and the experimental results validated the feasibility and effectiveness of the proposed method, which provides theoretical and experimental supports for engineering application.

Abstract:To study the bearing capacity of high strength bolt connection, static tensile tests on longitudinal seam of corrugated steel plate (CSPs) specimens were carried out by considering hot-dip galvanized and non-galvanized steel plates with different thicknesses, and flat plate specimens were designed under the same condition for comparison. The failure mode, the ultimate load and slip load of the longitudinal seam, and the limit and slip displacement of the specimens were analyzed. Results reveal that hot-dip galvanizing almost did not affect the ultimate load. When bearing failure at bolt hole occurred, the ultimate load of the CSP connections was about 12% to 20% higher than that of the flat plate specimens, while there was little difference in the limit displacement between them. When bolt shearing failure occurred, the ultimate displacement of the flat plate connections was about 1.3 to 1.7 times of the CSP ones, but their ultimate bearing capacities were similar. Based on the comparison between the standard calculation result and the test result, it suggests that the design formulae of JGJ 99—2015 are safe to calculate the bearing capacity of longitudinal seam strength of CSP with high strength bolt connection.

Abstract:To ensure that steel frames with unbonded steel plate brace encased in panel, which is also called as panel buckling restrained brace (panel BRB), can use yielding of panel BRBs to dissipate energy under large drifts while keeping regions of the frames connected with panel BRBs in elastic state, finite element analysis was conducted to investigate effects of factors, such as the type and connection location of panel BRBs, on force transfer mechanics of connection regions and corresponding reinforced measures. The analysis reveals that reinforced plates fixed on beam let yielding of beam occur near the ends of unreinforced segments. The distance between the plastic hinge of unreinforced segment and the end of reinforced plate was about half of the height of the beam, and the maximum bending moment at the plastic hinge, with small local buckling or without buckling for flange plates, was close to the plastic moment of beam within drifts of 1/50. Based on the conditions above, together with connection locations and axial forces of panel BRB, the internal forces at the ends of beam can be acquired, hence the shear resistance of panel zone of column can be checked. The analysis also shows that bending moments at ends of beam transferred to the panel zone according to the proportion of flexural rigidity for flange and wed of beam rather than according to only two flanges required by design codes. The shear deformation of panel zone greatly increased after shear yielding, inducing the increase of inter-story drifts. Based on the analysis results, design suggestions on the determination of the thickness of reinforced plates on flange and web of beam and panel zone of column were provided.

Abstract:Corrosion protection lining, as a type of trenchless rehabilitation technology, consists of installation of flexible high-density polyethylene corrosion protecting liner with V-shaped shear keys inside the existing pipe and filling the gap between the pad and the pipe with cement paste. The corrosion protection lining can effectively improve the flow capacity, corrosion resistance, deformation resistance, and anti-leakage performance of the pipeline and avoid large-scale excavation and replacement of components. To investigate its improving effect on the bending capacity and deformation resistance of ductile iron pipeline, corrosion protection lining was applied to the rehabilitation of the existing DN400 ductile iron water pipeline push-on joints, and a series of pseudo-static tensile and bending test were performed on the push-on joints of the water-pressurized ductile iron pipeline without soil coverage. The mechanical behaviors and failure modes of the push-on joints rehabilitated by the corrosion protection lining were investigated under both axial tensile loading and lateral bending. Failure criteria of the liner-reinforced pipeline joints were established. Comparison of the mechanical properties of the pipeline before and after rehabilitated by corrosion protection lining show that corrosion protection lining can significantly improve the axial tensile and flexural bending capacity of the push-on joint. The experimental results validate and support the application of corrosion protection lining to improving structural behaviors of the burial water pipelines in engineering practice.

Abstract:To study the influence of near-fault ground motion with directivity effect on curved girder bridges, a whole physical model of curved girder bridge with the scale ratio of 1∶10 was designed and manufactured, the ground motions in forward region (FR), middle region (MR), and backward region (BR) were selected, and seismic simulation shaking table test was carried out. Experimental results show that the seismic response of the curved bridge under the action of FR ground motion and MR ground motion was obviously higher than that of BR ground motion. In the case of unidirectional input, the structural response was greater under MR ground motion, while in bidirectional input, the structural response was related to the relative position of the curved bridge and the rupture direction. When the curved bridge was perpendicular to the rupture direction and the unidirectional input, the main girder rotated along the fixed pier. The rotational effect of the main girder under FR ground motion and MR ground motion was more obvious than that under BR ground motion in bidirectional input. The amplification effect of pier tangential displacement under FR ground motion and MR ground motion was greater than that of pier radial displacement. When the curved bridge was perpendicular to the rupture direction, the main girder was easier to rotate, making the displacement responses of the bearing and the beam end larger at the low pier. Therefore, in seismic design, rational analysis should be performed to avoid bearing shedding or girder falling.

Abstract:To study the effect of mountain topography on seismic amplification and meet the seismic design needs of mountain building in practical engineering, taking unimodal protruding topography as an example, dynamic substructure method was introduced to calculate the seismic response of 60 different-size rock bump terrains with slope angle of 30 ~ 60°, bump height of 20 ~ 80 m, and platform width 50 ~ 600 m under the ground motion input, and the seismic response law of amplification of different-size rock bump terrains was obtained. Results show that the dynamic substructure method can greatly improve the computation efficiency while ensuring the computation accuracy. The convex topography has a great influence on the amplification effect of ground motion. The response of ground motion increases constantly from base of slope to slope top, and the amplification effect of the central point of the platform is the largest. With the increase of slope angle and height, the amplification effect of topography on ground motion increases. When the slope angle and slope height remain unchanged and the topographic relief height is relatively small, as the topographic width increases, the seismic amplification effect increases; otherwise, when the bump height is larger, the seismic amplification effect decreases. The increase of topographic relief size leads to the intensification of high frequency response and the decrease of low frequency response peak.

Abstract:The vertical stiffness of laminated rubber bearings degrades with the increase of shear deformation under earthquake, and the influence on the isolated structure is not yet clear. Therefore, several isolated frame structure models with different floor numbers, floor heights, and column distances were established by ABAQUS. The modified two-spring model was adopted for the bearings, and a program considering the vertical stiffness degradation of bearings was developed by FORTRAN language based on the model and user subroutine interface UEL in ABAQUS. Then rare earthquakes were input and the elastic-plastic dynamic time history analyses were carried out. Influences of vertical stiffness degradation on structural response were studied. Results show that the vertical stiffness degradation of bearings had certain effects on the shear force, axial force, bending moment of column, and bending moment of beam, and the seismic response amplification factors ranged from 1.1 to 1.3. The vertical stiffness degradation of bearings had no obvious influence on the shear deformation of the bearings or the interlayer displacement of the structures. This study provides a reference for future calculation and analysis of isolated structures under rare earthquakes.

Abstract:To improve the energy dissipation efficiency of a planar eddy current damper (ECD), a nonlinear eddy-current inertial mass damper (NEMD) combining the rotary eddy-current damping with two-node inertial mass element based on ball screw mechanism is proposed in this paper. Overall conformations and working principles of the NEMD were well demonstrated. Through semi-theoretical and semi-numerical analysis, three-dimensional finite-element simulation analysis as well as mechanical performance test, axial force characteristics, and calculation method for rotary eddy-current damping of the NEMD were then obtained. A two-stage design method of the NEMD based on the semi-theoretical and semi-numerical analysis and three-dimensional electromagnetic finite-element simulation analysis was established. Results show that the double amplification of the inertial mass and the equivalent eddy-current damping coefficient of the NEMD was realized, which significantly improved the energy dissipation efficiency of the ECD. As the axial velocity of the NEMD increased, corresponding eddy-current damping force increased at the beginning, and then the eddy-current damping force began to decrease nonlinearly when the force reached a maximum. The computational accuracies of the semi-theoretical, semi-numerical analysis, and three-dimensional electromagnetic finite-element simulation analysis on the eddy-current damping could basically meet the design requirements of the NEMD.

Abstract:To study the hysteretic model of disc spring isolation (DSI) bearings, the mechanical property and deformation performance of DSI bearings were investigated,and the Origin-oriented (OO) hysteretic model of DSI bearings was proposed. The mechanical performance of a typical DSI bearing under reversed loadings was studied, and the OO hysteretic curves of the DSI bearing were investigated, whose results were used to verify the OO hysteretic model of the DSI bearings. The results indicate that the OO hysteretic model of the DSI bearings had the characteristic of asymmetry, and the friction forces had significant influence on the OO hysteretic force characteristic. The tested load-displacement hysteretic curves of the DSI bearing had the characteristic of asymmetry under reversed loadings.The loading frequency had little influence on the mechanical property of the DSI bearings, while the loading amplitude and vertical load had great influence on that of the DSI bearings. As the dynamic load amplitude increased, fullness of the load-displacement hysteresis curves of Model E gradually decreased, and the asymmetry of the curves gradually increased.As the preloading displacement increased, the load-displacement hysteresis curves of Model E tended to be full, indicating that its energy dissipation capacity gradually increased.Moreover, the OO hysteretic model can simulate the mechanical performance of the DSI bearings effectively, and the errors between the simulated results and the experimental results were within 8%.

Abstract:The increase of tall building density in large cities can potentially increase the risk of building facade damage caused by wind debris during strong winds, which has induced a major concern about cascading damage in design community. Cascading damage is a significant large area damage of cladding elements caused by small and localized facade crashes due to the increase of internal pressures. To assess the potential cascading damage, a probabilistic risk analysis method was proposed. By conducting the synchronous pressure integration and the best linear unbiased estimation (BLUE), the cladding wind pressures for undamaged configuration and various damaged configurations were calculated. The relationship between cladding wind pressures and probability of occurrence was established by using upcrossing analysis. The cladding design wind pressures were determined for a given facade accident probability. To demonstrate the method, a case study of a typical tall building was presented to determine the cladding design wind pressures by taking into account the probability of cascading damage. Results indicate that positive wind pressures in corner area were the most sensitive to local damages around building corners, followed by negative wind pressures in the corner area. The proposed method can be used to assess the impact of accidental facade damage on the cladding design wind loads, and is beneficial to identify the cladding area that is overly sensitive to accidental facade damage.

Abstract:To clarify the mechanism that two side-by-side circular cylinders will experience biased flow patterns, flow and aerodynamics of two side-by-side circular cylinders of various center-to-center spacing ratios (P/D) were investigated using large eddy simulation (LES) at a high Reynolds number of 1.4×10⁵. Efforts were devoted to study the characteristics of the biased flow and its influences on the aerodynamics of the two cylinders. Results revealed that the present numerical results are in good agreement with those by the wind tunnel test. With the spacing increase, three flow patterns were found, i.e., single-bluff-body pattern, biased flow pattern, and parallel vortex street pattern. When P/D=1.1, the two cylinders underwent the single-bluff-body flow pattern and biased flow pattern intermittently. There was a significant difference between flow field characteristics and aerodynamics under these two flow patterns. When P/D=1.2~1.5, the two cylinders underwent biased flow pattern. The flow field of the wake region and the aerodynamic forces were asymmetrical for the two cylinders. The direction of the biased flow switched intermittently from one side to the other. The intensity of the vortex shedding was weak, and the magnitude of the fluctuating forces was low. When P/D=2~4, aerodynamic interference between two cylinders was weak and there were two vortex streets behind the two cylinders, which resulted in large fluctuating forces.