Purpose–The paper aims to clarify the operation rationality of high speed trains(HSTs)under tunnel condition with the speed of 400 km/h through representative aerodynamic factors including running drag,eardrum comfor...Purpose–The paper aims to clarify the operation rationality of high speed trains(HSTs)under tunnel condition with the speed of 400 km/h through representative aerodynamic factors including running drag,eardrum comfort,carriages noise,aerodynamic loads on tunnel ancillary facilities and HST,micro-pressure waves,and then put forward engineering suggestions for higher speed tunnel operation based on the analysis.Design/methodology/approach–Based on the field measurement data of CR400AF-C and CR400BF-J tunnel operation,correlations between each aerodynamic indicators with HST speed were established.By analyzing the safety reserve of aerodynamic indicators at 350 km/h and the sensitivity of each indicator to HST speed increasing and the indicators’formation mechanism,the coupling relationship between various indicators was obtained.Findings–The sensitivity of different aerodynamic indicators to speed variation differed.The aerodynamic indicators representing flow field around HST showed a linear relationship with HST speed including noise,eardrum comfort,aerodynamic load on HST body.The positive aerodynamic load on tunnel auxiliary facilities and the micro-pressure wave at the entrance of the tunnel have the same sensitivity to the 3th-power relation of HST speed.The over-limit proportion of micro-pressure wave was the highest among the indicators,and aerodynamic buffering measures were recommended for optimization.The open tunnel pressure relief structure is recommended,while allowing trains to pass through the tunnel at an unconditional speed of 380 km/h.Originality/value–Comprehensive evaluation of multiple aerodynamic indicators for HST tunnel operation with higher speeds was realized.The main engineering requirements to release aerodynamic effect were identified and the optimization scheme is proposed.展开更多
Many studies have indicated that structural strain will be significantly influenced by temperature variations,and a good understanding of the effect of temperature on structural strain is essential.A structural health...Many studies have indicated that structural strain will be significantly influenced by temperature variations,and a good understanding of the effect of temperature on structural strain is essential.A structural health monitoring system has been installed in a typical Tibetan timber building to measure the structural strains and ambient temperature since 2012.This paper presents the correlation between temperature and strain data from the monitored structure.A method combining singular spectrum analysis and polynomial regression is proposed for modeling the temperature induced strains in the structure.Singular spectrum analysis is applied to smooth the temperature data,and the correlation between the resulting temperature time series and the measured strains is obtained by polynomial regression.Parameters of the singular spectrum analysis and the regression model are selected to have the least regression error.Results show that the proposed method has both good reproduction and prediction capabilities for temperature induced strains,and that the method is accurate and effective for eliminating the effect of temperature from the measured strain.A standardized Novelty Index based on the residual strain is also used for the condition assessment of the structure.展开更多
To quantify the seismic effectiveness of the most commonly used fishing line tie up method for securing museum collections and optimize fixed strategies for exhibitions,shaking table tests of the seismic systems used ...To quantify the seismic effectiveness of the most commonly used fishing line tie up method for securing museum collections and optimize fixed strategies for exhibitions,shaking table tests of the seismic systems used for typical museum collection replicas have been carried out.The influence of body shape and fixed measure parameters on the seismic responses of replicas and the interaction behavior between replicas and fixed measures have been explored.Based on the results,seismic effectiveness evaluation indexes of the tie up method are proposed.Reasonable suggestions for fixed strategies are given,which provide a basis for the exhibition of delicate museum collections considering the principle of minimizing seismic responses and intervention.The analysis results show that a larger ratio of height of mass center to bottom diameter led to more intense rocking responses.Increasing the initial pretension of fishing lines was conducive to reducing the seismic responses and stress variation of the lines.Through comprehensive consideration of the interaction forces and effective securement,it is recommended to apply 20%of breaking stress as the initial pretension.For specific museum collections that cannot be effectively protected by the independent tie up method,an optimized strategy of a combination of fishing lines and fasteners is recommended.展开更多
According to the Code for Seismic Design of Buildings （GB50011-2001）, ten typical reinforced concrete （RC） frame structures, used as school classroom buildings, are designed with different seismic fortification in...According to the Code for Seismic Design of Buildings （GB50011-2001）, ten typical reinforced concrete （RC） frame structures, used as school classroom buildings, are designed with different seismic fortification intensities （SFIs） （SFI=6 to 8.5） and different seismic design categories （SDCs） （SDC=B and C）. The collapse resistance of the frames with SDC=B and C in terms of collapse fragility curves are quantitatively evaluated and compared via incremental dynamic analysis （IDA）. The results show that the collapse resistance of structures should be evaluated based on both the absolute seismic resistance and the corresponding design seismic intensity. For the frames with SFI from 6 to 7.5, because they have relatively low absolute seismic resistance, their collapse resistance is insufficient even when their corresponding SDCs are upgraded from B to C. Thus, further measures are needed to enhance these structures, and some suggestions are proposed.展开更多
To consider the infl uence of aftershocks in engineering design, the correlations between main shocks and aftershocks should be examined, and an aftershock simulation method with main shock ground motions needs to be ...To consider the infl uence of aftershocks in engineering design, the correlations between main shocks and aftershocks should be examined, and an aftershock simulation method with main shock ground motions needs to be developed. In this study, the data on the sequences of main shock–aftershock ground motions and other related parameters were collected. Using these data, correlations between the magnitude, frequency, duration and energy of the main shock–aftershock ground motions were investigated. The results showed that the magnitude of the aftershock can be larger than that of the main shock. The shapes of the Fourier amplitude spectra of main shocks and aftershocks were similar;however, the predominant frequency and high-frequency components of the aftershock tended to be larger. Considering the magnitude diff erence between the main shock and the aftershock, the correlation of durations was explored. Additionally, a new concept, the duration ratio, was defi ned to describe the concentration of seismic energy release, and main shock energy was strongly positively correlated with the energy attenuated during the main shock–aftershock sequence. Finally, based on these results regarding correlation, an aftershock synthesis using recorded main shock ground motions was constructed with the trigonometric series method for seismic design, and some examples are given to analyze the rationality of this synthetic method.展开更多
One of the difficulties encountered in the study of dusty plasmas is related to the knowledge of the size of the dust particles present. A variety of sources, physical and chemical mechanisms of formation, causes a wi...One of the difficulties encountered in the study of dusty plasmas is related to the knowledge of the size of the dust particles present. A variety of sources, physical and chemical mechanisms of formation, causes a wide variety of sizes and morphologies of dust. The diameter of a dust will not be unique but spread over several orders of magnitude. Its distribution in number, surface, mass or volume is called distribution. It is important to know this distribution in particle size because it strongly impacts the physical and radiative processes. To have a dust distribution in situ is very difficult;the reverse method can identify the particle populations from light extinction measures. In this study, we present an inversion procedure with a Tikhonov regularization dedicated to the determination of volume size distribution (V-PSD) from extinction measurements corresponding to the different wavelengths obtained by the Extinction Spectrometry technique.展开更多
Double-column bridge piers are prone to local damage during earthquakes,leading to the destruction of bridges.To improve the earthquake resistance of double-column bridge piers,a novel swing column device(SCD),consist...Double-column bridge piers are prone to local damage during earthquakes,leading to the destruction of bridges.To improve the earthquake resistance of double-column bridge piers,a novel swing column device(SCD),consisting of a magnetorheological(MR)damper,a current controller,and a swing column,was designed for the present work.To verify the seismic energy dissipation ability of the SCD,a lumped mass model for a double-column bridge pier with the SCD was established according to the low-order modeling method proposed by Steo.Furthermore,the motion equation of the double-column bridge pier with the SCD was established based on the D′Alembert principle and solved with the use of computational programming.It was found that the displacement response of the double-column bridge pier was effectively controlled by the SCD.However,due to rough current selection and a time delay,there is a significant overshoot of the bridge acceleration using SCD.Hence,to solve the overshoot phenomenon,a current controller was designed based on fuzzy logic theory.It was found that the SCD design based on fuzzy control provided an ideal shock absorption effect,while reducing the displacement and acceleration of the bridge pier by 36.43%‒40.63%and 30.06%‒33.6%,respectively.展开更多
Two single-storey single-span reinforcement concrete （RC） frame structures strengthened with Y-eccentrically brace were designed and manufactured to be 1/3 scale. The pseudo-dynamic testing method was used to study ...Two single-storey single-span reinforcement concrete （RC） frame structures strengthened with Y-eccentrically brace were designed and manufactured to be 1/3 scale. The pseudo-dynamic testing method was used to study the mechanical characteristics and the seismic performance under E1-Centro earthquake action with different peak acceleration adjusted by China＇s Code for Seismic Design of Buildings. The test results indicate that RC frame structures strengthened with Y- eccentrically steel brace present perfect seismic performance under strong earthquake action owing to the good ductility, strong bearing capability and fine energy absorbing capability provided by energy dissipation element and high lateral stiffness provided by diagonal braces. The seismic performance is also affected by the length of outsourcing steel at the joint between energy dissipation element of eccentric steel brace and RC frame beam. The joint should be considerably designed to make sure that shear failure can firstly occur in energy dissipation element.展开更多
In order to obtain the principle of Pantadome lifting process and make theoretical foundation for practical applications, the core idea of Pantadome was introduced, which is to make a structure become a mechanism by t...In order to obtain the principle of Pantadome lifting process and make theoretical foundation for practical applications, the core idea of Pantadome was introduced, which is to make a structure become a mechanism by temporarily removing some members during the process of construction.The Abstract motion model was built. By determining the change of the coordinates of the hinge joint and that of each point of the structure, simulative analysis of the mechanical motion of Pantadome was realized. Then general program that simulates the lifting process of Pantadome was developed based on AutoCAD environment by Auto Lisp language. By completing the theoretical analysis of the lifting process of Pantadome, three-dimensional simulation of the lifting process of Pantadome was realized. And it is successfully applied to bidding work of practical engineering.展开更多
In this review,we primarily address the present state of the arts and latest progresses in a few frontier issues mostly relevant to free surface/interface in ocean engineering.They include TC(tropical cyclone)induced ...In this review,we primarily address the present state of the arts and latest progresses in a few frontier issues mostly relevant to free surface/interface in ocean engineering.They include TC(tropical cyclone)induced extreme surface wave,sloshing of LNG(liquefied natural gas),cavitation/bubble dynamics and VIM(vortex-induced motion)and VIV(vortex-induced vibration).In addition to general description,we mainly focus on the recent advances and challenging aspects of above-mentioned topics.Inspired by the achievements in the previous 70 years,mankind starts a new round of ocean exploration activities.Then,we can find obvious trends:the realm of ocean engineering is expanding from sea surface to deep sea,from low and middle latitude to polar region and from fossil to renewable energy in near future.展开更多
Four typical cases of storm tide inundation at one of the typical storm surge prone areas in China and worldwide,i.e.Southeast China coast,are presented to demostrate the impact of climate change.It is relied on the s...Four typical cases of storm tide inundation at one of the typical storm surge prone areas in China and worldwide,i.e.Southeast China coast,are presented to demostrate the impact of climate change.It is relied on the statistical trend analysis of tropical cyclone intensification(TCI)and sea level rise(SLR)considering temporally non-stationary and spatially non-uniform effects,numerical analysis taking into account the tide-surge-wave coupling effect and GIS-based analysis for inundation evaluation.The results show that the high sea surface elevation tends to occur in the bays and around the estuaries.The maximal sea surface elevations of the worst situation at present without considering TCI and SLR(i.e.scenario S2)are 6.06 m,5.82 m and 5.67 m around Aojiang,Feiyunjiang and Oujiang river estuaries,respectively.Whereas,the maximal sea surface elevations for the three estuaries would increase to 7.02 m,6.67 m and 6.44 m,respectively,when the non-stationary extreme wind speed of 100-year recurrence period and SLR equivalent to the situation of 2100s(i.e.scenario S4)are taking into account.The potential inundation area of scenario S4 would expand by 108%to about 798 km^(2) compared with scenario S2.In addition,the remotely sensed maps and inundation durations of the hardest hit regions are provided,which will aid the prevention and mitigation of storm tide inundation hazard and future coastal management there.展开更多
Aim of this work is to try to explain, on a Rational basis, some equations of Electro-Magnetism, which are based on Experimental data. Any Electric Field can produce a Field of many small Electric Dipoles, continuousl...Aim of this work is to try to explain, on a Rational basis, some equations of Electro-Magnetism, which are based on Experimental data. Any Electric Field can produce a Field of many small Electric Dipoles, continuously distributed in space. In a region, where the Electric Field is constant, in direction and magnitude, all the small Dipoles are parallel to the Electric Field, and are represented by a single, long, parallel to them, fixed in space, Electric Dipole, which is here called Compass. An Alternating current, in a straight Conductor, is studied, by a simple, short computer program, for step-by-step nonlinear dynamic analysis. It is found that, only an Alternating current, not a direct current, can produce an Electric Dipole, in a straight Conductor. The two above Dipoles (Compass-Conductor) are assumed with equal lengths ℓ, lying on two skew lines, perpendicular to each other, at a distance ℓ√2, thus forming, by their four ends, a Regular Tetrahedron, with side length ℓ. Repulsion, between Like Charges, obeys the simple Coulomb Electro-Static law. Whereas Interaction (Attraction or Repulsion), between Unlike Charges, obeys a more accurate Lennard-Jones law. The analysis of Dipole-Dipole (Compass-Conductor) Interaction is performed by hand calculator. The only out-of-balance forces, in the regular Tetrahedron, acting on the Rigid Conductor, are the so-called magnetic forces. Their direction is found, in a simple Rational way, with help of Regular Tetrahedron, without recoursing to a “right-hand-rule”. The proposed model is applied to 1) The force acting on an Electric Charge moving in a magnetic field. 2) The force acting on a Current carrying straight Conductor, due to a magnetic field. 3) The magnetic fields created around a Current carrying straight Conductor. In these applications, proposed model gives reasonable results. Particularly, in third application, results, obtained by proposed model, are found in satisfactory approximation with corresponding ones, obtained by an empirical formula, based on relevant Experimental observations of H.-C. Oersted and A.-M. Ampère. So, the reliability of proposed model is checked. Position and direction of magnetic field vector coincide with those of a corresponding fixed Compass of a constant Electric Field. Main point of present work is that, without introducing the concept of a magnetic field vector, by combining field of dipoles, produced by an electric field, with dipole of an alternating current carrying conductor, the magnetic forces can be determined.展开更多
To address the insufficient stiffness of the V-shaped reinforced concrete folded plate structure and its construction process causing environmental pollution,a novel assembled monolithic spherical-shaped reinforced co...To address the insufficient stiffness of the V-shaped reinforced concrete folded plate structure and its construction process causing environmental pollution,a novel assembled monolithic spherical-shaped reinforced concrete ribbed folded plate structure(AMRRFS)was proposed.The advantages of AMRRFS are that its construction process is environmentally friendly while it also exhibits great stability and rigidity.Therefore,an experimental and numerical investigation were conducted on the AMRRFS to investigate its mechanical properties.In addition,the parametric analysis of the AMRRFS was conducted,and some design recommendations were proposed.Under the design load,the experimental findings revealed that AMRRFS possessed excellent mechanical properties.During the overloading phase,the interface between the in situ casting area and the prefabrication area was severely damaged,leading to the loss of the structure’s ability to bear loads.The outcomes from the finite element simulations of AMRRFS closely mirrored the results of the experimental investigation.Based on the parametric analysis,it was recommended that the height of the AMRRFS,the height of the ribs,and the height of the secondary ridge beams shall be 1/7–1/5,1/65–1/50,and 1/34–1/30 of the span,and that the minimum reinforcing ratio for all types of plates shall exceed 1.0%.展开更多
The pseudo excitation method(PEM) has been improved into a more practical form,on which the analytic formulae of seismic response power spectral density(PSD) of simplified large-span structural models have been derive...The pseudo excitation method(PEM) has been improved into a more practical form,on which the analytic formulae of seismic response power spectral density(PSD) of simplified large-span structural models have been derived.The analytic formulae and numerical computing results of seismic response PSD have been derived to study the mechanism of multi-support excitation effects,such as the wave-passage effect and incoherence effect,for the seismic response of multiand large-span structures.By using a multi-span truss as an example,the influence of multi-support excitation effects on the seismic response of such structures is studied.展开更多
A novel distributed tuned liquid damper （DTLD） for reducing vibration in structures is proposed in this paper. The basic working principle of the DTLDs is to fill the empty space inside the pipes or boxes of cast-in...A novel distributed tuned liquid damper （DTLD） for reducing vibration in structures is proposed in this paper. The basic working principle of the DTLDs is to fill the empty space inside the pipes or boxes of cast-in-situ hollow reinforced concrete （RC） floor slabs with water or other liquid. The pipes or boxes then work as a series of small TLDs inside the structure, to increase the damping ratio of the entire structural system. Numerical simulation that accounts for the fluid- structure conpling effect is carried out to evaluate the vibration-reduction efficiency of the DTLDs. The results show that the DTLDs are able to considerably increase the damping of the structure and thus reduce its vibration. An additional benefit is that the DTLDs do not require architectural space to be added to the structure.展开更多
Replacing the viscous damper of tuned mass damper(TMD)with the proposed inerter-enhanced dampers(IEDs),novel vibration mitigation methods,namely the IED-TMDs,are proposed.Unlike the TMD,which brings only one additiona...Replacing the viscous damper of tuned mass damper(TMD)with the proposed inerter-enhanced dampers(IEDs),novel vibration mitigation methods,namely the IED-TMDs,are proposed.Unlike the TMD,which brings only one additional freedom into the system,the proposed IED-TMDs introduce more freedoms into the considered dynamic system.As a result,the traditional fixed-point theory cannot be used.To address this issue,this paper develops an extended fixed-point theory.Firstly,the inerter and the springs of the IED-TMDs are optimized considering that all four fixed points are of the same height.The closed-form solutions for the optimal inerter and springs of the IED-TMDs are obtained.Secondly,to obtain the optimal damping ratio for the IED-TMDs with multi-fixed points,a new optimization criterion is introduced.Different from the traditional fixed-point theory which controls the slope of the transfer function at the fixed points,the new optimization criterion assumes that the local peaks of the transfer function in between the four fixed points have the same height as the fixed points.And,a flat plateau is achieved in the transfer function.Further,the closed-form solutions for the optimal damping ratio are simplified in consideration of actual applications.Finally,the vibration mitigation performance of the IED-TMDs is evaluated.Results show that the vibration mitigation performance of IED-TMDs is superior to that of the conventional TMD.This superior vibration mitigation performance is more significant for the IED-TMDs with a smaller mass ratio.展开更多
To investigate the aerodynamic effect of wind barriers on a high-speed train-bridge system,a sectional model test was conducted in a closed-circuit-type wind tunnel.Several different cases,including with and without b...To investigate the aerodynamic effect of wind barriers on a high-speed train-bridge system,a sectional model test was conducted in a closed-circuit-type wind tunnel.Several different cases,including with and without barriers,with different barrier heights and porosity rates,and with different train arrangements on the bridge were taken into consideration;in addition,the aerodynamic coefficients of the train-bridge system were measured.It is found that the side force and rolling moment coefficients of the vehicle are efficiently reduced by a single-side wind barrier,but for the bridge deck these values are increased.The height and porosity rate of the barrier are two important factors that influence the windbreak effect.Train arrangement on the bridge will considerably influence the aerodynamic properties of the train-bridge system.The side force and rolling moment coefficients of the vehicle at the windward side are larger than at the leeward side.展开更多
Large span cable-supported structures have been developed rapidly in China, and they always adopt high-strength steel cables as structural members. However, the modulus of elasticity and yield strength of steel materi...Large span cable-supported structures have been developed rapidly in China, and they always adopt high-strength steel cables as structural members. However, the modulus of elasticity and yield strength of steel material will decrease seriously under fire conditions while fire protection is unlikely to be provided for steel cable. Several typical large span cable-supported structures such as cable truss, beam string structure and prestressed cable net are studied on their structural behaviour in this paper. Theoretical formulae are derived in terms of geometrical and material nonlinearity with high temperature effect. Finite element models are also established to simulate the structural performance under fire conditions. The calculation formulae for fire-resisting design are suggested for these three types of structures, while displacement and prestressed force variation rules are also given.展开更多
This paper focuses on the lateral buckling of laterally-unrestrained aluminum beams subjected to a concentrated, uniformly loading; pure-bending action. The design methods of lateral stability of aluminum beams in the...This paper focuses on the lateral buckling of laterally-unrestrained aluminum beams subjected to a concentrated, uniformly loading; pure-bending action. The design methods of lateral stability of aluminum beams in the current codes are discussed. The influence of material property on the lateral buckling of aluminum beams is investigated with finite element analysis (FEA) methods. Some numerical examples are given,; the results from current codes are compared with the FEA solutions. The design method on lateral stability of steel beams specified in the Chinese standard GB 50017-2003 is modified to calibrate the stability factors of aluminum beams according to the European code, British code,; American code,; the modified method is verified by FEA results. Through comparison with the available test results, the modified design method for overall stability of aluminum bending members is proposed in this paper; proved applicable in the design of lateral stability of aluminum beams.展开更多
The influential depth of moisture transport in a concrete surface subject to drying-wetting cycles was analyzed numerically. The moisture transport was described by a diffusion model with different diffusivities for d...The influential depth of moisture transport in a concrete surface subject to drying-wetting cycles was analyzed numerically. The moisture transport was described by a diffusion model with different diffusivities for drying and wetting. A finite difference scheme was developed to solve the partial differential equations The influential depth was then investigated numerically for initially saturated and unsaturated concretes exposed to drying-wetting actions in marine environments using an equilibrium time ratio concept. The equilibrium time ratio was calculated numerically for a saturated condition and the moisture influential depth is shown to be a linear function of the square root of the drying time. However, this equilibrium time ratio does not exist for an unsaturated condition and the moisture influential depth depends on the initial saturation as well as the drying-wetting time ratio. The results indicate that this model gives more realistic predictions of moisture transport of in situ structural concrete and its durability.展开更多
文摘Purpose–The paper aims to clarify the operation rationality of high speed trains(HSTs)under tunnel condition with the speed of 400 km/h through representative aerodynamic factors including running drag,eardrum comfort,carriages noise,aerodynamic loads on tunnel ancillary facilities and HST,micro-pressure waves,and then put forward engineering suggestions for higher speed tunnel operation based on the analysis.Design/methodology/approach–Based on the field measurement data of CR400AF-C and CR400BF-J tunnel operation,correlations between each aerodynamic indicators with HST speed were established.By analyzing the safety reserve of aerodynamic indicators at 350 km/h and the sensitivity of each indicator to HST speed increasing and the indicators’formation mechanism,the coupling relationship between various indicators was obtained.Findings–The sensitivity of different aerodynamic indicators to speed variation differed.The aerodynamic indicators representing flow field around HST showed a linear relationship with HST speed including noise,eardrum comfort,aerodynamic load on HST body.The positive aerodynamic load on tunnel auxiliary facilities and the micro-pressure wave at the entrance of the tunnel have the same sensitivity to the 3th-power relation of HST speed.The over-limit proportion of micro-pressure wave was the highest among the indicators,and aerodynamic buffering measures were recommended for optimization.The open tunnel pressure relief structure is recommended,while allowing trains to pass through the tunnel at an unconditional speed of 380 km/h.Originality/value–Comprehensive evaluation of multiple aerodynamic indicators for HST tunnel operation with higher speeds was realized.The main engineering requirements to release aerodynamic effect were identified and the optimization scheme is proposed.
基金National Natural Science Foundation of China for Excellent Young Scholars under Grant No.51422801National Natural Science Foundation of China under Key Program 51338001Beijing Natural Science Foundation of China under Key Program:8151003
文摘Many studies have indicated that structural strain will be significantly influenced by temperature variations,and a good understanding of the effect of temperature on structural strain is essential.A structural health monitoring system has been installed in a typical Tibetan timber building to measure the structural strains and ambient temperature since 2012.This paper presents the correlation between temperature and strain data from the monitored structure.A method combining singular spectrum analysis and polynomial regression is proposed for modeling the temperature induced strains in the structure.Singular spectrum analysis is applied to smooth the temperature data,and the correlation between the resulting temperature time series and the measured strains is obtained by polynomial regression.Parameters of the singular spectrum analysis and the regression model are selected to have the least regression error.Results show that the proposed method has both good reproduction and prediction capabilities for temperature induced strains,and that the method is accurate and effective for eliminating the effect of temperature from the measured strain.A standardized Novelty Index based on the residual strain is also used for the condition assessment of the structure.
基金Beijing Nova Program under Grant No.2022036National Key Research and Development Program under Grant No.2019YFC1521000。
文摘To quantify the seismic effectiveness of the most commonly used fishing line tie up method for securing museum collections and optimize fixed strategies for exhibitions,shaking table tests of the seismic systems used for typical museum collection replicas have been carried out.The influence of body shape and fixed measure parameters on the seismic responses of replicas and the interaction behavior between replicas and fixed measures have been explored.Based on the results,seismic effectiveness evaluation indexes of the tie up method are proposed.Reasonable suggestions for fixed strategies are given,which provide a basis for the exhibition of delicate museum collections considering the principle of minimizing seismic responses and intervention.The analysis results show that a larger ratio of height of mass center to bottom diameter led to more intense rocking responses.Increasing the initial pretension of fishing lines was conducive to reducing the seismic responses and stress variation of the lines.Through comprehensive consideration of the interaction forces and effective securement,it is recommended to apply 20%of breaking stress as the initial pretension.For specific museum collections that cannot be effectively protected by the independent tie up method,an optimized strategy of a combination of fishing lines and fasteners is recommended.
基金National Science Foundation of China Under Grant No.90815025&51178249the National Key Technologies R&D Program Under Grant No.2009BAJ28B01&2006BAJ03A02-01+1 种基金Tsinghua University Research Funds No.2010THZ02-1the Program for New Century Excellent Talents in University
文摘According to the Code for Seismic Design of Buildings （GB50011-2001）, ten typical reinforced concrete （RC） frame structures, used as school classroom buildings, are designed with different seismic fortification intensities （SFIs） （SFI=6 to 8.5） and different seismic design categories （SDCs） （SDC=B and C）. The collapse resistance of the frames with SDC=B and C in terms of collapse fragility curves are quantitatively evaluated and compared via incremental dynamic analysis （IDA）. The results show that the collapse resistance of structures should be evaluated based on both the absolute seismic resistance and the corresponding design seismic intensity. For the frames with SFI from 6 to 7.5, because they have relatively low absolute seismic resistance, their collapse resistance is insufficient even when their corresponding SDCs are upgraded from B to C. Thus, further measures are needed to enhance these structures, and some suggestions are proposed.
基金National Nature Science Foundation of China under Grant No.51778183the National Science Foundation for Distinguished Young Scholars of China under Grant No.51525802
文摘To consider the infl uence of aftershocks in engineering design, the correlations between main shocks and aftershocks should be examined, and an aftershock simulation method with main shock ground motions needs to be developed. In this study, the data on the sequences of main shock–aftershock ground motions and other related parameters were collected. Using these data, correlations between the magnitude, frequency, duration and energy of the main shock–aftershock ground motions were investigated. The results showed that the magnitude of the aftershock can be larger than that of the main shock. The shapes of the Fourier amplitude spectra of main shocks and aftershocks were similar;however, the predominant frequency and high-frequency components of the aftershock tended to be larger. Considering the magnitude diff erence between the main shock and the aftershock, the correlation of durations was explored. Additionally, a new concept, the duration ratio, was defi ned to describe the concentration of seismic energy release, and main shock energy was strongly positively correlated with the energy attenuated during the main shock–aftershock sequence. Finally, based on these results regarding correlation, an aftershock synthesis using recorded main shock ground motions was constructed with the trigonometric series method for seismic design, and some examples are given to analyze the rationality of this synthetic method.
文摘One of the difficulties encountered in the study of dusty plasmas is related to the knowledge of the size of the dust particles present. A variety of sources, physical and chemical mechanisms of formation, causes a wide variety of sizes and morphologies of dust. The diameter of a dust will not be unique but spread over several orders of magnitude. Its distribution in number, surface, mass or volume is called distribution. It is important to know this distribution in particle size because it strongly impacts the physical and radiative processes. To have a dust distribution in situ is very difficult;the reverse method can identify the particle populations from light extinction measures. In this study, we present an inversion procedure with a Tikhonov regularization dedicated to the determination of volume size distribution (V-PSD) from extinction measurements corresponding to the different wavelengths obtained by the Extinction Spectrometry technique.
文摘Double-column bridge piers are prone to local damage during earthquakes,leading to the destruction of bridges.To improve the earthquake resistance of double-column bridge piers,a novel swing column device(SCD),consisting of a magnetorheological(MR)damper,a current controller,and a swing column,was designed for the present work.To verify the seismic energy dissipation ability of the SCD,a lumped mass model for a double-column bridge pier with the SCD was established according to the low-order modeling method proposed by Steo.Furthermore,the motion equation of the double-column bridge pier with the SCD was established based on the D′Alembert principle and solved with the use of computational programming.It was found that the displacement response of the double-column bridge pier was effectively controlled by the SCD.However,due to rough current selection and a time delay,there is a significant overshoot of the bridge acceleration using SCD.Hence,to solve the overshoot phenomenon,a current controller was designed based on fuzzy logic theory.It was found that the SCD design based on fuzzy control provided an ideal shock absorption effect,while reducing the displacement and acceleration of the bridge pier by 36.43%‒40.63%and 30.06%‒33.6%,respectively.
基金Funded by National Natural Science Foundation of China (Grant No. 51078248)the Priority Academic Program Development of Jiangsu Higher Education Institutions (PAPD)
文摘Two single-storey single-span reinforcement concrete （RC） frame structures strengthened with Y-eccentrically brace were designed and manufactured to be 1/3 scale. The pseudo-dynamic testing method was used to study the mechanical characteristics and the seismic performance under E1-Centro earthquake action with different peak acceleration adjusted by China＇s Code for Seismic Design of Buildings. The test results indicate that RC frame structures strengthened with Y- eccentrically steel brace present perfect seismic performance under strong earthquake action owing to the good ductility, strong bearing capability and fine energy absorbing capability provided by energy dissipation element and high lateral stiffness provided by diagonal braces. The seismic performance is also affected by the length of outsourcing steel at the joint between energy dissipation element of eccentric steel brace and RC frame beam. The joint should be considerably designed to make sure that shear failure can firstly occur in energy dissipation element.
文摘In order to obtain the principle of Pantadome lifting process and make theoretical foundation for practical applications, the core idea of Pantadome was introduced, which is to make a structure become a mechanism by temporarily removing some members during the process of construction.The Abstract motion model was built. By determining the change of the coordinates of the hinge joint and that of each point of the structure, simulative analysis of the mechanical motion of Pantadome was realized. Then general program that simulates the lifting process of Pantadome was developed based on AutoCAD environment by Auto Lisp language. By completing the theoretical analysis of the lifting process of Pantadome, three-dimensional simulation of the lifting process of Pantadome was realized. And it is successfully applied to bidding work of practical engineering.
基金financially supported by the National Natural Science Foundation of China(Grant No.11902024).
文摘In this review,we primarily address the present state of the arts and latest progresses in a few frontier issues mostly relevant to free surface/interface in ocean engineering.They include TC(tropical cyclone)induced extreme surface wave,sloshing of LNG(liquefied natural gas),cavitation/bubble dynamics and VIM(vortex-induced motion)and VIV(vortex-induced vibration).In addition to general description,we mainly focus on the recent advances and challenging aspects of above-mentioned topics.Inspired by the achievements in the previous 70 years,mankind starts a new round of ocean exploration activities.Then,we can find obvious trends:the realm of ocean engineering is expanding from sea surface to deep sea,from low and middle latitude to polar region and from fossil to renewable energy in near future.
基金supported by the National Natural Science Foundation of China(Grant 11902024)the National Key R&D Program of China(Grant 2017YFC1404202)the Strategic Priority Research Programs(Category B)of the Chinese Academy of Sciences(Grant XDB22040203).
文摘Four typical cases of storm tide inundation at one of the typical storm surge prone areas in China and worldwide,i.e.Southeast China coast,are presented to demostrate the impact of climate change.It is relied on the statistical trend analysis of tropical cyclone intensification(TCI)and sea level rise(SLR)considering temporally non-stationary and spatially non-uniform effects,numerical analysis taking into account the tide-surge-wave coupling effect and GIS-based analysis for inundation evaluation.The results show that the high sea surface elevation tends to occur in the bays and around the estuaries.The maximal sea surface elevations of the worst situation at present without considering TCI and SLR(i.e.scenario S2)are 6.06 m,5.82 m and 5.67 m around Aojiang,Feiyunjiang and Oujiang river estuaries,respectively.Whereas,the maximal sea surface elevations for the three estuaries would increase to 7.02 m,6.67 m and 6.44 m,respectively,when the non-stationary extreme wind speed of 100-year recurrence period and SLR equivalent to the situation of 2100s(i.e.scenario S4)are taking into account.The potential inundation area of scenario S4 would expand by 108%to about 798 km^(2) compared with scenario S2.In addition,the remotely sensed maps and inundation durations of the hardest hit regions are provided,which will aid the prevention and mitigation of storm tide inundation hazard and future coastal management there.
文摘Aim of this work is to try to explain, on a Rational basis, some equations of Electro-Magnetism, which are based on Experimental data. Any Electric Field can produce a Field of many small Electric Dipoles, continuously distributed in space. In a region, where the Electric Field is constant, in direction and magnitude, all the small Dipoles are parallel to the Electric Field, and are represented by a single, long, parallel to them, fixed in space, Electric Dipole, which is here called Compass. An Alternating current, in a straight Conductor, is studied, by a simple, short computer program, for step-by-step nonlinear dynamic analysis. It is found that, only an Alternating current, not a direct current, can produce an Electric Dipole, in a straight Conductor. The two above Dipoles (Compass-Conductor) are assumed with equal lengths ℓ, lying on two skew lines, perpendicular to each other, at a distance ℓ√2, thus forming, by their four ends, a Regular Tetrahedron, with side length ℓ. Repulsion, between Like Charges, obeys the simple Coulomb Electro-Static law. Whereas Interaction (Attraction or Repulsion), between Unlike Charges, obeys a more accurate Lennard-Jones law. The analysis of Dipole-Dipole (Compass-Conductor) Interaction is performed by hand calculator. The only out-of-balance forces, in the regular Tetrahedron, acting on the Rigid Conductor, are the so-called magnetic forces. Their direction is found, in a simple Rational way, with help of Regular Tetrahedron, without recoursing to a “right-hand-rule”. The proposed model is applied to 1) The force acting on an Electric Charge moving in a magnetic field. 2) The force acting on a Current carrying straight Conductor, due to a magnetic field. 3) The magnetic fields created around a Current carrying straight Conductor. In these applications, proposed model gives reasonable results. Particularly, in third application, results, obtained by proposed model, are found in satisfactory approximation with corresponding ones, obtained by an empirical formula, based on relevant Experimental observations of H.-C. Oersted and A.-M. Ampère. So, the reliability of proposed model is checked. Position and direction of magnetic field vector coincide with those of a corresponding fixed Compass of a constant Electric Field. Main point of present work is that, without introducing the concept of a magnetic field vector, by combining field of dipoles, produced by an electric field, with dipole of an alternating current carrying conductor, the magnetic forces can be determined.
基金the financial support from the National Natural Science Foundation of China(Grant No.51568012)the Scientific Research Foundation of Guizhou University(GuiDaRenJiHeZi[2023]14)+1 种基金the Science Foundation for Youths of Education Commission of Guizhou Province(QianJiaoJi[2024]020)the Basic Research Project of Guizhou University(GuiDajiChu[2024]18).
文摘To address the insufficient stiffness of the V-shaped reinforced concrete folded plate structure and its construction process causing environmental pollution,a novel assembled monolithic spherical-shaped reinforced concrete ribbed folded plate structure(AMRRFS)was proposed.The advantages of AMRRFS are that its construction process is environmentally friendly while it also exhibits great stability and rigidity.Therefore,an experimental and numerical investigation were conducted on the AMRRFS to investigate its mechanical properties.In addition,the parametric analysis of the AMRRFS was conducted,and some design recommendations were proposed.Under the design load,the experimental findings revealed that AMRRFS possessed excellent mechanical properties.During the overloading phase,the interface between the in situ casting area and the prefabrication area was severely damaged,leading to the loss of the structure’s ability to bear loads.The outcomes from the finite element simulations of AMRRFS closely mirrored the results of the experimental investigation.Based on the parametric analysis,it was recommended that the height of the AMRRFS,the height of the ribs,and the height of the secondary ridge beams shall be 1/7–1/5,1/65–1/50,and 1/34–1/30 of the span,and that the minimum reinforcing ratio for all types of plates shall exceed 1.0%.
基金National Natural Science Foundation of China under Grant No.51038006Specializes Research Fund for the Doctoral Program of Higher Education under Grant No.20090002110045
文摘The pseudo excitation method(PEM) has been improved into a more practical form,on which the analytic formulae of seismic response power spectral density(PSD) of simplified large-span structural models have been derived.The analytic formulae and numerical computing results of seismic response PSD have been derived to study the mechanism of multi-support excitation effects,such as the wave-passage effect and incoherence effect,for the seismic response of multiand large-span structures.By using a multi-span truss as an example,the influence of multi-support excitation effects on the seismic response of such structures is studied.
基金Cultivation Fund of the Key Grant Scientifi c and Technical Innovation Project, Ministry of Education of China Under Grant No.704003
文摘A novel distributed tuned liquid damper （DTLD） for reducing vibration in structures is proposed in this paper. The basic working principle of the DTLDs is to fill the empty space inside the pipes or boxes of cast-in-situ hollow reinforced concrete （RC） floor slabs with water or other liquid. The pipes or boxes then work as a series of small TLDs inside the structure, to increase the damping ratio of the entire structural system. Numerical simulation that accounts for the fluid- structure conpling effect is carried out to evaluate the vibration-reduction efficiency of the DTLDs. The results show that the DTLDs are able to considerably increase the damping of the structure and thus reduce its vibration. An additional benefit is that the DTLDs do not require architectural space to be added to the structure.
基金supported by the Beijing Natural Science Foundation(8232010)the Fundamental Research Funds for the Central Universities(2024JBKY002)the National Natural Science Foundation of China(52178269).
文摘Replacing the viscous damper of tuned mass damper(TMD)with the proposed inerter-enhanced dampers(IEDs),novel vibration mitigation methods,namely the IED-TMDs,are proposed.Unlike the TMD,which brings only one additional freedom into the system,the proposed IED-TMDs introduce more freedoms into the considered dynamic system.As a result,the traditional fixed-point theory cannot be used.To address this issue,this paper develops an extended fixed-point theory.Firstly,the inerter and the springs of the IED-TMDs are optimized considering that all four fixed points are of the same height.The closed-form solutions for the optimal inerter and springs of the IED-TMDs are obtained.Secondly,to obtain the optimal damping ratio for the IED-TMDs with multi-fixed points,a new optimization criterion is introduced.Different from the traditional fixed-point theory which controls the slope of the transfer function at the fixed points,the new optimization criterion assumes that the local peaks of the transfer function in between the four fixed points have the same height as the fixed points.And,a flat plateau is achieved in the transfer function.Further,the closed-form solutions for the optimal damping ratio are simplified in consideration of actual applications.Finally,the vibration mitigation performance of the IED-TMDs is evaluated.Results show that the vibration mitigation performance of IED-TMDs is superior to that of the conventional TMD.This superior vibration mitigation performance is more significant for the IED-TMDs with a smaller mass ratio.
基金supported by the National Basic Research Program of China("973"Project)(Grant No.2013CB036203)the National Natural Science Foundation of China(Grant No.51308034)the"111"Project(Grant No.B13002)
文摘To investigate the aerodynamic effect of wind barriers on a high-speed train-bridge system,a sectional model test was conducted in a closed-circuit-type wind tunnel.Several different cases,including with and without barriers,with different barrier heights and porosity rates,and with different train arrangements on the bridge were taken into consideration;in addition,the aerodynamic coefficients of the train-bridge system were measured.It is found that the side force and rolling moment coefficients of the vehicle are efficiently reduced by a single-side wind barrier,but for the bridge deck these values are increased.The height and porosity rate of the barrier are two important factors that influence the windbreak effect.Train arrangement on the bridge will considerably influence the aerodynamic properties of the train-bridge system.The side force and rolling moment coefficients of the vehicle at the windward side are larger than at the leeward side.
文摘Large span cable-supported structures have been developed rapidly in China, and they always adopt high-strength steel cables as structural members. However, the modulus of elasticity and yield strength of steel material will decrease seriously under fire conditions while fire protection is unlikely to be provided for steel cable. Several typical large span cable-supported structures such as cable truss, beam string structure and prestressed cable net are studied on their structural behaviour in this paper. Theoretical formulae are derived in terms of geometrical and material nonlinearity with high temperature effect. Finite element models are also established to simulate the structural performance under fire conditions. The calculation formulae for fire-resisting design are suggested for these three types of structures, while displacement and prestressed force variation rules are also given.
文摘This paper focuses on the lateral buckling of laterally-unrestrained aluminum beams subjected to a concentrated, uniformly loading; pure-bending action. The design methods of lateral stability of aluminum beams in the current codes are discussed. The influence of material property on the lateral buckling of aluminum beams is investigated with finite element analysis (FEA) methods. Some numerical examples are given,; the results from current codes are compared with the FEA solutions. The design method on lateral stability of steel beams specified in the Chinese standard GB 50017-2003 is modified to calibrate the stability factors of aluminum beams according to the European code, British code,; American code,; the modified method is verified by FEA results. Through comparison with the available test results, the modified design method for overall stability of aluminum bending members is proposed in this paper; proved applicable in the design of lateral stability of aluminum beams.
基金the National Natural Science Foundation of China (No. 50538060)
文摘The influential depth of moisture transport in a concrete surface subject to drying-wetting cycles was analyzed numerically. The moisture transport was described by a diffusion model with different diffusivities for drying and wetting. A finite difference scheme was developed to solve the partial differential equations The influential depth was then investigated numerically for initially saturated and unsaturated concretes exposed to drying-wetting actions in marine environments using an equilibrium time ratio concept. The equilibrium time ratio was calculated numerically for a saturated condition and the moisture influential depth is shown to be a linear function of the square root of the drying time. However, this equilibrium time ratio does not exist for an unsaturated condition and the moisture influential depth depends on the initial saturation as well as the drying-wetting time ratio. The results indicate that this model gives more realistic predictions of moisture transport of in situ structural concrete and its durability.
