The investigation on fatigue lives of reinforced concrete （RC） structures strength- ened with fiber laminate under random loading is important for the repairing or the strengthening of bridges and the safety of the ...The investigation on fatigue lives of reinforced concrete （RC） structures strength- ened with fiber laminate under random loading is important for the repairing or the strengthening of bridges and the safety of the traffic. In this paper, two methods are developed for predicting the fatigue lives of RC structures strengthened with carbon fiber [aminate （CFL） under random loading based on a residual life and a residual strength model. To discuss the efficiency of the model, 12 RC beams strengthened with CFL are tested under random loading by the MTS810 testing system. The predicted residual strength approximately agrees with test results.展开更多
Firstly,the fatigue damages associated with the random loadings were always deemed as highcycle or very-high-cycle fatigue problems,and based on Chebyshev theorem,the number of rainflow cycles in a given time interval...Firstly,the fatigue damages associated with the random loadings were always deemed as highcycle or very-high-cycle fatigue problems,and based on Chebyshev theorem,the number of rainflow cycles in a given time interval could be recognized as a constant by neglecting its randomness.Secondly,the randomness of fatigue damage induced by the distribution of rainflow cycles was analyzed.According to central limit theorem,the fatigue damage could be assumed to follow Gaussian distribution,and the statistical parameters:mean and variance,were derived from Dirlik's solution.Finally,the proposed method was used to a simulate Gaussian random loading and the measured random loading from an aircraft.Comparisons with observed results were carried out extensively.In the first example,the relative errors of the proposed method are 2.29%,3.52%and 1.16%for the mean,standard deviation and variation coefficient of fatigue damage,respectively.In the second example,these relative errors are 11.70%,173.32%and 18.20%,and the larger errors are attributable to non-stationary state of the measured loading to some extent.展开更多
This paper presents a Monte-Carlo simulation method to calculate intensity reliability for a missile tank under random loading. The cumulative damage mathematical model is established , and it adopts a direct simulati...This paper presents a Monte-Carlo simulation method to calculate intensity reliability for a missile tank under random loading. The cumulative damage mathematical model is established , and it adopts a direct simulation method to present random loading and o-riginal intensity for a missile tank. It can effectively predict intensity reliability for a missile tank in the environment of transport and flight.展开更多
Fatigue damage of materials includes static damage and cyclic damage.Static damage is a ratio of the plastic energy in first static loading to the statictoughness, while cyclic damage is the ratio of the cyclic plasti...Fatigue damage of materials includes static damage and cyclic damage.Static damage is a ratio of the plastic energy in first static loading to the statictoughness, while cyclic damage is the ratio of the cyclic plastic hysteresis energy to thefatigue toughness. In the calculation, cyclic hardening (or softening) of a material istaken into account, which results in the increase (or decrease) of the yield stress. Forsimplification, it is assumed that stress and strain in cyclic loading vary in accordancewith the hysteresis loop. Fatigue toughness of a material can be detennined bysymmetric cyclic stress controlled fatigue test. A method, rational and convenient forengineering, is proposed to estimate the fatigue life under random loading based onplastic hysteresis energy theorem. Preliminary verification by test is satisfactory.展开更多
A new load balancing algorithm named dynamic weighed random （DWR） algorithm for the session initiation protocol （SIP） application server cluster is proposed. It uses weighted hashing random algorithm that supports...A new load balancing algorithm named dynamic weighed random （DWR） algorithm for the session initiation protocol （SIP） application server cluster is proposed. It uses weighted hashing random algorithm that supports dialog in the SIP protocol to distribute messages. The weight of each server is dynamic adaptive with feedback mechanism. DWR insures that the cluster is balanced, and it performs better than the limited resource vector （LRV） algorithm and minimum sessions first （MSF） algorithm.展开更多
In order to employ cost effective frequency domain analysis for off-shore structures treatment of hydrodynamic loading is essential. Drag and inertia dominated, resonating and antiresonating cases under random sea sta...In order to employ cost effective frequency domain analysis for off-shore structures treatment of hydrodynamic loading is essential. Drag and inertia dominated, resonating and antiresonating cases under random sea states are analyzed to highlight the implications and relative merits of four salient linearization techniques.展开更多
Extensive 3-D model tests have been performed to study the effects of wave obliquity and multi-directionality on the wave loads acting on vertical breakwaters. The variation of horizontal and uplift forces acting on a...Extensive 3-D model tests have been performed to study the effects of wave obliquity and multi-directionality on the wave loads acting on vertical breakwaters. The variation of horizontal and uplift forces acting on an unit length of a breakwater with wave direction, the longitudinal distribution of wave forces, as well as the longitudinal load reduction are analyzed. Some empirical formulae of the longitudinal distribution coefficient and the longitudinal load reduction factor are presented for practical use.展开更多
According to the concept of critical plane, a life prediction approach forrandom multiaxial fatigue is presented. First, the critical plane under the multiaxial randomloading is determined based on the concept of the ...According to the concept of critical plane, a life prediction approach forrandom multiaxial fatigue is presented. First, the critical plane under the multiaxial randomloading is determined based on the concept of the weight-averaged maximum shear strain direction.Then the shear and normal strain histories on the determined critical plane are calculated and takenas the subject of multiaxial load simplifying and multiaxial cycle counting. Furthermore, amultiaxial fatigue life prediction model including the parameters resulted from multiaxial cyclecounting is presented and applied to calculating the fatigue damage generated from each cycle.Finally, the cumulative damage is added up using Miner's linear rule, and the fatigue predictionlife is given. The experiments under multiaxial loading blocks are used for the verification of theproposed method. The prediction has a good correction with the experimental results.展开更多
A fatigue life estimation method for offshore structures under random stress response is studied in this paper. The method of broad band cumulative frequency number is used to determine the effect of band width of str...A fatigue life estimation method for offshore structures under random stress response is studied in this paper. The method of broad band cumulative frequency number is used to determine the effect of band width of stress frequency spectra on fatigue. A formula of correction factor for fatigue under broad band stress spectra is suggested and compared with that given by P. H. Wirsching.展开更多
The girder end restraint devices such as bearings and dampers on long span suspension bridge will deteriorate over time.However,it is difficult to achieve the quantitative assessment of the performance of the restrain...The girder end restraint devices such as bearings and dampers on long span suspension bridge will deteriorate over time.However,it is difficult to achieve the quantitative assessment of the performance of the restraint device through existing detection methods in actual inspections,making it difficult to obtain the impact of changes in the performance of the restraint device on the bridge structure.In this paper,a random vehicle load model is firstly established based on the WIM data of Jiangyin Bridge,and the displacement of girder end under the actual traffic flow is simulated by using finite element dynamic time history analysis.On this basis,according to the performance test data of the bearings and dampers,the performance degradation laws of the above two restraint devices are summarized,and the performance degradation process of the two restraint devices and the effects of different restraint parameters on the bridge structure are simulated.The results show that the performance degradation of the damper will significantly reduce the damping force at low speed,resulting in a significant increase in the cumulative displacement of the girder end;in the presence of longitudinal dampers,the increase in the friction coefficient caused by the deterioration of the bearing sliding plate has little effect on the cumulative displacement,but excessive wear of the bearing sliding plate adversely affects the structural dynamic performance.展开更多
基金supported by the National Natural Science Foundation of China(No.10672060)the Guangdong Provincial Nature Science Foundation of China(No.07006538).
文摘The investigation on fatigue lives of reinforced concrete （RC） structures strength- ened with fiber laminate under random loading is important for the repairing or the strengthening of bridges and the safety of the traffic. In this paper, two methods are developed for predicting the fatigue lives of RC structures strengthened with carbon fiber [aminate （CFL） under random loading based on a residual life and a residual strength model. To discuss the efficiency of the model, 12 RC beams strengthened with CFL are tested under random loading by the MTS810 testing system. The predicted residual strength approximately agrees with test results.
文摘Firstly,the fatigue damages associated with the random loadings were always deemed as highcycle or very-high-cycle fatigue problems,and based on Chebyshev theorem,the number of rainflow cycles in a given time interval could be recognized as a constant by neglecting its randomness.Secondly,the randomness of fatigue damage induced by the distribution of rainflow cycles was analyzed.According to central limit theorem,the fatigue damage could be assumed to follow Gaussian distribution,and the statistical parameters:mean and variance,were derived from Dirlik's solution.Finally,the proposed method was used to a simulate Gaussian random loading and the measured random loading from an aircraft.Comparisons with observed results were carried out extensively.In the first example,the relative errors of the proposed method are 2.29%,3.52%and 1.16%for the mean,standard deviation and variation coefficient of fatigue damage,respectively.In the second example,these relative errors are 11.70%,173.32%and 18.20%,and the larger errors are attributable to non-stationary state of the measured loading to some extent.
文摘This paper presents a Monte-Carlo simulation method to calculate intensity reliability for a missile tank under random loading. The cumulative damage mathematical model is established , and it adopts a direct simulation method to present random loading and o-riginal intensity for a missile tank. It can effectively predict intensity reliability for a missile tank in the environment of transport and flight.
文摘Fatigue damage of materials includes static damage and cyclic damage.Static damage is a ratio of the plastic energy in first static loading to the statictoughness, while cyclic damage is the ratio of the cyclic plastic hysteresis energy to thefatigue toughness. In the calculation, cyclic hardening (or softening) of a material istaken into account, which results in the increase (or decrease) of the yield stress. Forsimplification, it is assumed that stress and strain in cyclic loading vary in accordancewith the hysteresis loop. Fatigue toughness of a material can be detennined bysymmetric cyclic stress controlled fatigue test. A method, rational and convenient forengineering, is proposed to estimate the fatigue life under random loading based onplastic hysteresis energy theorem. Preliminary verification by test is satisfactory.
基金supported by the National Science Fund for Distinguished Young Scholars (60525110)the National Basic Research Program of China (2007CB307100, 2007CB307103)Development Fund Project for Electronic and Information Industry
文摘A new load balancing algorithm named dynamic weighed random （DWR） algorithm for the session initiation protocol （SIP） application server cluster is proposed. It uses weighted hashing random algorithm that supports dialog in the SIP protocol to distribute messages. The weight of each server is dynamic adaptive with feedback mechanism. DWR insures that the cluster is balanced, and it performs better than the limited resource vector （LRV） algorithm and minimum sessions first （MSF） algorithm.
文摘In order to employ cost effective frequency domain analysis for off-shore structures treatment of hydrodynamic loading is essential. Drag and inertia dominated, resonating and antiresonating cases under random sea states are analyzed to highlight the implications and relative merits of four salient linearization techniques.
文摘Extensive 3-D model tests have been performed to study the effects of wave obliquity and multi-directionality on the wave loads acting on vertical breakwaters. The variation of horizontal and uplift forces acting on an unit length of a breakwater with wave direction, the longitudinal distribution of wave forces, as well as the longitudinal load reduction are analyzed. Some empirical formulae of the longitudinal distribution coefficient and the longitudinal load reduction factor are presented for practical use.
基金This project is supported by National Natural Science Foundation of China (No.59775030).
文摘According to the concept of critical plane, a life prediction approach forrandom multiaxial fatigue is presented. First, the critical plane under the multiaxial randomloading is determined based on the concept of the weight-averaged maximum shear strain direction.Then the shear and normal strain histories on the determined critical plane are calculated and takenas the subject of multiaxial load simplifying and multiaxial cycle counting. Furthermore, amultiaxial fatigue life prediction model including the parameters resulted from multiaxial cyclecounting is presented and applied to calculating the fatigue damage generated from each cycle.Finally, the cumulative damage is added up using Miner's linear rule, and the fatigue predictionlife is given. The experiments under multiaxial loading blocks are used for the verification of theproposed method. The prediction has a good correction with the experimental results.
文摘A fatigue life estimation method for offshore structures under random stress response is studied in this paper. The method of broad band cumulative frequency number is used to determine the effect of band width of stress frequency spectra on fatigue. A formula of correction factor for fatigue under broad band stress spectra is suggested and compared with that given by P. H. Wirsching.
基金supported by the National Key Research and Development Program of China(No.2022YFB3706704)the Academician Special Science Research Project of CCCC(No.YSZX-03-2022-01-B).
文摘The girder end restraint devices such as bearings and dampers on long span suspension bridge will deteriorate over time.However,it is difficult to achieve the quantitative assessment of the performance of the restraint device through existing detection methods in actual inspections,making it difficult to obtain the impact of changes in the performance of the restraint device on the bridge structure.In this paper,a random vehicle load model is firstly established based on the WIM data of Jiangyin Bridge,and the displacement of girder end under the actual traffic flow is simulated by using finite element dynamic time history analysis.On this basis,according to the performance test data of the bearings and dampers,the performance degradation laws of the above two restraint devices are summarized,and the performance degradation process of the two restraint devices and the effects of different restraint parameters on the bridge structure are simulated.The results show that the performance degradation of the damper will significantly reduce the damping force at low speed,resulting in a significant increase in the cumulative displacement of the girder end;in the presence of longitudinal dampers,the increase in the friction coefficient caused by the deterioration of the bearing sliding plate has little effect on the cumulative displacement,but excessive wear of the bearing sliding plate adversely affects the structural dynamic performance.
