Energy-based damage assessment of continuous-span reinforced concrete highway bridges

This paper conducts a comparative study on seismic damage to reinforced concrete(RC)bridges,using three damage models:Park and Ang,Hindi and Sexsmith,and input energy-based damage(IEBD)indices,and presents a global cumulative damage model based on the IEBD index to establish a practical damage assessment of an overall bridge system.A series of RC bridges are studied under seismic loadings,and to compare the efficiency and reliability of the damage indices,damage curves of RC piers are developed,and damage levels of piers are calculated at design basis earthquake(DBE)and maximum considered earthquake(MCE)levels.The global cumulative damage index is calculated for bridge models regarding damage values of components.The results indicate that the IEBD index shows a gradual progression of damage and provides reasonable values for different damage levels of piers compared to two other damage indices.Moreover,the global cumulative damage index shows the impact of induced damage to a certain component regarding the damage level of the overall bridge system.Moreover,this new approach is a relatively simple and practical tool for seismic damage assessment of RC bridge systems,which can be implemented in finite element models,particularly in the absence of experimental data.

Mechanical responses of anchoring structure under triaxial cyclic loading

Dynamic load on anchoring structures(AS)within deep roadways can result in cumulative damage and failure.This study develops an experimental device designed to test AS under triaxial loads.The device enables the investigation of the mechanical response,failure mode,instability assessment criteria,and anchorage effect of AS subjected to combined cyclic dynamic-static triaxial stress paths.The results show that the peak bearing strength is positively correlated with the anchoring matrix strength,anchorage length,and edgewise compressive strength.The bearing capacity decreases significantly when the anchorage direction is severely inclined.The free face failure modes are typically transverse cracking,concave fracturing,V-shaped slipping and detachment,and spallation detachment.Besides,when the anchoring matrix strength and the anchorage length decrease while the edgewise compressive strength,loading rate,and anchorage inclination angle increase,the failure intensity rises.Instability is determined by a negative tangent modulus of the displacement-strength curve or the continued deformation increase against the general downward trend.Under cyclic loads,the driving force that breaks the rock mass along the normal vector and the rigidity of the AS are the two factors that determine roadway stability.Finally,a control measure for surrounding rock stability is proposed to reduce the internal driving force via a pressure relief method and improve the rigidity of the AS by full-length anchorage and grouting modification.

Master Curve Method of Cumulative Damage for Prediction of Service Life

Aim To study the theory and method for the prediction of service life of solid rocket propellant grain. Methods With the aid of discontiguous diagnostic technology and method of accumulated damage using accelerated aging or heat air oven, the aging isotherms for void content versus aging time were determined. According to the principle of time temperature equivalence the viscoelastic master curve for the prediction of service life were obtained. Results and Conclusion The service life of HMX CMDB solid rocket propellant grain were obtained. Because the critical storage life is measured, the accuracy of predicting the service life of the grain has been increased greatly.

Experimental and numerical investigations on the tensile mechanical behavior of marbles containing dynamic damage

To investigate the degradation mechanism of static tensile mechanical behaviors of marble containing dynamic damage,multiple impact loading tests were performed on the disc marble samples,and then static Brazilian tests were conducted for the damaged samples.Besides,coupling modeling technology of finite difference method(FDM)—discrete element method(DEM)was used to carry out the numerical investigation.The results show that after multiple impacts,more white patches appear on the surface,and some microcracks,macro-fractures as well as pulverized grains are found by optical microscopic.The static tensile strength decreases with the increase of the dynamic damage variable characterized by the ultrasonic wave velocity of sample.The interaction between grains in the damaged sample becomes intense in the subsequent static loading process,causing a relatively large strain.The volume of the fragments falling off around the loading points becomes larger as impact number increases.As the dynamic damage increases,the absorbed energy of sample during the static loading first decreases and then tends to be stable.Both the stress concentration and the breakage of the force chains are the root causes of the degradation of the static tensile strength.

Blasting cumulative damage effects of underground engineering rock mass based on sonic wave measurement

The principle of sonic wave measurement was introduced, and cumulative damage effects of underground engineering rock mass under blasting load were studied by in situ test, using RSM-SY5 intelligent sonic wave apparatus. The blasting test was carried out for ten times at some tunnels of Changba Lead-Zinc Mine. The damage depth of surrounding rock caused by old blasting excavation （0.8-1.2 m） was confirmed. The relation between the cumulative damage degree and blast times was obtained. The results show that the sonic velocity decreases gradually with increasing blast times, hut the damage degree （D） increases. The damage cumulative law is non-linear. The damage degree caused by blast decreases with increasing distance, and damage effects become indistinct. The blasting damage of rock mass is anisotropic. The damage degree of rock mass within charging range is maximal. And the more the charge is, the more severe the damage degree of rock mass is. The test results provide references for researches of mechanical parameters of rock mass and dynamic stability analysis of underground chambers.

A CUMULATIVE FATIGUE DAMAGE RULE UNDER THE ALTERNATIVE OF CORROSION OR CYCLIC LOADING

Fatigue damage increases with the applied loading cycles in a cumulative manner and the material deteriorates with the corrosion time. A cumulative fatigue damage rule under the alternative of corrosion or cyclic loading was proposed. The specimens of aluminum alloy LY12-CZ soaked in corrosive liquid for different times were tested under the constant amplitude cyclic loading to obtain S-N curves. The test was carried out to verify the proposed cumulative fatigue damage rule under the different combinations among corrosion time, loading level, and the cycle numbers. It was shown that the predicted residual fatigue lives showed a good agreement with the experimental results and the proposed rule was simple and can be easily adopted.

Cumulative damage effect on debris slopes under frequent microseisms

Debris slopes are widely distributed across the Three Gorges Reservoir area in China,and seasonal fluctuations of the water level in the area tend to cause high-frequency microseisms that subsequently induce landslides on such debris slopes.In this study,a cumulative damage model of debris slope with varying slope characteristics under the effects of frequent microseisms was established,based on the accurate definition of slope damage variables.The cumulative damage behaviour and the mechanisms of slope instability and sliding under frequent microseisms were thus systematically investigated through a series of shaking table tests and discrete element numerical simulations,and the influences of related parameters such as bedrock,dry density and stone content were discussed.The results showed that the instability mode of a debris slope can be divided into a vibration-compaction stage,a crack generation stage,a crack development stage,and an instability stage.Under the action of frequent microseisms,debris slope undergoes the last three stages cyclically,which causes the accumulation to slide out in layers under the synergistic action of tension and shear,causing the slope to become destabilised.There are two sliding surfaces as well as the parallel tensile surfaces in the final instability of the debris slope.In the process of instability,the development trend of the damage accumulation curve remains similar for debris slopes with different parameters.However,the initial vibration compaction effect in the bedrock-free model is stronger than that in the bedrock model,with the overall cumulative damage degree in the former being lower than that of the latter.The damage degree of the debris slope with high dry density also develops more slowly than that of the debris slope with low dry density.The damage development rate of the debris slope does not always decrease with the increase of stone content.The damage degree growth rate of the debris slope with the optimal stone content is the lowest,and the increase or decrease of the stone content makes the debris slope instability happen earlier.The numerical simulation study also further reveals that the damage in the debris slope mainly develops in the form of crack formation and penetration,in which,shear failure occurs more frequently in the debris slope.

Fatigue behavior and cumulative damage rule of concrete under cycli ccompression with constant confined stress

The effects of different lateral confinement stress on the fatigue behavior and cumulative damage of plain concrete were investigated experimentally. Eighty 100mm×100mm×100mm specimens of ordinary strength concrete were tested with constant-or variable-amplitude cyclic compression and lateral confinement pressure in two orthogonal directions. A fatigue equation was gained by modifying the classical Aas-Jakobsen S-N equation and used for taking into account the effect of the confined stress on fatigue strength of plain concrete. The present study indicates that the fatigue failure is greatly influenced by the sequence of applied variable-amplitude fatigue loading, and Miner’s rule is inapplicable to predict the residual fatigue life, especially in the sequence of low to high. The present research also shows that the exponent d of the Corten-Dolan’s damage formula is a constant depending on the materials and the levels of load spectrum, and d can be determined through the two-stage fatigue tests. The residual fatigue lives predicted by Corten-Dolan’s damage formula are found to be in good agreement with the results of the experiments.

A NEW FATIGUE CUMULATIVE DAMAGE DYNAMIC INTERFERENCE MODEL

On the basis of the statistical characteristics of fatigue cumulative damageand its critical value, a new dynamic interference model for reliability analysis is presented. Because the nonlinearity of fatigue damage accumulation is taken into account,this model is able to predict the fatigue reliability for random spectrum loadingconveniently. To verify the predicted results, a special fatigue expenment, in which thenumber of specimen is up to 101, is conducted using a fighter spectrum loading. It isshown that the new model is reliable, practicable and better than existing models.

Cumulative damage effects of mainshock-aftershock sequences on RC-frame structures

Frequent aftershocks often follow a strong mainshock.They can significantly increase cumulative damage to a structure.A model of a five-story reinforced concrete frame structure was designed and a nonlinear mathematical model of the structure was developed to investigate the damage states resulting from different mainshock-aftershock sequences.Mainshock-aftershock sequences consisting of one of three recorded mainshocks combined with one of five recorded aftershocks were created for input to the mathematical model.Inelastic energy dissipation and the Park-Ang damage index were used as measures of cumulative damage to the structure.The results demonstrate that consideration of only the single mainshock ground motion in seismic building design can result in the design and construction of unsafe buildings.Total cumulative damage to a structure is caused by the combination of damage states resulting from the mainshock and the aftershock(s).

NEW FATIGUE CUMULATIVE DAMAGE PROBABILISTIC MODEL OFTHE MECHANICAL PARTS

Fatigue failure of mechanical part is treated as a random event.the fatigue reliablility problem can be solved through researching the random event.A new definition δb that measures fatigue damage quantity in a cycle under cyclic stress is put forward. According to δ.the paper presents two new definitions K and D is fatigue damage strength.D is overall fatigue damage quantity.Using K and D to describe the fatigue failure of the parts,the paper puts forward a new fatigue cumulative damage probabilistic model of the mechanical parts.The model can be used to solve reliability fatigue problem.

A cumulative damage model for predicting and assessing raveling in asphalt pavement using an energy dissipation approach

Raveling is a common distress of asphalt pavements,defined as the removal of stones from the pavement surface.To predict and assess raveling quantitatively,a cumulative damage model based on an energy dissipation approach has been developed at the meso level.To construct the model,a new test method,the pendulum impact test,was employed to determine the fracture energy of the stone-mastic-stone meso-unit,while digital image analysis and dynamic shear rheometer test were used to acquire the strain rate of specimens and the rheology property of mastic,respectively.Analysis of the model reveals that when the material properties remain constant,the cumulative damage is directly correlated with loading time,loading amplitude,and loading frequency.Specifically,damage increases with superimposed linear and cosine variations over time.A higher stress amplitude results in a more rapidly increasing rate of damage,while a lower load frequency leads to more severe damage within the same loading time.Moreover,an example of the application of the model has been presented,showing that the model can be utilized to estimate failure life due to raveling.The model is able to offer a theoretical foundation for the design and maintenance of anti-raveling asphalt pavements.

The NBEE and NWEE classes of lifetime distributions and their properties

A class of lifetime distributions, new better than equilibrium in expectation （NBEE）, and its dual, new worse than equilibrium in expectation （NWEE）, are studied based on the comparison of the expectations of lifetime X and its equilibrium Xo. The relationships of the NBEE （NWEE） and other lifetime distribution classes are discussed. It is proved that the NBEE is very large, and increasing failure rate （IFR）, new better than used （NBU） and the L class are its subclasses. The closure properties under two kinds of reliability operations, namely, convolution and mixture, are investigated. Furthermore, a Poisson shock model and a special cumulative model are also studied, in which the necessary and sufficient conditions for the NBEE （NWEE） lifetime distribution of the systems are established. In the homogenous Poisson shock model, the system lifetime belongs to NBEE（NWEE） if and only if the corresponding discrete failure distribution belongs to the discrete NBEE（NWEE）. While in the cumulative model, the system has an NBEE lifetime if and only if the stochastic threshold of accumulated damage is NBEE.

Residual strength model for composite laminates

To research the approach of predicting composites fatigue life,the cumulative fatigue damage of fiber-reinforced plastic laminates(FRP) was investigated,and based on the complex exponential function,the residual strength model was obtained. This model can accurately describe the propagation of cumulative fatigue damage of FRP in three stages,especially in the initial stage and the ceasing stage. Applying this model in the experiment with two loading cycles,it can be found that the prediction result has good coincidence with experimental data. So a reliable residual strength model can be provided for studying the cumulative fatigue damage of FRP.

Fatigue Behavior of Plain Concrete Under Biaxial Compression: Experiments and Theoretical Model

The effects of different lateral confinement stress on the fatigue behavior of and cumulative damage to plain concrete are investigated experimentally. Eighty 100 mm x 100 mm x 100 mm specimens of ordinary strength concrete are tested under constant- or variable-amplitude fatigue loading and lateral confinement pressure in two orthogonal directions. A fatigue equation is developed by modifying the classical Aas-Jakobsen S-N equation for taking into account the effect of the confined stress on fatigue strength of plain concrete. The results of variable-amplitude fatigue tests indicate that the linear damage theory proposed by Palmgren and Miner is unreasonable in the biaxial stress state. A nonlinear cumulative damage model that could model the effects of the magnitude and sequence of variable-amplitude fatigue loading and lateral confinement pressure is proposed on the basis of the evolution laws of the residual strains in the longitudinal direction during fatigue tests. The residual fatigue. life predicted by this model is found to be in good agreement with the results of the experimental research.

Experimental Study on Performance of Plain Concrete Due to Triaxial Variable-Amplitude Tension-Compression Cyclic Loading

An experimental study on performance of plain concrete under triaxial constant-amplitude and variable amplitude tension- compression cyclic loadings was carded out. The low level of the cyclic stress is 0. 2f and the upper level ranges between 0. 20f and 0. 55f., while the constant lateral pressure is 0. 3 f . The specimen failure mode, the three-stage evolution rule of the longitudinal strains and the damage evolution law under cyclic loading were analyzed. Furthermore, Miner＇s rule is proved not to be applicable to the cyclic loading conditions, hereby, a nonlinear cumulative damage model was established. Based on the model the remaining fatigue life was evaluated. The comparison whh the experiment resuhs shaws that the model is of better precision and applicability.

Nonlinear Modeling for a Two-Stage Degradation System Based on Nonhomogeneous Poisson Process

The degradation process modeling is one of research hotspots of prognostic and health management(PHM),which can be used to estimate system reliability and remaining useful life(RUL).In order to study system degradation process,cumulative damage model is used for degradation modeling.Assuming that damage increment is Gamma distribution,shock counting subjects to a homogeneous Poisson process(HPP)when degradation process is linear,and shock counting is a non-homogeneous Poisson process(NHPP)when degradation process is nonlinear.A two-stage degradation system is considered in this paper,for which the degradation process is linear in the first stage and the degradation process is nonlinear in the second stage.A nonlinear modeling method for considered system is put forward,and reliability model and remaining useful life model are established.A case study is given to validate the veracities of established models.

Fatigue Life Estimation for an Aircraft Engine Fan Blade

In this paper,stress states under corresponding condition of an aero-engine fan blade using finite element stress-strain analysis for three work cycles in the 900 h load spectrum are obtained.Through the nominal stress method,we calculated the fatigue notch factor and combined the material characteristics of TC6 to correct the material curve to the fan blades curve. Finally,the fatigue life of a fan blade was estimated using the linear cumulative damage rule and nonlinear cumulative damage theory.

Efficient Method for Accelerated Reliability Qualification Testing

Based on the theoretical inference and experiment verification,a method was proposed to carry out the accelerated reliability qualification testing. First,theoretical inference was used to get the acceleration coefficients of super Gauss vibration stress and temperature stress. Then, by applying these coefficients, an accelerated reliability qualification testing curve was obtained from the standard tests. Finally,the actual experiment on a digital marine control device was carried out under the proposed testing method.The experiment result shows that the proposed method can reduce the total experiment time and improve the efficiency of the reliability qualification test.

Fatigue reliability for LNG carrier

The procedure of reliability-based fatigue analysis of liquefied natural gas(LNG) carrier of membrane type under wave loads is presented. The stress responses of the hotspots in regular waves with different wave heading angles and wave lengths are evaluated by global ship finite element method(FEM) . Based on the probabilistic distribution function of hotspots' short-term stress-range using spectral-based analysis,Weibull distribution is adopted and discussed for fitting the long-term probabilistic distribution of stress-range. Based on linear cumulative damage theory,fatigue damage is characterized by an S-N relationship,and limit state function is established. Structural fatigue damage behavior of several typical hotspots of LNG middle ship section is clarified and reliability analysis is performed. It is believed that the presented results and conclusions can be of use in calibration for practical design and initial fatigue safety evaluation for membrane type LNG carrier.