Influence of Soil-Structure Interaction Models on the Dynamic Responses of An Offshore Wind Turbine Under Environmental Loads

Offshore wind turbines(OWTs) suffer wind, wave and earthquake loads. The investigation of OWTs' dynamic response under environmental loads is essential for structural safety assessment. The soil-structure interaction(SSI)significantly affects the responses of OWT under environmental loads. However, there is few systematic research about the difference in the dynamic response of different SSI models under environmental loads. In order to solve the problem, the OWT is modeled by shell element, and several SSI models are built. The wind, wave and earthquake loads are taken into account. Moreover, the dynamic response, fatigue and buckling analysis are performed by ANSYS. The results indicate that SSI cannot be ignored in the dynamic response of the OWT under wind and wave loads. The SSI can decrease the displacement response of the OWT by 19% under wind and wave loads and reduce the fatigue damage of the pile. Multi-layer SSI can strongly influence the OWT's dynamic response under wind and wave loads or earthquake-only load. The vertical earthquake load increases the dynamic response in three directions.Besides, in order to simulate real environment, multi-layer SSI, soil damping and vertical SSI must be considered to evaluate the displacement response of the OWT under wind, wave and earthquake loads. The earthquake and gravity loads can cause more obvious response of the OWT than that of only wind and wave loads. The top and bottom of the tower are prone to occur buckling.

Semi-Probabilistic Evaluation of System Redundancy for Existing Offshore Structures

In this paper, a new definition of structure system redundancy is proposed in view of the various measures for structure redundancy. By introducing the terms of structure system failure at the mechanism level and equivalent reliability index, the safety for existing offshore platforms can be evaluated by the semi-probabilistic method presented in this paper. Some numerical examples are given and satisfactory results have been obtained.

Enhanced structural damage behavior of liquid-filled tank by reactive material projectile impact

A series of ballistic experiments were performed to investigate the damage behavior of high velocity reactive material projectiles(RMPs) impacting liquid-filled tanks,and the corresponding hydrodynamic ram(HRAM) was studied in detail.PTFE/Al/W RMPs with steel-like and aluminum-like densities were prepared by a pressing/sintering process.The projectiles impacted a liquid-filled steel tank with front aluminum panel at approximately 1250 m/s.The corresponding cavity evolution characteristics and HRAM pressure were recorded by high-speed camera and pressure acquisition system,and further compared to those of steel and aluminum projectiles.Significantly different from the conical cavity formed by the inert metal projectile,the cavity formed by the RMP appeared as an ellipsoid with a conical front.The RMPs were demonstrated to enhance the radial growth velocity of cavity,the global HRAM pressure amplitude and the front panel damage,indicating the enhanced HRAM and structural damage behavior.Furthermore,combining the impact-induced fragmentation and deflagration characteristics,the cavity evolution of RMPs under the combined effect of kinetic energy impact and chemical energy release was analyzed.The mechanism of enhanced HRAM pressure induced by the RMPs was further revealed based on the theoretical model of the initial impact wave and the impulse analysis.Finally,the linear correlation between the deformation-thickness ratio and the non-dimensional impulse for the front panel was obtained and analyzed.It was determined that the enhanced near-field impulse induced by the RMPs was the dominant reason for the enhanced structural damage behavior.

Rock Damage Structure of the South Longmen-Shan Fault in the 2008 M8 Wenchuan Earthquake Viewed with Fault-Zone Trapped Waves and Scientific Drilling

This article is to review results from scientific drilling and fault-zone trapped waves （FZTWs） at the south Longman-Shan fault （LSF） zone that ruptured in the 2008 May 12 M8 Wenchuan earthquake in Sichuan,China.Immediately after the mainshock,two Wenchuan Fault Scientific Drilling （WFSD） boreholes were drilled at WFSD-1 and WFSD-2 sites approximately 400 m and 1 km west of the surface rupture along the Yinxiu-Beichuan fault （YBF）,the middle fault strand of the south LSF zone.Two boreholes met the principal slip of Wenchuan earthquake along the YBF at depths of 589-m and 1230-m,respectively.The slip is accompanied with a 100-200-m-wide zone consisting of fault gouge,breccia,cataclasite and fractures.Close to WFSD-1 site,the nearly-vertical slip of ～4.3-m with a 190-m wide zone of highly fractured rocks restricted to the hanging wall of the YBF was found at the ground surface after the Wenchuan earthquake.A dense linear seismic array was deployed across the surface rupture at this venue to record FZTWs generated by aftershocks.Observations and 3-D finite-difference simulations of FZTWs recorded at this cross-fault array and network stations close to the YBF show a distinct low-velocity zone composed by severely damaged rocks along the south LSF at seismogenic depths.The zone is several hundred meters wide along the principal slip,within which seismic velocities are reduced by ～30-55％ from wall-rock velocities and with the maximum velocity reduction in the ～200-m-wide rupture core zone at shallow depth.The FZTW-inferred geometry and physical properties of the south LSF rupture zone at shallow depth are in general consistent with the results from petrological and structural analyses of cores and well log at WFSD boreholes.We interpret this remarkable low-velocity zone as being a break-down zone during dynamic rupture in the 2008 M8 earthquake.We examined the FZTWS generated by similar earthquakes before and after the 2008 mainshock and observed that seismic velocities within fault core zone was reduced by ～10％ due to severe damage of fault rocks during the M8 mainshock.Scientific drilling and locations of aftershocks generating prominent FZTWs also indicate rupture bifurcation along the YBF and the Anxian-Guangxian fault （AGF）,two strands of the south LSF at shallow depth.A combination of seismic,petrologic and geologic study at the south LSF leads to further understand the relationship between the fault-zone structure and rupture dynamics,and the amplification of ground shaking strength along the low-velocity fault zone due to its waveguide effect.

EXPERIMENTAL RESEARCH ON EVALUATING STRUCTURE DAMAGE WITH PIEZOELECTRIC DYNAMIC IMPEDANCE

A dynamic impedance-based structural health monitoring technique isintroduced. According to the direct and the converse piezoelectric property of piezoelectricmaterials, the piezoceramic (PZT) can be used as an actuator and a sensor synchronously. If damageslike cracks, holes, debonding or loose connections are presented in the structure, the physicalvariations of the structure will cause the mechanical impedance modified. On the basis ofintroducing the principle and the theory, the experiment and the analysis on some damages of thestructure are studied by means of the dynamic impedance technique. On the view of experiment, kindsof structural damages are evaluated by the information of dynamic impedance in order to validate thefeasibility of the method.

Damage Assessment of Reinforced Concrete Structures through Damage Indices:A State-of-the-Art Review

Due to the developments of computer science and technology in recent years,computer models and numerical simulations for large and complicated structures can be done.Among the vast information and results obtained from the analysis and simulations,the damage performance is of great importance since this damage might cause enormous losses for society and humanity,notably in cases of severe damage occurring.One of the most effective tools to handle the results about the damage performance of the structure is the damage index(DI)together with the damage states,which are used to correlate the damage indices with the damage that occurred in the actual structures.Numbers of damage indices proposed and developed rely on the fact that the damage causes noticeable changes in the structural and dynamic properties of the structural components or the whole structure.Therefore,this study presents a comprehensive review of the damage assessment of Reinforced Concrete(RC)structures.It presents step by step the development of the damage indices that are most widely used to estimate the performance of structural components in the structure and subsequently assess the damage degree of such these structures either based on the structural properties or dynamic properties of the structure.Also,several damage states have been introduced to estimate the performance level of the structure.Finally,case studies,methodologies,and applications on the damage assessment of RC structures are reviewed and presented.

Influence of structural damage on evaluation of microscopic pore structure in marine continental transitional shale of the Southern North China Basin:A method based on the low-temperature N2 adsorption experiment

Structural damage from sample preparation processes such as cutting and polishing may change the pore structure of rocks.However,changes in pore structure caused by this structural damage from crushing and its effect on marine continental transitional shale have not been well documented.The changes of microscopic pore structure in marine continental transitional shale during the sample preparation have important research value for subsequent exploration and development of shale gas.In this study,the pore structures of transitional shale samples from the Shanxi-Taiyuan Formation of the Southern North China Basin under different degrees of damage were analyzed through low-temperature N;adsorption experiments,combined with X-ray diffraction,total organic carbon,vitrinite reflectance analysis,and scanning electron microscopy.The results showed that(1)With increasing structural damage,the specific surface area(SSA)changed within relatively tight bounds,while the pore volume(PV)varied significantly,and the growth rate(maximum)exhibited a certain critical value with the crushing mesh number increasing from 20 to 200.(2)The ratio of SSA to PV can be used as a potential proxy for evaluating the influence of changes in the pore structure.(3)Correlation analysis revealed that the microscopic pore structure of marine continental transitional shale from the Shanxi-Taiyuan Formations is mainly controlled by organic matter and clay minerals.Clay minerals play a leading role in the development of microscopic pores and changes in pore structure.

Test analysis of detection of damage to a complicated spatial model structure

A two-stage damage detection approach is proposed and experimentally demonstrated on a complicated spatial model structure with a limited number of measurements. In the experiment,five known damage patterns,including 3 brace damage cases and 2 joint damage cases,were simulated by removing braces and weakening beam鈥揷olumn connections in the structure. The limited acceleration response data generated by hammer impact were used for system identification,and modal parameters were extracted by using the eigensystem realization algorithm. In the first stage,the possible damaged locations are determined by using the damage index and the characteristics of the analytical model itself,and the extent of damage for those substructures identified at stage I is estimated in the second stage by using a second-order eigen-sensitivity approximation method. The main contribution of this paper is to test the two-stage method by using the real dynamic data of a complicated spatial model structure with limited sensors. The analysis results indicate that the two-stage approach is ableto detect the location of both damage cases,only the severity of brace damage cases can be assessed,and the reasonable analytical model is critical for successful damage detection.

External blast load factors for dome structures based on reliability

Dome structures have been used extensively for industrial,residential,and military infrastructure.Therefore,it is necessary to understand the damage risk potential for such structures for blast-resistant design considerations.This paper investigates the effect of blast load variability on the design value and the structural dynamic response.Therefore,the sources of uncertainty in the external blast load on dome structures were discussed firstly.Then based on the probabilistic blast load model for the dome,the rationality of a deterministic mass-increase safety method was assessed.It was found that previous deterministic design method cannot provide a consistent and sound assurance factor or reliability index on the entire dome roof.In addition,it was also proved that the assurance-based load method fails to ensure compliance with structural safety design standards on the dome roof when compared with the reliability-based blast method.A sensitivity analysis on the probabilistic blast load was conducted,and the results indicate that stand-off distance and explosive mass both act as dominant sources to influence the mean and variability of blast load.Therefore,based on the Latin hypercube sampling method,a reliability-based external blast load factor technique was proposed.This technique was further used to estimate structural damage levels of a single-layer reticulated dome under different reliability requirements,associated with a low,medium,and high level of protection grades for a specific explosion scenario,and it indicated that this technique can be useful in the building design to achieve a higher structural anti-explosion capacity.This study herein can serve as a reference for the calculation method of designed blast load.

“Standby” EMT and “immune cell trapping” structure as novel mechanisms for limiting neuronal damage after CNS injury

The central nervous system （CNS） contains the two most important organs, the brain and spinal cord, for the orchestration of the mental and physical activities of life. Because of its importance, the human body has evolved barrier systems to protect CNS tissue from the external environment. This barrier is a membrane composed of tightly apposed cells and is selectively permeable to specific molecules by way of membrane transporters.

Damage Effects of Overload Axes on Pavement Structures

This paper established the axle load distribution model of overload axes by practical axle-meter investigations. To study the effects of overload axes on pavement distress, deflection and deflection basin tests with axle load from 60kN to 190kN were conducted on different pavement structures. The relationship between axle load and its deflection as well as its deflection basin curvature was obtained by statistical analyses. A methodology for deriving the equivalent conversion factors of overload axes to equivalent standard axle loads (ESAL) of 100kN is developed, obtaining the relationship between the equivalent conversion factors and the axle loads. Comparing the calculated defiections with the measured deflections, that elastic layered system theory is suitable for analyzing overload vehicles was verified. Consequently, the stresses and strains caused by overload axes were calculated by elastic layered system theory. The results showed that overload axes led to greater stresses and strains causing premature pavement fatigue distress. To guarantee the expected performance in overload axes pavement, the structure thickness needed increasing was obtained. The results are of referential values in the control of semi-rigid pavement overloadings.

Damage Characterization of Composite Structures Using Difference Peak Signal-to-Noise Ratio as a Function of Variable Wavelets (ΔPSNR-ΔW)

A novel approach employs the principles of medical image analysis using Wavelet Transform (WT) and Difference Peak Signal-to-Noise Ratio (ΔPSNR). Both techniques are combined as a function of different decomposing levels of wavelets and various image search through and slicing levels, which is implemented under MATLAB environment. In this new approach, the structural change due to damage in the component or the presence of foreign bodies appearing in an image taken for a specific structure is uncovered with its extent determined after applying the search through algorithm. Such alteration of the composite structure, which could be masked by the presence of noise, is accounted for using combined WT and PSNR. Effect of Artifacts and Blurring caused by different wavelet types is investigated before choosing an appropriate wavelet, namely Sym8. This new approach, which also reduces the required layers of search within an image, produces a pattern matrix per damaged area and is an excellent way in tracing and modeling damage in structures with ability to predict effects of further damage on components and further application to artificial limbs that could suffer damage and affect users mobility.

Structural Damage Identification Using Ensemble Deep Convolutional Neural Network Models

The existing strategy for evaluating the damage condition of structures mostly focuses on feedback supplied by traditional visualmethods,which may result in an unreliable damage characterization due to inspector subjectivity or insufficient level of expertise.As a result,a robust,reliable,and repeatable method of damage identification is required.Ensemble learning algorithms for identifying structural damage are evaluated in this article,which use deep convolutional neural networks,including simple averaging,integrated stacking,separate stacking,and hybridweighted averaging ensemble and differential evolution(WAE-DE)ensemblemodels.Damage identification is carried out on three types of damage.The proposed algorithms are used to analyze the damage of 4585 structural images.The effectiveness of the ensemble learning techniques is evaluated using the confusion matrix.For the testing dataset,the confusion matrix achieved an accuracy of 94 percent and a minimum recall of 92 percent for the best model(WAE-DE)in distinguishing damage types as flexural,shear,combined,or undamaged.

Damage assessment of aircraft wing subjected to blast wave with finite element method and artificial neural network tool

Damage assessment of the wing under blast wave is essential to the vulnerability reduction design of aircraft. This paper introduces a critical relative distance prediction method of aircraft wing damage based on the back-propagation artificial neural network(BP-ANN), which is trained by finite element simulation results. Moreover, the finite element method(FEM) for wing blast damage simulation has been validated by ground explosion tests and further used for damage mode determination and damage characteristics analysis. The analysis results indicate that the wing is more likely to be damaged when the root is struck from vertical directions than others for a small charge. With the increase of TNT equivalent charge, the main damage mode of the wing gradually changes from the local skin tearing to overall structural deformation and the overpressure threshold of wing damage decreases rapidly. Compared to the FEM-based damage assessment, the BP-ANN-based method can predict the wing damage under a random blast wave with an average relative error of 4.78%. The proposed method and conclusions can be used as a reference for damage assessment under blast wave and low-vulnerability design of aircraft structures.

Analysis of Concrete Crack Treatment Technologies in Buildings

With the continuous development of civil engineering,concrete crack treatment technology has become an important research field.This paper proposes treatment techniques for different types of cracks,including the prevention and repair of surface cracks,the reinforcement and grouting of structural cracks,and the design and construction of controlled cracks through the analysis of the causes and classification of concrete cracks.The methods and suggestions proposed in this paper are practical and can improve the quality and safety of buildings.

Simulation of the Whole Process of Ship-Bridge Collision

The simulation of the whole ship-bridge collision process can be effectively carried out by nonlinear dynamic finite element method. Based on the simple description of the theory, a scenario of a 40000 DWT oil tanker colliding with a bridge across the Yangtze River is designed for simulation. The technology of structure modeling and the determination of related parameters are introduced. The deformation of the bulb bow, the history,of collision force change, the exchange of collision energy and the stress distribution. of the bridge pier-are described in detail, which: are of great value to bridge design and bridge pier damage estimation. mechanical characters in the process of ship-bridge collision are described. More accurate results can be produced by finite element method than that by empirical formulas and simplified analytical methods.

Field reconnaissance of the 2007 Niigata-Chuetsu Oki earthquake

As part of the 2007 Tri-Center Field Mission to Japan, a reconnaissance team comprised of fourteen graduate students and three faculty members from three U.S. earthquake engineering research centers, namely, Multidisciplinary Center for Earthquake Engineering Research （MCEER）, Mid-America Earthquake Center （MAE）, and Pacific Earthquake Engineering Research Center （PEER）, undertook a reconnaissance visit to the affected area shortly after the 2007 Niigata- Chuetsu Oki earthquake. This mission provided an opportunity to review the nature of the earthquake damage that occurred, as well as to assess the significance of the damage from an educational perspective. This paper reports on the seismological characteristics of the earthquake, preliminary findings of geotechnical and structural damage, and the causes of the observed failures or collapses. In addition, economic and socio-economic considerations and experiences to enhance earthquake resilience are presented.

Some considerations on the physical mea-sure of seismic intensity

The study on seismic intensity can be traced prior to the time that modern seismology was established. In its early stage the seismic intensity was designed to serve as a measure in scaling the severity of earthquake damage to civil engineering and environmental structures. Also the seismic intensity is usually assigned by engineers and seismologists with one or two characteristic parameters of earthquake ground motions to reflect earthquake damage potential so as to be able to serve as an input earthquake load for seismic design of structures. So choosing a proper parameter to reflect the action of seismic intensity is the main objective of the research on physical measure of seismic intensity. However, since various kinds of structures have quite different damage mechanisms, there will exist great differences in damages to different structures located at the same area during the same earthquake. Particularly, in some cases, quite different damages have happened even to the structures of same kind due to many other factors such as different construction materials, different configurations or on the different types of sites where structures located. In addition, the ground motion parameters, which result in damage to structures, are not the single peak value of ground motion. Hence, this paper emphasizes that the research on new physical measure of seismic intensity should not only consider the structural characteristics but also take into account other parameters such as duration, energy of ground motion and so on. In particular, as the physical measures of intensity, different ground motion parameter should be adopted for different structures.

Analysis of nonlinear vibration for symmetric angle-ply laminated viscoelastic plates with damage

The behavior of nonlinear vibration for symmetric angle-ply laminated plates including the material viscoelasticity and damage evolution is investigated. By employing the von Karman＇s nonlinear theory, strain energy equivalence principle and Boltzmann superposition principle, a set of governing equations of nonlinear integro-differential type are derived. By applying the finite difference method, Newmark method and iterative procedure, the governing equations are solved. The effects of loading amplitudes, exciting frequencies and different ply orientations on the critical time to failure initiation and nonlinear vibration amplitudes of the structures are discussed. Numerical results are presented for the different parameters and compared with the available data.

THE INVESTIGATION OF THE METAL DAMAGE AT THE CREEP BY THE METHOD OF ELECTRICAL RESISTANCE MEASURING

In this paper the method of damage measurement of metal structure at the creep is proposed.In contrast to other methods,it allows the measurement of this damage to be carried out in the process of creep test without unloading and cooling of specimens.Experimental damage curves during creep are obtained as a result of test data processing by the suggested method.The analysis of these curves leads to a conclusion that the material damage at repture is monotonically decreasing function of the applied stress.This conclusion is an experimental verification of the theoretical result,obtained earlier.