Quantitative Damage Estimation Research Articles

Post-earthquake effects on the seismic performance of concrete gravity dams

Seismic damage assessment of concrete gravity dams is a challenging task due to the difficulty in establishing the damage states in relation to target performance levels. Post-seismic loading and uplift in cracking is generally not considered in this complex assessment and the effects are not clear. A quantitative damage estimation approach considering post-earthquake effects is proposed in this work to investigate this issue. A novel procedure to include post-earthquake effects on the monolith cracking was proposed in which demands from the aftershocks and uplift are assessed on the cracked state after the main event. Damage state was quantified in terms of the extent of crack propagation on the dam monolith. Categorising performance as such, the effects of post-earthquake factors were investigated on three representative systems in two steps. First, over 2000 nonlinear time history analyses were conducted to obtain damage states for the main shaking event. Then, the change in these states due to the effect of post-earthquake factors, including water pressure penetrating the cracks and aftershocks, were quantified. The results, as well as the methodology proposed, can serve organisations managing dam stock risk in re-assessment of seismic analysis results considering post-earthquake effects.

Disaster damage assessment based on fine-grained topics in social media

Social media data have been widely used to enrich human-centric information for situational awareness and disaster assessment. Owing to the granularity of topics detected from disaster-related contents, the effectiveness of social media in reflecting disaster losses is still limited. To address this limitation, this study developed a methodology for assessing disaster losses using social media data, which was composed of data preprocessing, fine-grained topic extraction, and quantitative damage estimation. The proposed methodology was demonstrated in a case study of Typhoons Hato & Pakhar, which caused persistent damage in southern China from August 22 to August 30, 2017. The results highlighted the capability of the proposed methodology in using fine-grained topics to assess disaster losses, e.g., the disaster losses were significantly correlated with infrastructure damage-related topics. The study provided useful insights in disaster damage assessment through the fine-grained topics in social media.

Solving the problem of risk synthesis as part of infrastructure facility management

Aim . Infrastructure facility management involves many decision-making problems that require estimating alternatives in the absence of clear criteria. Sufficiently common are problems that require the consideration of various numbers of factors. Those factors normally belong to different fields of knowledge and require the involvement of subject-area experts. Thus, for instance, the estimation of infrastructure facilities may involve economists, experts in land law, environment, logistics, design engineers and other specialists. The problem is often complicated by the existence of many alternatives. In such cases, it is difficult to organize even the initial expert evaluation in order to reduce the number of options for subsequent consideration. The paper primarily aims to develop a model of evaluation of the criteria that have an effect on the advisability of modernization of an infrastructure facility allowing to take into account factors from various fields of knowledge, as well as to elaborate a method of simplifying the process of evaluation of large numbers of alternative options. Therewith, such estimates can be expressed in various formats: both quantitatively and qualitatively. Such approaches have found application as part of the problem of ranking of airports as part of selection of candidates for inclusion into the Moscow air cluster (MAC). The specificity of this problem consists in the large set of various factors to be taken into account, as well as the great number of options, over 30 airports within 300 kilometers of Moscow. Methods . The risk synthesis model was used that relies on expert data that characterize the criteria that have an effect on the sought risk, as well as the values of damage for each facility by the given criteria. The criteria were estimated using a method based on pairwise comparisons allowing experts to define fuzzy and incomplete estimates of the preferability of the compared options. Damage estimation was done using the method of conversion of qualitative estimates into quantitative ones, as well as scaling of quantitative data into quantitative estimates of damage. Results . Implementing the ideas set forth in this paper allowed defining the contribution of eleven criteria that have an effect on the goals associated with relieving the MAC workload. Based on those criteria, specific risks for airports within 300 kilometers of Moscow were evaluated, and integral risks of modernization of each airport were obtained. The airports were then rated in terms of the integral risk of modernization. Conclusion . The suggested method is universal and can be used for decision-making under uncertainty in those domains where it is required to involve experts of various qualification and level of subject-matter knowledge, as well as accounting for many factors along with a great diversity of options.

Friction and wear behaviour of Ni-Cr-B hardface coating on 316LN stainless steel in liquid sodium at elevated temperature

The sliding friction and wear behaviour of Ni-Cr-B hardface coating made on 316LN stainless steel were evaluated in liquid sodium at 823 K by using a fabricated reciprocating-type tribometer. The test parameters have been selected based on operational conditions prevailing in the Indian sodium cooled fast breeder reactors (FBRs). Accordingly, the tests were carried out at sliding speeds of 2 and 16 mm/s under contact stresses of 10 and 40 MPa respectively using Ni-Cr-B coated pin and disc specimens. The static and dynamic friction coefficients are found to be in the ranges of 0.03–0.07 and 0.01–0.02 respectively under the imposed test conditions. The estimated wear rates (WR) are found to be in the range of 0.62 × 10−12 − 3.07 × 10−12 m3/m; the magnitude of WR increases with increase in the contact stress. The examination of the worn disc specimens by confocal laser scanning microscopy indicated higher damage in specimens tested at 40 MPa compared to that in specimens tested at 10 MPa; the quantitative estimation of damage was made by the number of scars and their depth. These observations corroborate well with the morphological features of the worn surfaces of the pin specimens examined by scanning electron microscopy. The results unambiguously indicate superior friction coefficients and wear resistance of Ni-Cr-B coatings in liquid sodium compared to that in air under identical test conditions.

Proposal of Elements for Creating Scenarios for Those Needing Support During National Disasters

This study proposes elements for creating scenarios covering those needing support during a natural disaster, comprising: 1) coefficients for scenarios concerning those needing support during a disaster, and 2) quantitative damage estimation cases related to facilities for those needing support during a disaster. These elements have not been incorporated into conventional damage estimation. The scenarios were applied to Tokyo, which is assumed to be an area affected by earthquakes occurring directly beneath the Tokyo Metropolitan Area, to establish a support system and implement map training.

Application of AE rate-process analysis to damaged concrete structures due to earthquake

Turkey is located on such a seismically active region that many high-magnitude earthquakes have attacked the areas. Large number of reinforced concrete structures are collapsed or heavily damaged due to these earthquakes. It is crucial to evaluate the condition of the concrete structures in seismically active zones before and after the earthquake to decide whether the structure could continue its service for habitation or not. Consequently, quantitative damage estimation of concrete material is conducted by applying acoustic emission (AE) testing under unconfined uniaxial compression test of core samples taken from the concrete structures. Damaged concrete samples are examined based on fracturing behavior under unconfined compression. AE behavior of concrete under compression is dependent on the degree of damage and could be analyzed by the rate-process analysis. Core samples were collected from two reinforced concrete buildings damaged by Simav Earthquake that hit Kutahya City on May 19, 2011. In compression tests, compressive strengths and Young’s moduli of these samples were determined. After estimating Young’s modulus of the intact state from the correlation between AE rate and a damage parameter in each core, the damage levels of structures are quantitatively estimated.

Damage estimation of concrete canal due to earthquake effects by acoustic emission method

The Great East-Japan Earthquake hit Tohoku area in Japan on March 11, 2011. A large number of concrete structures were damaged due to the 9.0 magnitude earthquake of the Richter-scale. Prior to reconstruction and retrofit of these structures, damage evaluation of in situ concrete structures is now in urgent demand. In this concern, quantitative damage estimation of concrete is proposed to be performed, applying acoustic emission (AE) measurement in a uniaxial compression test of core samples. Generating behavior of AE events in the core test is quantitatively analyzed, based on the rate process theory, because notable discrepancy of AE activity is observed between damaged concrete and undamaged concrete. The damage is quantitatively defined by a scalar damage parameter in damage mechanics. Correlating AE rate with the damage parameter, quantitative estimation of damage is proposed in terms of the relative modulus of elasticity (E0/E*). Concrete core samples were taken from reinforced concrete columns of an existing canal in the both periods of pre and post the earthquake. Prior to the compression test, distribution of micro-cracks in a concrete-core sample was inspected by helical X-ray computed tomography (CT), which scans at 1-mm intervals. The results suggest that the damage of concrete could be quantitatively estimated from damage parameter E0/E* without knowing the original state of the concrete at construction. The static moduli E0/E* and dynamic moduli Ed/E* is closely correlated. A relation between AE rate and the damage parameters is correlated, and thus the earthquake damage of concrete is quantitatively estimated using AE.

Guided wave generation, sensing and damage detection using in-plane shear piezoelectric wafers

This work presents guided wave generation, sensing, and damage detection in metallic plates using in-plane shear (d36 type) piezoelectric wafers as actuators and sensors. The conventional lead zirconate titanate (PZT) based on induced in-plane normal strain (d31 type) has been widely used to excite and receive guided waves in plates, pipes or thin-walled structures. The d36 type of piezoelectric wafer, however, induces in-plane (or called face) shear deformation in the plane normal to its polarization direction. This form of electromechanical coupling generates more significant shear horizontal (SH) waves in certain wave propagation directions, whose amplitudes are much greater than those of Lamb waves. In this paper, an analysis of SH waves generated using in-plane shear electromechanical coupling is firstly presented, followed by a multiphysics finite element analysis for comparison purposes. Voltage responses of both the conventional d31 and the new d36 sensors are obtained for comparison purposes. Results indicate that this type of wafer has the potential to provide a simple quantitative estimation of damage in structural health monitoring.

Use of acoustic emission and X-ray computed tomography for damage evaluation of freeze-thawed concrete

As a detailed inspection of a concrete structure in service, core samples are usually drilled out and then mechanical properties are measured. In this study, damage estimation of concrete structures from core samples is developed, applying acoustic emission (AE) and X-ray computed tomography method. Concrete-core samples were taken from reinforced concrete of an existing canal. These samples are strongly damaged by freezing and thawing process. Crack distributions of concrete-core samples were inspected with helical Computerized Tomography (CT) scans, which were undertaken at 1-mm intervals. After helical CT scan, damage of testing samples was evaluated, based on fracturing behavior under compression and AE activity. AE behavior is dependent on the degree of damage, and could be approximated by applying the AE rate-process analysis and damage mechanics. AE generation behavior is associated with crack volume due to damage accumulation in concrete. The damage is quantitatively defined by a scalar damage parameter in damage mechanics. Applying the scalar damage parameter, quantitative estimation of damage is proposed in terms of relative modulus of elasticity which is named “durability index”. By calculating the durability index, the initial damage of samples is estimated from AE database. The decrease in mechanical properties could be evaluated by comparing the average CT number with the durability index, both of which are affected by internal cracks generated. Thus, the damage of concrete structures is quantitatively evaluated by AE and X-ray computed tomography method.

Plastic deformation and creep damage evaluations of type 316 austenitic stainless steels by EBSD

The inspection method of plastic and/or creep deformations has been required as the quantitative damage estimation procedure for structural components especially used in electric power plants. In this study, the method using electron backscatter diffraction (EBSD) was applied to the deformation and damage evaluation of austenitic stainless steels strained by tension or compression at room temperature and also tested in creep at high temperature. It was found that the value of Grain Average Misorientation (GAM) which showed the average misorientation for the whole observed area including over several dozen grains, was a very useful parameter for quantifying the microstructural change as either the plastic or creep strain increased. The unique linear correlation was obtained between GAM and plastic strain in tension and compression. For creep damage evaluation, the difference of grain average misorientation from the value of the unstrained specimen (ΔGAM) showed an excellent correlation with the inelastic strain below strain at which the tertiary creep began.

THE LIFE ASSESSMENT OF STEAM TURBINE ROTORS FOR FOSSIL POWER PLANTS

The operational mode of thermal power plants has been changed from base load to duty cycle. From the changeover, fossil power plants cannot avoid frequent thermal transient states, for example, start up and stop, which results in thermal fatigue damage at the heavy section components. The rotor is the highest capital cost component in a steam turbine and requires long outage for replacing with a new one. For an optimized power plant operational life, inspection management of the rotor is necessary. It is known in general that the start-up and shutdown operations greatly affect the steam turbine life. The start-up operational condition is especially severe because of the rapid temperature and rotational speed increase, which causes damage and reduction of life of the main components life of the steam turbine. The start-up stress of a rotor which is directly related to life is composed of thermal and rotational stresses. The thermal stress is due to the variation of steam flow temperature and rotational stress is due to the rotational speed of the turbine. In this paper, the analysis method for the start-up stress of a rotor is proposed, which considers simultaneously temperature and rotational speed transition, and includes a case study regarding a 500MW fossil power plant steam turbine rotor. Also, the method of quantitative damage estimation for fatigue-creep damage to operational conditions, is described. The method can be applied to find weak points for fatigue-creep damage. Using the method, total life consumption can be obtained, and can be also be used for determining future operational modes and life extension of old fossil power units.

Quantitative damage estimation of concrete by acoustic emission

Damage estimation of structural concrete from concrete samples is developed, combining acoustic emission (AE) measurement with damage mechanics. The AE activity of a concrete sample during a uniaxial compression test is quantitatively analyzed, based on the rate process theory. AE activity under compression is very high from low stress level in the concrete sample which contains a number of microcracks. In contrast, AE activity of sound concrete remains low until impending final failure. This discrepancy of AE activity is quantitatively estimated from the rate. Empirically, it is confirmed that the rate is substantially associated with pore volume that is responsible for the damage in concrete. Then, the damage is quantitatively defined by damage mechanics. Correlating the rate with the damage parameter, quantitative estimation of the damage is proposed. The applicability of the procedure is confirmed in concrete samples of controlled damage due to freezing and thawing. Furthermore, the procedure is applied to concrete-core samples taken from an existing bridge. The results suggest that the damage of concrete at the current (initial) state could be readily estimated from AE rate process analysis without knowing the original state of the concrete at construction.

ＡＥ法に基づいたコンリートの定量的損傷度評価法の考察

Quantitative estimation of damage in concrete is investigated, introducing acoustic emission (AE) and damage mechanics. The damage of concrete is quantitatively evaluated by carrying out AE measurement in the uni-axial compression test. It is clarified that the process of damage accumulation could be evaluated by the rate process analysis. A damage parameter is determined from damage mechanics, applying Loland's model to a stress-strain relation. Correlating the variation of the rate with the damage evolution, a procedure to estimate the damage parameter is developed. The feasibility of the procedure is demonstrated by concrete samples damaged due to the freezing and thawing process.

Inelastic Effects of Microcracking: A New Continuum Damage Model

Microcracking is an important mechanism of damage accumulation in stressed solids. Two contributions to deformation can be distinguished: modification of the bulk effective elastic behaviour as cracks are introduced; and accumulation of an inelastic offset for each crack on formation. Equivalent medium approximations consider the former. In this study we have developed a new formulation to model the latter. The change in strain energy at the instant of formation of each individual microcrack is used to calculate the incremental inelastic strain increase during monotonic loading. This leads to integral equations describing the damage state, in which stress and strain are functions of damage. The macroscopic behaviour is path dependent. We obtain an explicit form of the stress-strain relation as a function of both intrinsic and extrinsic variables (damage and loading history) in order to test the model using experimental data for uniaxial tests on rock samples. Quantitative damage estimation is made through monitoring acoustic emissions emitted as microcracks form, which are related to crack dimensions through an independently determined scaling relation. The new model successfully reproduces the experimental stress-strain behaviour through failure, and also allows secondary effects, such as residual strain or hysteresis to be modelled, which is not possible with the equivalent elastic medium approach. The results suggest that (a) the incremental damage approach is needed to fully model behaviour in compression; (b) inelastic effects arising from cracking must be considered as well as modifications to the sample stiffness; and (c) acoustic emission parameters can be used in quantitative modelling of inelastic behaviour of cracked solids.

A synthesis of survey results: The Extent of Forest Decline in Europe

During the last ten years, the concern about forest decline attributable to air pollutants has increased dramatically. In the early days of industrialization, symptoms of damage were evident on trees in the vicinity of smokestacks. However, the problem gained wide publicity only in the early 1980s when the first quantitative estimates of damage were made in some European countries. The estimates, based sometimes on expert judgment and sometimes on statistically valid surveys, were made with varying degrees of precision, and the definition of damage were different among countries. Only recently have surveys of the extent of forest damage throughout Europe been more consistently based on statistically sound measurements, so that it is now possible to collect and synthesize substantial quantities of data on the extent of the phenomenon of forest decline in Europe. The objectives of this article are: to summarize current data on the extent of forest decline for as many European countries as possible, to draw conclusions about the significance of forest decline in the context of forest resources and annual fellings of the countries, and to draw conclusions about the improved quality and consistency of data on the extent of forest decline.

PROTOTYPE TESTS ON RIPRAP UNDER RANDOM WAVE ATTACK

This paper describes the performance of test panels of riprap on an offshore island in the Wash estuary, UK, for the first 2h years after their construction, by which time all but one had failed. It outlines the methods used in obtaining and analysing data on stone size, wind, tides and waves. The techniques used in surveying the test panels for damage and the reduction of the survey data to yield quantitative estimates of damage are described. Comparisons are made between the damage to the riprap panels and what might have been estimated using laboratory data. Results do not support any scale effect causing riprap sized on laboratory data to be larger than necessary, and this conclusion is supported by the outcome of model tests carried out retrospectively by the Hydraulics Research Station (now HRS Ltd) at Wallingford, UK. Slope protection is sensitive not only to wave height and stone size but also to construction methods and, bearing in mind possible departures from the desired specification, a cautious approach to the design of riprap protection is advisable.

Improved Morphological Technique for Screening Potentially Ototoxic Compounds in Laboratory Animals

A technique is described for morphological examination of the organ of Corti which can be used in routine toxicological studies. This involves the dissection of a critical point-dried cochlea and examination of a surface preparation of the entire organ by scanning electron microscopy. The procedure is simple and far less time consuming than that previously used for light microscopy. Quantitative estimates of damage induced in the organ of Corti either by the administration of ototoxic compounds or as a response to noise-induced or age-related changes can be obtained. Details are given for the application of this technique to two species commonly used in toxicity studies. With minor modifications it could be applied to many other species of animal.

Quantitative Estimation of Damage to Tobacco Caused by the Leaf Eating Caterpillar, Prodenia litura F.

Abstract An experiment was conducted to obtain information on the estimation of the reduction of yield of bidi tobacco due to different degrees of infestation by leaf eating caterpillar, Prodenia litura F. It was found that the reduction in yield was to an extent of 23.4, 44.2 and 50.4 per cent when the plants were infested with 2, 4 and 8 larvae per plant respectively, which gave a financial loss of Rs. 489.60 to Rs. 1,053.45 per hectare at Rs. 1.50 per kg., the average price of tobacco during the years under experiment.