Levels Of Damage Severity Research Articles

Temperature effect on electromechanical admittance–based concrete structural health monitoring

Concrete structures in service are often subjected to environmental/operational temperature effects, which change their inherent properties and also inflict a challenge to their extrinsic monitoring systems. Recently, piezoelectric lead zirconate titanate (PZT)-based electromechanical admittance technique has been increasingly growing into an effective tool for concrete structural health monitoring; however, uncertainty in the changes of monitoring signals induced by temperature impact on concrete/PZT sensor would inevitably cause interference to structural damage detection, which adversely hinder its application from laboratory to engineering practice. This article, aiming at exploring the temperature effect on the electromechanical admittance–based concrete damage evaluation, primarily covered a series of theoretical/numerical analysis with rigorously experimental verifications. Three aspects of comparative studies were performed in theoretical/numerical analysis: (1) thermal-dependent parameters were inclusively evaluated in contribution to the electromechanical admittance characteristics via PZT-structure interaction models; (2) three-dimensional finite element analysis in multi-physics coupled field was employed to qualitatively assess the singular temperature effect on the electromechanical admittance behaviors of free-vibrated PZT, surface-bonded PZT/inside-embedded PZT coupled healthy concrete cubes; and (3) depending on the modeling of surface-bonded PZT-/inside-embedded PZT-cracked concrete cube, thermal effect on damage evaluation was addressed via quantification on the electromechanical admittance variations. In the experimental study, rigorous validation tests were carried out on a group of lab-scale concrete cubes, where surface-bonded PZT/inside-embedded PZT transducers were simultaneously employed for electromechanical admittance monitoring in view of thermal difference between concrete surface and its inner part. Correlation coefficient deviation value-based effective frequency shifts algorithm was also employed to compensate the temperature effect. Moreover, temperature effect was further testified on the monitoring of a full-scale shield-tunnel segment structure. Experimental results indicated that temperature triggered different behaviors of electromechanical admittance signatures for surface-bonded PZT/inside-embedded PZT transducers and contaminated the electromechanical admittance responses for damage detection. Structural damage severity level can be disadvantageously amplified by temperature increment even if under the same damage scenarios.

Validation of Satellite Observations of Storm Damage to Cropland with Digital Photographs

ABSTRACTSevere storm events that include hail and wind often cause widespread contiguous swaths of damage; however, their occurrence is typically documented at individual and disjointed locations. Satellite-derived products, such as the normalized difference vegetation index (NDVI), can provide a more spatially uniform look at the extent of these events, particularly in rural or remote areas. The utility of incorporating satellite-based products into the damage identification and documentation process was assessed through high-resolution ground surveys, which included digital photographs, to classify three levels of cropland damage for three severe hail/wind events occurring in the Great Plains during the summer of 2014. Pre- and postevent NDVI values at the photograph locations were calculated using surface reflectance values from the Moderate Resolution Imaging Spectroradiometer (MODIS) and grouped by damage severity level. In general, more severe crop damage displayed a lower NDVI in the postevent imagery compared to undamaged crops. Additionally, the difference in the median NDVI between the pre- and postevent images was statistically significant between the damage categories with similar trends observed across the three summertime events. Thus, satellite-derived products should be promoted as a valuable tool for the initial assessment of damage severity and extent to agricultural crops and should be integrated when possible into the current hazard documentation process as a supplement to the currently available point-based observations of storm damage.

Pattern recognition framework using asynchronous discrete binary data for condition and damage assessment in plate-like structures

Recent advances in energy harvesting technologies have led to the evolution of self-powered structural health monitoring techniques that are energy-efficient. Concurrent to the emergence of self-powered sensing has been the development of power-efficient data communication protocols. One such technology is an energy-aware pulse communication architecture that employs ultrasonic pulses through the material substrate for information forwarding. This results in limited discrete binary data that raises the need for new data analysis methods for structural health monitoring purposes. A pattern recognition framework that allows interpretation of the resulting asynchronous discrete binary data for condition and damage assessment in plate-like structures is presented in this article. The proposed pattern recognition framework is based on integration of image-based pattern recognition using anomaly detection, a pattern anomaly measure, a focal density concept, and the k-nearest neighbor algorithm. Using numerical simulations, damage indication parameters were determined from the strain response of dynamically loaded plates. Simulated test cases considering different levels of damage severity, single and multiple damage regions, loading conditions, and measurement noise were studied to evaluate the effectiveness and robustness of the strategy. Furthermore, the effect of sensor density on the proposed strategy was explored. Results demonstrate satisfactory performance and robustness of the proposed pattern recognition framework for localized damage detection in plate-like structures using limited and low-resolution discrete binary data.

Novelty Detection in a Cantilever Beam using Extreme Function Theory

Damage detection and localisation in beam-like structures using mode shape features is well-established in the research community. It is known that by inserting a localised anomaly in a cantilever beam, such as a crack, its mode shapes diverge from the usual deflection path. These novelties can hence be detected by a machine-learner trained exclusively on the modal data taken from the pristine beam. Nevertheless, a major issue in current practices regards discerning between damage-related outliers and simple noise in observations, avoiding false alarms. Extreme functions are here introduced as a viable mean of comparison. By combining Extreme Value Theory (EVT) and Gaussian Process (GP) Regression, one can investigate functions as a whole rather than focusing on their constituent data points. Indeed, n discrete observations of a mode shape sampled at D points can be assumed as 1-dimensional sets of n randomly distributed observations. From any given point it is then possible to define its Probability Density Function (PDF) and the Cumulative Density Function (CDF), whose minima, according to the EVT, belong to one of three feasible extreme distributions - Weibull, Frechet or Gumbel. Thus, these functions - intended as vectors of sampled data - can be compared and classified. Anomalous displacement values that could indicate the presence of a crack are therefore identified and related to damage. In this paper, the effectiveness of the proposed methodology is verified on numerically-simulated noisy data, considering several crack locations, levels of damage severity (i.e., depths of the crack) and signal-to-noise ratios.

Damage Detection in Active Suspension Bridges: An Experimental Investigation.

This paper considers a Hilbert marginal spectrum-based approach to health monitoring of active suspension bridge hangers. The paper proposes to takes advantage of the presence of active cables and use them as an excitation mean of the bridge, while they are used for active damping. The Hilbert–Huang transform is used to calculate the Hilbert marginal spectrum and establish a damage index for each hanger of the suspension bridge. The paper aims to investigate the method experimentally, through a series of damage scenarios, on a laboratory suspension bridge mock-up equipped with four active cables; each active cable is made of a displacement actuator collocated with a force sensor. Different locations and levels of damage severity are implemented. For the first time, the investigation demonstrates experimentally the effectiveness of the technique, as well as its limitations, to detect and locate the damage in hangers of a suspension bridge.

Computational model for supporting SHM systems design: Damage identification via numerical analyses

This work presents a computational model to simulate thin structures monitored by piezoelectric sensors in order to support the design of SHM systems, which use vibration based methods. Thus, a new shell finite element model was proposed and implemented via a User ELement subroutine (UEL) into the commercial package ABAQUS™. This model was based on a modified First Order Shear Theory (FOST) for piezoelectric composite laminates. After that, damaged cantilever beams with two piezoelectric sensors in different positions were investigated by using experimental analyses and the proposed computational model. A maximum difference in the magnitude of the FRFs between numerical and experimental analyses of 7.45% was found near the resonance regions. For damage identification, different levels of damage severity were evaluated by seven damage metrics, including one proposed by the present authors. Numerical and experimental damage metrics values were compared, showing a good correlation in terms of tendency. Finally, based on comparisons of numerical and experimental results, it is shown a discussion about the potentials and limitations of the proposed computational model to be used for supporting SHM systems design.

Mode shape-based damage detection in plate structure without baseline data

In this paper, a mode shape curvature-based method for detection and localization of damage in plate-like structures is described. The proposed algorithm requires only the mode shape curvature data of the damaged structure. The damage index is defined as the absolute difference between the measured curvature of the damaged structure and the smoothed polynomial representing the curvature of the healthy structure. To examine the advantages and limitations of the proposed method, several sets of numerical simulations are carried out. Simulated test cases considering different levels of damage severity, measurement noise and sensor sparsity are studied to evaluate the robustness of the method under the noisy experimental data and limited sensor data. Applicability and effectiveness of the proposed damage detection method are further demonstrated experimentally on an aluminium plate containing mill-cut damage. The modal frequencies and the corresponding mode shapes are obtained via finite element models for numerical simulations and by using a scanning laser vibrometer for the experimental study. Copyright © 2016 John Wiley & Sons, Ltd.

Stochastic evaluation of mortgage default losses resulting from flood damages and different mortgage arrangements for post-Katrina Louisiana houses

Purpose – The purpose of this paper is to investigate the total number of mortgage default occurrence possibilities and monetary damage amounts to the sampled properties due to the excessive flooding caused by natural disasters. Mortgage default loss assessments due to natural catastrophic events are of great interest to lenders, insurance firms, forensic engineering professionals, inspecting agencies and the federal and state government planning officials and risk-mitigating teams. Design/methodology/approach – In this study, a stochastic methodology is used to address the risk of mortgage default losses and the homeowners’ investment returns, given: damage severity levels of hurricane floods and the mortgage types and arrangements on selected properties. Nine different houses, with various mortgage arrangements, located in different flood damage zones were investigated three years after Hurricane Katrina. To quantify the flood damage risk values which are compared with exceeding damage probabilities, the Poisson’s distribution is used through performing random variable analysis walks for each property during each house’s mortgage life cycle. Findings – Henceforth, through introduction and constructing the “Zonal Damage Matrix” for the investigated houses, the total number of mortgage default occurrence possibilities and monetary damage amounts to the properties are calculated for each exceeding flood. Thereafter, the homeowners’ net equity values and the investment returns are estimated for risk identification and evaluation purposes. Originality/value – For each of the sampled houses, the probability of mortgage defaults and the homeowners’ net equity values are estimated using Poisson’s distribution based on 60,000 randomly generated numbers to construct ten different hazard-related default scenarios for each property over the 30-year mortgage life cycle. The investment returns are therefore estimated for risk identification and evaluation purposes.

Exploring the effects of biophysical parameters on the spatial pattern of rare cold damage to mangrove forests

In recognition of the role of mangrove forests as natural barriers and bio-shields in protecting coastal population and property in the aftermath of the 2004 Indian Ocean tsunami disaster, many Asian countries have launched various projects to restore and conserve mangrove trees. The growth and vitality condition of mangroves may be negatively influenced by various anthropogenic and natural disturbances and stresses, such as cold weather events. This paper represents the first attempt to map the cold damage to mangroves in the tropical zone of Southern China using high resolution multispectral satellite imagery. In this study, the spatial distribution of severity level of cold damage to mangroves imposed by a rare blizzard in Southern China during early 2008 has been mapped and analyzed using IKONOS image. An object-oriented classification applied to the images achieved an overall accuracy of 90.9% for classifying mangroves into three categories: undamaged, damaged, and dead. Of the total 287.30ha of mapped mangroves, approximately 51.1% were damaged or died due to the cold stress of the blizzard. These results have been verified by more recent WorldView-II images. Furthermore, we explored the associations between the cold damage severity level of mangroves and climate and landscape factors, including elevation, surface slope, aspect, wind direction and velocity, wind shadow effect, and tree height. The surface topographical variables are derived from the ASTER Global DEM. The analysis results suggest that wind direction, terrain topography, and proximity to ocean are important local environmental factors controlling the vulnerability of mangroves to cold damage. Most damaged mangroves were located near the open sea, as a result of a possible edge exposure effect. The damage to the mangroves on the leeward side of a hill was also minimal. Such knowledge of climate and landscape controls can offer insight on how to better restore and protect the mangrove forest in the future.

Joint damage identification using Improved Radial Basis Function (IRBF) networks in frequency and time domain

In this paper, a novel two-stage Improved Radial Basis Function (IRBF) neural network technique is proposed to predict the joint damage of a fifty member frame structure with semi-rigid connections in both frequency and time domain. The effective input patterns as normalized design signature indices (NDSIs) in frequency domain and acceleration responses in time domain are simulated numerically from finite element analysis (FEA) by considering different levels of damage severity using Latin hypercube sampling (LHS) technique. The conventional RBF network is used in the first stage of IRBF network and in the second stage reduced search space moving technique is employed for accurate prediction with less than 3% error. The numerical simulation of the substructural joint damage identification of a fifty member frame structure with and without addition of 5% Gaussian random noise to the input patterns is presented and compared with conventional CPN–BPN hybrid method. The two-stage IRBF method is found to be superior in accuracy to conventional hybrid methods as well as to conventional RBF method. An important benefit of the proposed novel IRBF method is the significant reduction in the computational time with good accuracy of joint damage identification.

Compression after impact strength of thin laminates with various percentage of 0° plies

Conventional wisdom dictates that adding more 0° plies in the load-bearing direction of a laminate will increase its stiffness and strength. While this is true for undamaged laminates, the compression strength of laminates with impact damage may not be as straightforward. In this study, compression after impact strengths of relatively thin laminates with 25%, 33% or 50% of plies aligned in the 0° load-bearing direction were measured for three different damage severity levels. Results show that the increase in compression strength of the laminates with a higher percentage of plies in the 0° direction is lessened as impact damage severity increases indicating that a laminate that is stronger in compression when undamaged may not be stronger in compression when impact damage is accounted for.

Building pounding damage observed in the 2011 Christchurch earthquake

SUMMARYBuilding pounding damages observed in the February 2011 Christchurch earthquake are described in this paper. The extent and severity of pounding damage is presented based on a street survey of Christchurch's central business district. Six damage severity levels and two confidence levels are defined to classify the observed damage. Generally, pounding was observed to be a secondary effect. However, over 6% of the total surveyed buildings were observed to have significant or greater pounding damage. Examples of typical and exceptional pounding damage are identified and discussed. Extensive pounding damage was observed in low‐rise unreinforced masonry buildings that were constructed with no building separation. Modern buildings were also endangered by pounding when building separations were infilled with solid architectural flashings. The damage caused by these flashings was readily preventable. The observed pounding damage is compared to that observed in the September 2010 Darfield earthquake to explore if the damage could have been predicted. It is found that pounding prone buildings can be identified with reasonable accuracy by comparing configurations to characteristics previously noted by researchers. However, detailed pounding damage patterns cannot currently be precisely predicted by these methods. Copyright © 2011 John Wiley & Sons, Ltd.

The involvement of key DNA repair pathways in the formation of chromosome rearrangements in embryonic stem cells

It is vital that embryonic stem (ES) cells, which give rise to the diverse tissues of the mature organism, maintain genetic stability. To understand mechanisms for the prevention and causation of chromosomal instability, we have used spectral karyotyping (SKY) to analyse ES cells from wild-type and repair-gene knockout mice. We chose cells deficient in Ku70 (DNA end joining), Xrcc2 (gene conversion), Ercc1 (single-strand annealing) and Csb (transcription-coupled repair) to represent potentially-important DNA repair pathways, plus an Xpc-deficient line to examine loss of global nucleotide excision repair (NER). Spontaneous and radiation (X-ray or α-particle)-induced chromosome changes were assessed to measure the influence of different levels of damage severity on response. We show that most repair pathways (except for global NER) protect against chromosome changes induced by ionizing radiations, while only homology-dependent pathways protect against spontaneous chromosomal change in ES cells. However, for a given level of damage, the prevalence of different types of changes alters in the different repair-deficient lines. Thus, loss of Ercc1, Csb or Ku70 leads to increased fragment formation, but loss of Xrcc2 promotes exchanges between chromosomes. Strikingly, we found that loss of the Csb gene function specifically protects ES cells from complex exchanges, suggesting a role for transcription-associated events in complex exchange formation.

Determination of hygrothermal ageing effects in sandwich construction joints using thermoelastic stress analysis

Typical marine sandwich construction composite tee joints have been exposed to a hygrothermal ageing environment and were simultaneously subjected to one of three loading conditions: free standing, static compression and cyclic compression. The joints were removed from their environment for experimental evaluation after 60 and 144 days of ageing. The experimental approach adopted for this work was thermoelastic stress analysis (TSA), using the DeltaTherm equipment to obtain full-field thermoelastic data from the region of interest in the structural specimens. Readings from the aged joints have been obtained and compared to reference readings taken from an unaged joint. The implications of the changes in thermoelastic signal in specific regions of the joints have been discussed. The work shows the potential for using TSA to detect material changes due to hygrothermal ageing and for establishing damage severity levels resulting from mechanical loading during hygrothermal exposure.

An analysis of motorcycle injury and vehicle damage severity using ordered probit models

Problem: Motorcycles constitute about 19% of all motorized vehicles in Singapore and are generally overrepresented in traffic accidents, accounting for 40% of total fatalities. Method: In this paper, an ordered probit model is used to examine factors that affect the injury severity of motorcycle accidents and the severity of damage to the vehicle for those crashes. Nine years of motorcycle accident data were obtained for Singapore through police reports. These data included categorical assessments of the severity of accidents based on three levels. Damage severity to the vehicle was also assessed and categorized into four levels. Categorical data of this type are best analyzed using ordered probit models because they require no assumptions regarding the ordinality of the dependent variable, which in this case is the severity score. Various models are examined to determine what factors are related to increased injury and damage severity of motorcycle accidents. Results: Factors found to lead to increases in the probability of severe injuries include the motorcyclist having non-Singaporean nationality, increased engine capacity, headlight not turned on during daytime, collisions with pedestrians and stationary objects, driving during early morning hours, having a pillion passenger, and when the motorcyclist is determined to be at fault for the accident. Factors leading to increased probability of vehicle damage include some similar factors but also show some differences, such as less damage associated with pedestrian collisions and with female drivers. In addition, it was also found that both injury severity and vehicle damage severity levels are decreasing over time.

Empirical modeling of cutblock edge windthrow risk on Vancouver Island, Canada, using stand level information

Winter storms routinely damage stands along clearcut boundaries on Northern Vancouver Island, disrupting forest management plans. Empirical modelling of windthrow risk is more suitable than mechanistic modelling for the western hemlock ( Tsuga heterophylla (Raf.) Sarg.), redcedar ( Thuja plicata (Donn)) and amabilis fir ( Abies amabilis Forbes.) stands in this area which vary in composition, structure, density and age. Cutblock edge windthrow in a 900 km 2 study area was mapped using 1:15000 scale aerial photographs. A geographic information system (GIS) database for 3000–50 m long by 40 m deep cutblock edge segments was assembled using readily available topographic and inventory information. Logistic regression models for predicting probability of damage for various levels of damage severity were evaluated. Key variables in these models included site quality, stocking, boundary orientation, time since harvest and topographic exposure. The models correctly predicted the outcome of 71–76% of test segments, and adequately fit using χ 2 tests for test data grouped by stand characteristics. These models can be entered into GIS map calculations to produce landscape level maps of windthrow hazard, or into spreadsheets for evaluating the probability of damage for alternate cutblock design scenarios.