Changes In Structural Conditions Research Articles

Structural damage detection using low-rank matrix approximation and cointegration analysis

This paper proposes a novel approach of time series analysis to identify the potential changes in structural conditions, e.g., degradation owing to accumulated damage. Although the damage-sensitive features (DSFs) of structures depend on the environmental and operational conditions and thus vary over time, they usually have a common trend when the effects of environmental and operational variations (EOVs) are linear or quasi-linear. Therefore, cointegration analysis, which can combine several time series into a stationary residual purged of the common trend, is used to remove the effects of EOVs and assess the structural condition. The main contribution of this study is that a low rank matrix approximation (LRMA) algorithm is introduced to constrain the rank of the stacked DSF matrix, thereby suppressing the random errors inevitable in structural damage detection and both the linear and nonlinear effects induced by EOVs. The nonlinear effects have been observed in the identified natural frequency data of several bridges in service and cannot be easily handled by the general cointegration due to its linear nature. Another advantage of this process is that the missing entities in the DSF series can be automatically imputed, taking full advantage of incomplete data acquired for analysis. The effectiveness of the proposed method is demonstrated by using the benchmark data of the KW51 Railway Bridge in structural condition identification. Results indicate that the changes in the structural condition can be correctly detected despite the existence of random errors and nonlinear effects induced by EOVs. The proposed method can also work when only a small amount of incomplete data is available.

A change-point detection method for detecting and locating the abrupt changes in distributions of damage-sensitive features of SHM data, with application to structural condition assessment

Damage detection or structural condition assessment is an important objective of structural health monitoring (SHM). The damages or adverse changes in structural conditions can usually be manifested as pattern changes in damage-sensitive features (DSFs) extracted from SHM data; this enables us to shift damage detection to DSF change detection. Online monitoring can accumulate huge amounts of data, finding the changes from the massive DSF data through manual inspection is impractical; thus, automatic detection tools are required. If possible, relevant significance test is also desired to make a rational judgment on the existence of a change. In this sense, the change-point detection technique is an attractive choice, which is increasingly proved to be a powerful change detection tool in various SHM applications. However, existing change-point detection methods in SHM are mainly used for scalar or vector data, thus incapable of detecting changes in features represented by complex data, for example, the probability density functions (PDFs). Detecting abrupt changes in the distributions (represented by PDFs) of the DSF data is of crucial concern in structural condition assessment. However, relevant automatic diagnostic tools have not been well developed in the SHM community. To this end, a novel change-point detection method is developed in the functional data analytic framework for this task. The proposed approach has advantages in detecting changes for massive data and directly handling general PDFs. Considering that the major challenge in PDF-valued data analysis comes from the nonlinear constraints of PDFs, the PDFs are embedded into the Bayes space to develop the detection methodology by using the linear structure of the Bayes space. Comprehensive simulation studies are conducted to validate the effectiveness of the proposed method as well as demonstrate its superiority over the competing method. Finally, a case study involving cable condition assessment of a long-span bridge demonstrates its practical utility in SHM.

Shaking table tests on a masonry building monitored using smart bricks: Damage detection and localization

SummaryThe seismic behavior of unreinforced masonry buildings is typically characterized by premature brittle collapse mechanisms that can cause serious consequences for the protection of human lives and for the preservation of historical and cultural heritage. Structural health monitoring can be a powerful tool enabling a quick post‐earthquake assessment of the structure's performance, but its applications are still scarce as a consequence of the severe limitations affecting off‐the‐shelf sensing technologies, in terms of local nature of the measurements, costs, as well as long‐term behavior, installation, and maintenance. To overcome some of these limitations, the authors have recently proposed a new sensing technology, called “smart brick,” that is a durable clay brick doped with stainless steel microfibers, working as a smart strain sensor for masonry buildings. This paper presents the first full‐scale application of smart bricks, used for detecting and localizing progressive earthquake‐induced damage in an unreinforced masonry building subjected to shaking table tests. Smart bricks are employed to detect changes in load paths on masonry walls, comparing strain measurements acquired after each step of the seismic sequence with those referring to the undamaged structure. Experimental results are interpreted using a 3D finite element model built to reproduce the shaking table tests. Overall, the results demonstrate that the smart bricks can effectively reveal local permanent changes in structural conditions following a progressive damage, therefore being apt for earthquake‐induced damage detection and localization.

Direct democracy in mining conflicts in Latin America: mobilising against the La Colosa project in Colombia

ABSTRACT This article examines the conditions under which popular consultations serve as a means of protest against mining and the socio-political effects that result. Building on empirical research into the protests against the La Colosa gold mining project in Colombia, the analysis is rooted in social movement studies and democracy theory. It shows that the use of popular consultations is enabled by long-term political-institutional changes and short-term changes in structural conditions. The outcomes range from changes in project design to political agenda setting, and the opening of spaces for participation and public debate.

Cumulative effects of wildfires on forest dynamics in the eastern Cascade Mountains, USA.

Wildfires pose a unique challenge to conservation in fire-prone regions, yet few studies quantify the cumulative effects of wildfires on forest dynamics (i.e., changes in structural conditions) across landscape and regional scales. We assessed the contribution of wildfire to forest dynamics in the eastern Cascade Mountains, USA from 1985 to 2010 using imputed maps of forest structure (i.e., tree size and canopy cover) and remotely sensed burn severity maps. We addressed three questions: (1) How do dynamics differ between the region as a whole and the unburned portion of the region? (2) How do dynamics vary among vegetation zones differing in biophysical setting and historical fire frequency? (3) How have forest structural conditions changed in a network of late successional reserves (LSRs)? Wildfires affected 10% of forests in the region, but the cumulative effects at this scale were primarily slight losses of closed-canopy conditions and slight gains in open-canopy conditions. In the unburned portion of the region (the remaining 90%), closed-canopy conditions primarily increased despite other concurrent disturbances (e.g., harvest, insects). Although the effects of fire were largely dampened at the regional scale, landscape scale dynamics were far more variable. The warm ponderosa pine and cool mixed conifer zones experienced less fire than the region as a whole despite experiencing the most frequent fire historically. Open-canopy conditions increased slightly in the mixed conifer zone, but declined across the ponderosa pine zone even with wildfires. Wildfires burned 30% of the cold subalpine zone, which experienced the greatest increase in open-canopy conditions and losses of closed-canopy conditions. LSRs were more prone to wildfire than the region as a whole, and experienced slight declines in late seral conditions. Despite losses of late seral conditions, wildfires contributed to some conservation objectives by creating open habitats (e.g., sparse early seral and woodland conditions) that otherwise generally decreased in unburned landscapes despite management efforts to increase landscape diversity. This study demonstrates the potential for wildfires to contribute to regional scale conservation objectives, but implications for management and biodiversity at landscape scales vary geographically among biophysical settings, and are contingent upon historical dynamics and individual species habitat preferences.

Learning to learn differently

PurposeThis paper aims to investigate whether the formal and informal learning patterns of community health-care nurses changed in the wake of a reform that altered their work by introducing new patient groups, and to explore whether conditions in the new workplaces facilitated or impeded shifts in learning patterns.Design/methodology/approachData were collected through interviews with experienced nurses in community health care to learn whether and how they changed their learning patterns and the challenges they experienced in establishing new work practices.FindingsIn established learning patterns among nurses, the most experienced nurse passes on the knowledge to novices. These knowledge boundaries were challenged and they created new contexts and tasks calling for more cross-disciplinary cooperation. The informants acknowledged the need for formal and informal learning activities to change their learning pattern in addressing new knowledge challenges. Structural and cultural factors in community health care impeded changes in individual and collective learning patterns.Research limitations/implicationsThis paper reports a single case study. Further study is needed on how changes in structural and contextual conditions challenge the established formal and informal learning patterns.Practical implicationsIt is crucial that managers facilitate the development of new routines, structures and cultures to support individual initiatives and the growth of necessary changes in established practice to implement a new reform.Originality/valueThis study’s contribution to the literature primarily concerns how changes in structural conditions challenge formal and informal learning patterns, and the structural and cultural conditions for these learning patterns.

The Impact of Changed Structural Conditions on Regional Sustainable Mobility Planning in Norway

A primary impediment in achieving sustainable mobility objectives is the multi-level and cross-sectoral nature of land-use and transport planning. This paper investigates whether changes in structural conditions have affected the ability of Norwegian regional authorities to succeed in sustainable mobility planning. The effects of the changes were minor, as the national government acted in ways that undermined the power of regional authorities. By analysing the fine-grained inter-agency dynamics, this study contributes richer and more nuanced theoretical understandings of the challenges involved in sustainable transport planning. The new insights could assist discussions in many countries on how land-use and transport planning can be organized to facilitate more sustainable mobility patterns.

Extraordinary politics and durable reform: lessons from trade liberalisation in Estonia and Poland

ABSTRACTThis article analyses the significance of the period of extraordinary politics after the fall of communism for policy reform. It examines under what circumstances policy reforms enacted during such periods are durable by comparing trade liberalisation in Poland and Estonia in the early 1990s. The article relates this question to the historical institutionalist debate surrounding critical junctures, gradual change and the politics of stability and change. It argues that trade policy reform enacted during periods of extraordinary politics is most likely to be durable if it is associated with deeper changes in structural conditions, such as dominant ideas, interests and institutions.

Two decades of change in a field margin vegetation metacommunity as a result of field margin structure and management practice changes

Field margins have considerable ecological significance in agricultural landscapes by providing habitat and resources for farmland biodiversity. Few attempts have been made to examine the long term dynamics of multiple vegetation communities in field margins, at the landscape scale. In addition, drivers and processes governing such long term vegetation dynamics are poorly investigated. The aim of the study was to assess whether the diversity and composition of a field margin metacommunity have changed over the last two decades as a result of changes in both structural condition and management of field margins. In total, 309 field margins in north-western France, first surveyed in 1994, were resurveyed in 2015 by using the same protocol. Total species richness (gamma diversity) was stable over time while mean species richness per field margin (alpha diversity) increased. No difference in species composition dissimilarity (beta diversity) was recorded indicating that no biotic homogenization had occurred between 1994 and 2015. Species composition has shifted over time, with a decline of hemicryptophytes and an increase of shade-tolerant species. No change in Ellenberg nitrogen value was observed. Analysis of drivers revealed a significant influence of changes in the structural condition of field margins, i.e. the development of the tree layer, on vegetation diversity. Dominant height of vegetation and tree cover were highest in 2015 compared with 1994. This has likely been driven by a decline in intensity of field margin management. Despite changes in alpha diversity, the field margin metacommunity had a stable Clementsian structure over time, suggesting grouped distribution of species along environmental gradients. This study provides a rare example of the long term vegetation change in field margins in relation with margin structure and management changes, using permanent plots and diachronic data. Results highlight the need to maintain a variety of differently structured and managed field margins to preserve high plant diversity. They underline the need to place conservation strategies in the context of regional-scale processes to ensure the long-term conservation of field margin metacommunities.

Challenges in making an academic career in education sciences

The competitive university has brought about changes in structural conditions and created contradictions which are embedded in institutions. The present study is based on interviews with 42 early career researchers in the field of education sciences in Sweden. We analyse how members of this group handle career possibilities and limitations in relation to gender and to the structural ambivalence embedded in the higher education system. Our results illustrate that the structure of education sciences contains power relations and processes of differentiation, which give researchers different access to resources that can be used to handle structural ambivalence. This is illustrated in how, for example, women researchers, more than men, lack resources to solve the experienced tensions surrounding them, and therefore often work in areas where they are able to cope. Men researchers can often solve their career ambivalence by avoiding traps and gaining recognition, and are therefore able to advance.

Dynamic response mitigation of floating wind turbine platforms using tuned liquid column dampers.

In this paper, we experimentally study and compare the effects of three combinations of multiple tuned liquid column dampers (MTLCDs) on the dynamic performance of a model floating tension-leg platform (TLP) structure in a wave basin. The structural stability and safety of the floating structure during operation and maintenance is of concern for the performance of a renewable energy device that it might be supporting. The dynamic responses of the structure should thus be limited for these renewable energy devices to perform as intended. This issue is particularly important during the operation of a TLP in extreme weather conditions. Tuned liquid column dampers (TLCDs) can use the power of sloshing water to reduce surge motions of a floating TLP exposed to wind and waves. This paper demonstrates the potential of MTLCDs in reducing dynamic responses of a scaled TLP model through an experimental study. The potential of using output-only statistical markers for monitoring changes in structural conditions is also investigated through the application of a delay vector variance (DVV) marker for different conditions of control for the experiments.

EMANCIPATORY CITIZENSHIP EDUCATION IN ACTION: CREATIVE TEACHING/LEARNING OPTIONS (PART 2)

This is the second part of a two-part series on “Emancipatory citizenship education in action”, with a focus on the use of creative teaching and learning options with a group of students taking a course on Human Behaviour and the Social Environment. The student-centred teaching/learning strategies described in this paper allow students to actively engage in discourses of difference of various types, to develop an understanding of, and respect for diversities, to develop self-awareness, and awareness of self in relation to the broader socio-political and cultural world. The premise is that the development of such awareness and reflexivity, serves as a precursor to the recognition of the need to work toward change in structural conditions that maintian people in disadvantaged, marginalised and excluded positions.

The Political Economy of Participatory Democracy in Brazil: A Case Study of Lages, 1977–1982

J. Ricardo Tranjan’s “The Political Economy of Participatory Democracy in Brazil: A Case Study of Lages, 1977–1982” presents a historical, political-economic analysis of one of the precursory participatory municipal administrations in Brazil in the city of Lages, Santa Catarina. Tranjan considers how capitalist development may spur democratization processes by altering the balance of class power in favour of subordinate classes. This study of the Lages case demonstrates that including popular participation in local government was, at one point, a deliberate political move against one sector of the local ruling class, and was made possible by shifts in interclass power that resulted from changes in structural conditions. Tranjan’s political-economic analyses help us better understand the motivations of those pushing participatory reforms, the challenges they face, and the format of participatory initiatives.

Cointegration and why it works for SHM

One of the most fundamental problems in Structural Health Monitoring (SHM) is that of projecting out operational and environmental variations from measured feature data. The reason for this is that algorithms used for SHM to detect changes in structural condition should not raise alarms if the structure of interest changes because of benign operational or environmental variations. This is sometimes called the data normalisation problem. Many solutions to this problem have been proposed over the years, but a new approach that uses cointegration, a concept from the field of econometrics, appears to provide a very promising solution. The theory of cointegration is mathematically complex and its use is based on the holding of a number of assumptions on the time series to which it is applied. An interesting observation that has emerged from its applications to SHM data is that the approach works very well even though the aforementioned assumptions do not hold in general. The objective of the current paper is to discuss how the cointegration assumptions break down individually in the context of SHM and to explain why this does not invalidate the application of the algorithm.

Estimating Asset Deterioration and Life Expectancy by Using Levels of Service

As agencies have implemented maintenance quality assurance processes over the past 10 to 15 years, the agencies have also begun to amass valuable databases of condition and performance data, often expressed in terms of levels of service. These databases address a wide range of asset types, especially roadway and roadside features such as signs, pavement markings, traffic signals, lighting, culverts, sidewalks, and curbs. At the same time, element and condition state data have been gathered by most of the state departments of transportation for bridges and often for structures other than bridges. A few agencies have taken the next step in developing deterioration models to forecast changes in structure condition, either in the absence of maintenance activity or in response to specific agency actions or policies. The state of the practice in bridge deterioration modeling is a matter of active research but is increasingly becoming repeatable and relevant to asset management decision making. Moreover, some examples of bridge inspection and deterioration models already address a variety of nonbridge structures and a variety of performance concerns beyond physical deterioration. This study connects the level-of-service approach now frequently used in maintenance management with the quantitative forecasting of deterioration frequently used in bridge management. The result is a framework for prediction of levels of service and life expectancy that can be useful for management of all types of transportation assets.

The modal distribution method for statistical analysis of measured structural response

The newly proposed modal distribution method statistically quantifies overall differences between measured time-histories. In this method, power spectra of measured structural response are interpreted as collections of independent modal responses. Each modal response is isolated, re-scaled, and interpreted as a statistical distribution. Data-sets (windows in a measured time-history) are then compared using standard statistical methods, resulting in a quantitative significance level of the differences between power spectra. An example is presented to validate the new method and to quantify how long a time-history is required for the new method to meet confidence level requirements. The modal distribution method is found to be very effective at detecting subtle changes of mean modal frequencies, which may be used to infer changes in structural condition. The method is general and may find a broad variety of applications, but seems particularly well suited for structural health monitoring because it can be used to infer changes in structural condition from measured response data with only limited knowledge of the excitation.

The dynamic relationship between homicide rates and social, economic, and political factors from 1970 to 2000

After reaching their highest levels of the 20th century, homicide rates in the United States declined precipitously in the early 1990s. This study examines a number of factors that might have contributed to both the sharp increase and decline in homicide rates. We use a pooled cross-sectional time series model to assess the relationship between changes in structural conditions and the change in homicide rates over four decennial time points (1970, 1980, 1990, and 2000). We assess the extent to which structural covariates associated with social, economic and political conditions commonly used in homicide research (e.g., urban decay, poverty, and the weakening of family and social bonds) are related to the change in homicide rates. Along with these classic covariates, we incorporate some contemporary explanations (e.g., imprisonment rates and drug trafficking) that have been proposed to address the recent decline in urban homicide rates. Our results indicate that both classic and contemporary explanations are related to homicide trends over the last three decades of the 20th century. Specifically, changes in resource deprivation and in the relative size of the youth population are associated with changes in the homicide rate across these time points. Increased imprisonment is also significantly related to homicide changes. These findings lead us to conclude that efforts to understand the changing nature of homicide will require serious consideration, if not integration, of classic and contemporary explanations.

A Dynamic Model of Racial Competition, Racial Inequality, and Interracial Violence

Race relations and stratification literatures offer explicit expectations concerning interracial conflict. Causal arguments derived from these perspectives are examined in this study to explore their ability to explain interracial violence above and beyond criminological perspectives of economic deprivation and racial inequality. The vast majority of previous aggregate-level studies on violence are cross-sectional, ignoring the importance of a dynamic model that incorporates the influence of changing structural conditions in urban areas on interracial violence. We explore theories that incorporate dynamic explanations for the influence of structural factors related to crime as well as racial conflict and employ a methodological approach that models the change in structural conditions for rare events such as interracial homicide. We find that changes between 1980 and 1990 in urban Black and Hispanic population composition, racial competition and racial inequality differentially explain the variation in White and Black interracial homicide offending.

EFFECTS OF TESTING, ANALYSIS, DAMAGE, AND ENVIRONMENT ON MODAL PARAMETERS

Experimental and analytical modal analysis techniques have been widely used in civil engineering for a number of years, mostly in seismic applications. Since the beginning of this decade, these techniques have received considerable attention in non-seismic applications such as structural damage detection, analytical model calibration and remote-monitoring systems. In these applications, most studies have concentrated on correlating modal parameters to changes in structural condition. However, for reliable performance of modal techniques in field situations, it is essential to understand and establish the variability of modal parameters due to test procedures and in-service environments of structures. New York has been researching this subject extensively for the past few years, and has tested several structures including (1) a 1/6-scale model highway bridge, (2) an abandoned fracture-critical highway bridge and (3) an in-service highway bridge. Both the abandoned highway bridge and model bridge were tested under intact and simulated-damage conditions. This paper briefly describes these studies. Results indicate that modal frequencies in conjunction with mode shapes may be used to identify the existence of bridge damage or deterioration of interest, but it is difficult to isolate damage locations using these modal parameters. Operating conditions affect the modal properties and are critical in establishing a baseline for structural monitoring.

Structural transformations during preparation of fine forms of exfoliated graphite

Electron transmission microscopy and microdiffraction, X-ray phase analysis, electric conduction, and thermal-emf measurements are used to study the change in structural conditions of graphite bisulfate residual compounds (GBRC) in fine-grained exfoliated graphite with both free expansion and expansion within a closed volume. It is established that GBRC in all of the test temperature range (200–1000°C), including high-temperature rapid heating and with pressures of 5–20 MPa, in a structural respect are a heterogeneous system including graphite crystals areas of structure heterogeneity specified by the distribution of intercalate residues with a different degree of ordering, and also at least two intercalate residue phases of different fineness. Heating temperature, pressure, and the way of expansion govern the qualitative structure and quantitative ratio between various phase formations as well as the level of their disorder, i.e. the structural state of fine-grained exfoliated graphite. The effect of structural state on mechanical properties is studied by the method of repeated-static compression. It is shown that it is possible to obtain materials with prescribed mechanical properties by altering the structural state of fine-grained exfoliated graphite.