Subspace system identification of support excited structures—part II: gray‐box interpretations and damage detection

A theoretical framework is presented for the estimation of the physical parameters of a structure (i.e., mass, stiffness, and damping) from measured experimental data (i.e., input–output or output‐only data). The framework considers two state‐space models: a physics‐based model derived from first principles (i.e., white‐box model) and a data‐driven mathematical model derived by subspace system identification (i.e., black‐box model). Observability canonical form conversion is introduced as a powerful means to convert the data‐driven mathematical model into a physically interpretable model that is termed a gray‐box model. Through an explicit linking of the white‐box and gray‐box model forms, the physical parameters of the structural system can be extracted from the gray‐box model in the form of a finite element discretization. Prior to experimental verification, the framework is numerically verified for a multi‐DOF shear building structure. Without a priori knowledge of the structure, mass, stiffness, and damping properties are accurately estimated. Then, experimental verification of the framework is conducted using a six‐story steel frame structure under support excitation. With a priori knowledge of the lumped mass matrix, the spatial distribution of structural stiffness and damping is estimated. With an accurate estimation of the physical parameters of the structure, the gray‐box model is shown to be capable of providing the basis for damage detection. With the use of the experimental structure, the gray‐box model is used to reliably estimate changes in structural stiffness attributed to intentional damage introduced. Copyright © 2012 John Wiley & Sons, Ltd.     

Acoustic Emissions Monitoring during Inelastic Deformation of Porous Sandstone: Comparison of Three Modes of Deformation

In some reservoirs, large deformations can occur during oil or gas production because of the effective stress change. For very porous rocks, these production operations can be sufficient to cause inelastic deformation and irreversible damage. Rock formations can undergo deformation by different mechanisms, including dilatancy or pore collapse. In the laboratory, it has been shown that the inelastic deformation and failure mode of porous rocks are pressure sensitive. Indeed, when subjected to an overall compressive loading, a porous rock may fail by shear localization, compaction localization, or by cataclastic compaction. Acoustic emission (AE) records provide important information to understand the failure mode of rocks: the spatial evolution of damage as well as the source mechanisms can be followed using this technique. In this paper, we present three different laboratory axisymmetric compression experiments, performed on Bleurswiller sandstone, which enable us to compare the acoustic emission signature of these three modes of deformation. Our data show that compaction localization and cataclastic compaction are characterized by similar acoustic signatures (in terms of AE sources characteristics and evolution of AE number), in comparison to the acoustic signature from shear localization. This implies similar micromechanisms involved during compaction bands formation and cataclastic compaction.     

Improving exposure assessment in environmental epidemiology: Application of spatio-temporal visualization tools

A thorough assessment of human exposure to environmental agents should incorporate mobility patterns and temporal changes in human behaviors and concentrations of contaminants; yet the temporal dimension is often under-emphasized in exposure assessment endeavors, due in part to insufficient tools for visualizing and examining temporal datasets. Spatio-temporal visualization tools are valuable for integrating a temporal component, thus allowing for examination of continuous exposure histories in environmental epidemiologic investigations. An application of these tools to a bladder cancer case-control study in Michigan illustrates continuous exposure life-lines and maps that display smooth, continuous changes over time. Preliminary results suggest increased risk of bladder cancer from combined exposure to arsenic in drinking water (>25 g/day) and heavy smoking (>30 cigarettes/day) in the 1970s and 1980s, and a possible cancer cluster around automotive, paint, and organic chemical industries in the early 1970s. These tools have broad application for examining spatially- and temporally-specific relationships between exposures to environmental risk factors and disease.This study was supported by grant R01 CA96002-10, Geographic-Based Research in Cancer Control and Epidemiology, from the National Cancer Institute. Development of the STIS^TM software was funded by grants R43 ES10220 from the National Institutes of Environmental Health Sciences and R01 CA92669 from the National Cancer Institute. Access to cancer case records was provided by Michigan Cancer Surveillance Program within the Division for Vital Records and Health Statistics, Michigan Department of Community Health. The authors thank Michigan Public Health Institute for conducting the telephone interview and Stacey Fedewa and Lisa Bailey for entering written surveys into a database. The authors thank 3 anonymous reviewers for their helpful comments.     

Algorithms for time synchronization of wireless structural monitoring sensors

Dense networks of wireless structural health monitoring systems can effectively remove the disadvantages associated with current wire‐based sparse sensing systems. However, recorded data sets may have relative time‐delays due to interference in radio transmission or inherent internal sensor clock errors. For structural system identification and damage detection purposes, sensor data require that they are time synchronized. The need for time synchronization of sensor data is illustrated through a series of tests on asynchronous data sets. Results from the identification of structural modal parameters show that frequencies and damping ratios are not influenced by the asynchronous data; however, the error in identifying structural mode shapes can be significant. The results from these tests are summarized in Appendix A. The objective of this paper is to present algorithms for measurement data synchronization. Two algorithms are proposed for this purpose. The first algorithm is applicable when the input signal to a structure can be measured. The time‐delay between an output measurement and the input is identified based on an ARX (auto‐regressive model with exogenous input) model for the input–output pair recordings. The second algorithm can be used for a structure subject to ambient excitation, where the excitation cannot be measured. An ARMAV (auto‐regressive moving average vector) model is constructed from two output signals and the time‐delay between them is evaluated. The proposed algorithms are verified with simulation data and recorded seismic response data from multi‐story buildings. The influence of noise on the time‐delay estimates is also assessed. Copyright © 2004 John Wiley & Sons, Ltd.     

Microstructural evidence for crystallization regimes in mafic intrusions: a case study from the Little Minch Sill Complex,Scotland

The magma forming the 20 m thick crinanitic/picrodoleritic Dun Raisburgh sill, part of the Little Minch Sill Complex of NW Scotland, comprised a mafic carrier liquid with a crystal cargo of plagioclase and olivine (1 vol%). The olivine component of the cargo settled on the floor of the intrusion while the more buoyant plagioclase component remained suspended during solidification, resulting in a relatively high plagioclase content in the centre of the sill. The settled olivine grains form a lower fining-upwards sequence overlain by a poorly sorted accumulation formed of grains that grew within the convecting magma. The accumulation of olivine on the sill floor occurred over 5–10 weeks, synchronous with the upwards-propagation of a solidification front comprising a porous (~?70 vol% interstitial liquid) plagioclase-rich crystal mush.     

The Flatness of U.S. States

Does perception match reality when people judge the flatness of large areas, such as U.S. states? The authors conducted a geomorphometric analysis of the contiguous United States, employing publicly available geographic software, Shuttle Radar Topography Mission (SRTM) elevation data, and a new algorithm for measuring flatness. Each 90‐meter cell was categorized as not flat, flat, flatter, or flattest, and each state was measured in terms of percentage flat, flatter, and flattest as well as absolute area in each category. Ultimately, forty‐eight states plus the District of Columbia were mapped and ranked according to these values. Keywords: flatness, U.S. states, slope, Kansas, Florida.     

Seismic performance of highway bridges with fusing bearing components for quasi‐isolation

Modern highway bridges in Illinois are often installed with economical elastomeric bearings that allow for thermal movement of the superstructure, and steel fixed bearings and transverse retainers that prevent excessive movement from service‐level loadings. In the event of an earthquake, the bearing system has the potential to provide a quasi‐isolated response where failure of sacrificial elements and sliding of the bearings can cause a period elongation and reduce or cap the force demands on the substructure. A computational model that has been calibrated for the expected nonlinear behaviors is used to carry out a parametric study to evaluate quasi‐isolated bridge behavior. The study investigates different superstructure types, substructure types, substructure heights, foundation types, and elastomeric bearing types. Overall, only a few bridge variants were noted to unseat for design‐level seismic input in the New Madrid Seismic Zone, indicating that most structures in Illinois would not experience severe damage during their typical design life. However, Type II bearing systems, which consist of an elastomeric bearing and a flat PTFE slider, would in some cases result in critical damage from unseating at moderate and high seismic input. The sequence of damage for many bridge cases indicates yielding of piers at low‐level seismic input. This is caused by the high strength of the fixed bearing element, which justifies further calibration of the quasi‐isolation design approach. Finally, the type of ground motion, pier height, and bearing type were noted to have significant influence on the global bridge response. Copyright © 2013 John Wiley & Sons, Ltd.     

Carbon isotopes in the rivers from the Lesser Antilles: origin of the carbonic acid consumed by weathering reactions in the Lesser Antilles

In this paper, we use carbon isotopes in the dissolved load of rivers from the Lesser Antilles volcanic arc (Guadeloupe, Martinique and Dominica islands) to constrain the source of the carbon dioxide (CO₂) involved in the neutralization reactions during water–rock interactions. The δ¹³C data span a large range of variations, from –19‰ to –5 · 2‰ for DIC (dissolved inorganic carbon) concentrations ranging from 11 μM to 2000 μM. Coupled with major element concentrations, carbon isotopic ratios are interpreted as reflecting a mixture of magmatic CO₂ (enriched in heavy carbon (δ¹³C ≈ –3 · 5‰) and biogenic CO₂ produced in soils (enriched in light carbon (δ¹³C < –17‰)). Carbon isotopes show that, at the regional scale, 23 to 40% of CO₂ consumed by weathering reactions is of magmatic origin and is transferred to the river system through aquifers under various thermal regimes. These numbers remain first‐order estimates as the major uncertainty in using carbon isotopes as a source tracer is that carbon isotopes can be fractionated by a number of processes, including soil and river degassing. Chemical weathering is clearly, at least, partly controlled by the input of magmatic CO₂, either under hydrothermal (hot) or surficial (cold) weathering regimes. This study shows that the contribution of magmatic CO₂ to chemical weathering is an additional parameter that could explain the high weathering rates of volcanic rocks. The study also shows that a significant part of the carbon degassed from the Earth's interior is not released as CO₂ to the atmosphere, but as DIC to the ocean because it interacts with the groundwater system. This study calls for a better understanding of the contributions of deep carbon to the hydrosphere and its influence on the development of the Critical Zone. Copyright © 2013 John Wiley & Sons, Ltd.     

Producing landslide-susceptibility maps for regional planning in data-scarce regions

In many of the lesser developed areas of the world, regional development planning is increasingly important for meeting the needs of current and future inhabitants. Expansion of economic capability, infrastructure, and residential capacity requires significant investment, and so efforts to limit the negative effect of landslides and other natural hazards on these investments are crucial. Many of the newer approaches to identifying and mapping relative landslide susceptibility within a developing area are hindered by insufficient data in the places where it is most needed. An approach called matrix assessment was specifically designed for regional development planning where data may be limited. Its application produces a landslide-susceptibility map suitable for use with other planning data in a Geographical Information System (GIS) environment. Its development also encourages collecting basic landslide inventory data suitable for site-specific studies and for refining landslide hazard assessments in the future. This paper illustrates how matrix assessment methodology was applied to produce a landslide-susceptibility map for the Commonwealth of Dominica, an island nation in the eastern Caribbean, and how with a follow up study the relative landslide-susceptibility mapping was validated. A second Caribbean application on Jamaica demonstrates how this methodology can be applied in a more geologically complex setting. A validated approach to mapping landslide susceptibility which does not require extensive input data offers a significant benefit to planning in lesser developed parts of the world.     

The draining of Matthieu landslide-dam lake, Dominica, West Indies

Shortly before midnight on Wednesday, July 27, 2011, the landslide dam forming a lake on the Matthieu River, Dominica, West Indies rapidly breached. The complete draining of the lake caused major flooding along the lower Layou River Valley. No fatalities or injuries resulted despite significant property and infrastructure damage. Government estimates place the cost for immediate cleanup and long-term repairs between ECD$9 million and ECD$18 million. The lake created by the landslide dam was unusual for having persisted nearly 14 ?years. Formation of the Matthieu landslide dam was associated with formation and breaching of two smaller landslide dams on the Layou River in 1997. Available evidence is consistent with breaching due to landsliding on the face of the landslide dam. Landslides removed sufficient material to permit the lake to flow over the dam and erode the dam to about the level of the pre-existing channel of the Matthieu River.