Rocking Behavior of Irregular Free-Standing Objects Subjected to Earthquake Motion

Free-standing rigid objects and structures are dominantly found to exhibit rocking behavior and can be vulnerable to overturning during an earthquake as demonstrated by numerous past earthquake events. Such objects are typically considered to be displacement sensitive with their rocking response being well presented by the Peak Displacement Demand (PDD) parameter of the supporting floor’s motion. This in turn can be directly related to an object’s width (along the direction of motion) for assessing its vulnerability to overturn. Such findings have been sufficiently justified by refined dynamic analysis supported by experimental evaluations which were based on rigid blocks with uniform geometric format (i.e., regular in their mass distribution). However, vulnerable rocking objects can be asymmetric and accordingly their sensitivity to floor displacement cannot be directly related to their width. The key parameter which defines irregular objects’ response to rocking motion is represented by the degree of eccentricity of their center of mass. In this study, the well-known rocking equation of motion is reconfigured and devised to model the rocking responses for 280 irregular objects undergoing eight earthquake motions which included artificial and recorded earthquakes. Analytical results obtained from solving the adjusted equation of motion were evaluated with sophisticated finite element (FE) models simulating the 280 irregular cases. This experimentally validated FE modeling approach was found to be time- and cost-effective for understating the rocking behavior of asymmetric objects as well as clarifying an interesting relationship between the object’s damping level and the condition of the supporting base (i.e., whether being provided with supports at the points of rotation or not). The rocking response of irregular objects was found to be highly influenced by the level of eccentricity of the object when excited by motions with high displacement amplitudes, while such influence was not found noticeable by wider objects. Based on the developed trends between the maximum top displacement of irregular objects and the PDD, an expression for estimating the rocking amplitudes is proposed which is a function of the object’s eccentricity.     

Inelastic Displacement Demand of Strength-Degraded Structures

This article presents findings from parametric studies involving nonlinear time-history analyses of inelastic systems with and without strength degradation. Results showed that estimates based on the equal-displacement and equal-energy propositions can be exceeded significantly by the inelastic displacement demands in the acceleration and velocity-sensitive regions of the response spectrum. The displacement demand behaviour is sensitive to the strength degradation and the frequency properties of the ground shaking. With a modest strength reduction factor of 2, the inelastic displacement demand would typically be constrained by the Peak Displacement Demand as indicated on the elastic displacement response spectrum for 5% damping.     

A Simple Model for Estimating Shocks in Unrestrained Building Contents in an Earthquake

Building contents that include cabinets housing electronic equipment are typically not rigidly secured to the floor, nor to the adjacent wall except in regions of high seismic activities. The behavior of unrestrained building contents in an earthquake is a cause of concern because of the consequence of damage to certain equipment or other forms of fragile items. Much of the research reported in the literature has been devoted to studying the rocking and sliding motion behavior of base-excited rigid objects and their risks of overturning. In contrast, this paper is concerned with estimating the impact acceleration that can be generated by the pounding of the rocking object onto the floor. Algebraic expressions for predicting the acceleration level, which can be translated into dynamic force values, are derived and illustrated by case studies. Importantly, the proposed expressions have been verified by comparisons with results from both simulated and physical experiments. In illustrating the use of the proposed analytical procedure, a parametric experimental study has been undertaken on a cushion material to study the sensitivity of its static and dynamic stiffness to changes in the boundary conditions of the cushion. The proposed calculation procedure, while simple to apply, can be used as a means of predicting shock and the dynamic forces that can be generated in an object in the course of the response to an earthquake.     

Applications of integrated geophysical method in archaeological surveys of the ancient Shu ruins

The Jinsha site is one set of excavated ruins of the ancient Shu state, late Neolithic, early Bronze Age. The archaeological survey of the site is especially important for study of Shu culture, because there is hardly any written record of this period. As technology progresses, more and more advanced techniques and equipment have been used to conduct archaeological surveys. In this study, four nondestructive methods of geophysical detection were used to locate ancient relics at the site. The validity of these different types of archaeological detection methods (method of high-density resistivity, induced polarization, multi-frequency electromagnetic, ground-penetrating radar and so on) and techniques were analyzed. And a multi-scale, multi-method detection system to non-destructive detection of cultural relics was established.     

Urban Textural Analysis from Remote Sensor Data: Lacunarity Measurements Based on the Differential Box Counting Method

Lacunarity is related to the spatial distribution of gap or hole sizes. For low lacunarity, all gap sizes are the same and geometric objects are deemed homogeneous; conversely, for high lacunarity, gap sizes are variable and objects are therefore heterogeneous. Textures that are homogeneous at small scales can be quite heterogeneous at large scales and vice versa, and hence, lacunarity can be considered a scale-dependent measure of heterogeneity or texture. In this article, we use a lacunarity method based on a differential box counting approach to identify urban land-use and land-cover classes from satellite sensor data. Our methodology focuses on two different gliding box methods to compute lacunarity values and demonstrate a mirror extension approach for a local moving window. The extension approach overcomes, or at least minimizes, the boundary problem. The results from our study suggest that the overlapping box approach is more effective than the skipping box approach, but that there is no significant difference between window sizes. Our work represents a contribution to not only advances in textural and spatial metrics as used in remote-sensing pattern interpretation but also for broadening understanding of the computational geometry of nonlinear shape models of which lacunarity is the reciprocal of fractal theory.     

Spatial-Temporal Spread of the AIDS Epidemic, 1982–1990: A Correlogram Analysis of Four Regions of the United States

We applied correlogram analysis to county-level AIDS data of four regions—the Northeast (Delaware, the District of Columbia, Maryland, New Jersey, New York, and Pennsylvania), California, Florida, and Louisiana—for the period 1982–1990 to characterize the spatial-temporal spread of the AIDS epidemic. Correlograms computed from yearly incidence rates differ substantially among these four regions, revealing regional differences in the spatial patterns and intensity of AIDS spread. A general trend of increasing spread to rural America, however, can still be detected. Contagious spread was predominant in the Northeast throughout the nine-year period, whereas California was dominated by hierarchical spread through time. The spatial-temporal changes of AIDS incidence patterns were most drastic in Florida, where the correlograms show hierarchical spread in the early years and then contagious spread in the later years. As a representative region for most other states in the United States, Louisiana has low spatial autocorrelation and no definite spatial pattern of spread. Grouping data into three-year periods for states with low yearly incidence rates such as Louisiana should help identify the dominant trends for these states. The correlogram results could provide useful insights into the specification of spatial models for AIDS forecasting.     

Migrant mothers,left-behind fathers: the negotiation of gender subjectivities in Indonesia and the Philippines

The distinct feminization of labour migration in Southeast Asia – particularly in the migration of breadwinning mothers as domestic and care workers in gender-segmented global labour markets – has altered care arrangements, gender roles and practices, as well as family relationships within the household significantly. Such changes were experienced by both the migrating women and other left-behind members of the family, particularly ‘substitute’ carers such as left-behind husbands. During the women’s absence from the home, householding strategies have to be reformulated when migrant women-as-mothers rewrite their roles (but often not their identities) through labour migration as productive workers who contribute to the well-being of their children via financial remittances and ‘long-distance mothering’, while left-behind fathers and/or other family members step up to assume some of the tasks vacated by the mother. Using both quantitative and qualitative interview material with returned migrants and left-behind household members in source communities in Indonesia and the Philippines experiencing considerable pressures from labour migration, this article explores how carework is redistributed in the migrant mother’s absence, and the ensuing implications on the gender roles of remaining family members, specifically left-behind fathers. It further examines how affected members of the household negotiate and respond to any changing gender ideologies brought about by the mother’s migration over time.     

Negotiating Green Space with Landed Interests: The Urban Political Ecology of Greenway in the Pearl River Delta,China

Land‐centred urbanisation has precipitated shortage of green space in Chinese cities. However, in the Pearl River Delta, an ambitious greenway system has recently managed to flourish. It is intriguing to ask how this has become possible. Informed by the perspective of urban political ecology, this paper finds that the greenway project in the Pearl River Delta represents a set of politically realistic endeavours to alleviate urban green space shortage by adapting to, rather than challenging, powerful landed interests. Three interlocking dimensions about land—municipal land quota, rural land use claims, and real estate development—have influenced why, where and how greenways have been created. Based on these findings, we argue that research on China's politics of urban sustainability necessarily needs to understand the country's land politics.