Land desertification is one of the world’s most important global ecological environment problems and sensitive to global climate change. In this study, Moderate Resolution Imaging Spectroradiometer (MODIS) and Gaofen-1 (GF-1) data were used to obtain aeolian desertification land distribution in Northern China. Aeolian desertification land distribution from 2001 to 2015 was used to analyze the spatiotemporal change in this area. Results show that aeolian desertification situation of 70 counties is expanded with low slope values and 250 counties is reversed. Aeolian desertification situation in most areas is improved in recent 15 years. Gravity center of the aeolian desertification has a trend to move towards the direction of the high latitude and low longitude. It moves towards north about 0.06° and west about 2.2° from 2001 to 2015. The main distribution area is between 90–100°E, 30–?40°N and altitude which less than 2000 m in desert and steppe climate zone. Aeolian desertification is worsening in recent 5 years around rivers and lakes. In recent years, the government has made great efforts to strengthen ecological construction with positive effect, but we still need to pay more attention to environment deterioration of rivers, lakes and the nearby areas in the future. 相似文献
The concept of seismic resilience has received significant attention from academia and industry during the last two decades. Different frameworks have been proposed for seismic resilience assessment of engineering systems at different scales (e.g., buildings, bridges, communities, and cities). Testbeds including Centerville virtual community (CVC), Memphis testbed (MTB), and the virtual city of Turin, Italy (VC-TI) have been developed during the last decade. However, the resilience assessment results of Chinese cities still require calibration based on a unified evaluation model. Therefore, a geographic information system (GIS)-based benchmark model of a medium-sized city located in the southeastern coastal region of China was developed. The benchmark city can be used to compare existing assessment frameworks and calibrate the assessment results. The demographics, site conditions, and potential hazard exposure of the benchmark city, as well as land use and building inventory are described in this paper. Data of lifeline systems are provided, including power, transportation, water, drainage, and natural gas distribution networks, as well as the locations of hospitals, emergency shelters, and schools. Data from past earthquakes and the literature were obtained to develop seismic fragility models, consequence models, and recovery models, which can be used as basic data or calibration data in the resilience assessment process. To demonstrate the completeness of the data included in the benchmark city, a case study on the accessibility of emergency rescue after earthquakes was conducted, and the preliminary results were discussed. The ultimate goal of this benchmark city is to provide a platform for calibrating resilience assessment results and to facilitate the development of resilient cities in China.
Flexible pipelines are often used to connect hard pipes from a foundation to a superstructure to accommodate large deformation in the base isolation layer during an earthquake. Although Chinese seismic design guidelines suggest several configurations, they are different from the designs that have been proven in practice, e.g., Japanese styles, and extensive experimental investigation into their seismic performance is required. Three types of seals, rubber-, metal- and asbestine-based, were tested quasi-statically with infilled pressurized water at 2.5 MPa. The asbestine-based seal leaked at a smaller deformation than the other two types of seals. Based on the test results, three damage states were defined and the deformation capacity was estimated. To evaluate their performance, a three-dimensional model of a base-isolated medical building was developed using OpenSees, with the flexible pipelines simulated by a mechanical model calibrated from the experimental data. A probabilistic seismic demand model and the fragility function of the flexible pipelines were then developed to evaluate the seismic performance.
Nonstructural components(NSCs)are parts,elements,and subsystems that are not part of the primary loadbearing system of building structures but are subject to seismic loading.Damage to NSCs may disrupt the functionality of buildings and result in significant economic losses,injuries,and casualties.In past decades,extensive studies have been conducted on the seismic performance and seismic design methods of NSCs.As the input for the seismic design of NSCs,floor response spectra(FRS)have attracted the attention of researchers worldwide.This paper presents a state-of-the-art review of FRS.Different methods for generating FRS are summarized and compared with those in current seismic design codes.A detailed review of the parameters influencing the FRS is presented.These parameters include the characteristics of ground motion excitation,supporting building and NSCs.The floor acceleration response and the FRS obtained from experimental studies and field observations during earthquakes are also discussed.Three RC frames are used in a case study to compare the peak floor acceleration(PFA)and FRS calculated from time history analyses(THA)with that generated using current seismic design codes and different methods in the literature.Major knowledge gaps are identified,including uncertainties associated with developing FRS,FRS generation methods for different types of buildings,the need for comprehensive studies on absolute acceleration,relative velocity,and relative displacement FRS,and the calibration of FRS by field observations during earthquakes. 相似文献
