Shake table testing and numerical simulation of a self‐centering energy dissipative braced frame     

Jeffrey Erochko  Constantin Christopoulos  Robert Tremblay  Hyung‐Joon Kim 《地震工程与结构动力学》2013,42(11):1617-1635

The self‐centering energy dissipative (SCED) brace is a new steel bracing member that provides both damping to the structure and a re‐centering capability. The goal of this study was to confirm the behavior of SCED braces within complete structural systems and to confirm the ability to model these systems with both a state‐of‐the‐art computer model as well as a simplified model that would be useful to practicing engineers. To these ends, a three‐story SCED‐braced frame was designed and constructed for testing on a shake table. Two concurrent computer models of the entire frame were constructed: one using the opensees nonlinear dynamic modeling software, and a simplified model using the commercial structural analysis software sap2000 . The frame specimen was subjected to 12 significant earthquakes without any adjustment or modification between the tests. The SCED braces prevented residual drifts in the frame, as designed, and did not show any significant degradation due to wear. Both numerical models were able to predict the drifts, story shears, and column forces well. Peak story accelerations were overestimated in the models; this effect was found to be caused by the absence of transitions at stiffness changes in the hysteretic model of the braces. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

Evaluation of the response modification coefficient and collapse potential of special concentrically braced frames   总被引：1，自引：0，他引：1  

Po‐Chien Hsiao  Dawn E. Lehman  Charles W. Roeder 《地震工程与结构动力学》2013,42(10):1547-1564

Special concentrically braced frames (SCBFs) are commonly used for seismic design of buildings. Their large elastic stiffness and strength efficiently sustains the seismic demands during smaller, more frequent earthquakes. During large, infrequent earthquakes, SCBFs exhibit highly nonlinear behavior due to brace buckling and yielding and the inelastic behavior induced by secondary deformation of the framing system. These response modes reduce the system demands relative to an elastic system without supplemental damping using a response modification coefficient, commonly termed the R factor. More recently, procedures put forth in FEMAP695 have been made to quantify the R factor through a formalized procedure that accounts for collapse potential. The primary objective of the research in this paper was to evaluate the approach for SCBFs. An improved model for SCBFs that permits simulation of brace fracture was used to conduct response history analyses. A series of three‐story, nine‐story and 20‐story SCBFs were designed and evaluated. Initially, the FEMAP695 method was conducted to estimate collapse and the corresponding R factor. An alternate procedure for scaling the multiple acceleration records to the seismic design hazard was also evaluated. The results show significant variation between the two methods. Of the three variations of buildings studied, the largest vulnerability was identified for the three‐story building. To achieve a consistent margin of safety against collapse, a significantly lower R factor is required for the low‐rise SCBFs (three‐story), whereas the mid‐rise and high‐rise SCBFs (nine‐story and 20‐story) may continue to use the current value of 6, as provided in ASCE‐07. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

Reconstruction of a flash flood with large wood transport and its influence on hazard patterns in an ungauged mountain basin   总被引：2，自引：0，他引：2  

V. Ruiz‐Villanueva  J. M. Bodoque  A. Díez‐Herrero  M. A. Eguibar  E. Pardo‐Igúzquiza 《水文研究》2013,27(24):3424-3437

The reconstruction of past flash floods in ungauged basins leads to a high level of uncertainty, which increases if other processes are involved such as the transport of large wood material. An important flash flood occurred in 1997 in Venero Claro (Central Spain), causing significant economic losses. The wood material clogged bridge sections, raising the water level upstream. The aim of this study was to reconstruct this event, analysing the influence of woody debris transport on the flood hazard pattern. Because the reach in question was affected by backwater effects due to bridge clogging, using only high water mark or palaeostage indicators may overestimate discharges, and so other methods are required to estimate peak flows. Therefore, the peak discharge was estimated (123 ± 18 m³ s^–1) using indirect methods, but one‐dimensional hydraulic simulation was also used to validate these indirect estimates through an iterative process (127 ± 33 m³ s^–1) and reconstruct the bridge obstruction to obtain the blockage ratio during the 1997 event (~48%) and the bridge clogging curves. Rainfall–Runoff modelling with stochastic simulation of different rainfall field configurations also helped to confirm that a peak discharge greater than 150 m³ s^–1 is very unlikely to occur and that the estimated discharge range is consistent with the estimated rainfall amount (233 ± 27 mm). It was observed that the backwater effect due to the obstruction (water level ~7 m) made the 1997 flood (~35‐year return period) equivalent to the 50‐year flood. This allowed the equivalent return period to be defined as the recurrence interval of an event of specified magnitude, which, where large woody debris is present, is equivalent in water depth and extent of flooded area to a more extreme event of greater magnitude. These results highlight the need to include obstruction phenomena in flood hazard analysis. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

Historical trends in Florida temperature and precipitation   总被引：1，自引：0，他引：1  

Michelle M. Irizarry‐Ortiz  Jayantha Obeysekera  Joseph Park  Paul Trimble  Jenifer Barnes  Winifred Park‐Said  Erik Gadzinski 《水文研究》2013,27(16):2225-2246

Because of its low topographic relief, unique hydrology, and the large interannual variability of precipitation, Florida is especially vulnerable to climate change. In this paper, we investigate a comprehensive collection of climate metrics to study historical trends in both averages and extremes of precipitation and temperature in the state. The data investigated consist of long‐term records (1892–2008) of precipitation and raw (unadjusted) temperature at 32 stations distributed throughout the state. To evaluate trends in climate metrics, we use an iterative pre‐whitening method, which aims to separate positive autocorrelation from trend present in time series. Results show a general decrease in wet season precipitation, most evident for the month of May and possibly tied to a delayed onset of the wet season. In contrast, there seems to be an increase in the number of wet days during the dry season, especially during November through January. We found that the number of dog days (above 26.7 °C) during the year and during the wet season has increased at many locations. For the post‐1950 period, a widespread decrease in the daily temperature range (DTR) is observed mainly because of increased daily minimum temperature (Tmin). Although we did not attempt to formally attribute these trends to natural versus anthropogenic causes, we find that the urban heat island effect is at least partially responsible for the increase in Tmin and its corresponding decrease in DTR at urbanized stations compared with nearby rural stations. In the future, a formal trend attribution study should be conducted for the region. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

An automated cross‐correlation based event detection technique and its application to a surface passive data set     

Farnoush Forghani‐Arani  Jyoti Behura  Seth S. Haines  Mike Batzle 《Geophysical Prospecting》2013,61(4):778-787

In studies on heavy oil, shale reservoirs, tight gas and enhanced geothermal systems, the use of surface passive seismic data to monitor induced microseismicity due to the fluid flow in the subsurface is becoming more common. However, in most studies passive seismic records contain days and months of data and manually analysing the data can be expensive and inaccurate. Moreover, in the presence of noise, detecting the arrival of weak microseismic events becomes challenging. Hence, the use of an automated, accurate and computationally fast technique for event detection in passive seismic data is essential. The conventional automatic event identification algorithm computes a running‐window energy ratio of the short‐term average to the long‐term average of the passive seismic data for each trace. We show that for the common case of a low signal‐to‐noise ratio in surface passive records, the conventional method is not sufficiently effective at event identification. Here, we extend the conventional algorithm by introducing a technique that is based on the cross‐correlation of the energy ratios computed by the conventional method. With our technique we can measure the similarities amongst the computed energy ratios at different traces. Our approach is successful at improving the detectability of events with a low signal‐to‐noise ratio that are not detectable with the conventional algorithm. Also, our algorithm has the advantage to identify if an event is common to all stations (a regional event) or to a limited number of stations (a local event). We provide examples of applying our technique to synthetic data and a field surface passive data set recorded at a geothermal site.  相似文献   

Application of a multi‐temporal,LiDAR‐derived,digital terrain model in a landslide‐volume estimation     

Chih‐Ming Tseng  Ching‐Weei Lin  Colin P. Stark  Jin‐Kin Liu  Li‐Yuan Fei  Yu‐Chung Hsieh 《地球表面变化过程与地形》2013,38(13):1587-1601

Sediments produced by landslides are crucial in the sediment yield of a catchment, debris flow forecasting, and related hazard assessment. On a regional scale, however, it is difficult and time consuming to measure the volumes of such sediment. This paper uses a LiDAR‐derived digital terrain model (DTM) taken in 2005 and 2010 (at 2 m resolution) to accurately obtain landslide‐induced sediment volumes that resulted from a single catastrophic typhoon event in a heavily forested mountainous area of Taiwan. The landslides induced by Typhoon Morakot are mapped by comparison of 25 cm resolution aerial photographs taken before and after the typhoon in an 83.6 km² study area. Each landslide volume is calculated by subtraction of the 2005 DTM from the 2010 DTM, and the scaling relationship between landslide area and its volume are further regressed. The relationship between volume and area are also determined for all the disturbed areas (V_L = 0.452A_L^1.242) and for the crown areas of the landslides (V_L = 2.510A_L^1.206). The uncertainty in estimated volume caused by use of the LiDAR DTMs is discussed, and the error in absolute volume estimation for landslides with an area >10⁵ m² is within 20%. The volume–area relationship obtained in this study is also validated in 11 small to medium‐sized catchments located outside the study area, and there is good agreement between the calculation from DTMs and the regression formula. By comparison of debris volumes estimated in this study with previous work, it is found that a wider volume variation exists that is directly proportional to the landslide area, especially under a higher scaling exponent. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

Modeling the sediment yield from landslides in the Shihmen Reservoir watershed,Taiwan     

Zong‐Xian Tsai  Gene J.‐Y. You  Hong‐Yuan Lee  Yu‐Jia Chiu 《地球表面变化过程与地形》2013,38(7):661-674

Landslides generate enormous volumes of sediment in mountainous watersheds; however, quantifying the downstream transport of landslide‐derived sediment remains a challenge. Landslide erosion and sediment delivery to the Shihmen Reservoir watershed in Taiwan was estimated using empirical landslide frequency–area and volume–area relationships, empirical landslide runout models, and the Hydrological Simulation Program‐ FORTRAN (HSPF). Landslide erosion rates ranged from 0.4 mm yr^‐1 to 2.2 mm yr^‐1 during the period 1986–2003, but increased to 7.9 mm yr^‐1 following Typhoon Aere in 2004. The percentage of landslide sediment delivered to streams decreased from 78% during the period 1986–1997 to 55% in 2004. Although the delivery ratio was lower, the volume of landslide sediment delivered to streams was 2.81 × 10⁶ Mg yr^‐1 in 1986–1997 and 8.60 × 10⁶ Mg yr^‐1 in 2004. Model simulations indicate that only a small proportion of the landslide material was delivered downstream. An average of 13% of the landslide material delivered to rivers was moved downstream during the period 1986–1997. In 2004, the period including Typhoon Aere, the annual fluvial sediment yield accounted for approximately 23% of the landslide material delivered to streams. In general, the transfer of sediment in the fluvial system in the Shihmen Reservoir watershed is dominantly transport limited. The imbalance between sediment supply and transport capacity has resulted in a considerable quantity of landslide material remaining in the upper‐stream regions of the watershed. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

Annual to decadal morphodynamics of the foredune system at Greenwich Dunes,Prince Edward Island,Canada     

Jeff Ollerhead  Robin Davidson‐Arnott  Ian J. Walker  Sojan Mathew 《地球表面变化过程与地形》2013,38(3):284-298

The purpose of this study was to quantify relationships between season, sediment availability, sediment transport pathways, and beach/foredune morphology at Greenwich Dunes, PEI. This was done for periods ranging from a few days to multiple decades using erosion pins, bedframe measurements, annual surveys, and digital photogrammetry using historical aerial photographs. The relative significance of seasonal/annual processes versus response of the foredune system to broader geomorphic controls (e.g. relative sea level rise, storms, etc.) was also assessed. The data show that there are clear seasonal differences in the patterns of sand supply from the beach to the foredune at Greenwich and that there are differences in sediment supply to the foredune between the east and west reaches of the study area, resulting in ongoing differences in foredune morphology. They also demonstrate that models that incorporate wind climate alone, or even models that include other factors like beach moisture, would not be able to predict the amount of sediment movement from the beach to the foredune in this environment unless there were some way to parameterize system morphology, especially the presence or absence of a dune ramp. Finally, the data suggest that the foredune can migrate landward while maintaining its form via transfers of sediment from the stoss slope, over the crest, and onto the lee slope. Although the rate of foredune development or recovery after disturbance changes over time due to morphological feedback, the overall decadal evolution of the foredune system at Greenwich is consistent with, and supports, the Davidson‐Arnott (2005) conceptual model of dune transgression under rising sea level. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

Geomorphic response to an active transpressive regime: a case study along the Chaman strike‐slip fault,western Pakistan     

Shams Ul‐Hadi  Shuhab D. Khan  Lewis A. Owen  Abdul S. Khan 《地球表面变化过程与地形》2013,38(3):250-264

The Chaman left‐lateral strike‐slip fault bounds the rigid Indian plate boundary at the western end of the Himalayan‐Tibetan orogen and is marked by contrasting topographic relief. Deformed landforms along the fault provide an excellent record for understanding this actively evolving intra‐continental strike‐slip fault. The geomorphic response of an active transpessional stretch of the Chaman fault was studied using digital elevation model (DEM) data integrated with Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) Visible and Near Infrared/Short Wave Infrared (VNIR/SWIR) and images from GeoEye‐1. Geologic and geomorphic mapping helped in reconstructing the Late Quaternary landscape history of this transpessional strand of the Chaman strike‐slip fault and the associated Spinatizha thrust fault in western Pakistan. Topographic analysis of a part of the transpression (the thrust bounded Roghani ridge) revealed northward growth of the Spinatizha fault with the presence of three water gaps and two corresponding wind gaps. Geomorphic indices including stream length‐gradient index, mountain front sinuosity, valley floor width to valley height ratios, and entrenchment of recent alluvial fan deposits were used to define the lateral growth and direction of propagation of the Spinatizha fault. Left‐lateral displacement along Chaman fault and uplift along the Spinatizha fault was defined using topographic analysis of the Roghani ridge and geomorphic mapping of an impressive alluvial fan, the Bostankaul fan. The landforms and structures record slip partitioning along the Indian plate boundary, and account for the convergence resulting from the difference in the Chaman fault azimuth and orientation of the velocity vector of the Indian plate. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

Runoff and sediment yield from land under various uses in a Mediterranean mountain area: long‐term results from an experimental station     

Estela Nadal‐Romero  Teodoro Lasanta  José M. García‐Ruiz 《地球表面变化过程与地形》2013,38(4):346-355

In this study we analyzed runoff and sediment yield from land under various traditional and current land uses in Mediterranean mountain areas, using long‐term data from an experimental station in the Aísa Valley, Central Spanish Pyrenees. Monitoring at this station has provided 20 years of data that can help explain the hydrological and geomorphological changes that have been observed at larger spatial scales, and also the changes that have occurred to some of the most characteristic landscapes of the Mediterranean middle mountains. In spite of the problems associated with the use of small experimental plots, the results obtained are consistent with other studies in the Mediterranean region, and confirm the strong influence of land use changes on runoff generation and sediment yield. The results indicate that: (i) cereal cultivation on steep slopes (both alternating cereal cultivation and fallow on sloping fields and shifting agriculture on the steepest slopes) represents a major problem for soil conservation. This explains the occurrence throughout the Mediterranean mountains of many degraded hillslopes, which show evidence of sheet wash erosion, rilling, gullying and shallow landsliding; (ii) farmland abandonment has led to a marked reduction in runoff and sediment yield as a consequence of rapid plant recolonization, particularly by dense shrubs; (iii) the natural transformation of abandoned fields into grazing meadows has reduced runoff and sediment yield. Land use trends in the Mediterranean mountains are mainly characterized by generalized farmland abandonment and a decrease in livestock pressure. From a hydrological and geomorphological point of view the main consequences have been a reduction in overland flow from the hillslopes, and a reduction in sediment sources, with differences up to one order of magnitude in sediment yield from dense shrub cover and grazing meadow areas compared with areas under shifting agriculture. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献