Discussion of user-defined parameters for recursive subspace identification: Application to seismic response of building structures     

Shieh-Kung Huang  Jun-Da Chen  Kenneth J. Loh  Chin-Hsiung Loh 《地震工程与结构动力学》2020,49(15):1738-1757

Structural damage assessment under external loading, such as earthquake excitation, is an important issue in structural safety evaluation. In this regard, an appropriate data analysis and system identification technique is required to interpret the measured data and to identify the state of the structure. Generally, the recursive system identification algorithm is used. In this study, the recursive subspace identification (RSI) algorithm based on the matrix inversion lemma algorithm with oblique projection technique (RSI-Inversion-Oblique) is applied to investigate the time-varying dynamic characteristics. The user-defined parameters used in the RSI-Inversion-Oblique technique are carefully discussed, which include the size of the data Hankel matrix (i), model order to extract the physical modes, and forgetting factor (FF) to detect the time-varying system modal frequencies. Response data from the Northridge earthquake from the Sherman Oaks building (CSMIP) is used as an example to examine a systematic method to determine the suitable user-defined parameters in RSI. It is concluded that the number of rows in the data Hankel matrix significantly influences the identification of the time-varying fundamental modal frequency of the structure. An algorithmic model order selection method using the eigenvalue distribution of RSI-Inversion can detect the system modal frequencies at each appending data window without causing any abnormality.  相似文献   

Effects of variation in loading protocol on the strength and deformation capacity of ductile reinforced concrete beams     

Kai J. Marder  Christopher J. Motter  Kenneth J. Elwood  G. Charles Clifton 《地震工程与结构动力学》2018,47(11):2195-2213

Understanding the impact of prior earthquake damage on residual capacity is important for postearthquake damage assessment of buildings; however, interpretation of such impact is challenging when based on tests using traditional reversed‐cyclic loading protocols. A new loading protocol, consisting of a dynamic earthquake displacement history followed by quasi‐static reversed‐cyclic loading to failure, is presented as an alternative to traditional simulated seismic loading protocols. Data are analyzed from a set of 12 nominally identical ductile reinforced concrete beams that were tested by using variations of this protocol and traditional reversed‐cyclic and monotonic protocols. Differences in the cycle content of the earthquake displacement histories applied to the test specimens allowed for the effects of load history variation below 2.2% drift to be isolated. It is found that such variation had no effect on the beam deformation capacities. The effects of dynamic loading rates are also analyzed and compared against control quasi‐static specimens. Relative strength increases due to dynamic loading are found to be more significant at yield than at ultimate. Dynamic loading rates led to modest reductions in the beam deformation capacities, but the presence of causality between these variables remains uncertain.  相似文献   

Explicit stress–strain equations for modeling frictional materials     

Kenneth J. Xu  Martin D. Liu  Buddhima Indraratna 《Marine Georesources & Geotechnology》2018,36(6):722-734

In this paper, a comprehensive study on simulating the shearing behavior of frictional materials is performed. A set of two explicit equations, describing the relationship among the shear stress ratio and the distortional strain and the volumetric strain, are formulated independently. The equations contain three stress parameters and three strain parameters and another parameter representing the nonuniformity of stress and strain during softening. All the parameters have clear physical significance and can be determined experimentally. It is demonstrated that the proposed equations have the capacity of simulating the complicated shearing behavior of many types of frictional materials including geomaterials. The proposed equations are used to simulate the stress–strain behavior for 27 frictional materials with 98 tests. These materials include soft and stiff clays in both reconstituted and structured states, silicon sands and calcareous sands, silts, compacted fill materials, volcanic soils, decomposed granite soils, cemented soils (both artificially and naturally cemented), partially saturated soils, ballast, rocks, reinforced soils, tire chips, sugar, wheat, and rapeseed. It has been demonstrated that the proposed explicit constitutive equations have the capacity to capture accurately the shearing behavior of frictional materials both qualitatively and quantitatively. A study on model parameters has been performed.  相似文献   

Effect of thickness of planar nozzles on erosion depth of levee soils subjected to plunging water     

Chung Rak Song  Jinwon Kim  James Tyler Kidd  Alexander Cheng  David Admiraal 《国际泥沙研究》2018,33(3):243-249

In this study, the effect of the thickness of a planar jet on the erosion depth when the jet impinges on a surface composed of cohesive soil was analytically and numerically evaluated. The results showed that the erosion depth was practically independent of the nozzle thickness for erosion depths shallower than the potential core length (i.e. the region of the jet in which the central flow velocity is the same as the nozzle velocity). The relation between nozzle thickness and erosion depth was non-linear with continuously variable slope for erosion depths deeper than the potential core length. Finally, the relation was approximately linear when the erosion depth converged to the equilibrium erosion depth. The findings of this study indicate that direct and fast prediction of the erosion depth in the field is possible using the data from a small scale soil erosion test with similar flow velocities.  相似文献   

Researching and Teaching the Anthropocene     

Kenneth R. Young 《Geographical review》2019,109(2):258-264

  相似文献   

Surface melt-driven seasonal behaviour (englacial and subglacial) from a soft-bedded temperate glacier recorded by in situ wireless probes     

Jane K. Hart  Kirk Martinez  Philip J. Basford  Alexander I. Clayton  Graeme M. Bragg  Tyler Ward  David S. Young 《地球表面变化过程与地形》2019,44(9):1769-1782

We investigate the spatial and temporal englacial and subglacial processes associated with a temperate glacier resting on a deformable bed using the unique Glacsweb wireless in situ probes (embedded in the ice and the till) combined with other techniques [including ground penetrating radar (GPR) and borehole analysis]. During the melt season (spring, summer and autumn), high surface melt leads to high water pressures in the englacial and subglacial environment. Winter is characterized by no surface melting on most days (‘base’) apart from a series of positive degree days. Once winter begins, a diurnal water pressure cycle is established in the ice and at the ice/sediment interface, with direct meltwater inputs from the positive degree days and a secondary slower englacial pathway with a five day lag. This direct surface melt also drives water pressure changes in the till. Till deformation occurred throughout the year, with the winter rate approximately 60% that of the melt season. We were able to show the bed comprised patches of till with different strengths, and were able to estimate their size, relative percentage and temporal stability. We show that the melt season is characterized by a high pressure distributed system, and winter by a low pressure channelized system. We contrast this with studies from Greenland (overlying rigid bedrock), where the opposite was found. We argue our results are typical of soft bedded glaciers with low englacial water content, and suggest this type of glacier can rapidly respond to surface-driven melt. Based on theoretical and field results we suggest that the subglacial hydrology comprises a melt season distributed system dominated by wide anastomosing broad flat channels and thin water sheets, which may become more channelized in winter, and more responsive to changes in meltwater inputs. © 2019 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd.  相似文献   

Long-Term Evaluation of Mulch Biowall Performance to Treat Chlorinated Solvents     

Kenneth L. Walker Jr.  Travis M. McGuire  David T. Adamson  R. Hunter Anderson 《Ground Water Monitoring & Remediation》2020,40(1):35-46

Permeable reactive barriers (PRBs), such as mulch biowalls, have been installed at numerous groundwater cleanup sites, and laboratory and field studies have demonstrated biotic and abiotic processes that degrade chlorinated volatile organic compounds (CVOCs) in groundwater passing through these engineered remedies. However, the longevity of mulch biowalls remains a fundamental research question. Soil and groundwater sampling at seven mulch biowalls at Altus Air Force Base (AFB) approximately 10 years after installation demonstrated the ongoing degradation of CVOCs. Trichloroethene was not detected in five of seven groundwater samples collected from the biowall despite upgradient detections above federal drinking water standards. Microbial sampling established the presence of key dechlorinating bacteria and the abundance of genes encoding specific enzymes for degradation, high methane concentrations, low sulfate concentrations, and negative oxidation-reduction potential, all indicative of highly reducing conditions within the biowalls and favorable conditions for CVOC destruction via microbial reductive dechlorination. High cellulose content (>79%) of the mulch, elevated total organic carbon (TOC) content in groundwater, and elevated potentially bioavailable organic carbon (PBOC) measurements in soil samples further supports an ongoing, long-lived source of carbon. These results demonstrate the ongoing and long-term efficacy of the mulch biowalls at Altus AFB. In addition, concentrations of bacteria, TOC, PBOC, and other geochemical parameters suggest a modest impact of the biowalls downgradient. The continued presence of CVOCs downgradient may be attributable to back diffusion from low-permeability shale. However, the biowalls continue to provide benefits by removing CVOCs in groundwater, thus reducing further CVOC loading to the downgradient, low-permeability strata.  相似文献   

Reconstruction of the Sunspot Group Number: The Backbone Method     

Leif Svalgaard  Kenneth H. Schatten 《Solar physics》2016,291(9-10):2653-2684

  相似文献   

Louis Leakey and Piltdown Man     

S. Kenneth Donovan 《Proceedings of the Geologists' Association. Geologists' Association》2021,132(3):405-406

  相似文献   

Water Harvesting in Sub‐Saharan Africa edited by William Critchley and John Gowing (eds). Earthscan,Oxford and New York, 2013, pp. xv + 201 (ISBN: 978‐0‐415‐53773‐5) (hbk) (ISBN: 978‐0‐415‐53786‐5) (pbk).          下载免费PDF全文

Kenneth Irvine 《Singapore journal of tropical geography》2015,36(2):268-270

  相似文献