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1.
Current structural analysis software programs offer few if any applicable device-specifi c hysteresis rules or nonlinear elements to simulate the precise mechanical behavior of a multiple friction pendulum system(MFPS) with numerous sliding interfaces.Based on the concept of subsystems,an equivalent series system that adopts existing nonlinear elements with parameters systematically calculated and mathematically proven through rigorous derivations is proposed.The aim is to simulate the characteristics of sliding motions for an MFPS isolation system with numerous concave sliding interfaces without prior knowledge of detailed information on the mobilized forces at various sliding stages.An MFPS with numerous concave sliding interfaces and one articulated or rigid slider located between these interfaces is divided into two subsystems: the fi rst represents the concave sliding interfaces above the slider,and the second represents those below the slider.The equivalent series system for the entire system is then obtained by connecting those for each subsystem in series.The equivalent series system is validated by comparing numerical results for an MFPS with four sliding interfaces obtained from the proposed method with those from a previous study by Fenz and Constantinou.Furthermore,these numerical results demonstrate that an MFPS isolator with numerous concave sliding interfaces,which may have any number of sliding interfaces,is a good isolation device to protect structures from earthquake damage through appropriate designs with controllable mechanisms. 相似文献
2.
The available models for eff ective periods of site and structure are reviewed in context of frequency tuning in the inelastic seismic response of soil-structure system. The eff ect of seismic intensity and ductility demand, on the eff ective periods, is investigated, and inelastic site amplifi cation is shown to be strongly correlated to the normalized eff ective period. Two non-dimensional parameters, analogous to the conventional site amplifi cation factors in codes, are defi ned to quantify the inelastic site amplifi cation. It is shown that the inelastic site amplifi cation factor (i.e. ratio of constant ductility spectral ordinates at soil site to those at rock outcrop) is able to represent the site eff ects more clearly, as compared to the inelastic site amplifi cation ratio (i.e. ratio of inelastic spectral ordinates at soil site to the corresponding elastic spectral ordinates at rock outcrop). Further, the peak in the amplifi cation factor corresponding to the eff ective site period diminishes rapidly with increasing ductility demand. 相似文献
3.
Throughout the history of China, the Yellow River has been associated with flood disasters and changes in the course of its lower reaches because of sedimentation. From 602 B.C. to 1949 the river experienced 1593 levee bursts, flooding vast areas, and claiming millions of human lives. The river shifted its main course by avulsion 26 times with the apex around Zhengzhou, resulting in devastating calamities and numerous old channels. Training of the Yellow River has a history of more than 3000 yr. Levee construction has been the major strategy for flood control. Two extremely different strategies has been proposed and practiced in the past 2000 yr, i.e. the "wide river and depositing sediment" strategy and the "narrow river and scouring sediment" strategy. This paper analyzes the levee breaches and flood disasters in the past 2000 yr and compares the results of the two extremely different strategies. The "narrow river and scouring sediment" strategy has only short term effects on levee breach control and flood mitigation. The "wide river and depositing sediment" strategy can essentially mitigate flood disasters and reduce levee breaches for a long term period of time. The "wide river and depositing sediment" strategy has been used and no levee breach has occurred in the past 67 yr, which has been the only periods of more than 50 yr with no levee breaches in the history of the Yellow River since 700 A.D.Modern flood and sedimentation management methods have also been introduced, and the strategy of applying the ' "widen the river and enhance the levees" approach for the upper and lower reaches management is proposed. 相似文献
4.
Seismic safety of high concrete dams 总被引：2，自引：1，他引：1
Peak ground acceleration(PGA) estimation is an important task in earthquake engineering practice.One of the most well-known models is the Boore-Joyner-Fumal formula,which estimates the PGA using the moment magnitude,the site-to-fault distance and the site foundation properties.In the present study,the complexity for this formula and the homogeneity assumption for the prediction-error variance are investigated and an effi ciency-robustness balanced formula is proposed.For this purpose,a reduced-order Monte Carlo simulation algorithm for Bayesian model class selection is presented to obtain the most suitable predictive formula and prediction-error model for the seismic attenuation relationship.In this approach,each model class(a predictive formula with a prediction-error model) is evaluated according to its plausibility given the data.The one with the highest plausibility is robust since it possesses the optimal balance between the data fi tting capability and the sensitivity to noise.A database of strong ground motion records in the Tangshan region of China is obtained from the China Earthquake Data Center for the analysis.The optimal predictive formula is proposed based on this database.It is shown that the proposed formula with heterogeneous prediction-error variance is much simpler than the attenuation model suggested by Boore,Joyner and Fumal(1993). 相似文献
5.
Yantong FENG Wen ZHANG Zhaochu HU Yongsheng LIU Tao LUO Tao HE Hong LIU Kun YU 《中国科学:地球科学(英文版)》2022,65(1):182-196
We proposed a new laser analytical mode,which used the high-frequency laser ablation to deliberately obtain the peak-shape signal profile,combined with the linear regression calibration(LRC)method to calculate elemental or isotopic ratios.In order to assess the performance of the new laser analytical mode for the application in the field of earth science,we systematically investigated the elemental quantitative analysis with high spatial resolution(10μm),rapid U-Pb dating in zircons and accurate Sr-Hf isotope analysis in geological samples.The new high-frequency laser analysis technology(20 Hz,100 pulses)reduced the limit of detection(LOD)of 25 elements to 0.005-0.16μg g-1 with crater diameters of 10μm,which are significantly lower(decrease to 2-20%)than previous researches.The quantitative analysis of five silicate glass reference materials showed that the precision and accuracy of the 25 trace elements(with the concentration ranging from 0.17 to 683μg g-1)were better than 16% and 15%,respectively.The new methods raised the analytical throughput of zircon U-Pb dating,Sr isotope ratios and Hf isotope ratios to 250 analyses per hour,144 analyses per hour and 120 analyses per hour in theory,while the analytical accuracy and precision were not affected.The detailed investigations showed that the proposed new laser analytical mode has good application effects in the field of earth sciences. 相似文献
6.
The column-to-beam flexural strength ratio(CBFSR)has been used in many seismic codes to achieve the strong column-weak beam(SCWB)failure mode in reinforced concrete(RC)frames,in which plastic hinges appear earlier in beams than in columns.However,seismic investigations show that the required limit of CBFSR in seismic codes usually cannot achieve the SCWB failure mode under strong earthquakes.This study investigates the failure modes of RC frames with different CBFSRs.Nine typical three-story RC frame models with different CBFSRs are designed in accordance with Chinese seismic codes.The seismic responses and failure modes of the frames are investigated through time-history analyses using 100 ground motion records.The results show that the required limit of the CBFSR that guarantees the SCWB failure mode depends on the beam-column connection type and the seismic intensity,and different types of beam-column connections exhibit different failure modes even though they are designed with the same CBFSR.Recommended CBFSRs are proposed for achieving the designed SCWB failure mode for different types of connections in RC frames under different seismic intensities.These results may provide some reference for further revisions of the SCWB design criterion in Chinese seismic codes. 相似文献
7.
Coupled effects of railway vibration, rainfall, and drying-wetting cycles contribute to new types of loess disasters such as the collapse and vibration-induced settlement of the railway subgrade, loess mass disintegration, and slope sliding,during the large-scale construction and operation of high-speed or heavy-haul railways in China. This has significant consequences for railways that require millimetre-level deformation control, seriously threatening railway operation and people's lives. Therefore, for the first time, "five vibration-induced effects" on loess subjected to vibration, water immersion, and drywetting cycles are discussed including the vibration-induced acceleration of cracking, infiltration, disintegration, sliding, and subsidence. In this paper, the vibration-induced acceleration of infiltration is discussed mainly. The response of loess to locomotive vibration along railways was determined using field sampling and data processing. The dominant frequency of locomotive vibration are 18-22 Hz and the maximum amplitude is 0.4 mm. Tests regarding the vibration-induced acceleration of the permeability were conducted on intact loess using a newly developed vibration permeability apparatus. The results reveal that the vibration accelerates the water permeability and increases the water saturation of loess. The permeability coefficient of saturated loess under vibration is ~1.5-20 times of that without vibration, reaching a maximum at a vibration frequency of 20 Hz.Vibration-induced infiltration tests were carried out on a loess column and the vibration-induced acceleration of water infiltration, wetting front evolution, and air outflow were analysed. The vibration-induced acceleration of infiltration strongly depends on the dry density, vibration frequency, and vibration amplitude. This pioneering work explores the mechnism of loess disasters triggered by locomotive vibration, rainfall, and drying-wetting cycles. 相似文献
8.
The northwestward subduction of the Izanagi Plate beneath the eastern Eurasian Plate during the Late Mesozoic caused a series of compressional deformation events in the Yanshan fold and thrust belt(YFTB), but the tectonic deformation timing, tectonic properties and relationship between tectonic uplift and sediment accumulation in the intermontane basins continue to be debated. For this reason, the sedimentology, sediment provenance, and basin structure of the Qianjiadian Basin(QJB) in the northern Beijing region during the Late Jurassic and Early Cretaceous were studied in detail. The results suggest that a fault-propagation fold-type(FPFT) growth structure and growth strata developed on the western edge of the QJB and that the top part of Member 2 and Member 3 of the Tuchengzi Formation are growth strata controlled by the limb rotation mechanism. In two small thrust faults in the QJB, the Mesoproterozoic Xiamaling Formation is thrust over the Tuchengzi Formation, and these faults may have controlled the development of the fault-bend fold-type growth strata. An analysis of the "source-to-sink" process suggests that the hanging wall succession of the Shangyi-Pingquan fault(SPF) was the main source area of the Late Jurassic to early Early Cretaceous strata in the QJB. A zircon206 Pb/238 U age of 140.8±2.4 Ma for the volcanic rocks at the bottom of the FPFT growth strata represents the timing of the initiation of FPFT growth structure development. The discovery of the FPFT growth structure and growth strata in the QJB indicate that the QJB was an intermontane flexural basin controlled by fold and thrust structures during the early Early Cretaceous. Near the E-W-trending SPF, the NE-SW-trending Qianjiadian thrust fault(QJTF) and two small intrabasinal thrust faults may constitute a unified right-lateral strike-slip system that formed in response to the northwestward flat subduction of the Izanagi Plate beneath the East Asian continent during the Jurassic-Early Cretaceous. 相似文献
9.
Songtao Li Yong Xia Jianzhong Liu Zhuojun Xie Qinping Tan Yimeng Zhao Minghua Meng Lijin Tan Rong Nie Zepeng Wang Guanghong Zhou Haiyan Guo 《Acta Geochimica》2019,(4):587-609
The newly discovered Baogudi gold district is located in the southwestern Guizhou Province,China,where there are numerous Carlin-type gold deposits.To better understand the geological and geochemical characteristics of the Baogudi gold district,we carried out petrographic observations,elemental analyses,and fluid inclusion and isotopic composition studies.We also compared the results with those of typical Carlin-type gold deposits in southwestern Guizhou.Three mineralization stages,namely,the sedimentation diagenesis,hydrothermal(main-ore and late-ore substages),and supergene stages,were identified based on field and petrographic observations.The main-ore and late-ore stages correspond to Au and Sb mineralization,respectively,which are similar to typical Carlin-type mineralization.The mass transfer associated with alteration and mineralization shows that a significant amount of Au,As,Sb,Hg,Tl,Mo,and S were added to mineralized rocks during the main-ore stage.Remarkably,arsenic,Sb,and S were added to the mineralized rocks during the late-ore stage.Element migration indicates that the sulfidation process was responsible for ore formation.Four types of fluid inclusions were identified in ore-related quartz and fluorite.The main-ore stage fluids are characterized by an H2O–NaCl–CO2–CH4±N2system,with medium to low temperatures(180–260℃)and low salinity(0–9.08%NaCl equivalent).The late-ore stage fluids featured H2O–NaCl±CO2±CH4,with low temperature(120–200℃)and low salinity(0–7.48%Na Cl equivalent).The temperature,salinity,and CO2and CH4concentrations of ore-forming fluids decreased from the main-ore stage to the late-ore stage.The calculated δ^13C,d D,and δ^18O values of the ore-forming fluids range from-14.3 to-7.0%,-76 to-55.7%,and 4.5–15.0%,respectively.Late-ore-stage stibnite had δ^34S values ranging from-0.6 to 1.9%.These stable isotopic compositions indicate that the ore-forming fluids originated mainly from deep magmatic hydrothermal fluids,with minor contributions from strata.Collectively,the Baogudi metallogenic district has geological and geochemical characteristics that are typical of Carlin-type gold deposits in southwest Guizhou.It is likely that the Baogudi gold district,together with other Carlin-type gold deposits in southwestern Guizhou,was formed in response to a single widespread metallogenic event. 相似文献
10.
Adding dampers is a commonly adopted seismic risk mitigation strategy for modern buildings, and the corresponding design procedure of dampers has been well established by the Chinese Building Code. Even though all types of dampers are designed by the same procedure, actual seismic performance of the building may differ from one to the others. In this study, a nine-story benchmark steel building is established, and three different and typical types of dampers are designed according to the Chinese Building Code to realize structural vibration control under strong earthquake excitation. The seismic response of the prototype building equipped with a viscoelastic damper, viscous damper and buckling-restrained brace(BRB) subjected to 10 earthquake records are calculated, and Incremental Dynamic Analysis(IDA) is performed to describe progressive damage of the structure under increasing earthquake intensity. In the perspective of fragility, it shows that the viscoelastic damper has the highest collapse margin ratio(CMR), and the viscous damper provides the best drift control. Both the BRB and viscoelastic dampers can effectively reduce the floor acceleration responses in the mid-rise building. 相似文献
11.
Qian Lu Shijie Wang Xiaoyong Bai Fang Liu Shiqi Tian Mingming Wang Jinfeng Wang 《Acta Geochimica》2020,(1):116-126
In near-infrared spectroscopy,the traditional feature band extraction method has certain limitations.Therefore,a band extraction method named the three-step extraction method was proposed.This method combines characteristic absorption bands and correlation coefficients to select characteristic bands corresponding to various spectral forms and then uses stepwise regression to eliminate meaningless variables.Partial least squares regression(PLSR)and extreme learning machine(ELM)models were used to verify the effect of the band extraction method.Results show that the differential transformation of the spectrum can effectively improve the correlation between the spectrum and nickel(Ni)content.Most correlation coefficients were above 0.7 and approximately 20%higher than those of other transformation methods.The model effect established by the feature variable selection method based on comprehensive spectral transformation is only slightly affected by the spectral transformation form.Infive types of spectral transformation,the RPD values of the proposed method were all within the same level.The RPD values of the PLSR model were concentrated between 1.6 and 1.8,and those of the ELM model were between 2.5 and2.9,indicating that this method is beneficial for extracting more complete spectral features.The combination of the three-step extraction method and ELM algorithm can effectively retain important bands associated with the Ni content of the soil.The model based on the spectral band selected by the three-step extraction method has better prediction ability than the other models.The ELM model of the first-order differential transformation has the best prediction accuracy(RP^2=0.923,RPD=3.634).The research results provide some technical support for monitoring heavy metal content spectrum in local soils. 相似文献
12.
福建和台湾地震台网测定地震震级差异研究 总被引：1，自引：0，他引：1
介绍了闽、台地震台网及观测资料情况,统计了1971年以来两台网均有测定的在台湾及其邻近海域地区发生的6级以上地震,并计算了福建地震台网测定近震震级范围、闽台两地震台网测定震级的差量、平均偏差及标准偏差.结果表明,福建地震台网测定台湾及其邻近海域地区强震震级普遍偏小,存在0.3～0.5级的偏差.进而分析了闽、台地震台网测定台湾强震震级的差异关系,对福建地震台网测定台湾及其邻近海域强震震级偏差改正及闽、台今后开展地震联合观测有重要参考价值. 相似文献
13.
太湖鲫鱼数量变化的规律及与环境间关系的分析 总被引：6，自引：1，他引：5
通过食物组成分析和渔获物组成调查,并结合历年渔获量统计和环境监测资料,研究了太湖鲫鱼数量变化的规律、机制及与环境间的相互关系.渔获物调查和渔获量统计资料均表明:近年鲫鱼数量不断增加,已成为太湖仅次于鲚鱼的重要鱼类2004年渔获物调查中,鲫鱼占鱼类总重量的8.40%±2.69%,占鲤、鲫鱼渔获量的65.08%±15.47%;历年渔获量统计显示,1952-1998年鲤、鲫鱼渔获量相对稳定在1010.1±367.2 t、占鱼类总量8.89%±5.33%,1999年上升达到2547.4 t、占9.45%,2000年达到3708.7 t,占12.18%;年龄组成分析表明,鲫鱼低龄化趋势在加剧.食性分析表明:在7-12月,微囊藻占鲫鱼食物体积的83.65%-93.99%.分析认为:太湖鲫鱼以微囊藻为主要食物;富营养化加重为其提供了充足饵料,实施禁渔期、禁渔区等措施使其繁殖得到保障,捕捞强度过高导致其年龄组成低龄化、个体小型化.而太湖鲫鱼以蓝藻为主要食物,可能对蓝藻有抑制作用. 相似文献
14.
15.
Yanju Peng Yuejun Lu Jiaquan Yan Rongyu Tang Junqin Wang Jiagang Li 《地震工程与工程振动(英文版)》2010,9(2):223-231
This paper analyzes the seismicity in Bohai Sea,introducing a shape factor K to characterize the seismic risk distribution in sub-regions of the sea. Based on the seismic design ground motions for 46 platforms located in the Bohai Sea,a statistical analysis was performed for different peak ground acceleration (PGA) ratios at two different probability levels. In accordance with the two-stage design method,a scheme of two seismic design levels is proposed,and two seismic design objectives are established respectively for the strength level earthquake and the ductility level earthquake. By analogy with and comparison to the Chinese seismic design code for buildings,it is proposed that the probability level for the strength level earthquake and ductility level earthquake have a return period of 200 and 1000 - 2500 years,respectively. The validity of these proposed values is discussed. Finally,the PGAs corresponding to these two probability levels are calculated for different sub-regions of the Bohai Sea. 相似文献
16.
The Qaidam Basin on the Qinghai-Tibet Plateau is well endowed with a variety of critical metals,such as Li and Rb.However,little is known about the distribution,source,and enrichment mechanisms of these elements.In this paper,we present results of systematic geochemical and H-O-B isotopic analyses of brines in the Tertiary and Quaternary sediments of the Qaidam basin.The results reveal that the paleobrines from oil-bearing anticlines at Dafengshan,Nanyishan,Youquanzi,Jiandingshan,and Jianshishan are significantly enriched in Li and Rb,whose contents are 81.1-128.9 mg L-1and 4.5-29.2 mg L-1,respectively,reaching levels of economic significance.High Rb contents(up to 12.5 mg L-1)and well-endowment of Li also characterize the Dongtai,Xitai,Yiliping,and Senie salt lakes in the Qaidam Basin.The Tertiary paleobrine average inδD andδ18O at-40.7‰and 2.84‰,respectively.The paleobrine with the highest Li and Rb hasδD andδ18O values close to magmatic water.Theδ11B values are lower than those of river water but close to those of geothermal fluids,suggesting that replenishment by deep magmatic hydrothermal fluid is most likely the key mechanism for the anomalous enrichment of these elements in the paleobrines,though evaporation and water-rock reactions have contributed to the critical metal mineralization.The anomalous enrichment of Li and Rb in modern salt lake brines is closely related to the input of volcanic geothermal water.The relatively high Li and Rb contents of intercrystalline brines in salt lakes of the western Qaidam Basin and the increase of Li and Rb contents with increasing depth were caused by upwelling of local paleobrines along the fault zones. 相似文献
17.
Diverted sediment causes a wide range of problems at small diversion works.The difference in water levels between low flows and floods,low investment capital and presence of cohesive sediment and fine non-cohesive sediment coupled with a requirement for a high level of supply assurance makes the design of such hydraulic structures complex.Vortex settling basins(VSBs)offer a promising alternative to conventional settling structures or hydro-cyclones.In the current study,parameters affecting the trapping of particles>75 mm were numerically investigated using ANSYS Fluent and were validated by physical modeling.It was established that the inlet velocity needs to be maintained at 0.26 m/s,the underflow to inflow ratio should be between 0.05 and 0.10,the cylinder height to cylinder diameter ratio should be greater than 0.5,and the positioning of the inlet pipe to cylinder height ratio should be greater than 0.7,with a cone of slope ratio of 2:1(V:H)and the cylinder diameter to inlet diameter ratio should be 8.2.These parameters form the basic design guidelines for VSB use at small diversion works(<100 L/s duty capacity). 相似文献
18.
The effect of seawater on vertical ground motions is studied via a theoretical method and then actual offshore ground motion records are analyzed using a statistical method. A theoretical analysis of the effect of seawater on incident plane P and SV waves at ocean bottom indicate that on one hand, the affected frequency range of vertical ground motions is prominent due to P wave resonance in the water layer if the impedance ratio between the seawater and the underlying medium is large, but it is greatly suppressed if the impedance ratio is small; on the other hand, for the ocean bottom interface model selected herein, vertical ground motions consisting of mostly P waves are more easily affected by seawater than those dominated by SV waves. The statistical analysis of engineering parameters of offshore ground motion records indicate that:(1) Under the infl uence of softer surface soil at the seafl oor, both horizontal and vertical spectral accelerations of offshore motions are exaggerated at long period components, which leads to the peak spectral values moving to a longer period.(2) The spectral ratios(V/H) of offshore ground motions are much smaller than onshore ground motions near the P wave resonant frequencies in the water layer; and as the period becomes larger, the effect of seawater becomes smaller, which leads to a similar V/H at intermediate periods(near 2 s). These results are consistent with the conclusions of Boore and Smith(1999), but the V/H of offshore motion may be smaller than the onshore ground motions at longer periods(more than 5 s). 相似文献
19.
To study the effect of a strong underwater shock wave on a concrete dam, this research aims to improve hammer impact methods in model tests. Six 1:200 scale models were designed and tested under distributed impact loads. A device was deployed for a direct measurement of the impact force at the upstream face of the dams. The model dam bases were anchored to prevent displacement. The experimental results indicate that the top part of the concrete dam is a weak zone, and the impact failure initiates with a fracture on the top of the dam. The peak value of impact stress increases when the second crack appears in the concrete dam from the upstream face to the downstream face. And, the level of the second crack in the dam body is lower as the peak value of impact stress increases. In this study, dynamic analysis was conducted by calculating the results to verify the effectiveness of a device to directly measure the impact force. This method may be used to approximately forecast the damage of concrete dam and may also be useful in other engineering applications. 相似文献
20.
A velocity formula is proposed for flow over a mobile sediment bed induced by velocity-skewed waves and current. The formula is obtained by a separation of waves and current velocities and requires seven free variables related to free stream velocity and sediment characteristics. The formula includes two parts:(1) a wave part consisting of the free stream velocity and defect function, which considers phase lead, wave boundary layer thickness, and mobile bed level, and(2) a current part, which ch... 相似文献