A tendon system to re-center steel moment frames with weak stories

A wide open bottom story of a frame building is often expected by owners for use as a garage or shops.However,this leads to weak stories due to abrupt changes in lateral stiffness and often results in unexpected story collapse as observed in many previous earthquakes.To retrofit frame buildings that have experienced weak story damage,a tendon system is proposed in this study,which consists of a set of swaying columns and tendons.The swaying columns are used to uniformly redistribute the lateral deformation along the height,while the tendons provide extra lateral stiffness and renders the entire structural system a re-centering capability.To avoid unnecessary forces to swaying columns,pin-connections are used at the bottom.Tendons are placed over the entire story to gain large elastic displacements.Parametric analysis reveals that the swaying column,with a stiffness of about 0.9 times that of the weak story,and the tendons attached at the roof,with a stiffness of 0.04 times that of the weak story,can provide the optimal performance with a maximum residual story drift angle of less than 0.5%.Online hybrid tests were carried out,which demonstrated that uniformly distributed story drifts and acceptable residual deformation could be achieved by the proposed tendon system.

Increased population exposures to extreme precipitation in Central Asia under 1.5℃ and 2℃ global warming scenarios

The increase in extreme precipitation(EP)may pose a serious threat to the health and safety of population in arid and semi-arid regions.The current research on the impact of EP on population in Central Asia(CA)is insufficient and there is an urgent need for a comprehensive assessment.Hence,we opted for precipitation and temperature data under two Shared Socioeconomic Pathways(SSP2-4.5 and SSP5-8.5)from ten Global Climate Models(GCMs),which were obtained from the NASA Earth Exchange Global Daily Downscaled Projections(NEX-GDDP-CMIP6).By integrating population data in 2020 and 2050(SSP2 and SSP5),we investigated the future changes in EP and population exposure in CA under 1.5℃and 2℃global warming scenarios(GWSs).Our analysis indicates that EP in CA is projected to increase with global warming.Under the SSP5-8.5,the maximum daily precipitation(Rx1day)exhibits an average response rate to global warming of 3.58%/K(1.99-4.06%/K).With rising temperatures,an increasing number of areas and populations in CA will be impacted by EP,especially in the Fergana valley.Approximately 25%of the population(land area)in CA is exposed to Rx1day with increases of more than 8.31%(9.32%)under 1.5℃GWS and 14.18%(13.25%)under 2℃GWS.Controlling temperature rise can be effective in reducing population exposures to EP.For instance,limiting the temperature increase to 1.5℃instead of 2℃results in a 2.79%(1.75%-4.59%)reduction in population exposure to Rx1day.Finally,we found that climate change serves as the predominant factor influencing the population exposure to EP,while the role of population redistribution,although relatively minor,should not be disregarded.Particularly for prolonged drought,the role of population redistribution manifests negatively.

Research and Implementations of Structural Monitoring for Bridges and Buildings in Japan

This paper provides a review on the development of structural monitoring in Japan, with an emphasis on the type, strategy, and utilization of monitoring systems. The review focuses on bridge and building structures using vibration-based techniques. Structural monitoring systems in Japan historically started with the objective of evaluating structural responses against extreme events. In the development of structural monitoring, monitoring systems and collected data were used to verify design assumptions, update speci cations, and facilitate the ef cacy of vibration control systems. Strategies and case studies on monitoring for the design veri cation of long-span bridges and tall buildings, the performance of seismic isolation systems in building and bridges, the veri cation of structural retro t, the veri cation of structural control systems (passive, semi-active, and active), structural assessment, and damage detec- tion are described. More recently, the application of monitoring systems has been extended to facilitate ef cient operation and effective maintenance through the rationalization of risk and asset management using monitoring data. This paper also summarizes the lessons learned and feedback obtained from case studies on the structural monitoring of bridges and buildings in Japan.

A modified generalized scaling law for the similitude of dynamic strain in centrifuge modeling

Soil strain is the key parameter to control the elasto-plastic deformation and even the failure processes.To overcome the defect that the strain of the model soil is always smaller than that of the prototype in Iai′s generalized scaling law(GSL),a modified scaling law was proposed based on Iai′s GSL to secure the same dynamic shear strain between the centrifuge model and the prototype by modulating the amplitude and frequency of the input motion at the base.A suite of dynamic centrifuge model tests of dry sand level ground was conducted with the same overall scaling factor(λ=200)under different centrifugal accelerations by using the technique of“modeling of models”to validate the modified GSL.The test results show that the modified GSL could achieve the same dynamic strain in model as that of the prototype,leading to better modeling for geotechnical problems where dynamic strain dominates the response or failure of soils.Finally,the applicability of the proposed scaling law and possible constraints on geometry scaling due to the capability limits of existing centrifuge shaking tables are discussed.

基于InSAR同震形变观测反演2010年新西兰南岛M_w7.1 Darfield地震同震破裂分布

2010年9月4日新西兰南岛Canterbury平原发生了Mw7.1地震,震源深度约为10km.本次地震发生在一条震前不为人所知的断层上.我们利用覆盖整个震区的合成孔径雷达(SAR)观测资料,通过干涉处理分析获得雷达视线向(LOS)同震形变场;以此资料为约束反演了断层的几何参数以及同震破裂分布.结果显示,该地震造成四条相对独立断层的破裂.大部分的地震矩释放发生在Greendale断层(编号1—4),其错动以右旋走滑为主,最大破裂约为8.5m.其它三条断层中,经过震源的逆冲断层最大破裂为5.1m(编号6),位于Greendale断层以西的逆冲断层最大破裂为3.5m(编号5),位于Greendale断层北面的走滑断层最大破裂为1.9m(编号7).反演的Greendale断层地表滑动与地质调查得到的地表破裂在形态和数值上均吻合较好.本次地震释放的地震矩为5.0×1019 N.m,矩震级为7.1.板块边界带形变场分析表明,Darfield地震的发生受边界带应变分配在该地区残留构造应力场控制,其复杂性体现了区域构造应力场的特点.地震对其周围地区的应力场影响较大,库仑应力增加区与余震分布有一定对应关系,并在2011年Christchurch 6.3级地震发震断层区域造成约0.1bar的库仑应力增加,对此地震有一定的触发作用.

Accurate and rapid error estimation on global gravitational field from current GRACE and future GRACE Follow-On missions

Firstly, the new combined error model of cumulative geoid height influenced by four error sources, including the inter-satellite range-rate of an interferometric laser （K-band） ranging system, the orbital position and velocity of a global positioning system （GPS） receiver and non-conservative force of an accelerometer, is established from the perspectives of the power spectrum principle in physics using the semi-analytical approach. Secondly, the accuracy of the global gravitational field is accurately and rapidly estimated based on the combined error model; the cumulative geoid height error is 1.985× 10^-1 m at degree 120 based on GRACE Level 1B measured observation errors of the year 2007 published by the US Jet Propulsion Laboratory （JPL）, and the cumulative geoid height error is 5.825 × 10^-2 m at degree 360 using GRACE Follow-On orbital altitude 250 km and inter-satellite range 50 km. The matching relationship of accuracy indexes from GRACE Follow-On key payloads is brought forward, and the dependability of the combined error model is validated. Finally, the feasibility of high-accuracy and high-resolution global gravitational field estimation from GRACE Follow-On is demonstrated based on different satellite orbital altitudes.

利用地面观测计算地表通量(英文)

高原地表的感热和潜热通量在亚洲季风系统中有很重要的作用。由于高原地域辽阔,且自然环境较严酷,不利于建立完善的地面观测系统。因此,卫星遥感观测就成为测算高原整体感热和潜热通量的有效工具。地面场地的观测结果作为地表通量的真实值,对于卫星遥感测算是非常重要的。它也为构建陆面—大气模型提供了科学依据,是卫星资料的资料同化系统中的重要组成部分。计算场地热量通量有几种不同的处理方法。最简单的方法利用有效的观测和试验的参数,可以给出稳定连续的估计。愈精确的Bowen比或者廓线的观测能给出愈精确的信息。综合了湍流测量及辐射测量、土壤热通量的观测结果的估计对陆面—大气相互作用进行了详细的描述,以适应模式的发展。从1998年开始,这些方法联合应用到青藏高原;场地通量观测方面的成果以及目前对其理解将在本文中做一概述。

Physical Explanation on Designing Three Axes as Different Resolution Indexes from GRACE Satellite-Borne Accelerometer

The GRACE Earth＇s gravitational field complete up to degree and order 120 is recovered based on the same and different three-axis resolution indexes from satellite-borne accelerometer using the improved energy conservation principle. The results show that designing XA1（2） as low-sensitivity axis （3 × 10^-9 m/s^2） of accelerometer and designing YA1（2） and ZA1（2） as high-sensitivity axes （3 × 10^-10 m/s^2） are reasonable. The physical reason why the resolution of XA1（2） is one order of magnitude lower than YA1（2） and ZA1（2） is that non-conservative forces acting on GRACE satellites are mainly decomposed into YA1（2） and ZA1（2） in the orbital plane. Since XA1（2） is not orthogonal accurately to orbital plane during the development of accelerometer, the measurement of XA1（2） can not be thrown off entirely, but be reduced properly.

Optimal Active Control of Wave-Induced Vibration for Offshore Platforms

An obvious motivation of this paper is to examine the effectiveness of the lateral vibration control of a jacket type offshore platform with an AMD control device, in conjunction with H-2 control algorithm, which is an optimal frequency domain control method based on minimization of H-2 norm of the system transfer function In this study, the offshore platform is modeled numerically by use of the finite element method, instead of a lumped mass model This structural model is later simplified to be single-degree-of-freedom (SDOF) system by extracting the first vibration mode of the structure. The corresponding 'generalized' wave force is determined based on an analytical approximation of the first mode shape function, the physical wave loading being calculated from the linearized Morison equation. This approach facilitates the filter design for the generalized force. Furthermore, the present paper also intends to make numerical comparison between H-2 active control and the corresponding passive control using a TMD with the same device parameters.

Suppression of Wave-Excited Vibration of Offshore Platform by Use of Tuned Liquid Dampers

This paper describes experimental and theoretical investigations of Tuned Liquid Damper (TLD) characteristics for suppressing the wave-excited structural vibration. The structural model for the experiments is scaled according to a full size offshore platform by matching their dynamic properties. Rectangular TLDs of different sizes with partially filled liquid are examined. By observing the performance and behavior of TLDs through laboratory experiments, the Study investigates the influence of a number of parameters, including container size, container shape, frequency ratio, and incident wave characteristics. In an analytical study, a mathematical model that describes the nonlinear behavior of liquid in TLD and the interaction of TLD and structure is prerequisite. The validity of the model is evaluated and simulating results can reasonably match the corresponding experimental results.

Integrated rockfall hazard and risk assessment along highways: An example for Jiuzhaigou area after the 2017 Ms 7.0 Jiuzhaigou earthquake, China

This work addresses the integrated assessment of rockfall(including landslides) hazards and risk for S301, Z120, and Z128 highways, which are important transportation corridors to the world heritage site Jiuzhai Valley National Park in Sichuan, China. The highways are severely threatened by rockfalls or landslide events after the 2017 Ms 7.0 Jiuzhaigou earthquake. Field survey(September 14-18 th, 2017, May 15-20 th, 2018, and September 9-17 th, 2018), unmanned aerial vehicle(UAV), and satellite image identified high-relief rockfalls and road construction rockfalls or landslides along the highway. Rockfall hazard is qualitatively evaluated using block count, velocity, and flying height through a 3D rockfall simulation at local and regional scales. Rockfall risk is quantitatively assessed with rockfall event probability, propagation probability, spatial probability, and vulnerability for different block volume classes. Approximately 21.5%, 20.5%, and 5.3% of the road mileage was found to be subject to an unacceptable(UA) risk class for vehicles along S301, Z120, and Z128 highways, respectively. Approximately 20.1% and 3.3% of the road mileage belong to the UA risk class for tourists along Z120 and Z128 highways, respectively. Results highlighted that high-relief rockfall events were intensively located at K50 to K55(Guanmenzi to Ganheba) and K70 to K72(Jiudaoguai to Shangsizhai Village) road mileages along S301 highway and KZ18 to KZ22(Five Flower Lake to Arrow Bamboo Lake) road mileages, KZ30(Swan Lake to Virgin Forests), and KY10.5 kilometers in Jiuzhai Valley. Rockfalls in these locations were classified under the UA risk class and medium to very high hazard index. Road construction rockfalls were located at K67(Jiuzhai Paradise) and K75–K76 kilometers along S301 highway and KZ12 to KZ14(Rhino Lake to Nuorilang Waterfall), KZ16.5 to KZ17.5(Golden Bell Lake), KY5(Lower Seasonal Lake), and KY14(Upper Seasonal Lake) kilometers along Z120 and Z128 highway in Jiuzhai Valley. Rockfalls in these areas were within a reasonable practicable risk to UA risk class and very low to medium hazard index. Finally, defensive measures, including flexible nets, concrete walls, and artificial tunnels, could be selected appropriately on the basis of the rockfall hazard index and risk class. This study revealed the integration between qualitative rockfall hazard assessment and quantitative rockfall risk assessment, which is crucial in studying rockfall prevention and mitigation.

Different characteristics of the structure of atmospheric boundary layer between dry and rainy periods over the northern Tibetan Plateau

In this paper, based on in-situ observational data of the Coordinated Enhanced Observing Period （CEOP） Asia-Australia Monsoon Project （CAMP） on the Tibetan＇Plateau （CAMP-Tibet）, structure of the Atmospheric Boundary Layer （ABL） was preliminarily studied during the dry and rainy seasons. The main results show： （a） Diurnal variation of the ABL is obvious over the northern Tibetan Plateau area. The height of the ABL is different with the season change, which ranges from 2,211 m to 4,430 m during the pre-monsoon season and from 1,006 m to 2,212 m during the monsoon season. The ABL height is higher during the dry period than during the rainyigeriod. （b） The humidity is lower during the dry period than during the rainy period, and there are reverse humidity during both periods. （c） Horizontal wind direction is mostly west during the dry period, east under the height of 2,500 m and west above the height of 2,500 m during the rainy period. The wind speed is low during both the rainy and dry periods in the lower ABL layer. The wind speed is stronger within the upper ABL during the dry period than dtn-ing the rainy period.

Flexible substructure online hybrid test system using conventional testing devices

This paper presents a substructure online hybrid test system that is extensible for geographically distributed tests. This system consists of a set of devices conventionally used for cyclic tests to load the tested substructures onto the target displacement or the target force. Due to their robustness and portability, individual sets of conventional loading devices can be transported and reconfigured to realize physical loading in geographically remote laboratories. Another appealing feature is the flexible displacement-force mixed control that is particularly suitable for specimens having large disparities in stiffness during various performance stages. To conduct a substructure online hybrid test, an extensible framework is developed, which is equipped with a generalized interface to encapsulate each substructure. Multiple tested substructures and analyzed substructures using various structural program codes can be accommodated within the single framework, simply interfaced with the boundary displacements and forces. A coordinator program is developed to keep the boundaries among all substructures compatible and equilibrated. An Interuet-based data exchange scheme is also devised to transfer data among computers equipped with different software environments. A series of online hybrid tests are introduced, and the portability, flexibility, and extensibility of the online hybrid test system are demonstrated.

Disaster Risk Science:A Geographical Perspective and a Research Framework

In this article,we recall the United Nations’30-year journey in disaster risk reduction strategy and framework,review the latest progress and key scientific and technological questions related to the United Nations disaster risk reduction initiatives,and summarize the framework and contents of disaster risk science research.The object of disaster risk science research is the"disaster system"consisting of hazard,the geographical environment,and exposed units,with features of regionality,interconnectedness,coupling,and complexity.Environmental stability,hazard threat,and socioeconomic vulnerability together determine the way that disasters are formed,establish the spatial extent of disaster impact,and generate the scale of losses.In the formation of a disaster,a conducive environment is the prerequisite,a hazard is the necessary condition,and socioeconomic exposure is the sufficient condition.The geographical environment affects local hazard intensity and therefore can change the pattern of loss distribution.Regional multi-hazard,disaster chain,and disaster compound could induce complex impacts,amplifying or attenuating hazard intensity and changing the scope of affected areas.In the light of research progress,particularly in the context of China,we propose a threelayer disaster risk science disciplinary structure,which contains three pillars(disaster science,disaster technology,and disaster governance),nine core areas,and 27 research fields.Based on these elements,we discuss the frontiers in disaster risk science research.

Analysis of Turbulence Characteristics over the Northern Tibetan Plateau Area

Based on CAMP/Tibet [Coordinated Enhanced Observing Period （CEOP） Asia-Australia Monsoon Project （CAMP） on the Tibetan Plateau] turbulent data collected at the Bujiao （B J） site of the Nagqu area, the turbulent structure and transportation characteristics in the near surface layer during summer are analyzed. The main results show that the relationship between the normalized standard deviation of 3D wind speed and stability satisfies the similarity law under both unstable and stable stratifications. The relations of normalized standard deviation of temperature and specific humidity to stability only obey the ＂-1/3 power law＂ under unstable conditions. In the case of stable stratifications, their relations to stability are dispersing. The sensible heat dominates in the dry period, while in the wet period, the latent heat is larger than the sensible heat.

Swells of the East China Sea

Over the past few decades,an increasing number of marine activities have been conducted in the East China Sea,including the construction of various marine structures and the passage of large ships.Marine safety issues are paramount and are becoming more important with respect to the likely increase in size of ocean waves in relation to global climate change and associated typhoons.In addition,swells also can be very dangerous because they induce the resonance of floating structures,including ships.This study focuses on an investigation of swells in the East China Sea and uses hindcast data for waves over the past 5 years in a numerical model,WAVEWATCH III(WW3),together with historical climate data.The numerical calculation domain covers the entire North West Pacific.Next,swells are separated and analyzed using simulated wave fields,and both the characteristics and generation mechanisms of swells are investigated.

Modeling of random wave transformation with strong wave-induced coastal currents

The propagation and transformation of multi-directional and uni-directional random waves over a coast with complicated bathymetric and geometric features are studied experimentally and numerically. Laboratory investigation indicates that wave energy convergence and divergence cause strong coastal currents to develop and inversely modify the wave fields. A coastal spectral wave model, based on the wave action balance equation with diffraction effect （WABED）, is used to simulate the transformation of random waves over the complicated bathymetry. The diffraction effect in the wave model is derived from a parabolic approximation of wave theory, and the mean energy dissipation rate per unit horizontal area due to wave breaking is parameterized by the bore-based formulation with a breaker index of 0.73. The numerically simulated wave field without considering coastal currents is different from that of experiments, whereas model results considering currents clearly reproduce the intensification of wave height in front of concave shorelines.

Effect of different inter-satellite range on measurement precision of Earth’s gravitational field from GRACE

The precision of Earth＇s gravitational field from GRACE up to degree and order 120 was studied for different inter-satellite ranges using the improved energy conservation principle. Our simulated result shows that： For long wavelength （L≤20） at degree 20, the cumulative geoid-height error gradually decreased with increasing range, from 0. 052 cm for 110 km to 1. 156 times and 1. 209 times as large for 220 km and 330 kin, respectively. For medium-wavelength （ 100 ≤ L ≤ 120） at degree 120, the cumulative geoid-height error de- creased from 13. 052 cm for 110 km, to 1. 327 times and 1. 970 times as large for the ranges of 220 km and 330 km, respectively; By adopting an optimal range of 220 ± 50 km, we can suppress considerably the loss of precision in the measurement of the Earth＇ s long-wavelength and medium-wavelength gravitational field.

Identifying the most explainable fault ruptured of the 2018 Palu-Donggala earthquake in Indonesia using coulomb failure stress and geological field report

This study investigates the relation between the Coulomb failure stress of the mainshock with the aftershocks sequence following the 2018 Palu-Donggala earthquake in Indonesia.We calculate the Coulomb failure stress using the available coseismic fault models,which had varied moment magnitudes between M_W7.53~M_W7.62.Different interpretations of the fault sources were suggested by previous studies.While two fault models suggested that one inland fault segment ruptured during the earthquake,another fault model proposed that two fault segments ruptured inland of Central Sulawesi and along the coast of Palu bay.We further overlay the positive and negative values of Coulomb failure stress with the reported relocated aftershock.We find that only by conducting Coulomb failure stress analysis,we can not favour the preference of the coseismic fault which explains aftershock distribution.This investigation demonstrates that additional observational data from geological field surveys are required to identify the surface rupture in comparison with the coseismic fault model.

Lateral load performance and seismic demand of unbonded scrap tire rubber pad base isolators

The scrap tire rubber pad(STRP)made by natural or synthetic rubber and high strength reinforcing cords exhibits substantial vertical stiffness and horizontal flexibility,and these properties can be regarded as suitable for seismic isolators for structures.The use of environmentally burdensome scrap tires as STRP isolators might be convenient as an efficient and low-cost solution for the implementation of aseismic design philosophy for low-to-medium rise buildings,especially in developing countries.Finite element analyses of unbonded square and strip-shaped STRP isolators subjected to a combination of axial and lateral loads are conducted to investigate its lateral deformation performance under seismic loading.The rubber of the isolator is modelled with Mooney-Rivlin hyperelastic and Prony viscoelastic materials,including the Mullins material damage effect.The influence of the length-to-width ratio and bearing height on the isolator performance is assessed in terms of the force-displacement relationship,horizontal stiffness,damping,and isolation periods.It is shown that the dependence of stiffness on the length-to-width ratio is significant in the longitudinal direction and minor in the transverse direction.The STRP isolators following the proposed design criteria are shown to satisfy the performance requirement at different levels of seismic demand specified by the ASCE/SEI 7-2010 seismic provisions.