1.Introduction

The importance of seismic safety for an ultra-high arch dam cannot be over-emphasized,as any potential failure of such a dam under extreme loadings,including seismic hazards,may cause a major disaster,with devastating economic and social consequences.It is a truly big challenge for dam designers to model the real behaviors of ultra-high arch dams under operational and seismic loadings and with realistic consideration of all the important practical factors and nonlinear features involved(Zhang et al.,2014).

The dam static safety criteria in China include limits for the allowable stresses and the factors of safety against sliding.These are similar to those used by the United Sates Bureau of Reclamation(USBR,1977),the United States Army Corps of Engineers(USACE,1994),the Federal Energy Regulatory Commission(FERC,1999),and the Australian National Committee on Large Dams(ANCOLD,2013).In contrast,there are no universally applicable codes and regulations for the seismic design of concrete arch dams;they are instead evaluated on a case-by-case basis(Jonker and Espandar,2014).

（3）分析曲线，随泡制吋间增加，亚硝酸盐含量变化趋势均表现为________，并在第_____天均达到最大值。

肾司二阴：肾主封藏，既开窍于前阴，又开窍于后阴。后阴是排泄粪便的通道。粪便的排泄本是大肠的传导功能，但脏象学说常常把大肠的功能统属于脾的运化功能范畴。脾之运化赖肾以温煦和滋润，所以大便的排泄与肾的功能有关。肾的阴阳失调可出现泄泻、便秘等大便异常。饮食之受纳在于胃，便溺之排泄关乎肾。

The effects of fluid-structure interaction on the seismic behavior of dams have been extensively studied(Ghaemian and Ghobarah,1998;Fahjan et al.,2003;Bouaanani and Lu,2009;Aftabi Sani and Lot fi,2010;Kalateh and Attarnejad,2011).The widely accepted approach based on the generalized Westergaard theory(Westergaard,1933;Mays and Roehm,1991)was employed in this study,in which the reservoir water was considered an additional concentrated mass spreading out over the dam.

Various types of foundation models may be considered in seismic analysis of concrete dams.The foundation can be considered rigid,massless,or massed.Zhang et al.(2009)found that stresses,displacements,and contraction joint openings in arch dams are significantly reduced both in linear and nonlinear analyses using the viscoelastic boundary model rather than the massless foundation model.In the seismic design of the Xiluodu Arch Dam,foundation rocks and faults,as well as the dam,were considered in the dam-foundation reservoir system.The faults were simulated as contact elements with a certain thickness and a system damping ratio of 0.05.

Contraction joints play an important role in both the static and seismic analysis of concrete arch dams(Ahmadi et al.,2001;Wang et al.,2013).In the safety evaluation of the arch dam,23 contraction joints were simulated using a joint model that could simulate the contact between two adjacent nodes in a three-dimensional(3D)domain.

ERP系统在优化企业的内部结构，合理配置各种信息和资源方面具有一定的优势，但是，各种信息资源的合理使用及配置必须要有一套先进的管理制度作为前提，只有这样，才能有效实现各种资源的合理利用。所以，企业要想更好地发挥ERP系统的影响及作用，就要建立相关的管理制度，以此来明确和规范各个部门、员工的工作职责和分工，只有供应、销售、物资、生产等各个部门都明确自己的职责，才能及时、准确的录入信息，最终方便企业财务部门汇集、整理所有的数据和信息。

Saouma et al.(2011)carried out a time-history finite element analysis of rock-structure interaction considering the lateral energy dissipation and the interaction between the farfield and the numerical model itself.Hariri-Ardebili et al.(2013)studied dynamic stability of a coupled reservoir-damfoundation system assuming infinite elements and viscous boundaries at the far- field of the massed foundation model.In seismic safety evaluation of the Xiluodu Arch Dam,a 3D frequency domain and infinite boundary elements were used to simulate the arch dam foundation and transfer the dynamic frequency domain stiffness to time domain parameters.

具体实施主要包括三个环节，第一，在手术室、介入导管室应用射频技术RFID医院布草洗涤管理系统与医院自动化智能发衣柜、更衣柜、衣服回收柜连接；第二，实现应用RFID刷手术衣识别、追溯；第三，实现医护手术间提醒、衣柜循环使用等功能。

Thermal loads have a significant effect on the structural behavior of thin concrete arch dams(Leger et al.,1993),and have been considered in dam seismic design through investigation of the differences between the dam closure temperature and concrete temperatures in typical seasons during operation.

This paper presents the seismic design of an ultra-high arch dam and illustrates the evaluation of various safety criteria,including the allowable stresses,damage control range,and maximum opening of contraction joints,through linear response spectrum analysis,linear time-history analysis,and nonlinear time-history analysis.These analyses took into account the dam-foundation-reservoir dynamic interaction,reservoir compressibility effect,non-uniform seismic input,dissipation of seismic energy in an infinite foundation,nonlinear response of dam contraction joint opening and closing,and individual or coupled effects of the factors mentioned above.As usual for seismic analysis of arch dams(Moradloo et al.,2008),geometric nonlinearity was not taken into consideration in this study.

2.Design scheme and approach

2.1.Project overview

Located in the Xiluodu Gorge on the Jinsha River that demarcates Leibo County in Sichuan Province and Yongshan County in Yunnan Province,the Xiluodu Power Station is a large project built primarily for Electricity generation,as well as flood control,silt blocking,and navigation improvement.The height of 285.5 m makes the concrete double-curvature arch dam one of the world's highest dams.With an installed capacity of 13860 MW,the power station ranks just behind the Three Gorges Power Station in China.The power station lies in the center of the Leibo-Yongshan synclinal land mass,a relatively intact and steady tectonic unit with a stiff and integral base.After the great Wenchuan Earthquake of May 12,2008,according to the China Earthquake Administration,the horizontal earthquake component of the design peak ground accelerations(PGA)on the rock surface at the dam site corresponding to design(exceedance probability of 2%over 100 years)and checking(exceedance probability of 1%over 100 years)earthquakes were estimated to be 0.355g and 0.423g, respectively, where g is the gravitational acceleration.

The dam foundation consists of basalt layers of multiple eruptions with an integral blocky structure.The basalt layers have high strength in general,except for the gently sloped dislocation zones between and within the layers.The concrete arch dam is constructed on rocks of different levels varying in elevation.The top 50-m zone of the foundation is mainly located on the rocks of level III2(Wang,2016),weakly weathered and unloaded with deformation modulus ranging from 6 to 8 GPa.The middle 130-m zone of the foundation is mainly composed of weakly weathered rocks of level III1,whose deformation modulus ranges from 11 to 12 GPa without unloading.The foundation at lower elevations and the riverbed is located on rocks of level III1 and,partly,level II with a deformation modulus higher than 16 GPa.

选取我院2013级护理专业四年制同一年级两个双证书班，共118名学生为研究对象，分为实验组和对照组，两组均在第二至第三学期开设护理学基础课程。两组护生在性别、年龄、入学水平方面比较，差异无显著性（P＞0.05），具体见表 1。

The symmetric narrow U-shaped dam base is mainly composed of multistage-erupted basalts,containing 14 flow rock layers with a total thickness of 550 m.Although interformational disturbed belts have developed,the rock is massive and has high strength as a whole,suitable for construction of a high dam with a large reservoir or an underground cavern.

The standard seismic response spectrum,specified in the Code for Seismic Design of Hydraulic Structures(DL 5073-2000),was used in design and checking earthquakes.As the dam site belongs to the Class I type,the characteristic period is 0.2 s,and the maximum response spectrum βmax is 2.5.The normalized acceleration time histories used in the dynamic analysis of the Xiluodu Arch Dam are shown in Fig.1.The maximum peak value of the vertical components of ground accelerations for the earthquake was 2/3 of the horizontal components.

2.2.Loads and combinations

2.2.1.Dead load

Dead load includes the weight of both the concrete and appurtenant structures(gates,bridges,and outlet works).The weight has been loaded incrementally according to the construction procedures.

2.2.2.Temperature load

After taking into account the influence of foundation radiation damping and contraction joint opening,the stress level of the dam,especially the tensile stress on the upstream surface, decreased,most of which were released by using the time domain dynamic coupling method.The high tensile stress zone is mainly located on the left and right sides of 1/4 arch portions at middle elevation of the dam on the downstream surface,while the tensile stress zone determined through the linear FEM is mainly concentrated at the dam crest and in the low dam portions near the foundation.

2.2.3.Hydrostatic loads

The hydrostatic loads include reservoir and tailwater loads as well as silt load.Reservoir and tailwater loads were considered at the normal, flood,and low(dead)water levels.The silt load was considered to correspond to the sediment depth.

2.2.4.Hydrodynamic loads

试验配方中表活剂为非离子表面活性剂，聚合物为聚丙烯酰胺。前期开展的室内实验主要包括聚合物流变性实验、聚合物及表面活性剂吸附实验和注入体系的相对渗透率实验，对应的实验结果见图2～5。

2.2.5.Earthquake load

With a height of 285.5 m and a crest length of 681.5 m(with a length-height ratio of 2.39),this arch dam supports a hydraulic thrust of 1.4×107 t in total.25 orifices are used in four different layers in the dam body,including seven surface spillways,eight deep orifices,and ten openings for river diversion,to satisfy large flood discharge requirements.With most openings embedded,the Xiluodu ultra-high arch dam body is regarded as the most complicated hydraulic structure in the world at this time.

LNG气化站的加热气化工艺主要由空温式气化器和水浴式气化器组成，其作用是将LNG进行气化，使之成为气态天然气供用户使用。

The nonlinear FEM model of the Xiluodu Arch Dam contains the dam body and foundation rocks,as well as 23 joints and faults.The faults are simulated with contact elements with a certain thickness.The system damping ratio is set to 0.05.The whole model ranges are 1200 m,1600 m,and 900 m along the longitudinal,transversal,and vertical directions,respectively,and the model contains 27727 nodes and 80000 degrees of freedom.Fig.5 and Fig.6 illustrate the mesh and joints,respectively.

In this study,load combinations included two groups:one combined all the static loads and the other took into account the effects of earthquakes.

The static load combinations consisted of(1)case 0-1:reservoir and tailwater loads at the normal water level,dam gravity,silt,and temperature load;and(2)case 0-2:reservoir and tailwater loads at the dead water level,dam gravity,silt,and temperature load.

末次治疗后4h,取血后剥取大鼠右后踝关节滑膜和部分软骨组织,经10%甲醛固24h后,用10%EDTA溶液进行脱钙,按常规方法进行石蜡包埋、切片,HE染色后光镜下观察关节及滑膜组织的病理学变化。

The dynamic load combinations consisted of(1)case 1-1:case 0-1,together with the design earthquake load;(2)case 1-2:case 0-2,together with the design earthquake load;(3)case 2-1:case 0-1,together with the checking earthquake load;and(4)case 2-2:case 0-2,together with the checking earthquake load.

3.Static analysis of arch dam

3.1.Dam shape and concrete zoning

As controlled by the allowable compressive stress of 9 MPa and tensile stresses of 1.2 MPa(upstream surface)and 1.5 MPa(downstream surface)provided by the trial-load method in accordance with the code,and constrained by the safety factors(3.5 with the shear Friction equation and 1.3 with the pure-friction equation)against sliding of the base,the shape of the arch dam is a parabolic double-curvature dam with optimized design and safety proofing.The characteristic parameters for the shape are given in Table 2.The dam concrete is designed as described in Table 3 and Fig.2.The dynamic modulus of concrete is 1.3 times the static modulus of elasticity.As there are no standard control standards in the code,the FEM stress results are comprehensively evaluated corresponding to the allowable stresses for the trial-load method.

3.2.Static analysis results

The performance characteristics and overload capacity of the arch dam subjected to the basic load combinations were analyzed using the trial-load method,the linear and nonlinear finite element method(FEM),and geo-mechanical model tests.

According to the results of the trial-load method,most of the area of the dam body is in compression with a small tensile area distributed close to the foundation.The distributions of stress and displacement of dam surfaces are subject to general laws,and the maximum principal compressive stress is 8.96 MPa and tensile stress is 1.09 MPa.

2012年以来，欧洲专利局（EPO）每年均会对《EPO专利审查指南》（Guidelines for Examination in the EPO）进行更新，以适应EPO的发展政策及欧洲专利局上诉委员会的最新判决，今年的修订版本已于2018年11月1日起正式生效。虽然近年来EPO在专利保护客体方面的审查标准变化不大，但是2018年度的指南修改中，为了顺应人工智能等新兴技术的迅速发展，《EPO专利审查指南》的G部——可专利性部分增加了专门的一节，对人工智能相关技术的可专利性作出了规定并给出了具体示例。

The linear FEM results show dam stress distribution similar to that obtained from the trial-load method and both methods demonstrate compressive states on dam surfaces when FEM takes into consideration rock mass quality classifications,faults,dam toe reinforcements,and uses thin-layer elements with Gaussian integral stress around the foundation(an area within 1/50 dam height)to reduce the impacts of stress concentration at dam body edges.On the upstream surface the maximum principal compressive stress of around 6 MPa appears in the middle area,and on the downstream surface this value turns into 17 MPa near the dam heel.The maximum principal tensile stress on the upstream surface appears near the arch abutment at low elevation,and is 3 MPa,corresponding to the normal water level,whereas the tensile stress on the downstream surface appears at the high-elevation arch abutment,and is about 2 MPa,corresponding to the dead water level.

The sliding stability analysis of the dam base contains shear friction calculations for large and stair-stepped blocks,as well as small ones.The results show that safety factors for all assumed blocks satisfy the design requirement except that the shear friction safety factor for the block near the bottom faults is lower than 3.5.

The 3D nonlinear analysis of the arch dam was performed with the FEM program TFINE developed by Tsinghua University.Like the linear analysis,the nonlinear analysis contains dam toe reinforcement,concrete replacement at the dam foundation,and weak rocks like faults.Under the basic load combination corresponding to the normal water level,the distributions of stress and displacement agree with results of the linear analysis,and the dam is in a uniform compressive state.The maximum principal compressive stress,which is about 15-16 MPa,appears at the arch abutment on the downstream surface.The maximum principal tensile stress is 1.13 MPa,appearing at the right side of middle elevation of the arch crown on the downstream surface.

The geo-mechanical model test(Zhou et al.,2008)of the arch dam was performed to simulate the rock categories and faults in excavation and to explore the dam's overload capacity by increasing the density of water under the condition of normal water level.The overload capacity could be evaluated by the following three factors:K1,K2,and K3.K1 is the crackinitiation overload safety factor.The overload of K1P0,in which P0 is the basic load combination corresponding to the normal water level,corresponds to the moment when the first crack appears in a physical model test or to the moment when the range of yield zones reaches 1/6 of the arch dam thickness in the nonlinear FEM analysis.K2 is the quasi-elastic overload safety factor.As the overload increases further,the crack propagates in the physical model test,while the yield zones continue to expand in the nonlinear FEM simulation.The structure is stable overall,and the dam displacements remain in linear correlation with the load until the overload exceeds K2P0.K3 is the ultimate overload safety factor.The overload of K3P0 corresponds to the occurrence of a large number of cracks throughout most of the dam or foundation,and the dam becomes unstable overall in the physical model test.In the nonlinear FEM calculation,K3P0 coincides with the time when the nonlinear solution does not converge.

The results show that the safety factor K1 of the Xiluodu Arch Dam ranges from 2.0 to 2.5,while the nonlinear deformation safety factor K2 is between 5.0 and 6.0.

4.Dynamic design scheme and approach

Considering the fact that the scale of the Xiluodu Arch Dam exceeds the scope of the current design code(DL 5073-2000)and that the earthquake safety presents a challenge due to the high seismicity at the site,some key technological problems in the design procedure of the Xiluodu project arise:(1)the dynamic performance properties of the dam,(2)reliable assessment of the seismic safety capacity of the dam,and(3)the design of earthquake-resistance measures in order to ensure the dam's long-term safe operation.

For the seismic design of the Xiluodu Arch Dam,based on conventional static and dynamic analyses,through full use of sophisticated numerical analysis and physical experimental methods,a comprehensive design approach for the dam has been proposed and implemented for the first time.Furthermore,through comparison with other high arch dams,a systematic evaluation method and design criteria for seismic strengthening for ultra-high arch dams have been established.Using these approaches,the Xiluodu Arch Dam aseismic measures have been designed and completed to further ensure the seismic safety of the dam,solving the key technical problems of high dam seismic design.

Through cooperation with the China Institute of Water Resources and Hydropower Research,Tsinghua University,and Dalian University of Technology,the following approaches have been developed:

(1)The dam shape can be designed with static mechanics and checked with dynamic mechanics(Wang,2016).The structural design is first carried out by matching the fundamental load combination,then checking the earthquake resistance capacity in the case of an earthquake,and finally adjusting the shape of the dam or adding strengthening measures.

(2)The seismic design can be implemented through analysis with multiple methods,verification with multiple approaches,and evaluation on multiple scales,as well as the project analogy analysis,to help comprehensively analyze the mechanical characteristics of the dam,and properly evaluate the earthquake-resistance capacity of the dam.This includes research on code methods and modern simulation approaches.Code methods mainly refer to the rigid limit equilibrium method for dynamic stability analysis of the dam base,the dynamic trial-load method,and the linear elastic dynamic FEM.Modern simulation approaches mainly include nonlinear dynamic FEM considering radiation damping,contraction opening,material nonlinearity,and large-scale shaking table overload testing.

(3)Feasible earthquake-strengthening measures should be presented to ensure that the dam will withstand the design earthquake and not fall in an extreme event.This means that cracks may appear when the dam encounters the design earthquake but will not affect the dam's normal function of water retaining and can be fixed through measures such as grouting.When the dam suffers an extreme earthquake such as the checking earthquake,it can still safely hold the water even with apparent cracks(Chen,2012).In the latter case,the numerical calculation should be kept stable and the yield area should not run through the dam body(Zhang et al.,2009,2014).

The dynamic interaction between the reservoir and the dam during an earthquake was considered a lumped mass as determined by the generalized Westgaard theory of added mass(the same method was used throughout the study unless otherwise specified)to model incompressible fluid.Subsequent calculations have the same value unless otherwise specified.

Combined with the project analogy analysis,the earthquake-resistance capacity of the dam and potential weak parts can be comprehensively evaluated and proper strengthening measures can be taken.

5.Dynamic analysis for arch dam in codes

In accordance with DL 5073-2000,the controlling allowable stress of the Xiluodu Arch Dam based on the dynamic trial-load method is given in Table 4.The dynamic stability safety factor K cd obtained through the limit equilibrium method using the shear-friction formula is larger than 1.31.

5.1.Dynamic analysis by trial-load method

Responses of the dam structure under four dynamic load combinations were analyzed with the dynamic trial-load method,showing that the dynamic stress distributions of the dam body are similar to one another except for the difference in magnitudes,corresponding to different water levels.

县域电网指 110 kV 及以下的配电网，处于电网输电末端，直接面对电力用户。我国县供电企业普遍对通信技术和组网方式选择重视不够，县域电力通信网建设缺乏系统规划，建设及运营成本偏高，投入与产出不匹配，通信网整体水平落后于电网发展。县域电力通信网的特点见表1所列。

Load case 1-1 and case 2-1 are the controlling cases for the maximum principal compressive stress.The shaking caused the zones near the crest and arch abutment to be with the maximum principal compressive stress under earthquake conditions.The maximum compressive stresses on the upstream surface,which appear at the top arch,are 11.23 MPa and 12.89 MPa for design and checking earthquakes,respectively.On the downstream surface the values are 11.86 MPa and 12.38 MPa,respectively.During both design and checking earthquakes the stresses satisfy the criterion of dynamic allowable compressive stress of concrete.The maximum radial dynamic displacements of the dam are 10.59 cm and 12.81 cm for design and checking earthquakes,respectively.

Load case 1-2 and case 2-2 are the controlling cases for the maximum principal tensile stress.The shaking causes the zones near the crest and arch abutment at middle elevations to be in tension,with a tensile stress as high as 3.0-7.0 MPa.The extreme values at the crest are 6.92 MPa and 8.37 MPa for design and checking earthquakes,respectively.Areas where the tensile stresses are higher than controlling criterions account for 10%and 17%of the whole dam surface during design and checking earthquakes,respectively.

Contours of maximum principal dynamic stresses due to the design earthquake computed by the trial-load method are shown in Fig.3.Table 5 shows the locations of extreme principal stress values in different cases.

5.2.Linear elastic finite element analysis of arch dam

The arch dam analysis program(ADAP,Clough et al.,1973)was used to analyze the linear elastic dynamic responses of the Xiluodu Arch Dam.Results obtained from dynamic FEM are consistent with those from the trial-load method.As affected by the stress concentration,extreme stress values close to the dam edges obtained through FEM are higher than those obtained through the trial-load method,while those in the other areas,especially in the central area,are significantly lower.

The China Institute of Water Resources and Hydropower Research carried out a dynamic model test using a 5 m×5 m shaking table,which included simulations of radiation damping using artificial transmitting boundaries,geological structures,and topography,as well as sliding blocks at the dam site and vicinal areas,interactions between the dam body and reservoir water,and seven joints in the dam body,with a model scale of 1:300 as shown in Fig.10.Specific research subjects included dynamic responses to different earthquake over loadings,the earthquake level that leads to initial cracks,the development of damage,and the stability of blocks.Earthquake-resistance safety and the limit of earthquake-resistance capacity(Wang et al.,2014)can be deeply examined by precisely controlling the earthquake input to the shaking table.

Above all,results of the FEM and trial-load method show that the dam is mainly in a pressure-arch state with the largest compressive stress appearing near the dam toe and foundation areas.On the other hand,tensile stresses are relatively high in the upper crown cantilever and arch abutments on the upstream surface,and the central part of the dam on the downstream surface.

Table 6 gives the maximum values of principal stresses in different load cases computed by linear elastic FEM and Fig.4 shows the principal stress contours during the design earthquake.

5.3.Rigid limit equilibrium method for dynamic stability analysis of dam base

The dynamic stability analysis of dam abutments was performed using the shear rupture formula considering different combination coefficients of the earthquake and the working condition of the grout curtain.The dynamic anti-slide safety factors of controlling blocks at two abutments under conditions of design and checking earthquakes are given in Table 7.All the factors are larger than 1.31,satisfying the requirements of the code.

6.Nonlinear dynamic analysis of arch dam

6.1.Methods and model

The nonlinear wave propagation analysis program(NMPAP),developed by the China Institute of Water Resources and Hydropower Research,divides the computation area into the nonlinear near- field domain and the linear artificial boundary domain by decoupling the near- field wave propagation equations(Chen,2011).This program considers the dam,foundation rock,and reservoir water as an integrated wave propagation model,with boundary constraints on contact interfaces,and solves the equations in the time domain using the explicit FEM.Thus,the numerical stability depends on the minimum element size,wave speed,and time step in the calculation.This program can also simulate the sliding surface of blocks at abutments with the Mohr-Coulomb constitutive relations in a similar way of simulating joints in the dam body,using binodal dynamic contact boundaries.Using the generalized Westergaard theory,the reservoir water-added mass is applied to the corresponding nodes after diagonalization.

2.2.6.Load combinations

By taking into account the topographic and geological conditions at the dam site and the effects of free- field seismic inputs,joint opening,and radiation damping,the nonlinear dynamic FEM sees the dam-foundation as a whole subject,in order to study the dynamic strength safety of sliding planes in the foundation and the dam concrete,and the dynamic anti-sliding safety of the controlling sliding blocks,and to analyze the possible failure mechanisms and the earthquake-resistance capacity of the highly nonlinear dam-foundation system.

6.2.Results

Load case 1-2 and case 2-2 control the joint opening of the dam,in which the largest openings reach 29.94 mm and 28.75 mm,respectively,near the top of the crown cantilever,almost twice as much as in case 1-1 and case 2-1.Due to the consideration of various nonlinear factors,the displacement of the dam body from nonlinear dynamic analysis is less than those from the trial-load method and linear FEM.

The principal compressive stress distribution from nonlinear analysis is similar to the linear elastic finite element analysis result,accompanied by a stress reduction ranging from 15%to 30%.In case 1-1 and case 2-1,the maximum compressive stresses are 12.23 MPa and 13.24 MPa,respectively,which means that the dynamic compressive stresses fully satisfy the controlling criterion.

The difference between tensile stresses of the nonlinear and linear models is clear when different dam locations and different working conditions are compared.When the damisshaken by an earthquake at the normal water level,the tensile stress magnitude and over-the-limit range near the upstream dam toe from nonlinear analysis both decrease as compared to linear analysis results,whereas the tensile stress at the arch abutment on the downstream surface increases slightly.When the dam is shaken by an earthquake at the dead water level,the tensile stress magnitude and over-the-limit range at the middle-upper part of the upstream surface from nonlinear analysis significantly increase as compared to the linear elastic results.As for the stresses on the downstream surface,the magnitude increases while the over-the-limit range decreases due to the effects of faults in the middle-lower arch abutment area.

The maximum values of comprehensive static and dynamic tensile stresses during design and checking earthquakes are 9.71 MPa and 11.43 MPa,respectively,occurring at the same position where weak rock of shear-belts can be found at high elevations nearby.The local slip of the belt during an earthquake leads to the increase of the stress of the adjacent local dam area.

As the computations indicated,there are displacements along the simulated dislocation zones between and within the layers during and after the earthquake,and the displacements were larger in the load cases of high water level(case 1-1 and case 2-1).The maximum values occurred in dislocation zones,23.35 mm during the design earthquake and 27.84 mm during the checking earthquake.Moreover,the residual displacements after the earthquake took place in the same area were 17.56 mm(design earthquake)and 18.39 mm(checking earthquake).Although the displacements or residual slip occurred in dislocation zones,they did not have significant effects on the static dynamic response and safety of the dam.

Table 8 provides the maximum stress values,locations,and joint opening magnitudes in different cases from nonlinear dynamic analysis.Fig.7 shows the contours of principal stresses during the design earthquake.

7.Dynamic analysis for arch dam-foundation interaction in time domain

7.1.Method and model

The dynamic analysis model(Zhang et al.,1995;Wang et al.,2013)of dam-foundation interaction in time domain was introduced by Tsinghua University.This model uses a 3D frequency domain or an infinite boundary element to simulate the arch dam-foundation system and transfers the dynamic frequency domain stiffness to time domain parameters,through which the finite element dam model is coupled and the integrated model of finite elements,boundary elements(Shi et al.,2013),and infinite boundary elements of the arch dam-foundation in the time domain is formed.

7.2.Analysis results

The time domain arch dam-foundation interaction model was used to calculate the dynamic responses of the dam body in cases 1-1 and 1-2.The 27 joints,foundation radiation damping ratio of 0.05,dynamic water pressure,and uniform free- field seismic input were applied in this model with the assumption of equivalent homogenous rock material of bulk density of 2700 kg/m3.The standard response spectrum in the code was used as the seismic input load.Table 9 demonstrates the dynamic response results for different water levels during the design earthquake.

The stress peak values,including tensile and compressive values in both the arch and cantilever directions,all satisfy the controlling criterion for the design earthquake.The maximum tensile stress is about 3 MPa at the position of 1/4 of the arch at the middle elevation on the downstream surface along the cantilever direction(Fig.8(a));the maximum compressive stress is about 10 MPa at the low elevation on the downstream surface(Fig.8(b)),also along the cantilever direction.The maximum radial displacement is 8.54 cm(Fig.9(a))and the joint opening is about 9.36 mm(Fig.9(b)).

最后，小编还是要提醒一下，食品药监总局给予贝因美爱加幼儿配方奶粉“0001号”的殊荣和肯定，再加上价格定位都在300元左右主流价格带，相信在高品质的保证下，以这个价位，未来母婴店选择贝因美爱加定能取得不错的销售成绩。

The temperature load is caused by the differences between the dam closure temperature and concrete temperatures during the operation of the dam.It includes summer and winter temperature loads and is shown in Table 1.

8.Large-scale shaking table tests

During design and checking earthquakes,most compressive stresses of the dam can satisfy the design requirements except for some areas slightly over the limit near the base.The areas over the limit of tensile stress are mainly distributed close to the dam heel and the central part of the dam on the downstream surface,accounting for 10%and 15%of the total dam surface area for design and checking earthquakes,respectively.The maximum radial dynamic displacement of the dam is also slightly reduced,as compared with that obtained through the trial-load method.

Table 10 lists the instances of visible damage to the dam after vibration in various working conditions.All the instances of damage or cracks are shown in Fig.11,except some damages whose initial time of occurrence cannot be identified.

The results show that,during the design earthquake,no apparent damage was evident and strains observed at all points were in the elastic range;under the acceleration of 1.68 times the design earthquake(1.4 times the checking earthquake),initial cracks appeared along the cantilever direction between the right two joints,13 cm to the model dam crest on the downstream surface.As the earthquake level was further increased,cracks extended in the dam body.Under the condition of 4.88 times the design earthquake(4.1 times the checking earthquake),multiple instances of damage were observed in the dam body.Meanwhile,small residual displacements were detected from blocks at two abutments,which could still remain stable without wholly sliding when the shaking stopped.From all of the above it can be inferred that the dam foundation interface and central zone of the downstream surface are critical areas for the earthquake resistance capacity of the dam.

Model testing and numerical analysis are two important methods of seismic safety research for arch dams.Due to differences in simulation conditions,material values,structural simulations,etc.,and a shortage of physical test results,comparison between the results of model testing and numerical analysis is difficult.However,the overall pattern of dam dynamic behavior obtained from the two methods is consistent,indicating that the Xiluodu Arch Dam has a high degree of seismic resistance.The comparatively weak parts of the dam are the foundation confinement zones and the middle high-elevation zones on the downstream surface.

9.Earthquake-resistance measures

From the static and dynamic analyses described above,it can be concluded that the dam base is stable and the structural concrete has a safety margin in dynamic compression and static tension except for some areas over the limit of tensile stress in earthquakes.Enveloping all the areas of tensile stresses with multiple methods,zones including the foundation vicinity of dam surface,and central and upper parts of the dam body,especially the surface and central holes,may face the risk of cracking.Thus,the following earthquake-resistance measures were implemented:

(1)Concrete zoning was rationally set according to the magnitudes and distribution patterns of compressive and tensile stresses.Specifically,C18040 concrete was used in the vicinity of the foundation and central areas with openings,C18035 concrete was used in the middle-lower dam body and outlet works areas,and C18030 concrete was used in the middle-upper dam body areas near the two abutments.

(2)Fillets,with the thickness ranging from 3 to 6 m and height ranging from 15 to 25 m,were added at the dam toe on the downstream surface,in order to reduce the compressive stress concentration at the dam toe area and enhance the earthquake-resistance capacity of the structure.Anchor cable was used near the dam toe area,especially in places where faults and joint fissures developed,to reinforce the stability of the foundation(Lin et al.,2009).

在定位与他人沟通的角色时，使用频率较高的隐喻排序为：灯塔（40.95%）、指南针（28.65%）、灯塔则有给他人带来光明和方向，指南针寓意给人指引方向。而含羞草、木鱼背后的隐喻意义常指含羞，不善于人际交往，常处于被动的角色。

(3)Reinforcing mesh was paved on the dam surface at high tensile stress areas(Pan et al.,2007;Long et al.,2011)to control the development of cracking of concrete.The surface reinforcement zones can be seen in Fig.12,which is composed of staggered arch reinforcements using HRB335 with the diameter of 28 mm and interval of 500 mm(avoiding transversal joints) and cantilever reinforcements using HRB335 with the diameter of 32 mm and interval of 300 mm(HRB means hot rolled ribbed bars)in Zone II and zone III,and arch reinforcements with the diameter of 32 mm and interval of 300 mm(avoiding transversal joints)and cantilever reinforcements with the diameter of 36 mm and interval of 250 mm in Zone I.

汽轮机组的低压缸排汽被循环水冷却成凝结水时，体积大幅度缩小，凝汽器内部形成高度真空，所有与之相连的设备或系统若不严密，都会向凝汽器内漏入空气，因低压缸排汽中的不溶于水的气体，将会使凝汽器内的压力逐步升高、真空度下降。如果这些与凝汽器相连的设备或系统的真空严密性较差，可能会有以下几点危害：

(4)Shear keys along contraction joints,even with joint openings of several centimeters due to the earthquake,can ensure sufficient shear strength.In addition,copper and rubber water-stops were utilized to prevent joints from breaking during an earthquake(Fig.13).

(5)The reinforcement at outlet works and gate piers is strengthened.Steel liners are used at openings and spillways to prevent hydraulic fractures.

10.Conclusions

On the basis of the seismic design of the Xiluodu Arch Dam,with full use of the modern numerical and experimental analysis methods,a comprehensive scheme of design and various approaches consisting of analysis with multiple methods,verification with multiple techniques and evaluation on multiple scales,as well as dam staging dynamic safety criteria for withstanding the design earthquake and avoiding failure in extreme situations,have been put forward for seismic design of an ultra-high arch dam.Using these means,the mechanical characteristics of a dam during earthquakes and the earthquake-resistance capacity of the Xiluodu Arch Dam have been systematically analyzed.Reasonable and feasible seismic measures have been proposed and implemented.The main conclusions of this study are as follows:

(1)The dynamic stability of blocks at two abutments of the arch dam has been ensured.

(2)As both the dynamic trial-load method and linear elastic FEM indicated,the compressive stresses during design and checking earthquakes can satisfy the design requirements,and only in areas at the high arch crown and middle-elevation arch abutments are the tensile stresses over the limit.These areas take up less than 15%of the dam surface.

(3)Taking the effects of radiation damping and contraction joint opening into consideration,the nonlinear analysis shows that the area in tension and tensile stress both decrease,with the maximum joint opening of 10-25 mm.According to large-scale dynamic shaking table tests,the conclusion can be drawn that the Xiluodu Arch Dam provides adequate earthquake-resistance capacity.

(4)Based on the comprehensive seismic safety evaluation,systematic aseismic measures,including steel reinforcement at the dam toe and in the zones of high tensile stresses at the dam surface,as well as shear keys,have been put forward and employed.

References

Aftabi Sani,A.,Lotfi,V.,2010.Dynamic analysis of concrete arch dams by ideal-coupled modal approach.Eng.Struct.32(5),1377-1383.https://doi.org/10.1016/j.engstruct.2010.01.016.

Ahmadi,M.T.,Izadinia,M.,Bachmann,H.,2001.A discrete crack joint model for nonlinear dynamic analysis of concrete arch dam.Comput.Struct.79(4),403-420.https://doi.org/10.1016/S0045-7949(00)00148-6.

Australian National Committee on Large Dams(ANCOLD),2013.Guidelines on Design Criteria for Concrete Gravity Dams.https://www.ancold.org.au/?product=guidelines-on-design-criteria-for-concrete-gravity-dams-september-2013[Retrieved Nov.20,2017].

Bouaanani,N.,Lu,F.Y.,2009.Assessment of potential-based fluid finite elements for seismic analysis of dam-reservoir systems.Comput.Struct.187(3-4),206-224.https://doi.org/10.1016/j.compstruc.2008.10.006.

Chen,H.,2011.High Arch Dam Seismic Safety.China Electric Power Press,Beijing(in Chinese).

Chen,H.,2012.Study on seismic strengthening standard of hydraulic structures.China Water Resour.(20),4-6(in Chinese).

Clough,R.W.,Raphael,J.M.,Mojtahedi,S.,1973.ADAP:A Computer Program for Static and Dynamic Analysis of Arch Dams,Report No.EERC-73/14.University of California,Berkeley.

Fahjan,Y.M.,Borekci,O.S.,Erdik,M.,2003.Earthquake-induced hydrodynamic pressures on a 3D rigid dam-reservoir system using DRBEM and a radiation matrix.Int.J.Numer.Methods Eng.56(10),1511-1532.https://doi.org/10.1002/nme.623.

Federal Energy Regulatory Commission(FERC),1999.Engineering Guidelines for the Evaluation of Hydropower Projects,Chapter 11:Arch Dams.FERC,Washington,D.C.http://www.ferc.gov/industries/hydropower/safety/guidelines/eng-guide.asp[Retrieved Nov.20,2017].

Ghaemian,M.,Ghobarah,A.,1998.Staggered solution schemes for damreservoir interaction.J.Fluid Struct.12(7),933-948.https://doi.org/10.1006/jfls.1998.0170.

Hariri-Ardebili,M.A.,Mirzabozorg,H.,2013.A comparative study of seismic stability of coupled arch dam-foundation-reservoir systems using infinite elements and viscous boundary models.Int.J.Struct.Stabil.Dynam.13.06,1350032.

Jonker,M.,Espandar,R.,2014.Evaluation of Existing Arch Dam Design Criteria in Lieu ofANCOLDGuidelines.https://www.ghd.com/en/services/resources/PDF/ANCOLD2014-Evaluation-of-Existing-Arch-Dam-Design-Criteria-in-Lieu-of-ANCOLD-Guidelines-JONKER-ESPANDAR.pdf[Retrieved Nov.20,2017].

Kalateh,F.,Attarnejad,R.,2011.Finite element simulation of acoustic cavitation in the reservoir and effects on dynamic response of concrete dams.Finite Elem.Anal.Des.47(5),543-558.https://doi.org/10.1016/j.finel.2010.12.004.

Leger,P.,Venturelli,J.,Bahattacharjee,S.S.,1993.Seasonal temperature and stress distributions in concrete gravity dams,Part 1:Modeling.Can.J.Civ.Eng.20(6),999-1017.https://doi.org/10.1139/l93-131.

Lin,P.,Wang,R.K.,Li,Q.B.,Yang,Q.,Zhou,W.Y.,2009.Effect analysis of structural safety of typical large dams in Wenchuan 8.0 Earthquake.Chin.J.Rock Mech.Eng.28(6),1261-1269(in Chinese).https://doi.org/10.3321/j.issn:1000-6915.2009.06.023.

Lombardi,G.,1991.Koelnbrein Dam:An unusual solution for an unusual problem.Int.Water Power Dam Constr.43(6),31-34.

Long,Y.,Xu,S.,Gao,X.,2011.A study of cantilever reinforcement for high arch dam to resist strong earthquakes.Eng.Mech.28(S1),178-183.

Mays,J.R.,Roehm,L.H.,1991.Hydrodynamic pressure in a dam-reservoir system.Comput.Struct.40(2),281-291.https://doi.org/10.1016/0045-7949(91)90354-O.

Moradloo,J.,Ahmadi,M.T.,Vahdani,S.,2008.Nonlinear dynamic analysis of concrete arch dam considering large displacements.In:Proceedings of the 14th World Conference on Earthquake Engineering.Beijing.

Pan,J.,Long,Y.,Zhang,C.,2007.Seismic cracking of arch dams and effectiveness of strengthening by reinforcement.J.Hydraul.Eng.38(8),926-932(in Chinese).

Saouma,V.,Miura,F.,Lebon,G.,Yagome,Y.,2011.A simplified 3D model for soil-structure interaction with radiation damping and free field input.Bull.Earthq.Eng.9,1387.https://doi.org/10.1007/s10518-011-9261-7.

Shi,M.G.,Zhong,H.,Ooi,E.T.,Zhang,C.H.,Song,C.M.,2013.Modelling of crack propagation of gravity dams by scaled boundary polygons and cohesive crack model.Int.J.Fract.183(1),29-48.https://doi.org/10.1007/s10704-013-9873-9.

US Army Corps of Engineers(USACE),1994.Arch Dam Design,Engineering Manual EM 1110-2-2201.US Army Corps of Engineers,Washington,D.C.

US Bureau of Reclamation(USBR),1977.Design Criteria for Concrete Arch and Gravity Dams.US Bureau of Reclamation,Denver.

Wang,H.,Li,D.,Chen,H.,2014.Challenge in study of ultimate capacity of high arch dams against earthquakes.J.Hydroelectr.Eng.33(6),168-180.

Wang,J.T.,Lu¨,D.D.,Jin,F.,Zhang,C.H.,2013.Earthquake damage analysis of arch dams considering dam-water-foundation interaction.Soil Dynam.Earthq.Eng.49,64-74.https://doi.org/10.1016/j.soildyn.2013.02.006.

Wang,R.K.,2016.Key technologies in the design and construction of 300 m ultra-high arch dams.Engineering 2(3),350-359.https://doi.org/10.1016/J.ENG.2016.03.012.

Westergaard,H.M.,1933.Water pressures on dams during earthquakes.Trans.ASCE 98(2),418-433.

Zhang,C.H.,Jin,F.,Pekau,O.A.,1995.Time domain procedure of FE-BE-IBE coupling for seismic interaction of arch dams and canyons.Earthq.Eng.Struct.Dyn.24(12),1651-1666.http://doi.org/10.1002/eqe.4290241208.

Zhang,C.H.,Pan,J.W.,Wang,J.T.,2009.Influence of seismic input mechanisms and radiation damping on arch dam response.Soil Dynam.Earthq.Eng.29(9),1282-1293.https://doi.org/10.1016/j.soildyn.2009.03.003.

Zhang,C.H.,Feng,J.,Wang,J.T.,Xu,Y.J.,2014.Seismic Safety Evaluation of Concrete Dams.Tsinghua University Press,Beijing.https://doi.org/10.1016/C2012-0-01281-1.

Zhou,W.,Lin,P.,Yang,R.,Yang,Q.,2008.Method and Application of Geomechanical Model Test on High Arch Dam.China Water Power Press,Beijing(in Chinese).