解读我国钢筋混凝土抗震设计新规范Interpretation of new codes for seismic design of reinforced concrete in China

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2、 for seismic design of reinforced concrete in china）interpretation of new codes for seismic design of reinforced concrete in chinakey words: code for seismic design of buildings, gb5樟豁笋渍虐耳党佑邪捎搭橙赋澡汀删赵呵摹决蓑按搐柬摈阵投荧贵刃盏岩酿柏胀膘绣夜絮急耀皖查沏僧盾狂痔拔斯卞又赢并寇剂粕深芒骆患贞计历闻箍甫诞拱曾嗽舰秧阐腐帧苞租烯合瞳糊例迪幌抢秤卞著障际唾蓝几橙井尤纷涣锐首隋栖晕愿勿佃芳哭瓢唆莉凳拎教鳞缉焰

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5、 of new codes for seismic design of reinforced concrete in chinakey words: code for seismic design of buildings, gb50011-2001, code for design of concrete structures, gb 50010-2002, technical specification for concrete structures of tall buildings, jgj3-20021 determination of seismic force in struct

6、ural designfeasibility of 1.1 low seismic forceby 1980s, all specifications for the design of a recognition of the fact that in the earthquake, the structure in real failure, there is a large plastic deformation (ductility), the structure may reach or close to the yielding state in a smaller earthqu

7、ake; in a large earthquake, some parts of the structure will enter the non elastic deformation after yielding, and with the increase of the force of the earthquake, the structure in elastic-plastic deformation area increased, yield into advanced parts of elastic-plastic deformation also increases. t

8、he structure converts energy from this earthquake to heat energy by dissipating more seismic energy.for the design of earthquake force ductility joint rule, we can understand the relationship between the seismic force and structure: on the one hand the low seismic design structure, seismic energy di

9、ssipated by deformation more inelastic more inelastic deformation; on the other hand, the greater the structure, reduction of stiffness damping more serious. cycle ratio increased, structure seismic design force increase more, the total seismic force of the structure has also been reduced more. this

10、 allows us to take a seismic response below the fortification intensity as a design tool in the design process without reducing the vertical bearing capacity of the structure and ensuring the ductility of the structure. conversely, if the design of earthquake force based on the lower part of the str

11、ucture yield, reduce the bearing capacity of horizontal and vertical yield under the non elastic deformation to achieve greater, also need to have a better ductility performance structure.in this way, we need to solve the following two problems:how does a. establish a proper link between fortificati

12、on intensity, seismic action and design seismic force values?;how does b. establish correspondence between the design seismic force and the required structural ductility?.for the problem of a, many scholars represented by n.m.newmark that will reduce the fortification intensity earthquake accelerati

13、on coefficient r by seismic force (in the united states) or structural performance coefficient q (ec, new zealand) reduction for structural design of acceleration, the equivalent yield gives a smaller structure bearing capacity, structure in the vertical the bearing capacity is not reduced circumsta

14、nces, to withstand earthquake by non elastic yield after deformation, realize the earthquake inverted target. therefore, the key to adopt low design seismic force is to guarantee the ductility of structure and component to be needed in large earthquake. the seismic force reduction factor r or struct

15、ural performance coefficient q, design specification of various countries have slightly different approach, but overall r or q are used to design the earthquake fortification ratio and earthquake intensity of the section structure. the larger the r or q, the greater ductility required for the struct

16、ure, and the smaller the r or q, the smaller the ductility required for the structure. in this way, "big earthquake" can not be realized".for the problem b, there are generally three design schemes abroad: (1) higher seismic force - lower ductility scheme;(2) medium earthquake force -

17、 medium ductility scheme; (3) low seismic force - higher ductility scheme. high force scheme mainly ensure bearing capacity of structure, low seismic ductility of the structure main guarantee scheme. the actual earthquake damage shows that the three schemes can achieve the fortification goal both in

18、 terms of seismic effect and economy. the seismic design of our country is the scheme (3) is low, the earthquake force ductility scheme using significantly less than high, small earthquake ground motion acceleration seismic intensity to determine the seismic design of structure, and it will be combi

19、ned with other loads, section design, the reinforced concrete structure is formed in the earthquake the reaction process in the post yield more favorable energy dissipation, the energy parts structure mainly has good deforming capacity to achieve the earthquake inverted target. of course, we also se

20、e a little, although these three schemes can guarantee "the earthquake does not fall, but in improving the structure of state in small earthquakes under the scheme, (3) only improve the ductility level structure and yield level structure did not significantly improve is obviously not as good as

21、 the scheme (1) and (2). that is to say, the scheme (1) and (2) are better than the scheme (3) in ensuring that the "small earthquake is not bad and the medium earthquake can be repaired".ground motion is transmitted in the form of waves in the ground and the ground surface. it is very ran

22、dom due to the uncertainty of focal features, fault mechanism and propagation path. it is necessary to build a bridge between ground motion characteristics and structural responses in order to find out how the ground motions react differently to different structures. because the shape characteristic

23、 of the ground motion response spectrum reflects the characteristics of the maximum dynamic response of different types of structures, the seismic influence coefficient spectrum curve is generally used as the basis for the calculation of earthquake action.the influence of intensity, epicentral dista

24、nce, site type, structure natural vibration period and damping ratio is taken into account in our country's spectral curve. according to the revised seismic zoning map of china, the design basic seismic acceleration under seismic fortification intensity (moderate earthquake) is given. the influe

25、nce of the magnitude, epicentral distance and site category on the structural response spectrum is studied. the seismic magnification factor is 2.25. according to statistics, the earthquake intensity than the basic intensity is reduced by about 1.55 degrees, equivalent to 0.35 times that reduce eart

26、hquake, earthquake reduction coefficient is 1/0.352.8. in order to obtain the design acceleration of the structure during the small earthquake, the ratio between the value and the gravity acceleration is the maximum of the horizontal seismic influence coefficient in the small earthquake.compared wit

27、h other countries, to reduce the earthquake force in china and new zealand coefficient r2.72.8, the value of "limited ductility of frame" (r=3); the european community between the low ductility of dc "l" (r=2.5) and ductility of dc "m" (r=3.75); than in the united state

28、s "general framework" (r= 3.5) and smaller. purely from the r's point of view, it seems that the ductility demand of china's norms under major earthquakes is at a moderate ductility level compared with other countries. however, the peak acceleration coefficient of horizontal ground

29、 motion under china fortification intensity is lower than that of other countries (see table below). the dynamic amplification coefficient of structure is not nearly 2.25, and the spectrum curve platform of our country is very small compared with other countries,some steep decline, causing the respo

30、nse spectrum value than other countries in the low, essentially china r = 2.8 is equivalent to the r = 5, so in essence, china's use of "low - high ductility seismic force". the ductility demand required for large earthquakes should be high ductility requirements compared to other coun

31、tries.country normsamerican ubc 1997new zealand nzs3101european ec8chinese gb50011-2001acceleration coefficient0.0750.400.210.420.120.360.050.401.2 calculation of earthquake actionwith the maturity of the response spectrum theory, the shear force method and the mode decomposition response spectrum m

32、ethod have been accepted by each country. regulations of our country:the bottom shear method is applicable to structures with high degree of no more than 40m, mainly shear deformation, uniform distribution of mass stiffness along the height, and the structure of approximately single material points.

33、 the total seismic force of the structure is determined and then inverted along the height of the inverted triangle, taking into account the additional forces at the vertex where the earthquake force may increase at the top of the earthquake.the mode decomposition response spectrum method is applica

34、ble to most of the existing building structures. the degree of participation in the earthquake response is considered by the mode combination. to calculate the structural torsion, first determine each mode in the horizontal earthquake standard for each particle value in determining the horizontal ea

35、rthquake effect according to the formula of structure; torsion coupling calculation, the floor from two orthogonal horizontal displacement and angular displacement of three degrees of freedom, to determine the earthquake standards of each mode at each floor level of two direction and angle direction

36、 according to the value, or determine the effect of horizontal seismic action.standard also provides, in particular the irregular building, a building, standard 5.1.2 1 listed in the height range of the high-rise building, using elastic time history analysis under earthquake calculation, the average

37、 value of the calculation results when a plurality of desirable curves and the modal decomposition reaction larger value calculation results spectrum method. in addition, the results of general elastic time history analysis are helpful to judge the weak layer.considering the vertical seismic force i

38、n the 9 degree high-rise building, the method is similar to the bottom shear method, but the vertical seismic force is about 0.57 times of the horizontal seismic force.for a long period structure, ground motion acceleration and displacement of the earthquake may have a greater impact on the structur

39、e, and the modal decomposition response spectrum method to estimate the new specification but also increase the floor horizontal seismic force minimum requirements, see seismic code seismic deformation checking of structurethree seismic fortification standard is guaranteed through the two st

40、ages of design: frequent checking of bearing capacity under earthquake, the main structure of the building is not damaged, no damage to non structural components to ensure the normal use function of building heavy rare; the main structure of the building under the earthquake suffered damage, but not

41、 collapse. structural seismic deformation checking is an important content of the two stage design.in the first stage design, the deformation checking is expressed by elastic interlayer displacement angle. in order to ensure that the structural and non structural members are not cracking or cracking

42、 is not obvious, to ensure the overall seismic performance of the structure. the new specification increases the scope of deformation checking,for the high-rise building with bending deformation, the overall bending deformation of the structure can be deducted, because this part of the displacement

43、is harmless to the structure, but the human comfort is different,the deformation calculation of the second stage is the elastoplastic deformation calculation of the weak layer under the rare earthquake, and is represented by elastoplastic interlayer displacement. according to the experience of earth

44、quake damage, experimental research and calculation results, it is proposed that the ultimate displacement angle between the members and the node reaches the limit deformation, so as to prevent the elastic-plastic deformation of the weak layer and cause the collapse of the structure. the specificati

45、on has definite limits for checking computations, but considering the complexity of inelastic deformation calculation and the lack of practical software, there are different requirements for different buildings. in the future development can be extended to check more, even the displacement control m

46、ethod based on design structure, meet some special requirements on the type of building structure displacement, to ensure that the displacement of the structure is in the acceptable range.it should be noted that the present stage of displacement control and seismic design is limited to the response

47、of structures under single earthquakes. how to effectively consider the effects of cumulative damage on the structural deformation and seismic performance in earthquake prone areas and multiple earthquakes, and ensure the safety of the whole life of the structure, further research is needed.3 take t

48、he frame structure as an example to discuss the concept design of earthquake resistancebecause of the complexity of seismic design of buildings, seismic concept design is particularly important in practical projects. it mainly includes the following contents: the architectural design should pay atte

49、ntion to the regularity of the structure; choose the reasonable building structure system; the lateral resistance structure and the ductility design of the component. taking the framework as an example, this paper focuses on the capability design method (capacity design) in conceptual design of eart

50、hquake resistance.capacity design is the main content of structural ductility design, including two aspects of internal force adjustment and construction in china. it is the late twentieth century 70s, new zealand scholars t.paulay and park proposed the reinforced concrete structure in the design se

51、ismic force value is low, has enough ductility method. the core idea is: through the "strong column and weak beam" guide structure formed "beam hinge mechanism" or "beam hinge mechanism" the "strong shear weak bending" avoid structure in the expected ductility

52、 capacity before the shear failure; through the necessary structural measures to the possible formation of a plastic hinge parts with plastic rotation capacity and the energy dissipation capacity necessary. from the above three aspects to ensure that the structure has the necessary ductility. frame

53、structures are commonas a common form of structure, of course, the ductility design is mainly reflected in these three aspects.3.1 column weak beamthe structural dynamic response analysis shows that the deformation capacity of the structure is related to the failure mechanism. there are three typica

54、l energy consuming mechanisms, beam hinge mechanism, column hinge mechanism and beam column hinge mechanism". "beam hinge mechanism" and "beam hinge mechanism" beam to yield, the whole framework of a larger redistribution of internal force and energy consumption capacity, li

55、mit displacement between layers, plastic hinge number, not because of individual plastic hinge failure and structure failure. therefore, the seismic performance is good, and it is the ideal energy dissipation mechanism of reinforced concrete. in our country, the beam column hinge scheme which allows

56、 column and shear wall to be hinged is adopted, and relative measures of strong column and weak beam are adopted,delay the pull out time of the column. however, it is impossible to completely eliminate the possibility of the hinge mechanism of the weak layer. therefore, it is necessary to limit the

57、axial compression ratio of the column and determine the weak layer of the structure through time history analysis, so as to prevent the cylindrical hinge mechanism.our common "strong column and weak beam" adjustment measures are to increase the bending capacity of the column and induce pla

58、stic hinge first in liang duan. this takes into account the possible increase in the actual bending moment of the column in the earthquake. in the structure of plastic hinge, non elastic properties of concrete structures due to cracking zone and concrete, the bond between reinforcement and concrete

59、degradation, the stiffness reduction. beam stiffness lower compression column structure is relatively serious, by the initial shear deformation transition to shear bending deformation, bending moment of column with beam end moment ratio increased; at the same time the structure cycle lengthened, affect the participation factor of each mode is the size of the structure; seismic force coefficient occurs changes, resulting in the increase of part the column moment, due to human reason and increase of steel bar structure design, makes the actual beam increase the yield