Chapter 5 Chapter 5 Earthquake Effect and Seismic Design principles Earthquake Effect and 5.1 Seismic conceptual design Seismic Design principles 6 aionhethoedologyofselsmcacion 5emeCcnranmentesandsneal 5.1 Seismic conceptual design 5.1 Seismic conceptual design The building with good seismic performance can hardly be obtained only by "accurate calculation seismic conceptual design ndnhtrayis 5.1.1 Confieuration Characteristics 5.1.I Configuration Characteristics .of the designer will be tos
1 Chapter 5 Earthquake Effect and Seismic Design principles Chapter 5 Earthquake Effect and Seismic Design principles 5.1 Seismic conceptual design 5.2 Building classification and seismic fortification 5.3 Calculation Methodology of seismic action 5.4 Seismic Check of structural members and structural lateral deformations In the very early stage of building design, the configuration, the basic material, structure, and framing of the building have to be chosen. The architects and the structural engineers should therefore cooperate and thoroughly discuss the matter at this early stage. Seismic design in this stage is generally termed seismic conceptual design 5.1 Seismic conceptual design Bamboo • Since earthquake is a stochastic process, the seismic action that the building might be expected to be suffered in its life time can not be quantified accurately. • A building is not a homogenous block, but a complicated assembly of parts. Considerable simplifications are always needed in the structural analysis. The building with good seismic performance can hardly be obtained only by “accurate calculation’’. 5.1 Seismic conceptual design • The desirable aspects of building configuration are simplicity, regularity, and symmetry in both plan and elevation. • Irregularities, often unavoidable, contribute to the complexity of structural behavior. Any irregularity in the distribution of stiffness or mass is likely to lead to an increased dynamic response. 5.1.1 Configuration Characteristics • The first task of the designer will be to select a structural system most conductive to satisfactory seismic performance within the constraints dictated by architectural requirements. • Configuration is generally defined as building size and shape, and the characteristic of proportion. • The extended definition also includes the location of the structural elements. And location of nonstructural elements. 5.1.1 Configuration Characteristics • Configuration largely determines the ways in which seismic forces are distributed throughout the building, and also influences the relative magnitude of those forces
1.Building Height 2.Aspect Rati a beizht is e 3.Plan Configuration Plan Arrangement F-skapedplan L-shapedplan affect the Sywmetrical foms are preferred. U-shaped plan
2 1. Building Height • As a building grows taller, its period will tend to increase, and a change in period means a change in the building response. • It is easy to visualize the overturning forces associated with height as a seismic problem. • In Chinese Code for Seismic Design of Buildings, height limits are imposed, relating to type of structure and earthquake intensity. With the increasing of earthquake intensity, the allowed maximum height is decreased. Structure Noun Intensity 6、7 Intensity 8 Intensity 9 Frame 5 4 3 / Plate-wall 6 5 4 / Frame-wall, wall 7 6 5 4 Frame-tube 8 7 6 4 Tube in tube 8 8 7 5 Question： What is the purpose for the requirements? 2. Aspect Ratio • The term symmetry denotes a geometrical property of building plan configuration. • Structural symmetry means that the center of mass and center of resistance (center of rigidity) are located at, or close to the same point (unless live loads affect the actual center of mass). • Symmetrical forms are preferred. 3. Plan Configuration T-shaped plan L-shaped plan U-shaped plan Cruciform plan Source from :1980 SEAOC Recommended Lateral Force Requirements and Commentary Plan Arrangement — Irregularity Split levels Other complex shapes Setbacks Multiple tower Unusual high story Unusual low story nonuniform mass distribution, or converse Soft lower levels
Large openings in she Plan Arrangement-Regularity Cable-supported structures Lcng ith Control of t 8,9 fn:Code ae of (Code GRS0011-2010) In Chinese Code for Seismic Design of Buildings Reentrant corner ype of 学增 of 凿中]学 3
3 Large openings in shear walls Interruption of columns Interruption of beams Openings in diaphragms Shear walls in some stories, moment-resisting frames in others Interruption of verticalresisting elements Abrupt changes in size of members Drastic changes in mass/stiffness ratio Cable-supported structures Shells Staggered trusses Buildings on hillsides Plan Arrangement — Regularity Intensity L/B l /Bmax l / b 6，7 6.0 0.35 2.0 8，9 5.0 0.30 1.5 Length-Width ratio —— Control of torsion Source from : Code of Seismic Design of Building （Code GB50011-2010) Plan irregularity Type of irregularity Definition Torsional irregularity The maximum elastic floor displacement or inter-story drift is more than 1.2 times of the corresponding average of two ends of the floor. Irregularity of reentrant corners The projection beyond a reentrant corner is greater than 30 percent of the total plan dimension in the given direction. Diaphragm discontinuity The dimensions and stiffness of diaphragm change abruptly, including those having the effective width of diaphragm less than 50 percent of the typical width, the cutout or open area greater than 30 percent of the gross enclosed floor area, or staggered floor. In Chinese Code for Seismic Design of Buildings Reentrant corner 3 max B 0. B Bmax Bmax 3 max B 0. B Bmax 3 max B 0. B Bmax 3 max B 0. B Bmax 3 max B 0. B Bmax 3 max B 0. B 3 max L 0. L Lmax
Diaphragm Discontinuity 3.Plan Configuration Torsional r actua center of mass 4>0.34A=BL ppp00CJ Plan Configuration In addition.there exists cou ground motion +6>1a + Separated buildings 4.Separation The width of a gap:d Temperature Gap 。Frame System and the podiums and between the diffcrent kn me-wall system,0%d Seismicgap/joint Wall system,da50% Question:
4 Diaphragm Discontinuity b 0.5B B B A0 0.3A A B L • Generally the torsional response will inevitably occur even in the symmetrical structure when attacked by the earthquake. • In general case torsion arises from eccentricity in the building layout. The accidental eccentricity are very likely caused by construction which may change the actual center of resistance, or the distribution of live loads in occupancy which affects the actual center of mass. Torsional irregularity 3. Plan Configuration • The effective force exerted by lateral ground movement acts at the center of mass of each floor creating a torsional moment about the center of structural resistance. • In addition, there exists torsional component in earthquake ground motion. Plan Configuration Seismic force C Separated buildings The L-shaped building • If the ground motion occurs with a north-south emphasis at the L-shaped building, the wing oriented north-south will, tend to be stiffer than the wing oriented east-west. • The north-south wing, if it were a separate building, would tend to be deflect less than the east-west wing, but the two wings are tied together and attempt to move differentially at their notch, pulling and pushing each other. 4. Separation Temperature Gap When the length of a Frame (Cast-in-situ) is larger than 55m, or a wall larger than 45m, it is better to set the Temperature Gap Settlement gap Between the main tower and the podiums and between the different kind of foundations. Seismic gap/joint separating the irregular plan to regular plan，in case to reduce torsion. Source from : Code of Seismic Design of Building （Code GB50011-2010) The width of a gap: d Frame System when H15m，dframe＝70mm in the area of intensity 6, 7,8, 9, every 5m、4m、3m、2m taller, +20mm wider。 Frame-wall system, dframe-wall＝ 70%*dframe Wall system, dwall ＝ 50%*dframe Question: 1. Why the widths of gaps are different ? 2. What is the main reason? 3. How to reduce the unfavorable deformation? Source from : Code of Seismic Design of Building （Code GB50011-2010)
5.Vertical Configuration Vertical irregularity Definition insoft story or weak stery. c2gngaopisnwdauw ontinuity in vertical lateral forre resisting system Lateral stiffnessirregry(sof story) K<07K 口口口 of Abrupt changeof story carrying capacity (weak story) Vertical Configuration ak story insteac <082 月朋月 5
5 • Regularity should prevail in elevation, in both the geometry and the variation of story stiffness and strength, so as not to result in soft story or weak story. • The vertical configuration comprises uniformity and continuity, avoiding drastic changes. • The shape of rectangle, trapezoid, or triangle without abrupt change is preferable. • In Chinese Code for Seismic Design of Buildings, some critical vertical irregularities are defined and quantified. 5. Vertical Configuration Type of irregularity Definition Lateral stiffness irregularity The lateral stiffness of the story is less than 70 percent of that of the story above or less than 80 percent of the average lateral stiffness of the three stories above; The horizontal size of setback is larger than 25 percent of totalsize of the adjacent lower story. Discontinuity in vertical lateral force resisting member Loads applied on the vertical lateral force resisting member (column, shear wall, and brace) are transferred downward by horizontal transfer member (beam, truss etc.). Abrupt change of story carrying capacity The shear strength of the story is less than 80 percent of that of the story above. Vertical irregularity Discontinuity in vertical lateral force resisting system Ki1 Ki i i i u V K 1 0.7 K K i i ui Vi inter-story drift of the ith story shear force of the ith story 1 2 3 0.8( ) 3 i i i i K K K K Ki3 Ki2 Ki1 Ki Lateral stiffness irregularity (soft story) Abrupt changeof story carrying capacity (weak story) Qy,i1 Qy,i , , 1 0.8 Q Q y i y i • Pure cases of soft-story or weak-story failures are rare and generally the same floor is both soft and weak, therefore justifying the use of the term soft/weak story instead. • The soft/weak story problem is commonly magnified by torsional response. • Probably among all urban habitat structural problems, the soft/weak story failures have been responsible for more deaths and destruction than any other. Vertical Configuration
Vertical Configuration 二 出 5.1.2Additional requirements for the analysisof irregular configurations 1.The structure with plan irregularity
6 • The soft/weak stories have consistently claimed a large number of lives and have caused serious destruction during many 20th century earthquakes. • From Turkey to Taiwan and from northern California to southern California , the mark of soft/weakstory failures can be seen on the face of many collapsed structures. Vertical Configuration Soft/weak story collapse of a residential complex during the 1906 San Francisco Earthquake Soft/weak story failure of a residential reinforced concrete complex during the 1999 Turkey earthquake Soft/weak story failure of a reinforced concrete building during the 1999 Taiwan earthquake Soft-story failure of an open-front building during the 1989 Loma Prieta earthquake 1.The structure with plan irregularity • The three-dimensional analytical model must be applied in the structural analysis. 5.1.2 Additional requirements for the analysis of irregular configurations
5.1.3Configuration Influences on Seismic Performance 5.1.4 Essentials of Structural System The desig ch 1.Sclectionof materialsand types of construction abers on the perimteter whenever possibl is 二e情ge 回 回 Better ·Reasonable cost 2.Major Characteristics of Building structures Summary Requirements for seismic structural system and rein rete composite structures en structure cast co e stru 7
7 2.The structure with vertical irregularity • The story shear force of the soft/weak story must be increased by 15%. • The elasto-plastic analysis must be conducted for the tall building exceeding the specified height. • The shear strength of the weak story should not be less than 65 percent of that of the adjacent upper story for the structure with abrupt change of story carrying capacity. 3. The structurewith both plan irregularity and vertical irregularity • The above two terms must be followed simultaneously. • In addition, for the structure with seriously irregularity, time history analysis must be carried out to check the analytic results obtained by modal analysis. • For the building with seriously irregularly configuration, seismic joints can be provided to separate the building into simple and regular individual units. There must be enough clearance at the seismic joints so that the adjoining portions do not pound each other. • The design characteristic of redundancy plays an important role in seismic performance. • Placing resisting members on the perimeter whenever possible is always desirable. • The detailing of connections is a key factor in seismic performance, since the more integrated and interconnected a structure is the more load distribution possibilities there are. • The lower of the density center of a building, the better resistant performance. 5.1.3 Configuration Influences on Seismic Performance Better 5.1.4 Essentials of Structural System 1. Selection of materials and types of construction • Structural materials have their own performance characteristics and should be selected according to the location and condition of the building to be planned in order to accomplish safe, economical, and superior architecture. • High strength-to-weight ratio • High deformability • Low degradation • High uniformity • Reasonable cost • Steel structures • Steel and reinforced-concrete composite structures • Wooden structures • Cast-in-situ reinforced concrete structures • Precast concrete structures • Prestressed concrete structures • Masonry structures • Mixed structures 2. Major Characteristics of Building structures Requirements for seismic structural system 1. It shall have a clear analytical model and reasonable path for seismic action transfer. 2. It should have several lines of defense against earthquakes. It should avoid loss of either earthquake resistance capacity or gravity load capacity of the whole system due to damage to part of the structure or members. 3. It shall possess the necessary strength, adequate deformability, and better energy dissipation ability. Summary
Regular rmely large Redundancy Conceptual Design 5.2 Building classification and seismic fortificatior 2)The second level 1.Seismic fortification objectives Three-level Repairable under moderate earthquake 1)The first level on the code are 2.Seismic design method Two-stage 2.Seismic design method 1)The first level In Summary: and ond level
8 4. It should possess a rational distribution of stiffness and strength, avoid weakening of some parts of the structure due to local weakening or abrupt changes; avoid appearance of extremely large concentration of stress and plastic deformation; when weak parts do appear, measures should be taken to enhance their earthquake resistance capacity. 5. It should have similar dynamic characteristics in the direction of individual primary axis. 6. Designing the connections and details of a structure to be earthquake resistant is almost as important as checking the structure’s overall dynamic behavior. Simplicity Regular Symmetry Integral Construction Redundancy Seismic Conceptual Design Three-level 1. Seismic fortification objectives 5.2 Building classification and seismic fortification 1) The first level When buildings designed based on the code are subjected to the influence of frequently occurred earthquakes with an intensity of less than the fortification intensity of the region, they will not be, or will be only slightly damaged and will continue to be serviceable without repair. ------------- No damage under minor earthquake. 2) The second level When buildings are subjected to the influence of earthquakes equal to the fortification intensity of the region, they may be damaged but will still be serviceable after ordinary repair or without repair. ------ Repairable under moderate earthquake 3) The third level When buildings are subjected to the influence of expected rare earthquakes with an intensity higher than the fortification intensity of the region, they will not collapse nor suffer damage that would endangerhuman lives. ------------- No collapse under major earthquake. 1) The first level By the elastic analysis, the carrying capacity of the structure is checked under the fundamental combination of effects of seismic action of minor earthquake and other loads, and the elastic seismic deformation is checked under the action of minor earthquake. Calculation is necessary under the first level. 2. Seismic design method 2) The second level The objective of this level is realized mainly by seismic conceptual design and constructional measures or detailing. 3) The third level The elasto-plastic deformation is checked under the action under rare earthquake. Two-stage In Summary: Level 1 Level 2 Level 3 minor earthquake level moderate earthquake level major earthquake level No damage Repairable No collapse 1) Elastic force 2) Elastic deformation Structural detailing 1) Elastoplastic deformation 2. Seismic design method
3.minor /moderate/major earthquake 3.minor/major/majorearthquake Probability Density Function (PDF)of Earthquake the 3N Extreme Value Distributio like the ne Val ibutio -卦 -The r 3.minor /major major earthquake siy(设防烈度) R0e》 'e6 Pere 5.2建筑的分类与建筑抗震设防 5.2建筑的分类与建筑抗震设防 一、建筑抗履设防分类 1.中图围寒标准速筑抗晨设防分类标准(GB50223),根据 甲类建筑（特殊设防觉） 地展被坏后会对社会有严重 意筑物重要性、在地展中及地膜后破环对社会和是济造 成的影响及在抗展防灾中的作用，艳建筑分为四类： 甲类建（传殊设防类 乙类建筑（量点设类） 地展中使用功能不能中断戒 乙类建筑值点慢 Q: 为什么要分类？ 院、中小学校，大型 人员集中的公共意筑等， 如何设防？ 9
9 49 Probability Density Function (PDF) of Earthquake Intensity is look like the 3rd Extreme Value Distribution (地震烈度的概率密度函数符合极限Ⅲ型分布） ( ) ( ) ( ) The maximum value of Earthquake Intencity = ; Earthquake Intencity Shape Parameter; Mean Intensity. I k 1 k k k I f I e 12 I k ， ； 3. minor / moderate / major earthquake 50 the 3rd Extreme Value Distribution Exceedance Probability (EP) PDF Eq. Intensity 3. minor / major / major earthquake 51 Distribution Function: When ( ) . % EP ( ) . % 1 I F I e 36 8 1 F I 63 2 ： ： k I F I e ( ) EP in Design Reference Period（设计基准期内的 超越概率）is 10% Basic Intensity Moderate Earthquake Mean Intensity： Minor Earthquake 3. minor / major / major earthquake EP in Design Reference Period is 2~3% Rare occurred Intensity Major Earthquake 52 Fortification Intensity（设防烈度）： In 50 years, if EP is 10%， the return years is 475。 Frequently occurred Intensity (小震，多遇地震)： In 50 years, if EP is 63.5%， the return years is 50； It is about 1.55 grade lowerthan Fortification Intensity。 Rare Occurred Intensity（大震，罕遇地震）： In 50 years, if EP is 3%~2%，the return years is 1461~2475。 It is about 1 grade higherthan Fortification Intensity。 3. minor / major / major earthquake 53 1. 中国国家标准建筑抗震设防分类标准（GB50223)，根据 建筑物重要性、在地震中及地震后破坏对社会和经济造 成的影响及在抗震防灾中的作用，将建筑分为四类： • 甲类建筑(特殊设防类) • 乙类建筑(重点设防类） • 丙类建筑(标准设防类) • 丁类建筑(适度设防类) 5.2 建筑的分类与建筑抗震设防 Q: 为什么要分类？ 如何分类？ 如何设防？ 一、建筑抗震设防分类 54 •甲类建筑(特殊设防类)——地震破坏后会对社会有严重 影响，对国民经济有巨大损失或有特殊要求的建筑物。专 门研究确定。如生命线工程。 •乙类建筑(重点设防类)——地震中使用功能不能中断或 需迅速恢复的建筑物及破坏后会对社会有重大影响，对国 民经济有重大损失。如医院、中小学校校舍、大型商场或 人员集中的公共建筑等。 5.2 建筑的分类与建筑抗震设防
5.2建筑的分类与建筑抗震设防 5.2建筑的分类与建筑抗震设防 二、抗展设防标准抗展作用计算、构迪排嘴 丙类建筑（标准设防类） 地展破环后对社会有一般影 1.甲类意第，地震作用应高于本地区执膜没防烈度的要 求，其值应批准的地安全性评价结果确定。6一8 提高1度进行抗展设防，9度时应比9度设 2.乙类速英，地膜作用应符合本地区教膜设脑烈度的要 的素筑物。如位时流筑或附圆德坡物第 施高1度采取抗展清施，9度 5.2建筑的分类与建筑抗震设防 Summary Building dassification and seismic fortificatior 降低。 5抗设防烈度为度时，除特殊要求外， 一情况下对 乙类、丙类和丁类建筑可不进行地震作用计算。 高层建敏需渠行地膜作用下和计算) Review and read this chapter,please. Do Group work,please! Thanks! o
10 55 •丙类建筑(标准设防类)——地震破坏后对社会有一般影 响，对国民经济有一般损失的建筑物。如一般工业与民用 建筑、公共建筑、住宅、旅馆、厂房等。 •丁类建筑(适度设防类)——地震破坏后对社会影响轻微， 对国民经济影响轻微，且不致影响其它甲、乙、丙类建筑 的建筑物。如临时建筑或附属建筑物等。 5.2 建筑的分类与建筑抗震设防 56 1. 甲类建筑，地震作用应高于本地区抗震设防烈度的要 求，其值应按批准的地震安全性评价结果确定。6〜8 度设防时，提高1度进行抗震设防，9度时应比9度设防 更高的要求。 2. 乙类建筑：地震作用应符合本地区抗震设防烈度的要 求，一般情况6〜8度时，提高1度采取抗震措施，9度 时应比9度设防更高的要求。 二、抗震设防标准 抗震作用计算、构造措施 5.2 建筑的分类与建筑抗震设防 57 3. 丙类建筑：地震作用和抗震措施均应符合本地区抗震 设防烈度要求。 4. 丁类建筑：一般情况下，地震作用应符合本地区抗震 设防烈度要求，抗震措施可适当降低，但6度抗震时不 降低。 5. 抗震设防烈度为6度时，除特殊要求外，一般情况下对 乙类、丙类和丁类建筑可不进行地震作用计算。 （高层建筑需进行地震作用下和计算） 5.2 建筑的分类与建筑抗震设防 Summary Building classification and seismic fortification Review and read this chapter, please! Do Group work, please! Thanks!
