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Karayolu köprülerinin sismik boyutlandırılmasıyla ilgili bazı yönetmeliklerin incelenmesi, karşılaştırılması ve uygulamalar

Investigations and comparisons on some rugulations for seismic design of highway bridges and applications

  1. Tez No: 39550
  2. Yazar: ŞÜKRÜ EROL
  3. Danışmanlar: DOÇ.DR. METİM AYDOĞAN
  4. Tez Türü: Yüksek Lisans
  5. Konular: İnşaat Mühendisliği, Civil Engineering
  6. Anahtar Kelimeler: Belirtilmemiş.
  7. Yıl: 1994
  8. Dil: Türkçe
  9. Üniversite: İstanbul Teknik Üniversitesi
  10. Enstitü: Fen Bilimleri Enstitüsü
  11. Ana Bilim Dalı: Belirtilmemiş.
  12. Bilim Dalı: Belirtilmemiş.
  13. Sayfa Sayısı: 199

Özet

ÖZET Bu çalışmada, köprülerin sismik boyutlandırılma- sıyla ilgili Amerikan ve Japon şartnameleri incelenerek karşılaştırmalar yapılmış ve konu ayrıntılı bir şekilde incelenmiştir. Çalışma 8 bölümden oluşmaktadır. Birinci bölümde sismik boyutlandırmayla ilgili te¬ mel kavramlar verilmiş, mevcut boyutlandırma felsefeleri tartışılmış, şartnamelerin felsefeleri verilmiş ve karşı¬ laştırmalar yapılmıştır. ikinci bölümde, her iki şartnamenin genel esasları incelenmiş ve karşılaştırmalar yapılmıştır. üçüncü bölümde, analiz ve boyutlandırma esasları ele alınmış; bu Çerçevede analizde izlenecek yolun belir¬ lenmesi ve elemanların boyutlandırıimasına esas olan kuv¬ vet ve yerdegiştirmelerin hesaplanmasıyla ilgili bilgi verilmiş ve şartnamelerin ilgili esasları karşılaştırıl- mıştır. Dördüncü bölümde, boyutlandırmaya esas olan kuv¬ vetlerin hesabı için Amerikan şartnamesinde önerilen Tek Mod ve Çok Mod spektral analiz yöntemleri ayrıntılı ola¬ rak incelenmiştir. Beşinci bölümde, depreme karşı yeterli dayanımın sağlanması için temel ve kenar ayaklarla ilgili şartname esasları verilmiş ve konu ayrıntılı bir şekilde incelen¬ miştir. Altıncı bölümde, betonarme elemanların depreme karşı yeterli dayanımı sağlayacak bir şekilde boyutlan- dırma felsefesine uygun olarak boyutlandırıiması için A- merikan şartnamesinde verilen esaslar incelenmiştir. Yedinci bölümde, seçilen 4 açıklıklı bir karayolu köprüsünün her iki şartnamede önerilen yöntemler kullanı¬ larak deprem hesabı yapılmış ve elde edilen sonuçlar kar¬ şı laştırılmıştır. Daha sonra yapısal elemanlar, depreme karşı yeterli dayanımın sağlanması için verilen esaslar göz önünde bulundurularak boyutlandırıimiş ve detaylandı- rılmıştır. Sekizinci bölümde, bu Çalışmada elde edilen sonuç¬ lar açıklanmıştır. vii

Özet (Çeviri)

INVESTIGATIONS AND COMPARISONS ON SOME REGULATIONS FOR SEISMIC DESIGN OF HIGHMAY BRIDGES AND APPLICATIONS SUMMARY in this study, seismic design of highway bridges is examined on the basis of the American and Japanese Gödeş. Furthermore, requirements of these regulations are compared. This study consists of 8 parts: 1-Introduction 2-General requirements 3-Analysis and design requirements 4-Analysis methods 5-Foundation and abutment design requirements 6-Reinforced concrete 7-Application 8-Results in the first part, the principles and the basic concepts that used for the development of the provisions are presented. These principles are: a- Small to moderate earthquakes should be resis- ted within the elastic range of the structural compo- nents without significant damage. b- Realistle seismic ground motion intensities and forces are used in the design procedures. c- Exposure to shaking from large earthquakes should not cause collapse of ali ör part of the bridge. The basic concepts that used for the development of the provisions in the American Code are: a- Hazard to life be minimized. b- Bridges may suffer damage but have low proba- bility of collapse due to earthquake motions. viiic- Function of essential bridges be maintained. d- Design ground motions have low probability of belng exceeded during normal lifetime of bridge. e- Provisions be applicable to ali of the United States. f- Ingenuity of design not be restricted. Furthermore, design philosophies and design pro- cedures flow charts are given in the first part. Con- ceptually there are two seismic design approaches cur- rently in use and both employ a“force design”concept. These are the current New Zealand and CalTrans eriteria. in the New Zealand Code, which accepts the philo- sophy that it is uneconomical to design a bridge to re- sist a large earthquake elastically, bridges are desig- ned to resist small-to-moderate earthquakes in the elas- tic range. For large earthquakes the design philosophy is that bridges be düetile where possible. in the CalTrans approach the member forces are determined from an elastic design response spectrum for a maximum credible earthquake. The design forces for each component of the bridge are then obtained by divi- ding the elastic forces by a reduction factor (Z). The methodology used in the American Code is, in part, a combination of the CalTrans and New Zealand“force design”approaches but also relative displacement problem. The complexity of the methodology increases as the seismic intensity of an area increases. Four addi- tional concepts are included in the American Code that are not included in either the CalTrans ör New Zealand approach. These concepts are: 1-Minimum requirements are specified for support lengths of girders at abutments, columns and hinge seats to account for some of the important relative displace¬ ment effects that cannot be calculated by current state- of-the-art methods. 2-Member design forces are calculated to account for the directional uncertainty of earthquake motions and the simultaneous occurence of earthquake forces in two perpendicular horizontal directions. 3-Design requirements and forces for foundations are intended to minimize foundation damage which is not readily detectable. 4-Â basic premise in developing the Regulation was that they be applicable to ali parts of the U.S.A. ixThe methodology used in the Japanese Code is si¬ mi lar to the New Zealand approach but also relative dis- placement problem. in the second part, general requirements are pre- sented. These requirements include the applicability of regulations and the determination of the seismic coeffi- cient, the intportance coefficient, and the response mo- difications factors. These. regulations are for the design and const- ruction of new bridges to resist the effect of earthqu- ake motions. The provisions in the American Code apply to bridges of conventional steel and concrete girder and box girder construction with spans not exceeding 150 m. The provisions in the Japanese Code apply to bridges with spans not exceeding 200 m. The seismic countur maps in the American Code are based on (1) a realistic appraisal of expected levels of ground motion shaking, (2) approximately the same proba- bility that the design ground shaking will be.exceeded for ali parts of the ünited States, and (3) the frequen- cy of occurence of earthquakes in various regions of the country. The seismic map in the Japanese Code is the zone map which is based on estimates of maximum ground sha¬ king experienced during the recorded historical period without any consideration of how frequently such motions might occur. The importance Classification (IC) is used in conjunction with the Acceleration Coefficient (A) to determine the Seismic Performance Category (SPC) for bridges with an Acceleration Coefficient greater than 0.29 in the American Code. Two importance classifications are specified. An IC of I is assigned for essential bridges and II for ali others. The determination of the împortance Classi- fication of a bridge is necessarily subjective. Consi¬ deration should be given to Social/Survival and Securi- ty/Defense requirements. Essential bridges are those that must continue to function after an earthquake. The importance Coefficient is used to determine the seismic coefficient in the Japanese Code. The seismic performance category controls the degree of complexity and sophistication of the analysis and design requirements in American Code. Four SPC were defined. The four categories permit variation in the requirements for methods of analysis, minimum support xlengths, column design details, foundation and abutment design requirements in accordance with the seismic risk associated with a particular bridge location. Response modifiçation factors are used to modify the component forces obtained from the elastic analysis in American Code. Inherent in the R values is the as- sumption that columns will yield when subjected to for¬ ces with, little, if any, damage. in the third part, analysis and design require- ments are presented. These repuirements include the analysis procedures of the regulations and the determi- nation of design forces and displacements. Two minimum analysis procedures are defined and the applicable procedure för a given type of bridge, which depends on the number of spans, the geometrical complexity and the seismic performance category, gene¬ ral ly accepted procedure may be used in lieu of the re- commanded minimum in the American Code. The two analy¬ sis procedures to be used are Single-Mode Spectral Met- hod and Multimode Spectral Method. For bridges classified as SPCB, C ör D the elas¬ tic forces and displacements shallbe determined inde- pendently along two perpendicularaxes by use of the analysis procedure specified. The elastic seismic forces and moments resulting from analyses in the two perpendicular directions are combined to form two load cases. A detailed seismic analysis is not required för single span bridges. However, the connections between the bridge span and the abutments shall be designed both longitudinally and transversely to resist the gravity reaction force at the abutment muitipiied by the accele- ration coefficient of the site. For bridges classified as SPC A the connection of the superstructure to the substructure shall be designed to resist a horizontal seismic force equal to 0.20 times the dead load reaction force in the restrained direc¬ tions. Seismic design forces for bridges classified as SPC B shall be determined by dividing the elastic seismic forces obtained from Load Case l and Load Case 2 by the apropriate response modification factor. The mo¬ dif ied seismic forces resulting from the two load cases shall then be corabined independently with forces from other loads. Each component of the structure shall be designed to withstand the forces resulting from each load combination. xiTwo sets of design forces are specified for brid- ges classified as Category C ör D. First, the modified design forces shall be determined as above. Second, the forces resulting from plastic hinging at the top and/or bottom of the column shall be calculated after prelimi- nary design of the columns is complete. in the Japanese Code, the seismic coefficient method (the equivalent lateral force method) is propo- sed to determination of design forces. in the third part, furthermore, minimum support lengths are given in the American and Japanese Codes. The length of support provided at abutments, columns and hinge seats raust accommodate displacements resulting from the overall inelastic response of the bridge struc- ture, possible independent movement of different parts of the substructure, and out-of-phase rotation of abut¬ ments and columns resulting from traveling surface wave motions. The minimum support lengths specified are de- pendent on the deck length between expansion joints and the column height since both dimensions influence öne ör more of the factors that cause the differential displa¬ cements. in the fourth part, the dynamic analysis methods are given. These methods are the Single-Mode Spectral Method and the Multimode Spectral Method. The single mode spectral analysis method is used to calculate the seismic design forces for bridges that respond predomi- nantly in the first mode of vibration. The method, alt- hough completely rigorous from a structural dynamics point of view, reduces to a problem in statics after the introduction of inertia forces. The system is conveni- ently formulated using energy principles. The principle of virtual displacements are used to formulate a genera- lized parameter model of a continuous system in a manner which approximates the overall behaviour of the system. The multimode response spectrum analysis should be performed with a suitable space frame linear dynamic analysis computer program. Program generally available with these capabilities include: STRUDL, SAP4, SAP6, SAP80, SAP90, STARDYN, NASTRAN, EASE, and MARC. This method applies to bridges with irregular geometry which induces coupling in the three coordinate directions wit- hin each mode of vibration. The bridge should be mode- led as a three-dimensional space frame with joints and nodes selected to realistically model the stiffness and inertia effects of the structure. Foundation conditions at the base of the columns and at the abutments may be modeled using equivalent linear spring coefficients. The member forces and displacements can be estimated by combining the respective response quantities from the xiiindividual modes by the Square Root of the Sum of the Squares (SRSS) method. The fifth part includes foundation and abutment design requirements that are specifically related to se ismic resistant construction. It assumes compliance with all the basic requirements necessary to provide support for vertical loads and lateral loads other than those due to earthquake motions. These include, but are not limited to, provisions for the extent of foundation investigation, fills, slope stability, bearing and late ral soil pressures, drainage, settlement control, and pile requirements and capacities. Liquefaction of saturated granular foundation soils has been a major source of bridge failures during historic earthquakes. Where possible, the best design measure is to avoid deep, loose to medium-dense sand si tes where liquefaction risks are high. Where dense or more component soils are found at shallow depths, stabi lization measures such as densif ication may be economi cal. The use of long ductile vertical steel piles to support bridge piers could also be considered. A recent review of methodologies identifies two basic approaches for evaluating the cyclic liquefaction potential of a deposit of saturated sand subjected to earthquake shaking: 1- Empirical methods based on field observations of the performance of sand deposits in previous earth quakes, and correlations between sites which have and have not liquefied and Relative Density or Standard Pe netration Test (SPT) blowcounts. 2- Analytical methods based on the laboratory de termination of the liquefaction strength characteristics of dynamic site response analysis to determine the mag nitude of earthquake- induced shearing stresses. The numerous case histories of damage to, or fai lure of, bridges induced by abutment failure of displa cement during earthquakes have clearly demonstrated the need for careful attention to abutment design and de tailing in seismic areas. Damage is typically asso ciated with fill settlement or slumping, displacements induced by high seisraically-induced lateral earth pres sures, or the transfer of high longitudinal or transver se inertia forces from the bridge structure itself. Settlement of abutment backfill, severe abutment damage or bridge deck damage induced by the movement of abut ments may cause loss of bridge access, and hence abut ments must be considered as a vital link in the overall seismic design process for bridges. xmDesign features of abutments vary tremendously, and depend on the nature of the bridge site, foundation soils, bridge span length and load magnîtudes. Abutment types include free-standing gravity walls, cantilever walls, tied back walls and monolithic dîaphragms. For free-standing abutments such as gravity ör cantilever walls, which are able to yield laterally du- ring an earthquake the well-established Mononobe-Okabe pseudo-static approach, is widely used to compute earth pressures induced by earthquakes. For free-standing abutments iri highly seismic areas, design of abutments to provide zero displacement under peak ground accelera- tions may be unrealistic, and design för an acceptable sınai l lateral displacement may be preferable. Monolithic ör end diaphragm abutments are common- ly used för single and för two span bridges. The end diaphragm is cast monolithically with the superstructure and may be directly supported on piles, ör provision may be made for beam shortening during post-tensioning. The diaphragm acts as a retaining wall with the superstruc¬ ture âcting as a prop between abutments. in the sixth part, reinforced concrete require- ments are given. The purpose of the these requirements is to ensure, especially for bridges in highly seismic risk areas, that the design of the components of a brid¬ ge are consistent with the overall design philosophy and that the potential for failures observed in past earth- quakes is minimized. The coluran design requirements of this chapter for bridges classified as SPC C and D are such that a column is forced to yield in flexure with a reasonable ductility capacity and that the potential for a shear, compression ör loss of anchorage mode of failu- re is minimized. The design requirements for piers pro¬ vide for some inelastic çapacıty; however, the R-factor specified for piers is such that the anticipated inelas¬ tic capacity is significantly less than that of columns. in the seventh part, the earthquake forces of a chosen reinforced concrete bridge has been estimated according to the American and Japanese Codes, and the comparisons have been made. Furthermore, the structural elements have been designed. in the eighth part, the results which are obta- ined in this study are presented. xivc

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