1、Section 1 INTRODUCTION 1.1 PURPOSE AND PHILOSOPHY These Specifications establish design and construction provisions for bridges to minimize their susceptibility to damage from earthquakes. The design earthquake motions and forces specified in these provisions are based on a low probability of their
2、being exceeded during the normal life expectancy of a bridge. Bridges and their components that are designed to resist these forces and that are constructed in accor- dance with the design details contained in the provisions may suffer damage, but should have low probability of collapse due to seism
3、ically induced ground shaking. The principles used for the development of the provi- sions are: 1. Small to moderate earthquakes should be resisted within the elastic range of the structural components without significant damage. 2. Realistic seismic ground motion intensities and forces are used in
4、the design procedures. 3. Exposure to shaking from large earthquakes should not cause collapse of all or part of the bridge. Where possible, damage that does occur should be readily de- tectable and accessible for inspection and repair. A basic premise in developing these seismic design guidelines w
5、as that they are applicable to all parts of the United States. The seismic hazard varies from very small to high across the country. Therefore, for purposes of de- sign, four Seismic Performance Categories (SPC) are de- fined on the basis of an Acceleration Coefficient (A) for the site, determined f
6、rom the map provided, and the Impor- tance classification (IC). Different degrees of complexity and sophistication of seismic analysis and design are spec- ified for each of the four Seismic Performance Categories. An essential bridge must be designed to function dur- ing and after an earthquake. In
7、 areas with an Acceleration The probability of the elastic design force levels not being exceeded in 50 years is the range of 80 to 95%. However, the design earthquake force level by itself does not determine risk; the risk is also affected by the design rules and analysis procedures used in connect
8、ion with the de- sign ground motion. Coefficient greater than 0.29 essential bridges must meet additional requirements. A bridge is designated essential on the basis of Social/Survival and SecurityDefense clas- sifications presented in the Commentary. 1.2 BACKGROUND The 1971 San Fernando earthquake
9、was a major turn- ing point in the development of seismic design criteria for bridges in the United States. Prior to 1971, the American Association of State Highway and Transportation Offi- cials (AASHTO) specifications for the seismic design of bridges were based in part on the lateral forces requi
10、re- ments for buildings developed by the Structural Engineers Association of California. In 1973, the California Depart- ment of Transportation (CalTrans) introduced new seis- mic design criteria for bridges, which included the rela- tionship of the site to active faults, the seismic response of the
11、 soils at the site and the dynamic response characteris- tics of the bridge. In 1975, AASHTO adopted Interim Specifications which were a slightly modified version of the 1973 CalTrans provisions, and made them applicable to all regions of the United States. In addition to these code changes, the 197
12、1 San Fernando earthquake stimu- lated research activity on seismic problems related to bridges. In the light of these research findings, the Federal Highway Administration awarded a contract in 1978 to the Applied Technology Council (ATC) to: 0 Evaluate current criteria used for seismic design of h
13、ighway bridges. Review recent seismic research findings for design applicability and use in new specifications. Develop new and improved seismic design guide- lines for highway bridges applicable to all regions of the United States. 0 Evaluate the impact of these guidelines and modify them as approp
14、riate. The guidelines from this ATC project (known as ATC-6) were first adopted by AASHTO as a set of Guide 439 440 HIGHWAY BRIDGES 1.2 Specifications in 1983. They were later adopted as seis- mic provisions within the Standard Specifications in 1990. After damaging earthquakes occurred in Californi
15、a (1989), Costa Rica (1991) and the Philippines (1991), AASHTO requested the Transportation Research Board to review these criteria and prepare revised specifications as appropriate. Funded through the National Cooperative Highway Research Program under NCHRP Project 20- 7/45, the National Center fo
16、r Earthquake Engineering Re- search (NCEER) prepared this current set of seismic de- sign provisions. They closely follow the previous criteria but remove ambiguities and technical errors, correct tech- nical omissions and introduce new material which is based in part on recent field experience and
17、partly on new research findings. In addition, a new format is introduced so as to assist the application of these specifications to bridges in different seismic zones. 1.3 BASIC CONCEPTS The development of these specifications was predi- cated on the following basic concepts. 0 Hazard to life to be
18、minimized. 0 Bridges may suffer damage but have low probabil- 0 Function of essential bridges to be maintained. Ground motions used in design should have low probability of being exceeded during normal life- time of bridge. 0 Provisions to be applicable to all of the United States. Ingenuity of desi
19、gn not to be restricted. ity of collapse due to earthquake motions. 1.4 PROJECT ORGANIZATION The ATC-6 project was advised by a Project Engineer- ing Panel comprising the following members: Mr. James Cooper, Federal Highway Administra- tion; Mr. Gerard Fox, HNTB, New York; Mr. James H. Gates, Califo
20、rnia Department of Transportation; Mr. Veldo Goins, Oklahoma Department of Trans- portation; Dr. William Hall, University of Illinois, Urbana; Mr. Edward Hourigan, New York Depart- ment of Transportation; Mr. Robert Jarvis, Idaho De- partment of Transportation; Mr. Robert Kealey, Modjeski and Master
21、s, Harrisburg; Mr. James Libby, Libby Engineers, San Diego; Dr. Geoffrey Martin, Fugro Inc., Long Beach; Mr. Joseph Nico- letti, URS Blume, San Francisco; Dr. Joseph Pen- zien, University of California, Berkeley; Dr. Walter Podolny, Federal Highway Administration; and Dr. Robert Scanlan, Princeton U
22、niversity, New Jersey. The ATC project manager and technical director were In a similar manner, the NCHRP project was also Mr. Roland Sharpe and Dr. Ronald Mayes, respectively. guided by a Project Panel. The members were: 0 Mr. James D. Cooper, Federal Highway Administra- tion; Mr. James H. Gates, C
23、alifornia Department of Transportation; Mr. Veldo Goins, Oklahoma Depart- ment of Transportation; Mr. Ayaz Malik, New York Department of Transportation; Mr. Charles Ruth, Washington Department of Transportation; and Mr. Edward Wassermaa, Tennessee Department of Transportation. 0 Liaison members were
24、 Dr. John Kulicki, Modjeski and Masters (NCHRP 12-33 Liaison) and Dr. Walter Podolny (Federal Highway Administration Liaison). 0 The principal investigator for NCEER was Dr. Ian Buckle; subcontractors included Computech Engi- neering Services, Berkeley, CA, and Imbsen and As- sociates, Sacramento, C
25、A. NCHRP Project Officers were Mr. Ian Friedland and Mr. Scott Sabol. The work was conducted in several stages: Review of 1992 Standard Specifications (Division 1-A); survey of designer experience with the ap- plication of Division I-A and evaluation of design philosophy. Review of bridge performanc
26、e in recent earth- quakes. Review of revised CalTrans seismic design criteria (ATC-32 project). Review of seismic criteria in the proposed LRFD Bridge Specification (NCHRP 12-33). Conduct of certain special studies. Development of draft revisions in various formats of Evaluation of proposed revision
27、s. Modification and preparation of final standards, as increasing complexity. appropriate. 1.5 QUALITY ASSURANCE REQUIREMENTS There are numerous instances of structural failures which have occurred during earthquakes that are directly traceable to poor quality control during construction. The litera
28、ture is replete with reports noting that collapse may have been prevented had proper inspection been exer- 1.5 DIVISION IA-SEISMIC DESIGN 44 1 cised. To provide adequate seismic quality assurance re- quirements the engineer specifies the quality assurance re- quirements, the contractor exercises the
29、 control to achieve the desired quality and the owner monitors the construc- tion process through special inspection. It is essential that each party recognizes its responsibilities, understands the procedures and has the capability to carry them out. Be- cause the contractor does the work and exerc
30、ises quality control it is essential that the inspection be performed by someone approved by the owner and not the contractors direct employee. In recognition of the fact that responsibility must be coordinated during construction, the Project Engineering Panel (PEP) for the ATC-6 project examined t
31、he respon- sibility of each party in the current AASHTO (Division I) specifications. This PEP found the quality assurance re- quirements of the Division I specifications adequate to cover seismic as weil as other design requirements. There- fore, no special quality assurance requirements are in- clu
32、ded in Division I-A. 1.6 FLOW CHARTS Flow charts outlining the steps in the seismic design procedures implicit in these specifications are given in Figures 1.6A and 1.6B. 442 HIGHWAY BRIDGES 1.6 DETERMINE SEISMIC PERFORMANCE CATEGORY Article 3.4 APPLICABILITY OF STANDARDS Article 3.1 I I PRELIMINARY
33、 DESIGN DETERMINE ACCELERATION COEFFICIENT Article 3.2 I DETERMINE IMPORTANCE CLASSIFICATION Article 3.3 I I 1 DETERMINE SITE COEFFICIENT 1 Article 3.5 I DETERMINE RESPONSE MODIFICATION FACTOR I Article 3.7 Y ES DETERMINE DESIGN FORCES Article 3.1 1 DISPLACEMENTS Article 3.1 O DETERMINE SEISMIC PERF
34、ORMANCE CATEGORIES B, C AND D See Figure 2 for Sub DESIGN FORCES Article 5.2 DESIGN DIS PLACEMENTS FIGURE 1.6A Design Procedure Flow Chart 1.6 DIVISION IA-SEISMIC DESIGN 443 DETERMINE COMPONENT ELASTIC FORCES AND DISPLACEMENTS Article 3.8 DESIGN SETTLEMENT SLABS Article 7.4.5 - SPC D only r DETERMINE DESIGN FORCES Article 6.2 - SPC B Article 7.2 - SPC C and D DETERMINE DESIGN DISPLACEMENTS Article 6.3 - SPC B DESIGN STRUCTURAL COMPONENTS Section 6 - SPC 6 Section 7 - SPC C and D SEISMIC DESIGN COMPLET FIGURE 1.6B Sub Flow Chart for Seismic Performance Categories B, C, and D
