1、S. K. Ghosh Associates Inc. Report to BFRL/NIST 1 Comparison of the Seismic Provisions of the 1997 Uniform Building Code to the 1997 NEHRP Recommended Provisions S.K. Ghosh Associates, Inc. Northbrook, Illinois A report to: Building and Fire Research Laboratory National Institute of Standards and T
2、echnology Gaithersburg, MD 20899 February 2001 S. K. Ghosh Associates Inc. Report to BFRL/NIST 2 ACKNOWLEDGEMENT Project Participants S.K. Ghosh Associates Inc. S.K. Ghosh Susan Dowty Madhu Khuntia Kihak Lee Building and Fire Research Laboratory, NIST: H.S. Lew Stephen A. Cauffman S. K. Ghosh Assoc
3、iates Inc. Report to BFRL/NIST 3 TABLE OF CONTENTS 1.0 EXECUTIVE SUMMARY 1 2.0 INTRODUCTION 2 3.0 1997 NEHRP PROVISIONS 4 3.1 Overview of NEHRP Provisions 4 3.2 Overview of Major Changes from NEHRP 1994 to 1997 4 4.0 1997 Uniform Buidling Code . 7 4.1 Overview of 1997 UBC 7 4.2 Seismic Design Provi
4、sions of 1997 UBC . 8 5.0 COMPARISON OF 1997 UBC TO 1997 NEHRP. 11 5.1 Chapter 1: General Provisions 11 5.2 Chapter 2: Glossary and Notations . 11 5.3 Chapter 3: Quality Assurance . 11 5.4 Chapter 4: Ground Motion 11 5.5 Chapter 5: Structural Design Criteria 12 5.6 Chapter 6: Architectural, Mechanic
5、al, and Electrical Components Design Requirements. 13 5.7 Chapter 7: Foundation Design Requirements . 13 5.8 Chapter 8: Steel Structure Design Requirements 13 5.9 Chapter 9: Concrete Structure Design Requirements . 14 5.10 Chapter 10: Composite Steel and Concrete Structure Design Requirements . 14 5
6、.11 Chapter 11: Masonry Structure Design Requirements . 14 5.12 Chapter 12: Wood Structure Design Requirements 16 5.13 Chapter 13: Seismically Isolated Structures Design Requirements 16 5.14 Chapter 14: Nonbuilding Structure Design Requirements . 16 5.15 Chapter 15: Conclusions Regarding IBC 17 6.0
7、CONCLUSIONS. 19 REFERENCES . 20 Table 1. Detailed Comparison of Structural Provisions of 1997 UBC and 1997 NEHRP 21 S. K. Ghosh Associates Inc. Report to BFRL/NIST 4 1.0 EXECUTIVE SUMMARY Executive Order 12699, Seismic Safety of Federal and Federally Assisted or Regulated New Building Construction,
8、 requires that all new federally owned, leased, assisted, and other regulated buildings be designed and constructed in accordance with the appropriate seismic standards. The Interagency Committee on Seismic Safety in Construction (ICSSC) has recommended the use of building codes which are substantia
9、lly equivalent to the 1997 National Earthquake Hazards Reduction Program Provisions for the Development of Seismic Regulations for New Buildings (NEHRP Provisions). The objective of this study is to determine whether or not the seismic and material design provisions of the Uniform Building Code (UBC
10、) 2000 edition are substantially equivalent to, or exceed, the 1997 NEHRP Provisions. This report follows three previous reports prepared for the National Institute of Standards and Technology (NIST GCR 91-598, NIST GCR 95-674 and NIST GCR 98-755). Each previous report evaluated the equivalency of t
11、he latest edition of the NEHRP Provisions available at the time of the report and the latest editions of the following model codes and standards available at the time of the report: the BOCA National Building Code (BOCA/NBC), the Standard Building Code (SBC), the Uniform Building Code (UBC), ASCE 7
12、Minimum Design Loads for Buildings and Other Structures (ASCE 7) and CABO One- and Two-Family Dwelling Code (OFTDC). This report also follows a draft report prepared for the National Institute of Standards and Technology, which evaluated the equivalency of the 1997 NEHRP Provisions and the seismic a
13、nd material design provisions of the International Building Code (IBC) 2000 edition, the International Residential Code for One- and Two-family Dwellings (IRC) 2000 edition, and ASCE 7-98 Minimum Design Loads for Buildings and Other Structures. The seismic design provisions of the 1997 Uniform Build
14、ing Code are based on Appendix C of the 1996 edition of the Recommended Lateral Force Requirements published by the Structural Engineers Association of California (SEAOC Blue Book). It also includes many of the features of the 1994 NEHRP Provisions. The earthquake regulations of the 1997 NEHRP Provi
15、sions are substantially different from the corresponding requirements of the 1994 Provisions. Partly as a result of this and partly because the 1997 UBC did not include some important features of the1994 NEHRP Provisions, the seismic and material design requirements of the 1997 UBC were found to be
16、not equivalent to those of the 1997 NEHRP Provisions. S. K. Ghosh Associates Inc. Report to BFRL/NIST 5 2.0 INTRODUCTION Executive Order 12699, Seismic Safety of Federal and Federally Assisted or Regulated New Building Construction, requires that all new federally owned, leased, assisted, and other
17、 regulated buildings be designed and constructed in accordance with the appropriate seismic standards. The Interagency Committee on Seismic Safety in Construction (ICSSC) has recommended the use of building codes, which are substantially equivalent to the 1997 National Earthquake Hazards Reduction P
18、rogram Provisions for the Development of Seismic Regulations for New Buildings (NEHRP Provisions). The objective of this study is to determine whether or not the seismic and material design provisions of the Uniform Building Code (UBC) 1997 edition are substantially equivalent to, or exceed, the 199
19、7 NEHRP Provisions. This report follows three previous reports prepared for the National Institute of Standards and Technology (NIST GCR 91-598, NIST GCR 95-674 and NIST GCR 98-755). Each previous report evaluated the equivalency of the latest edition of the NEHRP Provisions available at the time of
20、 the report and the latest editions of the following model codes and standards available at the time of the report: the BOCA National Building Code (BOCA/NBC), the Standard Building Code (SBC), the Uniform Building Code (UBC), ASCE 7 Minimum Design Loads for Buildings and Other Structures (ASCE 7) a
21、nd CABO One- and Two-Family Dwelling Code (OFTDC). This report also follows a draft report prepared for the National Institute of Standards and Technology, which evaluated the equivalency of the 1997 NEHRP Provisions and the seismic and material design provisions of the International Building Code (
22、IBC) 2000 edition, the International Residential Code for One- and Two-family Dwellings (IRC) 2000 edition, and ASCE 7-98 Minimum Design Loads for Buildings and Other Structures. Comparisons between the 1997 NEHRP Provisions and the UBC are made on the basis of seismic provisions, material design pr
23、ovisions, foundation design requirements, quality assurance provisions, and non-structural element design requirements. In the comparisons, the UBC is judged equivalent if its provisions are equivalent to, or more stringent than, the corresponding requirements in the 1997 Provisions. The UBC is judg
24、ed not equivalent if the requirements of the 1997 NEHRP Provisions are more stringent than the requirements in the model code. In certain instances NEHRP includes provisions that the UBC does not. When a model code or standard does not have specific provisions regarding criteria, elements or systems
25、, the design is left to the discretion of the designer. Depending on the judgment of the designer, the design may or may not be equivalent to NEHRP. Therefore, when the UBC is silent on certain issues, equivalency may not be judged. One item of overriding importance for the purposes of this comparis
26、on must be noted at the outset. In the Uniform Building Code, the seismic zone in which a structure is located determines permissible structural systems, including the level of detailing required for structural S. K. Ghosh Associates Inc. Report to BFRL/NIST 6 members and joints that are part of th
27、e lateral-force-resisting system and for the structural components that are not. It also determines applicable limitations on height of a structural system and structural irregularity, the type of lateral analysis that must be performed as the basis of design, as well as nonstructural component requ
28、irements. Seismic zones are regions in which seismic ground motion, corresponding to a certain probability of occurrence, is within certain ranges. The United States is divided into Seismic Zones 0 through 4, with 0 indicating the weakest earthquake ground motion, and 4 indicating the strongest. The
29、 1997 NEHRP Provisions uses Seismic Design Categories (SDC) as the determinant of seismic design and detailing requirements. The SDC is a function of the locations seismicity, building occupancy and soil type. Although the 1997 USC “seismic zone” only considers the seismicity of a location (whereas
30、the 1997 NEHRP “Seismic Design Category” takes into account the building occupancy and soil type as well as seismicity), an equivalency between “seismic zone” and “Seismic Design Category” was assumed for this comparison study. The following table identifies which seismic zones were assumed equivale
31、nt for Seismic Design Categories A-F: NEHRP SDC Assumed Equivalent Seismic Zone A,B 0,1 C 2 D, E, F 3,4 S. K. Ghosh Associates Inc. Report to BFRL/NIST 7 3.0 1997 NEHRP PROVISIONS 3.1 Overview of NEHRP Provisions The Federal Emergency Management Agency (FEMA) has contracted the Building Seismic Saf
32、ety Council (BSSC) to develop the National Earthquake Hazards Reduction Program (NEHRP) Provisions for new buildings. One of the primary goals of the program is to reduce or mitigate losses from earthquakes. The NEHRP Recommended Provisions for Seismic Regulations for New Buildings are recommended p
33、rovisions that have increasingly been adopted in recent times by model codes and standards. The first edition of the NEHRP Provisions was dated 1985. The document is updated on a 3- year cycle. The 1997 edition of the NEHRP provisions is the fourth update of the document. The NEHRP Provisions presen
34、t a strength-based approach to design that represents the state of knowledge of seismic design. The seismic design provisions incorporate current research and knowledge from previous earthquakes. Seismicity maps are used to assess the seismic hazard at a particular site. Forces and seismic design re
35、quirements are increased with increasing seismic hazard. In the 1997 edition of the NEHRP Provisions, the seismic design category (SDC) of a structure, which is based on occupancy as well as on soil-modified seismic risk at the site of a structure, determines the level of detailing and design requir
36、ements. The seismic design category is used to obtain higher levels of performance; however, it does not influence the force level which is increased for structures in higher occupancy categories through an importance factor. In the design base shear equation, a factor R which accounts for system re
37、sponse and inelastic deformability, reduces the strength that would have been needed for elastic response to the design earthquake to a design level. Detailing requirements that are formulated to provide a commensurate amount of inelastic deformability are given in the materials chapters. The design
38、 base shear varies with 1/T, where T is the elastic fundamental period of the structure. 3.2 Overview of Major Changes from NEHRP 1994 to 1997 The earthquake regulations of the 1997 NEHRP Provisions are substantially different from the corresponding requirements of the 1994 Provisions. The biggest c
39、hange is the completely new set of ground motion maps and resulting design ground motion parameters which are now SDS and SD1, rather than the Ca and CV of the 1994 Provisions and Aa and AV of earlier Provisions. SDS and SD1 are 5%-damped design spectral response accelerations at short periods and 1
40、 sec. period, respectively. SDS and SD1 are two-thirds of SMS and SM1 which are soil-modified (Maximum Considered Earthquake) spectral response accelerations at 0.2 sec. and 1 sec. period, respectively. SMS and SM1 are obtained by multiplying mapped MCE spectral response accelerations SS (at 0.2 sec
41、. period) and S1 (at 1 sec. period), respectively, by Fa, the acceleration-related soil factor and FV, the velocity-related soil factor, respectively. The maximum considered earthquake is the 2500- year return period earthquake (2% probability of exceedance in 50 years) in most of the country, excep
42、t that in coastal California, it is the largest (deterministic) earthquake that can be generated by the known seismic sources. The design earthquake of the 1997 NEHRP provisions is two-thirds of the MCE, whereas the design earthquake of the 1994 S. K. Ghosh Associates Inc. Report to BFRL/NIST 8 NEH
43、RP Provisions has an average return period of 475 years (10% probability of exceedance in 50 years). The two-thirds is the reciprocal of 1.5 which is agreed to be the “seismic margin” built into structures designed by the 1994 and older editions of the NEHRP Provisions. In other words, a structure d
44、esigned by the 1994 or older editions of the NEHRP Provisions is believed to have a low likelihood of collapse under an earthquake that is one and one-half times as large as the design earthquake of those documents. The redefinition of the design earthquake in the 1997 NEHRP Provisions is intended t
45、o provide a uniform level of safety across the country against collapse in the Maximum Considered Earthquake. This was not the case before because the MCE is only 50% larger than the design earthquake of the 1994 NEHRP Provisions in coastal California, while it can be four or five times as large as
46、the design earthquake of the 1994 Provisions in the Eastern United States. Aa and AV of the 1994 NEHRP Provisions indicated the effective peak acceleration and the effective peak velocity-related acceleration of the ground corresponding to the design earthquake of the 1994 Provisions on Type SB soil
47、 or soft rock. The mapped MCE spectral response accelerations SS and S1 of the 1997 NEHRP Provisions are also mapped on Type SB soil. The soil classification and the associated site coefficients first introduced in the 1994 NEHRP Provisions have been retained unchanged in the 1997 Provisions. The se
48、cond most important difference between the 1994 and the 1997 editions of the NEHRP Provisions is the replacement of the Seismic Performance Category (SPC) with the Seismic Design Category (SDC). In the 1994 and older editions of the NEHRP Provisions, restrictions on building height and structural irregularity, choice of analysis procedures that form the basis of seismic design, as well as the level of detailing requ
