The seismic provisions of the International Code Councils (ICC) 2003 International Building Code (IBC) are quite different from the seismic provisions in the 2000 IBC because they rely heavily upon the American Society of Civil Engineers Minimum Design Loads for Buildings and Other Structures (ASCE 7-02) seismic provisions. The 2003 IBC seismic provisions are designed so that the code includes all of the seismic provisions within the code itself, for structures that can use the Simplified Analysis Procedure. More complex structures that do not qualify to use the Simplified Analysis Procedure can be designed in accordance with ASCE 7-02 Sections 9.1 through 9.6, 9.13 and 9.14 per Exception No. 1 to Section 1614.1, or designed in accordance with 2003 IBC Sections 1614 through 1623. If Exception No. 1 to Section 1614.1 is used, you need only ASCE 7-02 and do not need the 2003 IBC at all, except that the materials chapters of the 2003 IBC still apply.
For some subjects in 2003 IBC Sections 1614 through 1623, reference is made to ASCE 7-02 for code requirements. These references can be ignored if one uses the Exception 1 to Section 1614.1 option and ASCE 7 for design. Otherwise, when addressing these subjects, it is necessary for the code user to work with the 2003 IBC and ASCE 7-02 side by side, because in many cases the 2003 IBC makes modifications to ASCE 7-02. See the box below for a table that outlines which sections of the 2003 IBC references which sections of ASCE 7-02 and where modifications are made.
There are distinct and definite differences between the seismic provisions of the 2000 IBC and the 2003 IBC/ASCE 7-02.
Answers to FAQs:
Q: Is it true that 2003 IBC Table 1617.6.2 can only be used if the Simplified Analysis Procedure is being used and that ASCE 7-02 Table 9.5.2.2 is to be used otherwise.
A: Remember, there are some differences between the two tables. For example, systems included in 2003 IBC Table 1617.6.2 that are not found in ASCE 7-02 Table 9.5.2.2 include the following:
ordinary plain, intermediate, and special prestressed masonry shear walls (Bearing Wall and Building Frame Systems);
shear wall-frame interactive systems with ordinary reinforced concrete moment frames and ordinary reinforced concrete shear walls; and
cantilevered column systems (Inverted Pendulum System).
The prestressed masonry wall systems have been added by the 2003 IBC through modifications to ASCE 7-02 Table 9.5.2.2 made in 2003 IBC Section 1617.6.1. Thus a designer wanting to use any of these systems cannot choose the option of Exception 1 to Section 1614.1.
Systems included in ASCE 7-02 Table 9.5.2.2 that are not found in 2003 IBC Table 1617.6.2 include the following:
light frame wall systems using flat strap bracing (Bearing Wall System); and
ordinary steel concentrically braced frames (Dual Systems with Special Moment Frames and Intermediate Moment Frames).
This means that the above systems cannot be used if the Simplified Analysis Procedure is used. Also, there are differences in assigned R and Cd values and height limits. Some of these differences are removed by modifications made in 2003 IBC Section 1617.6.1.
Q: Why are there differences between 2003 IBC Table 1617.6.2 and ASCE 7-02 Table 9.5.2.2?
A: There are differences because the IBC table was developed under ICCs code development process and the ASCE 7 table was developed under ASCEs consensus standard process. Seismic design provisions of ASCE 7-02 adopted by reference in 2003 IBC
2003 IBC Referenced
Section Subject ASCE 7-02 Section
1616.5 Building Configuration 9.5.2.3
1616.6 Analysis Procedures 9.5.2.5.1
1617.1 Seismic Load Effects, E and Em 9.5.2.7
1617.2* Redundancy 9.5.2.4
1617.3 Deflection and Drift Limits 9.5.2.8
1617.4 Equivalent Lateral Force Procedure 9.5.5
1617.6* Seismic-force-resisting systems 9.5.2.2
1618 Dynamic Analysis 9.5.6, 9.5.7, 9.5.8
1619 Soil Structure Interaction Effects 9.5.9
1620* Earthquake Loads 9.5.2.6
1621* Arch., Mech., and Elec. Components 9.6
1622* Nonbuilding Structures 9.14
1623* Seismically Isolated Structures 9.13
*Note that this section of the 2003 IBC modifies ASCE 7-02.S.K.
Ghosh Associates, Inc., is a structural, seismic, and code consulting firm located in Palatine, Ill. and Laguna Niguel, Calif. President S.K. Ghosh, Ph.D., and Susan Dowty, S.E., are active in the development and interpretation of national structural code provisions. They can be contacted at skghosh@aol.com and dowtyskga@cox.net, respectively.
