CE 147 - 03 2006 IBC Seismic Loads

CE 147 - 03 2006 IBC Seismic Loads - Estimating Earthquake...

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1 Estimating Earthquake Demands Using the 2006 International Building Code (IBC Using the 2006 (IBC) Introduction Establishing seismic loads using the 2006 IBC requires both 2006 IBC (Chapter 16) 2005 ASCE 7 ( Minimum Design Loads for Buildings and Other Structures ) (Chapters 11 and 12) Unfortunately, the requirement to use both 2006 IBC and 2005 ASCE 7 is not very “user friendly” but that’s life… These notes attempt to organize the process of establishing the seismic demand and contain the relevant material from ASCE 7
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2 These notes are a brief summary. To fully appreciate the meaning of Introduction specific requirements, refer to actual sections in ASCE 7 and the IBC. IBC Section 1613 (Earthquake Loads) ASCE 7 Ch.11: Seismic Design Criteria Ch. 18: Damping Systems Ch. 12: Seismic Design Requirements Ch. 19: Soil-Structure Interaction Most relevant to this class Ch. 13: Nonstructural Seismic Design Ch. 20: Site Classifications Procedure Ch. 14: Material Specific Design Requirements Ch. 21: Site-Specific Ground Motion Procedure Ch. 15: Nonbuilding Structures Ch. 22: Ground Motion and T L Maps Ch. 16: Seismic Response (time history) Ch. 23: Seismic References Ch. 17: Seismically Isolated Structures Variety of methods that can be used to estimate earthquake loads Index Force Method (not used) Analytical Methods Simplified Analysis (only applicable to very simple structures) Equivalent Lateral Force (ELF) Analysis (most structures) Modal Response Spectrum Analysis (more complex situations or tall structures – fairly common) Linear Response Time History Analysis (hardly ever used) Nonlinear Response History Analysis (used for very complex structures)
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3 The Index Force, Simplified Analysis, and ELF methods “pretend” that seismic forces can be represented by loads applied TO the Analytical Methods building In reality, seismic loads are inertial loads (i.e. they are caused by the inertial resistance of the building to being displaced as the ground moves) “Applied” forces “Inertial” forces Equivalent Lateral Force Inertial Force due to Ground Movement Base Shear Force (‘reaction”) Force displacing ground This is more of a theoretical difference than a practical difference, but it is important to understand that there isn’t a “big hand” Analytical Methods pushing the building over. The other methods reflect the dynamic response of the structure in obtaining the seismic loads and are, therefore, more theoretically sound.
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4 How do you decide what “size” earthquake should be used for design? Probability Considerations Current approach tries to define an earthquake with a specified probability of occurrence. Smaller earthquakes are more likely to occur over a given length of time and larger earthquakes are less likely to occur Example: On the average, which length of time will have the largest earthquake occurring: a 1-day period or a 50-year period?
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This note was uploaded on 01/14/2010 for the course CEE 147 taught by Professor Sabol during the Winter '09 term at UCLA.

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CE 147 - 03 2006 IBC Seismic Loads - Estimating Earthquake...

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