2013-10-17 Seaoc Ssdm Series Ppt Vol 1 Handout
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Structural Engineers Associa1on of California Webinar: 2012 IBC SSDM – Volume 1 – Code Applica=on Examples
Structural Engineers Association of California Ryan A. Kersting, S.E., Volume Manager & Presenter Buehler & Buehler Structural Engineers, Inc.
The 2012 IBC SEAOC Structural Seismic Design Manual Introduction to the 2012 Edition: • Expanded scope – 5 Volumes
• Examples based on latest standards • Application of SEAOC Blue Book recommendations illustrated • More elements and systems addressed – Collectors – Diaphragms – Base plates
– Isolation – Supplemental damping 2
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Structural Engineers Associa1on of California Webinar: 2012 IBC SSDM – Volume 1 – Code Applica=on Examples
The 2012 IBC SEAOC Structural Seismic Design Manual
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Volume 1 Acknowledgements Authors / Reviewers / Contributors • Ryan A. Kersting, S.E., Buehler & Buehler Structural Engineers • April Buchberger, S.E., Clark Pacific • Timothy S. Lucido, S.E., Rutherford + Chekene • Kevin Morton, S.E., Hohbach-Lewin Structural Engineers • Nicolas Rodrigues, S.E., DeSimone Consulting Engineers • Ali Sumer, Ph.D., S.E., State of California Office of Statewide Health Planning and Development (OSHPD) • Additional contributions from members of SEAOC Seismology Committee and Subcommittees 4
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Structural Engineers Associa1on of California Webinar: 2012 IBC SSDM – Volume 1 – Code Applica=on Examples
Structural Engineers Association of California Ryan A. Kersting, S.E., Volume Manager & Presenter Buehler & Buehler Structural Engineers, Inc.
Learning Objectives • Become familiar with changes in seismic provisions of: – 2012 International Building Code (IBC) - Chapter 16 – American Society of Civil Engineers (ASCE) - Minimum Design Loads for Buildings and Other Structures ASCE/ SEI 7-10 (ASCE 7-10) – 2013 California Building Code (CBC) - Chapter 16A
• Learn to use Volume 1 of the 2012 IBC SEAOC Structural Seismic Design Manual (SSDM)
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Learning Objectives • Learn overall approach to implementing specific seismic provisions of 2012 IBC / ASCE 7-10, including those pertaining to: – Design Spectral Response Acceleration Parameters – Site-specific Ground Motion Procedures – Combinations of Structural Systems – Configuration Irregularities / Discontinuous Systems – Scaling Results of Modal Response Spectrum Analysis – Wall and Anchorage Design for Out-of-Plane Forces
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Volume 1 Presentation Overview • Introduction to SSDM Volume 1 • Seismic code changes relevant to Vol. 1 – 2012 IBC Chapter 16 – ASCE 7-10 Chapters 11 and 12 – 2013 CBC Chapter 16A
• Selected Examples • Questions
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PART 1 – INTRODUCTION Volume 1 Scope, Purpose, Reference Standards, Contents, Organization, and Format
Introduction to SSDM Volume 1 Scope / Purpose of SSDM (all volumes): • Intent of examples is to illustrate a design approach engineered to achieve good performance under severe seismic loading, including some SEAOC recommendations for exceeding minimum code requirements in order to achieve that performance
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Introduction to SSDM Volume 1 Scope / Reference Standards for Vol. 1: • 2012 IBC − Seismic provisions within Chapter 16 − Refers to ASCE 7-10 for most provisions
• ASCE 7-10 − Chapters 11 (with ref. to 21 & 22), 12, 13, and 15 − Primary focus on Chapter 12
• SEAOC Blue Book
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Introduction to SSDM Volume 1 Contents: • Examples illustrate application of specific section or provision within ASCE 7-10 − Some re-written to reflect changes to code provisions & SEAOC recommendations − Others cover new topics or new approaches not previously addressed − Increased consistency with and reference to SEAOC Blue Book − Application of material design standards is covered in Volumes 2, 3, and 4 12
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Introduction to SSDM Volume 1 Contents (cont.): • 58 total examples distributed across ASCE 7-10 as follows: − Chapter 11 Seismic Design Criteria – 4 − Chapter 12 Seismic Design Requirements for Building Structures – 45 − Chapter 13 Seismic Design Requirements for Nonstructural Components – 5 − Chapter 15 Seismic Design Requirements for Nonbuilding Structures – 4 13
Introduction to SSDM Volume 1 Contents (cont.): • Examples distributed across ASCE 7-10 Chapter 12 as follows: − − − − − −
§12.1 Structural Design Basis - 1 §12.2 Structural System Selection - 5 §12.3 Irregularities & Redundancy - 16 §12.4 Seismic Load Effects / Combos - 2 §12.7 Modeling Criteria - 1 §12.8 Equivalent Lateral Force Procedure - 7 14
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Introduction to SSDM Volume 1 Contents (cont.): • Examples distributed across ASCE 7-10 Chapter 12 as follows (cont.): − − − − − −
§12.9 Modal Response Spectrum Analysis - 1 §12.10 Diaphragms - 3 §12.11 Structural Walls and Anchorage - 3 §12.12 Drift and Deformation - 3 §12.13 Foundation Design - 2 §12.14 Simplified Design Procedure - 1 15
Introduction to SSDM Volume 1 Organization / Format: • Examples are organized in same order as ASCE 7 provision(s) being addressed • Each problem statement provides detailed “given” information followed by list of items to determine in order to arrive at the solution • Most examples contain introductory overview and/or additional commentary after solution
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PART 2 – SEISMIC CODE CHANGES 2012 IBC Chapter 16 ASCE 7-10 Chapters 11 and 12 2013 CBC Chapter 16A
Seismic Code Changes 2012 IBC Chapter 16: • Section 1604.5 Risk Category – “Risk Category” replaces former “Occupancy Category” terminology – Table 1604.5 maintains I, II, III, and IV classifications with some minor revisions within table • NOTE: ASCE 7 Table 1.5-1 also addresses Risk Category, but IBC Table 1604.5 should be used as IBC language is more specific and governs – CBC Table 1604A.5 is similar with subtle differences
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Seismic Code Changes 2012 IBC Chapter 16 (cont.): • Section 1605 Load Combinations – Load combinations with seismic load including overstrength are included by reference to applicable ASCE 7 provisions but not reprinted • Text added to clarify how the ASCE combinations with overstrength replace IBC combinations • Subtle but significant improvement
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Seismic Code Changes 2012 IBC Chapter 16 (cont.): • Section 1613 Earthquake Loads – Refers to ASCE 7-10 for earthquake effects (no change) • “in accordance with ASCE 7, excluding Chapter 14 and Appendix 11A”
– IBC alternatives / revisions to ASCE 7 are very limited (see §1613.4) • Most 2009 IBC alternatives / revisions to ASCE 7-05 were incorporated into ASCE 7-10 • CBC amendments in §1616A discussed later
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Seismic Code Changes 2012 IBC Chapter 16 (cont.): • Section 1613 Earthquake Loads – Re-prints much of ASCE 7 Chapter 11 for determining: • Ground motion values (including “new” maps from ASCE 7 Ch. 22) – More on this later
• Seismic Design Category (SDC)
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Seismic Code Changes ASCE 7-10 Chapter 11: • Section 11.4 Seismic Ground Motion Values – Refers to maps in Chapter 22 – Introduces new term “Risk-Targeted Maximum Considered Earthquake” (MCER) which is incorporated in the “new” ground motion maps
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Seismic Code Changes ASCE 7-10 Chapter 11 (cont.): • Section 11.4 Seismic Ground Motion Values – “New” (ASCE 7-10) ground motion maps reflect four significant changes (USGS “Project 07”): 1. 2. 3. 4.
USGS updates (seismic sources and NGA) Risk-targeted ground motion Maximum-direction ground motion Modified deterministic ground motion
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Seismic Code Changes ASCE 7-10 Chapter 11 (cont.): • Section 11.4 Seismic Ground Motion Values – “New” (ASCE 7-10) ground motion maps reflect four significant changes (USGS “Project 07”): 1. USGS updates • Incorporates 2008 USGS data for seismic sources/ models and next-generation attenuation (NGA) relationships • This factor by itself generally decreases ground motion parameters in many parts of U.S. 24
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Seismic Code Changes ASCE 7-10 Chapter 11 (cont.): • Section 11.4 Seismic Ground Motion Values – “New” (ASCE 7-10) ground motion maps reflect four significant changes (USGS “Project 07”): 2. Risk-targeted ground motion • Fundamental shift in ground motion basis from “uniform hazard” (2% probability of exceedance in 50 years) to “uniform risk” (1% probability of collapse in 50 years) based upon generic structural fragility • Significant decrease in ground motion for New Madrid zone and Charleston, S.C.; otherwise < ±15% change 25
Seismic Code Changes ASCE 7-10 Chapter 11 (cont.): • Section 11.4 Seismic Ground Motion Values – “New” (ASCE 7-10) ground motion maps reflect four significant changes (USGS “Project 07”): 3. Maximum-direction ground motion • Change from “geo-mean” calculation to use of the acceleration in the direction of maximum response • Increases short-period accelerations by factor of 1.1 and long-period accelerations by factor of 1.3 26
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Seismic Code Changes ASCE 7-10 Chapter 11 (cont.): • Section 11.4 Seismic Ground Motion Values – “New” (ASCE 7-10) ground motion maps reflect four significant changes (USGS “Project 07”): 4. Modified deterministic ground motion • Certain areas governed by “deterministic cap” (many areas of California) • Deterministic MCE formulation changed to 84th percentile, or from 1.5x to 1.8x median characteristic earthquake ground motion 27
Seismic Code Changes ASCE 7-10 Chapter 11 (cont.): • Section 11.4 Seismic Ground Motion Values – Additional resources regarding this change: • 2007 SEAOC Convention paper by Luco, et. al. (www.seaoc.org/bookstore, search “Proceedings”) • EERI Seminar “Project 07-Reassessment of Seismic Design Procedures and Development of New Ground Motions for Building Codes” (www.eeri.org/products-page/technical-seminars)
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Seismic Code Changes ASCE 7-10 Chapter 11 (cont.): • Section 11.4 Seismic Ground Motion Values – What is net effect of “new” ground motion maps? • Depends on location, but in general: – SS values in central and eastern U.S. have generally decreased by 10% - 25% compared to ASCE 7-05 values – SS values in western U.S. generally within ±15% of ASCE 7-05 values, although some areas have significantly higher increase – S1 values across most of U.S. generally within ±15% of ASCE 7-05 values, although some western U.S. areas show higher increase 29
Seismic Code Changes – Comparison of Ground Motion Values
From EERI “Project 07…” Seminar by Kircher, Luco, & Whittaker
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Seismic Code Changes – Comparison of Ground Motion Values
From EERI “Project 07…” Seminar by Kircher, Luco, & Whittaker
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Seismic Code Changes – Comparison of Ground Motion Values
From EERI “Project 07…” Seminar by Kircher, Luco, & Whittaker
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Seismic Code Changes – Comparison of Ground Motion Values
From EERI “Project 07…” Seminar by Kircher, Luco, & Whittaker
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Seismic Code Changes ASCE 7-10 Chapter 12: • §12.2.3.1 R, Ω0, & Cd for vertical combination – If lower system has lower R value: • Permitted to use R, Ω0, & Cd of upper system for design of upper system (but not as separate upper structure) • R, Ω0, & Cd of lower system shall be used for design of lower system (but not as separate lower structure) – ASCE 7-05 required that Ω0 & Cd values could not decrease for design of lower system
• Different than two-stage analysis (see §12.2.3.2) 34
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Seismic Code Changes ASCE 7-10 Chapter 12: • §12.2.3.1 R, Ω0, & Cd for vertical combination – If upper system has lower R value: • R, Ω0, & Cd of upper system shall be used for design of both systems – ASCE 7-05 required similar treatment of R (cannot increase as go down the structure)
– SSDM Vol. 1 Design Examples 7 and 9
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Seismic Code Changes ASCE 7-10 Chapter 12: • §12.2.3.1 R, Ω0, & Cd for vertical combination – 2013 CBC §1616A.1.5 replaces ASCE 7-10 language with language from ASCE 7-05: • Value of R used for design within a story shall not exceed lowest value of R in any story above • Value of Ω0 & Cd used for design within a story shall not be less than largest value of each in any story above
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Seismic Code Changes ASCE 7-10 Chapter 12: • §12.2.3.2 Two Stage Analysis Procedure – Allows analysis of upper and lower portions as separate structures if certain conditions are met • Only change is new criteria item ‘e’ that upper may be analyzed with ELF or MRSA procedure, but lower must be analyzed with ELF procedure
– 2013 CBC §1616A.1.6 adds item ‘f’ such that: • Where design of upper elements is governed by special seismic load combos, then those special loads must be considered in design of lower portion 37
Seismic Code Changes ASCE 7-10 Chapter 12: • §12.3.2 Irregular & Regular Classification – T12.3-1 Horizontal Structural Irregularities • Torsional Irregularity Types 1a and 1b – Definitions improved by specifying accidental torsion for this check only needs to consider case with Ax = 1.0 (no iteration)
• Nonparallel System Irregularity Type 5 – Definition improved by deleting “or not symmetric about” such that irregularity only occurs if systems are not parallel
– SSDM Vol. 1 Design Examples 11 – 16 address horizontal irregularities 38
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Seismic Code Changes ASCE 7-10 Chapter 12: • §12.3.2 Irregular & Regular Classification – T12.3-2 Vertical Structural Irregularities • In-Plane Discontinuity Irregularity Type 4 – Definition improved such that irregularity exists when in-plane offset such that overturning demands are placed on supporting beam, column, truss, or slab (rather than being based on amount of offset versus length of system)
– SSDM Vol. 1 Design Examples 17 – 23 address vertical irregularities 39
Seismic Code Changes ASCE 7-10 Chapter 12: • §12.8.1.1 Calculation of Cs – Minimum base shear equation 12.8-5: • Cs = 0.044SDSIe ≥ 0.01 • Incorporated from ASCE 7-05 Supplement No. 2 • Need not be considered for computing drift per §12.8.6.1
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Seismic Code Changes ASCE 7-10 Chapter 12: • §12.9.4 Scaling Design Values from Modal Response Spectrum Analysis (MRSA) results – §12.9.4.1 Scaling of Forces: • If the combined response for the modal base shear (Vt) is less than 85% of the calculated equivalent lateral force (ELF) base shear (V), then forces shall be multiplied by (0.85V)/(Vt)
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Seismic Code Changes ASCE 7-10 Chapter 12: • §12.9.4 Scaling Design Values from Modal Response Spectrum Analysis (MRSA) results – §12.9.4.2 Scaling of Drifts: • If the combined response for the modal base shear (Vt) is less than 0.85CsW, where Cs is per Eq. 12.8-6, then drifts shall be multiplied by (0.85CsW)/(Vt) in addition to being multiplied by Cd / Ie per §12.9.2 – Otherwise, drifts need not be scaled beyond per §12.9.2
– SSDM Vol. 1 Design Example 37 (new) 42
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Seismic Code Changes ASCE 7-10 Chapter 12: • §12.9.4 Scaling Design Values from Modal Response Spectrum Analysis (MRSA) results – 2013 CBC §1616A.1.13 replaces ASCE §12.9.4 with: • Modal base shears used to determine forces and drifts shall not be less than those calculated per the equivalent lateral force procedure of §12.8
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Seismic Code Changes ASCE 7-10 Chapter 12: • §12.10.2.1 Collectors Requiring Overstrength Load Combinations for SDC C through F – Collectors shall be designed to resist load combinations including the maximum of: • Ω0QE, where QE is from V per §12.8 or §12.9 • Ω0QE, where QE is from Fpx per §12.10 Eq. 12.10-1 • QE, where QE is from Fpxmin per §12.10 Eq. 12.10-2 • Exceptions… – (1) limitation of maximum relative to Fpmax (see next slide) – (2) no Ω0 required for light-frame shear wall structures 44
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Seismic Code Changes ASCE 7-10 Chapter 12: • §12.10.2.1 Collectors Requiring Overstrength Load Combinations for SDC C through F – Collectors shall be designed to resist… max of: • Exception 1 limits maximum based on Fpmax: – ASCE 7-10 limits maximum to QE, where QE is from Fpxmax per §12.10 Eq. 12.10-3, but intent is being debated by multiple committees (SEAOC, ASCE, BSSC PUC, etc.) – 2013 CBC §1616A.1.14 limits maximum to Ω0QE, where QE is from Fpxmax per §12.10 Eq. 12.10-3 – Recommend using CBC basis for ALL projects until clarified 45
Seismic Code Changes ASCE 7-10 Chapter 12: • §12.11.2.1 Wall Anchorage Forces – Revised such that only one equation is used, with a new variable to account for diaphragm rigidity / flexibility • Fp = 0.4SDSkaIeWp (Eq. 12.11-1) > 0.2kaIeWp where: – ka = 1.0 + (Lf / 100) ≤ 2.0 – Lf = span (in feet) of flexible diaphragm between vertical elements of LFRS; use Lf = 0 for rigid diaphragm
• ka = 1.0 for rigid, = 2.0 max for flexible 46
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Seismic Code Changes ASCE 7-10 Chapter 12: • §12.11.2.1 Wall Anchorage Forces – Where anchorage is not at roof and where all diaphragms are not flexible, Fp from Eq. 12.11-1 may be multiplied by (1 + 2z/h)/3 where: • z is height of anchor above the base of structure • h is height of the roof above the base
– SSDM Vol. 1 Design Examples 41 – 43
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Seismic Code Changes ASCE 7-10 Chapter 12: • §12.12.3 Structural Separation – 2012 IBC incorporates 2009 IBC revisions to ASCE 7-05 • Defines δM = Cdδmax/Ie – 2013 CBC 1616A.1.15 defines δM = Cdδmax (provides additional separation for higher risk category structures)
• Adjacent structures on same property shall be separated by δMT based on SRSS of δM1 and δM2 • Structures shall be setback from property line by minimum of δM 48
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Seismic Code Changes ASCE 7-10 Chapter 12: • §12.12.4 Members Spanning Between Structures (new section) – Connections shall be designed for maximum anticipated relative displacements, including: • Multiplying calculated deflections (Cdδxe/Ie) by 1.5R/Cd • Considering diaphragm rotations, including torsional amplification if either structure is torsionally irregular • Considering diaphragm deformations • Assuming structures are moving in opposite directions and using absolute sum of displacements 49
PART 3 – SELECTED EXAMPLES DE1 – Design Spectral Response Acceleration Parameters DE3 – Site-Specific Ground Motion Values DE9 – Combination Framing Detailing DE24 – Elements Supporting Disc. Systems DE37 – Scaling Modal Resp. Spectrum Results DE42 – Out-of-plane Effects on 2-story Wall Panel
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Design Example 1 – §11.4 Design Spectral Response Acceleration Parameters • Given a site location and soil Site Class • Determine: – Mapped MCER parameters: SS and S1 – Site Coefficients: Fa and Fv – MCER parameters adjusted for site class: SMS and SM1 – Design Spectral Acceleration Parameters: SDS and SD1
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Design Example 1 – §11.4 Design Spectral Response Acceleration Parameters • Mapped MCER parameters: SS and S1 – “U.S. Seismic Design Maps” application available from USGS website (if accessible): http://geohazards.usgs.gov/designmaps/us/application.php • • • • •
Choose applicable code: 2012 IBC or ASCE 7-10 Input address or latitude and longitude Input site class (will calculate site coefficients) Input risk category (although it doesn’t affect results) Output will include: – SS and S1 , Fa and Fv , SMS and SM1 , and SDS and SD1 52
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Design Example 1 – §11.4 Design Spectral Response Acceleration Parameters • Mapped MCER parameters: SS and S1 – OR, spreadsheet of data points based on latitude and longitude or maximum values by county or zip code from USGS or skghoshassociates.com (in upper right corner) • Obtain SS and S1 • Determine Fa and Fv from Tables 11.4-1 and 11.4-2 • Calculate SMS and SM1: – SMS = FaSS – SM1 = FvS1
• Calculate SDS and SD1: – SDS = (2/3)SMS – SD1 = (2/3)SM1 53
Design Example 3 – §11.4.7 Site-Specific Ground Motion Procedures • Given: – Calculated SDS and SD1 from mapped MCER SS and S1 – Site-specific MCER and Design Response Spectra
• Determine: – Design response spectrum per §11.4.5 (map-based) – Scaled site-specific design response spectrum per §21.3 – Design acceleration parameters per §21.4
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Design Example 3 – §11.4.7 Site-Specific Ground Motion Procedures • Design response spectrum per §11.4.5 – Determined based on calculated SDS and SD1 from mapped MCER SS and S1 in conjunction with §11.4.5 and Fig. 11.4.1
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Design Example 3 – §11.4.7 Site-Specific Ground Motion Procedures • Scaled site-specific design response spectrum per §21.3 – Design spectral response acceleration at any period shall not be taken less than 80% of Sa determined in accordance with §11.4.5 • Sa (scaled s-s) ≥ 80% Sa (mapped)
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Design Example 3 – §11.4.7 Site-Specific Ground Motion Procedures • Scaled site-specific design response spectrum per §21.3
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Design Example 3 – §11.4.7 Site-Specific Ground Motion Procedures • Design acceleration parameters per §21.4 – SDS = greatest of: • site-specific Sa at T = 0.2 sec • 90% of largest site-specific Sa at any T > 0.2 sec • 80% of SDS per Section 11.4.4
– SD1 = greatest of: • site-specific Sa at T = 1.0 sec • two times (2x) site-specific Sa at T = 2.0 sec • 80% of SD1 per Section 11.4.4
– Refer to §21.4 for rules regarding use of these values • Note: mapped S1 still required to be used in Eq. 12.8-6
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Design Example 9 – §12.2.4 Combination Framing Detailing Requirements • §12.2.4 requires structural members common to different framing systems to be designed using the detailing requirements for the system with the highest value of R • Given a two-story steel special moment-resisting frame (SMRF, R = 8, Ω0 = 3) supported by a onestory special concrete shear wall (R = 5, Ω0 = 2.5) • Determine the design axial force and detailing requirements for the concrete pilasters supporting the steel SMRF columns 59
Design Example 9 – §12.2.4 Combination Framing Detailing Requirements
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Design Example 9 – §12.2.4 Combination Framing Detailing Requirements • Design axial force for concrete pilaster: – Since common to both the steel SMRF and the concrete shear wall, pilaster must be designed using requirements for SMRF (higher R factor) – Design axial force on steel SMRF columns must include amplified seismic loads (combinations including Ω0) when loads exceed a certain threshold • Assuming this is the case, concrete pilaster would need to be designed using the same load combinations and with Ω0 = 3.0
– SEAOC Seismology Blue Book article recommends capacity-based approach as illustrated in SSDM 61
Design Example 9 – §12.2.4 Combination Framing Detailing Requirements • Detailing requirements for concrete pilaster: – Concrete pilaster shall be detailed in accordance with special concrete shear wall provisions at a minimum • Special “boundary zone” requirements would effectively provide equivalent performance to SMRF detailing
• For more information, refer to SEAOC Seismology Blue Book article "Structural Detailing for Combined Structural Systems" available at: http:// www.seaoc.org/bluebook/index.html 62
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Design Example 24 – §12.3.3.3 Elements Supporting Discontinuous Systems • Example provides a specific worked-out solution but also includes commentary with considerations for other common configurations • New suggestion from SEAOC Seismology regarding design of “transfer diaphragm” in outof-plane offset configuration
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Design Example 24 – §12.3.3.3 Elements Supporting Discontinuous Systems
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Design Example 24 – §12.3.3.3 Elements Supporting Discontinuous Systems • §12.3.3.3 requires elements supporting discontinuous systems to be designed to resist special load combinations including overstrength • §12.10.1.1 and §12.10.2.1 require transfer forces to be considered in design of diaphragms and collectors, respectively – intent is being debated by multiple committees (SEAOC, ASCE, BSSC PUC, etc.)
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Design Example 24 – §12.3.3.3 Elements Supporting Discontinuous Systems • SEAOC Seismology Committee suggests the engineer apply the special load combinations to the transfer diaphragm when the performance of the diaphragm is critical to the performance of the primary LFRS
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Design Example 37 – §12.9.4 Scaling Modal Response Spectrum Analysis Results • Given the following: – Fundamental geometry and weight data for the structure – Design response spectrum from either §11.4.5 or §21.3 – Mapped value of S1 – Seismic Importance Factor, Ie – Value of R, Cd, Ta, Cu, and Tcalc in each orthogonal direction (x and y)
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Design Example 37 – §12.9.4 Scaling Modal Response Spectrum Analysis Results • Determine the following: – Combined modal response design base shear Vt in each orthogonal direction using MRSA per 2012 IBC – Scaling of seismic forces from MRSA results per 2012 IBC – Scaling of drifts from MRSA results per 2012 IBC – Scaling of seismic forces and drifts from MRSA results per 2013 CBC
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Design Example 37 – §12.9.4 Scaling Modal Response Spectrum Analysis Results • Combined modal response design base shear Vt in each direction per 2012 IBC (cont.): – §12.9.1 - Build analysis model for modal analysis with enough modes such that modal mass participation is at least 90% of actual mass in each orthogonal direction – §12.9.2 - Perform MRSA with design response spectrum in each direction divided by (R/Ie). Further multiply drift and displacement results by (Cd/Ie) – §12.9.3 - Obtain combined response for each parameter of interest, including base shear Vt in each direction, using appropriate modal combination procedure 69
Design Example 37 – §12.9.4 Scaling Modal Response Spectrum Analysis Results • Scaling of seismic forces from MRSA results per 2012 IBC: – §12.9.4 - Determine the base shear V in each orthogonal direction using the procedures in §12.8 with the calculated fundamental period (Tcalc from MRSA) – §12.9.4.1 - For scaling of forces, if Tcalc > CuTa, use CuTa in §12.8 base shear calcs. – §12.9.4.1 - If Vt < 85%V, force results shall be multiplied by: (0.85V)/(Vt) 70
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Structural Engineers Associa1on of California Webinar: 2012 IBC SSDM – Volume 1 – Code Applica=on Examples
Design Example 37 – §12.9.4 Scaling Modal Response Spectrum Analysis Results • Scaling of seismic drifts from MRSA results per 2012 IBC: – §12.9.4.2 • If Vt < 0.85CsW, and • If Cs is determined (governed) by Eq. 12.8-6 – Cs = 0.5S1/(R/Ie) (using mapped S1≥0.6g),
• Then, the drifts shall be multiplied by (0.85CsW)/(Vt) – Otherwise, drifts need only be scaled per §12.9.2
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Design Example 37 – §12.9.4 Scaling Modal Response Spectrum Analysis Results • Scaling of seismic forces and drifts from MRSA results per 2013 CBC: – 2013 CBC §1616A.1.13 replaces ASCE §12.9.4 with: • Modal base shears used to determine forces and drifts shall not be less than those calculated per the equivalent lateral force procedure of §12.8 • If Vt < 100%V, force results shall be multiplied by: (V)/ (Vt) – If Tcalc > CuTa, two separate comparisons can be made as it is acceptable to calculate V for drift comparison based on full calculated fundamental period per §12.8.6.2 72
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Structural Engineers Associa1on of California Webinar: 2012 IBC SSDM – Volume 1 – Code Applica=on Examples
Design Example 42 – §12.11 Out-of-plane Effects on Two-Story Wall Panel • Given the following: – Wall dimensions and weight – Seismic parameters SDS and Ie – Flexible roof diaphragm, Lf = 300 ft – Rigid floor diaphragm
• Determine the following: – Out-of-plane forces for: • Wall panel design • Wall anchorage design 73
Design Example 42 – §12.11 Out-of-plane Effects on Two-Story Wall Panel • Out-of-plane forces for wall panel design – Fp = 0.40SDSIeww ≥ 0.1ww
(§12.11.1)
• Force does not vary with height of wall • Depending on SDS, Ie, and ww, wind forces may govern • Parapet forces shall be determined per §13.3.1 (see DE 41)
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Structural Engineers Associa1on of California Webinar: 2012 IBC SSDM – Volume 1 – Code Applica=on Examples
Design Example 42 – §12.11 Out-of-plane Effects on Two-Story Wall Panel • Out-of-plane forces for wall anchorage design – Fp = 0.4SDSkaIeWp (Eq. 12.11-1) > 0.2kaIeWp
(§12.11.2)
• ka = 1.0 + (Lf / 100) ≤ 2.0
– At flexible roof diaphragm with Lf = 300ft, – ka = 1.0 + (300 / 100) = 4.0 ≤ 2.0
• Fp = 0.8SDSIeWp > 0.4IeWp
– At rigid floor diaphragm with Lf = 0 (by definition), – ka = 1.0
• Fp = 0.4SDSIeWp > 0.2IeWp
– If all diaphragms are not flexible, then Fp could be modified by (1 + 2z/h)/3 per §12.11.2 75
QUESTIONS?
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Structural Engineers Associa1on of California Webinar: 2012 IBC SSDM – Volume 1 – Code Applica=on Examples
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The 2012 IBC SEAOC SSDM Webinar Series • • • • •
Oct 17th Oct 30th Nov 7th Nov 14th Jan 16th
Vol. 1: Code Application (ASCE 7) Vol. 3: Concrete Vol. 2: Wood and Masonry Vol. 4: Steel Vol. 5: Isolation and Damping
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