Structural(Engineers(Associa1on(of(California(! Structural Engineers Association of California Constantine Shuhaibar, Shuhaibar Engineers, Presenter The 2012 IBC SEAOC Structural Seismic Design Manual Introduction to the 2012 Edition: Expanded scope 5 Volumes Examples based on latest standards Application of Blue Book recommendations illustrated More elements and systems addressed Collectors Diaphragms Base plates Isolation Supplemental damping 6 Page!1!
The 2012 IBC SEAOC Structural Seismic Design Manual Volume 1 Code application (ASCE 7) Volume 2 Light-Frame, Tilt-up & Masonry Volume 3 Concrete Volume 4 Steel Volume 5 Base Isolation and Dampers 7 Acknowledgements Authors 1. Mason Walters 2. René Vignos 3. Chris Petteys 4. Michael Gemmill 5. Anthony Giammona 6. H. Kit Miyamoto 7. Amir Gilani Reviewers 1. Martin Button 2. Ronald Mayes 3. Troy Morgan 4. Constantine Shuhaibar 5. Mark Sinclair Volume Manager Constantine Shuhaibar 8 Page!2!
Structural(Engineers(Associa1on(of(California(! Structural Engineers Association of California Constantine Shuhaibar, Shuhaibar Engineers, Presenter Learning Objectives Become familiar with design standards for Protective Systems in the 2012 IBC Learn to use Volume 5 of the SEAOC Structural Seismic Design Manual Learn the overall approach to designing 10 Page!3!
Why is it important? 11 Types of Base Isolators - Friction Pendulum(Single, Double, or Triple) - Natural or Plain Rubber - High-Damping Rubber - Lead Rubber - Cross Linear - Sliding Plate 12 Page!4!
Types of Base Isolators Triple(Fric1on(Pendulum(Isolator( 13 Outline 1. Building Geometry and Loads 2. Ground Motions 3. Design Goals 4. Isolation System Layout and Preliminary Design 5. Coordinate with Isolator Manufacturer(s) 6. Analyze Building with Suggested Bearing Properties 7. Code-Minimum Calculations 8. Determine Member Forces 9. Determine Prototype Tests Requirements 10. Design Review 11. Develop Specifications for Isolators 12. Verify Tested Bearing Properties Match Design Assumptions 14 Page!5!
Building Information Appendix - 120 ft x 150 ft - Six stories - Office Occupancy on all floors - Located in San Francisco, CA (Latitude 37.783, Longitude 122.392 ) - Site Class D - Risk Category II 15 Building Geometry Appendix 16 Page!6!
Building Geometry Appendix 17 Building Geometry Appendix 18 Page!7!
Ground Motions Appendix 19 Ground Motions Appendix 20 Page!8!
Design Example Overview Design of new structures with base isolation per ASCE/SEI 7-10 Chapter 17 Example focuses on the design of the isolation system only superstructure design is similar to other SDM examples 21 Design Example Overview: Friction Pendulum (FP) and Lead Rubber (LR) dual example same building designed with different isolation systems Plane of isolation at the ground and at the first floor same building designed with different levels of isolation Design example follows typical practice Commentary is included to discuss code intent 22 Page!9!
Design Example Overview: Nonlinear Response History Analysis (NLRHA) is common for the design of isolated buildings and this example adopts this practice ETABS is used as the analysis program and an example model file is included with the examples www.seaoc.org/2012ibc-seaoc-ssdm-volume5-models 23 Design Goals Main parameters to consider limiting: Total maximum displacement at base Base shear Floor accelerations Story Drift Base isolation can also be used to provide enhanced seismic performance 24 Page!10!
Isolation System Layout Layout of both FP and LR systems is discussed Commentary discusses design issues such as isolation plane location, center of rigidity of isolation system, and bearing type selection 25 Isolation System Layout Commentary discusses key items to consider in system layout: 1. Isolation moat detailing 2. Stairs/elevators that cross the isolation plane 3. Mechanical systems that cross the isolation plane 4. Isolator P-Delta moment treatment 5. Avoiding configurations that produce isolator uplift 26 Page!11!
Isolation System Preliminary Design Goal is to determine suitability of base isolation Treat the entire isolation system as one single isolation bearing Two methods are presented 1. A quick method for initial feasibility studies based on displacement spectrum 2. A more accurate, but more in depth, method based on SDOF response history analysis 27 Isolation System Preliminary Design Either method can be used for either system Both methods can provide a reality check for the more in depth full building NLRHA model to follow 28 Page!12!
Coordinate with Isolator Manufacturer(s) Isolation bearings are not yet off the shelf so manufacturer input is typically needed Estimates of bearing properties can be used for preliminary analysis, but exact properties of available bearings should be verified Commentary discusses what information should be provided to the manufacturer(s) 29 Analysis of Building with Isolator Properties from Manufacturer Full 3D NLRHA model Beams and columns modeled as linear elements Isolators modeled as nonlinear elements 30 Page!13!
Computer Modeling Issues NLRHA is complex Careful attention must be paid to settings in modern analysis programs Commentary discusses key items to consider in analysis program Very important to perform an independent model verification! 31 Computer Modeling Issues Modeling isolators as nonlinear elements can be one of the more complicated parts of a base isolation design Example provides detailed instructions for how to model these elements 32 Page!14!
Bounding Analysis Current language of ASCE 7 does not completely address bounding analysis to consider variability of isolator properties This example performs a bounding analysis as recommended by several research documents A dual set of analyses models are carried through the example (upper and lower bound isolator properties) 33 Code Minimum Equations Example illustrates how to check the code minimum equations in a typical design Requires design engineer to interpret test data Commentary discusses some of the pitfalls and challenges of checking code requirements If results from ETABS model are less than code minimums, then ETABS results must be scaled up 34 Page!15!
Determine Member Forces Design of the superstructure is not addressed, but the example outlines how to extract and scale member forces 35 Additional Topics Prototype and production testing of bearings Design Review Specifications for Isolators Verify that production bearings match design assumptions 36 Page!16!
Why is it important? 37 Types of Dampers - Viscous (Linear or Nonlinear) - Visco-Elastic - Hysteretic - Friction - Tuned-Mass 38 Page!17!
Types of Dampers Viscous(Damper( 39 Outline 1. Building Geometry and Loads 2. Preliminary Design 3. SMF Design Sizes for Code Strength Requirements 4. Selection of Analysis Procedure 5. Damper Properties 6. Equivalent Lateral-Force Procedure 7. Nonlinear Response History Analysis (NLRHA) 8. Damping Components and Connections 9. Items not Addressed in this Design Example 10. Revisions to Chapter 18 of ASCE 7 40 Page!18!
Building Geometry 41 Building Geometry 42 Page!19!
Design Example Overview Design of new structures with supplemental damping per ASCE/SEI 7-10 Chapter 18 Design the building using normal code procedures of Chapter 12, as follows Base shear for 75% of code minimum Only perform strength design Drifts will not meet code limits of Chapter 12 but will be controlled with dampers 43 Design Goals Devices added to the building to reduce demand on members and control drift Many types of dampers; this example focuses on viscous dampers Target is to add 20%+ damping to structure 44 Page!20!
Viscous Dampers Initially developed for defense and aerospace Velocity dependent devices Do not add stiffness to building (no change in period) Placed in structure using same configuration as braces Hundreds of structures built or retrofitted with these devices 45 Initial Design Use code load comb. Design for 75% Vb Size members, check for compactness, panel zone, SCWB, etc. per AISC Drift ratios do not meet code limit of 2% Story X Y ROOF 4.7% 2.4% STORY6 4.7% 2.5% STORY5 4.7% 2.8% STORY4 4.6% 2.8% STORY3 3.9% 2.7% STORY2 2.1% 1.7% 46 Page!21!
Dampers to Control Drift Can use approximate ELF procedure or NLRH analysis Specify damper properties (constant and exponent) Initial trial assumes stiffness proportional damping 47 NLRH Analysis Place dampers at all floors (to prevent single story response) Use velocity exponent of 0.3-0.5 to avoid large damper forces Diagonal dampers in this design example Use accel. records per ASCE 7-10 Force Linear Nonlinear Velocity 48 Page!22!
Design Example Analysis 3 pairs of records from past earthquakes Scale or match to target spectrum Conduct analysis and use largest of responses Spectral acceleration, g 1.2 Target Component 1 1.0 Component 2 0.8 0.6 0.4 0.2 0.0 0 1 2 3 4 5 6 Period, sec 49 Strength Checks Code allows structural members (not dampers) to be modeled as elastic if DCR<1.5 If DCR>1.5 then Can increase member sizes Increase damper size Conduct analysis accounting for material nonlinearity 50 Page!23!
Strength Checks DCR <1.5 Will need to include forces from seismic loading and from damper Since velocity dependent, damper forces not in-phase with inertial or elastic forces 51 Drift Ratios Large reduction in drift ratios Meet code limits of Chapter 12 Dampers effective in controlling displacement and drifts Story X Y ROOF 0.7% 1.4% STORY6 1.5% 1.6% STORY5 1.8% 1.6% STORY4 1.8% 1.6% STORY3 1.6% 1.5% STORY2 0.9% 0.9% 52 Page!24!
Energy Dissipation Most of seismic energy dissipated by dampers Thus, members do not have to undergo inelastic deformation to dissipate energy Energy, in-kips 70000 60000 50000 40000 Seismic input 30000 Inherent (5%) damping 20000 Supplementary damping 10000 0 0 5 10 15 20 25 30 Time, sec 53 Damper Devices and Connections Need to design members and connections in-line with dampers AISC procedure Drive brace check for adequate stiffness and comp. strength 54 Page!25!
Structural(Engineers(Associa1on(of(California(! QUESTIONS? 55! Page!26!