2007 Structures Congress Selected New Provisions of ASCE/SEI 7-2005: - PowerPoint PPT Presentation

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2007 Structures Congress Selected New Provisions of ASCE/SEI 7-2005:

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  1. 2007 Structures CongressSelected New Provisionsof ASCE/SEI 7-2005: Jim Harris J. R. Harris & Company Denver, Colorado May 18, 2007 John Hooper Magnusson Klemencic Associates Seattle, Washington

  2. Overview • Reorganization • New maps; Long period map • New systems, revised R factors and limitations • Diaphragm assumptions • Redundancy factor • Dynamic analysis triggers • Near fault spectral shape applicability • Modal response spectrum analysis • Simplified design method Seismic Design Under ASCE 7-2005

  3. ASCE 7-05 Reorganization Goals of Seismic Section Reorganization 1. To improve clarity and use • Reduce depth of section numbering from 6 max typical to 4 max typical (i.e. Sec. 9.5.2.5.2.2 is now Sec. 12.5.3) 3. Simplify table and figure numbering (i.e. Table 9.5.2.5.1 is now Table 12.6-1) 4. Create logical sequence of provisions aim at the structural engineering community 5. Improve headings and clarify ambiguous provisions Seismic Design Under ASCE 7-2005

  4. ASCE 7-05 Reorganization 1. Changed major subjects to Chapters rather than Sections (similar to the IBC) 2. Replaced Section 9 with Chapters 11-23 • Incorporated the material appendices 4. Put the Chapters into a logical sequence • Rewrote ambiguous headings • Examined and rewrote sections to eliminate ambiguity 7. Provided Cross Reference Table C-11-1…02 to 05 Seismic Design Under ASCE 7-2005

  5. ASCE 7-2002 Sections 1. General 2. Combinations of Loads 3. Dead Loads 4. Live Loads 5. Soil and Hydrostatic …and Flood Loads ASCE 7-2005 Chapters General Combinations of Loads Dead Loads, Soil … and Hydrostatic Live Loads Flood Loads Comparison of Contents Seismic Design Under ASCE 7-2005

  6. ASCE 7-2002 Sections 6. Wind Loads 7. Snow Loads 8. Rain Loads 9. Earthquake Loads 10. Ice Loads Supplemental (QA) Serviceability ASCE 7-2005 Chapters Wind Loads Snow Loads Rain Loads (not used) Ice Loads - 23. Seismic A & B. QA & Existing Comparison, continued Seismic Design Under ASCE 7-2005

  7. ASCE 7-2002 9.1 General Provisions 9.2 Definitions/ Symbols 9.3 (not used) 9.4 Ground Motion 9.5 Structural Design Criteria, Analysis, and Procedures ASCE 7-2005 Seismic Design Criteria Seismic Design Requirements for Building Structures Seismic Design Requirements for Nonstructural Comp. Seismic Contents Seismic Design Under ASCE 7-2005

  8. ASCE 7-2002 9.6 Arch, Mech, Elect Comp and Sys 9.7 Foundations 9.8 Steel 9.9 Concrete 9.10 Composite Struct. 9.11 Masonry ASCE 7-2005 14. Material Specific 15. Nonbuilding Structures 16. Response Hist Anal 17. Seismic Isolation 18. Damping Systems 19. Soil-Struct. Interact. Seismic Contents, continued Seismic Design Under ASCE 7-2005

  9. ASCE 7-2002 9.12 Wood 9.13 Seismic Isolation 9.14 Nonbuilding Structures A9. Quality Assurance ASCE 7-2005 20. Site Classification 21. Site-Specific Ground Motions 22. Maps 23. Reference Docs 11A. Quality Assurance 11B. Existing Buildings Seismic Contents, continued Seismic Design Under ASCE 7-2005

  10. 11 Seismic Design Criteria 11.1 General 11.2 Definitions 11.3 Notation 11.4 Seismic Ground Motion Values 11.5 Importance Factor 11.6 Seismic Design Category 11.7 Design Req’ts for Category A 11.8 Geologic Hazards & Geotechnical Invest. Seismic Design Under ASCE 7-2005

  11. 11.1 Purpose “…specified earthquake loads are based upon post-elastic energy dissipation in the structure, and because of this fact, the requirements for design, detailing, and construction shall be satisfied even for structures and members for which load combos w/o EQ exceed those with EQ…” Seismic Design Under ASCE 7-2005

  12. 11.4 Seismic Ground Motions 1 Determine basic values from maps for bedrock conditions 2, 3 Classify soil conditions at site and determine site coefficients 4 Determine site-adjusted values 5 Take two-thirds for use in design 6 Construct design response spectrum 7 Site-specific studies permitted/required Seismic Design Under ASCE 7-2005

  13. Mapped Acceleration Parameters • Two updated sets of basic maps for the response spectrum accelerations • SS for spectral response acceleration at 0.2 secs • S1 for spectral response acceleration at 1.0 secs • New map for long period transition: TL in seconds Seismic Design Under ASCE 7-2005

  14. Ground Motion Parameters & Seismic Hazard SSandS1are the mapped 2% in 50 year spectral accelerations for firm rock SDSandSD1are the design level spectral accelerations (modified for site and “expected good performance”) Mapped Contours of SS Seismic Design Under ASCE 7-2005

  15. With ASCE 7-02 Changes everywhere, but mostly minor Deterministic area around New Madrid With UBC 97 Lots of change Lower in most areas Higher in high hazard areas, except near fault in California Three maps, not one General Comparison of Maps Seismic Design Under ASCE 7-2005

  16. Long Period Transition Maps (Fig 22.15) Seismic Design Under ASCE 7-2005

  17. Site Specific Studies • Clarification of two types: • Basic ground motion hazard at a point in rock • Site amplification in overburden soil • First type never required, but permitted; limits placed upon results • Second type encouraged; required in some instances Seismic Design Under ASCE 7-2005

  18. F A D E C B Cumulative Nature of Provisionsby Seismic Design Category Seismic Design Under ASCE 7-2005

  19. Seismic Design Category A • 11.7 is a self-contained section; defines E • Horizontal force = 1% of dead load • Load path for horizontal forces • connections = 5% of weight of smaller part • Beam, truss connections = 5% D + L • Anchor concrete and masonry walls • 280 pounds per foot Seismic Design Under ASCE 7-2005

  20. Geologic Hazards andGeotechnical Investigations • SD Category E and F: • Do not locate on active fault • SD Category C: • Evaluate slope instability, liquefaction, differential settlement, surface displacement • SD Category D, E, F: • More detail than C plus lateral pressures on basement walls and retaining walls Seismic Design Under ASCE 7-2005

  21. Overview • Reorganization • New maps; Long period map • New systems, revised R factors and limitations • Diaphragm assumptions • Redundancy factor • Dynamic analysis triggers • Near fault spectral shape applicability • Modal response spectrum analysis • Simplified design method Seismic Design Under ASCE 7-2005

  22. 1 Design Basis Structural Systems Diaphragm Flexibility; Configuration; & Redundancy Load Effects & Combinations of Loads Direction of Loading Selection of Analysis Modeling Criteria ELF Method Modal RS Method Diaphragms, Chords Collectors Structural Walls (out-of-plane) Drift and Deformation Foundation Design Simplified Alternate 12 Seismic Design of Building Structures Seismic Design Under ASCE 7-2005

  23. 12.1.1 Basic Requirements • Strength, Stiffness, Energy Dissipation • Design Motion in Any Horizontal Direction • Construct Mathematical Model • Evaluate Model for Effects • Limitations on methods of evaluation • Modifications to internal forces (R, 0) • Modifications to deformations (Cd) • Alternate Procedures Must Be Consistent Seismic Design Under ASCE 7-2005

  24. Minimum Connection Forces • Very Similar to 11.7 for SD Category A • Continuous Load Path: “…from point of application to final point of resistance…” • 0.133 SDS WP 0.05 WP • Does not apply to overall design of SFRS (Seismic Force Resisting System) • Beams, Trusses to Support 5% of D + L Seismic Design Under ASCE 7-2005

  25. 12.2 Structural System Requirements • System identification and limitations • Combos of systems: different direction • Combos of systems: same direction • Combos of systems: detailing • Specific system requirements Seismic Design Under ASCE 7-2005

  26. System Identification • “Basic lateral and vertical SFRS shall conform to one (or a permitted combo) of the systems from Table 12.2-1…” • “Selected SFRS shall be designed and detailed per referenced requirements…” • SFRS not from table permitted only if analytical and test data establish basis Seismic Design Under ASCE 7-2005

  27. Basic system parameters Obtain from table and use in seismic design: • R Response Modification Factor - measure of system inelastic capabilities • Cd Deflection Amplification Factor - increase elastic  to total  • o System Overstrength Factor - accounts for actual strength greater than design strength; used to protect vulnerable items. Seismic Design Under ASCE 7-2005

  28. R factor comparisons Seismic Design Under ASCE 7-2005

  29. R factor comparisons Seismic Design Under ASCE 7-2005

  30. R factor comparisons Seismic Design Under ASCE 7-2005

  31. R factor comparisons Seismic Design Under ASCE 7-2005

  32. Height Limits • Most shear wall and braced frame systems limited to 160 feet high in SD Categories D and E, and to 100 feet in SD Category F • These limits can be increase to 240 feet and 160 feet, respectively for some structures • No line resists more than 60% of base shear • Torsional force < 20% of total force in the line • Many exceptions, especially for nonbuilding Seismic Design Under ASCE 7-2005

  33. Concrete Shear Wall - Frame • Limited to SD Category B • Ordinary detailing for wall and frame • Analyze for interaction and provide as a minimum • Walls strong enough for 0.75 Vx at each story • Frames strong enough for 0.25 Vx at each story Seismic Design Under ASCE 7-2005

  34. 12.3 Diaphragms, Configuration, and Redundancy • Diaphragm Flexibility in Analysis • Identification of Irregularities in System Configuration • Limitations on and Penalties for Irregularities • Redundancy • Significant changes from prior edition Seismic Design Under ASCE 7-2005

  35. Assume Flexible if Wood or steel deck with concrete or masonry walls 1 or 2 family residential if light frame Compute ΔDia > 2 * δvert Assume Rigid if Concrete slab (or filled deck) with span to depth < 3 and no horizontal irregularity Otherwise: Must analyze system including actual stiffness of diaphragm! Diaphragm Flexibility Seismic Design Under ASCE 7-2005

  36. Configuration: Basic Parameters Size Shape Proportion Seismic Design Under ASCE 7-2005

  37. Plan Irregularities Type Measure 1a Torsional irregularity  corner > 1.2  center 1b Extreme torsional irregularity  corner > 1.4  center Note: torsional irregularity not checked for flexible diaphragms 2 Re-entrant corners Both projections > 15% of respective sides 3 Diaphragm discontinuity 50% change in a level or from level to level 4 Out-of-plane offsets absolute 5 Nonparallel systems absolute Seismic Design Under ASCE 7-2005

  38. Vertical Irregularities Type Measure 1a Stiffness-Soft Story Story stiffness < 70% above 1b Stiffness- Extreme Soft Story Story stiffness < 60% above 2 Weight (Mass) More than 150% adjacent story Note: 1 and 2 dropped if no story drift exceeds 130% of story above 3 Vertical Geometric Length of SFRS >130% of that in adjacent story 4 In-Plane Discontinuity Offset > length of element or a reduction in stiffness below 5a Capacity-Weak Story Lat strength < 80% of above 5b Extreme Weak Story Lat strength < 65% of above Seismic Design Under ASCE 7-2005

  39. Configuration Limitations • Horiz 1b not permitted in SD Cat E+ • Vert 1b, 5a not permitted in SD Cat E+ • Vert 5b not permitted in SD Cat D+ • Vert 5b limited to 2 stories or 30 feet in SD Cat B or C, unless weak story strength capable of 0 times design force Seismic Design Under ASCE 7-2005

  40. Configuration Penalties • Horiz 4 and Vert 4 (column, slab, beam, or truss elements supporting discontinuous elements) to resist 0 force (all SD Categories) • Horiz 1, 2, 3, 4 and Vert 4 have 25% increase in force for connection of diaphragm to vert element and collectors in SD Cat D+; also req’d for collectors except those already designed for 0 force Seismic Design Under ASCE 7-2005

  41. Overview • Reorganization • New maps; Long period map • New systems, revised R factors and limitations • Diaphragm assumptions • Redundancy factor • Dynamic analysis triggers • Near fault spectral shape applicability • Modal response spectrum analysis • Simplified design method Seismic Design Under ASCE 7-2005

  42. Redundancy factor Seismic Design Category Reliability Factor B or C D, E or F  is always 1.0 for drift and P-delta calcs and for design of: • Nonstructural components • Nonbuilding structures not similar to buildings • Members designed for 0 forces • Diaphragms • Structures with damping systems Seismic Design Under ASCE 7-2005

  43. Redundancy Factor  = 1.3 Unless following loss does not an extreme torsional irregularity and does not reduce story strength by more than 33%: • Braced frame: removal of a single brace • Moment frame: loss of moment resistance at both ends of a single beam (or at base of a single cantilever column) • Shear walls: removal of any single pier with h/l > 1.0 (or collector to such a pier) Seismic Design Under ASCE 7-2005

  44. 12.6 Analysis Method Selection Methods Defined • Equivalent (Static) Lateral Force: ELF • Modal Response Spectrum: MRS • Seismic Response History (Linear and Nonlinear): SRH (Defined in section 16) Alternate classifications: Static / Dynamic Max / Dynamic History Linear / Nonlinear Seismic Design Under ASCE 7-2005

  45. What type of Analysis? • The answer depends on: • what performance level you are hoping to achieve • the configuration of the structure • how accurate you need to be • A wide range of choices are available- Seismic Design Under ASCE 7-2005

  46. Superior Performance Levels • Behavior will be essentially elastic • For regular structures with short periods, linear static procedures are fine • For regular structures with long periods and all irregular structures - linear dynamic procedures are better, response spectra accurate enough Seismic Design Under ASCE 7-2005

  47. Poorer Performance Levels • Inelastic behavior is significant (elastic analyses are the wrong approach!) • For structures dominated by first mode response, pushover analysis may be adequate • For structures with significant hire mode response, nonlinear time history necessary Seismic Design Under ASCE 7-2005

  48. Methods Permitted • SD Cat B and C: any defined method • SD Cat D+: ELF permitted for • Occ Cat I/II < 3 stories • Occ Cat I/II of light frame < 4 stories • Reg structures with T < 3.5 TS • Reg structures of light frame any T • Irreg structure with T < 3.5 TS limited to horiz types 2, 3, 4, or 5 and vert types 4, 5a, or 5b • Other SD Cat D+ must use MRS or SRH Seismic Design Under ASCE 7-2005

  49. Design Response Spectrum Sa = SD1 / T Sa = SDS(0.4 + 0.6 T/T0) Drawn for SS = 1.0, Fa = 1.0 S1 = 0.4, Fv = 1.5 TL = 4 Spectral Acceleration, g 0.4SDS Sa = SD1 TL / T2 T0 TS Period, seconds Seismic Design Under ASCE 7-2005

  50. Design Response Spectrum Drawn for SS = 1.0, Fa = 1.0 S1 = 0.4, Fv = 1.5 TL = 4 Sa = SD1 / T Sa = SDS(0.4 + 0.6 T/T0) Sa = 0.5 S1 Spectral Acceleration, g 0.4SDS Sa = SD1 TL / T2 T0 TS Period, seconds Seismic Design Under ASCE 7-2005