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  • 1. William M. Bulleit, Michigan Tech
    Dave K. Adams, Lane Engineers, Inc
    Philosophy of Structural Building Codes
  • 2. Chair: Jon Schmidt
    SEI/ASCE Engineering Philosophy Committee
  • 3. Define minimum standards
    Give legal requirements
    Assist engineers
    Enhance consistency across designs
    Assist code officials
    Enhance safety
    Protect property
    Reduce uncertainty
    Maintain heuristics
    Why Building Codes?
  • 4. Resistance > Load Effect
    Format definition
    Loads
    Load application
    Load combinations
    Resistance calculations
    Detailing
    Goal of Structural Building Codes
  • 5. Implicit or Explicit
    Explicit requirements generally reduce variability
    Implicit requirements generally increase variability
    Optimize the relative amount of each
    Evolution
    Cost
    Uncertainty reduction
    Avoid future failures
    How?
  • 6. Allowable Stress/Strength Design
    Load and Resistance Factor Design (Partial Factor Code)
    Reliability Design
    Performance-Based Design – likely based around reliability design
    Format
  • 7. Loads should be explicit to use a consistent basis (e.g., 50-year return period, 2% annual probability of exceedance)
    Load application should be a balance. (ASCE 7 seems to have become too explicit in this area.)
    Load combinations are usually explicit due to the need for a consistent basis for loads
    1.2D + 1.6L + 0.5S
    Loads
  • 8. Overall: 7-88 94 pages 7-05 388 pages (smaller font)
    Live Loads:
    7-88: 2.5 pgs. spec., 5.5 pgs. comm.
    7-05: 5 pgs. spec., 6 pgs. comm.
    Snow Loads:
    7-88: 9 pgs. spec., 13 pgs. comm.
    7-05: 13 pgs. Spec., 14 pgs. comm.
    Wind Loads:
    7-88: 15 pgs. spec., 11 pgs. comm.
    7-05: 60 pgs. spec., 40 pgs. comm.
    ASCE 7
  • 9. Codes such as ACI-318 and the AISC specification are strongly weighted toward resistance calculations.
    Generally becoming more and more explicit.
    Increases design consistency
    Helps engineers – to a point
    Helps code officials
    Often material based (e.g., ACI-318), but sometimes structure based (e.g., AASHTO bridge code)
    Codes should help reduce model error.
    e.g., rectangular stress block versus designer’s choice
    Resistance Calculations
  • 10. 1983 : 111 pgs. spec., 155 pgs. comm; 266 pgs. total
    1989: 353 pgs. total
    2005: 430 pgs. total
    ACI 318
  • 11. Anchorage of concrete wall to roof diaphragm must resist 200 plf. (Explicit)
    Structures must provide a complete load path to transmit loads from their point of origin to the load resisting element. (Implicit)
    Seismic Design Example
  • 12. Generally very explicit
    Sometimes difficult to separate where detailing requirements differ from design requirements
    Example: Minimum ties for square concrete columns.
    No. 3 bars for No. 10 or smaller longitudinal bars, No.4 for larger long. bars
    Vertical spacing: 16 long. bar dia’s, 48 tie dia’s, or least dimension
    Other placement requirements
    Detailing
  • 13. In the end, codes should lead to safer structures.
    Generally, more explicit codes would appear to lead to safer structures.
    But at some point the complexity of the code may lead to more errors by the designer
    Too implicit increases designers’ decisions and increases inconsistency among designs
    Too explicit makes it harder for designers to know what part of the code to use. Tends to CYA.
    What is wrong?
  • 14. Specification: Includes legal aspects and necessary explicit information (e.g., load characterization)
    Commentary: Includes possible techniques for design (e.g., load application, resistance calculation) and possible details.
    Supplement: Design aids for designs done to the Commentary
    Designs done to the Commentary and Supplement would be ‘deemed-to-comply’ with the Specification
    Possible Solution
  • 15. Codes need to find a balance between explicit requirements and implicit requirements
    Over emphasis on either can reduce safety and/or increase cost
    One possible solution is to have a relatively implicit specification with a commentary that makes design suggestions that are ‘deemed-to-comply’ with the specification.
    Conclusions
  • 16. Questions?