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Recent content by UKJim

  1. UKJim

    Miami Pedestrian Bridge, Part V

    Yup. Sorry. I see that now. Hard to tell.
  2. UKJim

    Miami Pedestrian Bridge, Part V

    Looks like 11’s upper tendon to me. Nope. That’s not it. Maybe an empty duct left from where 11’s lower tendon ripped through? Tough to say.
  3. UKJim

    Miami Pedestrian Bridge, Part V

    Thanks. I see that now in one of the night photos. Still seems an odd thing in such a highly designed structure.
  4. UKJim

    Miami Pedestrian Bridge, Part V

    I am curious as to what led to the (apparently) field-enlarged pocket for 11’s top tendon anchorages. Suggests to me that they were unable to get to the tendons for releasing the PT force, or?? Tendons too short seems highly unlikely to me. But why the need to expand the pocket?
  5. UKJim

    Miami Pedestrian Bridge, Part V

    Yes. A beam or wall element at that location is usually referred to as a diaphragm.
  6. UKJim

    Miami Pedestrian Bridge, Part IV

    My estimate for the load on 11 is smaller (see my previous post above). Based on the member sizes in the conceptual design, I calculated a reaction at the north pier of 910 kips (slightly less than the 950 kips in the press accounts). A portion of this total reaction is the dead weight of...
  7. UKJim

    Miami Pedestrian Bridge, Part IV

    By my estimates, the unfactored (external) forces in the members at time of collapse were very roughly: - diagonal 11 = 1150 kips (comp) - vertical 12 = 75 kips (comp) - base slab = 950 kips (tens) Further, the interface shear demand between the 11/12 joint and the base slab I estimated to...
  8. UKJim

    Miami Pedestrian Bridge, Part IV

    The applicable US code would be AASHTO LRFD. The load factor on DC (dead weight of components, i.e. self weight) is 1.25 for this situation. The load factor on LL, which was essentially nil at time of failure, is 1.75.
  9. UKJim

    Total Lateral Building Drift

    No code reference, strictly judgment/experience: h/500. If the cost to provide h/500 is significant (I'm guessing it is not), only then sharpen your pencil. Making a quantitative estimate of the velocities a person on the top level would sense from wind gusts would be a pain, as would a...
  10. UKJim

    Shear key design for to support column in 14-storey building

    Have you investigated a post-tensioned concrete transfer girder? I like the concept of intentionally roughened column surfaces combined with large, permanent P/T force to transfer the shear.
  11. UKJim

    Unbraced Length of Wood Beams

    I would generally be comfortable with a point brace designed for 2% of the total compression stress resultant in the beam. The "2% rule" has been around for a long time and has served the profession well. If the beam in question had an extraordinary amount of sweep, then I may reevaluate this...
  12. UKJim

    ASCE 7-16 partially open buildings

    The issue still, in 2016 edition, is that there is no treatment of "partially open" outside of chapter 26. Only the legacy classifications (open, enclosed, partially enclosed) are addressed in 27, 28, 29, 30.
  13. UKJim

    ASCE 7-16 partially open buildings

    Thanks for the reply. I agree that there is some room for interpretation of what is considered open vs enclosed with regard to openings (doors, windows, etc.). This has been the case for many years and the 2016 edition does not seem to make this any better or worse. However, "partially open"...
  14. UKJim

    ASCE 7-16 partially open buildings

    Chapter 26 defines "partially open" as the new catch-all for buildings that don't classify as enclosed, partially enclosed, or open. For purposes of internal pressure coefficient, the new partially open classification is treated the same as enclosed. This is numerically consistent with the...
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