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  1. WAstruc10

    Grade beam seismic hoops - overkill?

    For SDC of D, looking at ACI 318-14 section 18.13.3.4: "Grade beams and beams that are part of a mat foundation subjected to flexure from columns that are part of the seismic-force-resisting system shall be in accordance with 18.6." My situation requires large grade beams NOT spanning between...
  2. WAstruc10

    Liquefiable Soils - Where Is The "Base" of the Structure?

    Thanks. So I think you agree that a 1-stage analysis would not be appropriate (shifting some of the concrete weight up to the steel roof system, in effect). I agree. But if a two stage analysis is appropriate, what R would you base that on? Doesn't make much sense to me to assign an R value and...
  3. WAstruc10

    Liquefiable Soils - Where Is The "Base" of the Structure?

    I am designing a large but lightweight one-story steel building, similar to a PEMB. The foundation system is augercast piles due to liquefiable (seismic) soil conditions. The slab-on-grade is considered sacrificial and non-structural (so if the subgrade settles 7 inches during liquefaction, the...
  4. WAstruc10

    Hole Size in Steel for Post-Installed Anchors

    Though AISC requires +1/16" oversized holes for bolts, shop drawings for weldments (angle ledgers, etc) being attached to concrete with post-installed anchors often come back with +1/8" or +3/16" oversized holes proposed, presumedly so they'll have more tolerance for installation. Are +1/16"...
  5. WAstruc10

    Brick Veneer at Exterior Canopy

    I'm designing a cantilevered (steel HSS) column freestanding canopy. The architect now wants the steel columns surrounded by a wrap of brick veneer, with air gap. We're in seismic SDC=D here. First thought would be to provide veneer anchors to the sides of the HSS column. However, it would be a...
  6. WAstruc10

    Unusual Platform Framing Scheme

    I am working on a mixed-use project that is pretty typical for the pacific northwest...3 or 4 stories of wood-framed apartments platform framed over two stories of post-tensioned concrete flat plates (for parking & retail). However, the owner and contractor think it might save them some money to...
  7. WAstruc10

    "Micropile" minimum diameter

    Small diameter steel pipe piles (2 to 6 inch nominal) are fairly common in our region. I have always heard these referred to as "micropiles". However, just noticed 2012 IBC section 1810.3.5.3.2 limits minimum pipe diamter to 8", followed by an exception "There is no minimum diameter for steel...
  8. WAstruc10

    Wood Post - Holdown Shim Fastening

    I realize Simpson leaves it up to us to design the attachment of the shim stud to the typ stud. In this case the shim stud can't be full height because it's below a window sill. My question is, based on principles of mechanics, why wouldn't simply using longer SDS screws do the job? It seems to...
  9. WAstruc10

    Wood Post - Holdown Shim Fastening

    Let's say we have a shearwall endpost holdown which utilizes SDS screws, but it's installed misaligned by one stud's width, so a short piece of 2x6 shim is needed to fill the gap. Do you think it would be acceptable to simply lengthen the SDS screws by 1.5" and assume that the shim is now acting...
  10. WAstruc10

    Holdown Shim Fastening

    When a shearwall endpost holdown which utilizes SDS screws is misaligned by one stud's width, so a short piece of 2x6 shim is needed, do you think it would be acceptable to simply lengthen the SDS screws by 1.5" and assume that the shim is now acting as an integral part of the endpost? Or do I...
  11. WAstruc10

    Subdiaphragm in light-framed wood building??

    Thanks Dave, we're actually using open-web wood chord floor trusses, so there is no rim or blocking per se. Wall double top plate is up at underside of subfloor ply. With a subdiaphragm ratio of 2.5 max this seems to mean, with 32' floor truss span, that I have to block/strap back every so often...
  12. WAstruc10

    Subdiaphragm in light-framed wood building??

    I certainly understand the ASCE 7-05 Section 12.11 requirements for wall anchorage and subdiaphragms when it's a concrete or masonry wall tied into my floor. But what about light-framed wood wall structures...it seems like there is no exception to 12.11.2.2.3, so when I have exterior studwalls...
  13. WAstruc10

    Diaphragm Cross-Ties

    For retrofit of an existing URM building with wood joist floors, my understanding from ASCE/SEI 31-03 is that the joists must form continuous cross-ties from one wall anchorage to the opposite side wall anchorage (in the absence of subdiaphragms). Pretty straight forward. But what about the...
  14. WAstruc10

    Spiral Reinforcing in Seismic Pile

    Not sure I follow that logic. My core diameter can only be 12" (16"-2"-2"), which gives Ac=113.1 in^2. So equation 10-5 gives rho_s = 0.45((256/113.1)-1)(6/60) = 0.057. And then I'm using pitch = (4*Asp)/(rho_s*Dc) = (4*0.31)/(0.057*12) = 1.81". Can you clarify where this might be going wrong...
  15. WAstruc10

    Spiral Reinforcing in Seismic Pile

    I have a fixed pier in a high seismic zone, for which the geotech has specified 16" square prestressed piles. For the spiral reinforcing, I need 2" cover (marine environment) so I am left with a core diameter (Dc) of 12". Works fine with equation 21-2 (ps=0.12f'c/fyt), which calculates to #3...
  16. WAstruc10

    Slag in the mix design

    I agree with most of the above - I've used 40-45% replacement on many jobs with good success, only been scared at some very low 7-day breaks but it seems to go off the charts after that. Hard to sell it on multi-story flatwork but for everything else the delayed set and slow strength gain seems...
  17. WAstruc10

    Tilt-up hooked dowels

    For tilt-up wall panels (especially 5.5" ones), how would you typically provide hooked dowels to the slab pour strip (or to a concrete mezzanine floor if needs be), since the hook development length is too long? It seems like a commonly overlooked error - even the TCA engineering manual shows...
  18. WAstruc10

    Cantilever Beam Bracing

    Good idea for stiffening up the flange, but it's already built and the owner has come to the manufacturer of this conveyor support after-the-fact looking for a sealed engineering analysis. The MC18's work fine even at an unbraced length of 20', so I'm getting fairly comfortable with the ability...
  19. WAstruc10

    Cantilever Beam Bracing

    Braced to each other...so you are saying both compression flanges may buckle in the same direction, correct? I think that buckling translation will induce bending in the transverse brace, as the rectangular shape of the brace is forced into a parallelogram. So it seems to me that if the web of...
  20. WAstruc10

    Cantilever Beam Bracing

    I've got a situation that doesn't seem to fit traditional AISC theory too well...essentially a horizontal "ladder" shape made out of MC18 channels as the primary stringers (ie. the legs of the ladder) spaced about 36" apart, with C6 channel cross members (ie. "rungs" of the ladder) welded to...

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