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  1. doejohn

    Exterior stair tower independent gravity system

    We're looking at replacing an exterior steel stair tower at an industrial facility. The stairs serve as a means of emergency egress for 4 elevated floors of an industrial-use building (not open to public, IBC occupancy Group F). The tower is non-enclosed, non-combustible construction, and...
  2. doejohn

    triangular trusses

    I'm inclined to agree with JAE about LTB--the section is torsionally efficient, so there isn't much tendancy for any localized "compression flange" instability to develop. The truss stability should be controlled by the global bending and torsion buckling limit states. If this is a concern, then...
  3. doejohn

    Excel Matrix

    It's a little late, but FWIW, here's another approach using the LINEST function: 3 known points in cells A1:C3 A B C 1| x1 y1 z1 2| x2 y2 z2 3| x3 y3 z3 define plane that may be expressed by equation z = Py + Qx + R where P = INDEX(LINEST(C1:C3,A1:B3),1) Q =...
  4. doejohn

    Fundamental Natural Frequency

    I got the following from Chopra (1995) *Dynamics of Structures*, pp. 589-592. For a member of length L, constant bending stiffness EI, and uniform distribution of mass per unit length M, the natural frequencies w of "beam" (moment = curvature*EI) response are given by: wi = Ai²*sqrt(EI/M)...
  5. doejohn

    capacity of conc section with correded reinf

    Thanks Dinosaur, JAE, and SlideRuleEra, for your insights! In particular, the reference in SlideRuleEra's first link (a 1994 report sponsored by Fed Highway Admin and Illinois DOT) was helpful.
  6. doejohn

    capacity of conc section with correded reinf

    I may shortly be asked to compute the axial compression and flexural bending moment capacities of a reinforced concrete section with assumed amounts of the reinforcement "lost" through corrosion. That is, I know what the section looks like today, before any corrosion, and I'll be given the...
  7. doejohn

    maximum piston speed?

    Trying again... Here's some equations for piston kinematics I had worked out some time ago. They might even be correct! let c = conn rod length let s = stroke let r = ½s let p = "rod ratio" = c/s let Q = crank angle from TDC let w = dq/dt = engine speed (radians/time, not rev/time) let x =...
  8. doejohn

    maximum piston speed?

    Whoops, Looks like some fancy characters that showed fine in "Preview" of my post above didn't survive actual posting! They all turned into question marks! I hope to repost with corrections later...
  9. doejohn

    maximum piston speed?

    Here's some equations for piston kinematics I had worked out some time ago. They might even be correct! let r = rod ratio = (length conn rod)/(stroke) let ? = crank angle from TDC let ? = d?/dt = engine speed (radians/time, not rev/time) let u = piston position from mid-stroke) let ú = du/dt =...
  10. doejohn

    Asymmetric bending in wood roof purlins

    I think I get it--the axis of the member along its length is horizontal, the member is "tilted" about this axis such that plane of member edge coincides with roof plane, plane of member face is perpendiular. Question: is sheathing supported by purlins also fastened to whatever is supporting the...
  11. doejohn

    Components and Cladding Wind loads

    Following up on tfl's lead--which I think is right--would it be fair to say that: 1. If the wind pressure acts directly on an element/connnection, it must resist CC loads. 2. If the element's resistance to, or distribution of, wind forces is part of the wind force-resisting system, it must...
  12. doejohn

    arched or cambered trailer frames

    More agreement with recent posts (and with original post by Tmoose): it's a deflection thing. Regarding some details raised in earlier posts: Trailer beam resists load like a "beam", not an arch; besides the camber being too small for arch action, there's no mechanism to resist horizontal arch...
  13. doejohn

    IBC SEISMIC: Eqn 16-28

    Per sect 1602 Notations, D = dead load, E = combined effect of horizontal and vertical earthquake-induced forces. First term in equations 16-28 and 16-29 are horizontal component of E, second term is vertical component. E is to be combined with other load effects per load combinations in sect...
  14. doejohn

    Can a 'U' shaped flexible even stan up?

    Well, I think it's an over-extension of the the flexible diaphragm concept to say that they are theoretically incapable of resisting eccentric load. But even if the theory (as I understand it) doesn't really rule out being able to resist eccentric load, as a practical matter, buildings such as...
  15. doejohn

    horizontal distribution of seismic forces

    Well, I'm not a Staad user, but it's approach would make the inertial load distribution proportional to the mass (weight) distribution--sounds like F=ma to me, just like when we consider the lateral load to act at the floor CG. How much of that force ends up being distributed to the vertical...
  16. doejohn

    Designing For Geotechnical Acceleration vs UBC

    I agree with Foch3, you'll have to ask your Geotechnical Engineer. The following is only general info... The UBC, as typical with structural design codes and standards, defines most loads (D=Dead, L=Live, etc.) at "service level" (meaning roughly a maximum value that may be experienced in...

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