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The Correct Time

Homework:

Verify the Table 7 value (LRPF page [7-63]) for a bolted connection consisting of 3 bolts horizontal, and 2 bolts deep. The bolts are spaced 6″ horizontally, and 3″ vertically. The load is directed downwards at an angle of 30 degrees clockwise from vertical, as shown on all Table 7 figures, and is 9 inches to the right, and level with the elastic centroid of the bolts. Use 1″ diameter A325 bolts with the threads in the shear plane, with slip permitted (LRFD page [7-22]).

Use the Excel spreadsheet Design Aids to solve this problem. Look for the tab labeled Plastic Bolts X&Y Loads.

Note that you may have to load Excel’s Solver, if it is not already installed on your computer.  Click on Excel’s Help and search for Solver installation.

Note Segui’s comment on page 307:

If the bending moment and axial force are from a second-order analysis, you can go straight to the interaction equations from AISC Specification Chapter H [16.1-73]

To get the plate thickness, you would actually have to know if the load pointing down on the top flange was caused by another beam running across the top of our beam, or if it was due to a vertical column sitting on the top of the flange.

We will assume that it is a beam going across our beam.  Design the plate thickness just like you would if our beam were pressed up into a plate embedded in a concrete ceiling. I.e. get a reasonable plate size, at least one dimension of which extends across the width of the top flange of our beam and no shorter than the flange width of the crossing beam (you could assume the plate is square), unless you need a longer value for N from web shear/crippling/etc.

Then divide the load coming into our beam by the plate area to get the pressure between the top flange of out beam and the plate, and design the plate thickness using equation 5.13 on page 256.

These are notes from last year.  This problem may have been fixed to be reasonable, i.e. able to be solved using the beam graphs.

 This is one of the new problems, and we didn’t notice that the charts don’t go to 40 feet.

Segui gets a first guess by looking on page [3-119] to see what beams are stronger than needed, and sees a W24x146 and tries it first.  Sadly, it doesn’t work, so he skips several and finally gets up to a W24x146 and it works.

I don’t mind that, but guessing at an initial beam and checking it using the long equations, then finding it wrong, and having to do it another 6 times is nonsense.  OK, if they’re paying me by the hour, but not that much.

The answer was a W24x146.  Start there, and just check it out using the equations.

L^3

Incidentally, when the charts for anything gives an answer outside the graphs, they are trying to get you to refer to note (c)

Notes:

(c) Hey, jackass.  Ever think of buying a brace?  It will cost you about 10% of what it will cost to find a beam that will span 300 feet without being braced every now and then.  It’s not like it’s at a column that restricts visibility, you know.  The bracing goes above the ceiling tiles.  Goodness.

On 4.7-13, you can’t get started designing the column about the strong axis, since you don’t know the Ixx for the columns.  Thus we start designing assuming that the weak axis will control.

About the weak axis, K = 1.0 since the column is supported by girders which provide no rotational resistance.

Note above that you have tremendous moment resistance from the beams coming in from each side.  However, you have no moment resistance when connecting to the beams coming in from the front and back (in the center of the drawing).  Thus the column will freely rotate, without resistance, about its weak yy axis, and thus has a Kyy = 1.0

Knowing that we can get started by assuming that the weak axis controls.  KL = known, Fy = known, Load = known, use Table 4-1 to select the lightest column that works about the weak axis.

Now having a W shape to start, we have all information required to see if it will work about the strong xx axis.  If you are lucky, it will work.  If not, you should be able to select a larger column of reasonable size.

Rinse and repeat.

An HSS 6.625 x 0.250 is on page [1-98].

It’s a tube and you’re probably rummaging around in the rectangular shapes.  You’ll get more familiar with these things as you spend more time looking around at what’s in the Manual.

L^3