Need a book? Engineering books recommendations...

Return to index: [Subject] [Thread] [Date] [Author]

Re: Foundation A.B. Capacity

[Subject Prev][Subject Next][Thread Prev][Thread Next]
At 06:25 PM 7/20/99 -0600, Jake Watson, E.I.T. of Salt Lake City UT, wrote,
with respect to making sense of the UBC using the provisions of ch19, div
III to design a 1.25 in. diam anchor "bolt" in a 8 in. foundation stem for a
big-a_ _ Simpson hold-down , the following invitation:   "Suggestions?"

Sure, here's some suggestions. First, I can tell that you have been in
school a lot more recently than I have, and that you are both observant and
uninhibited in reporting on what you see. Splendid. We need much more of this. 

If you are up to date but still "very confused" then I am unlikely to be
better off in explaining the procedure you have chosen. Perhaps ACI 318 (or
PCI or whatever the source's) Commentary has something for you. No Code or
portion thereof should ever be considered for adoption until an accompanying
commentary is furnished and approved, and both thoroughly beta-tested.
Necessity, clarity, and consistency with other provisions (and with
principles of mechanics) should have to be confirmed against challenge by
any affected person, just like for other government regulations in many
states, or adoption is automatically rejected by a review agency empowered
to do so. 

Now back to the problem. There is a principle that says, "If what you're
doing isn't working, don't do it harder. Stop doing it and do something

In this case something to stop doing is trying to make sense of the method
you chose, and try a different method. And use the principle called
"Reframing." You called the anchorage device an "anchor bolt."  Stop doing
that; call it something else and thereby get a different perspective on it,
like you did when you imagined it was a vertical rebar.

An approach I can suggest from "reframing" is to develop the upward pull
from the hold-down with a big, thick bearing plate down low in what is in
effect a concrete beam, a grade beam. ACI has been pretty simple about
figuring bearing pressures onto concrete. Then design stirrup rebar as
needed to take the shear going each way from the upward concentrated load
location. Design flexural rebar for the moment. Connect the bearing plate up
to the hold-down with a steel rod that conveniently has threaded ends for
nuts. But your focus is on anything but an "embedded anchor bolt", so you
don't have to go near the code provisions on embedment and tension
resistance for those things, which provisions likely depend solely on
tension in concrete without benefit of reinforcing to resist the failure
cone's breakout. 

So much for that suggestion, which avoids the Code method that bugs you, and
merely advances the design you're doing.

Now your second, follow-up message is in. Assuming you have followed the
code the way it wants you to, it appears you have found an anomaly or stupid
outcome in it. However if in spite of being careful you haven't followed it
the way it wants of you, it may well be badly written and fails to
communicate. Either way, the inadequacy is likely with the rule writers, not
you. You're the customer; they're supposed to cater to you.

In the 1954 film musical "Hans Christian Andersen," Danny Kaye sings about
the vainglorious King's new clothes, which are sold to him as magnificent,
but in fact do not exist. Everyone tactfully pretends the king is regally
outfitted although he is actually going about quite naked. Everyone pretends
except for one small boy who didn't get the word, doesn't understand
hypocrisy, and points out the problem to everybody.  Looks like that's what
you've done here. Wish I could write new lyrics to the catchy old tune: "The
Code is in the altogether, the altogether, naked as the day its draft
was born." 

Keep up the comments and questions. But you are going to be forever
frustrated if you expect any tidy consistency or simple clarity in
structural parts of the Building Code. The Structural community is so good
it doesn't need those attributes, and can stand behind a book of rules as
transparent and illusory as the King's robe, conceived to cover everything
so elegantly, but an observant newcomer can see right through it.  

Charles O. Greenlaw  SE      Sacramento CA
(source of principles cited: books on Neuro Linguistic Programming)