From: Bill Polhemus <bpolhem(--nospam--at)swbell.net>
Date: Thu, 01 Feb 2001 10:55:49 -0600
> It seems the structure is leveled via levelling bolts but is never grouted.
> In addition, there are no shear lugs on the bottom of these columns. Some
> of the projections are quite large and the number of bolts quite few. Going
> by the various schools of thought - some rely on friction between base
> plates and grout in friction against vertical load and some rely on shear
> lugs for lateral force transfer. Seems to me that these structures transfer
> via bolt bending. Not sure the designer intended it this way. Some of
> these lateral loads could get quite large.
> Am I making a mountain out of a mole hill? Are contractors lazy? Is this
> what the designer intended?
It IS what the designer intended, but as for making a mountain out of a
molehill, well, "it depends".
First of all, when you say "anchor bolts" you need to be more specific. Is this
a round or polyhedral tower/post section with a round base plate, and multiple
anchor bolts? If so, then it is likely "okay", even if you check it using the
conventional methods of anchorage analysis that we structural guys typically
However, what I have seen in dealing with this as a consultant to a traffic
engineer, is that "they" (and by this I mean our state department of
transportation and the consultants who do work for them) have taken to using the
same sort of design for square and rectangular base plates with four bolts.
Of course the problem is that they won't WORK that way.
After having my designs for such baseplates (including grout) rejected, I have
had many discussions with our DOT folks asking them for a rational basis for the
designs that they say they prefer.
First of all, the highway people rule such organizations. The highway folks say
that they don't want grout, because (or so they say) the condensation inside the
tubular members "can't escape" (they won't tell me how it manages to get in, but
not get out) and because they want to be able to take the poles down for repair
or replacement (they won't tell me how they know that any replacement structure
will not be a problem for the existing foundation or anchor rod anchorage).
In short, "that's the way they've always done it" and that's the way they'll
keep doing it (doing work for a DOT is weird; they firmly believe they know how
to do this stuff better than you do, and they're simply constrained by politics
to allow you to do the work instead. In a sense, they're right: They know how to
do the work they do the same way they've done it for the past half century,
better than anyone else does).
The only way I've been able to resolve this is to refuse to use ANY sort of
structure that requires a square or rectangular base plate.