Tower Anchor Bolts with Leveling Nuts below the Base Plate
Tower Anchor Bolts with Leveling Nuts below the Base Plate
(OP)
thread507-42018: Tower Base Plate Anchor Bolts û should they have adjusting nuts? has reference.
The practice of having a (tower) base plate resting on levelling nuts, and more than often, also without filling up below with grout, keeps bugging me... As pointed out in the referenced thread, one could take measures, and even do maintenance, to protect the threaded portions of the bolts against corrosion. However, my concern is the absence of tensile preload guarding against wind induced fatigue failure of the bolt at a location just below the levelling nut... Yet, everybody seems to be applying the levelling nut practice all around... Are we going to see a lot of failures say 2-3 decades from now? Or, do you think this is good practice?
The practice of having a (tower) base plate resting on levelling nuts, and more than often, also without filling up below with grout, keeps bugging me... As pointed out in the referenced thread, one could take measures, and even do maintenance, to protect the threaded portions of the bolts against corrosion. However, my concern is the absence of tensile preload guarding against wind induced fatigue failure of the bolt at a location just below the levelling nut... Yet, everybody seems to be applying the levelling nut practice all around... Are we going to see a lot of failures say 2-3 decades from now? Or, do you think this is good practice?






RE: Tower Anchor Bolts with Leveling Nuts below the Base Plate
The US Federal Highway Administration (FHWA) considers NOT grouting to be good practice:
See pages 31 and 32 of this link for the complete explanation:
FHWA Guidelines for the Installation, Inspection, Maintenance and Repair of Structural Supports for Highway Signs, Luminaires, and Traffic Signals
www.SlideRuleEra.net
www.VacuumTubeEra.net
RE: Tower Anchor Bolts with Leveling Nuts below the Base Plate
Other considerations: lower bend stiffness at base accompanied by lower bend frequency, and also, neutral axis against bending through centre compared to pivot point closer towards edge (will affect total available bolt area to work in tension).
RE: Tower Anchor Bolts with Leveling Nuts below the Base Plate
the guide that I have only reduces the capacity of the bolt due to the bending of the bolt.
RE: Tower Anchor Bolts with Leveling Nuts below the Base Plate
RE: Tower Anchor Bolts with Leveling Nuts below the Base Plate
When the beam is leveled, the bolts are loaded in compression. Wind or other loads applied to the column will load some (or all) of the bolts in tension, but when the grout has set it isn't going to do much for you with regard to preventing load reversal on the bolts.
This particular application seems to me to be one of those instances where you have to take the load reversal into account during the design phase, because there is little or nothing you can do to prevent reversed loads in service.
Disclaimer: I'm not in a field that deals with "Highway Signs, Luminaires, and Traffic Signals" but I've designed and installed hundreds of machine bases with leveling bolts, supporting machines weighing a few hundred pounds on up to hundreds of tons.
RE: Tower Anchor Bolts with Leveling Nuts below the Base Plate
I'm not involved with any particular application/project here - is just kind of getting that uneasy feeling when observing this practice all around. I guess if one is to go for the convenient levelling nuts design, then maybe one should use a lower than usual allowed design stress (don't know what the relevant codes are saying about this) and pay special attention to long term corrosion protection. Especially in windy and corrosive coastal regions.
RE: Tower Anchor Bolts with Leveling Nuts below the Base Plate
RE: Tower Anchor Bolts with Leveling Nuts below the Base Plate
Also, SDG&E used to order pre-threaded rebar (Grade 40, or what we used to call 20 ksi design stress rebar) in large quantities from local fabricators for use as owner-furnished anchor bolts on their projects. They did this after contractors repeatedly whined about their threaded rebar anchor bolts being impossible to get. The anchors were generally oversized for most projects.
RE: Tower Anchor Bolts with Leveling Nuts below the Base Plate
As said, it just appears to be questionable or less robust practice - granted, personally I do not know what the codes/standards cover and say...
RE: Tower Anchor Bolts with Leveling Nuts below the Base Plate
The issue I would see with grout packing as that in an exposed condition, assuming the fasteners are appropriately spec'd and sealed, there is very little to trap water and accelerate corrosion. If the assembly is grout packed, and the grout ever chips or cracks, you now have one or more locations for water to collect. Obviously that can be catastrophically bad.
RE: Tower Anchor Bolts with Leveling Nuts below the Base Plate
RE: Tower Anchor Bolts with Leveling Nuts below the Base Plate