huangyhg

contractor forgot washers
does anyone know of a code reference (aisc, ubc, ibc, etc..) that requires flat washers under the nuts of anchor bolts in tension.
the contractor forgot to install washers under the nuts that hold down a column base plate. due to the forces on the structure, these bolts are in tension in a seismic event.
the bolts are 1 1/2" a36 threaded rod with nuts on both ends (1 end in concrete, 1 end above base plate). the hole in the plate is 1 5/8" diameter. the nuts are standard hex nuts.
as it stands, the nuts completely cover the hole in the base plate. however, i'm concerned with the hole distorting and possibly ripping the nut through the base plate.
the design force on the bolt is 50,000 lbs in a seismic event.
any thoughts would be appreciated.
thanks
why not weld the tightened nuts to the base plate?
make the contractor fix it.
it depends on what the base plate
material is. how do you know if he
used any in the concrete?
i agree, make him fix it, it should be straight forward enough.
the exercise will help concentrate the mind next time he is bolting down baseplates.
other option would be to do a test and demonstrate that his construction technique meets your requirements. onus is on him, of course.
cheers
greg locock
don't know of anyplace where a washer is mandated code wise. the latest steel code says it is likely necessary due to the beyond oversize holes likely in baseplate. if it shows up in your construction documents as mandatory, that is probably enough. with hole only 1/8" bigger than anchor rod, the nut will always be bearing on plate. going back to steel basics, and analyzing the potential failure mechanisms might let you know if you have a problem. welding a hardened washer could result in weakening of the nut / potential britle failure.
our dot construction specs require heavy hex nuts and washers. this goes for hs bolts as well as anchor rods. we even have the pay item adjusted to account for the washers and nuts.
i recommend you look at the standard specification language in the contract you use to see if it is in there.
who needs a code reference? demonstrate that the surface area of the washer (not enough area is in contact with the bolt) is required to resist the tension forces.
the hole in the base plate is not oversized and the steel is mild. there should be no problem with the anchor rod and nut developing the force.
in most jurisdictions, the eor is responsible to verify any alteration to the anchorage system.
dik
i thought that one of the purposes of a washer is to prevent nut/base galling. such galling would affect nut torquing, possibly resulting in less tension.
with mild steel, galling shouldn't be an issue... hardened washers are often used for slip critical a325 high strength bolts...
dik

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