A394 & A325 1

[leo5cn]

Can anyone tell what the major difference is between A394 and A325. They have the same tensile and shear strength, can we use A325 for tower bolts?

 

[transmissiontowers]

The A394-T0 is a regular strength bolt (IIRC it is comparable to A-307) while the A394-T1 is a high strength (and more expensive) bolt that is the same strength (shear anyway) as a A325 bolt. The physical difference is the bolt head dimensions. The A394-T1 (and T0) has the smaller head while A325 has the larger bolt head. The A394 also has limited thread length because the bolts are used in shear and you don't want the threads in the shear plane.

If you have larger angles you can use the A325, but if you have 2x2x3/16 or smaller, the A325 bolt head is large enough to be too close to the fillet of the inside of the angle. Take a look at the bolt dimensions to see what I am talking about.

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I have been called "A storehouse of worthless information" many times.

 

[leo5cn]

I take off my hat to you, 'Transmissiontowers'. This answer for sure is NOT from 'A storehouse of worthless information'.

Because I am so used to A394 Type 1, I never bothered to compare the geometrical details until recently I had a situation where the A325 was being used when the connection is under TENSION. If A394 & A325 have the same nut, they should have the same tensile property as well. So why under tension, we use A325?

 

[transmissiontowers]

You have only scratched the surface of my worthless information. IIRC, the T1 does have the same tension allowable as A325, but I'm home today and away from my office and can't check my references. The T-Line industry (for lattice towers anyway) has used bolts in mostly shear for many years where the connection does not have to be tight. The bolts just need to be in the hole. The A394 with shorter threads were developed to keep the threads out of the shear plane and the T1 was developed to give higher shear capacity for larger loads. When I first started (over 40 years ago) there were no T1 or T0 designations, just A394 and if you wanted more capacity you went from 5/8 to 3/4 bolts.

I am only guessing, but with the larger bolt head of the A325, the tension capacity may have more safety factor with the larger head. Also the A394 typically does not use washers while I think the A325 uses them to get a better clamping force for the torque input.

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I have been called "A storehouse of worthless information" many times.

 

[leo5cn]

I think the larger bolt head makes sense in that it enhances the local bearing.

It's true tower bolts are predominantly under shear, but we use pretty tight clamping force. We use lock washer (helical spring) to secure the bolt and nut. The torque is 90 for 5/8 and 120 for 3/4

 

[transmissiontowers]

Way back in the 70's we used Stover lock nuts and I had to check the torque required to put them on and back them off. I was getting less than 90 ft-lbs to install and the crews were complaining it was tearing their impact guns up. Now any pneumatic impact wrench should be able to put out 300 ft-lbs but I guess tightening 3000 bolts per day may have taken their toll over the years. We abandoned the Stover's and went with plain nuts and just painted the threads to lock them on.

We used to buy bolts and nuts separate in 2 boxes of about 25 pounds. I joke about our crews that they would make up a connection and pour out the box of bolts onto the holes and the ones that went in the hole would get a nut installed and the rest of the bolts were left on the ground so when it god muddy, they would have something to walk on.

We don't use any lock washers or washers (except on wood H-Frames to combat wood shrinkage) and just paint the threads after assembly. For a while we tried ZEP (zinc electro plated) bolts and nuts but went back to galvanized when the ZEP did not hold up in our hot and wet climate (South Texas gulf coast).

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I have been called "A storehouse of worthless information" many times.

 

[leo5cn]

I never knew that bolt could be installed without a locking device (washer) until I read your post.

What if some lunatics or punk kids steal the bolt for fun? If the clamping force is too low. They would be able to remove the bolt with regular wrench ...

Just some thoughts ...

 

[transmissiontowers]

We don't seem to worry much about people taking bolts out and have not had much problem with it. We do have copper theft problems with idiots going into substations and stealing the copper grounds. We also have problems with unauthorized climbers on towers, where they climb up to see the sights (and drink beer). Several years ago we had a teenage kid climb up to the middle arm and walk out to the end where he was going to pee off the arm. He got within the flash distance and was electrocuted by the top phase. They found several empty beer bottles and some full ones around the tower.


My own PSA: For those unfamiliar with the T-Line industry reading this thread, the wires are not insulated. They will kill you if you even get close (within 10' for 345kV) under ideal conditions. As they transmit power, the conductors get very hot and sag down with thermal expansion. We run them at hot as 250°C under an emergency. This is why you don't see many birds sitting on the conductor because it burns their toes and the E-Field on their feathers makes them not like it either. We count on the wind blowing over the bare wire to transfer heat away. The big blackout in the Northeast a few years ago was due to a T-Line sagging into some trees underneath. This tripped the circuit and the power tried to roll to other lines which quickly overloaded and tripped out. The cascading failures put several states in the dark.

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I have been called "A storehouse of worthless information" many times.

 

[leo5cn]

What's the criteria of your emergency? For example, the peak load of 100 hours in ten years?

 

[transmissiontowers]

I'm a structural guy and only vaguely know that we have an emergency rating for electrical issues. Our really high temp wire is ACSS where the aluminum is fully annealed and the steel core caries all the tension so there is no loss of strength in the aluminum as it runs hot. AAC and ACSR use tempered aluminum that looses strength as it operates hot.

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I have been called "A storehouse of worthless information" many times.

 

[leo5cn]

Do you require impact property for welded steel, anchor bolt and hardware? What's their charpy test value?

 

[transmissiontowers]

Our very large A-Bolts use smooth F-1554 with nuts on the bottom. We do have the Jumbo #18 rebar for deformed bar bolts and it has a charpy requirement but I don't recall what it is right now. AFAIK, we don't have charpy requirements for welded steel, but we don't use much for lattice towers.

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I have been called "A storehouse of worthless information" many times.

 

[leo5cn]

We use #18 quiet often. We only weld angle stub to base plate as the shoe footing.