Thermally Cut Bolt Holes 4

[jike]

Thermally cut bolt holes shall be permitted if approved by the EOR.

Reference "Specification for Structural joints Using ASTM A325 or A490 Bolts, June 23, 2000 Research Council on Structural Connections Section 3.3"


Is there any concern to be aware of with thermally cut bolt holes?

 

[archeng59]

will the holes be cut in the field? if so, my concern is that the person using the torch often is not interested in making the proper sized hole and that the edge is often jagged. If the hole is sized properly and the edge of the hole is clean and smooth, there should not be a problem.

 

[jike]

This is a request for shop fabrication. I will not allow thermally cut holes in the field.

Further the spec requires all holes for cyclically loaded joints to be ground smooth. This is not required for statically loaded joints. When holes exceed the specified tolerances, they must be treated as the next larger size which I interprept as adding additional or larger bolts.

 

[rholder98]

I've heard another concern is that the thermal cutting alters the material properties of the steel. Any validity in that?

 

[mapelCE]

rholder98

You are correct concerning the material properties change.

I looked through some of my resources and there's a great summary of flame cutting under the introduction section of one of our vendors at

http://www.torchcutter.com

Summary:

Mild Carbon steels- some hardening around the local area but no significant detrimental changes.

Mid to High Carbon Steels - Hardening and potential cracking. Can be moderated with proper procedures.

The fabricators we use for our steel work can flame cut a hole so smooth its hard to tell if they cut it or drilled it.

I agree that hand torching bolt holes is bad Karma.

 

[archeng59]

there is some information about acceptable methods of creating holes at the AISC website (

http://www.aisc.org),

Steel Solutions Center, Technical Resources, Engineering FAQs. section 2 has several items. this from section 5:

5.1.3. Does flame-cutting of bolt holes affect connection strength and performance?


Generally, no. Iwankiw and Schlafly (1982) investigated the performance of double-lap joints with holes made by punching, punching with burrs removed, sub-punching and reaming, drilling, flame-cutting, and flame-cutting and reaming. The comparison of 18 samples using 1/2-in. thick ASTM A36 steel plates with standard holes indicated that there is no significant variation in connection strength according to the method of hole formation under static load. Additional considerations may be warranted for much thicker plates, steel grades other than those tested, and Cyclically Loaded Structures.

Iwankiw, N.R. and T.J. Schlafly, 1982, “Effect of Hole-Making on the Strength of Double Lap Joints,” Engineering Journal, Vol. 19, No. 3, (3rd Qtr.), AISC, Chicago, IL.

last modified 23 August 2002

 

[Qshake]

Please note that when we're mentioning cracks in thermally altered steel, we're not usually talking about something visible to the human eye. I've often had the notion that "I've been doing this for years and never seen any cracking" pointed out to me. So with a little patience I explain the cracks begin as micro-cracks and in some cases propagate to larger problems later on in service. That said I mainly work with cyclic joints rather than static loaded joints.

Regards,
Qshake

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