Atypical Bolting Application Qestions

[jdonville]

Note:
**I have already posted this in the Mechanical Engineering Other Topics and Structural Engineering Other Topics fora inadvertently. I will direct replies from those fora to this thread.**

I am working on connecting a planar frame to the counterweight of a heavy crane. The current scheme has a single line of high-strength bolts connecting through both of the cantilevered frame members up into a tapped plate (call them the "Bolt Plate"s) that will in turn be welded to the bottom of the counterweight.

The crane manufacturer suggested 1-inch diameter Grade 8 bolts. From what I can determine, this closely corresponds to ASTM A354 Gr BD, which I understand is equivalent to the material requirements for ASTM A490 bolts.

Owing to the required moment capacity at the point of attachment, the frame member is rather deep (9 inches). So, to clarify, the bolt will pass through the 9-inch deep member and connect to the Bolt Plate. Based on the plate and bolt materials, the required length of engagement is about 2 inches. Throw in an allowance for washers and I'm looking at a bolt length on the order of 12 inches overall, with a thread length of at least 2 inches.

I have chosen a bolted connection over welding to permit easy removal of the frame should it ever need to be done for using the crane in a different situation.

I anticipate that the bolts will be loaded primarily in tension, and will be subject to cyclic "impact" loads as the load on the frame bounces while the crane travels, rotates or hoists loads.

Shear loads should be infrequent and of much lower magnitude and duration than the tension loads.

**Questions**

How should I analyze the capacity of the bolts?
Is pretensioning required?
How will the pretension affect the capacity of the bolt?
Can a bolt this long be pretensioned using the bolt head?
How should I incorporate fatigue into the analysis?

Most of the literature that I have relates to typical structural bolted connections using nuts, and may not be applicable. Any guidance and assistance is appreciated. I have access to the 2005 AISC codes and materials and AASHTO 2002 (HB-17) if you would like to quote code references.

Jeff

 

[jdonville]

After taking some time to digest the responses and advice given, I believe that a design can be found that places any bolts in shear only. The design also eliminates the need for a complicated (to me) welded connection located away from the CW area.

The AISC documents available to me should provide the design information and criteria that I need. I am also considering locating a copy of the new edition of Bickford's bolting book.

Thanks to all for your assistance.

Jeff

 

[desertfox]

Hi jdonville

Sadly all bolts are not loaded in shear only, have a look at this example of a bracket-

http://www.mech.uwa.edu.au/DANotes/threads/fatigue/exampleB.html#top

I suspect your bolts are not only loaded in shear however you need to know exactly how they are loaded to complete any
meaningful analysis and avoid a diaseter.
I wish you the best of luck

regards

desertfox

 

[jdonville]

I have redesigned the connection with bolts in shear and have received verbal approval from the crane manufacturer.

Thanks to all for helping me come to this much better solution.

Jeff

 

[desertfox]

Hi jdonville

Glad you got it worked out.

Regards

desertfox