Al-Ko Trailer Tongue failure

On Friday, July 8, 2016 at 9:29:13 AM UTC-7, Craig Funston wrote:
On Friday, July 8, 2016 at 9:05:24 AM UTC-7, wrote:
On Friday, July 8, 2016 at 10:26:09 AM UTC-5, Eric Greenwell wrote:
wrote on 7/8/2016 7:36 AM:
Per is right, a properly engineered bolted connection is never meant
to hold shear loads. The longitudinal tension in the bolted
connection should press the pieces together with a force that causes
friction sufficient to withstand the bending moment.

Bolts are routinely used in shear, from toys to airliners. On my glider,
the tail wheel, landing gear, and propeller are fastened with bolts in
shear, along with many other items.

--
Eric Greenwell - Washington State, USA (change ".netto" to ".us" to
email me)
- "A Guide to Self-Launching Sailplane Operation"

https://sites.google.com/site/motorg...ad-the-guide-1
- "Transponders in Sailplanes - Dec 2014a" also ADS-B, PCAS, Flarm

http://soaringsafety.org/prevention/...anes-2014A.pdf

Sorry Eric, you are wrong. Pretension (torque) on the bolt results in parts being pressed together. That force with a coefficient of friction normally being assumed at 0.1 results in the parts staying together without slippage. Shear can only occur if the parts slip, a properly designed connection never does.

Herb,

There are some cases where friction is what is relied on for a bolted shear connection, but these are very special cases and require specific installation procedures. In building structures, these bolts are designated ASTM A325 SC or ASTM A490 SC. The "SC" designating slip critical. In order to perform as slip critical connections there needs to be enough capacity in the bolted sandwich to allow the bolt to yield slightly in tension during tightening. This provides a consistent preload to develop the friction. This type of connection is impossible to achieve when bolting though a hollow tube unless there is a bearing sleeve through the tube to allow development of full tension in the bolt. Without the bearing sleeve the bolt simply crushes the tube and sufficient clamping force is never achieved. Many buildings and other structures are designed and constructed using bolts in shear without relying on friction between the faying surfaces. Slip critical bolting (friction bolting) is a nice solution when cyclic loads and fatigue are a consideration because it eliminates the movement that happens when bearing bolts (bolts in plain shear) are cycled from one load direction to another. Cyclic loading can also be accommodated by interference fit bolts, but the degree of accuracy required in fabrication is too expensive for all but specialty applications.

Best regards,
Craig Funston, P.E. , S.E. , P.Eng.

I was about to start in with the shear versus friction discussion on bolted joints when I saw Craig's discussion. He is absolutely correct. I have been in the crane design industry for many decades and use the friction joint technique when using many bolts in a connection but when one bolt is used, shear is usually the design mode. Lynn Wyman, P.E.