More often, anchor bolts break from too little tightening than too much.
We fix broken and loosened anchor bolts, couple them with new sections or, if necessary, replace them with new proper ones.
We check the material strength of the bolts and the specified torque to ensure that the fastening load of approximately 50% of the yield strength is utilised. Under-tightened anchor bolts are a major source of broken bolts, and machinery problems.
Anchor bolts need sufficient stretch length to be tightened properly. When there is a termination in the bolt embedded in the foundation, it creates zones in which the concrete works in tension, not compression. If in addition there are sharp edges, you have stress risers with concrete in tension. This will make cracks appear soon and propagate horizontally throughout the entire foundation. Oil presence will worsen this situation.
Other unsuited anchor bolts types used when installing machinery are the hook type, the l type and the fish-tail type.
New installations and repairs should use:
• High strength bolts satisfying ASTM spec A-193, with 105,000 psi tensile yield.
• Nuts should satisfy ASTM spec A-194.
• Super Nuts ™.
• Hardened steel spherical washers should be used to compensate for any lack of perpendicularity between the bolt and frame.
• Bolt threads should be rolled, not cut.
We advocate for straight, full threaded rods, with no more than half of its length isolated with PE foam and grouted with our epoxy grout. This is the best way to disperse evenly the stresses from the anchor bolt to the foundation, without stress risers. The adhesion concrete-grout and grout-steel is stronger than the cohesion of the substrates.
Watch how our anchor bolt replacement method works on this video on Alphatec' YouTube Channel.
The job was part of the foundation repair of a Mitsubishi–MAN diesel engine, type 18V52/55B, that drives a brushless alternator of 13 MW capacity.
Epoxy grout specialists and concrete repair, Alphatec Engineering.