Mercy Health – Rockford, Illinois
The fabricator had a unique application that required some connections to be left in the snug tight condition for an extended period of time, up to 6 months, prior to pretensioning. The project called for tension control bolts to be used in all connections. However, the concern about leaving tc bolts in a connection for an extended period of time without full tension has been an ongoing concern within the industry. Because tc bolts rely solely on nut lubrication to achieve final tension, extended weathering can render the water based nut lubricant less effective. The degrading of the nut lubricant can cause the tc bolts to not reach minimum tension.
As a solution, the fabricator and erector agreed to use ASTM F3148 TNA bolts. TNA bolts rely on nut lubricant during the snug tightening process only. Once the bolts are in the snug condition the erector can come back at any time and perform the final tensioning process using angle. The Torque and Angle Fastening System is the only system that allows for this installation scenario using a single tool from a single side. As long as the tool has the required torque to turn the nut the specified angle, the bolts will always achieve the minimum required tension. No other system on the market can offer this level of accuracy over time.
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