A new option for a high strength fastener has been included in AISC 360 and engineers may be interested in the benefits of using this new system.  With the possibility of saving on material and labor costs, the new TnA bolt could be a solution on your next project.

In the March 2026 SEU session, Matt Mester, PE, SE from MiTek, Inc. presented Changes to Steel: ASIC 360 and 341 Code Updates.  Matt reviewed when the building code requires the use of AISC 360/341-16 versus AISC 360/341-22.  He noted significant changes in AISC 360 and 341 and described some of the new structural systems and materials/grades that are allowed in the new AISC 360 and 341.

Matt noted the addition of a new bolt in AISC 360 which meets the ASTM F3148 specification.  The torque and angle bolt, or TnA bolt, grade 144 has been added in the A3 section as well as within Chapter J.  The TnA bolt installation process ensures each bolt is installed to an accurate snug tight condition and then is turned to the required angle to reach a precise final tension.  The new bolt offers more reliability than a typical snug tight installation. The TnA bolt grade is 144 which falls between the popular A325 bolt which is grade 120 and A490 bolts which are grade 150.  The higher strength could require the use of less bolts compared to the standard A325, which could reduce costs.  

As you can see in the slide below, this new bolt has a stub on the end which is similar to a Tension Controlled bolt. However, while the TC bolt stub falls off once the bolt reaches the required pretension force, the stub on the TnA bolt remains in place even after the bolt is torqued to a snug tight condition.  This could be a potential downside on jobs where the design tolerances are quite minimal, and the remaining stub could cause a conflict.  However, it also allows for removal of the bolt using the same wrench which could be an advantage, especially in structures that may be temporary in nature.  The addition of the TnA bolt to the specification gives engineers a new option for a fastener with a mid-grade strength.