CoreBrace, the leading designer and fabricator of Buckling Restraint Braces, recently tested our ASTM F3148 TNA Fastening System at UCSD. CoreBrace calls for an exacting installation process of it’s BRB’s to ensure their performance. The installation process requires the installer to perform systematic snug passes followed by final tensioning through all rows of bolts. Each brace connection requires an initial snug pass of all bolts in the connection. Step 2 is rechecking the snug condition in rows 1 and 2 and re-tightening as necessary. Then step 3 is to pretension row one and check the snug condition in row 3. This sequential tightening occurs in the same pattern until all bolts are pretensioned.
One of the issues seen in the field during BRB installation is the lack of control of the snug process. With bolts getting 3-4 snug passes there is a possibility of bolts being over tightened in the field prior to final tensioning. In some cases, bolts can break during installation due to the lack of control during the snug operation. Our ASTM F3148 TNA Fastening System is the perfect solution for this type of application.
Our TAe Series installation tools use a calibrated torque setting for snug tight. Each bolt assembly is tested, assembled, certified and sold as a matched set. By providing control of the assemblies and the tool output, the snug process is controlled precisely every time, ensuring the bolts are not under or over snugged and that all plies are in contact prior to final tensioning. Here’s how it works.
The tool is set to Snug Mode. The tool engages the nut and splined end of the bolt from a single side. The operator pulls and holds the trigger until the tool shuts off. The tool is calibrated to a predetermined torque value so that when the bolt is installed in the snug mode the tool will register torque output and stop turning when the value is met. This can be done for each bolt in the connection. The operator can perform subsequent snug passes with the TAe tool. If the bolt is at the required value the tool will not turn the nut. If tension has been lost due to compression the tool will recognize that the torque value has been lowered and will turn the nut until the required torque value has been reach and then stop again. This process can be performed on every bolt in the connection as many times as required to ensure a proper snug condition. This snug tightening process can ensure that all bolts in the connection are installed to the same value and that the plies are in firm contact. Once the uniform snug condition has been reached, the operator can switch the tool to Angle Mode and set the tool to the specified degree of angle using the Angle Dial. Once the tool is set the operator can systematically install each bolt assembly by placing the tool on the nut and spline end of the bolt. The operator pulls and holds the trigger until the tool stops turning. The tool will turn to the exact degree of angle set on the dial.
By controlling each installation step with the same tool using torque and angle and producing bolts as certified matched sets the ASTM F3148 can provide consistent reliable bolt installation every time. You can read more about the testing by visiting the CoreBrace LinkedIn page.