The Calibrated Wrench Connection method is used to achieve the desired tension in bolts by using a calibrated wrench to apply a specific torque. The design criteria for a Calibrated Wrench Connection include determining the required torque, selecting the appropriate wrench, verifying the connection strength and safety, and interpreting the torque readings. Here is a step-by-step procedure for designing a Calibrated Wrench Connection:
Step 1: Identify the Connection Requirements Determine the specific requirements of the connection, including the type and size of the connected elements, the applied loads, and the desired level of performance and safety.
Step 2: Determine the Applied Loads Identify the loads that will be applied to the connection, such as shear forces, tension forces, and, if applicable, compression forces. Determine the magnitude, direction, and distribution of these loads.
Step 3: Select the Bolt Size and Material Select the appropriate bolt size and material based on the design requirements and specifications. Consider factors such as load capacity, corrosion resistance, and compatibility with the connected elements.
Step 4: Determine the Required Torque Calculate the required torque based on the applied loads and the desired safety factor. The torque provides the clamping force necessary to resist the applied loads. The formula to calculate the required torque is:
T = K x D x F
Where: T is the required torque K is the torque coefficient (depends on the type of connection and bolt size) D is the nominal diameter of the bolt F is the applied tension force
The torque coefficient K can be obtained from manufacturer data, design codes, or engineering references.
Step 5: Select the Calibrated Wrench Choose a calibrated torque wrench suitable for the desired torque range and the bolt size. The wrench should be properly calibrated and provide accurate torque readings.
Step 6: Verify Connection Strength and Safety Perform a comprehensive design verification to ensure that the Calibrated Wrench Connection meets the desired strength and safety requirements. This may involve additional checks for bolt shear strength, bearing strength, bolt spacing, edge distances, and other connection details as per the design code provisions.
Step 7: Apply the Torque Using the selected calibrated wrench, apply the specified torque to the bolts. The torque wrench should be set to the required torque value.
Step 8: Interpret Torque Readings Monitor the torque readings on the calibrated wrench as the torque is applied. Ensure that the desired torque (T) has been achieved.
Example: Consider a Calibrated Wrench Connection joining two steel members subjected to a tension force of 100 kN. The bolt diameter is 20 mm, and the desired safety factor is 1.5.
Step 1: Identify the Connection Requirements The connection requires a Calibrated Wrench Connection to transfer a tension force of 100 kN with a safety factor of 1.5.
Step 2: Determine the Applied Loads The applied load is a tension force of 100 kN.
Step 3: Select the Bolt Size and Material Assume a suitable bolt size and material based on the design requirements.
Step 4: Determine the Required Torque Calculate the required torque using the formula: T = K x D x F
Assume K = 0.2 (torque coefficient for the given connection type and bolt size) D = 20 mm (nominal diameter of the bolt) F = 100 kN (applied tension force)
T = 0.2 x 20 mm x 100 kN = 400 N·m
Step 5: Select the Calibrated Wrench Choose a calibrated torque wrench suitable for the desired torque range (400 N·m) and the bolt size.
Step 6: Verify Connection Strength and Safety Perform a comprehensive design verification considering the bolt shear strength, bearing strength, and other connection details.
Step 7: Apply the Torque Using the selected calibrated wrench, apply the specified torque of 400 N·m to the bolts.
Step 8: Interpret Torque Readings Monitor the torque readings on the calibrated wrench to ensure that the desired torque (400 N·m) has been achieved.
It is important to note that the specific design requirements, torque coefficients, and safety factors may vary based on the design codes, industry practices, and project specifications. Therefore, it is crucial to refer to the applicable design codes and consult with a qualified engineer for accurate and compliant design of Calibrated Wrench Connections.
