A high-strength bolted connection is a type of connection where the shear force is transferred between connected elements through the bearing of high-strength bolts. The design of a high-strength bolted connection ensures that the connection can safely transfer the applied loads without failure. Here is a step-by-step procedure for designing a high-strength bolted 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 Bolt Type and Size Select the appropriate bolt type and size based on the connection requirements, including the applied loads, desired level of performance, and design code provisions. High-strength bolts are typically specified by their nominal diameter, strength grade, and thread type.
Step 4: Determine the Bolt Shear Strength Calculate the shear strength of the selected bolts based on their nominal diameter and strength grade. The formula to calculate the bolt shear strength is:
Vsb = Asb x Fub / γmb
Where: Vsb is the bolt shear strength Asb is the tensile stress area of the bolt Fub is the ultimate tensile strength of the bolt material γmb is the safety factor for bolt shear strength
Step 5: Check Bolt Shear Strength Check that the calculated bolt shear strength is greater than or equal to the applied shear force. If the calculated shear strength is lower than the applied shear force, select a larger bolt size or higher strength grade.
Step 6: Determine the Bolt Bearing Strength Calculate the bearing strength of the connected elements based on the bolt diameter, material properties, and design code provisions. The formula to calculate the bolt bearing strength is:
Vpb = Ab x Fyb / γmb
Where: Vpb is the bolt bearing strength Ab is the effective bearing area of the connected elements Fyb is the yield strength of the connected element material γmb is the safety factor for bolt bearing strength
Step 7: Check Bolt Bearing Strength Check that the calculated bolt bearing strength is greater than or equal to the applied bearing force. If the calculated bearing strength is lower than the applied bearing force, increase the bolt diameter or modify the connection details to increase the bearing area.
Step 8: Verify Connection Strength and Safety Perform a comprehensive design verification to ensure that the high-strength bolted connection meets the desired strength and safety requirements. This may involve additional checks for bolt tension, bolt spacing, edge distances, and other connection details as per the design code provisions.
Example: Consider a high-strength bolted connection joining two steel plates subjected to a shear force of 150 kN. The connection will use M20 bolts with a strength grade of 8.8. The ultimate tensile strength of the bolt material is 800 MPa, and the yield strength of the connected element material is 250 MPa. The safety factor for bolt shear strength and bolt bearing strength is 1.25.
Step 1: Identify the Connection Requirements The connection requires a high-strength bolted joint to transfer a shear force of 150 kN.
Step 2: Determine the Applied Loads The applied load is a shear force of 150 kN.
Step 3: Select Bolt Type and Size Select M20 bolts with a strength grade of 8.8.
Step 4: Determine the Bolt Shear Strength Calculate the bolt shear strength using the formula: Vsb = Asb x Fub / γmb
For M20 bolts (nominal diameter of 20 mm) with a strength grade of 8.8, the tensile stress area (Asb) is approximately 245 mm². The ultimate tensile strength (Fub) is 800 MPa, and the safety factor (γmb) is 1.25.
Vsb = 245 mm² x 800 MPa / 1.25 = 157,600 N = 157.6 kN
Step 5: Check Bolt Shear Strength The calculated bolt shear strength (157.6 kN) is higher than the applied shear force (150 kN), so the bolt shear strength is satisfactory.
Step 6: Determine the Bolt Bearing Strength Calculate the bolt bearing strength using the formula: Vpb = Ab x Fyb / γmb
The effective bearing area (Ab) depends on the connection details and can be obtained from design code provisions. Let’s assume it is 300 mm². The yield strength of the connected element material (Fyb) is 250 MPa, and the safety factor (γmb) is 1.25.
Vpb = 300 mm² x 250 MPa / 1.25 = 60,000 N = 60 kN
Step 7: Check Bolt Bearing Strength The calculated bolt bearing strength (60 kN) is higher than the applied bearing force (150 kN), indicating that the bearing strength is insufficient. In this case, the bolt diameter or connection details need to be revised to increase the bearing area.
Step 8: Verify Connection Strength and Safety Perform a comprehensive design verification, considering other factors such as bolt tension, bolt spacing, edge distances, and other connection details as per the design code provisions. This step ensures that the high-strength bolted connection meets all the desired strength and safety requirements.
It’s important to note that the example provided is simplified, and actual design calculations for a high-strength bolted connection can be more complex, considering various factors such as load combinations, bolt preload, surface conditions, and design code provisions. It is essential to consult the relevant design code or consult with a qualified structural engineer to ensure accurate and compliant connection design.
