NASCLA Accredited Commercial General ContractorMetalsHard
A structural engineer is reviewing shop drawings for a steel frame building. The drawings specify the use of ASTM A325 bolts in tension for several critical connections. According to AISC specifications, what is the primary method of installation for A325 bolts in tension-type connections to ensure proper clamping force?
- ASnug-tight method
- BCalibrated wrench method
- CTurn-of-nut method
- DDirect tension indicator (DTI) method
Show answer & explanationAnswer & explanation
Correct answer: D. Direct tension indicator (DTI) method
While turn-of-nut and calibrated wrench methods are common, for tension-type connections, Direct Tension Indicators (DTIs) are often preferred as they directly measure the tension in the bolt, providing a more reliable and verifiable indication of proper clamping force compared to torque-based methods.
Why the other options are wrong
- A. Snug-tight is insufficient for tension-type connections, only providing minimal clamping.
- B. Calibrated wrench relies on consistent friction coefficients, which can vary, making it less reliable for direct tension measurement than DTIs.
- C. Turn-of-nut is a common method but requires careful control of initial snug-tight condition and can be less direct than DTIs for tension measurement.
Direct Tension Indicator (DTI) Method
A bolting installation method that uses a washer-like device with protrusions that flatten as the bolt is tensioned, providing a direct visual or tactile indication that the specified clamping force has been achieved.
- Directly measures bolt tension, not torque.
- Provides a highly reliable and verifiable method for critical connections.
- Commonly used with high-strength bolts (e.g., A325, A490) in structural steel.
Memory trick: Tension Bolts: Directly Indicate Tightness.