NASCLA Accredited Commercial General ContractorMetalsHard
A structural engineer specifies that all bolted connections in a moment frame must be 'slip-critical' to prevent any relative movement between connected members under service loads. Which of the following is a critical requirement for achieving a slip-critical connection?
- AUsing ASTM A307 bolts for their ductility.
- BApplying paint to the faying surfaces for corrosion protection.
- CEnsuring the bolts are tightened to a specified minimum pretension.
- DLeaving a small gap between the connected plates to allow for thermal expansion.
Show answer & explanationAnswer & explanation
Correct answer: C. Ensuring the bolts are tightened to a specified minimum pretension.
Slip-critical connections rely on friction between the faying surfaces, which is generated by a high clamping force from pretensioned bolts. Therefore, tightening bolts to a specified minimum pretension is absolutely critical. Paint on faying surfaces would reduce friction, A307 bolts are not high-strength, and gaps would defeat the purpose.
Why the other options are wrong
- A. ASTM A307 bolts are standard-strength and not suitable for the high pretension required in slip-critical connections; high-strength bolts like A325 or A490 are required.
- B. Applying paint to faying surfaces (contact surfaces) would reduce the coefficient of friction, which is detrimental to a slip-critical connection's performance. Surfaces must be clean and free of contaminants.
- D. Leaving a gap between connected plates would prevent the development of clamping force and friction, making a slip-critical connection impossible.
Slip-Critical Connection
A bolted structural steel connection designed to resist relative movement (slip) between connected members under service loads by relying on the friction developed from highly pretensioned bolts.
- Requires high-strength bolts (A325, A490).
- Bolts must be tightened to a specified minimum pretension.
- Faying surfaces must be clean, unpainted, and have a specified coefficient of friction.
- Primary load transfer is through friction, not bearing.
Memory trick: Friction's Key: Pretension, Clean Surfaces, Strong Bolts.