What bolt types are typically used for high-strength connections in structural steel framing, and how do they differ?

• A. ASTM A325 and A490 high-strength bolts; A490 bolts have higher strength and are used in more demanding connections; both require proper washers and nuts and pretensioning for slip-critical joints.
• B. ASTM A307 and A325; A307 has higher strength.
• C. A325 bolts and A490 bolts have equal strength.
• D. These bolts are not used in slip-critical joints.

Answer: (A)

High-strength bolting in structural steel relies on bolts that can develop a strong clamping force to keep joint surfaces pressed together, so slip between members is resisted by friction rather than bearing. The bolts commonly used for this purpose are ASTM A325 and ASTM A490. A490 bolts have higher strength than A325 bolts, so they’re chosen for more demanding connections where greater load capacity or stricter performance is required. Both types are suitable for slip-critical joints, where the connection must be pretensioned to a specified bolt tension to achieve the necessary friction. Proper washers and nuts are used, and the bolts are tightened to a target pretension (often with calibrated tools) to ensure the joint will not slip under load. A307 is a lower-strength bolt and is not used for these high-strength, slip-critical applications, and the two high-strength bolts do not have equal strength.