Bolted Connections: Bolts, Washers, Installation and Tensioning
Structural Steel Materials: Grades, Certificates, and Traceability
Candidates must recognize the common ASTM designations and what each buys you. A36 is the baseline carbon steel (Fy = 36 ksi). A992 is the workhorse for rolled W shapes: Fy = 50 ksi (50–65 ksi range), Fu = 65 ksi minimum, with restricted chemistry for weldability. A572 Gr. 50 is a higher-strength plate and shape specification; A500 and A1085 cover hollow structural sections; A588 is weathering steel; A307 covers low-strength bolts, while high-strength bolts now fall under ASTM F3125 (Grades A325 and A490, plus F1852 twist-off tension-control bolts).
Material arrives with mill test reports (MTRs) carrying heat numbers, chemistry, and mechanical results, and with markings rolled or painted on the piece per ASTM A6. Traceability is the point: heat number on the MTR must match the heat number on the member, and the grade must match the drawings. Fabricator or erector substitution of a grade, thickness, or section - even an "equivalent" one - requires EOR approval before use.
Traps to expect
- Confusing A36 (36 ksi) with A992 (50 ksi) when checking a connection's bolt or weld demand.
- Treating an MTR for one heat as covering an entire shipment.
- Assuming a shape with the right nominal size has the specified grade.
- Forgetting that toughness (Charpy V-notch) requirements can attach to specific members in the general notes.
Worked example: a bundle of W14x68 arrives stamped A572 Gr. 50 but the drawings call for A992. Chemistry and strength may be similar, but the substitution is not the inspector's call - record the discrepancy and route it to the EOR. Rule of thumb: no grade, no heat number, no use.
Bolted Connections: Bolts, Washers, Installation, and Tensioning
Bolted-connection questions test the RCSC Specification. Know the three joint types: snug-tight (the plies are in firm contact from a few impact-wrench blows or full effort on a spud wrench - no specified tension), pretensioned (a specified minimum tension is installed), and slip-critical (pretensioned plus special faying-surface and hole requirements, with the joint designed to resist slip).
Installation methods for pretensioned joints
- Turn-of-nut: from snug-tight, rotate the nut a prescribed fraction of a turn related to bolt length (roughly 1/3 turn for short bolts, 1/2 for medium, 2/3 for long), with the rotation table governing.
- Calibrated wrench: torque determined by a tension calibrator (Skidmore-Wilhelm) using three representative bolts, verified at least once per shift and after changes.
- Direct tension indicators (DTI): feeler-gauge refusal in the gaps confirms tension.
- Twist-off tension-control bolts (F1852): splined end shears at the specified tension.
Other essentials
Hole size for a standard hole is bolt diameter plus 1/16 in.; oversize and slotted holes have larger allowances and demand hardened washers. Minimum edge distances and spacing come from AISC 360 tables. Pretension is typically about 70 percent of the bolt's minimum tensile strength.
Traps: assuming every bolt in a building is pretensioned; confusing snug-tight with a torque value; forgetting that washer requirements change with hole type; accepting a turn-of-nut joint where the inspector never saw the snug-tight condition.
Worked example: a 3/4 in. A490 bolt requires roughly 35 kips pretension - verify the method, the calibration record, and the match marks before accepting the connection.