Misfit Holes on a 40-ft Girder: Drift, Pull, or Ream?
A four-story structural steel frame is being erected in 30°F weather. A 40-ft W24x76 girder frames into a W14x132 column with 3/4-in. A325N bolts in 13/16-in. standard holes, six per connection. The erector snug-tightens the far-end connection first, then finds the near-end holes offset about 5/8 in. horizontally; the beam cannot be drawn into place by hand. The foreman wants to drive a drift pin with a sledge and pull the girder with a 2-ton come-along, then run the bolts down with an impact wrench. The shop drawing shows no slotted holes, and the girder was fabricated 60 days ago at 70°F. The column was plumbed within tolerance yesterday. A bolted connection is not a pull point, and the crew is behind schedule. The inspector is on site but has not been asked.
1. Is temperature a plausible explanation for the 5/8-in. misfit? Show the reasoning.
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Use the thermal expansion relationship ΔL = L × α × ΔT, with α ≈ 6.5 × 10⁻⁶ in./in./°F for steel. A 40-ft girder is 480 in. long. If the steel is 30°F rather than the 70°F fabrication temperature, ΔT = 40°F and ΔL = 480 × 6.5 × 10⁻⁶ × 40 ≈ 0.125 in., or about 1/8 in. Even a 60°F differential gives only about 0.19 in. That is an order of magnitude smaller than the 5/8-in. offset, and the column and girder are at essentially the same temperature, so differential thermal movement is not the cause.
The likely causes are fabrication or fit-up: incorrect hole spacing, beam sweep or camber, column twist, or the far end being pulled into a fit that does not match the near end. Before forcing anything, back off the far-end bolts and check the member with a tape and stringline, verify column plumb and twist, and compare hole locations to the shop drawing. The 5/8-in. misfit should be treated as a nonconformance requiring measurement and documentation, not as a temperature problem to be overcome with force.
2. Evaluate the proposed sledge-drift-pin and come-along method. What should be done instead?
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Drift pins are alignment tools for holes that are essentially coincident; they are not pulling tools. Driving a pin with a sledge into a 5/8-in. offset deforms the hole wall, enlarges or ovalizes the hole, and can induce locked-in stress in the beam and column. A come-along pulling the girder into position loads the connection and can bow the column or twist the beam. Running an impact wrench on misaligned holes damages threads and hole walls and gives a false sense that the bolts are properly tensioned.
The correct sequence is to loosen the far-end bolts to permit movement, re-fit with drift pins used only for alignment, and confirm whether the members will come together without force. If they will not, stop and write a nonconformance report. The engineer of record can then evaluate options: correcting the fabrication, approved reaming within the limits permitted for 3/4-in. bolts, or replacing the connection material. Flame cutting or elongating holes with a torch is never acceptable. The inspector should be brought in before any corrective work so the condition is recorded.
3. If the engineer authorizes reaming, what field controls and records are needed?
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Reaming must follow the engineer's written direction and stay within the hole-size limits permitted for the bolt size. Ream only the affected holes, keep the reamer perpendicular to the connection face, remove burrs, and do not let cumulative enlargement push any hole beyond the approved maximum. If the connection is slip-critical, oversize or reamed holes change the design assumption, so the engineer must confirm the connection type before work starts; if it is bearing-type, the same review still applies to edge distance and net section.
Damaged galvanizing must be repaired with a zinc-rich coating according to the project's repair standard, and bare steel must be protected. After reaming, verify bolt grip length and re-tension the entire connection with the approved method, such as turn-of-nut or a calibrated tension device, not by impact-wrench feel. Record the original offset, hole locations, reamed diameters, approvals, coating repairs, and final inspection results on the nonconformance report and as-built drawings.