Steel Erection Guide — Planning, Equipment, Safety, Bolting, Welding, and Alignment

Steel erection is the high-stakes phase where months of engineering and shop fabrication converge on site. A typical steel erection crew of 6–8 ironworkers can set 20–40 pieces per day (40–80 tons) for a multi-story building, with each pick representing thousands of pounds suspended overhead. Getting it right — safely, accurately, and efficiently — requires pre-planning, the right equipment, rigorous temporary bracing, and disciplined field connection practices. This guide covers the complete erection workflow: planning and sequencing, crane selection, temporary stability, field bolting and welding, alignment and plumbing, and OSHA safety requirements per Subpart R.

PRELIMINARY — NOT FOR CONSTRUCTION. Erection methods, equipment, and safety procedures must be developed by a qualified erection engineer for the specific project and site conditions. This guide provides general reference information only.

1. Pre-Erection Planning

The Erection Plan

Every steel erection project begins with a written erection plan that addresses:

1. Piece identification and delivery sequence — the shop drawings assign a unique mark to every piece. The erection plan sequences delivery trucks so pieces arrive in erection order. Pieces needed first (base plates, first-tier columns) are loaded last on the truck. On-site shakeout (sorting pieces by mark) occurs adjacent to the crane, not under the hook.

2. Crane location and pick radii — the crane must be positioned to reach every pick and landing point within its rated capacity at the required radius. Crane mats (timber or steel) distribute outrigger loads (typically 50–100 psi ground pressure) to prevent settlement. Underground utilities within the crane footprint must be located and protected or relocated.

3. Temporary bracing plan — every erection stage must be laterally stable before the crane hook is released. The plan identifies brace locations, sizes, and connection details for columns, beams, and bracing bays. Temporary bracing is removed only after the permanent lateral force-resisting system is fully connected.

4. Fall protection plan — per OSHA 1926.760, ironworkers connecting steel above 15 ft (or 30 ft for connectors actively engaged in connecting) must use fall protection. The plan identifies anchor points, lifeline routes, safety nets, and the location of perimeter safety cables.

5. Bolting and welding sequence — defines which connections are snug-tightened during erection vs. fully tightened after plumbing, and the sequence for field welding to minimize distortion.

Sequencing for Multi-Story Buildings

The standard sequence for a braced or moment frame building:

Column splices are typically 3–4 ft above the finished floor to provide a convenient working height for ironworkers — the "splice point" is just above the floor beam connection, not at it.

2. Crane Selection and Rigging

Mobile Hydraulic Cranes — Low to Mid-Rise (1–10 Stories)

Mobile cranes (truck-mounted or rough-terrain) are the workhorses of structural steel erection. Key selection parameters:

The crane load chart is always derated for:

• Wind > 20 mph: 15% capacity reduction
• Operating near power lines (within 20 ft): 25% reduction or power shutdown
• Personnel lifting: 10% reduction + anti-two-block device + load test

Tower Cranes — High-Rise (10+ Stories)

Tower cranes are fixed to the building (internal climbing) or freestanding (external) and provide consistent capacity at all radii, typically 12–25 tons at up to 230 ft radius. The tower crane foundation (reinforced concrete mat, typically 20 ft × 20 ft × 5 ft thick) must be designed for the overturning moment — the governing load case is typically out-of-service wind, not maximum lifted load.

Jumping (climbing): Internal climbing tower cranes are raised 2–3 stories at a time as the building rises. The climbing section (the 3-story zone around the crane) receives only enough steel to stabilize the crane support collars — full framing of this zone is completed after the crane jumps to the next position.

Rigging Hardware

3. Temporary Stability During Erection

Column Stability Before Connection

A free-standing column after the crane sets it on the base plate is unstable against even small lateral loads (wind, accidental bump). OSHA 1926.755(a)(2) requires:

• A minimum of two temporary guys (wire rope, 3/8-inch minimum diameter) in orthogonal directions, OR
• One diagonal brace member (pipe or angle), OR
• A column base that provides full moment fixity (4-bolt base plate with anchor bolts torqued per specification), verified by the erection engineer

Each temporary guy must be anchored to a deadman, adjacent column, or building floor with capacity for the specified erection wind load (not less than 2% of the piece weight applied horizontally at the column top, or per the project-specific erection engineering).

Frame Stability — The "First Bay" Rule

The first erected bay establishes the building alignment and provides the tie-in point for all subsequent bays. This bay must be:

1. Completed from foundation to first-tier roof (columns + beams + vertical bracing or moment connections)
2. Brought to plumb and held with diagonal bracing in both directions (horizontal plan bracing in the roof plane)
3. Fully bolted (snug-tight minimum) before the crane moves to erect the adjacent bay

Temporary Horizontal Bracing (Diaphragm Action)

Until the permanent floor/roof deck is installed and welded, the steel frame has no diaphragm to transfer lateral loads to the braced bays or moment frames. Temporary horizontal bracing — typically 3/8-inch or 1/2-inch diameter wire rope with turnbuckles in an X-pattern across each bay — provides temporary diaphragm action. These are tension-only bracing elements; two crossing cables are required for reversing wind loads.

OSHA Subpart R Height Limits

OSHA 1926 Subpart R (Steel Erection) Section 1926.754(b)(3) limits the height of unbraced steel frames during erection:

• No more than 8 stories (or 100 ft, whichever is less) of uncompleted bolting/welding above a fully secured tier
• Each tier (a group of floors that has been fully bolted, plumbed, and has the floor deck installed) counts as "secured"
• The columns, beams, and connections of the top tier above the highest secured tier must be at least snug-tight

In practice, this means that on a 20-story building, at least 2–3 complete "secured tiers" exist at all times, and the erector works within a 6–8 floor window of active construction.

4. Field Bolting — Snug-Tight and Final Tightening

Two-Stage Tightening Process

Bolted connections during erection are tightened in two distinct stages:

Stage 1 — Snug-tight (Erection Bolting):

• Defined by RCSC as "the tightness attained by the full effort of an ironworker using an ordinary spud wrench"
• Brings the connected plies into firm contact (no visible gaps)
• Sufficient for temporary stability and for bearing-type connections in the final structure (where pretension is not required)
• All bolts in the erection area must be snug-tight to at least 50% of the holes before the crane hook is released and the next piece is landed

Stage 2 — Final Tightening (Pretensioning):

• Performed after plumbing the tier
• Required for: slip-critical connections (fatigue, vibration, oversize holes), connections subject to direct tension (AISC 360 Section J3.1), and column splices in moment frames
• Verified by one of four RCSC-approved methods (see below)

Pretensioning Methods (RCSC Section 9.2)

Bolt Installation Sequence for Multi-Bolt Connections

Bolts in a connection shall be tightened from the most rigid part of the joint outward toward the free edges. For a beam-to-column flange moment connection:

1. Snug-tight all bolts, starting at the beam web centerline and working outward to the top flange, then down to the bottom flange
2. Plumb the frame (columns aligned, beams at correct elevation)
3. Final-tighten using the same sequence: center → top flange → bottom flange

Failure to follow a systematic tightening sequence can trap gaps in the connection, reducing slip resistance by 20–30% compared to a properly tightened joint.

5. Field Welding — AWS D1.1 Requirements

When Field Welding Is Used

Field welding is used for:

• Moment connections requiring complete-joint-penetration (CJP) groove welds at beam flanges (pre-qualified per AWS D1.1)
• Column splices (partial-joint-penetration groove welds)
• Horizontal bracing connections to gusset plates
• Shear tab to column web fillet welds where bolting is not practical
• Embed plates and field modifications approved by the engineer

Field Welding Challenges

Field welding faces conditions that the fabrication shop controls:

• Wind — wind speeds above 5 mph at the arc disrupt the shielding gas (SMAW) or flux coverage (FCAW), causing porosity. Wind shields (tents) are required above 5 mph; welding stops above 25 mph.
• Moisture — rain, snow, or condensation on the steel surface introduces hydrogen, causing delayed cracking (hydrogen-induced cracking, or "cold cracking"). Preheat at 200–300°F drives off moisture even when the base metal preheat temperature would otherwise be 50°F.
• Position — most field welds are made in the vertical or overhead position, requiring 3G or 4G qualified welders. Welding productivity is roughly 1/3 of the shop rate for the same joint in the flat (1G) position.
• Access — limited clearance around beam-to-column joints restricts electrode angle and travel speed, increasing the risk of lack-of-fusion defects.

Field Welding Quality Control

Per AWS D1.1 Section 6, field welding inspection includes:

• Visual inspection (VT) — 100% of all field welds, checking for cracks, undercut, overlap, porosity, and incomplete fusion
• Ultrasonic testing (UT) — CJP groove welds in tension flanges of moment frames and column splices (typically 100% UT per AISC 341 seismic requirements)
• Magnetic particle (MT) or dye penetrant (PT) — surface-breaking defects in fillet welds and partial-penetration groove welds
• Welder continuity — each welder's qualification is verified as current (within 6 months of last use of the process/position)

6. Plumbing, Alignment, and Final Geometry Control

Plumbing Sequence

After the first tier is erected and snug-tightened, the entire tier is plumbed (aligned vertically) as a unit. The plumbing sequence:

1. Establish two orthogonal reference baselines on the ground (building grid lines)
2. Plumb the corner columns using a transit or laser on both axes — these become the "control columns" for the tier
3. Plumb intermediate columns by measuring column-to-column distances at the floor level, matching the theoretical building grid
4. Check plumb against the 1:500 story height tolerance (AISC 303 Section 7.13.1.1)
5. Final-tighten bolts in the plumbed tier
6. Install and weld floor deck to lock in the plumbed geometry

Common Alignment Problems and Field Corrections

7. OSHA Safety Requirements — Subpart R Summary

Key OSHA Provisions (1926 Subpart R — Steel Erection)

Critical Safety Checklist — Daily

1. Crane inspection (daily visual + monthly documented) complete — hoist cables, boom, outriggers, anti-two-block
2. Fall protection harnesses inspected, anchor points identified, lifelines rigged
3. All workers below the active erection zone aware and protected (hard hat, safety glasses, steel-toe boots minimum)
4. Perimeter safety cables installed at floor edges within one floor of erection (maximum two-floor gap permitted)
5. No workers under suspended loads — crane operator's "no-pass" path enforced
6. Wind speed monitored — cease crane operations at manufacturer's limit (typically 25–30 mph for mobile cranes, 35–45 mph for tower cranes)

8. Post-Erection — Completion and Handover

Before the structural steel is considered complete and the ironworkers demobilize:

1. 100% bolting inspection — visual check that all bolts are installed and snug-tight at minimum; pretension verification for all slip-critical and tension connections
2. 100% welding visual inspection + NDT (UT/MT) per contract requirements
3. Plumb and alignment survey — third-party surveyor verifies column plumbness, beam elevations, and building grid alignment against AISC 303 tolerances; results compiled in a final survey report
4. Punch list — any missing bolts, incomplete welds, damaged paint/galvanizing, or alignment deviations documented for resolution
5. Grouting of base plates — non-shrink grout placed under all column base plates after final plumbing. Grout must fully fill the space between the base plate and concrete foundation with full bearing — no voids permitted. Dry-pack or flowable grout per manufacturer specification.

Quick Reference — Steel Erection Checklist

References

• OSHA 29 CFR 1926 Subpart R — Steel Erection (Sections 1926.750–1926.761)
• AISC 303-22 — Code of Standard Practice for Steel Buildings and Bridges, Sections 7 and 8
• RCSC Specification for Structural Joints Using High-Strength Bolts (2020), Section 9
• AWS D1.1/D1.1M:2020 — Structural Welding Code — Steel, Section 6 (Inspection) and Section 8 (Strengthening and Repair)
• AISC 360-22 — Specification for Structural Steel Buildings, Chapter M (Fabrication and Erection)
• ASME B30.5-2018 — Mobile and Locomotive Cranes
• ASME B30.3-2019 — Tower Cranes
• AISC Design Guide 23 — Constructability of Structural Steel Buildings
• SEI/ASCE 37-14 — Design Loads on Structures During Construction