Steel erection estimating: pieces, picks and cost per ton

Why cost per ton misleads

Cost per ton is useful for comparing bids and checking a finished estimate. It's a poor way to build one, because field work doesn't scale with weight. A crane cycle is hook on, lift, swing, land, hang at least two bolts per end (the OSHA minimum before the hook is released), unhook and swing back. That cycle takes about the same time whether the piece is a W12x26 or a W21x62.

Illustrative comparison:

	Office building	Industrial building
Tons	180	180
Pieces	1,150	450
Average weight per piece	313 lb	800 lb
Picks per crane-day (assumed)	24	24
Crane days	48	19

Same tonnage, about 2.5 times the crane time. If both jobs were priced at the same dollars per ton, one of them was priced wrong.

Build the erection takeoff from the member list

Use the same member list as the fabrication estimate so the two never drift apart, but group it by what drives field work:

• Columns by tier, with splices, base plates, leveling plates or nuts, and grouting (check whether grout is in your scope or the concrete contractor's).
• Beams and girders by floor and weight class. Light infill beams can sometimes be rigged in multiples (Christmas-treeing), which OSHA 1926.753 allows only under specific conditions.
• Bracing and moment frames. More field time per piece, more bolts, often field welds.
• Joists and joist girders by count, with bridging. OSHA 1926.757 has specific erection bridging and attachment requirements for joists that affect sequence and labor.
• Deck by square foot, with the fastening pattern (puddle welds or powder-actuated fasteners, plus side-lap fasteners) from the deck schedule.
• Misc. steel by the erector: lintels, edge angles, roof frames, screen walls, stairs and rails if they're in scope.
• Connections: field bolts by installation type and field welds by length and position.

Picks and crane days

Crane productivity sets the pace of most erection jobs. Calculate it separately from labor:

crane days = picks ÷ picks per crane-day
labor days = field man-hours ÷ (crew size × hours per day)

Your last few comparable jobs are the best source for picks per day. Published planning figures for conventional low-rise framing with good access are mostly in the 15 to 25 range per crane per day. Treat that as a rule of thumb. Adjust down for:

• Height and long hook cycles.
• Tight sites without laydown, where steel has to be shaken out in sequence or delivered just in time.
• Heavy members needing tandem picks or special rigging.
• Field-welded moment connections that hold the crane while connectors fit up.
• Sequencing with other trades (deck pours, precast, elevator rails).
• Wind and cold-weather days. Crane days are calendar days.

Then size the crane for the heaviest pick at the longest radius, not the average one, and carry mobilization, assembly and dismantling as separate lines. A raising gang (typically a foreman, two hooking on and two connectors) is sized to one crane. Adding ironworkers doesn't speed up the crane; it creates a second gang that needs a second crane.

Bolting and welding: connection type sets the labor

The RCSC Specification for Structural Joints defines three installation types, and they price very differently:

Joint type	Field work	Estimating note
Snug-tight	Bolts brought to snug-tight	Fastest; most shear connections in buildings
Pretensioned	Snug, then pretension by turn-of-nut, calibrated wrench, twist-off (TC) bolts or DTIs	More time per bolt and pre-installation verification
Slip-critical	Pretensioned plus specified faying surface condition	Surface prep, coating control and inspection

Read the structural general notes and the steel spec for which joints are pretensioned or slip-critical. Bracing, moment connections and anything with cyclic loading often are. Also check special inspection requirements, since you'll support the inspector's access and schedule.

For field welds, count by length, size and position. Overhead and vertical welds are slower than flat, and moment connections often need backing bars, weld access holes and ultrasonic testing.

OSHA Subpart R items that show up in the price

Subpart R (29 CFR 1926.750 to 1926.761) is the federal steel erection standard. A few provisions directly affect cost:

• Column anchorage (1926.755): at least four anchor rods per column. Coordinate anchor rod surveys and repairs before you mobilize; AISC 303 also addresses who is responsible for anchor rod placement and repairs.
• Connections (1926.756): at least two bolts per connection, wrench-tight, before the hoisting line is released. Double connections at columns need specific provisions.
• Fall protection (1926.760): connectors working above two stories or 30 feet, whichever is less, need fall protection. Between 15 and 30 feet there are specific connector rules. Perimeter cable is part of many erectors' scope; check the contract.
• Joists (1926.757) and decking (1926.754) have their own requirements for bridging, attachment and decking controlled-decking zones.

State plans (for example Cal/OSHA) can be stricter, so price to the jurisdiction.

Worked outline: putting the number together

An illustrative build-up for the 180-ton office building above:

Pieces                     1,150
Picks/crane-day (history)  24      → 48 crane days
Crane                      48 days × crane day rate + mob/demob
Raising gang               5 × 10 hr × 48 days = 2,400 MH
Bolt-up and plumb crew     from bolt count × MH per bolt by joint type
Deck                       sq ft × MH per square + fastener pattern
Misc. and stairs           by piece
Safety and perimeter cable lump sum per floor
Supervision and surveys    duration-based
Total ÷ 180 tons           → compare to similar past jobs

If the per-ton result lands well outside your history for this building type, look for a missed mobilization, the wrong picks-per-day rate, or a piece count that double-counts loose material.

Common holes in erection bids

• Crane cost buried inside an hourly composite rate, so nobody sees it's short.
• One crane priced when the schedule needs two gangs.
• Small picks ignored: stairs, rails, roof frames and screens all cost a crane cycle.
• Grouting, anchor rod repairs or perimeter cable assumed to be by others without saying so in the proposal.
• No allowance for weather days or other trades' delays.

Where RenderDraw fits

The erection estimate starts with an accurate piece list by type. RenderDraw's AI takeoff proposes member counts and lengths from framing plans and schedules, with the source sheet on every row, so fabrication and erection can work from the same list. Picks per day, crane selection and labor rates remain your call.