Eight on-site stages, the bridge assembly checks that decide whether the crane runs true, 2026 installation cost ranges from 20 to 100 tons, and the load test rules you have to satisfy before production starts. Written for plant engineers and project managers who own the installation contract.
A double girder overhead crane typically needs 5 to 10 working days on site, roughly three times the erection window of a comparable single girder unit. The extra time goes into lifting two main girders as one assembled bridge, checking bridge diagonal and girder parallelism, and commissioning a heavier hoisting system. Hold span tolerance to plus or minus 5 mm up to 16 m, cap the height difference between opposite rails at 10 mm, and pass the ASME B30.2 load test before the crane touches production.
Most double girder installations that run late are not delayed by the crane. They are delayed by the runway, the mobile crane, or the electrical scope, in that order. This guide walks the eight stages, the timing you should budget by capacity, the bridge assembly checks nobody puts in the contract, ISO 12488-1 runway values, 2026 cost ranges and the load test rules that decide when the crane can go to work.
Installation, assembly and commissioning get used interchangeably, and that causes arguments over scope. Installation is the whole physical setup on site. Assembly is the mechanical joining of girders, end ties, end trucks, trolley and hoist. Commissioning is the testing and calibration that turns a bolted-together structure into a certified lifting appliance. A supplier quoting "installation and commissioning" may only mean the middle one, so read the scope line carefully.
The work runs through eight stages. Some belong to the crane supplier, some to your civil or steel contractor, and one belongs to a mobile crane hire company you may not have booked yet.
| Stage | Typical duration | Usually done by |
|---|---|---|
| 1. Site survey and structural check | 1-3 days | Owner plus crane engineer |
| 2. Design approval and shop drawings | 5-15 days | Crane manufacturer |
| 3. Runway beams, rails, corbels and end stops | 5-15 days | Civil or steel contractor |
| 4. Delivery, heavy lift planning and staging | 2-3 days | Logistics, rigging crew and mobile crane hire |
| 5. Girder positioning, end tie assembly and bridge lift | 2-4 days | Installation crew |
| 6. Trolley, hoist, festoon and electrical installation | 2-4 days | Electrical crew |
| 7. Alignment, rail gauge and calibration | 1-2 days | Installation crew |
| 8. Load test and commissioning | 2-3 days | Commissioning engineer plus independent inspector |
Compare this to a single girder job and the pattern is obvious. Stages 3 and 5 grow by 50% to 80%, because a double girder runway carries far heavier wheel loads and the bridge has to be assembled on the ground before it can be lifted. Stage 4 is a whole new line item for most buyers: a mobile crane that can pick 20 tons at a 15 m radius is a different machine from the one that lifts a single girder assembly.
Stage 3 remains the stage that slips, and it is almost never in the crane supplier's scope. If you are buying a double girder crane for a building where the runway has to be built from scratch, run the runway as its own project with its own schedule and its own quality hold points.
Five to seven working days is a fair answer for a 10 to 20 ton unit in a building that is ready for it. Above 20 tons the numbers climb quickly, because the lifts get heavier, the bolted connections get bigger and the load test needs more ballast and more people to arrange it.
| System | Typical on-site duration |
|---|---|
| Double girder 5-10 t, existing runway | 3-5 days |
| Double girder 10-20 t, existing runway | 5-7 days |
| Double girder 20-50 t, existing runway | 7-10 days |
| Double girder 50-100 t, steel mill duty | 2-4 weeks |
| Any capacity, new runway included in contract | Add 1-2 weeks |
| Total project, enquiry to handover, custom crane | 8-16 weeks |
The gap between 7 days on site and 16 weeks end to end is the number that catches first-time buyers. It should not. A 50 ton double girder crane with VFD travel drives, a maintenance platform and a cabin is engineered to order, shop-assembled and tested before it is broken down for shipping, then moved by sea. Nothing about that fits in a fortnight.
One practical note. Book the mobile crane only after the assembled bridge weight is confirmed in writing. We have seen projects where the bridge was estimated at 15 tons for the lift plan and came in at 21 tons with the trolley and hoist, which forced a re-book, a new lift plan and a five-day stoppage. Ask for the bridge weight with trolley, hoist, festoon and maintenance walkway included, not just the bare girders.
The runway standard does not change because the crane has two girders instead of one. What changes is how much a miss costs you. A double girder crane puts two heavy wheels the same distance apart but carries far more load on each of them, so a span error that would be a slow annoyance on a 5 ton crane becomes rapid flange and rail head wear on a 50 ton unit.
ISO 12488-1:2012, identical to GB/T 10183.1-2018, gives the acceptance values. Grade 1 applies where total travel distance over the service life is very high, or where the system is tolerance-sensitive, for example a long-span crane with a short end carriage wheelbase.
| Check | Grade 2 | Grade 1 |
|---|---|---|
| Span tolerance, span up to 16 m | ±5 mm | ±3 mm |
| Span tolerance, span over 16 m | ±[5 + 0.25 × (S − 16)] mm, max ±15 mm | max ±10 mm |
| Rail straightness, horizontal plane, full length | ±10 mm | ±10 mm |
| Height difference between opposite rails (E) | ±1.0 × S mm, max ±10 mm | ±0.5 × S mm, max ±5 mm |
| End stop and buffer parallelism (F) | ±1.0 × S mm, max ±10 mm | ±1.0 × S mm, max ±10 mm |
Run the formula against realistic double girder spans and the numbers bite. At 22.5 m the Grade 2 span tolerance is ±[5 + 0.25 × 6.5] = ±6.6 mm. At 28 m it is ±8 mm. At 31.5 m it is ±8.9 mm. Grade 1 at 22.5 m drops to ±5.6 mm, and at 35 m it sits at the ±10 mm cap while Grade 2 has only reached ±9.75 mm.
There is also a check that rarely makes it into a runway contract: rail gauge along the full length, not just at the ends. Measuring span at both end stops and finding it good tells you nothing about the middle. We have measured runways that were 5 mm over at the ends and 14 mm over at mid-length on a hot afternoon, which is a flutter the operator feels, not a smooth ride. Measure at five points minimum, and measure in the same thermal conditions you expect in service.
This is the part of a double girder installation that has no equivalent on a single girder job, and it is where quality control pays for itself. The two main girders are laid parallel on the floor and joined with end ties at both ends. End trucks are mounted to the tie assemblies. Then the complete bridge goes up as one lift and lands on the runway rails.
Every acceptance value below is measured on the ground before the lift, while you can still adjust with shims, jacks and a portapower. After the bridge is in the air, all you can do is watch.
| Bridge assembly check | Typical acceptance | Why it matters |
|---|---|---|
| Bridge diagonal difference (D1 − D2) | ≤5 mm on a 22.5 m span, scaled with span | A skewed bridge loads the four wheels unequally and climbs rails |
| Girder parallelism over full length | ≤5 mm | Trolley rail gauge must stay constant for the crab to travel freely |
| High-strength bolt torque at end ties | Per drawing, commonly 190-450 N·m for M20-M24 grade 10.9 | Under-torqued joints slip, fret and crack in fatigue |
| Trolley rail straightness, horizontal | ≤2 mm over any 2 m length | Stops crab binding, wheel lift and rail edge wear |
| Camber at mid-span | Per drawing, typically 0.1-0.15% of span | Keeps loaded deflection inside the design limit |
| End truck wheelbase and skew | ≤2 mm | Even wheel load, no flange climbing under travel |
Bolts are worth a separate word. On a double girder crane the end tie connections are the joint between two heavy steel members, and they carry a significant share of the torsional load during skew travel. Torque them in the sequence shown on the drawing, with a calibrated wrench, and record the values. If your erection contractor tells you the bolts were "done up tight", ask for the torque log. Missing torque records on a double girder bridge are the single most common documentation gap we see on handover.
Installation is a separate line from the crane price, and it is the line that makes comparisons go wrong. The ranges below reflect 2026 pricing for standard double girder systems in prepared buildings. Structural work is excluded because it varies too widely to quote as a range.
| Cost component | Typical range (USD) |
|---|---|
| Installation labour and commissioning, 10-20 t | 8,000 – 14,000 |
| Installation labour and commissioning, 50 t | 15,000 – 25,000 |
| Installation labour and commissioning, 100 t | 25,000 – 40,000 |
| Runway steel, rail, corbels and end stops | 12,000 – 60,000 |
| Mobile crane hire for the bridge lift | 1,500 – 8,000 per lift day |
| Electrical and control scope | 6,000 – 25,000 |
| Freight and insurance | 3,000 – 18,000 |
| Structural reinforcement, if required | Project-specific, can exceed crane cost |
Put that together and the installed cost lands here:
| Configuration | Crane equipment, FOB | Total installed |
|---|---|---|
| 20 t, 22 m span, A5-A6 | 38,000 – 55,000 | 65,000 – 80,000 |
| 50 t, 25 m span, A6-A7 | 75,000 – 130,000 | 141,000 – 165,000 |
| 100 t, 30 m span, A7-A8 | 150,000 – 280,000 | 275,000 – 318,000 |
Across the whole project, plan 25% to 45% on top of the bare crane price for a double girder system. That is a higher uplift than the 20% to 40% a single girder job carries, and the difference is the mobile crane plus the heavier runway. Our double girder crane cost and TCO guide covers the ten-year view including maintenance and energy, which is often a bigger number than the installation itself.
The awkward case is a building that was never designed for crane loads. General warehousing steel is usually specified for roof loads only, and a 50 ton double girder crane puts roughly 22 to 28 tons on each wheel with the dynamic factor included. New columns, new footings or local reinforcement can pass the price of the crane. Better to know that before you sign than after the girders land in the yard.
Commissioning is where a bolted steel structure becomes a certified lifting appliance. The order matters: no-load operation first, then static load, then dynamic load, with safety device verification running alongside all three.
| Test | Load applied | What it verifies |
|---|---|---|
| No-load operational test | 0% | Full-stroke bridge and trolley travel, hoist motion, limit switches, emergency stop, brake release |
| Static load test | 100-125% of rated capacity | Structural integrity, mid-span deflection, residual deformation after the load is set down |
| Dynamic load test | 110% of rated capacity | Brake performance, gearbox and coupling behaviour, stability through repeated cycles |
| Safety device verification | n/a | Limit protection, overload limiter, emergency stop, horn, warning light, anti-collision if fitted |
ASME B30.2-2.3.2 sets the rules for the test itself. The test load must be at least 100% of rated capacity and must not exceed 125% unless the manufacturer or a qualified person recommends otherwise. The operations are defined: hoist the load to confirm the brakes hold it, run the trolley the full length of the bridge, travel the bridge the full length of the runway in both directions with the trolley positioned near each end, then lower, stop and hold the load to check the brakes again. A written load test report documenting the load and the operations performed is required.
Deflection is the double girder number worth watching. Limits come from the design standard and duty class rather than the girder count, and heavy-duty double girder cranes are commonly specified to L/1000 at rated load while single girder units more often land at L/800 or L/700. On a 25 m span that is 25 mm versus 31 mm at full load, and it is measured at mid-span during the static test with the trolley parked in the centre. If the measured figure is over the drawing value, the problem is usually not the girder but the runway level under it.
Load testing is triggered by new, reinstalled, altered, repaired or modified cranes. Replacing wire rope or load chain is explicitly excluded, though an operational hoist test is still needed before the crane returns to service. Maintenance managers get caught by that distinction more often than anyone else. The maintenance and overhaul guide covers what triggers a retest over the crane's service life.
Do not accept a verbal "all good" on handover day. These ten items are the ones that cause trouble later when they get waved through.
| # | Item to verify and record |
|---|---|
| 1 | Span, rail gauge at five points and bridge diagonal within the specified ISO 12488-1 grade |
| 2 | Runway level, rail joint gaps, corbel seating and end stop alignment |
| 3 | End tie bolt torque log with wrench calibration certificate |
| 4 | Wheel and rail contact over full travel, no flange climbing or wheel lift |
| 5 | Trolley rail straightness and crab travel over the full bridge length |
| 6 | Hook height, upper lift limit and hoist rope reeving matching the approved drawing |
| 7 | Overload limiter set to crane rating and calibrated, not left at factory default |
| 8 | Brake torque and stopping distance measured, with the figures written down |
| 9 | Measured static deflection against the drawing value, recorded at mid-span |
| 10 | Load test report, certification documents, wiring diagrams and O&M manual handed over |
Item 7 is the quiet one. An overload limiter that ships set to a default value and never gets re-calibrated will either nuisance-trip on legitimate loads or fail to protect the structure. Ask for the calibration record, not a tick on a form. Item 9 matters just as much on a double girder crane, because that is the number that proves the runway and the bridge are working together rather than fighting each other.
Runway readiness is the most common cause of a delayed erection date in the installations our commissioning team attends. It is almost never a technical failure. It is a scheduling failure, because the runway belongs to a different contractor working to a different standard, and the crane crew arrives to find rails that were never aligned.
The second most common problem is that the span was never re-measured after the runway was finished. A double girder bridge is built to the span on the approved drawing, and both girders and both end ties are fabricated to that number. If the as-built span differs by more than the tolerance, the bridge arrives and the wheels do not sit on both rails. Re-measure the span and rail gauge after the runway is complete and send the figures to the manufacturer before shipping is authorised. It takes an hour and prevents weeks.
Third, the mobile crane is booked on an estimate rather than a confirmed weight. Assembled bridge weight with trolley, hoist, festoon and walkway is a written figure your supplier can provide. Get it, add the rigging, and book the lift accordingly. A 50 ton crane whose bridge weighs 40 tons fully dressed needs a very different mobile crane from a 25 ton estimate.
Fourth, buildings get assumed to be crane-rated when they are not. Retrofitting a heavy runway onto general warehousing steel is a structural project, not a steelwork detail. Have a structural engineer review the actual wheel loads including the dynamic factor before capacity is locked in. Buyers who get this right are the ones who read the standards comparison before they order, not after.
And fifth, the electrical scope is left vague. Who runs the power feed to the crane, and to which point? Who supplies the isolator, the festoon or conductor rail, and the control panel enclosure? Ambiguity here means a finished crane sitting idle while an electrician is booked two weeks out, which is how a 7 day installation becomes a 3 week one.
A double girder crane in the 10 to 20 ton range goes up in 5 to 7 working days on site when the runway already exists. Units from 20 to 50 tons generally take 7 to 10 days, and heavy steel mill duty cranes above 50 tons run 2 to 4 weeks. If the runway has to be built as part of the contract, add 1 to 2 weeks. Total project time from enquiry to handover is 8 to 16 weeks for a custom double girder crane, because design, fabrication, shop assembly and pre-delivery inspection all happen before anything arrives at your site.
Because the bridge is lifted as one complete subassembly. The two main girders are joined on the floor with end ties and end trucks, then the whole structure goes up in a single pick. A 20 ton double girder crane with a 22.5 m span has an assembled bridge weight of roughly 18 to 26 tons once the trolley and hoist are included. A single girder crane of the same capacity lifts as a much lighter, narrower assembly. Undersizing the mobile crane is one of the most common and most expensive on-site mistakes, because a crane with insufficient capacity at the required radius cannot complete the lift at all.
ISO 12488-1:2012, identical to GB/T 10183.1-2018, sets the acceptance values. For spans up to 16 m, span tolerance is ±5 mm at Grade 2 and ±3 mm at Grade 1. Above 16 m the Grade 2 span tolerance becomes ±[5 + 0.25 × (S − 16)] mm, capped at 15 mm. The height difference between opposite rails is capped at 10 mm at Grade 2 and 5 mm at Grade 1, and rail straightness in the horizontal plane is 10 mm over the full runway length. Double girder cranes are commonly built at 22.5 m to 35 m spans, so the over-16 m formula applies to most of them.
On-site installation labour and commissioning runs USD 8,000 to 14,000 for a 20 ton unit, USD 15,000 to 25,000 for 50 tons, and USD 25,000 to 40,000 for 100 tons. Runway steel and rail adds USD 12,000 to 60,000 depending on span and capacity, electrical and control scope adds USD 6,000 to 25,000, and freight and insurance adds USD 3,000 to 18,000. Budget 25% to 45% on top of the bare crane price for a double girder system, which is a higher uplift than a single girder crane because of the heavier runway and the mobile crane needed for the bridge lift.
ASME B30.2-2.3.2 requires the test load to be at least 100% of rated capacity and not more than 125% unless the manufacturer or a qualified person recommends otherwise. The test involves hoisting the load to confirm the brakes hold it, running the trolley the full length of the bridge, travelling the bridge the full length of the runway in both directions with the trolley near each end, and lowering, stopping and holding the load to verify brake function. Mid-span deflection is measured during the static test. A written load test report documenting the load and the operations performed is required for new, reinstalled, altered, repaired or modified cranes.
Rarely for the heavier sizes. The wheel loads decide it. A 50 ton double girder crane on a 25 m span produces roughly 22 to 28 tons per wheel including the dynamic factor, and general warehousing steel is normally specified for roof loads only. A structural engineer has to check the existing columns, corbels and roof beams against the actual wheel load figures from the crane supplier before capacity is fixed. On retrofit projects, reinforcement work on a double girder installation frequently costs more than the crane itself.
Send us your building dimensions, existing structure details and lifting requirement. Our engineering team will confirm the crane that fits, the wheel loads your structural engineer needs, the assembled bridge weight for your lift plan, the runway tolerance your contractor must hold, and a full installation and commissioning scope so nothing falls between contracts.
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