Last updated October 2026

Single Girder vs Double Girder Overhead Crane: Which Do You Need?

This is the first real decision in any bridge crane project, and getting it wrong is expensive in both directions: a double girder where a single would do wastes $50,000+ on steel you don't need, while a single girder pushed past its limits becomes a maintenance problem and a safety risk. Here's how to choose correctly.

The structural difference

A single girder bridge crane runs the hoist and trolley on a single bridge beam spanning the runway — the hoist typically rides on the bottom flange. A double girder crane uses two bridge beams with the hoist riding on top on its own trolley rails, between or above the girders. That structural difference drives everything else: capacity, span capability, headroom, and cost.

When single girder is the right call

Most Texas facilities — fabrication shops, warehouse maintenance bays, equipment service centers — never need more than a single girder crane. If your heaviest routine lift is under 10 tons, your span is under 60 feet, and the crane runs intermittently (CMAA Class A–C duty), a single girder gives you everything you need at roughly half the installed cost of a double girder. It's also lighter, which means lighter runway steel and lower installation costs — the savings compound.

When you need double girder

Step up to double girder when any of these are true:

• Capacity above 10–15 tons. The physics of a single beam stop working economically here.
• Long spans. Past ~60–75 feet, a single girder gets impractically deep and heavy.
• Maximum hook height. The top-running trolley on a double girder puts the hook as close to the runway as physically possible — critical when you're lifting tall loads in a building with limited clear height.
• Heavy duty cycles. CMAA Class D and above (frequent, heavy, or continuous service) generally call for double girder construction, which handles fatigue loading far better.
• Special below-the-hook equipment. Magnets, rotating hooks, and twin-hook configurations for long loads mount far more naturally on a double girder trolley.

The headroom question

This deserves special attention because it's the most common regret we hear about. A single girder crane's hoist hangs below the bridge beam, which can cost you 2–4 feet of hook height versus a double girder in the same building. If your lifts are tall — standing a vessel upright, loading tall equipment — measure your required hook height first and work backward. A cheaper crane you can't lift with is no bargain.

Top-running vs underhung

One related choice: single girder cranes come in top-running (bridge rides on top of the runway rails — higher capacity, needs runway structure) and underhung (bridge hangs from runway beams suspended from the building structure — lighter loads, uses existing steel). Underhung systems suit capacities under ~5–10 tons where the building steel can carry the loads, and they're common in workstation crane applications. Your structural engineer makes this call, not the crane salesman.

Retrofit and replacement considerations

Replacing an existing crane constrains the choice: the runway gauge, rail size, and building steel were designed for the old crane's wheel loads. A double girder replacement on a runway built for single girder often requires runway reinforcement — which can erase the equipment savings of reusing the structure. Before committing to a configuration for a replacement project, have the vendor verify wheel loads against the existing runway capacity. In many retrofits, matching the existing configuration (single for single) is the economic winner even when a greenfield analysis would favor double girder.

Total cost of ownership

Over 20 years, the purchase price is roughly half the story. Double girder cranes cost more to maintain (two hoists or a larger single hoist, more rope, more brake rebuilds) but the productivity of a second hoist and the aux-hook flexibility often pays back in plants where the crane paces production. Single girder cranes are cheaper to own outright — fewer components, simpler controls — which is why they're the default for intermittent-use facilities. Model it honestly: purchase + installation + 20 years of inspection contracts and component replacements, discounted against the production value of the crane's availability.