For 2026 brownfield and greenfield projects the girder choice on an overhead bridge crane is driven by four measurable gates: rated capacity, CMAA/FEM duty class, building hook approach, and total installed cost. The decision is rarely about girder count in isolation; it is about which combination of girder, hoist and end-truck best meets the duty cycle inside the existing bay geometry.
Chinese factory output published the week of 2026-06-25 splits the market cleanly: electric single-beam units are offered 1–30 t at M3–M5, and electric double-beam units 3–500 t at M5–M7 [S3]. That 30 t / M5 boundary is the practical break line most procurement specs fall on, not the marketing-driven 10 t line still seen on older datasheets.
Capacity and Duty Class Envelopes
A single-girder crane in 2026 catalogs tops out around 20 t at the light industrial end (Yaplex lists 0.1–20 t for manual and powered single/double combinations) and 30 t on powered units from major Chinese OEMs [S1][S3]. Duty class tracks capacity: most single-girder shipments land at FEM 2m / ISO M3–M5, the band for general workshop, warehouse and assembly-line service [S3].
Double-girder bridge cranes take over from roughly 3 t upward on heavy industrial builds, with the standard 2026 envelope running 3–500 t at M5–M7 [S3]. Specialized 150 t class IP54/IP65 double-girder units for steel mills and shipyards are listed as catalog stock by the same Chinese vendors [S3]. The duty class jump is the real spec gate: a 20 t single-girder can match a 20 t double-girder on capacity, but cannot match the M7 starting/ stopping frequency of a mill-duty double-girder without overdriving the hoist motor and reeving.
Headroom, Hook Approach and Building Fit
Single-girder cranes mount the hoist on the lower flange of the I-beam, which eats into available lift height. Double-girder cranes run the hoist between the two beams on a trolley, so the hook can approach the top of the beams — typically saving 300–600 mm of headroom on a 20 t class unit. On low-bay retrofits where the existing building cannot raise its truss, that 300 mm swing often decides the spec. [S1]
Building fit also turns on span. Light-duty single-girder kits from 2026 Chinese catalogs target 7.5–31.5 m spans with relatively light end-truck wheel loads, which keeps existing runway rail and column foundations in scope. Double-girder 100 t+ units push wheel loads past 100 kN per corner and frequently force a runway audit or reinforcement, a cost that wipes out the girder-price delta on a 30 t project.
Total Cost of Ownership Across a 10-Year Cycle
Entry pricing in mid-2026 Chinese catalogs sits around US$2,000–10,000 per set for ISO/CE single-girder workshop units [S5], while a 10 t QD double-girder hook crane is quoted around US$120,000 ex-works Shanghai with annual production capacity in the low hundreds [S2]. The 10–20× price gap on a 10 t class machine is the headline number, but the relevant comparison is installed cost divided by ton handled per year.
For light-duty 1–10 t workshop service at < 10 cycles/shift, single-girder units win on first cost and on maintenance (fewer gearboxes, simpler reeving, one hoist service point). For 20 t+ and any service above M5, double-girder wins on life-cycle cost: heavier hoist frames, larger drums, and better service access from above the girder cut annual maintenance hours roughly in half versus an overdriven single-girder. A useful rule of thumb from the 2026 sourcing pages: any 2026 spec above 30 t, M5, or 20 m span should default to double-girder before the cost model runs [S3].
Decision Matrix: Which Girder When
Map the project against four numbers — capacity (t), FEM/ISO duty class, span (m), and required hook approach (mm). The 2026 Chinese OEM lineup makes the cut straightforward: 1–20 t and M3–M5 with standard hook approach fits single-girder; 3–500 t and M5–M7 with tight headroom fits double-girder. Anything in the 20–30 t overlap zone goes to double-girder if cycles/shift exceed 10 or the duty class must reach M5 sustained. [S2]
The same matrix flags the cases where neither standard option is right. Outdoor service without a building typically points to a gantry crane instead, and the 2026 gantry price/span analysis covers the cost levers that drive that swap. Likewise, light portable 0.1–2 t assembly jigs under 6 m span are usually cheaper served by a crawler crane rental or a jib than by any overhead bridge crane at all.
Selection Standards and Verification Points
2026 procurement specs should name the duty class by both FEM 9.511 and CMAA 70 / ISO 4301, plus the building clearance drawing marked in millimetres, not just “low headroom.” Chinese OEM datasheets in the June 2026 wave consistently publish working level M3–M5 (single) and M5–M7 (double) [S3], which lets a buyer cross-check vendor claims against the FEM table without a site visit. For hazardous-area service, also confirm the hoist enclosure and pendant rating to IEC 60079 series or the local equivalent before signing.
On the buying side, this 2026 spec cut pairs naturally with the broader overhead bridge crane buying guide for 2026, which expands on duty class, span and hoist sizing. For projects sitting on the gantry/overhead boundary, the gantry vs overhead bridge crane 2026 spec cut covers the wheel-load and foundation trade. A wider view of cost levers, including the steel surcharge impact on girder plate pricing, is in the 2026 steel supply chain note.
Trackable Signals for the Next Buying Cycle
Two datapoints to watch into late 2026: (1) Chinese OEM catalog updates pushing the single-girder top capacity past 30 t at M5 — that would compress the overlap zone and force a redraw of the 20 t boundary; (2) Any tightening of FEM 2m/3m cycle counts in published spec sheets, which would shift the single-girder win zone down by one duty class. Both are visible in monthly catalog refreshes from the major Chinese vendors and do not require a trade-show visit to catch. [S3]