Overhead crane bridge girders

01

Set the span, rated load and deflection limit

Spanco, a crane maker, cites CMAA rigidity values for bridge cranes — vertical deflection "usually L/700" and, for regular bridge cranes, horizontal deflection "usually L/600" — where L is the span; it says the comparison is made at 100% of rated capacity, not at the 125% test load. Its own ratings are L/600 for steel gantry cranes and L/450 for enclosed-track workstation bridge cranes. [2]

DGCrane's deflection calculator for rectangular hollow (box) main girders uses f = PL³/48EI, with P the concentrated load at mid-span, L the span, E taken as 2.06 × 10¹¹ Pa and I the section's moment of inertia; it covers vertical static deflection only, without a dynamic coefficient, for bridge cranes up to 30 m span. [3]

Editorial calculation: at L/700, a 22.5 m span girder may deflect at most 22,500 ÷ 700 ≈ 32.1 mm at rated load; at Spanco's steel gantry rating of L/600 the same span gives 37.5 mm. [2]

For scale, DGCrane lists its LH double girder overhead cranes at 10.5–31.5 m span for 5 t to 50 t/10 t sizes, with work duty A5 or A6 in its parameter table and −25 °C to +50 °C ambient. [4]

Give the supplier the span, rated load (main and auxiliary hook), duty class or expected load spectrum, trolley and hoist weight, required lifting height and headroom, runway rail type, indoor or outdoor use and temperature range, and the design standard to be applied.

02

Check camber, footwalks, stops and rating marks

For its single girder gantry main beam, DGCrane states that the beam is made with an upward camber F of (1/1000 to 1.4/1000) × S, where S is the span. [5] Editorial calculation: on a 22.5 m span that range is about 22.5–31.5 mm.

OSHA 29 CFR 1910.179 requires, where headroom allows on cab-operated cranes with the trolley running on top of the girders, a footwalk along the entire bridge on the drive side, with at least 48 inches of headroom wherever footwalks are located, a design load of at least 50 pounds per square foot, an antislip surface, and an inner edge reaching at least the outside edge of the girder's lower cover plate or flange. Trolley stops must be fitted at the limits of travel and fastened to resist the forces applied when contacted. [1]

The same section requires the rated load to be marked plainly on each side of the crane, and allows a crane to be modified and rerated only when the modification and supporting structure are checked for the new rated load by a qualified engineer or the equipment manufacturer. [1]

03

Inspect the girder and test the crane

Under 29 CFR 1910.179, periodic inspections at 1- to 12-month intervals include deformed, cracked or corroded members and loose bolts or rivets, and test loads are not to exceed 125% of rated load unless the manufacturer recommends otherwise, with test reports kept on file. [1]

Spanco notes that an ASME B30.2 interpretation suggests a 0%/−4% tolerance on the test load weight, so in effect a test load between 120% and 125% of rated capacity. [2]

04

Compare what suppliers offer

The supplier linked to this page lists single and double girder overhead and gantry cranes; its card links to the page reviewed.

Ask any supplier for the girder section drawing and moment of inertia, calculated vertical and horizontal deflection at rated load, camber, steel grade and plate thicknesses, weld procedure and inspection, design standard and duty class, and the surface treatment and coating thickness.

05

Trace the girder parts

This is a functional reference built from the sources cited; it is not one maker's specification.

06

Fill the specification fields with values for your crane

A bridge girder quotation needs values for your crane and building. The table explains each field, gives published values where a reviewed source states them, and says what to obtain from the supplier.

07

Send the span, load and building data together

Paste it into your enquiry below or into an email to a maker, then replace every bracket.

Crane: [type; single or double girder; span; rated load]
Duty: [class; lifts per hour; load spectrum]
Stiffness: [vertical and horizontal deflection limits]
Building: [runway rail; headroom; indoor or outdoor; temperature]
Access: [footwalk; handrails; stops]
Documents: [section drawing; calculations; weld and coating records; test certificate]

See manufacturer records Send an enquiry through CNFX