Crane runway beams and stepped columns: fabrication tolerances and inspection

Which structures these figures are for

The figures in this article belong to the typical solution that grew up for single-storey industrial buildings with general-purpose overhead electric cranes up to 50 t capacity. Beams: simply supported welded I-beams made of three plates, spans of 6 and 12 m, light, medium and heavy crane duty. Columns: welded stepped columns with a solid-web upper part and a lattice lower part; buildings 10.8 to 18 m high, spans of 18–36 m, one tier of cranes.

The design outdoor temperature for such solutions goes down to minus 65 °C, and seismicity up to 9. For buildings with moderately aggressive environments the column pitch is taken as at least 12 m and the outer branch of the columns as channel section only.

These are guide values, not the requirements of a standard in force. For cranes over 50 t, other spans, box girders or non-typical columns the tolerances are set by the project, and the documents in force are listed at the end. For what to demand from the fabrication of any structure, see quality control of steel structures.

Crane runway beam: fabrication requirements

Beams are either intermediate or end beams, the latter next to the building ends and expansion joints. They consist of top and bottom flanges, a web, stiffeners and bearing stiffeners. All parts are made to KMD drawings.

Flange-to-web welds are made by automatic welding with a smooth transition to the parent metal. In the welds joining the top flange to the web, the web must be fused through its whole thickness. All welds are continuous. Shop splices of flange and web plates are made as butt joints without cover plates and with two-sided welding; one-sided welding is allowed only with back-gouging of the root. The surface of butt welds in the flanges is ground flush with the parent metal, and the grinding may be limited to the places where the crane rail will lie and where the flange meets the web.

Flange edges after machine oxygen cutting must not have unevenness over 0.3 mm. The end of the bearing stiffener is machined. Beams are primed and painted.

Beam tolerances: linear dimensions

All deviations are in millimetres. They apply to the nominal dimensions on the drawing: beam length is taken between the outer faces of the bearing stiffeners, height from the outer face of the top flange to the end of the bearing stiffener.

Beam tolerances: form and position of surfaces

Here limits are put on what does not show in the dimension chain but spoils the work of the joint: straightness of the flanges, squareness, web concavity. These parameters decide how the crane track will lie and how the bearing stiffener sits on the column.

Stepped column: layout and requirements

Columns come in two types: with a one-sided crane bracket for the outer row and with a two-sided one for the middle row. Each type is made in two versions: for buildings without walkways along the crane tracks and with walkways. In middle-row columns with walkways the upper part is offset from the longitudinal setting-out axis to leave room for passage on one side.

The upper part and the branches of the lower part are I-sections, and the lattice of the lower part is two-plane, made of single angles. A channel is allowed for the outer branch of outer-row columns. The ends of the upper and lower parts and the top face of the base plates are machined as shown on the drawing, and the roughness there is specified separately.

Welding is automatic and semi-automatic; manual welding is allowed for site connections. Strips with holes for special anchor bolts are welded to the base plates; they are used to align the column and fix it in the design position before the concrete is grouted. Setting-out marks are punched on the bases. Columns are primed and painted.

Column tolerances: linear dimensions

Deviations in millimetres, both signs. The last two groups of rows relate to the splices of the upper and lower parts, where holes and gaps decide whether the column will fit up on site.

Column tolerances: form and position of surfaces

The size to which the tolerance is tied is the element length (for straightness), the section size (for ends) or the flange width. Tolerances on ends are strict because the end transfers force, and out-of-square gives uneven contact at the splice.

Tolerances after erection

Erection on site is done by our partner construction company, but the designer and the customer should know what the column is being prepared for. Guide values for erected columns: level of the top of the base plate ±1.5 mm; mutual vertical displacement of base plates 0.6 mm for a size up to 1000 mm, 0.8 mm for 1000–1500 mm and 1.3 mm for larger ones; base plate slope 0.2 mm for a size up to 250 mm, 0.3 mm for 250–500 mm, 0.5 mm over 500 mm; displacement of the axes of the lower-part branches from the setting-out axes at the bottom 5 mm; column deviation from vertical at the top section 15 mm.

These numbers show why the shop pays so much attention to the bases. Every tenth of a millimetre taken up by a base deviation is later spread over the verticality of the whole column.

What is inspected in the shop

Inspection of linear dimensions, form and position of surfaces, weld quality and surface preparation for protective coatings is done before priming. After priming you can no longer measure as you should. Dimensions are checked with universal tools: tape measures, calipers, squares, templates, straightedges.

Beams are accepted piece by piece by the manufacturer’s quality control. The welds of columns are checked by visual inspection and measurement of all welds. Butt welds joining the upper part of a column to the lower are additionally tested by ultrasound on the first and on every twenty-fifth column; we do not carry out radiographic testing — if the project calls for it, tell us at the enquiry stage. If columns are supplied in parts, the first and every tenth column are trial-assembled to confirm that holes and ends fit.

For middle-row columns a template for assembly is made: one per twenty columns, but not fewer than two.

Completeness, marking, storage

Beams and columns are supplied as complete sets. A beam set includes 6 mm thick erection spacers (one per beam) and technical documentation. Beams for the middle row of columns are supplied in blocks of two beams joined at the top flange by a braking structure, with vertical bracing for the time of transport. A column set includes the shipping elements (upper and lower parts), anchor plates, 4 per column, base plates, 2 per column, and templates. Base plates can be shipped separately and earlier.

On every beam and on every shipping element of a column, the order number, the KMD drawing number and the KMD designation with the serial number of manufacture are applied in indelible paint. On a beam the marks go on the outer side of the bearing stiffener above the erection spacer and on the outer side of the bottom flange in the middle. On a column they are in two places on each part, and on a base plate on the machined face.

In transport and storage beams and columns lie on timber supports: not thinner than 50 mm in transport and not thinner than 150 mm in storage, with spacers not thinner than 25 mm, longer than the bearing width by at least 100 mm. A stack of beams is not higher than 2.3 m, of columns not higher than 2 m. The erection spacers are joined to the bearing stiffeners with temporary bolts.

What to put on a KMD drawing

The designer takes tolerances from the documents in force, but on the drawing they must be tied to the specific structure. The minimum list: design temperature and steel class; crane duty and capacity; weld designations with their character (butt, fillet, full penetration) and the inspection requirement; which ends and faces of base plates are machined and the roughness; coordinates and tolerances of holes for fixing rails, braking structures and anchor plates; whether a trial assembly and templates are needed; coating requirements.

State separately what is taken as the datum for measurement, and if the requirements are tighter than typical, write them down rather than imply them. For the steel for such structures see steel grade selection. We prepare the KM and KMD drawings: KM and KMD design; we fabricate beams and columns to the customer’s drawings: steel fabrication. If the beams are already in service and the rail track or the condition of the joints has to be assessed, that is a technical inspection.

Standards and validity

Calculation and design of crane runway beams and columns are done to DBN V.2.6-198:2014 «Steel structures. Design standards» (in force; edition with Amendment No. 1 of 2022). Requirements for the execution of steel structures, tolerances on geometry and the inspection procedure are in DSTU EN 1090-2:2019 «Execution of steel structures and aluminium structures. Part 2. Technical requirements for steel structures» (in force from 01.07.2020). For deflection limits of crane runway beams and horizontal deflections of columns under crane loads see the article on deflection and displacement limits.

The validity and current edition of each of these documents must be checked. The tolerance values in the tables of this article are guide values for typical structures that have grown out of fabrication practice; for a specific project the tolerances and accuracy classes are set by the project, and must be checked against the current document and not against this article.