How to Calculate the Span of an Overhead Crane?

Doing crane sales and technical support for many years, the most common question asked by customers is “what span of overhead crane should be selected for the workshop”. Many people mistakenly think that they only need to measure the width of the workshop, but in fact, the span is the core parameter of overhead crane design, and miscalculation will affect the installation, safety, wheel pressure distribution and equipment life. In this article, we will explain the definition of span, calculation methods, factors and common misunderstandings, to help you avoid the pit.

What is the span of an overhead crane?

The basic definition of crane span

Crane span is not the width of the workshop or the edge of the track distance, but the horizontal distance between the centerline of the two crane tracks. For example, when the width of the track is 100mm and the distance between the outer edges is 22.7 meters, it is wrong to directly take 22.7 meters as the span, the correct practice is to find the midpoint of the width of the two tracks and measure the distance between the midpoints, single girder and double girder overhead cranes are applicable to this standard.

Why span is crucial in crane design

Span directly determines the selection of crane structure: small span can be used single girder overhead crane (single girder overhead crane), large span needs double girder overhead crane (double girder overhead crane), otherwise the main girder is easy to deformation. It also affects the wheel pressure and end beam design, the larger the span, the more uneven distribution of wheel pressure, end beams need to be more robust; at the same time associated with the workshop layout, hook coverage, as well as manufacturing costs and equipment stability, and need to comply with the GB/T 14405-2011 standard span series requirements.

The standard meaning of span in different crane types

Overhead crane span

The span of overhead bridge crane is the distance between the centerlines of two runway tracks on the steel beams of the workshop, and the measurement should be based on the centerline of the tracks on the runway beams, not the edge of the steel beams.

Gantry crane span

The span of gantry crane (gantry crane) is the distance between the centerline of two runway tracks on the ground, mostly used in open field, the measurement needs to be carried out in windless horizontal conditions to avoid thermal expansion and contraction errors, and its span is usually 18-40 meters, graded in 5-meter intervals (GB/T 14406-2021 standard).

The span difference between single girder and double girder crane

The span definition of single girder and double girder overhead crane is the same, but the structural arrangement and gap requirements are different: double girder cranes need to reserve more safety gaps, and single girder cranes gap requirements are relatively loose, but they all need to comply with safety standards.

How to calculate the span of overhead crane

Core formula

Crane span = distance between two runway track centerlines, no need for complex calculations, the key is to find the right centerline, measure the distance.

Step 1: Find the centerline of the runway tracks

Can measure the width of a single track and take the midpoint mark, if the track has been installed, the laser range finder can be aligned with the midpoint of the inside of the track, Henan Mine Crane engineers commonly used in home surveys this method, accurate and efficient.

Step 2: Measure the distance between the centerlines of two tracks.

Need to use qualified tape measure or laser rangefinder on-site measurement, can not directly use the theoretical value of the drawings (old workshop track is easy to offset, wear and tear); measurement of the tape measure needs to be naturally sagging, large spans need to be measured more than a few points to take the average value.

Step 3: Confirm the tolerance and design standard

According to ISO and GB/T 14405-2011 standards, the tolerance is allowed to be ±3mm when the span is ≤10 meters, and the larger the span is, the larger the tolerance range is, but not more than ±5mm; at the same time, it needs to be combined with the manufacturer's design requirements, and Henan Mine Crane will adjust the dimensions of the main girder and end girder according to the actual measured span and the tolerance to guarantee the stability of the operation.

Calculation example

If the distance from the center line of the left rail to the center line of the right rail measured on site is 22.5 meters, the crane span is 22.5 meters. This value directly determines the main girder, end girder design and wheel pressure accounting, which is the core basis of the quotation and design program, and miscalculation will lead to rework and additional costs.

The difference between building width and crane span

Why the building width can not be directly equal to the crane span

Workshop columns, track beam supports, pedestrian access and track beam offset will narrow the distance from the centerline of the track, and the two cannot be equated. According to GBJ6 “plant building modulus coordination standard”, crane span S = plant span L - b (b is the difference between the two, determined by the presence or absence of access).

Example comparison

A workshop building width of 24 meters, the measured distance from the centerline of the track is only 22.5 meters, due to the two sides of the columns need to reserve a safety gap and track beam offset. If the span is set at 24 meters, the crane will not be able to be installed and will need to be re-customized.

Key factors affecting the span selection of overhead cranes

Workshop or steel structure layout

Column spacing determines the upper limit of the span (track beams need to be fixed to the columns), and the runway beam layout also affects the distance from the centerline of the track; the existing building needs to be combined with the steel structure limitations to determine the span according to the existing track.

Lifting Coverage Requirements

The span needs to meet the hook to cover all the operation areas (material area, production line, etc.), to avoid affecting the production efficiency due to insufficient span.

Crane type and tonnage

Light load cranes (5 tons, 10 tons) span can be slightly larger, heavy load cranes (50 tons, 100 tons) span should not be too large, otherwise the strength of the main beam is insufficient; different tonnage cranes have a standard span series (GB/T 14405-2011), Henan Mine Crane will be recommended according to the need.

Safety clearance requirements

The clearance between the crane and the column and wall should be not less than 100mm and 50mm respectively, and at the same time, the space for maintenance and installation should be reserved to facilitate component maintenance.

Future expansion considerations

The span can be reserved for a small amount of margin, to adapt to the workshop's future expansion needs, to avoid the later replacement of the crane to increase costs.

How the span affects the cost and performance of the crane

The larger the span, the more steel structure is required.

The larger the span, the longer the main beam, the larger the cross-section size, the increase in steel consumption (every 5 meters increase in span, the average increase in steel consumption of the main beam by 15%), and the need for high-strength steel, manufacturing costs rise.

Impact on wheel pressure and track system

The larger the span, the more uneven the wheel pressure, the need to reinforce the track beams, replacement of wear-resistant wheelsets, otherwise easy to lead to track deformation, fracture, and increase maintenance costs.

Balance between coverage and economy

The span only needs to meet the coverage requirements, too large will only increase costs and reduce stability, Henan Mine Crane engineers will help customers measure the optimal span, to achieve a balance between economy and practicality.

Common mistakes when calculating crane span

Confusing the distance between the outer edge of the track and the centerline of the track

Directly measure the distance of the outer edge of the rail as the span, ignoring the thickness of the rail, which will easily lead to a large span, the crane can not be installed.

Replacing track spacing with building width

Neglecting the space occupied by the workshop structure and setting the span according to the building width will lead to the crane not being able to adapt to the site and increase the rework cost.

Neglecting installation tolerances

Track installation deviations (e.g. non-parallel) exceeding the allowable range will lead to crane runout, jamming, and damage to the wheelset and track.

Failure to check hook coverage and side approach distance

Accounting for spans only and ignoring hook coverage and side approach distances can result in the inability to lift materials in a specific area, affecting production.

Assuming that all crane suppliers have the same reference dimensions

Different manufacturers crane structure design is different, span reference size is different, according to other manufacturers size accounting, easy to size mismatch.

What information should you provide to crane suppliers?

Necessary dimensions

It is necessary to provide the measured distance from the centerline of the track, lifting height, crane tonnage, actual dimensions of the workshop and detailed parameters of the runway beam to provide a basis for the design.

Useful supporting documents

Workshop CAD drawings, site photos, existing runway dimensions and production handling requirements can help the supplier to accurately give span recommendations and optimize the configuration.

Example of workshop overhead crane span calculation

The workshop of a machinery processing factory is 25m wide, with 23m spacing between columns, lifting 5 tons of mechanical parts, which needs to cover the whole workshop and reserve space for maintenance. Henan Mine Crane engineers measured the centerline distance of the track 22.5 meters, and finally determined the span, which not only meets the installation requirements, meets the demand for coverage, but also adapts to the single girder crane, saving costs and stable operation.

Frequently asked questions about overhead crane spans

Is crane span the same as crane width?

No, they are not. Span is the distance from the centerline of the track, the width is the size of the equipment itself, such as Henan Mine Crane 22.5 m span single girder crane, its own width is only about 2.5 meters.

Can only rely on architectural drawings to calculate the span?

No. The drawings are theoretical values. Drawings for the theoretical value, the site track may be offset, need to measure the centerline distance of the track to be accurate.

What if the workshop has already been built?

If the track has been installed, the centerline distance will be measured; if not installed, we can contact Henan Mine Crane engineers to come to the workshop to determine the location and span of the track.

Does the span have a big influence on the price?

The impact is large, every 1 meter increase in span, the cost increases, the span of more than 30 meters after the increase is more pronounced, the same tonnage of 20 meters and 25 meters span crane price difference of about 10% -15%.

Is the final span confirmed by the buyer or the manufacturer?

Both sides to confirm: the buyer to provide site and demand information, manufacturers combined with standards and experience to give advice to avoid mistakes.

Conclusion

The core of calculating the span of overhead crane is to measure the distance between the centerlines of two rails, and determine it by combining the tolerance, workshop layout and production demand. Do not calculate by feeling or building width, ignoring the actual measurement and tolerance will cause problems.

Henan Mine Crane has rich experience in survey and design, and can help customers accurately calculate the span.

Need to confirm the span of your overhead crane? Send us your workshop drawings, track dimensions or on-site photos, Henan Mine Crane engineering team will check the span, lifting height and configuration free of charge, and provide you with professional advice within 24 hours to help you avoid pitfalls and save money.