Crane Background

A crane is a machine that is capable of raising and lowering heavy objects and moving them horizontally. Cranes are distinguished from hoists, which can lift objects but that cannot move them sideways. Cranes are also distinguished from conveyors that lift and move bulk materials, such as grain and coal, in a continuous process. The word crane is taken from the fact that these machines have a shape similar to that of the tall, long-necked bird of the same name.


Human beings have used a wide variety of devices to lift heavy objects since ancient times. One of the earliest versions of the crane to be developed was the shaduf, first used to move water in Egypt about four thousand years ago. The shaduf consists of a long, pivoting beam balanced on a vertical support. A heavy weight is attached to one end of the beam and a bucket to the other. The user pulls the bucket down to the water supply, fills it, and then allows the weight to pull the bucket up. The beam is then rotated to the desired position and the bucket is emptied. The shaduf is still used in rural areas of Egypt and India.
As early as the first century, cranes were built that were powered by human beings or animals operating a treadmill or large wheel. These early cranes consisted of a long wooden beam, known as a boom, connected to a rotating base. The wheel or treadmill powered a drum, around which a rope was wound. The rope was connected to a pulley at the top of the boom and to a hook that lifted the weight.
An important development in crane design occurred during the middle Ages, when a horizontal arm known as a jib was added to the boom. The jib was attached to the boom in a way which allowed it to pivot, allowing for an increased range of motion. By the sixteenth century, cranes were built with two treadmills, one on each side of a rotating housing containing the boom.
Cranes continued to rely on human or animal power until the middle of the nineteenth century, when steam engines were developed. By the end of the nineteenth century, internal combustion engines and electric motors were used to power cranes. By this time, steel rather than wood was used to build most cranes.
During the first half of the twentieth century, European and American cranes developed in different ways. In Europe, where most cranes were used in cities with narrow streets, cranes tended to be built in the form of tall, slender towers, with the boom and the operator on top of the tower. Because quiet operation was important in crowded cities, these tower cranes were usually powered by electric motors when they became widely available.
In the United States, cranes were often used in locations far away from residential areas. Cranes tended to be built with the boom connected to a trolley, which could be moved easily from place to place. These mobile cranes tended to be powered by internal combustion engines. During the 1950s, the availability of stronger steels, combined with an increased demand for taller buildings, led to the development of cranes with very long booms attached to small trucks, or to crawlers with caterpillar treads. Mobile cranes and tower cranes of many different kinds are used extensively in construction sites around the world.


The Purpose of Overhead Cranes

Overhead bridge cranes are some of the most versatile and widely employed types of cranes on the market. They can be found in warehouses and manufacturing facilities across the country.


The function of an overhead bridge crane is to lift a workload, removing it from one location and depositing it in another location. To perform a lift with an overhead bridge crane, a workload is rigged to the crane’s hook. A cable raises and lowers the hook. The cable is attached to a trolley, which travels side by side along the crane’s bridge. The bridge can travel along two runways to deposit a work piece to another location.


Only people who have been certified by OSHA (Occupational Safety and Health Administration) are qualified to operate overhead bridge cranes in America. Overhead bridge crane certification facilities are located throughout the country. For example, in Atlanta, Georgia, consumers can find OSHA training courses at Georgia Tech Institute.

Safety Measures

An overhead bridge crane must pass regular safety inspections (performed by OSHA-certified inspectors) before it can be used to lift a work piece. Overhead bridge crane operators should be careful to never lift a work piece that weighs more than the crane’s maximum load limit. Load limits are usually clearly marked on the sides of the crane, where they would be clearly visible to the crane operator at all times.


How to Determine Travel and Lifting Speeds part 2

Bridge Cranes:

The length of the runway, type of load carried and operator convenience are the important factors in speed selection. For floor operated cranes and runways up to 100′, one hundred fpm will usually be recommended. For runs over 200′, one hundred and thirty fpm may be more satisfactory. Cab operated crane speeds can range from 160 fpm to 350 fpm. The specific operating conditions will determine which speed is best. On two speed cranes and trolleys, slow speed is generally one-half the main speed. Multiple speed cranes generally have approximately equal speed steps.

Chain or Wire Rope Electronic Hoists:

  • Electric chain hoists are effective and efficient. They are available up to five tons capacity and larger. Wire rope hoists are available with an extensive variety of speeds and other options. In either type, both lift safely, and operate with similar ease and efficiency.
  • Wire rope hoists are more expensive because a wide grooved drum and larger housing to support the drum is required. Multiple and fast speeds or high production operations will usually require the selection of a wire rope hoist.
  • Chain type hoists are generally smaller and provide closer side clearances. They also permit a wider angle of pull than wire rope.
  • As a lifting medium, link chain is superior to wire rope. It is more flexible and much easier to inspect for wear or abuse. If it has been overloaded, it can be inspected for possible stretch and replaced before failure occurs. Wire rope can fray from the inside out and separate without warning. Link chain also gives a true vertical lift since it does not move from side to side as cable does. Generally, link chain will offer longer life than cable.
  • Electric link chain hoists are available up to 10 ton capacity in a limited selection of speeds.
  • Chains seldom require replacing while wire rope cables should be replaced periodically and are easily subjected to damage, crushing, fraying, weld burns, etc.


How to determine Travel and lifting speeds Part 1

How to Determine Travel and Lifting Speeds:

The speed of trolleys and cranes depends upon the length of the runway or the size of the area covered. Generally, faster speeds are used for longer runways. Short runways will run at slower speeds. If floor areas are crowded or congested, then slower speeds will probably be desirable. The slower the speed, the more accurately loads can be positioned. Maximum flexibility is gained with variable speed cranes. The fast speeds are used for long runs and the slower speeds for positioning.
Single speed hoists are the most popular in light capacity and meet most requirements at substantial savings. Two speed hoists are most common at five ton and heavier.
The following is a guide to speed selection. If in doubt, order the slower speed. Operators seldom complain about speeds being too slow. Speeds which are too fast can create problems.

Hoist Lifting Speeds:

  • Lifting speeds are largely determined by the application and use. Average speed is generally between 10 and 26 fpm. Speeds under 10 fpm are usually not practical except in special cases. For some continuous uses, speeds faster than 26 fpm may be desirable.
  • Most hoist motors are rated for 15 minute continuous operation. By dividing length of lift by lifting speed in feet per minute, you can determine if you have exceeded this rating. If there is any doubt, contact CraneTec.
  • On two speed hoists, the slow speed is generally one-fourth the hoist main speed. Hoist creep speeds are generally one-tenth the main hoist speed and variable speed hoists generally start at one-tenth and are variable to full speed.

Trolley Speeds:

The convenience of the operator and smoothness of travel are the principal factors in selection of the motorized trolley speed. For spans up to 60’, 65 FPM, is generally recommended. For longer spans, 80 fpm may be more efficient. The average walking speed is about 100 fpm.


What is CMAA?


CMAA is the Crane Manufacturers Association of America, Inc., an independent trade association affiliated with the United States Division of Material Handling Industry.
The voluntary association of CMAA members has existed since 1955. Member companies have been and are industry leaders today.
CMAA member companies are concerned, conscientious manufacturers who have come together in an industry association for the purpose of providing voluntary standards for mechanical, structural and electrical design of cranes, as well as formulating guidelines for the proper use, operation and maintenance of those cranes. Members donate countless hours of their time toward these earnest efforts.
To qualify for membership a company must engineer and design its cranes and assemble continuously the major crane components for at least a two-year period before being admitted.
Member companies of the Crane Manufacturers Association of America, Inc., meet regularly to review, discuss and revise the standards for design, performance and proper operation of engineered crane systems. CMAA member companies have committed to the development, maintenance and publishing of industry standard specifications for Top Running, Under Running, Single and Multiple Girder Cranes
Additionally, CMAA has prepared, published and distributes Training, Inspection and Maintenance recommendations that are available to all overhead crane users.
Member companies are required to participate in a requisite number of regularly scheduled meetings which among other things, further the ongoing process of revising and updating today’s standards to meet the ever-changing demands of technology and the modern industrial environment.
For more information about the CMAA and specifications please contact us.


Choosing an Electric Hoist

The conditions in which an electronic hoist must work should be considered when making a selection. It is essential that careful consideration be given to the frequency of use, load weight, length of lift, distance of horizontal travel, efficiency, safety and economy. There are literally hundreds of options available in electric hoisting equipment to answer the industries need for a powered lifting tool that speeds hoisting, conserves human effort, provides maximum safety and cuts handling cost.

Three Factors to Consider When Contemplating an Electric Hoist for your Application:

  • Capacity: The load to be lifted is the primary consideration, and the maximum load weight governs the minimum capacity of the hoist. This capacity must include the largest weights that you anticipate lifting, plus the weight of any grab, spreader bar, or other lifting device which attaches to the hook.
  • Headroom: It is generally desired in normal plant applications to have as high a hook height as possible for off-loading trucks, turning over large fabrications, etc.; however, this consideration should be weighed closely against the cost of the crane and in the required height of a building to accommodate excessive lift.
  • Many options are available to achieve maximum hook height. Some of these options can be rather expensive and must be evaluated against construction costs of the building in which the crane will operate. Even though close headroom options for the crane are costly, it is often less expensive than adding additional building height to accommodate standard lift equipment.
  • Headroom is defined as the distance between the beam, or track, and the bottom of the hook. Headroom distance varies between manufacturers and styles of hoists. If headroom is critical, check with CraneTec for exact dimensions.
  • Speeds: Electric hoists can be furnished for single speed, one-step automatic acceleration, two- speed, or variable speed operations. Most applications can be handled with single speeds due to the wide range of single speeds available. One step acceleration permits a gradual increase from zero to full speed. Two speed options allow a selection of low speed for spotting loads and higher speeds for fast lifting. Variable speed allows lift at any speed between zero and full speed.
  • “Creep” speeds on hoists are very slow, accurately positioning, second speeds. The speed is usually one-tenth to one-fifteenth the main hoist speed, yet this extreme slow speed is very essential in accurate placement of delicate loads. This type of speed arrangement is normally accomplished by separate motor drive attached to the main hoist motor. Two speed hoists are more common and the low speed will be one-fourth of the main hoisting speed.


Which Type of Overhead Crane Suits Your Needs?

Top Running or Under Running Cranes

  • Dependent on the type of building, comparative costs of the basic cranes are almost identical. Costs of runways and supports however, can vary tremendously.
  • Underhung cranes are almost universally used in capacities up to 3 tons and frequently up to 10 tons. If your building has been engineered to support from the roof girders, joists, etc., then the cost of runways and installation is relatively inexpensive, and underhung cranes can be used.
  • When the overhead beams cannot support the crane load, then a top running crane, operating from self supporting runways, is required. Headroom requirements for top running cranes are generally less than for underhung models; however, recessing the bridge girder on the underhung crane may give a similar headroom savings.

Single Girder or Double Girder Cranes

  • Single girder cranes are substantially less expensive to build, but are limited to shorter spans and lighter capacity applications. They are ideal for capacities up to 10 tons and spans to 60′. Longer spans and larger lifting capacities are available under certain circumstances. Intermittent duty service will allow capacities up to 15 tons and spans to 60′ which allows the economy of simple design and the use of the lower cost monorail style hoists.
  • Double girder cranes give the maximum stability for high speed cranes and are essential for long spans and large capacities and a must in heavier duty applications. Somewhat lower headroom clearances may be achieved with the double girder design; however, properly designed single girder cranes with low headroom hoists can offer the same or less space requirements at substantially lower cost.

Hand Push or Hand Geared Cranes

  • For very light capacity cranes of one or two ton capacities, hand push cranes can be furnished. They have either a hand or an electric hoist, and are without motor drives on the trolley and bridge crane wheels.
  • Hand geared drives are for cranes of heavier capacities up to 10 tons and suited for short runway applications of stand-by service (i.e., located over a specific piece of machinery for refined areas). These cranes will normally have a hand hoist or a slow speed lift electric hoist with a geared trolley and hand geared bridge.

Gantry Cranes – Great in the Right Application

  • Gantry cranes can offer a unique solution in answering a need for additional and supplementary crane coverage, off-setting costs of the building structure and in covering outside storage and fabrication areas.
  • Gantry cranes can be an inexpensive solution to overhead crane requirements when existing building structures cannot support a crane or when the cost of a self supporting crane runway structure is prohibitive.
  • The initial expense of a Gantry crane is somewhat greater than a conventional overhead crane of the same size, however, the larger cost is more than compensated by the elimination of the overhead structure and runways.
  • The major drawback to the use of a Gantry crane is the moving structure rolling along the floor, and the necessity of a clear floor space along the length of the runways. The in-floor tracks may prove bothersome to wheel carts and fork lift trucks operating across these areas.
  • Gantry cranes normally travel on small gauge ASCE railroad rail similar to the travel of the top-running crane. The rails can either be recessed into the floor or set directly on top of an adequate floor surface. Two specific types of Gantry cranes are commonly employed:

Single-Legged Gantry Cranes

  • These cranes are normally used to offer additional crane coverage in plants having large capacity and long span bridge cranes operating overhead. An additional rail system is mounted below the rail on the overhead bridge crane. One side of the Gantry crane rolls on a rail on the floor and the other side rolls on the supplementary overhead crane rail. This type of crane is used to cover long work areas where the swing area coverage of a jib crane would not be sufficient.

Double-Legged Gantry Cranes

  • These cranes are used on two parallel in-floor tracks and are excellently adapted for very heavy lifts, supplemental inside crane systems, and outside cranes.

Jib Cranes – A Lot of Work for the Money

  • Jib cranes are primarily used as supplementary light capacity lifting systems to service a single machine or manufacturing operation. They are available in a wide variety of styles and can be mounted on existing building columns, or on an independent, self supporting post located virtually anywhere a lifting task must be performed. Jib cranes are a rotation boom suspended on a fixed hinge point and can be designed to allow hook coverage with up to 20 ft. radius and 360 degrees around the center support point.
  • Jib cranes are normally available up to 5 ton capacity and are a relatively inexpensive structure compared to a full coverage overhead crane system.


Mechanical Principles


There are three major considerations in the design of cranes. First, the crane must be able to lift the weight of the load; second, the crane must not topple; third, the crane must not rupture.

Cranes illustrate the use of one or more simple machines to create mechanical advantage:

The Lever:

  •  A balance crane contains a horizontal beam pivoted about a point called the fulcrum. The principle of the lever allows a heavy load attached to the shorter end of the beam to be lifted by a smaller force applied in the opposite direction to the longer end of the beam. The ratio of the load’s weight to the applied force is equal to the ratio of the lengths of the longer arm and the shorter arm, and is called the mechanical advantage.

The Pulley:

  •  A jib crane contains a tilted strut that supports a fixed pulley block. Cables are wrapped multiple times round the fixed block and round another block attached to the load. When the free end of the cable is pulled by hand or by a winding machine, the pulley system delivers a force to the load that is equal to the applied force multiplied by the number of lengths of cable passing between the two blocks. This number is the mechanical advantage.

The Hydraulic Cylinder:

  • This can be used directly to lift the load or indirectly to move the jib or beam that carries another lifting device.
  • Cranes, like all machines, obey the principle of conservation of energy. This means that the energy delivered to the load cannot exceed the energy put into the machine. For example, if a pulley system multiplies the applied force by ten, then the load moves only one tenth as far as the applied force. Since energy is proportional to force multiplied by distance, the output energy is kept roughly equal to the input energy (in practice slightly less, because some energy is lost to friction and other inefficiencies).
  • The same principle can operate in reverse. In case of some problem, the combination of heavy load and great height can accelerate small objects to tremendous speed. Such projectiles can result in severe damage to nearby structures and people. Cranes can also get in chain reactions; the rupture of one crane may in turn take out nearby cranes. Cranes need to be watched carefully.


Basic Crane History

  • A crane, also known as a bridge crane or overhead crane, is a type of machine used for lifting. Cranes are generally equipped with a winder (also called a wire rope drum), wire ropes or chains and sheaves, that can be used both to lift and lower materials and to move them horizontally. It uses one or more simple machines like a hoist to create mechanical advantage and thus move loads beyond the normal capability of a human. Cranes are commonly employed in the transport industry for the loading and unloading of freight, in the construction industry for the movement of materials and in the manufacturing industry for the assembling of heavy equipment.
  • The first construction cranes were invented by the Ancient Greeks and were powered by men or beasts of burden, such as donkeys. These cranes were used for the construction of tall buildings. Larger cranes were later developed, employing the use of human tread wheels, permitting the lifting of heavier weights. In the High Middle Ages, harbor cranes were introduced to load and unload ships and assist with their construction – some were built into stone towers for extra strength and stability. The earliest cranes were constructed from wood, but cast iron and steel took over with the coming of the Industrial Revolution.
  • For many centuries, power was supplied by the physical exertion of men or animals, although hoists in watermills and windmills could be driven by the harnessed natural power. The first ‘mechanical’ power was provided by steam engines, the earliest steam crane being introduced in the 18th or 19th century, with many remaining in use well into the late 20th century. Modern cranes usually use internal combustion engines or electric motors and hydraulic systems to provide a much greater lifting capability than was previously possible, although manual cranes are still utilized where the provision of power would be uneconomic.
  • Cranes exist in an enormous variety of forms – each tailored to a specific use. Sizes range from the smallest jib cranes, used inside workshops, to the tallest tower cranes, used for constructing high buildings. For a while, mini – cranes are also used for constructing high buildings, in order to facilitate constructions by reaching tight spaces. Finally, we can find larger floating cranes, generally used to build oil rigs and salvage sunken ships.


Overhead Cranes in New Buildings

Industrial buildings, as well as some other building types, require large clear spans and heavy loadings. It is generally conceded that a tapered web-rigid frame is one of the most economical types of framing for the loads and spans normally encountered in crane buildings. When conditions beyond the normal are encountered, a truss frame may be more appropriate.

The building manufacturer should be given the opportunity of recommending the building type and support system to be used for the cranes.

Top-running Cranes

Runway beams for top-running cranes located within the building may be supported by brackets attached to the building frame columns, by separate columns located inside and in line with the building frame columns, or by stepped. When crane aisles extend outside the building, A-frames are commonly used to support the runway beams.

Brackets on the building columns are commonly used to support the runway beams for cranes up to 10-ton capacity. However, cranes with up to 20-ton capacity may be supported in this manner depending on the type, span, and service classification of the crane.

For cranes of more than 20-ton capacity, it may be more economical to support the runway beams with separate support columns. However, the columns for buildings having high eave heights and/or large wind and snow loads may support heavier cranes without substantial weight penalty.

Runway beams for cranes with capacity of 20 tons or less, but with bridge spans greater than 50 feet, may also be more economically supported by separate columns.

Underhung Bridge Cranes

Runway beams are supported by hangers or brackets attached to the rafter of the building frame. The location of the support hanger can materially affect the design, shape and economy of the building frame.

It is usually more economical to purchase a crane with a bridge span approaching the building width. This places the crane end trucks near the building columns. The savings in the building support framing will normally exceed the extra bridge cost. This savings can be substantial in long buildings with a large number of frames.

Underhung Monorail Cranes

Runway beams for underhung monorail cranes are supported similar to runway beams for an underhung bridge crane.

Crane loads and other crane data varies between crane manufacturers. These variations can affect the design and economy of a crane building. Significant economics may be achieved if the crane manufacturer is selected prior to the design of the building. This provides the building manufacturer with specific crane data for design of the crane building. For crane loading information, please consult us.


Preventative Maintenence

Why does Crane-Tec recommend performing a preventive maintenance service on a quarterly basis?

  • Many crane owners have inspections performed on an annual basis. This is an OSHA requirement. What many companies don’t know is OSHA also requires that the crane must be maintained on a scheduled basis, complete with dated records based upon the manufactures criteria. The maintenance can be performed in house or by a third party and the schedule is based on the duty cycle of the equipment along with following the manufacturer’s requirements.
  • Aside from the mandatory requirements listed and their costs, there may be additional costs involved by doing only an annual inspection. Historically, cranes with only an annual inspection/preventive maintenance service incur more break downs than cranes serviced quarterly. Small problems or adjustments normally taken care of during a quarterly inspection/preventive maintenance service have become bigger problems by the time the annual inspection/preventive maintenance service is due. Deficiencies found on an annual inspection/preventive maintenance service may be multiplied vs. cranes being inspected and maintained quarterly.
  • When breakdowns do occur, production time is lost and repair costs rise. If one was to look at two identical cranes of the same age, running at the same duty cycle and one unit maintained quarterly, the other maintained annually; you would find that the equipment maintained annually would cost more in higher operating costs, with lost time and expensive repair bills.

Benefits of Performing a Quarterly Inspection/Preventive Maintenance Service

  • 1) Lower your costs on repairs, including expediting costs and airfreight bills when purchasing replacement parts.
  • 2) Decrease your equipment down time due to breakdowns.
  • 3) Allows you, the Crane Owner and Crane Service Company to schedule repairs around your production.
  • 4) Provides you and your staff advanced notice of equipment condition for future and existing budget requirements.
  • 5) The above cost savings alone can be enough to allow for future upgrades or equipment replacement.

Are you proactive or reactive when it comes to maintaining your overhead cranes and hoists? Why take a chance, let a qualified Crane –Tec specialist recommend the correct program for your operation.


What Is an Overhead Bridge Crane?

According to the United States Department of Labor’s Occupational Safety and Health Administration, “Overhead crane” means a crane with a movable bridge carrying a movable or fixed hoisting mechanism and traveling on an overhead fixed runway structure. These devices are widely used in many industrial environments where large and heavy items require moving from one location to another.


Overhead bridge cranes have long been used in factories and warehouses to hoist and move heavy objects, often in small or cramped areas that may not allow for proper and safe maneuvering of forklift trucks. An overhead bridge crane can remedy this situation by providing an effective manner to hoist and move heavy loads that require significant power capability. It can readily meet numerous requirements that are sometimes performed by other types of equipment.


Overhead bridge cranes can be divided into two groups: top-running bridge cranes and under-running bridge cranes. The primary distinction is the manner in which the end trucks are attached to the crane. Top-running overhead bridge cranes have the end trucks supported on rails attached to the top of the crane runway, while under-running bridge cranes have the end trucks supported on tracks attached to the bottom flanges of the beams.


The benefits of an overheard bridge crane, whether top-running or under-running, are fairly numerous and can be significant solutions to alternative methods such as forklifts and elevators. A major benefit is that overhead bridge cranes are considerably less expensive than other options. They are also of a relatively simple design, lending to ease of operation and can be ordered as kits and installed on-site by the purchaser. They are designed so that in case of failure, they lock their load in place and prevent it from falling.

Shortcomings of Overhead Bridge Cranes

The primary–and possibly only–drawback to having an overhead bridge crane is that they are not very mobile. However, even this situation can be remedied by installing a track network to extend the range of the crane. This added expense still allows an overhead bridge crane to be a more economical choice than a forklift. The fact that an overhead bridge crane can actually reduce or even eliminate the need for forklifts or freight elevators is also a considerable benefit.


When pondering the need to acquire equipment that allows for the safe and efficient relocating of heavy objects as is required in warehouse environments and the like, an overhead bridge crane is a candidate for serious consideration. They are readily available to be shipped in kit form, can be configured to meet just about any application requirements and are safe when properly installed and operated. They are very suitable for small spaces and require less electricity to operate.

For any help in deciding your crane needs please contact us at Crane-Tec 800-755-6378 or


Overhead Crane Classification

Determine the proper CMAA classification for your crane:

Having been in the crane industry for more than 30 years, I have noticed that a reoccurring  problem I encounter on a daily basis is the determination of the CMAA classification of a particular crane. The problem lies in the broad wording used in the classification charts as well as an end user, builder and even some crane sales persons I have encountered just making a determination without even looking at the specification charts and true application.
The proper determination is crucial to the correct crane being specified for each application. In the current state of our industry, this is becoming even more critical as crane manufactures are engineering all their components to much tighter specifications in order to be cost competitive. Today,components are no longer being over built and almost everything is built to the specification required. Thus the proper classification is extremely important in today’s crane world.
I came across this simple way to determine the specification necessary years ago and still implementing this strategy today. While in some of the higher specifications further examination may be necessary but this will get you pretty close in almost any situation. It is based on a points system and pretty self explanatory. You go through each area and make the proper number selection and then add them all up and use the matrix to determine your classification. The key here is to be honest in the application, there is no use in cutting corners as you might as well just be pulling it out of the sky again!

1. Operating Factor

  • The first factor is the operating factor. How often will the crane be used? Is it for stand-by or maintenance service? Is it for 2,000 hours per year or less, which is the one shift operation, 4,000 hours per year, which is the 2 shift operation, or the 6,000 hours per year, which is the three shift operation
  • Stand-By or Maintenance 5
  • 2000 Hours/Year or less (1 Shift) 8
  • 4000 Hours/Year or less (2 Shifts) 15
  • 6000 Hours/Year or less (3 Shifts) 25


2. Relative Load Factor

  • The next factor to consider is the relative load factor. How does the average lifted load compare to the rated capacity of the crane?
  • Several loads per week at rated capacity 5
  • Several loads per day at rated capacity 15
  • (Majority of loads less than 50% of rated capacity)
  • Several loads per day at rated capacity 25
  • (Majority of loads greater than 50% of rated capacity)
  • Frequent capacity loads per day 35
  • (Majority of loads greater than 50% of rated capacity)

3. Load Impact Factor

  • The load impact factor considers the relative severity of the cranes operation. Is the service low and smooth as in a powerhouse operation? Will the crane be subject to the high impact forces inherent in magnet/bucket service found in steel mills or cement mills? Or does the service fall somewhere in between?
  • Stand-by, Maintenance, Powerhouse 5
  • Warehouse, Machine Shop, Assembly Shop 8
  • Foundry, Hot Metal 15
  • Bucket, Magnet, Grapple 25

4. Relative loss factor (Downtime)

  • The relative loss factor is a measure of the importance of the crane to your operation. If the crane is down for unscheduled maintenance, what is the effect; an inconvenience, a slowdown of operations, or a plant shutdown?
  • Low value on downtime (Inconvenience) 5
  • Medium value on downtime (Slowdown of operation) 15
  • High value on down time (Plant shutdown) 25

5. Ambient Temperature and Environmental Factor

  • Are the ambient temperatures extremely high or low? Or is there a combination of these conditions affecting the crane? The A and E factor considers where the crane is located. Is the environment normal, corrosive or highly contaminated?
  • Normal Indoor or Outdoor Service 5
  • Corrosive, Highly Contaminated Area, or Temperature Extremes 10
  • Corrosive and Highly Contaminated Area 15

6. Maintenance Factor

  • The last factor to consider is the Maintenance factor. While a true preventive maintenance program is ideal, it is very seldom the case.
  • Preventive Maintenance Program 5
  • Normal Maintenance Handled by Maintenance Department but
  • Reactionary other than Lube and minor adjustments 15
  • No In-House Maintenance Capabilities 25
  • This is where you need to add up your points and see where you fall in the matrix key.
  • 0 to 40 Points = CMAA Class “A” and “B”
  • 41 to 65 Points= CMAA Class “C”
  • 66 to 85 Points= CMAA Class “D”
  • 86 to 115 Points= CMAA Class “E”
  • 116 to 150 Points= CMAA Class “F”

I have found over the years there are two areas overlooked or misunderstood the most when determining the classification, the relative loss factor and the Maintenance Factor. If you use this and understand it, it will save you time and possibly money in the future by specifying the correct crane for the application.



Top Running Overhead Crane Runway Systems


Runway Beams:

  • Runway beams and columns for top-running bridge crane applications may be provided by the building supplier or the crane supplier. The design of these beams takes into account the vertical impact of the crane, the lateral force resulting from the effect of moving crane trolleys and longitudinal force from moving cranes. Typical sections include mill shapes and welded built-up plate sections. Support Columns-The columns can be part of the building columns, Independent tie back columns, or an independent column. For new construction the runway system is designed as part of the building. For use in an existing building you have two options.
  • 1) Independent tie back columns that use the building structure to take the horizontal load of the runway system.
  • 2) Independent columns that are freestanding on the foundation or floor, that take the horizontal and vertical loads.

Runway Rail:

  • Runway Rail should be installed in such a manner so that wear to the crane, runway beam supports and the rail itself will be minimized. Rails should be arranged so that joints on opposite runway beams for the crane will be staggered with respect to each other and with respect to the wheel base of the crane. Rail joints should not coincide with runway beam splices. Runway rails should be ordered in standard lengths with one short piece on each side to complete a run. The short piece should not be less than 10′ long. Rail ends will normally be furnished saw cut only, unless otherwise specified by the buyer. Rail ends will normally be furnished with standard drilling for commercial rails splices, unless otherwise specified by the buyer.
  • Common methods of fastening rails to runway beams are hook bolts, bolted clamps, welded stud clamps and welded clamps with a pad. Crane rails should not be painted as this may cause the wheels to slip, resulting in skewing of the bridge and columns.


Overhead Crane Alternatives

Jib Cranes and Gantry Cranes are good alternatives to an overhead crane where a small area is being covered and light loads are being lifted:

The Jib Crane:

  • The Jib crane is a type of crane that has a rotating horizontal boom attached to a fixed support. A standard trolley equipped with electric or hand-geared chain hoist normally operates on the lower flange of the jib crane boom.
  • Jib cranes may be appropriate for servicing machinery located outside of the coverage of an overhead crane, or for assembly lines where jib boom areas can overlap for staged operations.
  • Jib cranes may be floor mounted or supported by the building frame. Floor mounted jib cranes are generally preferred. Jib cranes which must be supported by the building frame may be mounted directly to the building column or mounted to a supplemental column.
  • The floor-mounted jib crane requires no top braces or supports of any kind from the building structure. The jib boom will rotate through a full 360 degrees. Under ordinary conditions, these base-mounted jib cranes can be anchored directly to a properly-designed reinforced concrete floor or separate foundations.
  • The column-mounted jib crane is generally mounted on a building column. The boom rotation is limited to approximately 200 degrees.
  • The application of a column-mounted jib crane requires that the building column, column base anchorage and bracing be designed to account for the special loads imposed by the jib crane. This will usually increase the building column size.

The Gantry Crane:

  • Gantry cranes are adapted to applications where overhead runways would be very long and costly to furnish. They are also appropriate where overhead runways would interfere with handling operations, storage space, or service areas.
  • Single-leg gantry cranes are used in those installations where it is convenient to have one end of the bridge supported on an overhead runway rail and the other end supported on a gantry leg. This design can then utilize adjacent building framing to support the overhead runway rail. This application requires that the building framing, column base anchorage and bracing be designed to account for the special loads imposed by the gantry crane.


Overhead Crane Types

In planning a crane building, and in selecting overhead cranes, it is important to consider future operations that may increase loading and service requirements in addition to present operations. Be certain to plan for both crane building and cranes to satisfactorily meet the increased service conditions that may arise in the future. This planning effort will minimize the possibility of overloading or of placing the structure in a more severe classification than intended.

There are many types of cranes in use today to meet material handling requirements.The types described here include those cranes currently being supplied by major crane manufacturers support of these crane types usually affects the design of the building in which the crane is installed.

Top Running Cranes

Top-running bridge cranes are characterized by bridge end trucks bearing on top rails attached to the runway beams. Top-running bridge cranes are generally used for more severe applications with heavier loads and high service classifications. They are generally applicable when one crane isle extends the full width of a building aisle, and they are frequently used where high travel speeds are required. In comparison to underhung cranes, top-running cranes usually provide greater hook height and clearance below crane girder.
Top-running bridge cranes may be single girder, double girder, or box girder. Single girder cranes are generally used on shorter spans and lower capacities or service classifications. The trolley of a single girder crane is suspended from the girder. Cranes are normally operated by a pendant pushbutton station suspended from an independent track or radio remote.

Double girder cranes

Double girder cranes are generally used on moderate spans and higher capacities or service classifications. The trolley of a double girder crane usually bears on rails attached to the upper flange of the crane girders. Low headroom double girder cranes are available that are designed to produce maximum clearance beneath the bridge.

Box girder cranes are generally used on larger spans and high capacities or service classifications. The trolley bears on rails attached to the upper flange of the crane girders. Box girder cranes are normally operated from a pendant pushbutton station suspended from an independent track or a radio remote.

Underhung bridge cranes

Underhung bridge cranes are characterized by the bridge end trucks being suspended from the lower flange of the runway beam. Underhung bridge cranes are generally used for less severe applications with lighter loads and lower service classifications. They are frequently used where multiple crane aisles are required in a building aisle,where the crane aisle is only a portion of the building aisle, and when materials must be transferred between building aisles. In comparison to top running cranes, underhung cranes usually provide greater hook cover, clearance beneth the runway beam, and clearance for overhead obstructions.

Underhung bridge cranes may be single or double girder with the trolley suspended from the lower flange of the girder or girders. The power source of the hoist, trolley, or bridge may be hand geared or electric. Electric powered cranes are normally operated by a pendant pushbutton station suspended from the hoist.

  • Crane Type Power Source Description Span or Reach Capacity
  • Underhung 1. Hand Geared Single Girder 10’ to 50’ Spans ½ to 10 Tons
  • 2. Electric Single Girder 10’ to 60’ Spans 1 to 10 Tons
  • Top-Running 1. Hand Geared Single Girder 10’ to 50’ Spans ½ to 10 Tons
  • 2. Electric Single Girder 10′ to 60′ Spans ½ to 10 Tons
  • 3. Electric Double Girder 20′ to 60′ Spans 5 to 25 Tons
  • 4. Electric
  • Box Girder
  • Pendant-Operated
  • 4-Wheel End Truck 20′ to 100′ Spans
  • 5 to 25 Tons
  • 5. Electric
  • Box Girder
  • Radio Controlled
  • 4-Wheel End Truck 50′ to 100′ Spans
  • Up to 60 Tons
  • 6. Electric Box Girder
  • Radio Controlled
  • 8-Wheel End Trucks 50′ to 100′ Spans Up to 100 Tons
  • Jib Cranes 1. Hand Geared or Electric Floor-Mounted
  • 280 to 360 8′ to 20′ Reach
  • ¼ to 5 Tons
  • 2. Hand Geared or Electric Column-Mounted
  • 180 8′ to 20′ Reach ¼ to 5 Tons


Overhead Crane Service Class Selection

Overhead Crane Service Class Selection easy as 1-2-3:

Selecting the correct service class for your overhead crane is usually quite simple.

1)Determine how you are going to use the crane.

  • a)How much weight will you be picking up.
  • b) How often you will be picking up the weight
  • c)How far will it be moved.

The class of crane service can significantly affect the design and the cost of the building framing used for the support of the crane system. The buyer should specify the crant service classification when requesting quotes from crane vendors or general contractors.

CMAA Crane Service Specifications:

  • 1) Service classes have been established to enable the buyer to specify the most economical carrier (trolley) or crane for the particular installation.
  • To determine proper service classification of equipment, it should be noted that there are three possible basic modes of operation to be considered. They are Crane travel, Carrier (Trolley) travel and Hoist travel. Specific requirements are shown for these components where design is influenced by classifications All classes of cranes are affected by the operating conditions; so for the purpose of these definitions, it is assumed that the crane will be operating in normal ambient temperatures (0°to 100°F) and normal atmospheric conditions (free from excessive dust, moisture and corrosive fumes)
  • 2) Class A
  • This class is further divided into two subclasses due to the nature of the loads to be handled.
  • 2.1 Class A-1 (Standby Service) – This service class covers cranes used in installations such as power houses, public utilities, turbine rooms, motor rooms and transformer stations, where precise handling of valuable machinery at slow speeds with long idle periods between lifts is required.
  • 2.2 Class A2(Infrequent use) – These cranes will be used in installations such as small maintenance shops, pump rooms, testing laboratories, and similar operations where the loads are relatively light , the speeds are slow and a low degree control accuracy is required. The loads may vary anywhere from no load to full capacity with a frequency of a few lifts per day or month.
  • 3. Class B (Light Service)
  • This service covers cranes such as those used in repair shops, light assembly operations, service buildings, light warehousing, etc.,where service requirements are light and the speed is slow. Loads may vary from no load to full-rated load with an average load of 50% of capacity with 2 to 5 lifts per hour and averaging 15 feet, with no more than 50% of the lifts at rated capacity.
  • 4. Class C (moderate service)
  • This service coveres cranes such as those used in machine shops, paper mill machine rooms, etc., where the service requirements are moderate.
  • In this type of service the crane will handle loads which average 50% of the rated capacity with 5 to 10 lifts per hour and averaging 15 feet, with no more than 50% of the lifts at rated capacity.
  • 5. Class D (heavy Duty)
  • This service covers cranes, usually cab operated, such as those used in heavy machine shops, foundries, fabricating plants, steel wharehouses,lumber mills, etc., and standard duty bucket and magnet operation where heavy duty production is required but no cycle of operation. Loads approaching 50% of the rated capacity will be handled constantly during the working period. High speeds are desirable for this type of service with 10-20 lifts per hour averaging 15 feet, with no more than 65% of the lifts at rated capacity.
  • 6. Class E&F (Severe Duty & Steel Mill Service)
  • Cranes in E&F class are covered by the current issue of The Association of Iron and Steel Engineers Standard No. 13for Electric Overhead Travelling Cranes for Steel Mill Service.


Overhead Crane Terminology

Overhead Crane Terminology

Overhead CranesMove in 3 Directions:

  1. Length, the length of a building or bay.
  2. Width, the width of a building or bay.
  3. Height, up or down.
  • The part of the crane moving the length is called the Bridge.
  • The part of the crane moving the width is called the trolley.
  • The part of the crane moving up and down is called the hoist.
  • These  three parts, bridge, trolley, and hoist together are called a crane
  • or overhead crane.

The following is a glossary of terms related to overhead cranes:

  • BAY: The space between the building frames measured parallel to the ridge of the building.
  • Brake: A device for retarding or, stopping motion by friction or by power means.
  • Bridge: a part of an overhead crane consisting of girders, trucks, and drive mechanism which carries the trolley and travels the length of the runway.
  • Building Aisle: A space defined by the length of a building and the space between building columns.
  • Capacity: the Maximum rated load (in tons) which a crane is designed to handle.
  • Collectors: Contacting devices for collecting current from the runway conductors. The mainline collectors are mounted on the bridge to transmit electrical current from the runway conductors.
  • Crane Aisle: That portion of the building aisle in which the crane operates, defined by the crane span and the uninterrupted length of the crane runway.
  • Crane girder: The principal horizontal beams of the crane bridge which supports the trolley and is supported by the end trucks.
  • Crane Span: the horizontal distance center to center of the runway beams.
  • Hand Geared: The operation of the bridge, hoist, or trolley of a crane by the manual use of chain and gear without electric power.
  • Hoist: a Machinery unit that is used for lifting and lowering a load.
  • Holding Brake: a brake that automatically prevents motion when the power is off.
  • Lift: The maximum safe vertical distance through which the hook can move.
  • Limit Switch: A device designed to cut off the power automatically at or near the limit of travel for the crane motion.
  • Pendant Push Button Station: Means suspended from the crane for operating the controllers from the floor or other level beneath the crane.
  • Rated load: The maximum load a crane is designed to handle.
  • Remote Operated Crane: a crane controlled by Radio Remote Controls.
  • Rotating Axle: An axle which rotates with a wheel.
  • Runway: The rails beams, brackets, and framework on which a crane operates.
  • Runway Conductors: the main conductors mounted on or parallel to the runway which supply electrical current to the crane.
  • Runway Rail: The rail supported by the runway beams on which the bridge travels.
  • Single girder Cranes: An electric overhead traveling crane having one main girder which supports a hoist mounted on a under running trolley.
  • Span: The horizontal distance center to center of runway rails.
  • (End)Stop: A device to limit the travel of a trolley or crane bridge. This device normally is attached to a fixed structure and does not normally have energy absorbing ability.
  • Support Column: A separate column which supports the runway beam of a top running crane.
  • Suspension system: The system (rigid or flexible) used to suspend the runway beams of under hung or monorail cranes from the rafter of the building frames.
  • Top Running Crane: An electric overhead traveling crane having the end trucks supported on rails attached to the top of the crane runway beams.
  • Under Running Crane: An electric overhead crane having the end trucks supported on track attached to the bottom flanges of beams or supported on the bottom flanges of the beams; these beams make up the crane runway.
  • Wheel Base: The distance from center to center of outermost wheels.
  • Wheel Load: The load without impact on any wheel with the trolley and lifted load (rated capacity) positioned on the bridge to give maximum loading.


Largest Floating Crane on Planet Earth

Do yourself a favor and click through to the full-sized images. They. Are. Insane.

Meet Kaisho, a floating crane owned by IHI in Japan with a lifting capacity of 4,100 tons. Kaisho is the largest floating crane on the planet. Dry Roasted Blend covered Kaisho’s smaller sister, Yoshida, back in 2007, but Kaisho is even bigger, towering more than 450 feet over the sea.

In fact, the 2 cranes worked together, along with a third massive floating crane, on the Tokyo Bay Highway Project in Japan. Pictured below, from left to right, is Musashi, Yoshido, and Kaisho.

Kaisho, Yoshida floating cranesSource: ykanazawa1999

The helicopter really puts the sheer size of these behemoths into perspective.

Massive Floating Cranes

3 Floating Cranes

The three cranes were used to hoist 760-foot bridge spans weighing 7,400 tons for the Tokyo Bay Highway Project . In an incredibly complex engineering ballet, these three monsters moved inch-by-inch from barges carrying the bridge spans to the installation point. During the move, GPS was used to coordinate both the position and height of each bridge span as it was carried into position. Because each crane’s hooks had different rolling speeds, Kaisho had to radio lift positions to each of the two smaller cranes over and over again so they could keep the massive spans balanced until they were in position.

Floating cranes with a bridge truss

If you take a look at the original size of the image above on Flickr you can see tiny little people on top of the concrete pillars.

Japanese cranes Kaisho and Yoshida

Largest Japanese crane Kaisho

Massive crane lift

Huge cranes with Ship

I managed to track down a photo taken from that same restaurant ship pictured above as it passed by the Yoshida:

Floating cranesSource: Symphony Cruise

This was the first time in 15 years that 3 floating cranes were used in a simultaneous lift in Japan.

After a bridge span was in place, one of the massive floating cranes lifted a 450 ton crawler crane 200 feet above sea level and deposited it into the girders to work on the upper truss. If you click the photo below to see the larger version you can really get an idea of the scale of these cranes. Notice the yellow crawler crane that looks like a toy compared to the massive floaters.

Floating crane lifts crawler crane into girdersSource: ykanazawa1999

A shot of Kaisho all alone.

Massive floating craneSource:

Kaisho largest craneSource:

Lifting a crawler crane into the bridge girders:

Biggest floating crane - KaishoSource

A photographer named Gunnar Horpestad has some images in his gallery of Kiasho working on the Dalia build at DSME.

And if you’re technically-inclined, you can read more about the lift here (pdf).

For more information on Crane-Tec, visit our product pages on single and double girder cranes, runway systems, jib cranes, and all types of hoisting systems.

Other Sources used: