Overhead Crane

Overhead crane

Overhead Crane

 

Overhead Crane Case Study

The Challenge:

  • To provide our customer, a leading trucking accessories supplier, with a complete design build of an under running 5 ton overhead crane system. The job incorporated the 5 ton overhead crane system and (2) ½ ton jib cranes.

Special Considerations:

  • The general contractor needed design build capabilities for the overhead crane and runway system. Crane-Tec provided complete design of the under hung runway system and incorporated it into the general contractors special overhead crane truss system.

Our Team Approach:

  • Our engineers, armed with building drawings, determined runway steel and hanger design. Engineered drawings with overhead crane loads were submitted to the general contractor for approval. Crane-Tec’s experienced field crew installed the complete system and jib cranes in under 3 days to meet the G.C.’s demanding schedule.

Results: 

  • The general contractor maximized the strength of the building while Crane-Tec supplied a turn key overhead crane system and the owner maximized floor space. The overhead cranes were ahead of schedule allowing the owner to set up manufacturing machinery with the use of the overhead crane.

 

Case Study

The Challenge:

  • To provide our customer, a leading forklift manufacturer, with a complete under running 12 ton overhead crane system. The job incorporated the 12 ton runway system and four under running overhead cranes.

Special Considerations:

  • The customer needed design build capabilities for the overhead crane and runway system. Crane-Tec provided complete design of the under hung runway system and incorporated it into the customers metal building.

Our Team Approach:

  • Our engineers, armed with building drawings, determined runway steel and hanger design. Engineered drawings with loads were submitted for approval. Crane-Tec’s experienced field crew installed the complete system and overhead cranes in under 4 days, allowing the customer to use the equipment in the installation of new machinery.

 

Job History: 5 Ton Crane Syetem

5 Ton Overhead Crane

The Challenge:

  • To provide our customer, a major wire manufacturer, with multiple free-standing overhead crane systems for a new manufacturing facility. The job incorporated a 5 ton capacity free-standing runway system and (2) 5 ton top running double girder tie-back runway systems.

Special Consideration:

  • The general contractor needed design build capabilities for the overhead crane and runway systems. Existing building height limitations requires use of both single girder and double girder overhead crane systems, both with custom low headroom hoists.

Our TEAM Approach:

  • Our engineers, armed with the metal building drawings, determined runway steel locations and sizes. Engineered drawings with loads were submitted to the general contractor for approval.

For Immediate Results
Call 800-755-6378
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Insulated Safety Bar

Over the last few years, many new insulated type safety electrification systems have been developed. All of these systems provide a safe means for bringing power to hoists and bridge cranes.

  • The Enclosed Duct Type:  Has two or more conductors inside a square metal track, or individual insulated bars of galvanized steel, copper, or aluminum. These bars are completely enclosed with an insulated shield which has a split on the front edge. A set of collector shoes on the passing crane or hoist equipment bears firmly against the electrification bar and virtually opens the insulated jacket which springs closed again as the equipment passes. This type of electrification can be used for straight or curved requirements.

To accommodate for icing and extreme climate problems, sheet metal covers can be placed over the bars for weather protection and high temperature jackets are available in most situations. The duct type systems are considerably more expensive, utilizing a multiple collector trolley riding inside the square duct. It is a sturdier system and generally offers good weather protection for outside installations. By far the most popular style of insulated system used by crane manufacturers is the individual insulated bar.

 

FESTOONING ELECTRICIFICATION

Festooning (looped wire) cable systems are simple and inexpensive types of available electrification and offer a relatively trouble free method of bringing electric power to moving equipment. Typically, the only problem with festooning is that the hanging loops could tangle with obstructions or interfere with lifts if installed in areas with low ceilings. Modern festooning systems are normally designed so these possible trouble areas can be eliminated. Festooning systems are an exceptionally valuable system when extensive electrification is required to accommodate numerous push button stations in a pendant control suspended from the crane hoist.

The systems are also extremely effective in high moisture areas or where chemical fumes are present. Festooning may be the only type of electrification that can be used for these applications.  Festoon systems are not recommended for long runways and are generally used for travel lengths limited to 60 feet. Also, festooning wire suspended from a small track and trolley system can be extended for usage up to 150 feet.

 

Bare Wire Electrification

The most popular system presently on older bridge cranes is bare, hard drawn, copper wire although it is rarely provided today on new equipment. Local electrician codes prohibit their use except under specific conditions.  These systems are installed by a number of hard drawn solid copper or aluminum wires being stretched along the sides of the crane track or under the roof beams and held in place by insulated hangars. This system can only be insulated on straight runs.

For special applications where it is possible to isolate equipment and personnel from electrical lines or when extreme temperatures prevent the use of insulated types of electrification, bare wire can offer an excellent means of bringing power to the equipment.  These bare wires do present a very dangerous safety hazard for service personnel working on equipment or where metal bars, ladders, scaffolding  or other obstructions may come in contact with the lines.

 

Different Kinds of Electricification

Cord Reels are a very popular method of electrification systems for the smaller capacity hoists and cranes. They offer an inexpensive method of bringing power to moving equipment and most models permit installation in the center of the track to double the effective length of the cord reel cable travel.  Special reels are available for extreme lengths up to 500 feet or more and may be the only type of electrification for outside installation of Gantry cranes where standard overhead electrification systems have no method of support.

Large capacity reels with high amperage ratings, long lengths, or reels with many collector rings may be as expensive as more efficient conventional insulated conductor bar systems. Larger systems should be closely evaluated before choosing this type of electrification.  Contrary to popular usage, cord reels may not be desirable for light weight electric hoists mounted on push type trolleys. The spring tension of the reel can pull the hoist back, even with light loads. Moving the hoist on the track can also be a struggle against the pull of the reel, particularly when the cable is near its extended length.

 

Monorail Systems

Monorail systems allow exceptional versatility for in-plant handling from simple straight beams to complex curved and interlocking track configurations that can connect many shop and manufacturing areas together. The more complex systems are available with literally hundreds of options and require a study of your plant to best determine a design which will obtain optimum productivity in your application.

I-Beam System:

I-Beam systems are quite practical and relatively inexpensive for low production and simple plant layouts. Often a simple monorail beam will meet your lifting needs without going into the cost of a full area coverage crane system.

I-Beam systems are normally not used for curved and interlocking track applications. The primary advantage of an I-Beam versus Patent Track is the initial cost.

In high usage areas, the soft metal of the I-Beam lower flange will “peen-over” from the highly concentrated trolley wheel loads, resulting in difficulty in moving the trolley and eventually require replacement of the trolley and tracks.

Patent Track System:

Patent Track on the other hand, has precision hardened and ground flanges. Trolley wheels are individually suspended on articulating trunnions which assure equal wheel loading and provide much less effort to move heavy loads. These systems are ideally suited for high production applications. They are also suited ideally for integrated installations which require a crane mounted hoist for full area coverage to align with an interlocking monorail beam and deliver parts to remote assembly or storage areas.

It is possible with a monorail system to move loads down halls, around corners, up inclines, and even vertically lift entire hoist, load, and rail section between floor levels.
To obtain maximum usage of your plant potential, monorails should be seriously evaluated to interface with crane and fork lift operations.

For questions concerning monorails, contact Crane-Tec or call us at 800-755-6378.

 

Crane Design

Very few machines exist in as wide a variety of designs as cranes. Before the crane is constructed, the manufacturer must consider the site where it will be used and the weight it will need to lift. In addition, cranes are often modified to suit the needs of the user. For this reason, it is not much of an exaggeration to say that no two cranes are exactly alike.

Cranes used for industrial purposes are generally designed to remain permanently in one location. These cranes often perform repetitive tasks that can be automated. An important type of industrial crane is the bridge crane. Traveling on tracks attached to two horizontal beams, known as a bridge, a trolley enables the movement of the bridge crane. Usually, the bridge itself can be moved along a pair of parallel rails, allowing the crane to reach a large, rectangular area. A bridge crane may also be designed so that one end of the bridge is supported by a central pivot while the other end moves on a circular rail, allowing a large, round area to be reached. An overhead traveling crane is a kind of bridge crane in which the rails are located high above the ground. Usually supported from the ceiling of a building, an overhead traveling crane has the advantage of causing no obstruction in the work area.

Cranes used in construction often perform a variety of tasks and must be controlled by highly skilled operators. Construction cranes are divided into mobile cranes and tower cranes:

Mobile cranes:

  •  Mounted on trucks or crawlers in order to travel from place to place. An articulating crane is a mobile crane in which there is a joint between two sections of the boom, allowing it to move in a way similar to a knuckle in a human finger. Articulating cranes are generally used to lift objects located a relatively short distance away, but with a wide range of motion. A telescoping crane is a mobile crane in which two or more sections of the boom can extend and retract, changing the length of the boom. Telescoping cranes are less versatile than articulating cranes, but are usually able to lift heavier objects located a greater distance away.

Tower Cranes:

  •  Used in the construction of tall buildings. They are installed when construction begins and dismantled when the building is completed. An external tower crane is installed outside the building. As the building increases in height, the crane is raised by lifting the upper part of the crane and adding a new section of tower beneath it. An internal tower crane is installed within the building. As the building increases in height, the crane is raised by lifting the base of the crane to a higher level within the building..

 

 

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.

History:

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.

Function

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.

Certification

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?

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.