Overview of Electric Overhead Traveling (EOT) Cranes


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Overview of Electric Overhead Traveling (EOT) Cranes
Course No: D06-003 Credit: 6 PDH
A. Bhatia
Continuing Education and Development, Inc. 22 Stonewall Court Woodcliff Lake, NJ 07677 P: (877) 322-5800 [email protected]

OVERVIEW OF
ELECTRIC OVERHEAD TRAVELING (EOT) CRANES

CONTENTS PART – 1: General Overview
 Introduction  Type of Overhead Cranes  Components of Bridge Crane  Essential Terminology when Specifying Overhead Cranes PART-2: Classification of Cranes  Crane Duty Groups  CMAA Service Classification  HMI/ASME Hoist Duty Ratings  FEM Service Classification  Comparison between different Standards  Crane Speeds PART-3: Hoists  Hoists Types  Hoists Lifting Media – Chains or Ropes  Hoist Selection Factors  Components of Hoisting Equipment  Safety Features  Hoist Standards PART-4: Structural Design Considerations  Crane Runway  Crane Loads on the Runway Girder  Design of Crane Runway Girder  Typical Profile of Crane Girder  Crane Runway Girder and the Building Structure

 Crane Rails, Stops and Bumpers PART-5: Crane Electrification & Power Supply
 Methods of Crane Electrification  Bridge and Runway Electrification  Festoon Systems  Motors and Controllers  Enclosures – NEMA Standards  Electrical Grounding  Control Systems PART-6: Design Specifications  Specifications and Codes  Structural Requirements  Mechanical Requirements  Electrical & Control Requirements PART-7: Inspection & Testing Requirements  Key Crane Inspection Areas  OSHA Inspection Requirements  Testing Requirements Appendix – A: KEY WORDS AND DEFINITIONS Appendix – B: STEEL BUILDING USING CRANE – GLOSSARY OF TERMS Appendix – C: INTERNATIONAL CODES, STANDARDS AND REGULATIONS

PART – 1

GENERAL OVERVIEW

In this section we will discuss the following:

 Introduction

 Type of Overhead Cranes

 Basic Crane Components

 Essential Terminology when Specifying Overhead Cranes

Introduction
A crane is a machine that is capable of raising and lowering heavy objects and moving the objects from one place to other. An overhead crane usually consists of three separate motions:
1. The first motion is the hoist, which raises and lowers the material.
2. The second is the trolley (cross travel), which allows the hoist to be positioned directly above the material for placement.
3. The third is the gantry or bridge motion (long travel), which allows the entire crane to be moved along the working area.
Cranes are distinguished from hoists, which can lift objects but cannot move them sideways.
The design of overhead cranes vary widely according to their major operational specifications such as: type of motion of the crane structure, weight and type of the load, location of the crane, geometric features, operating regimes and environmental conditions. Selecting the right type of overhead crane is critical to streamline workflow and maximize productivity. Many factors are taken into consideration which includes:
1. What bridge capacity is required?
2. How often is the crane to be used?
3. What span is required?
4. How long is the runway travel?

5. How high must the hoist lift? 6. Is the bridge going to be supported by the building, self-supported, or
both? 7. Is the bridge going to be indoors or outdoors? 8. How is the crane powered? All motorized push-pull, hand geared, or
combination? 9. If motorized, how fast? Single or dual speeds? Variable frequency drives? 10. What voltages are required? 11. What type of control? Pendant from hoist, separate track or remote
control? 12. Any special features? Cabs, walkways, horns, lights? 13. What specifications, codes or local regulations are applicable? We will address all these aspects in this course. TYPES OF ELECTRIC OVERHEAD CRANES
There are various types of overhead cranes with many being highly specialized, but the great majority of installations fall into one of four categories:
1. Single Girder Cranes - The crane consists of a single bridge girder supported on two end trucks. It has a trolley hoist mechanism that runs on the bottom flange of the bridge girder.
2. Double Girder Bridge Cranes - The crane consists of two bridge girders supported on two end trucks. The trolley runs on rails on the top of the bridge girders.
3. Gantry Cranes - These cranes are essentially the same as the regular overhead cranes except that the bridge for carrying the trolley or trolleys is rigidly supported on two or more legs running on fixed rails or other runways. These “legs” eliminate the supporting runway and column system and run on a rail either embedded in, or laid on top of the floor.
4. Monorail - For some applications such as production assembly line or service line, only a trolley hoist is required. This type of crane is designed

using I-beams like those found in ceiling structures of many factories. The trolleys run along the flat surface on the bottom horizontal bars of the beam. The hoisting mechanism is similar to a single girder crane with the difference that the crane doesn’t have a movable bridge and the hoisting trolley runs on a fixed girder.
Which Crane should you choose – Single Girder or Double Girder
Based on the CMAA (Crane Manufacturers Association of America) specifications, both single and double girder cranes are equally rigid, strong, and durable. The principle difference between single and double girder cranes is hook height (how far above the floor your hoist will lift). Double girder cranes typically allow 18-36 inches higher lift, because the hoist is placed between the cross girders rather than under them. Therefore, the depth of the cross girder is gained in switching to double girders.
Cost Considerations
Single girder cranes may cost less for several reasons:
 Only one girder is required
 The trolley is simpler
 Fright expenses are reduced
 Installation is faster
 Runway beams are lighter
However, not all cranes should be designed with a single girder. Generally, if the crane has to handle more than 15 ton or the span is more than 80 feet, a double girder crane is a preferred option. Double girder cranes are also highly suitable where the crane needs to be fitted with walkways, cabs, magnet cable reels or other special equipment.
The Crane Manufacturers Association of America (CMAA) is pretty much the head kahuna of the US crane industry. Every reputable crane builder conforms to CMAA Spec 70 (for double girder cranes) or CMAA Spec 74 (for single girder cranes).

Crane Configurations
1. Under Running (U/R)
2. Top Running (T/R) Under running cranes
Under running or under slung cranes are supported by using a suspension type support which is connected to the bottom of the frame. The crane wheels are supported from the bottom of flange of the crane beams which act as a crane rail and usually only span a portion of the column-to-column span of the structure. Under running cranes are typically available in standard capacities up to 10 tons (special configurations up to 25 tons and over 90 ft spans). Under hung cranes offer excellent side approaches, close headroom and can be supported on runways hung from existing building members if adequate.
The under running crane offers the following advantages:
 Very small trolley approach dimensions meaning maximum utilization of the building's width and height.
 The possibility of using the existing ceiling girder for securing the crane track.
The following are some limitations to under running cranes:
 Hook Height - Due to the location of the runway beams, hook height is reduced
 Roof Load - The load being applied to the roof is greater than that of a top running crane
 Flange Loading - Lower flange loading of runway beams require careful sizing; otherwise, you can "peel" the flanges off the beam

Top Running Cranes
The crane bridge travels on top of rails mounted on a runway beam supported by either the building columns or columns specifically engineered for the crane. Top running canes are the most common form of crane design where the crane loads are transmitted to the building columns or free standing structure. These cranes have the greatest variation in capacity, span and service class and usually span the full width of the framing supports. These are available in both single girder and double girder configuration.

COMPONENTS OF BRIDGE CRANES The function of a crane is to move the lifted load horizontally and longitudinally in the building. The lifted load is usually supported with a hook which is cabled to a hoist. The hoist is supported by a trolley which moves horizontally along the crane bridge. The crane bridge is connected to a number of crane trucks at each end depending on the capacity and span. The crane trucks can have 2, 4 or 8 wheels based on the capacity of the crane. The wheels ride along a crane rail which is supported by runway beams. The figure below illustrates the basic crane components;
1. Bridge - The Bridge is the principal structural component of an overhead crane. It spans the width of the building and comprises one or more load bearing beams or girders. These may be fabricated steel box-girders or rolled-steel joists. The bridge carries the hoist trolley, which travels along the length of the girders during operation.

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Overview of Electric Overhead Traveling (EOT) Cranes