Which Crane should you choose – Single Girder or Double Girder?

Hii..this post is about which crane should you choose either Single Girder or Double Girder?

A common misconception is that double girder cranes are more durable! Per the industry standards (CMMA/DIN/FEM), both single and double girder cranes are equally rigid, strong and durable. This is because single girder cranes use much stronger girders than double girder cranes. The difference between single and double girder cranes is the effective lifting height.

Generally, double girder cranes provide better lifting height. Single girder cranes cost less in many ways, only one cross girder is required, trolley is simpler, installation is quicker and runway beams cost less due to the lighter crane dead weight. The building costs are also lower. However, not every crane can be a single girder crane. Generally, if the crane is more than 15 ton or the span is more than 30m, a double girder crane is a better solution.

The advantages and limitations of Single / double girder cranes are as follows:

Single Girder Cranes

o Single girder bridge cranes generally have a maximum span between 20 and 50 feet with a
maximum lift of 15-50 feet.
o They can handle 1-15 tonnes with bridge speeds approaching a maximum of 200 feet per minute (fpm), trolley speeds of approximately 100 fpm, and hoist speeds ranging from 10-60 fpm.
o They are candidates for light to moderate service and are cost effective for use as a standby (infrequently used) crane.
o Single girder cranes reduce the total crane cost on crane components, runway structure and building.

Double Girder Cranes

o Double girder cranes are faster, with maximum bridge speeds, trolley speeds and hoist speeds approaching 350 fpm, 150 fpm, and 60 fpm, respectively.
o They are useful cranes for a variety of usage levels ranging from infrequent, intermittent use to continuous severe service. They can lift up to 100 tons.
o These can be utilized at any capacity where extremely high hook lift is required because the hook can be pulled up between the girders.
o They are also highly suitable where the crane needs to be fitted with walkways, crane lights, cabs, magnet cable reels or other special equipment.

TYPES OF ELECTRIC OVERHEAD CRANES - Part 2

Hii...we continued the last post that talk about overhead crane generally or basically..

There are various types of overhead cranes with many being highly specialized, but the great majority of installations fall into one of three categories:

a) Top running single girder bridge cranes,
b) Top running double girder bridge cranes and
c) Under-running single girder bridge cranes.

Electric Overhead Traveling (EOT) Cranes come in various types:

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 runway. These “legs” eliminate the supporting runway and column system and connect to end trucks which 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. The hoisting mechanism is similar to a single girder crane with a difference that the crane doesn’t have a movable bridge and the hoistingtrolley runs on a fixed girder. Monorail beams are usually I-beams (tapered beam flanges).

Ortie, see u next post..thanks.

General Overview - Overhead Crane Part 1

Cranes are industrial machines that are mainly used for materials movements in construction sites, production halls, assembly lines, storage areas, power stations and similar places. Their design features 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.

When selecting an electric overhead traveling crane, there are a number of requirements to be taken into account.

1) What specifications, codes or local regulations are applicable?
2) What crane capacity is required?
3) What is the required span?
4) What is the lift required by the hoist?
5) What will be the duty cycle (usage) of the crane?
6) What is the hoist weight? Do you need the use of a second hoist on the bridge crane?
7) What is the hook approach required?
8) What length of runway system is desired?
9) What factors need to be considered in the design of runway and building structure?
10) What will the operating environment be (dust, paint fumes, outdoor, etc)?
11) What are the necessary crane and trolley speeds?
12) What is the supply voltage/phases/amperage?
13) What control system is desired?
14) Is there existing cranes on the runway?

15) What safety considerations are to be followed?

16) Consider maintenance aspects of the crane.

17) Consider other accessories such as lights, warning horns, weigh scales, limit switches, etc.

But before we discuss further, you have need to know a general clarity of the terminology used in the overhead crane industry.

Ok..wait for the next post..see you!!

Factors To Consider When Purchasing A Crane 2010

Hello to my readers..

If you own a business in one of these industries, the choice of a crane is critical for the success and efficiency of your business. So, here are some important factors that you must take into account for buying a crane.

Types of Crane

To begin with, you must know the different types of cranes available in the market. You must decide whether you need a mobile or fixed crane. You must also learn about overhead cranes, gantry cranes, monorail cranes, material lifting cranes, heavy duty cranes and other options to decide which one suits your requirements.

Lifting Capacity

An important consideration while choosing a crane is the maximum weight lifting capacity specified by the manufacturer. Different applications require materials with different weights to be lifted. So, the crane you select must be capable of supporting the maximum weight to be lifted at your workplace. Make sure that you dont oversize the capacity of the crane purchased.

Usage Limit

Another deciding factor to buy one of the industrial cranes is the limit of its usage. You must know how many times the crane would be used per hour or per shift. Besides, you must also know the shifts per day and the days per week for which the crane would be used. This should help you choose the crane that withstands a particular usage limit.

Learn about Components

Cranes with different components are suitable for different working environments. So, you must take into account the components like mechanical components and electrical components. Besides, you must also learn about the motor controls and operator controls to ensure that the right crane is purchased.

Speeds and Distances

Learn about the speed with which the crane lifts a particular quantity of eight. At the same time, you must learn about the maximum height or horizontal distance that the crane can move. All these factors help you choose the suitable industrial cranes that add efficiency to your working style.

Maintenance Required

Finally, you must consider the maintenance required for different parts of the crane, including motors, gearboxes, bearings, wire ropes and so on. Ask for warranty from the seller of industrial cranes.

Taking all these things into consideration should help you invest money in right types of gantry cranes, heavy duty cranes or other cranes.

Ok, thats all for this post..
See u next post..

Avoiding Pitfalls In Crane Projects

You have a shiny new building with a shiny new crane and everything looks great. For some reason, though, the crane won’t clear the building columns, even though the contractor and the crane manufacturer are saying everything is to spec and it’s not their problem. Common sense says somebody is wrong and that somebody should have to pay (because it’s going to cost a bundle). Unfortunately in this case, there’s a giant crack in the building specs, and you’ve just fallen through it. This means that after all the arguing and legal costs, you’re still going to have to pay to get it fixed. If you’ve already fallen in this black hole, there’s not much you can do, but if you are about to embark on a new building with an overhead crane, this article will show you where the cracks are and suggest how to bridge them safely.

What Is Required?

The runway alignment specs—written by the Crane Manufacturers Association of America (CMAA) and adopted by the Metal Building Manufacturers Association (MBMA), the American Institute of Steel Construction (AISC), and the Association of Iron and Steel Engineers (AISE)— fill an entire page and take considerable time to interpret. A simplistic summary is that runways must be ±1⁄4 inch in a single bay and no more than ±3⁄8 inch over the full length of the runway.
These tolerances must be maintained in four ways: left/right, up/down, parallel to each other, and level in respect to each other. Figure 1 shows an actual AISC/ CMAA chart.



A second set of crane-related numbers to remember are the crane-to-building tolerances. CMAA and the Occupational Safety and Health Administration (OSHA) require that all moving
objects (the crane and hoist) must clear all stationary objects (the building) horizontally by 2 inches and clear all vertical objects (roof trusses, lights, pipes, etc.) by 3 inches. Although this meets the legal requirements, this author highly recommends the horizontal be increased to
4 inches and the vertical to 6 inches to allow for unforeseen problems.

Where’s the Villain?

As in a detective story, the first move is to round up the suspects. The problem can be found
in one of four areas:
1. Mill steel tolerances
2. Building steel fabrication tolerances
3. Building erection tolerances
4. Overhead crane runway tolerances (measuring and verification methods)

One big problem is that runways usually are built with building steel (wide flanges), fabricated
by building steel fabricators, and installed by building steel erectors, but runway steel is not building steel. In fact, building steel and runway steel are incompatible in the first three ways listed previously. Following is an illustration of just the first point—mill steel tolerances—but the other two items exhibit similar shortcomings. The mill tolerance for structural wide-flange
beams basically is 1⁄8 inch per 10 feet of length, although this oversimplifies the American
National Standards Institute (ANSI)/AISC specification somewhat (see Figure 2).


Therefore, in a common 30-foot bay, the wide-flange beam can have a sweep (horizontal bow) of 3⁄8 inch, which means that putting up this first piece of steel exceeds the acceptable CMAA/MBMA/AISC
runway tolerance already. To compound the problem, the opposing runway can have an equal (but opposite) sweep, doubling the problem.

Solutions

How should this seemingly simple problem be addressed? Three potential solutions exist:
1. Adjust the rail laterally in relation to the girder. Although this solution is the most commonly used, it is bad engineering practice and actually is prohibited by the AISC specifications.
The runway beam/girder is the wide-flange structural shape that supports the runway, while the rail (commonly American Society of Civil Engineers (ASCE) rail, similar to railroad rail) is the track upon which the end truck wheels traverse (see Figure 3). It is a common misconception that the runway beams have no particular installation tolerance and that only the rail is at issue. Further, this assumption seems to be confirmed by the lateral adjustment of the rail fasteners (for example, Jbolts/ hook bolts or patented clips). Actually, the tolerance of the beam installation is governed by the tolerance of the rail installation. This is because, according to AISC Design Guide 7, paragraph 19a, the centerline of the rail should be within ±3⁄4 inch of the girder web thickness. This prevents top flange rollover and subsequent fillet cracking and possibly girder failure.

This conventional wisdom is so commonly accepted that it has evolved into generally accepted practice. Unfortunately, like so much conventional wisdom, it’s wrong, it’s bad for the equipment, it will result in significantly shorter service life, and it can be dangerous.

2. Augment the specs. Just because the generally accepted specs have left the crane runways as an orphan does not mean that you as a prospective new building owner should not include a stop-gap page of specs to cover yourself. If you buy the steel from the same vendor, fabricate
with the same fabricator, and install with the same installation crew, you very likely will end up with the same problem. It defies reason that any efficient contractor can buy, fabricate, and install 20+ pieces of apparently identical red primed steel to a tolerance two to four times tighter than the other several thousand pieces of red steel in that same building. This is not meant to slight building contractors.
Successful contractors have set up a well-disciplined system to produce and install building steel, but runway steel, although similar-looking, is a significantly different animal. While it is unlikely the contractor would adopt this more stringent standard temporarily, it is not impossible.
The silver lining for you, the buyer, in using the augmented specs as part of the contract is that the corrections no longer are your problem or expense.

3. Redefine the scope of building contractor and crane supplier responsibilities. This technically
correct, practically viable solution is the least used of the three, simply because of lack of knowledge and higher up-front costs. The common scope of the crane builder’s contract is to supply and install the crane, runway rail, and conductor bar. This leaves a critical gap in which the buyer is exposed to the previously mentioned problems. The scope should be changed to move responsibility for the runway girders from the building contractor to the
crane builder. Chances are, the crane builder will insist on very tight tolerances from the steel supplier and will take precautions to account for reasonable floor and column tolerances. Also, having the crane builder’s employees install the runways can help to improve installation accuracy because this job is their specialty. If the plant is a union plant, however, the runway conductor bar installation should be awarded to a local electrical contractor, while the crane builder remains responsible for the bar.

Get It Right the First Time

In summary, runway steel is not building steel. Poor runways will result in premature wheel failure, motor and or gearbox failure, and premature runway replacement. With a typical wheel replacement costing $8,000 and new runways costing $50,000 or more, not to mention downtime, getting it right the first time can be a real bargain. Using augmented overhead crane runway specs in conjunction with the information provided here can help you to stay out of court and maintain good relations with valuable vendors.

Overhead Crane - General

There are many types of overhead cranes, all of which can pose hazards if they are not used properly and with adequate safety precautions. Strict guidelines and safety regulations are published by OSHA (US Department of Labor's Occupational Safety & Health Administration Department). By adhering to these standards and rules, you protect your company from some of the injuries and lawsuits that can be served against companies requiring employees to operate heavy machinery.

Some of OSHA's laws on crane design and manufacture govern the following things.
1-Uniform crane control design and manufacture
2-Trolley and bridge bumper design
3-Stairway and ladder design
4-Trolley and bridge brakes
5-Design and manufacture of electrical components
6-Hoisting equipment design and manufacture

There are several basic types of overhead cranes. OSHA's laws and regulations apply to the following cranes.
1-Cantilever gantry
2-Gantry
3-Semi-gantry
4-Storage bridge
5-Wall

All of these require using the appropriate overhead crane parts for all repairs, as substitutions may result in accidents or defective operation of the machinery.

If you or your employees will be operating cranes and other heavy machinery, here are some safety tips to remember.
1-Cranes should only be used and operated by designated persons.
2-If a crane has been installed since 1971, it must meet all OSHA specifications.
3-An equipment manufacturer or engineer must inspect any crane that has been altered to change its load capacity.
4-You must have a cleared walkway on the side of the crane and above it.
5-You must clearly mark the load capacity of a crane so that everyone who might operate it can see it.
6-If a crane has two or more hoists, you have to clearly mark the load capacity of each hoist so that everyone who might operate it can see it.

Concrete Formwork - Structural Engineer

The concrete is required to be poured for curing and formation of the desired shape. The general techniques used for formwork are roadform that is a permanent arrangement of shuttering, and timber shuttering that is a customized temporary structure.

Concrete Formwork Basics

Concrete needs to be poured into an enclosed space and remain there until it adequately consolidates to maintain its shape. Concrete that has been poured newly for concrete slabs can be preserved in shape by existing features like walls and edgings. Alternatively, provisional shuttering, which is also called formwork, could be necessary. On vertical structures, formwork construction can be difficult and is therefore usually carried out by professional formwork erectors. However, slab work at ground level is usually less difficult and needs only a simple formwork. In all the cases, whether vertical structures or work at the ground, the formwork should be strong. It must be able to bear the forces produced by the wet concrete, including the weight of the vibration producing equipment. The formwork joints must be fastened adequately and prevent the mix leak during the vibration and curing. The primary formwork types being used for producing ground slabs are steel roadform and customized timber shuttering.

Roadform

Roadform, a permanent type of formwork used for poured concrete for housing and other structures is usually preferred for use since it is strong, capable of bearing different loads, and is a permanent arrangement. It can beconcrete formwork 1 used for construction work at different sites, involves a moderate skill to configure the necessary arrangement, and is inexpensive. It consists of steel sections that are channel-shaped, binding brackets, and an arrangement for the linking of adjacent sections. The units are stacked to create space for the required concrete depth. However, the maximum height is determined by the height of the steel pins that hold the system in its position. The steel pins are located with the bracket and forced into the ground. Each section is aligned accurately and held by tightening the fastening wedge. It is ensured that the roadform is firmly held in its place. Roadform is erected by aligning the sections with a rigid cord and by ensuring that the sections are accurate vertically. The pins should be firm with no gaps between the sections.

Timber Shuttering

Timber shuttering Roadform is only suitable for simple slabs. Timber shuttering, however, may be necessary for complicated work. The enormous benefit of the timber shuttering is that since it is created at the site, it can be customized to any desired configuration. Timber shuttering is the normal option for vertical concrete works. It is also used in combination with the steel elements. The shutter part in contact with concrete is called "form lining," while the supporting timbers are identified as "bracing." The bracings are created from timber that is straight, robust, and capable of bearing the desired loads. The form lining is generally some type of plywood or hardboard. Formwork is a professional trade, especially for the vertical structures. Bracing that is exceptionally intricate is designed by structural engineers.