Tower Cranes: A Closer Look

Tower Cranes: A Closer Look
1/15/2017 1:38:47 PM
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Anatomy of the Tower Crane Elevator

Tower cranes are fascinating. The size of these cranes makes them a visual spectacle in the sky, and their T-shape appears impossible to maintain. They can be assembled and disassembled very quickly, leaving many people wondering what goes into building them in the first place.

Perhaps the most interesting piece of the tower crane is its elevator. It lies within the central fixture of the tower crane and hoists up the operators of to extreme heights.

Tower Crane elevatorsThe tower crane itself is built on a concrete base. The tower that springs is often the future elevator shaft of the building being constructed. This allows construction workers to operate around the elevator shaft while simultaneously building upwards, growing the structure around the elevator.

These crane structures are created by stacking cube-shaped steel structures atop one another with a smaller, lower crane. They are placed in one at a time and then bolted in. The resulting structure is sturdy, durable, and able to support the crane as well as the crane elevator. When construction is finished, it is also easily deconstructed, one cube piece at a time.

The elevator itself is often powered by an electrical power source. Much like a typical elevator, a tower crane elevator can hoist a significant amount of weight.

Advantages to a Tower Crane Elevator

Avoiding Dangers: Construction, while essential to developing the infrastructure of the United States, is an extremely dangerous job. 828 construction workers lost their lives on the job in 2013, which is more than two every day. According to the Occupational Safety & Health Administration, falls accounted for 302 of these deaths, or 36.5%. Falls are known as one of the "Fatal Four” ways that over half of construction workers die, along with being hit by an object, shocked by electricity, or crushed or caught in a deadly position.

Enhancing Safety: With this in mind, the safety of construction is of the utmost importance, especially when placing workers at great heights. That is why the tower crane elevator serves such an important purpose: It safely delivers the operator to the top of the tower without the need for them to climb most (if not all) of the exterior ladder—a dangerous activity which is often performed without a harness.

Adding Convenience: Modern tower crane elevators are now more convenient than ever. Companies now specialize in making a variety of tower crane elevators in order to best suit the size, weight, and length of time for various tasks. In addition, they come in a variety of speeds, ranging from 21 meters per minute to 40 meters per minute.

Abiding Law: Around the world, new laws are being passed in order to ensure the safety of construction rulers. As an initiative that started in France and that is now spreading throughout the rest of Europe, it is a requirement that tower crane elevators must be utilized if the operator must climb more than sixty meters in order to get to his post. In 2017, that number will be reduced to 30 meters.

What it’s Like Inside a Tower Crane Elevator

For a video example of what’s it’s like to be inside a tower crane elevator that goes up nearly 300 feet, check out this YouTube video:




Tower Cranes: A Closer Look

Much of the information here originally appeared at CraneCrews.com. To read the original article, click here.


Tower cranes lift heavy loads efficiently and safely and can be found on almost every major construction site in America.

Let's look at the components of these incredible machines.


Jib

tower crane jib

​The jib extends horizontally at various lengths depending on the model and configuration of the crane. Hoist and trolley lines run throughout the jib enabling vertical and horizontal movement of the load. Rotation of the jib is achieved by employing the "slewing" action.


Trolley

tower crane trolley

A trolley attached to the underside of the jib moves loads in and out from the crane's center axis. Powering the trolley is the trolley drive mounted on the horizontal jib. A cable from the trolley drive runs through the jib and is attached to the trolley. A trolley then controls the load's radial movement and helps stabilize the load.


Hook Block

tower crane hook block

The hook block allows the free rotation and positioning of a load. A hook or hoist is attached to the hook block assembly. Hook block assemblies house a series of sheaves and pulleys that carry the rope. The block provides greater flexibility and facilitates the lifting of a load. The shape and weight of the hook block can make a big difference in how the hook moves and will affect how much swing the hook will have when moving.

 

Counter Jib

A crane's drives, drums, gears, electronics, and counter-weights are found on the counter-jib platform. Located behind the operator cab, the counter-jib provides a balancing force to the load on the horizontal jib. Drives, drums and electronics are located to the rear of the counter-jib to maximize torque and to make maintenance easier.


Counterweights

It's important to balance the forces on the crane caused by the load. This is a primary function of the counterweight. Counterweights are fabricated from concrete and come in modular units. The number of counterweights depends on the expected max load capacity, jib length and tower height.

 

Hoist Unit

The hoist unit houses the hoist drum, gear box, gear shift, brake, and supporting components. Typical placement is behind the counterweights, toward the extreme rear of the counter-jib. Placing all hoist and trolley components in one location makes for efficient servicing of the crane.

 

Hoist Drum

A component of the hoist unit that lifts and lowers a load by means of the hoist line. Power to the drum is supplied by the hoist drive. The hoist drum winds the rope or cable in a specific cross-pattern to avoid entanglement of the line.

 

Tower Top / A-frame

Hammerhead or "high-top" cranes use a tower top section for greater torque and stability. Pendant bars are attached from the tower top to the jib and counter-jib that provides further stability. Anemometers and aircraft-warning lamps are placed on the top of the tower.

 

Pendant Bars

Pendant bars provide additional stability to the crane. The bars are attached from the tower top to the jib and counter-jib. Flat top tower cranes eliminate the need for pendant bars and a frame by making the crane jib larger and thus stronger.

 

Trolley and Hoist Lines

Loads are moved up and down by the hoist line and in and out by the trolley line. These lines run throughout the horizontal jib, counter-jib and tower top through a series of pulleys and guides. The trolley line is connected to the trolley unit and the hoist line is connected to the hook block.

 

Slewing Assembly

The jib, counter-jib, tower top, and slewing assembly collectively make up the slewing unit. This section allows the crane to rotate and perform lifting.

 

 

Operator Cabin

tower crane cab

The movement of the crane is controlled from the operator's cabin. Within the cabin you’ll find the operator’s chair with joystick controls, electronic monitoring devices and communication systems. Many cabins come with climate control to ensure a comfortable work environment. The operator cab is part of the slewing assembly.

 

Slewing Ring

The slew ring drives the rotational movement of the slewing unit (jib, counter-jib, cab, and tower top). Powered by the slewing gear drive, the slew ring is fixed to a ball track and is made up of several hundred precisely machined gear teeth. The slewing ring is capable of enormous torque, yet precise movement.

 

Top Climbing Unit

tower crane climbing unit

The top climbing unit is an essential piece of any tower crane. It enables tower crane sections to be inserted and connected to the tower. A large hydraulic jack then lifts the Slewing Assembly, Jib, and Counterjib one tower section higher. Another section can then be inserted. The top climbing unit adds tower sections to the tower crane; the bottom climbing unit keeps the tower at the same height but raises the whole crane up, repositioning it at a higher point inside the building.

 

Bottom Climbing Unit


Climbing inside buildings is made possible by the bottom climbing unit. Climbing collars are used with a hydraulic power pack to lift the tower sections upward. The crane is completely supported by the structure of the building it is constructing. This leaves the lower levels of a building accessible for finish work.

 

Bolts and Pins

Secure connections are an essential component of any tower crane. Anchor bolts must be of high tensile strength and pins and other bolts should be routinely re-torqued according to manufacturer specifications.

 

Tie-in

A tie-in secures the tower mast to a structure or framework and provides stability when the crane is under load or experiencing wind forces. The number of tie anchors are calculated by taking into account such factors as the type of crane, jib length, height under hook, and maximum out-of-service wind speed.

 

 

Undercarriage

tower crane undercarriage

Also known as a the static base, this is used so you do not have to excavate and build a concrete in-ground base, which would take up more room and require quite a lot of counterweight. The undercarriage of the crane acts as a base for the tower mast and surrounding lower structure.

 

 

Knee Brace

The knee brace makes up the undercarriage truss, spreading the weight of the crane out to the small corner pad foundations.

 

 

Central Ballast

Central ballasts stabilize the tower crane. Ballasts are made of concrete and come in modular sections that are stacked above the cross frame.

 

 

Cross Frame

The cross frame is a square section that connects to the bogies and knee braces as an integral part of the base structure of the crane.

 

 

Bogies/Pads

tower crane bogies

Bogies are used for moving the crane on rails to allow the crane to cover more job site area. Rail-mounted cranes use electric-driven bogies, so the operator in the top of the crane can control the drive on the rail at the bottom of the crane. Stationary cranes can use corner plates and economical corner pads under the undercarriage.


Foundation Anchors

Foundation anchors are steel posts embedded in reinforced concrete bolted to the tower. These anchors provide a secure connection that prevents the tower crane from swaying or experiencing structural failure due to overload and wind forces.

 

Tower Sections

tower crane tower sections

A crane’s tower mast is constructed of a series of tower crane sections, each one reinforced by a braced square or truss. Sections are bolted together as the tower crane is erected. Access ladders in the interior of each section allow workers to move up and down the crane.

 

Tower Cranes: Considerations, Problems and Solutions

Tower cranes are ubiquitous in the world of construction, with well over 100,000 operating at any given time.

Despite their widespread use, these cranes pose several problems for the construction industry.

Tower Cranes over the treeline

Here are just a few of their problems and solutions:

Costs vs Savings

Tower cranes are expensive, but when used properly, they can save contractors 50% of their material-handling budget. When compared to mobile cranes, a popular alternative, tower cranes offer a significantly wider radius and easier, compact placement.

For contractors who cannot afford a tower crane, these cranes are also available to rent.

Operation & Safety

Tower cranes regularly come under scrutiny due to their large size, perch, and prominence in the construction field. This scrutiny is especially heightened after accidents and other incidences. Many of these situations typically involve equipment defects, and inadequately-trained crane service personnel or operators.

Scrutiny needs to be handled proactively through safe, and informed operational procedures, like having an extra man on hand to avoid tower crane collisions when more than one crane is present. Another preventative safety measure mandates crane service personnel be properly trained to recognize defects, damage, and other hazardous potentialities.

Anchoring & Training

Most all cranes are heavy, but tower cranes are specifically top heavy. This top-heavy structure requires precise, strong, and well-maintained anchoring to a steady foundation. In order to keep this anchoring secure, the crane operator must be well-trained and experienced, as jerk movements, side and shock loading, fast swinging, and abrupt stopping can all cause the crane, anchor, and concrete to prematurely wear due to stress.

Inadequate operator training is a major cause of tower crane accidents, especially in relation to machine wear. An additional cause is crane operators’ misunderstanding of proper operating procedures when it comes to load-stability elements, like weather conditions, surface areas, and load size. Due to this scant knowledge, these crane operators may not know whether a foreman is giving accurate or inaccurate instruction. All of these elements result in higher accident rates.

However, operator training isn't the only form of education necessary to maintain and preserve the life cycle, and safety, of tower crane equipment. Crane service technicians should also be taken into account. An improperly trained crane service tech won't be able to spot important defects, or the potentiality of crane and anchor wear, which can all lead to future accidents. This makes training a top priority for contractors who utilize tower cranes.

Repair & Maintenance

Crane service maintenance and repair are often looked at as a troublesome expense, when it should be considered a cost saver. If you've ever had a tower crane break down, or been involved in an accident, then you understand why. Finding fully-trained technicians who have the knowledge to spot defects before they happen, who know which tools to use, and who can properly inspect their own welds, is much easier said than done.

That's where Larry Collier Crane Parts & Service come in. Our ability to provide fully-trained, ready-to-go crane service technicians can help you troubleshoot problems, increase uptime, reduce accidents, and extend the life-cycle of your mobile cranes.Call us for your tower crane needs, too, and we'll provide a referral.

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