Construction tower cranes are the focal points of jobsites throughout the world. They are the backbone and workhorses of most large construction sites. If they aren’t working; the jobsite isn’t working to it’s full capacity.
Most of the questions I’ve received from people in my life who aren’t in construction tend to focus on the subject of tower cranes. I get asked all of the time how are tower cranes erected? how does the operator get into the cab? How do they make the crane go higher in the building?
Despite their widespread usage people (even the workers on site) know very little about the machines that move us. We are going to answer some of the most basic questions as well as dive deeper.
What Is A Construction Tower Crane?
A construction tower crane is a common piece of lifting equipment found on construction sites. It is called a tower crane because of the large tower like structure the crane pivots around. The tower mast supports the jib and counter jib which in turns supports the cabling, trolley and hook which does the lifting.
Why Are Tower Cranes Used?
Tower cranes are used because they are efficient at lifting and moving heavy materials while having a relatively small footprint on site.
Tower cranes are great at lifting material and moving across long distances. Their reach allows them, in a lot of locations to have unencumbered access to the entire job site.
Why Use a Tower Crane Over A Mobile Crane?
Traditional mobile cranes require large setups at the ground level. If setup in the middle of a project this would have a large impact on the surrounding construction activities.
While the reach of the crane (jib and hook locations) are large the actual physical space a tower crane takes up on site is relatively small (think how small the tower is relative to the reach).
What Are The Different Types of Construction Tower Cranes?
By driving through a city like Toronto or New York you will quickly realize that tower cranes come in many different shapes and sizes. The different types of tower cranes are:
- Hammerhead Crane (Jib Type)
- Luffing Jib Tower Cranes (Jib Type)
- Derrick Cranes (Jib Type)
- Self Supporting Tower Cranes (Mast Type)
- Travelling Tower Cranes (Mast Type)
- Self Climbing Tower Cranes (Mast Type)
What is a Hammerhead Tower Crane?
A hammerhead tower crane is a common type of tower crane found on construction projects throughout the world. The hammerhead tower crane is recognizable through it’s vertical mast (tower) with a horizontal jib which supports both the cab. A trolley runs along the mast horizontally carrying the cable and hook. This allows the hook position to be in any position along the mast.
Luffing Jib Tower Crane
A luffing jib tower crane, often called just a luffing or luffer crane is another common type of construction tower crane. The crane is recognizable due to its diagonal arm which extends out from the top of the mast (tower) on an angle. Unlike the hammerhead the hook point is located off the end of the jib. The crane counter weights are located closer to the tower, when combined with the angled arm the luffing jib tower crane typically has a higher capacity then the hammerhead crane.
Unlike the hammerhead crane, the diagonal arm can move in and out (from vertical to a 30 degree angle). This movement allows them to fit within tight spaces which is why you often see luffing jib cranes within downtown urban environments.
Similar in nature to the luffing jib type you can think of Derrick cranes as their little brother. These cranes are unique in nature as their size is typically designed to sit on rooftops or small spaces. Derrick cranes are unique in nature because of their outriggers which allow them to sit on a surface.
They are assembled in pieces and are often used to either assemble or disassemble tower cranes. Derrick cranes are unique because often times they do not have a cab for an operator. Instead they are operated by remote control which is either wired or wireless.
Mast Type – Self Supporting Tower Cranes
A self supporting mast type is a typical tower crane that is put to use in shorter structures where tower extensions are not required. Self supporting tower cranes are anchored at the base with a weight or reinforced concrete block. Piles may be required to anchor the base to bed rock.
Self supporting tower cranes are anchored in place, have a tower extending out of the anchor point and they rotate around the tower. Considerations for the tower’s reach need to be made prior to installation as they cannot be moved easily once in place.
Mast Type – Travelling Tower Crane
A travelling tower crane is often used on projects which have a large footprint that require equipment be relocated regularly for lifting. A travelling tower crane is either track mounted or rail mounted. The tracks or rails allow the crane to travel horizontally along a path.
Depending upon the base or track design loads may or may not be able to be carried during the travelling period. If using this type of crane you need to ensure that you leave a path clear enough and flat enough on a project site to allow the crane to travel. If a path is not completely level and clear of debris you could risk the crane tipping over.
Mast Type – Self Climbing Tower Crane
Self climbing tower cranes are one of the most fascinating pieces of equipment that can be found on a construction site. A self climbing tower crane starts it’s life as with a typical self supporting tower crane. A tower is erected and anchored to a concrete reinforcing base.
As the building extends vertically the tower is anchored to the existing structure. When the building reaches a point where the crane will not clear the structure the crane then increases it’s height by inserting a piece of tower within the existing tower and “climbing” upwards.
The below video will help to explain the process of self erecting a tower crane.
What Are The Various Parts Of A Tower Crane?
Tower cranes are incredibly complex machines. When you look back to structures of the past it’s amazing the scale that we as a species were able to achieve without them. Today tower cranes allow us to reach new heights.
Tower cranes are broken into several different parts, each of which is crucial to the operation of the machine. There are hundreds of parts on a tower crane but the major parts on a tower crane can be broken down into the following:
- Base Support
- Tower (Mast)
- Operator’s Cab
- Jib and Counter Jib
- Trolley and Hook Block
The below is an illustration on the various parts of a tower crane.
The base support is the part of the tower crane that attaches the tower to the ground or surrounding structure. When a crane is attached to the ground this is typically done with reinforced concrete as well as piles to extend the support to bedrock. It’s important to engage an engineer to design this component of the tower.
The tower or mast of a tower crane is the vertical portion of the crane that extends upward from the ground. It’s purpose is to support the cab, mast, hook and counter weights as they rotate around it. Towers or masts are typically fabricated using a square lattice work of steel similar to an open web steel joist.
Tower Crane Operators Cab
The operators cab is where the crane operator sits in order to make the crane function. It is recognizable as a glass box on the side or underside of the mast. The cab is typically attached to a computer which feeds information to the operator and allows them to operate the crane with a pair of joysticks.
The tower crane turntable is the part of the crane that allows the jib and counter jib to spin on top of the mast. The mast is made up of two plates which insert inside of one another and rotates with bearings. The actual circular component that rotates is called a slewing bear ring – it’s a technology which is in use in windmills.
When a crane lifts a heavy object it needs a counter weight to balance the load of the lift. Without the counter weight in place the tower crane’s capacity would be significantly reduced. The counter weight is located on the opposite end of the jib as the hook. Counterweights are made from a variety of materials including reinforced concrete, steel and other heavy materials. Their weight is calculated based on what the capacity of the crane will be during it’s final use.
Jib and Counter Jib
The jib and counter jib are the most recognizable part of a tower crane. The jib and counter jib are the lattice work of steel that you see extending out horizontally from the top of the tower or mast. The purpose of the jib is to carry the trolley, cabling hook and load of the crane. The purpose of the counter jib is to offset the weight of the jib and hold the counter weights in place.
Trolley and Hook Block
The trolley and hook block to alot of the work on the crane. The trolley moves back and forth across the mast extending as needed to place the hook overtop of whatever load requires lifting. The hook block acts as a pulley system to go up and down depending upon how much cabling is released or pulled back into the spool. The hook block supports the hook which allows loads to be attached to the crane.
With all of the above components being made up of hundreds of parts it’s not hard to see why there are companies that are dedicated to crane installation. Maintenance on the tower cranes is crucial.
How Are Construction Tower Cranes Erected?
One of the most common questions I get asked by family members is how are tower cranes erected. When a crane is in place it’s a massive machine so it can be hard to comprehend how this piece of equipment made it into place.
Like a jigsaw puzzle a tower crane is erected in pieces. The various components are delivered on transport trucks one at a time and assembled utilizing a mobile crane. The tower is first constructed, followed by the turn table and cab, then the jib and counter jib are hoisted and attached. Lastly the counterweights and cables are installed to complete the erection.
The process of erecting a tower crane can take many hours and sometimes days depending upon the location and size. For this reason the erection of a tower crane typically requires shutting down adjacent streets if in a tight urban environment.
Below is a video which shows how a typical tower crane is erected:
How Are Tower Cranes Dismantled?
More then how are tower cranes erected, I get asked how these monster machines get removed? Seeing a tower crane on top of a 50 floor tower it’s hard to imagine how someone would begin to safely remove one. Yet, the construction industry has come up with some incredibly creative ways to remove a tower crane.
Tower cranes are traditionally removed by other cranes. Component are taken apart one piece at a time starting with the hook, cables and counterweight which is followed closely by the jib, cab and tower. In general there are two types of cranes used for removal of a tower crane:
- Mobile Crane
- Derrick cranes
Mobile Crane Tower Crane Removal
If your site allows a mobile crane can be utilized to remove a tower crane from your site. In this situation a mobile crane is brought in and set up close to the base of the crane. The mobile crane takes the crane apart one piece at a time. The mobile crane hooks onto a piece and workers remove the fasteners allowing it to be freed and lowered to the ground.
This technique is typically used in low or mid-rise construction though some mobile cranes have a reach of hundreds of feet and can be used on lower high rise construction.
If a tower crane is out of reach from mobile cranes then Derrick cranes need to be utilized in order to remove it. Because some derrick cranes are too large to be brought up in an elevator typically a progressively small set of derrick cranes are used with the largest being used to remove the tower crane. The next smallest then removes the large derrick, and another smaller one removes that derrick. This goes on until the parts can be lowered to the ground using either an elevator or electric hoist.
While this method can take longer it also has less impact on the surrounding site as a large mobile crane does not need to be brought in. This method is fascinating to watch. Below is a video showing the progressive removal of a tower crane using derricks:
In areas where flight paths are not a concerned another method that can be used to take apart a tower crane are helicopters. These represent a challenge in high rise settings as a result they are rare to see.
Things To Consider When Deciding On A Tower Crane
If you’re planning a tower crane on your project site it’s important to take a number of key factors into consideration. The key considerations to take into account when planning for a tower crane are:
- Capacity Required
- Space availability (Surrounding structures and infrastructure)
- Pick Locations
- Flight Paths
- Installation and Removal
Depending upon what your tower crane will be used for you may require a different model or design. If your crane will be lifting things like formwork and buckets of concrete your crane will be a relatively light model. However, if you need your crane to lift equipment such as a generator or large steel members you may need to reconsider.
Cranes have typical lifts and lifts that are designed as critical. Critical lifts are typically those that are within 10% of the cranes total capacity. These lifts require special engineering. If you only have one heavy lift on the project it may be worthwhile to engineer your crane to accommodate all other loads except the one and have it engineered as a critical lift. Your other alternative could be to bring in a mobile crane to complete the lift.
This one is critical. Noone wants to put up a tower crane only to find out that it can’t travel where they wanted it to. It’s important when planning your tower crane location that it’s not being impacted by surrounding buildings. If it is and there’s not much you can do about it having procedures in place to ensure it doesn’t hit them is equally important.
Try to plan your crane location away from structures and critical infrastructure such as overhead power lines.
If your tower crane is located near sidewalks or a public roadway be aware that overhead protection or special procedures may be required to protect the public.
In instancing where more then one tower crane is on site the swing radius of each crane should be considered. Optimizing the area of each lift to provide the most coverage while not hitting the other cranes towers while rotating.
Why put up a tower crane if it’s lowest capacity is at your loading dock? Planning your pick locations around your tower crane OR planning your tower crane around your pick locations is important. Loading docks are important – they help material come into and out of your jobsite. Cranes get weaker the further the load is from the mast – plan your crane close to these locations to maximize the capacity of your crane.
While most people wouldn’t be concerned about planes flying into tower cranes aviation authorities typically are. If your crane is located within a certain distance to an airport it may require a special permit and restrictions on it’s operating time / height. Review with your local flight authority to ensure that you take out the proper paper work prior to erecting your crane.
Installation and Removal
As I noted above, the installation and removal can be a very intensive process requiring large pieces of equipment. While planning out your crane location it’s important to consider this. You don’t want to put your crane in a location that will make it challenging to get off the site. This could delay your finishing phases.
If you have more then one tower crane on site, it may be worth sequencing the removal and installation to allow one or two of the cranes to remove or install the others. This will save time and allow areas of your building to be finished in advance of the complete crane removal.
Who Operates A Tower Crane?
A tower cranes operation is not just a one man job. Picking materials is a team job which requires both an operator, a swamper or lift director and a rigging crew.
The operator’s job is to run the crane from the cab. They are responsible for the movement and lifting operations of the crane. When lifting loads are typically out of vision from the operators direct line of sight. Cameras are used but they must also rely on their swamper or lift director.
The swamper or lift directors job is to supervise the lifting from the ground. They typically have direct communication with the operator via radio. They’re role is to ensure the load is safely attached and within the capacity of the crane. They are also responsible to ensure that the path of travel is clear for the operator.
The rigging crew are the team that actually attaches the load to the hook of the crane. They are responsible for safely tethering the load and ensuring it is safely attached to the crane.
Together this group of individuals is essential to the operation of the construction site.
Tower Cranes Future In Construction
Tower cranes have and will continue to be the work horses of the construction industry. They have allowed us to reach new heights building higher and faster then we ever dreamed. Construction companies will continue to rely on them due to the minimal space required on a construction site and their versatility when it comes to lifting things.
Have you used a tower crane on your construction site? Let me know below in the comments and share some of the success stories or tips you have.