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Types of Jibs
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Today we will explore the different types of jibs used in tower cranes. To start, who can tell me what a luffing boom is?
Isn't it the one that can adjust its angle to go up or down?
Yeah, it helps when you don't need it to reach out far horizontally!
Exactly! Luffing booms are great for maximizing height. Now, what about the articulated jib?
That's the one that can reposition to convert horizontal reach into vertical height, right?
Correct! They allow great flexibility in operation but tend to be costlier. Remember: *Luffing is for angles, articulated is adaptable.*
Got it! So, luff to go up and articulated to adjust, that's easy to remember.
Great! Let's dive deeper into the erection process of these cranes.
Introduction & Overview
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Quick Overview
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In this section, we explore the installation of tower cranes, focusing on the erection process using climbing cages and articulated jibs. Key steps include foundation preparation, utilizing a mobile crane for initial setup, and the self-erection technique enabled by climbing cages. The importance of structural considerations and alternative crane types for tall structures is also highlighted.
Detailed
Installation Process
This section details the process involved in installing tower cranes, emphasizing the methods used for erecting these cranes efficiently. Tower cranes are crucial for construction projects, and understanding their installation is essential for ensuring safety and effectiveness.
Key Types of Jibs
- Luffing Boom: A jib type that can adjust its angle to allow cranes to ascend vertically rather than horizontally when excess reach is not required.
- Articulated Jib: A more sophisticated jib that allows enhanced manipulation of height and reach by repositioning hinged sections to convert horizontal reach into vertical height, albeit at a higher cost.
Erection Process
Step by Step:
- Foundation Preparation: A heavy foundation is constructed with reinforcement to ensure stability, which is crucial for supporting the tower crane.
- Initial Assembly with Mobile Crane: The first sections of the tower crane are lifted into place using a mobile crane. This includes setting up the turntable, operator cab, and slewing ring.
- Utilizing the Climbing Cage: Once initial sections are erected, a climbing cage allows for further self-erection without the need for additional cranes:
- A hydraulic jack raises the turntable to create space for introducing new sections.
- New sections are added sequentially, bolted to the existing structure.
- Dismantling Process: When the crane is no longer needed, it can be dismantled in reverse order, highlighting the efficiency of using a climbing cage.
- Height Limitations: A maximum height of 60 to 120 meters is mentioned for free-standing cranes, beyond which additional supports are required. Special climbing tower cranes can be used for buildings exceeding this height.
- Structural Considerations: Special attention needs to be paid to stability and support when designing buildings that will accommodate climbing cranes.
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Articulated Jib Cranes
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There is another type of jib apart from the horizontal boom, luffing boom. You also have this articulated jib tower crane. You can see the picture. These articulated jib cranes are able to reposition their hinged jibs to convert the excess hook ridge to added hook height. You can reposition the jib in such a way that whenever you do not need excess horizontal reach, you can convert the horizontal reach into vertical height. These articulated jibs are costlier cranes.
Detailed Explanation
Articulated jib cranes are a type of crane that offers flexibility in how they can reach their target height. Unlike traditional cranes that may only extend horizontally, articulated jib cranes can adjust their jibs (the arms) to maximize vertical height as needed. This means if a project requires less horizontal reach, the crane can be adjusted to use that reach for lifting higher, allowing for increased productivity on a construction site. However, it's important to note that because of their advanced technology and versatility, articulated jib cranes tend to be more expensive than standard jib cranes.
Examples & Analogies
Imagine a robotic arm in a manufacturing plant that can pivot, reach, and extend in various directions. Just like this arm can adjust to grab items from different heights and angles, articulated jib cranes can modify their reach to best suit the lifting task at hand, allowing construction workers to manage their operations more efficiently.
Erection of the Tower Crane with Climbing Cage
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Now, let us see how the erection of the tower crane is done with climbing cage. In modern tower cranes, we have this climbing cage facility which facilitates the self-erection process of the crane. First, you have to prepare the foundation for the tower crane according to the requirement, put heavy reinforcement, and then bolt the tower sections to the foundation after construction of the first few sections of the tower crane. Then you erect your turntable or slewing ring, operator cap, and the tower top, with the help of another mobile crane.
Detailed Explanation
The erection of a tower crane begins with preparing a strong foundation that can support the structure's weight. This includes using heavy reinforcements and bolting the initial tower sections to that foundation. After establishing the foundation, additional components like the turntable, which allows the crane to swivel, and the operator’s cap are lifted into place using a mobile crane. This stage is crucial as it sets the basis for further construction and lifting capabilities of the tower crane.
Examples & Analogies
Think of building a house starting with a strong foundation. Just as the house needs a solid base to support its walls and roof, a tower crane needs a well-constructed foundation to hold its weight and equipment securely in place. Without this foundational work, the crane can’t function effectively or safely.
Counterweights and Final Stabilization
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Now, you put the counter jib with a few counterweights. First, you put a few counterweights, then slowly increase the jib portion. As you increase the jib portion sections, you can increase the number of counterweight blocks. When this is done, till this, you need the support of another mobile crane. After this, you can do the erection process yourself with the climbing cage help without the help of another crane.
Detailed Explanation
The counter jib is added to the crane to balance the load from the operational jib. This is achieved by gradually increasing the number of counterweights as the jib (the arm used to lift loads) lengthens. Initially, the assistance of a mobile crane is required to manage these parts, but once stabilized, the process can continue with just the climbing cage, indicating the crane’s self-sufficiency in further erecting itself.
Examples & Analogies
Consider the balance needed when lifting weights in the gym. If you lift weights on one side without balancing the other side, you will tip over. Similarly, the crane uses counterweights to ensure stability while lifting heavy materials, adjusting to maintain balance just like a weightlifter adjusting their stance to lift safely.
Self-Erection Procedure
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Once this is done, then you can do the self-erection of the tower crane. First, you have to introduce a new section to increase the height of the tower crane with the help of trolley action. By the trolling action, you can bring the new section closer to the tower with the trolling action. Now, what you do is unbolt your turntable base, lift it with the hydraulic jack in the climbing cage, create space to introduce a new section, and bolt the new section to the turntable.
Detailed Explanation
To increase the height of the tower crane, a new section must be introduced systematically. This is done by bringing the new section close using a trolley mechanism, followed by unbolting and lifting the turntable, creating space below it. The new section is then secured in place, allowing the crane to grow taller incrementally as needed. This method highlights the efficiency of using a climbing cage for subsequent erecting processes.
Examples & Analogies
Imagine adding a new floor to a building. Just as construction workers would need to ensure the existing structure can support the new floor, the crane must carefully add sections while ensuring its stability. It’s like stacking blocks — you have to be careful how you add each block to make sure everything stays balanced and stable.
Dismantling the Crane
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Similarly, if you want to dismantle it, you do the entire thing in reverse order. You can remove the section one by one with the tower crane. After the desired height is reached with the help of another mobile crane, you can remove the jib and the counter jib portion. The necessary steps involve removing the trolley, counterweights, jib, counter jibs, operator cap, and turntable, then dismantling sections one by one.
Detailed Explanation
The dismantling of the tower crane follows a reverse order of the erection process. This involves carefully taking off each component step by step, starting from the uppermost parts like the operator cap to the turntable, and gradually removing counterweights and jibs. This method ensures the safety of the dismantling operation, highlighting the importance of each stage in crane management.
Examples & Analogies
Think of it like taking apart a Lego model. You don't just yank off the last piece—you need to strategically remove pieces starting from the top, or the whole thing might collapse. Similarly, dismantling a crane requires careful planning and execution to ensure full safety and stability during the process.
Height Restrictions for Tower Cranes
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The maximum free standing tower crane height permissible is 60 to 120 meters. Beyond 120 meters, the tower crane should take help from the structure. Proper bracing must be provided to transfer the overturning movement. The maximum brace height possible is only 300 meters.
Detailed Explanation
Tower cranes have limitations on how high they can stand safely. They can operate independently from 60 to 120 meters, but beyond that, they must be secured to the structures they are building to prevent tipping or instability. The need for lateral bracing becomes crucial in these cases, highlighting the interactions between the crane and the building's design.
Examples & Analogies
Imagine playing with a tall tower of blocks. As you stack higher, the structure becomes less stable, and it needs a wall or support to hold it up without falling over. Tower cranes work similarly; they can stand independently only so high before they need to be anchored to a building to maintain balance and safety.
Climbing Tower Cranes
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If you need a tower crane for a structure which is greater than 300 meters, certain special cranes called climbing tower cranes can grow along with the structure. They will take support from the actual structure being constructed. Climbing cranes are located mostly in the opening of the lift or elevator and use hydraulic jacks to shift from floor to floor as the building rises.
Detailed Explanation
For skyscrapers or exceptionally tall structures, climbing tower cranes are employed. They are designed specifically to adjust as the building grows taller. Initially anchored to the ground, as more floors are added, these cranes detach and attach to new floors using a hydraulic jack system, which allows them to climb alongside the structure throughout the construction process.
Examples & Analogies
Think of a tree climbing vine that grows tall along with the tree. Just as the vine wraps around different sections of the tree as it grows, a climbing tower crane adjusts to reach new heights along with the structure it is helping to build. This adaptability is essential for constructing very tall buildings where traditional cranes would be insufficient.