Construction Technology in Tall Buildings

CONSTRUCTION TECHNOLOGY IN TALL BUILDINGS

Abstract

To a certain extent the high-rise buildings not only represents the prosperity of a nation or a city, but the level of modern science and technology development. High-Rise Buildings are product of our time and solutions for the urban habitat. In recent years, developed countries have emerged as centres for new high-rise buildings. Land is scarce and expensive particularly in big cities. As the height of a building increases, the difficulties in construction increases and ultimately gets challenging for the adaptation of construction technology. Thus, with the rise in urban development, construction industry has improved itself in construction techniques, technologies and the equipment required to carry not only the construction process but to mitigate the risk of hazards. The overall turnover for a high-rise project maybe roughly estimated by tracking down time & cost invested in the construction. Construction equipment is the focus of all the challenges faced in the construction of high-rise or super high-rise buildings. With the growing demand of high-rise construction, the building codes may not provide the most economical, efficient and safe tall buildings because the codes are general in nature. In this paper, the key technologies in construction of modern steel and concrete high-rise building have been studied. The new inventions including the operation platform, tower crane and hoist are put forward solving the most important issues such as vertical transportation and operation environment. The recent R&D for adaptation of BIM as well as Robotics in construction has been taken into interest. In the end, the paper summarizes the main problems in the further development of construction equipment and safety hazards.

Keywords: High-Rise Buildings, Technologies, Equipment, Urban development, Time & Costs, Concrete and steel buildings, cranes and platforms, BIM, Robotics, Safety Hazards.

1. Introduction

The High-Rise buildings is great significant in modern building trade. Great breakthroughs have been made in the building function, structural system, building services and other aspects of super high-rise building. As the construction process is concerned, however, intensive labour, low level of mobilization, long construction period, high cost and environmental pollution still restricts the industrialization level and comprehensive benefits.

Because of less storage and workable space on the site (in a big city), the vertical transfer of construction materials, labors and equipment operation environment for the cranes along with other heavy equipment becomes a challenge. There can be many materials and components that has to be transferred to a high altitude. The transfer is not retained only to vertical movement but also horizontal. The traditional environment of operation across a platform becomes limited because of the ongoing construction process and activities. Thus, improving the transfer process and operation environment is the key to increase the construction efficiency. In the end of 19^th Century, vertical transportation was greatly improved by the introduction of tower cranes and construction hoists. By summarizing Engineering innovation practices, some of the key modern technologies such as (a) Tower Crane supporting frame suspension disassembly technology (b) Self-Elevating platform technology (c) Automatic welding technology (d) Integrated platform (e) Crane Slewing system (f) Circular Hoist (g) Up-down Construction have been mentioned in this paper, which provide good reference for the future high-rise construction

1.1 Tower Crane supporting frame suspension disassembly

For recent years, cranes have been widely used for the vertical transportation during the construction stage. Thus, the construction time for a certain project depends upon the efficiency of the cranes. Depending upon the workable space, there are two types of cranes i-e, External attached and Internal climbing cranes. The selection of crane depends upon the structure, material and height of the building. Generally used external attached crane can only be used till 200 m height of the structure. That is why, internal climbing cranes are used for high-rise structures. Usually 2-4 internal climbing cranes are sufficient and can be located inside or outside of the core. There are two main types of framings required for supporting the cranes, simply supported frame and cantilevered frame. Whereas, fixation and jacking system plays an important role for transport operations. There are many risks of disassembly caused by large and heavy loads therefore tower cranes are differentiated on the basis of loading applications, fixation systems etc. By using this technology, material stockyard area is reduced as well as efficiently managed.

1.1.1.      Mechanism

Due to the presence of neighbouring structures and cranes, the mechanism of disassembly should be efficient. Keeping in view of the strict site workability conditions, a new suspension disassembly technology for cantilevered frame internal climbing crane has been developed (Dai and Liao, 2014).
The crane is attached to the outer surface of core or frame-core system. There are three fixation brackets for mounting the crane, whereas only two are involved in jacking. There are three supporting frames A, B and C as shown in the figure. Each frame is attached through brackets. Initially the chain block is installed at one end by which the brackets A and C are connected. Supporting bracket A is disconnected with the core tube system and is lifted by the chain block. At termination of disassembly the bracket A is suspended in the air and is ready for use.

1.1.2.      State-of-the-art Case Application:

Shenzen Ping’an Finance centre was Asia’s first high-rise building of 660m height for which towers cranes with suspension disassembly technology was used. Following are the silent features of the building.

*In comparison with traditionally disassembled cranes.

1.2.        Self-Elevating Platform

Depending upon the working mechanism, self-elevating platform can be divided into two types as scaffolding operation platform and assembled section steel platform. Both of these systems are currently used at various projects. One of the advantage for scaffolding operation platform is that it can be rotated or moved around the building easily but it requires a large number of labor and the operational safety is challenged as it moves at high altitudes. Whereas, the assembled steel platform is lightweight and compact. Considering the time, both of the platforms take a lot of time during installation. Moreover, a few modifications as discussed below can overcome the amount of time required to mount the platform.

1.2.1.      Mechanism

There are three major systems in self elevating platforms. That are; jacking system, platform system and central control system. Moreover, for the smooth movement jacking system is composed of hydraulic and gear systems. Self-elevating platform is mechanically operated for steel column construction. After completing the erection of one column, the platform gets ready to be elevated to the new position for the upper column. Following schematic diagram represents the step by step elevation process.

Due to innovations and with the help of latest technologies, platform has been upgraded to be elevated along the column of variable cross-section. The platform can rotate freely at a very large angle, thus making it possible to climb along the variable cross-section. The platform can be maneuverd in case there is a beam along the axis of rotation. Safety enclosure is also retractable so that the integrity of the platform is maintained.

1.2.2.      State-of-the-art Case Application:

Guangzhou East Tower is a mega frame-tube structure that was constructed using the self-elevating platform. The silent features of the project are as follows:

1.3.        Crane Slewing System

For multiple tower cranes working on the same high-rise building construction, the cranes must be at safe distance apart. Moreover, the cranes interfere with other construction equipment. Thus, the cranes cannot work efficiently.

To solve the problem, a crane slewing system was introduced in the construction industry. The slewing system integrates all the tower cranes on a single platform at different levels if required. Platform itself is mounted on a core tube and has the ability to slew around the core. Due to this advancement, the cranes can cover more area as the platform can accommodate many sizes of cranes.

1.3.1.      Mechanism

The crane slewing system consists of four important parts; supporting power system, slewing driving system, steel frame system and control system as shown in the above figure.

The slewing driving system has slewing bearing with an upper joint and a lower joint. The upper joint holds the steel frame that has all the cranes. Whereas, the lower joint is fixed to the lower frame that is attached to the platform. To provide motion to the platform, there are hydraulic motors just between the slewing bearing and the core. The bearing system has the ability to take up to 2000 tons of axial loading and 9000 tons-meter of turning moment.

1.4.        Circular Hoist

For high-rise buildings, the biggest challenge is the vertical transportation. The means of transportation cannot be only cranes. For minor transportation, hoists can be used to streamline the construction efficiently. There are usually more than 10 hoists working on a high-rise construction but too many hoists can slow down the construction as large operational area is required. Using multiple hoists can save time only in vertical transportation but affecting the finishing of lower floors such as fixation of facades or masonry wall construction.

A new hoist system was proposed having multiple cages running on along a single mast. Cages run upwards on one side of the mast and has the tendency to rotate at 180 degrees to descend from the other side. The system cannot assist the transportation in horizontal direction.

1.4.1.      Mechanism

The Circular hoist is composed of rotating system, attachment system, power supply system, monitoring and dispatching system. Rotating system is the core constituent as it hoists and transfers the load to lower mast. There are two attachments for the loading and unloading, vertical and horizontal attachments. For the management of cages and to control the operation there is a central control system in a room on the construction site.

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The rotating system consists of driving and positioning system and an electric control system. The key working mechanism includes a load bearing shaft and a slewing frame that is driven by a servo motor. To power up the system, the bus duct helps the hoist to slew freely. For maintaining the operational safety, central control system checks the distance between the cages. Minimum distance of 40 meters is maintained between the cages as the cages move at high speeds. But under special circumstances if cages are required to move at lower speeds, a safe distance of 25 meters is maintained. As the distance between two adjacent cages drops to 15 meters, the central control unit shutdowns the system.

Hoist can be controlled remotely on the site through the control room. To call the hoist to a specific floor, the floor numbers can be input. Whereas, up and down commands can also be used. When the cage receives the signals, operator get informed through the voice and screen.

1.5.        Integrated Platform

The integrated platform consists of steel frame system, supporting and power system, suspended handling frame, suspended formwork, integrated tower cranes and a monitoring system. Wide operation spaces and enough capacity allows the platform to carry the equipment and facilities, various other construction technologies thus providing a highly efficient construction technology.

1.5.1.      Mechanism

Integrated platform has 8 to 14 supporting units that empowers the platform with vertical load capacity of 600 tons per unit and sum of 5000 tons for the whole supporting system. Each supporting frame is composed of three major parts, micro convex fulcrum, supporting frame and hydraulic cylinder. The supporting frame includes the upper frame and lower frame. There are three statuses of the power and supporting system i.e. operation status, jacking status and lifting status. The platform and supporting frame is equipped with various sensors that monitor the strain, verticality, levelness wind speed and temperature throughout the operational status. Monitoring system has the ability to collect, store, display and analyse the information from the sensors and in case of any irregularity can send signals for alarm.

Tower cranes of varying heights and capacity can be integrated to the platform. There are three tie-backs as top, middle and lower tie-backs. The top tie-back is a screw jack on the platform that provides horizontal support to the crane. Whereas, middle and lower tie-backs transfer the horizontal load to the concrete walls. Before initiating the jacking, the tower crane shall be balanced with weight such that its center of gravity is gets closer to it centroid. During the jacking process, the three tie-backs provide firm support to the tower crane in case of strong wind or bad weather.

1.6.        Use of Robotics in Construction Industry

The population of Robots in construction industry has rapidly increased over the last decade. They are increasingly becoming important in applications ranging from quality control to small scale transportation. There are more trained people in robotics now but some new challenges for robotic researchers are better human-robot collaboration interfaces, robot mobility and navigation in unknown surroundings, better robot intelligence for service industries such as construction. The application of robotics in construction industry have been researched, explored and prototyped for the last 20 years. Robotics in the construction industry are in large part based on the advances in robotics developed first for the industries and this trend is expected to continue.

One of the most successful areas for applying automation and robotics has been the building envelope. A look at construction technologies in development suggests a near-term revolution in how we build and operate our facilities. A few of these seemingly futuristic technologies are already commercially available and in use today, including 3D Printing, unarmed drone aircrafts and robotic construction systems.
Earth and foundation works are important sub-phase works at any construction regardless of the height of the building. Foundation works has many repetitive works and also are a threat to safety. Therefore the research work related to automation and the technologies involved in foundation works is one of the pioneers in the construction industry. The studies of such automation can be divided into four categories; equipment tracking and fleet management, safety management, equipment pose estimation and machine control and autonomous operation.

For the erection of super structure of highrise buildings, the construction becomes significantly difficult. There are three major concerns related to construction of highrise buildings; low productivity, safety and vertical transportation of equipment and workers. These three aspects are targeted to be simplified by using robotics and latest technologies such as automated lifting systems, robot-based steel assembly systems and automated construction systems.

With the development of automated construction systems, assessment methods were proposed to measure the economic and construction efficieny process for the application of robot-based construction automation systems, which can measure the viability of the automated systems.

Automated lifting systems for highrise buildings has significantly improved the vertical transportation of workers, equipment and materials. Operation planning and optimization are major factors to determine the productivity of the automated lifting process. Unmanned smart lifting systems are proposed and devised which can reduce work hours and traffic queues, such as twin or multi-caged lifts. Operation monitoring is another important aspect for smart tower cranes. According to a research, an automated lifting-path tracking system was proposed for a robotic tower crane that used laser devices to calculate the linear distance, angular movements horizontally and vertically. The system also provides safety management for the tower crane and path planning aswell.

1.7.        Up-down Construction

Basement construction and excavation for tall buildings usually face three constraints; not sufficient working space at site, poor subsoil conditions and the proximity to old neighbouring buildings. Due to weak subsoil conditions and to protect neighbouring buildings, a rigid excavation system and support system is required. Top-down basement construction addresses all the above mentioned problems. Its consists of basement slabs which are permanent structural members as internal struts in association with diaphragm walls or contiguous pile walls. Overall construction costs are also lowered as the temporary excavation works become unnecessary. The up-down approach allows the overlap of super-structure and sub-structure activities thus saving 10% – 20% of construction time. The need for construction in congested urban environments where site and subsurface conditions are increasingly more challenging makes makes the use of up-down construction a valuable technique for facilitating the cost-effective development of projects.

1.7.1.      Mechanism

Up-down construction is innovative because it requires no radical changes in construction techniques but is a creative sequencing of techniques that have already been proven in either the building or heavy construction industry. Up-down construction involves the installation of substructure walls, below grade columns and foundation system prior to excavation. Concrete Diaphragm walls constructed by slurry trench method are typically used for perimeter walls. They serve the dual purpose of lateral support during construction and as perimeter walls for the final structure. After completion of walls, the structural columns and foundation elements are installed from the existing ground surface. The floors also serve the function of cross-lot braces during construction by providing lateral support to walls.

Following is the breakdown of construction sequence;

1. A thick concrete diaphragm wall is installed by the slurry trench method below the lowest excavation level around the perimeter of the building.
2. High capacity foundation elements, such as drilled piers or load bearing elements are advanced from ground surface to bear in the competent soils below the lowest floor level. They are filled with concrete only to the lowest basement level.
3. Columns are set on the drilled piers and the annular space filled with sand or weak concrete to ground surface.
4. The street-level concrete floor slab is the cast and the superstructure erected above the column supports.
5. The below-grade excavation proceeds to the next floor level by mining below the street level floor slab. The next floor level is concreted to provide cross bracing for the walls. This is repeated down to the lowest basement.

2. Conclusions

This paper studied the key technologies for modern high-rise steel and concrete structures. There are still major requirements in the super high-rise building for development of construction equipment innovation, which is important breakthrough to change the production mode of the construction industry and realise the industrial transformation and upgrading. The tower crane supporting frame suspension disassembly technology has successfully realized the turnover of supporting frame in the without occupying materials stockyard, thus increasing the workable space. The barrier avoiding technology of self-elevating tower crane platform reduced the occupancy time of other tower cranes, realised the climbing along varying cross-section steel columns with a size change in a range of 600mm. By using the crane slewing system, multiple cranes can work together thus saving time and workable space. Since time, costs and performance are the key stakeholders for a successful project and a perfect balance between them should be developed. The choice of the construction technology depends upon the neighbouring buildings, workable space and most important; the type of structural system.

In the last 30 years, modern high-rise structure construction technologies have made great progress. In the major cities of the world, with the land crisis more and more serious, future super high-rise buildings will become higher and higher. These are challenging the construction technologies, especially in the construction quality assurance and construction efficiency. Today, with the globalization of information, the development direction of intelligent, flexible and detailed technology and management is the mainstream of future development of high-rise construction.

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