PREFABRICATION

PREFABRICATION• A construction industry term used to describe

a building or structural components that are manufactured in industrialized/factory conditions and then transported to construction sites to be assembled into a building, and civil engineering works

• Offsite locations can be considered as equivalent to an industrialized manufacturing facility, where things are built in controlled plant conditions

• Construction is done as per the same design, and specifications, and using the same materials as in the traditional onsite construction approach

• Offsite fabricated buildings or components are then transported to the construction site and then erected in place using cranes

HISTORICAL BACKGROUND• Prefabrication or Modular construction

may sound like a new term to many, but this practice of construction has been used for a long time

• Rome in AD-43• the Romans used prefabricated

building elements to build their forts quickly and efficiently

• the Britishers also transported simple prefabricated houses by ships to their new settlements in the colonies to provide comfortable European Style living to its officers in these colonies

HISTORICAL BACKGROUND

• Prefabrication method also helped address British and European housing shortages during Post World War I era

• Again during the Post Second World War era, prefabrication came to rescue, as it alleviated the shortage of skilled labor in the midst of the population outburst due to the baby boom

APPLICATIONS OF PREFABRICATION• Prefabricated buildings are used for

sites which are not suitable for normal construction method, and also when normal construction materials are not easily available, or when there is difficulties to provide enough workers.

• Prefabrication is usually applied in structures which are used repeatedly and can be standardized such as; mass housing, sheds, bus stands, security cabins, site offices, and road bridges.

AIMS

REDUCED LABOR COSTS-For example, rather than paying a team of framers to travel to a job site, cut lumber, nail it into place and clean up, framing panels can be produced at a factory by people who do one job and do it well, in a facility that lets them work at maximum efficiency.

REDUCED MATERIAL COSTSAgain, off-site fabrication benefits from specialization and economies of scale. A company that manufactures certain products in large quantities can negotiate better prices from its own suppliers, and competition forces companies making similar components to pass these savings along to the customer.

HIGHER QUALITY MATERIALS Components produced off-site can often be manufactured to tighter specifications and using better raw materials than the same components built on-site.

General materials used in prefab construction

• Concrete• Steel• Treated wood• Aluminum• Cellular concrete• Light weight concrete elements• Ceramic products, etc

Site-assembled systems

• All components, including the frame, are manufactured at the factory and transported to the building site in pieces.

• All assembly takes place at the building site.

Volumetric or modular construction units could be manufactured from 2D wall panels and floor cassettes, and they are assembled into load-bearing ‘boxes’ or ‘3d sections’ which are fitted out and transported to the construction site. The primary disadvantage of this system is ‘transportation constraints’ that limit the width and height of the unit.

Volumetric Systems

Factory-assembled systems

• All building elements are manufactured, assembled and finished at the factory.

• Once on the building site, the building is installed on the foundation and hooked up to utilities.

Transportation of prefab units Prefab buildings are commonly shipped

by trucks or railways, but sometimes ships are used for delivering prefab homes.

Studies have shown that shipping modules becomes cost prohibitive when they must travel more than 150 to 200 miles from factory to site.

The industry generally recognizes 125 miles as the maximum practical distance modules should need to travel from factory

ADVANTAGES OF PREFABRICATED BUILDINGS

• Prefabricated components speed up construction time, resulting in lower labor costs.

• Prefabrication allows for year-round construction, work is not affected by weather delays (related to excessive cold, heat, rain, snow, etc.).

• The mechanization used in prefabricated construction ensures precise conformity to building code standards and greater quality assurance.

• There are less wasted materials than in site-built construction.• Worker safety and comfort level are higher than in site-built construction.• Computerization of the production process permits a high degree of

customization, at an affordable cost.• Quality control and factory sealing and design can ensure high energy

efficiency.

DISADVANTAGES OF PREFABRICATED BUILDINGS

• Increased production volume is required to ensure affordability through prefabrication.

• Prefabricated buildings typically depreciates more quickly than traditional site-built housing. Because of its shorter economic life.

• Transportation problem.• Local jobs are lost.• Required heavy duty cranes and precision measurement

Precast Concrete Beams and Girders Provide support for slabs. The projecting reinforcing bars will bond with

concrete cast on site. Right: Inverted tee beams supported by precast

columns.

CONCRETEPrecast Concrete SlabsUsed for floor and roof decks. Deeper elements (toward the right below) span further than those

that are shallower (toward the left). Right: Hollow core slabs.

Precast Concrete Columns and Wall Panels

• Provide support for beam and slab elements.

• Since these elements carry mainly axial loads with little bending force, they may be conventionally reinforced without prestressing.

• Or, long, slender multistory elements may be prestressed to provide resistance to bending forces during handling and erection (columns at right).

• Precast concrete wall panels may be solid (right), hollow, or sandwiched (with an insulating core).

• Wall panels can be ribbed, to increase their vertical span capacity while minimizing weight, or formed into other special shapes (below).

Other Precast Concrete Elements• Precast concrete stairs (below)• Uniquely shaped structural elements for

a sports stadium (right).

STEEL STRUCTURE

• The steel frame is inside the wall, the structure is connected by bolts and the walls are fixed with rivets. The steel structure parts and panels are light and easy to pack and transport. The prefab house can be broken-down and reassembled couple of times.

Main Advantages• Our one/ two/three floors steel home are custom designed• The houses are easy to construct and save on time and labor• They are fireproof and insulated against heat and cold• The steel home has a useable lifespan of more than 25 years• Flexibility of fixing doors, windows and interior partitions• Beautiful appearance, different colors for the walls and roof.• Cost saving and convenient to transport• Long term service life

SHIPPING CONTAINER

WOODEN STRUCTURE• They can be readied in as less as 7 days whereas a

concrete structure takes a minimum of 1 year. • Log houses do not require tons of waterin

construction whereas concrete consumes hundreds of litres of water approximately, and water involves cost which is both monetary and social.

• They are also considered energy efficient as they cool down sooner comparatively and remain cool for longer time and hence do not consume electricity to the same extent as concrete structures.

OTHER ADVANTAGES•Architectural Flexibility •Durability - As durable as any concrete structure •Time Saving and Energy Efficient •Can be dismantled, relocated and reused •Increased Thermal Performance and Better Insulation •Easy to Install Mechanical and Electrical Services •Lower Carbon Footprint •12 times more insulating than concrete

Nakagin Capsule Tower

LOCATION • GINZA 8-CHOME , CHUO-KU, TOKYO ,JAPANBUILDING STATISTICS• SITE AREA: 442sqm• BUILDING AREA: 430sqm• TOTAL FLOOR AREA : 3091sqmSTRUCTURE DETAILS• STRUCTURE STEEL FRAME PARTLY ENCASED IN CONCRETE• MAX OF 140 CAPSULE UNITS (PREFABRICATED)• 11-13 STORIES INCLUDING 1 BASEMENTMATERIAL DETAILS• CAPSULE EXTERIOR :STEEL WITH SPRAYED PAINT FINISH• CAPSULE INTERIOR: STEEL CAPSULE WITH CLOTH CEILING AND

FLOOR CARPET• TOWER: CORTEN STRUCTURAL STEEL FRAM• LOWER LEVELS: FAIR-FACED REINFORCED CONCRETE

Case study

STRUCTURE • REPUTED TO BE THE WORLD’S FIRST

STRUCTURE THAT IMPLEMENTED THE INNOVATIVE IDEA OF CAPSULE ARCHITECTURE

• KISHO KUROKAWA DESIGNED THE NAKAGIN CAPSULE TOWER

• NAKAGIN CAPSULE TOWER IS A “MIXED SYSTEM” STRUCTURE, UTILIZING BOTH TRADITIONAL ARCHITECTURE WITH MODERN TECHNOLOGY WITHIN ONE ENTITY. IT IS MADE OF TWO REINFORCED CONCRETE AND STEEL FRAME PILLARS OF ASYMMETRIC HEIGHTS, BOTH HOUSING PUBLIC UTILITIES SUCH AS STAIRS, ELEVATORS,PLUMBING,AND ELECTRICAL SYSTEM

• THE 14 STORY HIGH TOWER HAS 140 CAPSULES STACKED AT ANGLE ARROUND THE CENTRAL CORE

THE CAPSULE• THE STEEL FRAME CAPSULES (WHICH

HAVE BEEN DESIGNED TO BE REPLACEABLE, REMOVABLE, AND TRANSPORTABLE) WERE PREFABRICATED IN SPECIALIST FACTORIES AND ASSEMBLED AT A PLANT BEFORE BEING DELIVERED TO THE SITE. EACH ONE WAS LIFTED BY MECHANICAL CRANES AND WERE ATTACHED TO THE TOWER SHAFTS USING 4 HIGH TENSION BOLTS .

• THE CAPSULE INTERIOR WAS PRE-ASSEMBLED IN A FACTORY THEN HOISTED BY CRANE AND FASTENED TO THE CONCRETE CORE SHAFT.

INSIDE THE CAPSULE• KUROKAWA’S DESIGN CONCEPT

FOCUSES ON HOW TO MAKE THE MOST EFFICIENT USE OF LIVING SPACE TO ACCOMMODATE THE EVERYDAY ESSENTIALS OF A PERSON. HE BORROWED THE “CAPSULE” TERMINOLOGY FROM THE AEROSPACE INDUSTRY AND RETROFITTED A RECTANGULAR CABIN OF 8 FEET BY 12 FEET FLOOR SPACE WITH A BUILT IN BATHROOM, DOUBLE BED , DESK, STORAGE SPACES , TV, TAPEDECK, TYPEWRITER, CALCULATOR, CLOCK RADIO, AND A BURNER STOVE.

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