Feature-Prefab Structures

 

Feature-Prefab Structures

Readymade for construction

Felix Lobo takes a closer look at pre fabrication methodologies.

Prefabrication is the manufacture of an entire building or components cast in a factory or on site before being placed in position assembling the structural units so that they can be easily and rapidly erected. Prefabricated buildings are pre-cut, pre-drilled, and pre-engineered before the actual building is constructed.

Prefabricated Structures (PFS) are useful for sites, which are not suitable for normal construction methods such as hilly regions, and also when normal construction materials are not easily available. PFS facilities can also be created at or near a site as is done to make concrete blocks used in place of conventional bricks.

Structures which are used repeatedly and can be standardised such as mass housing, storage sheds, godowns, shelters, bus stands, security cabins, site offices, foot over bridges, road bridges, tubular structures, concrete building blocks etc, are prefabricated structures.

The swiftly developing prefabricated structures' market in India has vast potential for growth. The market is attractive and the presence and entry of several players in the field confirms this fact. The sector is growing at a healthy rate of 10 per cent annually. Despite the plethora of problems faced by the industry, most of the players are optimistic about the future prospects of the sector. Saving on construction time will make the sector further attractive for prospective customers. In the years to come, the prefabricated structures industry is confident of total acceptance of this concept over conventional means of construction of industrial factories. Prefabrication building methodologies are ideal for low cost housing. In a building the foundation, walls, doors and windows, floor and roof are the most important components. These components can be analysed individually based on the needs. This will improve the speed of construction and reduce the construction cost. Various types of foundations normally adopted are: Open foundations; Rib foundations; Columns and Footings.

RCC raft foundation

Conventional methods using in-situ techniques are found to be economical and more practical for low cost housing, which generally consists of low-rise structures. In seismic regions, special attention is required to make the foundations continuous using horizontal reinforcement. Prefabrication is not recommended for foundations in normal situations.

Walls

In the construction of walls, rammed earth, normal bricks, soil cement blocks, hollow clay blocks, dense concrete blocks, small, medium and room size panels, etc of different sizes are used. However, bricks continue to be the backbone of the building industry. In actual construction, the number of the bricks or blocks that are broken into different sizes to fit into position at site is very large.

As a result of this, there is wastage of material and the quality of construction also suffers. Increasing the size of wall blocks will prove economical due to greater speed and less mortar consumption, which can be achieved by producing low density, larger size wall blocks, and taking advantage of industrial waste like blast furnace slag and fly ash. Several prefabrication techniques have been developed for walls, but these medium and large panel techniques have not proved economical for low-rise buildings as compared to traditional brickwork.

Floor and roof

Floors and roofs account for a substantial cost of a building. Therefore, any savings achieved in floor/roof considerably reduces the cost of buildings. Traditional cast-in-situ concrete roofs involve the use of temporary shuttering, which adds to the cost and time of construction. Use of standard and optimised roofing components where shuttering is avoided is economical, fast and better in quality. Some of the prefabricated roofing /flooring components found suitable in many low-cost housing projects are: Precast RC planks; Precast hollow concrete panels; Precast RB panels; Precast RB curved panels; Precast concrete/ferrocement panels; and Precast RC channel units.

Prefabrication as applied to low cost housing:

In India, adoption of prefabrication building techniques has many merits, like availability of materials, labour, and technical skills. Advantages of prefabrication are multiple as the components are readymade and self-supporting, shuttering and scaffolding is eliminated, with a saving in shuttering cost. In traditional construction, the repetitive use of shuttering is limited, as it gets damaged due to frequent cutting, nailing, etc. On the other hand, the mould for the precast components can be used for a large number of repetitions, thereby reducing the cost of the mould per unit. In the prefabricated housing system, there is saving of time, as the elements can be cast beforehand during the course of the foundation being laid. Even after laying slab, the finishes and services can be done below the slab immediately. In the conventional in-situ RCC slabs, due to props and shuttering, the work cannot be done till these are removed. Saving of time means saving of money. In prefabricated construction, there is better quality control, shape and size of precast elements. Therefore, in structural design, full advantage of the properties of cement and steel can be taken. There is disciplined use of expensive materials like cement, steel and timber.

In precast construction, similar components are produced repeatedly, resulting in increased productivity and economy in cost too. The construction is not affected by rain, wind, and other weather elements. The work at the site is reduced to a minimum, and therefore, work is qualitatively better, more reliable and cleaner. Because of faster completion and reduction in time period of construction, the houses can be occupied earlier, which means early returns on the investment.

Limitations of prefabrication: As the Precast elements have to behave monolithic on erections, extra reinforcement may be necessary to take care of handling and erection stresses. Temporary props may be required in some cases, before the in-situ concrete joints achieve strength. Cracks may develop at the joints between the Precast and in-situ concrete due to shrinkage and temperature stresses. To overcome them, extra steel is required across the joint. As there are chances of leakage/seepage through the joints between the precast components, extra care is required to make them leak proof.
Criteria for selection of prefab in India: In India, the technology adopted for housing components should ensure that the production and erection technology be adjusted to suit the level of skills and handling facilities available under metropolitan, urban and rural conditions. In other words, the structural systems and components selected should ensure minimum material utilization with maximum structural advantage. However, the component and systems so designed need to be manufactured and erected by manual means in villages, semi-mechanical techniques in towns, and more or less fully mechanical operations in the metropolitan cities.

In urban areas, the concentration of construction activity does not justify prefabrication. The answer is hybrid construction combining standardised mass-manufactured roofing and other components (at site) with in-situ brick walls or other masonary structures. A wide variety of roofing methods to suit these requirements have been developed and used on mass scale in many housing projects such as funicular shell, cored slabs, RCC channel units, Precast cellular units, Precast RC planks and joists, prefab brick panels and joists, RCC joists and hollow concrete blocks.

Mahaphant Fibre-Cement (South Asia) Pvt. Ltd., Mumbai, is a part of Mahaphant Group of Companies, based in Thailand. Established in 1974 in Bangkok Thailand, the company is emerging as one of very few manufacturers of unique and environment-friendly fibre cement and concrete products.

Its products include the environment friendly, non asbestos, fibre cement boards manufactured with autoclave technology under high pressure steam curing process for very high strength and dimensional stability under the brand name SHERA.

These Boards are manufactured as per ISO 8336:1993, type A and are therefore suitable for interior as well as exterior applications. They are resistant to weather, fire and termites, immune to water damage, sound insulation, low shrinkage, high workability & non brittle. Shera is a unique composite of natural fibers bonded in a high-grade silicate matrix giving stability in all climatic conditions. These fibre-cement products offer necessary strength, stability and versatility in applications. Shera planks offer the best substitution to natural wood. SHERA Decorstone offers the substitute for Natural Stone. We also manufacture the concrete products in the category of concrete roof tiles and artificial stone tiles for cladding & flooring applications. These products are offered in unmatched range of colors and contemporary styles best suitable for the décor of modern and classical style buildings. Along with the aesthetical characteristics, these products also provide the best suitability for earthquake-proof building structures.

Address:
101, D. S. Udyog Bhavan,
Veera Desai Road,
Andheri (West),
Mumbai - 400 053. INDIA.
Tel. +91-22-26744343 /4646 Fax: +91-22-26734115
Email: info@mahaphant.in.     

Savvy Buildfab Pvt. Ltd. is a leading insulated roofing and cladding company that manufactures insulated panels for wall cladding and roofing sheets with two side sheet and insulation material like PUF, Glass Wool, and Rock Mineral Wool in between to maintain better temperature, high strength, unique for cold rooms and sound insulation. Also adept at Pre-Engineered Steel Buildings involving Design, Fabrication, Erection, Erection and installation of Metal Building Systems, the products custom made, easy, fast to erect and can withstand severe climatic conditions.

Turnkey projects for building for Industrial, Commercial, Institutional, Retail, Aircraft Hanger, Shopping Centers, Warehousing, and Offices etc. are also undertaken. The company has the expertise in Trapezoidal Roofing & Cladding in Galvanized, Galvalume Bare & Precoated steel sheets. It manufactures Roof & Floor Deck Panels and Clip fix Roofing System too that is leak proof.

Metallic False Ceiling Systems manufactured by us are in vogue. Metal Crash Barrier are manufactured out of structural grade steel to provide safety on highway as well as act as a guideline to drivers in rainy & foggy conditions and also during night driving.

Mumbai: Contact - C. Vijay Kumar
Tel: 0091 - 22 - 6512 7237.
Mobile: 0091 - 98701 44492
Tele Fax: 0091 - 22 - 671 20 635
e-mail : chagalvijay@yahoo.com,
Delhi: Contact - Sanjiv Jain
Tel: 0091 - 129 - 2258720
Tele Fax: 0091 - 129 - 4128169
Mobile: 0091 - 98116 40014
e-mail : sjain373@hotmail.com.      

THE PLAYERS

Skandwill India Pvt Ltd
Contact: MR. P. K. Vijay Krishnan
Address: B-12, MIDC, Taloja, Dist-Raigad-410208. INDIA
Tel: (022) 27412025 / 55907725

Silver Star Construction (India) Pvt Ltd
S - 220, Manipal Centre, 47, Dickenson Road
Bangalore - 560042, Karnataka.
Tel: 91-80 -255 94474|191 80 255 87578 Fax: 91-80 -255 94474

New life Steel Structures Pvt. Ltd
Address: No 1, Shiv Darshan,Radhabai Mhatre Rd.,
Dahisar (W), Mumbai - 400068 India
Tel: 022 28933330 / 28923558. Fax: 022 28933330.
E-mail : response@newlifesteel.net

Enercon (India) Ltd.
Contact: MR. NISHIT JANI
Address: Kolsite House, Plot No. 31, Shah Ind.Est., Veera Desai Rd., Andheri-W, Mumbai-400053. INDIA
Tel: (022) 56924848 Fax: 022) 26730085 / 89

Malu Group
No. 8, 1st Main,Gandhinagar, Bangalore - 560009, Karnataka
Tel: 91-80 -222 63663191 80 222 68253 Fax: 91-80 -222 81819

 

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