As per article Published on Construction world Magazine on February 2017 by Professor M K Madhvan IIT Hyderabad.
Cold-formed steel, a cost-effective and sustainable material, can soon make 'Housing for All' a reality.
Affordable housing is still a major concern in India as it urgently needs to provide economical housing in the shortest timeframe. While the selection of construction technology and material should satisfy aspects such as ease of construction and lower cost, it is equally important to ensure sustainability. In an effort to provide quality, affordable housing in the shortest possible time, Prof Mahendrakumar Madhavan, Faculty-Civil Engineering, IIT Hyderabad, has been researching to arrive at cost-effective sustainable solutions using cold-formed steel (CFS). He shares more on CFS, its advantages, and the need for India to build right with CW. CFS and its application: A type of steel, CFS is a thin rolled sheet, which is run through cold rolled mills. Initially in the form of a coil, it is sent through a series of rollers to produce several structural shapes and sizes, unlike hot rolled steel, which is manufactured using billets. For installation, a fibre or gypsum sheathing is connected to the CFS structural member with self-tapping screws resulting in a formation of a wall panel. Inside this panel, rockwool or other insulating materials can be placed for thermal comfort. It is similar to the timber framed houses constructed in the US. CFS is thin, flexible, lightweight, and significantly helps in reducing the cost of construction. This lightweight steel is best suitable for affordable housing; in urban housing, to build up to five floors. With a slab cycle of two to three days for one floor, it can also be achieved in a day or two with skilled labour and equipment operators, which are currently lacking. Further, IIT Hyderabad is carrying out research to identify the optimal shape and geometry of the cross-section to make CFS more effective for load bearing. CFS for disaster-prone regions: While it is flexible, and manufactured and disassembled off site, it can be quickly assembled and installed on-site, making it ideal for use in disaster or earthquake-prone areas. Conventional structures are heavy, and most structures are primarily designed for vertical or gravity load with little attention being paid for lateral load resistance – earthquake, tsunami or wind. This is because such proper detailing leads to increase in cost, and India is still not adaptive to new methods. India’s seismic map is changing; the country has experienced earthquake several times over the last decade. In addition, the frequent occurrence of cyclone has only been a proof of the vulnerability of our present housing stock, which is primarily constructed using unreinforced masonry and concrete. There needs to be a paradigm shift from using an unsustainable (one that is difficult to be reused at its native strength) and brittle material such as masonry and concrete to using structural steel as a material of choice for construction. Also, instead of looking at the initial cost, which may be higher, one should consider the life-cycle cost. Besides, if the structure has to be relocated in future, it will result in significant savings as the material can be reused. In addition to a reduced carbon footprint, this makes the salvage value of the steel intensive structure high, as the material can be designed at its native strength with no loss due to ageing. Several school buildings and anganwadis in the Northeast are using CFS. This is also suitable in hilly areas where transporting cement, concrete and other materials to higher altitudes is challenging.
Advantages and shortcomings: CFS is a green material, which means it can be reused at the same native strength at which it was produced. It is innovative and flexible as it can be rolled in to desired shapes. Being light in weight, it is easily transportable. In pre-engineered buildings (PEBs) too, it can be used as purlins to support the roof cladding and as girts to support the wall cladding. Here, CFS purlins and girts act as a secondary member. Several green-rated structures too use components of CFS. A huge challenge lies in creating awareness regarding the choice of material to be used for construction especially in coastal areas and areas where the risk of seismic activity is high (Zone V). Typically a “one size fits all” approach is adopted and a wrong choice of using concrete is made considering that the initial cost of steel is more. Also, home owners spend a huge amount on non-structural elements like false ceiling, tiles, bathroom fittings, etc, but skimp when it comes to structural applications. Therefore, a paradigm shift in mindset – from a concrete to a steel intensive structure – is needed to ensure wind and earthquake resistance, etc. Another challenge is lack of skilled labour; training is crucial to use such innovative technologies and materials.
Lack of robust design procedure: Houses cannot be built and then recalled; thus, extensive testing is required, which would enable introducing our own design specifications that could work in Indian conditions. Thereafter, these can be incorporated in the building codes. Currently, there is lack of consistency in the design and implementation of new technologies such as CFS. Indian products are designed using foreign design specifications for CFS. Typically, both the product and the design specification should go together. Hence, for adoption of CFS technology there is an urgent need in India to create a design procedure, test it, collect data, create guidelines and incorporate them in building codes. Further, we need to take advantage of faster construction techniques for which we need to adopt a sound technology, have a strategic mission and choose the right materials. The way forward: In China, manufacturing and even building the floors – HVAC duct, electrical wiring, light fitting, etc – happen in the factory. The final product is only lifted, placed and bolted on site. Thus, they are able to do two to three floors a day. For India to adopt such technologies and materials as CFS, there is a need to evaluate the choice of materials, labour cost, maintenance cost, RoI, salvage value, whether it is green and economical, whether we have enough sand to build, and the quality of construction.
Posted on : 09/08/2017 05:30:45
-- By : Somu Pandey
Established in 1996, Nipani Industries with vast experience of over 20 years is today one of the leading Steel building products manufacturer and complete structural steel.
Nipani Industries provides turnkey solutions right from concept, design, supply, erection installation (including Civil, Mechanical, Electrical & plumbing) & commissioning of Pre-engineered, Light Gauge Steel Building & Communication Tower.
We are pioneer in Light Gauge Steel Frame (LGSF) technology in INDIA, we have successfully executed several government projects on time in full (100% OTIF).
Posted on : 09/08/2017 05:33:22
-- Somu Pandey
About the technology
Light Gauge Steel Framed Structures (LGSF) is based on factory made galvanized light gauge steel components, designed as per codal requirements. The system is produced by cold forming method and assembled as panels at site forming structural steel framework of a building of varying sizes of wall and floor.
The basic building elements of light gauge steel framing are cold formed sections which can be prefabricated at site using various methods of connection. The assembly is done using special types of screws and bolts.
Cold formed sections are widely used in construction including residential floors, industrial buildings, commercial buildings, hotels and are gaining greater acceptance in the residential sector. LGSF is a well established technology for residential construction in North America, Australia and Japan and is gaining ground in India.
LGSF is typically ideal for one to three storey high buildings, especially for residential and commercial buildings. Due to its flexibility, fast construction and durability, this technology has great potential for counties like India.
LGSF can be combined with composite steel / concrete deck resting on light steel framing stud walls. Apart from having potential for mass housing, modular buildings can be used for long term temporary or permanent structures such as schools and classroom, military and civil housing needs, post – disaster relief structures and industrial buildings. Advisable maximum span for LGSF buildings should be 7.5 m.
Specifications for the System
Main Section are Studs & Track Studs serve as a general all purpose framing component used in a variety of applications including external curtain walls, load bearing walls, headers floors & roof joists, soffits and frame components.
Track is used as closure to stud and joists end as well as head and sill conditions. It is also used for blocking and bridging conditions.
Load bearing steel framing members shall be cold – formed to shape from structural quality sheet steel complying
with the requirements of one of the following:
i) ASTM A 653 / A 653 M -13 Grade 33, 37, 40 & 50 (Class 1 and 3) or
ii) ASTM A 792 / A 792 M -13 Grade 33, 37, 40 & 50; or
iii) ASTM A 875 / A 875 M – 13 Grade 33, 37, 40 & 50; or
iv) Sheets, that comply with ASTM A 653 except for tensile and elongation with requirements, shall be permitted, provided, the ratio of tensile strength to yield point is at least 108 and the total elongation is at least 10 percent for a 5 mm gauge length or 7 percent for a 20 mm gauge length.
Consists of top track (U shape configuration) with a depth compatible with that of the studs of the same nominal size. Minimum height of track flanges shall be 19 mm.
Load Bearing Walls
C section studs with depth of 90 and 200 mm and thickness between 2.7 mm and 2.0 mm shall be provided at a distance of 300 mm / 400 mm / 610 mm to ensure efficient use of cladding material. Multiple studs are used at heavily loaded application such as adjacent to openings or in braced panels. C section with 94 x 50 mm is used for noggins.
Alteration shall be required for the local details at the head & the base of the wall to ensure that loads are adequately transferred without local deformation of the joists & studs.
Non Load Bearing Walls
It is similar to that of load bearing walls except that noggins and diagonal bracing are not required to stabilize the studs.
Deflection Limit of Walls
Suggested deflection limit for external walls subject to wind loading are as follow:
Full height glazing Height / 600
Masonry wall Height / 500
Board / reduced finish Height / 360
Steel cladding Height / 250
Other flexible Cladding Height / 360
Wall cladding shall be designed to resist wind load. Sheet has to be screwed to the joist / purlin with maximum spacing of 300 mm c/c. All the joints of sheet in longitudinal direction require a minimum lap of 150 mm in order to make them leak proof.
Following materials are generally used on wall cladding:
• Gypsum board conforming to IS 2095 (Pt. 1): 2011
• Heavy duty cement particle board conforming to IS
Bracing and bridging shall have configuration and steel thickness to provide secondary support for the studs in accordance with the relevant specification for the design of Cold – formed steel structure of members.
For speed of construction, floor joist may be pre-assembled to form floor cassettes. This works well for regular floor places but care shall be taken when the geometry of the building requires the cassettes to vary in size with location or when non – right angel corners are required. Resistant may be provided to the top flange of the joists by the flooring board. The floor should be designed for the combined effect of dead and imposed load.
The construction of a suspended floor comprising cold formed steel floor joists is similar to that for a floor using timber joists. The strength to weight ratio of light steel joist is higher than that of other material. Steel joists are stable and do not suffer, the long term problems of drying out, creep and Shrinkage. Joists are generally positioned at 300, 400 & 600 mm centres, depending on the spacing capabilities of the floor materials used.
Flat roof is made up of joists, where steel decking form a flat roof, a minimum fall of 1:4 should be introduced to ensure that any moisture runs off. To avoid local ponding to rain water, the pitch may need to be increased to overcome the effective reduction in roof angle caused by the deflection of long span roof purlin or decking.
Use of Light Steel roof truss is economical for larger span building. In attic or open roof truss creates usable roof space, uses fewer components than Fink truss and provides an economical solution, since it utilizes the high strength of the steel members.
The trusses are placed at 600 mm maximum spacing and are battened and tiled in a conventional manner.
Screws as per the details given below shall be used:
• Panel Assembly – Low profile screws
• LGS-LGS Wall panel to roof cassette – 12-14x15mm
• LGS to concrete – Tapcon screw 14-12x60mm Hex head
• Wire mesh = EPS board – SDS Hex head with Ceresin without washer
• HRS-LGS – Hex heat
• CP board 6mm – WT 8 CSK Phillips
• Gypsum board – Flat heat self-driven type
• Deck sheet/Wire mesh – SDS WT, CSK, Flat head
Extended Polystyrene Panel
Shall be of minimum density of 15 kg/m3.
Shall be made of 4 mm dia wire of UTs 480 MPa with spacing 150 mm x 150 mm or 1.4 m dia of spacing 40 mm x 40 mm.
Shortcrete when used shall be of minimum grade M 25 Grade of concrete.
The LGSS is designed based on provision of the following standards:
●● Indian Standard IS 801: 1975 Code of Practices for use of cold formed and welded section and light gauge steel
structural members in general building construction.
●● British Standard BS 5950 (Part 5):1998 – Structural use of steel in Building Part 5 – Code of Practice for design
of cold formed thin gauge structure.
●● British Standard BS 5950 (Part 1): 2000 Structure use of steel work in Building Part 1 with loading requirement
as per IS 875 (Part 1)
●● Indian Standard IS 875 - Code of Practice for design loads
Part 1 - Dead Loads - Unit Weights of Building Material and Stored Materials
Part 2 - Imposed Loads
Part 3 - Wind Loads
●● IS 1893 (Part 1):2002 Criteria for Earthquake Resistant Design of Structures - Part 1 : General Provisions and
The sections are manufactured using Centrally Numerical Control (CNC) automatic four Pinnacle Roll Forming
machine having production speed of 450-900 m/hr with very high precision.
Foundations for light steel framing are essentially the same as for any form of construction, although dead loads applied by the light steel frame will be much lower than in the concrete or masonry construction.
Construction phases of steel buildings resembles the phases of conventional reinforced concrete buildings. The sections manufactured as per design are numbered properly. The profiles are sent to site either as profile or panellized parts, considering the distance of the construction site and transportation conditions. Profiles are assembled by trained assembly team at the construction site in line with the architectural plan. Only special studs are used during assembly, no welding is done.
Once the assembly is done, the frame is filled with insulation materials (fibreglass, rockwool etc). Walls are then covered with standard boards or similar approved materials. The sequence of construction comprises of foundation laying, fixing of tracks, fixing of wall panels with bracings as required,
fixing of floor panels, fixing of roof panels, decking sheet, fixing of electrical & plumbing services and finally fixing of insulation material & walling panels. Electrical Gas and plumbing, services are installed through pre-punched service holes in the web of the steel forms.Plastic grommets and silicon seals are used to fasten and protect wiring and pipes from corrosion and damage arising from vibrations
Electrical cables running within floor insulation layer in the separating floor construction should be protected with cartridge fuses or mini circuit breaker.
Wall panels are generally made by using heavy duty Cement Particle Board and Gypsum board. It can also be made using high density extended polystyrene core plastered from outside using wire mesh and chicken mesh. Galvolume sheet of appropriate thickness can also be used as cladding. This technology is certified by BMTPC under PACS.
LGSF is based on established system of light gauge steel structures and designed as per codal provisions with loading requirements as per Indian Standards. The merits of the system encompasses:
• Fully integrated computerised system with CNC machine provides very high accuracy upto 1 mm.
• High strength to weight ratio. Due to low weight, significant reduction in design earthquake forces. Chance of
progressive collapse are marginal due to highly ductile and load carrying nature of closely spaced studs/joists.
Speed in Construction
• Construction speed is very high. A typical four storeyed building can be constructed within one month.
Saving in foundation
• Structure being light, does not require heavy foundation.
• Structural element can be transported any place including hilly places to remote places easily and structure can
be erected fast.
• Structure can be shifted from one location to other without wastage of materials.
• Steel used can be recycled when required.
Certification - Other Referred Standards
IS 801: 1975 Code of Practices for use of cold formed and welded section and light gauge steel structural members in general building construction.
IS 2095 (Part 1) : 2011 Specification for Gypsum Plaster Boards - Part 1 Plain Gypsum Plaster Boards
IS 14862 : 2000 Specification for Fibre Cement Flat Sheets
ASTM – A653/ A 653 M -13 Specification for steel sheet, zinc coated (galvanized) on zinc – iron alloy coated by hot dip process.
ASTM – A 792/792 M -13 Specification for steel sheet, 55% aluminium zinc alloy coated by hot dip process
ASTM – A 875/875 M -13 Specification for steel sheet, zinc 5% aluminium alloy coated by hot dip process.
Posted on : 12/08/2017 01:24:47
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