Precast concrete.docx

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recast concrete is a construction product produced by casting concrete in a

reusable mold or "form" which is then cured in a controlled environment, transported to

the construction site and lifted into place. In contrast, standard concrete is poured into

site-specific forms and cured on site. recast stone is distinguished from precast

concrete by using a fine aggregate in the mixture, so the final product approaches the

appearance of naturally occurring rock or stone.

By producing precast concrete in a controlled environment (typically referred to as a

precast plant), the precast concrete is afforded the opportunity to properly cure and

be closely monitored by plant employees. Utilizing a Precast Concrete system offers

many potential advantages over site casting of concrete. The production process for

Precast Concrete is performed on ground level, which helps with safety throughout a

project. There is a greater control of the quality of materials and workmanship in a

precast plant rather than on a construction site. Financially, the forms used in aprecast plant may be reused hundreds to thousands of times before they have to be

replaced, which allows cost of formwork per unit to be lower than for site-cast

production .[1]

Prefabrication is the practice of assembling components of a structure in a factory or

other manufacturing site, and transporting complete assemblies or sub-assemblies to

theconstruction site where the structure is to be located. The term is used to distinguish this

process from the more conventional construction practice of transporting the basic materials tothe construction site where all assembly is carried out.

The term prefabrication also applies to the manufacturing of things other than structures at a

fixed site. It is frequently used when fabrication of a section of a machine or any movable

structure is shifted from the main manufacturing site to another location, and the section is

supplied assembled and ready to fit. It is not generally used to refer to electrical or electronic

components of a machine, or mechanical parts such as pumps, gearboxes and compressors

which are usually supplied as separate items, but to sections of the body of the machine which

in the past were fabricated with the whole machine. Prefabricated parts of the body of the

machine may be called 'sub-assemblies' to distinguish them from the other components.Contents

[hide]

1 The process and theory of prefabrication

2 History

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3 Current uses

4 Advantages of prefabrication

5 Disadvantages

6 Off-site fabrication

7 See also

8 External links

The process and theory of prefabrication[edit]

An example from house-building illustrates the process of prefabrication. The conventional

method of building a house is to transport bricks, timber , cement, sand, steel andconstruction

aggregate, etc. to the site, and to construct the house on site from these materials.

In prefabricated construction, only the foundations are constructed in this way, while sections

of walls, floors and roof are prefabricated (assembled) in a factory (possibly with window and

door frames included), transported to the site, lifted into place by a craneand bolted together.

Prefabrication is used in the manufacture of ships, aircraft and all kinds

of vehicles and machines where sections previously assembled at the final point of manufacture

are assembled elsewhere instead, before being delivered for final assembly.

The theory behind the method is that time and cost is saved if similar construction tasks can be

grouped, and assembly line techniques can be employed in prefabrication at a location where

skilled labour is available, while congestion at the assembly site, which wastes time, can be

reduced. The method finds application particularly where the structure is composed of repeating

units or forms, or where multiple copies of the same basic structure are being constructed.

Prefabrication avoids the need to transport so many skilled workers to the construction site, and

other restricting conditions such as a lack of power, lack of water, exposure to harsh weather or

a hazardous environment are avoided. Against these advantages must be weighed the cost of

transporting prefabricated sections and lifting them into position as they will usually be larger,

more fragile and more difficult to handle than the materials and components of which they are

made.

History[edit]

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"Loren" Iron House, at Old Gippstown inMoe, Australia

Prefabrication has been used since ancient times. For example, it is claimed that the world's

oldest known engineered roadway, theSweet Track constructed in England around 3800 BC,

employed prefabricated timber sections brought to the site rather than assembled on-site.[citation

needed ]

Sinhalese kings of ancient Sri Lanka have used prefabricated buildings technology to erect giant

structures, which dates back as far as 2000 years, where some sections were prepared

separately and then fitted together, specially in the Kingdom of Anuradhapura and Kingdom

of Polonnaruwa

In 19th century Australia a large number of prefabricated houses were imported from the United

Kingdom.

The method was widely used in the construction of prefabricated housing in the 20th century,

such as in the United Kingdom to replace houses bombed during World War II. Assembling

sections in factories saved time on-site and reduced cost. However the quality was low, and

when such prefabricated housing was left in use for longer than its designed life, it acquired a

certain stigma.[citation needed ].

The Crystal Palace, erected in London in 1851, was a highly visible example of iron and glassprefabricated construction; it was followed on a smaller scale by Oxford Rewley Road railway

station.

Current uses[edit]

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A house being built with prefabricated concrete panels.

The most widely-used form of prefabrication in building and civil engineering is the use of

prefabricated concrete and prefabricated steelsections in structures where a particular part or

form is repeated many times. It can be difficult to construct the formwork required

tomould concrete components on site, and delivering wet concrete to the site before it starts to

set requires precise time management. Pouring concrete sections in a factory brings the

advantages of being able to re-use moulds and the concrete can be mixed on the spot without

having to be transported to and pumped wet on a congested construction site. Prefabricating

steel sections reduces on-site cutting and welding costs as well as the associated hazards.

Prefabrication techniques are used in the construction of apartment blocks, and housing

developments with repeated housing units. The quality of prefabricated housing units had

increased to the point that they may not be distinguishable from traditionally-built units to those

that live in them. The technique is also used in office blocks, warehouses and factory buildings.

Prefabricated steel and glass sections are widely used for the exterior of large buildings.

Detached houses, cottages, log cabin, saunas, etc. are also sold with prefabricated elements.

Prefabrication of modular wall elements allows building of complex thermal insulation, window

frame components, etc. on an assembly line, which tends to improve quality over on-site

construction of each individual wall or frame. Wood construction in particular benefits from the

improved quality. However, tradition often favors building by hand in many countries, and the

image of prefab as a "cheap" method only slows its adoption. However, current practice alreadyallows the modifying the floor plan according to the customer's requirements and selecting the

surfacing material, e.g. a personalized brick facade can be masoned even if the load-supporting

elements are timber.

Prefabrication saves engineering time on the construction site in civil engineering projects. This

can be vital to the success of projects such as bridges and avalanche galleries, where weather

conditions may only allow brief periods of construction. Prefabricated bridge elements and

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5. Local jobs may be lost, if the work done to fabricate the components being located in a

place far away from the place of construction. This means that there are less locals

working on any construction project at any time, because fabrication is outsourced.

Off-site fabrication[edit]

Off-Site fabrication is a process that incorporates prefabrication and pre-assembly. The process

involves the design and manufacture of units or modules, usually remote from the work site, and

the installation at the site to form the permanent works at the site. In its fullest sense, off-site

fabrication requires a project strategy that will change the orientation of the project process

from construction to manufacture to installation. Examples of off-site fabrication are wall panels

for homes, wooden truss bridge spans, airport control stations.

Dr. Abhay Gupta, Vice President (Engineering) Era Building Systems Ltd. Noida

PEB: A New Technological Wave

Technological improvement over the year has contributed immensely to the enhancement of

quality of life through various new products and services. One such revolution was the pre–

engineered buildings. Though its origin can be traced back to 1960's, its potential has been

felt only during the recent years.

An estimated 70% of all new commercial buildings in the US are pre-engineered! There is

really no dispute in the fact that pre-engineered building systems are the new wave in

construction.

Definition

"Pre-engineered steel buildings" are those which are fully fabricated in the factory after

designing, shipped to site in CKD(completely knocked down) condition; and all components

are assembled and erected at site with nut-bolts, thereby reducing the time of completion.

Pre–engineered means, generally speaking, is any part of a structure that is manufactured

prior to its arrival on the building site. The concept of the pre-engineered building (PEB) is

one where the fabrication is completed in a controlled environment with the latest

technology, and then subsequent erection is carried out.

Though initially only off the shelf products were available in these configurations aided by

the technological development tailor made solutions are also made using this technology in

very short durations.




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The designs were ready-made but the building components were either ready-made or

manufactured against specific orders. These buildings were pre-designed or 'pre-engineered'

into standard sizes, spans, bays and heights, and use standard details for fixing cladding,

roofing, gutters, flashing, windows, doors etc taking advantage of industrial practices of

mass production of components economically.

Although PEB systems are extensively used in industrial and many other nonresidential

constructions worldwide, it is relatively a new concept in India. These concepts were

introduced to the Indian markets in the late 1990's with the opening up of the economy;

and a number of multi–nationals setting up their projects. The current pre–engineered steel

building manufacturing capacity is 6.0 lac ton per annum. The industry is growing at the

compound rate of 25 to 30%.

With respect to design of the structure and aesthetic appearance India is way behind. Indian

manufacturers are trying to catch up; comparatively PEB is a new concept in India.

A healthy trend in the form of growth in demand for construction works in residential,

Commercial, Institutional industrual and infrastructure sectors are being seen over the past

decade. Modern Structures are much more complex and sophisticated as compared to

earlier period. One of the major changes which are being felt by all is that the present

structures are taller and thinner. Modern day requirement of structures is that these should

be lighter yet not compromising on functionality. Civil engineering construction has seen a

continual economic competition between steel, concrete and other construction materials.

Currently, the total steel production in the country is about 45Mn Ton against 1280Mn ton of

world. Per capita steel consumption in India is 42kg whereas it is 270kg in China. About

10% of steel goes to the construction industry and amidst it PEB accounts only for the0.5Mn ton. As on date. In the next 5 years, the steel production will be doubled and with

efforts of organisations like BIS and INSDAG, steel intensive construction may rise up to

22Mn ton. Owing to advantages of PEB, several non-conventional segments are also getting

attracted to use PEB and the potential will rise up to 2.2Mn ton which is four to five times of

today's scenario.

Subsequent paragraphs are only a humble attempt to present the various aspects of

conceptual development, technology of design and manufacture; and future growth aspects

of Pre–engineered building Industry in India along with its grey areas.

he Concept: Superiority of PEB over Conventional Construction

Pre–engineered steel buildings use a combination of built-up sections, hot rolled sections

and cold formed elements which provide the basic steel frame work with a choice of singleskin sheeting with added insulation or insulated sandwich panels for roofing and wall

cladding. The concept is designed to provide a complete building envelope system which is

air tight, energy efficient, optimum in weight and cost and, above all, designed to fit userrequirement like a well fitted glove.



These Pre–engineered Steel Buildings can be fitted with different structural accessories

including mezzanine floors, canopies, fascias, interior partitions, crane systems etc. The

building is made water-tight by use of special mastic beads, filler strips and trims. This is a

very versatile building system and can be finished internally to serve any required function

and accessorized externally to achieve attractive and distinctive architectural styles. It ismost suitable for any low-rise building and offers numerous benefits over conventional

buildings.

It is very advantageous over the conventional buildings and is really useful in case of the

low rise buildings. Pre-engineered buildings are generally low rise buildings; however the

maximum eave heights can go up to 25 to 30 meters. Low rise buildings are ideal for

offices, houses, showrooms, shop fronts etc. The application of pre-engineered concept to

low rise buildings is very economical and speedy. Buildings can be constructed in less than

half the normal time especially when complimented with other engineered sub-systems.

Table-1 presents an overview of comparison between RCC, Conventional steel and PEB

structures.

Advantages



Pre-engineered building systems provide real value to clients without sacrificing durability,seismic and wind resistance, or aesthetic appearance. Cost savings begin right at the

drawing preparation stage. Systems engineering and fabrication methods help reduce

interim financing costs through faster construction and minimised field erection expense. Anadded benefit is earlier occupancy of the facility and a head start on day-to-day operations

by the client.

Apart from costs, there is an assurance of factory-built quality and uniformity in design and

fabrication. These systems are also energy efficient; incorporate watertight roofing systems;enable easy disassembly or future expansion and have the lowest life cycle maintenance

costs.

Adding to these; there is no mess of sand and cement; power savings; walkable ceilings;

progressive and non-progressive panel systems for walls. A poor man can be provided witha home created under strict quality control and having a longer life span, with greater safety

against natural disasters like earthquakes and cyclones.



Moreover, It is possible to create the building in required form and shape. And the 'system

approach' renders a holistic way of thinking at one platform for consultants, designers,

architects, and builders. Thus it tends to achieve a perfect harmony among variousstringent specifications and aesthetic requirements in a most economic way.

In nutshell, the benefits may be summarized as under: Increased speed of construction, quicker return on investment

Ensured quality of material, Design and construction

Unlimited architectural possibilities

Enhanced Durability and seismic reliability

Easy construction, maintenance and refurbishing

Increased Life cycle performance and cost competitiveness

Environment–friendly structures

Better value for money

Cleaner and unencumbered sites

Sustainability in construction through reuse of most materials

Suitability for Hilly regions and other geographically difficult areas Hassle Free

Optimized design of steel reducing weight

Better Earthquake & Wind pressure resistant.

Energy efficient roof and wall system using insulations.

Easy integration of all construction materials

The building can be dismantled and relocated easily.

Future extensions, expansion modification can be easily accommodated without

much hassle.

Faster delivery and erection, saving around 30-40% of project time

Column-free large spans, up to 90 m.

Virtually maintenance free

Single-source responsibility

'Systems approach' ensures integrity and safety of all building components

Lighter weight; savings in foundation cost of 10-20 percent

Insulated from sound and heat, as per the requirement

Better rainwater harvesting through gutters and down-take arrangements

Overall economy

Diversified Applications



Almost every conceivable building use has been achieved with PEB; the most common

applications are industrial, institutional and commercial.

In India, Pre-engineered building systems find application primarily in the construction of

Warehouses, & Industrial sheds & Buildings. The recent focus has also shifted to cover Rural

as well as urban, individual and mass housing projects, farmhouses, slum re-organisationprojects and rehabilitation projects, amenity structures like health centres, kiosks, primary

schools, panchayat ghars etc. The pharmaceutical industries and exhibition centres, andfunctional requirements like offices, seminar halls, call centres, supermarkets, showrooms

etc. have also attracted PEB. Earthquake-resistant buildings are the recent applications of

PEB with wide and immediate acceptance.

PEB concept has acted as a catalyst in the infrastructure development of the country. Singlestoried houses for living take minimum time for construction and can be built in any type ofgeographic location like extreme cold hilly areas, high rain prone areas, plain land, extremehot climatic zones etc.

Applications of pre-engineered steel buildings include (but are not limited to) the following: Industrial Buildings & Workshops



Warehouses

Commercial Complexes & Supermarkets

Showrooms

Corporate Office Buildings

Schools

Indoor Stadiums

Outdoor Stadiums with canopies

Fuel Stations

Metro Stations, Bus Terminals, Parking Lots

Highrise Buildings

Customized Housing

Large Exhibition Centers

And many more…

Aircraft Hangers

Labor Camps

Community Centers

Railway Stations & Railway Storage yards

Equipment housing/shelters Telecommunication shelters

"Almost" any low-rise building

There is a great possibility of improving the aesthetic quality with a choice of roofingelements, exterior finishes, weather-sheds, color system and variations in planning as well

as massing. Main Components

There are following major components in a pre-engineered building: Primary or Main frame

Gable End framing or Wind columns

Secondary frame or Purlins, girts etc.

Roof & Wall Sheeting

Bracing system

Crane system

Mezzanine system

Insulations

Attachments like canopies, fascia etc

Doors, Windows, Ventilators

Accessories like Turbo vents, Ridge Vents, Skylights etc.

Main Framing



Main framing basically includes the rigid steel frames of the building. The PEB rigid framecomprises tapered/straight columns and tapered rafters (steel plate fabricated 'I' or 'H'

sections are referred to as built-up members). The frame is erected by bolting the end

plates of connecting sections together.

Secondary frame or Purlins, girts etc.

Purlins, girts and eave struts are also known as secondary cold-formed members. There is

no welding involved in their preparation. They are prepared by press bending the HR steel

coil giving it the desired shape(Z- or C-shape).

Roof & Wall Panels

Metallic plain or color coated profiled steel sheets are used as roof and wall sheeting. The

steel sheets are generally made from Zincalume or Galvalume coils in thickness range of0.47mm to 0.55mm. The base steel is either galvanized having a zinc coating varying from

a minimum Mass of 120 gsm./m2 to a maximum of 275 gsm./m

2 (total of both sides) or a

base steel coating of zinc – aluminum (zinc 45%, aluminum 55%) of total Mass of 150

gsm./m2 (total of both sides) are available with permanent color coating. The color coating

is also available in various options in polyester paint coating like regular modified polyester,silicon modified polyester and super polyester coatings. Special organic coatings like PVF2

(Poly Vinyl Fluoride) are also made available. These various color coatings on the base steelwith galvanized or zinc aluminum coating provides suitable resistance for various kinds of

environment hazards. Metal roofing and siding profiles can be manufactured to any length – limited only by transportation constraints (usually to 12 meters). Lap joints with 150mm to

200mm overlap virtually eliminate water ingress.

Profiling can be carried out at site itself with no limit in lengths. This permits a totally joint-less run of roofing, a major advantage to the designers to create roofing with the minimum

pitch. Machines have been developed which permit rolling at the eaves level so that even

the task of lifting and shifting the rolled profiles in to position is avoided. Standing seamprofiles with a pre-determined height of up-stands can be chosen to accommodate the

expected run-off of water without overflow on to the crest of the profile.

At the initial project planning stage, roof slope is a key consideration for architectsincorporating roof systems into their designs. Slopes as shallow as 1:20 are possible

ensuring sufficient drainage of water and good long term performance of roof panels.

These profile steel sheets are usually categorized into two types depending upon the type offixing arrangement followed. These two types are known as Through Fastened and second

one is Standing Seam.

Installation of this type of roofing & cladding system can provide 30 years or more of



trouble-free service in most environments.

Insulations

These buildings can be properly insulated by providing fibrous insulation slabs/rolls of non-combustible Rockwool, Aluminum foil laminated, placed over a metal mesh bed created

between the purlins, and then the roofing steel sheet fixed over it. The siding walls can alsobe insulated by providing a double skin profile steel sheet wall cladding having RockwoolInsulation slab sandwiched in between and held in position with the help of 'Z' spacers in

between the two profile steel sheets. In similar pattern a double skin insulated roofingsystem can also be erected.

Sandwich Panels

Another alternative is to provide pre-fabricated insulated panels, which comprises two singleskin panels (plain steel sheets zincalume color coated) with polyurethane foam insulation inbetween. These panels are intended for use as thermally efficient roof and wall claddings for

buildings e.g., in high altitude areas and cold storages. In addition to the above sandwichpanels also find extensive use in residential as well as non-residential buildings. The panels

provide sufficient insulation and noise reduction properties. Nowadays large cold storageunits (Potato, Onion, vegetables, processed foods etc.) are also made with this pre-

engineered building technique.

Crane systems

These pre–engineered buildings can be equipped with Overhead EOT cranes, Semi-gantry

cranes, wall mounted cranes, Mono rails and under slung cranes for various material and

equipment handling operations inside. These buildings are being designed for crane



capacities ranging from 1MT to 250MT. The crane runway beams (Gantry Girders) are

simply supported built-up sections with/without cap channels and with maintenance

platforms and ladders. Catwalks for crane maintenance are usually mounted alongside thecrane beams, suspended under rigid frame rafters or elevated above the top of the building

roof. Cranes at various levels can also be provided. PEB vendors generally do not keep thesupply of rail and Crane Bridge with crane in their scope.

Mezzanine systems

Standard mezzanine structure consists of built-up beams that support built-up, hot-rolled orcold-formed mezzanine joists which in-turn support a metal deck. A concrete slab is cast on

the metal deck as a finished surface. Steel checkered plates may also be used as topsurface. These mezzanines are used for office space, storage or equipment supports in

industries. For commercial buildings and highrise structures several types of light weight

panel boards are available as horizontal surface.

Bracing system

Longitudinal cross bracing, used to provide lateral stability to the structure against wind,seismic or other forces, comprises of rods, pipes, angles or cables with an eye bolt and an

adjusting nut at both ends, located near the outer flange of columns or rafters and attachedat the web of the rigid frame.

Paints and finishes

Any desired finish can be achieved as per the architect/client recommendations. Various

choices are synthetic enamel or epoxy based paints, depending upon the environment insideand outside the building.

Accessories, Attachments etc.

As per the functional and architectural requirements, accessories are supplied in ready to fit

condition. Ventilation and lighting systems should be properly designed in consultation with

an expert. High Strength Materials

The standard mild steel used in civil engineering construction have nominal yield stress

values of approximately 250MPa but the PEB industry is using high tensile hot rolled steelplates and coils of 345MPa. Recent revision of IS2062:2006 has incorporated these hightensile grades of steel for structural uses and there are a good number of manufacturers

like TATA, SAIL, etc. who are manufacturing these in India. The new materials like Fe540B

gives yield stress as large as 410MPa in plate thickness lower than 20mm. the galvalume orzincalume roofing and wall sheets have strengths in the range of 550MPa. Steel became

more popular in design and construction of larger structures as well structures with unusual

geometry due to its large strength to weight ratio, viability of economical fabrication, andease of erection.

A typical sample of material specs for a PEB project, as defined and freezed in advance is

enclosed for ready reference. This indicates that the client is assured of the quality ofmaterial that is being supplied.



The design Process & Principles

Pre-engineering of metal buildings can be optimized to meet specific design criteria. LargelyIndian and American practice of design is followed by most of the consultants and PEBvendors in India these days. A brief of design codes used in each of these is attached

herewith:

PEB Design Process in Brief

The Load calculations are done as in the case of a regular frame. Normally, the critical casegoverning the designs would be (DL+WL) or (DL+LL) conditions as the PEB slopes are minor(like 1 in 10). The support conditions are normally hinged, but it is some times beneficial,

on a selective basis to use a fixed condition giving a gussetted base plate and Anchor boltcombination. In Hinged base condition, the section is normally tapered down and providedwith a Bolted connection to the base. All the other Joints would be normally designed as

rigid joints and steel connections are moment connections, transferring the axial, momentand shear values between the sections connected. In the Wind load calculations, the designwind pressures should be arrived at after a careful analysis and combinations of internal and

external pressure coefficients or force coefficients, referring to IS-875 pt.3 latest version.

Proper load combinations with Wind, Earthquake and Crane loads should be investigated.

Any standard structural analysis and design software can be employed for PEB designs, like

STAAD etc. However, couple of good dedicated software is also available for PEB like MBS,Precision Plus etc. Since detailing and connectivity of various components is much moreimportant, owing to CKD nature, it is good to use a high end detailing software that also has

a BIM capability, like TEKLA Structures, which provides a complete integration of complete

analysis, design, detailing, Bill of material preparation and production/dispatch/erectionplanning.

Usually, Checking the Combination Stresses and comparing with the limiting values (in LSD

or WSD) is done using interactive software, which calculates the Exploitation efficiency of

the section, i.e., if the Actual Stress/permitted stress is 0.95, it means that the section isexploited for 95% of its strength. For this, the total weight of the frame is calculated. A no.

of trails are done such that sections are designed with Variables like Flange thk, Web thk,Flange Width, Web Depth, so that the Entire frame becomes theoretically safe, and is of

minimum wt! Checking for defections is the next step. Many times sections need to berevised to hold the theoretical maximum deflections within the permissible ones. Some

Vendors exploit 90% of the section, leaving 10% for probable lapses in manufacturing,transporting, assembling & erection. But the competition has made (forced) people believe

that there are no lapses anywhere! The Next important step is to design the welds between

the flanges and Webs. Here too, Efficiency of the weld plays an important part. Hence, PEBmanufacturer will avoid any weld at the site, because a 4.5 mm weld at the shop may be

better than 6 or 8 mm weld at the site.

Next step is to design the Field joints (Where the parts are assembled at the site). Theresultant forces are known at the joints; design a bolted connection, preferablyperpendicular to the plane of frame, to exploit tensile capacity of bolts for BMs rather thanthe shear capacities. Hence, Number of bolts required for the connection will reduce. These

joints are also placed at Optimum locations! That is the advantage of pre engineering.

The secondary members like Purlins and Girts are designed as per codes for thin Cold

Formed Sections, with or without lip. One can use many span reducing and Lateral





High Engineering Production/Erection Process

The PEB production process primarily consists of FOUR major parallel processing lines, asunder:

1. Built-up members for Primary frame

2. Cold forming for Secondary framing3. Profiling for Roof and Wall sheeting

4. Accessories & Bracings like Gutters, down take pipes, ridge Vents, Skylights, clips

etc.

The flow chart in image explains the parallel processing and then after final inspection,ready for shipment in CKD conditions.

The production & shipment of these components for a PEB structure uses followingprocesses:

1. Plate cutting using Shear/Plasma/Multi-torch through nesting software for optimized

use of plate area.2. H-beam welding on automatic welding machines using SAW or MIG welding process

3. Fabrication for fitments like end plates, stiffeners and connections cleats.

4. Cleaning the surface for painting

5. Slitting HR coils for cold forming operations to make Z and C sections with punching

6. Cutting and threading sag rods and bracing rods

7. Fabrication of Diagonal bracing angles or pipes

8. Profiling the Galvalume/Zincalume sheets for roofing and wall cladding

9. Manufacturing Gutters, down take pipes in press bend

10. Procuring and assigning required matching fasteners for connections

11. Organizing some bought out accessories

12. Quality control tests & inspection; and matching with project wise Bill of Quantitiesas given by the engineering department.

13. Dispatching to project sites as per sequence of erection

Erection

Steel framing members are delivered at site in pre-cut sizes, which eliminates cutting andwelding at site. Being lighter in weight, the small members can be very easily assembled,

bolted and raised with the help of cranes. This system allows very fast construction and

reduces wastage and labour requirement. These buildings can then be provided with roofdecking and wall cladding with metal profile sheets and proper insulation. The framing are

so designed that electrical and plumbing services are part of it and can be very easily

concealed.

However, the erection process is highly technical and needs skilled and trained manpower to

handle heavy construction equipments. Proper training of erection engineers for

understanding of drawings and execution of work is necessary. A qualified and experiencedwork agency should be employed for erection work. Grey Areas: Points of Concern: What Glitters is not always GOLD…????



The evolution of the application of steel in civil engineering practice gives rise to many

issues from the point of view of engineering design, research and development of steel

structures.

Issues of Concern

Fire protection

Although great advances have been made in lighter and more economical fire

protection systems but fire protection remains an issue of greater concern for steel

structures than compared to concrete or other construction materials. The smaller

members and thermal mass associated with steel structures makes it more

vulnerable. The memories of collapse of world trade centre towers in USA due to fire

caused by burning of aviation fuel and sudden rise of temperature leading to

complete destruction of structure might not have faded away. Fire protection adds

up to larger part of structural cost. It would be a challenge to engineers toward

reducing these costs, while assuring adequate resistance to elevated temperatures

expected during a fire.

BucklingBuckling and stability become more critical in Steel structures due to smaller

members and large stress levels.

Micro Cracks

The increasing yield stress, operating stress levels, emphasis on plastic and ultimate

capacity, and use of welded construction have resulted in increased frequency of

initiation of micro cracks and cause of fracture in bridges and industrial structures.

Further development of Micro Cracks and crack growth become a major concern in

areas of seismically vulnerable areas.

Corrosion

Steel has great tendency to corrode when exposed to the environment, which leads

to deterioration, increased maintenance costs, and increased reconstruction costs.

Although Galvanization, paint, and coatings may provide protection against

corrosion, yet they increase the overall fabrication costs of the steel structure

appreciably. In hot and humid regions and industrially polluted severe environments

problem is more pronounced. Therefore, engineers have to continually seek

economically viable solutions to aim at reducing these costs.

Welding

Presently welded constructions are more commonly used, for these provide stiffer,

stronger structures with reduced building weight. Increased steel yield strength

requires new innovative welding methods, because high strength steels pose more

difficulty to weld without affecting adversely the ductility and performance of the

structural system. Recently the use of fully automatic and semi-automatic

submerged arc welding results in increase in welding speed apart from the goodquality. The elimination of any fumes, smoke or any visible arc column gives an ease

of operation and efficiency; better quality & thus encourages its application in

welding industry.

Ductility from seismic considerations

Seismic design is today a must requirement for almost all civil engineering

structures. Although steel is an ideally more suited material from point of view of

seismic design because of its property inherent material strength, stiffness, and



ductility. Weldability may affect the seismic performance and it follows that new

methods to improve inelastic seismic performance of steel structures need to be

investigated.

Meliorations

Critics point to poor aesthetics with a typical 'industrial' or 'warehouse' look; minimal

flexibility regarding location, shape and size of structural members; the need to utilise offthe shelf building shapes and sizes in order to realise cost savings; and a lighter structurewhich does not achieve the longevity of more conventional structural systems.

"The most basic prerequisite of PEB is 'single sourcing' of the entire building. Any slightdeviation from this can deprive the customers of the real advantages. Also, as steel is prone

to corrosion, it would require various protective coatings which may sometimes make PEB

unfeasible economically."

Maintenance

In PEB the maintenance area is the steel roofing & cladding. Installed roofing must beinspected at least once a year. Any exposed metal that can rust or has rusted should be

painted. Leaves, branches, and trash should be removed from gutters, at ridge caps and incorners. Also watch out for discharge from industrial stacks, and particulate matter and highsulphur exhaust from space heaters which could get piled up. The Future Bright Towards the Economic growth

Steel is a preferred material for construction, due to its various advantages like quality,aesthetics, economy and environmental conditions. This concept can have lot of scope in

India, which can actually fill up the critical shortage of housing, educational and health care

institutions, airports, railway stations, industrial buildings & cold storages etc.

Pre-engineered Metal building concept forms a unique position in the construction industry

in view of their being ideally suited to the needs of modern Engineering Industry. It wouldbe the only solution for large industrial enclosures having thermal and acoustical features.The major advantage of metal building is the high speed of design and construction for

buildings of various categories.

The present construction methodology for buildings calls for the best aesthetic look, highquality & fast construction, cost effective & innovative touch. One has to think for

alternative construction system like pre-engineered steel buildings. India has an installed

steel capacity of 35 to 40 million ton & apparent steel consumption is around 27 to 30million ton. In pre-engineered building concept the complete designing is done at the

factory and the building components are brought to the site in knock down condition. These

components are then fixed / jointed at the site and raised with the help of cranes.





will need to develop suitable Codes and specifications for the purpose to meet the

requirements of future generations. There is increased invest more for research and

development for innovative material and construction methodologies.

One has to use the PEB products, with a word of caution, and frame the contract provisions

accordingly. We are fairly close to a day when steel buildings should be the rule, rather thanbeing the exception, if we work together to give the Client, best value for his money.

Documents

Precast concrete.docx