Pre Engineered Buildings

1. INTRODUCTION

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. Through its origin can be traced back to 1960’s its potential has been felt only during the recent years. This was mainly due to the development in technology, which helped in computerizing the design and design.

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. A recent survey by the Metal Building Associations (MBMA) shows that about 60% of the non residential low rises building in USA are pre engineered buildings.

Although PEB systems are extensively used in industrial and many other non residential constructions world wide, it is relatively a new concept in India. These concepts were introduced to the Indian markets lately in the late 1990’s with the opening up of the economy and a number of multi nationals setting up their projects. The market potential of PEB’s is 1.2 million tones per annum. The current pre engineered steel building manufacturing capacity is 0.35 million tones 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’s is a new concept in India. Beside, in fabrication and other areas of PEB India is very good. As compared to other countries Indian codes for building design are stringent but safer. IS standards are upgraded continuously. In India, American codes are also followed.

- 1 -

Pre engineered steel buildings can be fitted with different structural accessories including mezzanine floors, canopies, fascias, interior partitions etc. and the building is made water proof by use of special mastic beads, filler strips and trims. This is very versatile buildings systems and can be finished internally to serve any functions and accessorized externally to achieve attractive and unique designing styles. It is very advantageous over the conventional buildings and is really helpful in the low rise building design.

Pre engineered buildings are generally low rise buildings however the maximum eave height can go upto 25 to 30 metres. Low rise buildings are ideal for offices, houses, showrooms, shop fronts etc. The application of pre engineered buildings concept to low rise buildings is very economical and speedy. Buildings can be constructed in less than half the normal time especially when complemented with the other engineered sub systems.

The most common and economical type of low rise buildings is a building with ground floor and two intermediate floor plus roof. The roof of low rise buildings may be flat or sloped. Intermediate floors of low rise buildings are made of mezzanine systems. Single storied houses for living take minimum time for construction and can be built in any type of geographical location like extreme cold hilly areas, high rain prone areas, plain land obviously and extreme hot climatic zones as well.

- 2 -

2. BUILDING COMPONENTS

1. Prime Steel Framing Systems

We can design prime steel framing systems according to the provided specifications for type, height, width, bay spacing and other parameters. These prime steel framing systems are constructed using premium quality, high grade steel plates with minimum yield strength ranging from 245MPa to 345MPa. The steel plates are painted with a minimum of 25 Microns DFT of red oxide primer. Each steel structural framing system is designed by experienced engineers and manufactured to precision tolerances under rigid quality controlled plant conditions. Some of common primary steel structural framing systems include:

Clear Span (CS)

Building without interior columns- maximum practical width = 80 m

- 3 -

Single Slope (SS)

Building without interior columns- maximum practical width = 50 m

Multi-Span “1” (MS-1)

Building with one interior column- maximum practical module width = 70 m

- 4 -

Multi-Span “2” (MS-2)

Building with two interior columns- maximum practical module width = 70 m

Multi-Span “3” (MS-3)

Building with three interior columns- maximum practical module width = 70 m

Multi-Gable (MG)

- 5 -

Maximum practical module width = 80 m

Roof System (RS)

Maximum practical width = 30 m

2. Secondary Systems

- 6 -

Secondary structural steel framing system refers to purlins, girts, eave struts, wind bracing, flange bracing, base angles, clips and other miscellaneous structural parts. Some common examples are structures like typical "Z" section, typical "C" section, eave strut, etc.

The secondary structural steel framing system is available in 1.5 mm to 3 mm thickness with a minimum yield strength of 245 to 345 MPa. The structures are made of imported steel and are factory painted with a minimum of 15 microns DFT of red oxide primer.

Purlins, girts and eave struts are secondary structural members used to support the wall and roof panels.  Purlins are used on the roof; girts are used on the walls and eave struts are used at the intersection of the sidewall and the pump stations.

Secondary members have two other functions: they act as struts that help in resisting part of the longitudinal loads that are applied on the building such as wind and earthquake loads, and they provide lateral bracing to the compression flanges of the main frame members thereby increasing frame capacity.

3. Coated Steel Sheet Products

- 7 -

Coated steel sheet products have many attributes that make them suitable for diverse use in construction industry. These colours coated steel sheets and coated wall panels provide a combination of strength formability, jointability, paintability and economy. Colour coated sheets provide excellent resistance to corrosion and hence has become the most preferred material for a wide range of construction uses, particularly roofing and walling.

Coated steel sheets make a unique building material. These colours coated steel sheets combines the strength of steel with corrosion protection of zinc or zinc/aluminum alloy coatings. These colour coated sheets can be punched, pressed, roll-formed and joined into a number of structural and decorative building components.

4. Decking Sheets

Flordec Sheets (Corrugated Sheet for Composite Floor)

Flordec decking sheets are composite floor systems, constructed with cold-rolled corrugated steel decking covered with concrete. These advanced steel floor decks are designed to provide an impact and abrasion resistant surface on concrete subject to extreme wear and tear. The formulation of floor decking sheets is self-leveling and ideal for use in material distribution facilities, warehouses, assembly plants etc.

- 8 -

These steel deck sheets have a unified bond with all the characteristics of traditional reinforced concrete, where the decking sheet, after having performed the function of frame work, acts as a metal reinforcement. Appropriate crop ends in these steel deck sheets are provided to absorb the negative moments.

Insulation (PEBI)

DescriptionPre-Engineered Building Insulation (PEBI) is a highly efficient, lightweight,

strong resilient and easy to handle flexible blanket insulation composed of fine, stable and uniformly textured inorganic glass fibers bonded together by a non-water soluble and fire-retardant thermosetting resin. It is free from coarse fibers and shot due to its mineral composition.

- 9 -

3. DESIGN OF PRE ENGINEERED BUILDINGS

The main framing of PEB systems is analyzed by the stiffness matrix method. The design is based on Allowable Stress Design (ASD) as per the American Institute of Steel Construction specification or the IS 800. The design program provides an economic and efficient design of the main frames and allows the user to utilize the program in different modes to produce the frame design geometry and loading and the desired load combinations as specified by the building code opted by the user. The program operates through the maximum number of cycles specified to arrive at an acceptable design. The program uses the stiffness matrix method to arrive at an acceptable design. The program uses the stiffness matrix method to arrive at the solution of displacements and forces. The strain energy method is adopted to calculate the fixed end moments, stiffness and carry over factors. Numerical integration is used.

Design Cycle

The design cycle consists of the following steps:

1. Set up section sizes and brace locations based on the geometry and loading specified for the frame design.

2. Calculate moment, shear, and axial force at each analysis point for each load combination.

3. Compute allowable shear, allowable axial and allowable bending stress in compression and tension at each analysis point.

4. Compute the corresponding stress ratios for shear, axial and bending based on the actual and allowable stresses and calculate the combined stress ratios.

5. Design the optimum splice location and check to see whether the predicted sizes confirm to manufacturing constraints.

6. Using the web optimization mode, arrive at the optimum web depths for the next cycle and update the member data file.

7. At the end of all design cycles, an analysis is run to achieve flange brace optimization.

- 10 -

Frame Geometry

The program has the capability to handle different types of frame geometry as follows:

Frames of different types viz. rigid frames, frames with multiple internal columns, single slope frames, lean to frames etc.

Frames with varying spans, varying heights and varying slopes etc.

Frames with different types of supports viz. pinned supports, fixed supports, sinking supports, supports with some degrees of freedom released.

Unsymmetrical frames with off centric, unequal modules, varying slopes etc.

User specified purlin and girt spacing and flange brace location.

Frame Loading

Frame design can handle different types of loadings as described below:

All the building dead loads due to sheeting, purling, etc. and the self weight of the frame.

Imposed live load on the frame with tributary reductions as well.

Collateral load such as false ceiling, light fixtures, AC ducting loads, sprinkler systems and many other suspended loads of similar nature.

Wind loads input such as basic wind speed or basic wind pressure that will be converted to deign wind pressure as per the building code specified by the user and shall be applied to the different members of the building according to the coefficients mentioned in the codes prescribed by the user. The standard building codes like MBMA, UBC, ANSI, IS: 875 part 3 etc are used fro this purpose.

Crane and non crane loading can be specified by the user and the program has the capability to handle these special loads and combine them with the other loads as required.

- 11 -

Seismic loads corresponding to the different zone categories of various international codes can also be defined and combined with other load cases as required. Temperature loads can also be specified in the form of different differential temperature value on centigrade and specifying the appropriate coefficient for the thermal expansion. Load combinations with appropriate load factors can be specified by the user as desired.

Design Codes

Following are the main design codes generally used:

AISC: American institute of steel construction manual

AISI: American iron and steel institute specifications

MBMA: Metal building manufacturer’s code

ANSI: American national standards institute specifications

ASCE: American society of civil engineers

UBC: Uniform building code

IS: Indian standards

Latest International Codes & Deflection

- 12 -

Design Criteria

DESIGN METHOD: Allowable stress design method is used as per the AISC specifications.

DEFLECTIONS: Unless otherwise specified, the deflections will go to MBMA, AISC criteria and standard industry practices.

PRIMARY FRAMING: Moment resisting frames with pinned or fixed bases.

SECONDARY FRAMING: Cold formed Z sections or C sections for purlins or girts designed as continuous beams spanning over rafters and columns with laps.

LONGITUDANAL STABILITY: Wind load on building end walls is transferred through roof purlins to braced bays and carried to the foundations through diagonal bracing.

DESIGN SOFTWARE

The latest software that is used for design is STAAD 2007.

- 13 -

4. ERECTION SYSTEM

Preparation for Erection

1. Pre Erection checks2. Receiving Materials at site3. Unloading Containers

. Erection of the Framing

1. Preparation of the First Bay2. Main frames3. Mezzanine floors4. Crane Beams

Sheeting & Trimming

1. Sheeting preparation2. Sheeting the walls3. Sheeting the roofs4. Miscellaneous trimmings5. Fascia

- 14 -

5. PRE ENGINEERED BUILDING vs CONVENTIONAL STEEL BUILDINGS

PROPERTY PEB BUILDINGS CONVENTIONAL STEEL BUILDINGS

STRUCTURE WEIGHT Pre engineered buildings are on the average 30% lighter because of the efficient use of steel. Primary framing members are tapered built up section. With the large depths in areas of higher stress.

Primary steel members are selected hot rolled “T” sections. Which are, in many segments of the members heavier than what is actually required by design? Members have constant cross section regardless of the varying magnitude of the local stresses along the member length.

Secondary members are light weight roll formed “Z” or “C” shaped members.

Secondary members are selected from standard hot rolled sections which are much heavier.

DESIGN Quick and efficient: since PEB’s are mainly formed by standard sections and connections design, time is significantly reduced. Basic design based on international design codes are used over and over.

Each conventional steel structure is designed form scratch with fewer design aids available to the engineer.

Specialized computer analysis design programs optimize material required. Drafting is also computerized using standard detail that minimizes the use of project custom details.

Substantial engineering and detailing work is required from the very basic is required by the consultant with fewer design aids.

Design shop detail sketches and erection drawings are supplied free of cost by the manufacturer. Approval drawing is usually prepared within in 2 weeks.

Extensive amount of consultant time is devoted to the alterations that have to be done.

PEB designers design and detail PEB buildings almost every day of the year resulting in improving the quality of designs every time they work

As each project is a new project engineers need more time to develop the designs and details of the unique structure.

DELIEVERY Average 6 to 8 weeks Average 20 to 26 weeksFOUNDATIONS Simple design, easy to construct Extensive, heavy foundation

- 15 -

and light weight. required.ERECTION SIMPLICITY Since the connection of

compounds is standard the learning curve of erection for each subsequent project is faster.

The connections are normally complicated and differ from project to project resulting tin increasing the time for erection of the buildings.

Periodic free of charge erection is provided at the site by the manufacturer.

There has to be separate allocation of labour for the purpose of erection.

ERECTION COST AND TIME

Both costs and time of erection are accurately known based upon extensive experience with similar buildings.

Typically, conventional steel buildings are 20% more expensive than PEB in most of the cases, the erection costs and time are not estimated accurately.

The erection process is faster and much easier with very less requirement for equipment.

Erection process is slow and extensive field labour is required. Heavy equipment is also needed.

SEISMIC RESISTANCE The low weight flexible frames offer higher resistance to seismic forces.

Rigid heavy frames do not perform well in seismic zones.

OVER ALL PRICE Price per square meter may be as low as by 30 % than the conventional building.

Higher price per square meter.

ARCHITECTURE Outstanding architectural design can be achieved at low cost using standard architectural details and interfaces.

Special architectural design and features must be developed for each project which often requires research and thus resulting in higher cost.

SOURCING AND COORDINATION

Building is supplied complete with all accessories including erection for a single “ONE STOP SOURCE”.

Many sources of supply are there so it becomes difficult to co ordinate and handle the things.

COST OF CHARGE ORDER

PEB manufactures usually stock a large amount of that can be flexibly used in many types of PEB projects.

Substitution of hot rolled sections infrequently rolled by mills is expensive and time consuming.

Change orders are easily accommodated at all stages of the order fulfillment process. Little or no material is wasted even if a change order is made after fabrication starts.

Change orders that are made after the dispatch of hot rolled sections result in increasing the time and cost involved in the project.

- 16 -

BUILDING ACCESSORIES

Designed to fit the system with standardized and inter changeable parts. Including pre designed flashing and trims. Building accessories are mass produced for economy and are available with the building.

Every project requires different and special design fro accessories and special sourcing for each item. Flashing and trims must be uniquely designed and fabricated.

FUTURE EXPANSIONS All project records are safely and orderly kept in electronic format which make sit easy for the owner to obtain a copy of his building record at any time.

It would be difficult to obtain project records after a long period of time. It is required to contact more than one number of parties.

Future expansion is very easy and simple.

Future expansion is most tedious and more costly.

SAFETY AND RESPONSIBILTY

Single source of responsibility is there because all the job is being done by one supplier.

Multiple responsibilities can result in question of who is responsible when the components do not fit in properly, insufficient material is supplied or parts fail to perform particularly at the supplier/contractor interface.

PERFORMANCE All components have been specified and designed specially to act together as a system for maximum efficiency, precise fir and peak performance in the field.

Components are custom designed for a specific application on a specific job. Design and detailing errors are possible when assembling the diverse components into unique buildings.

Experience with similar buildings, in actual field conditions world wide, has resulted in design improvements over time, which allow dependable prediction of performance.

Each building design is unique, so predication, of how components will perform together is uncertain. Materials which have performed well in some climates may not do well in other conditions.

- 17 -

6. PRE ENGINEERED BUILDING vs CONCRETE BUILDINGS

Evaluation Criteria

PRE ENGINEERED BUILDINGS CONCRETE BUILDINGS

Building Dimensions

Suitable for spans 20-30m. Can sustain much larger spans.

Suitable for short span buildings, 5-8m. Becomes difficult and heavy for larger spans.

Fabrication

Members fabricated in a controlled environment.

Precise fabrication.

Fabrication done on site.

Requires building the reinforcement cage and shuttering work prior to pouring.

Delivery and Logistics

Can be delivered anywhere in the world.

Can be properly sequenced.

Might have to build batch plant on site if site is secluded or huge.

Erection Time

Fast erection. Virtually no idle time

Slow erection and time consuming.

Pouring should take place in limited amount of time. If exceeded, the concrete quality may be jeopardized.

The contractor will have to wait for the previous cast to harden (14-28 days) before being able to cast another batch.

Industrial Applications

Can easily handle equipment such as multiple cranes within building.

Sways can be controlled.

Precision can be achieved during installation.

Heavy equipment usage such as cranes is limited.

To solve precision problems, contractors use steel I beams and platforms in concrete building.

Quality Quality of steel is guaranteed because:

It is a homogeneous product.

Many factors lead to quality deterioration:

Concrete is not a homogeneous product

- 18 -

Pieces are tailored according to shop drawings.

Precise machinery is used for fabrication.

It is fabricated under shop control.

Quality is not affected by weather conditions

Concrete mix ingredient ratios are difficult to maintain.

Quality of water used may vary.

Weather conditions. Labor experience in

pouring. Adequate use of vibrators. Using proper curing

methods. Concrete shrinkage.

High manpower count may weakan control.

Cost

Low man power count needed.

Erection cost is low at site

Construction cost is high at site

Modulability & Scalability

Can change a section of the building or even cancel a section with controlled effort and with little effect on structure stability and functionality.

Expansion is easy. Longitudinally expansion is about adding more bays and connecting the secondary members and the sheeting to the old building.

Needs a lot of planning and has usually major consequences. Might be even impossible.

To expand, the contractor has to build a new structure with foundations, columns and might have to break part of the old structure in order to expand it.

Error Modification

Easy to modify on site, even after erection.

Modification can be done by cutting, welding or attaching steel pieces.

Have to break concrete if modification is necessary.

Consistency and Reliability

Strength is assured from design.

Steel properties are stable with time.

Strength cannot be guaranteed without testing.

Concrete properties may change over time and environmental conditions

Seismic Ductility of steel provides Poor flexibility under

- 19 -

Effect

flexible behavior under seismic loads. Light Steel structures minimize the seismic effect on the structure.

Steel is heavier than concrete but is 18 times stronger. A steel member can hold 6 times its own weight.

seismic loads. Heavy structures maximize the seismic effect on the structure.

  Heavy self weight. Large portion of concrete strength consumed to resist effect of its own weight.

Ductility

Show signs of failure when overloaded.

Gives chance to fix the problem.

No warning signs. May result in disastrous

collapse.

Steel reinforcement is used to prevent brittle failure.

Environment

Steel is fully recyclable. Steel recycling technology is mature and standardized.

Recycled steel results in better quality than Iron Ore.

Shy trials have been done on recycling of concrete.

No standards adopted. Quality Problems.

Almost zero residual value

7. APPLICATIONS

- 20 -

More than 70% of all single storey non-residential construction, in the USA, utilizes pre-engineered buildings. The applications of pre-engineered buildings range from small car parking sheds to 90 m (+) wide clear span aircraft hangars to low-rise multi storey buildings. Almost every conceivable building use has been achieved using the pre-engineered building approach.

The most common applications of pre-engineered buildings are:

Industrial

Factories Workshops Warehouses Fuel stations Cold storages Car parking sheds Slaughter houses Bulk product storage and Godowns.

Institutional

Schools Exhibition halls Hospitals Theaters Auditoriums Indoor Sports halls.

Aviation & Military

Aircraft hangers Administration Buildings Residential barracks Support facilities

8. ADVANTAGES

- 21 -

REDUCED CONSTRUCTION TIME: Buildings are typically delivered in just a few weeks after approval of drawings. Foundation and anchor bolts are cast parallel with finished, ready for the site bolting. Our study shows that in India the use of PEB will reduce total construction time of the project by at least 50%. This also allows faster occupancy and earlier realization of revenue.

LOWER COST: Due to the systems approach, there is a significant saving in design, manufacturing and on site erection cost. The secondary members and cladding nest together reducing transportation cost.

FLEXIBILTY OF EXPANSION: Buildings can be easily expanded in length by adding additional bays. Also expansion in width and height is possible by pre designing for future expansion.

LARGE CLEAR SPANS: Buildings can be supplied to around 80M clear spans.

QUALITY CONTROL: As buildings are manufactured completely in the factory under controlled conditions the quality is assured.

LOW MAINTENANCE: Buildings are supplied with high quality paint systems for cladding and steel to suit ambient conditions at the site, which results in long durability and low maintenance coats.

ENERGY EFFICIENT ROOFING AND WALL SYSTEMS: Buildings can be supplied with polyurethane insulated panels or fiberglass blankets insulation to achieve required “U” values.

ARCHITECTURAL VERSTALITY: Building can be supplied with various types of fascias, canopies, and curved eaves and are designed to receive pre cast concrete wall panels, curtain walls, block walls and other wall systems.

SINGLE SOURCE RESPONSIBILTY: As the complete building package is supplied by a single vendor, compatibility of all the building components and accessories is assured. This is one of the major benefits of the pre engineered building systems.

CONCLUSION

- 22 -

India being a developing country massive house building construction is taking place in various parts of the country.

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 would be 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 pre-engineered building calls for very fast construction of buildings and with good aesthetic looks and quality construction. Pre-engineered Buildings can be used extensively for construction of industrial and residential buildings. The buildings can be multi storeyed (4-6 floors). These buildings are suitable to various environmental hazards. The requirement of housing is tremendous but there will always be a shortage of house availability as the present masonry construction technology cannot meet the rising demand every year. Hence one has to think for alternative construction system like pre-engineered steel buildings. India has an installed steel capacity of 35 to 40 million tonnes & apparent steel consumption is around 27 to 30 million tonnes. There is a surplus capacity of flat steel products available in India particularly of hot and cold rolled sheets. These steel components can be utilized in the construction of pre-engineered building components.

PEB concept has been very successful and well established in North America, Australia and is presently expanding in U.K and European countries. PEB construction is 30 to 40% faster than masonary construction. PEB buildings provide good insulation effect and would be highly suitable for a tropical country like India. PEB is ideal for construction in remote & hilly areas.

- 23 -

REFERENCES

KIRBY Building System KUWAIT.

KARTHIK FABRICATORS India P Ltd.

MULTCOLOR PROJECTS India Ltd.

LLOYD INSULATIONS India Ltd

MABANI STEEL LLC, U.A.E

STRUCTURAL ENGINEERING at WSP Asia Limited Philippines

ZAMIL STEEL Building India Pvt.Ltd

- 24 -