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A pre-engineered steel building is a modern technology where the complete designing is done at the factory and the building components are brought to the site in CKD (completely knock down condition) and then fixed/jointed at the site and raised with the help of cranes.
An efficiently designed pre-engineered building can be lighter than the conventional steel buildings by up to 30%. Lighter weight equates to less steel and potential price savings in structural framework.
In this article, we discuss the components, advantages, applications, and comparison of pre-engineered steel buildings with conventional buildings.
Major Components of Pre-Engineered Steel Building
The major components of the PESB are divided into 4 types-
1. Primary Components
Primary components of the PESB consists of mainframe, column, and rafters-
A. Main Frame
The main framing basically includes the rigid steel frames of the building. The PESB rigid frame comprises of tapered columns and tapered rafters. Flanges shall be connected to webs by means of a continuous fillet weld on one side.
The main purpose of the columns is to transfer the vertical loads to the foundations. In pre-engineered buildings, columns are made up of I sections which are most economical than others. The width and breadth will go on increasing from bottom to top of the column.
A rafter is one of a series of sloped structural members (beams) that extend from the ridge or hip to the wall-plate, downslope perimeter or eave, and that are designed to support the roof deck and its associated loads.
2. Secondary Component
Purlins, Grits and Eave struts are secondary structural members used as support to walls and roof panels.
A. Purlins and Girts
Purlins are used on the roof; Grits are used on the walls and Eave struts are used at the intersection of the sidewall and the roof. Purlins and girts shall be cold-formed "Z" sections with stiffened flanges.
B. Eave Struts
Eave struts shall be unequal flange cold-formed "C" sections. Eave struts are 200 mm deep with a 104 mm wide top flange, a 118 mm wide bottom flange, both are formed parallel to the roof slope. Each flange has a 24 mm stiffener lip.
Cable bracing is a primary member that ensures the stability of the building against forces in the longitudinal direction such as wind, cranes, and earthquakes. Diagonal bracing in the roof and side walls shall be used.
3. Sheeting or Cladding
The sheets used in the construction of pre-engineered buildings are Base metal of either Galvalume coated steel conforming to ASTM A 792 M grade 345B or aluminum conforming to ASTM B 209M which is cold-rolled steel, high tensile 550 MPA yield stress, with hot dip metallic coating of Galvalume sheet.
Non-structural parts of the buildings such as bolts, turbo ventilators, skylights, lovers, doors and windows, roof curbs and fasteners make the accessories components of the pre-engineered steel building.
Comparison between Pre-Engineered and Conventional Steel Building.
|Properties||Pre-Engineered Steel Building||Conventional Steel Building|
|Structural Weight||Pre-engineered buildings are on the average 30% lighter because of the efficient use of steel.|
Secondary members are light weight roll formed “Z” or “C” shaped members.
|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.|
Secondary members are selected from standard hot rolled sections which are much heavier.
|Design||Quick and efficient design since PEB’s are mainly formed by standard sections and connections design, time is significantly reduced.||Each conventional steel structure is designed from scratch with fewer design aids available to the engineer.|
|Construction Period||Average 6 to 8 weeks||Average 20 to 26 weeks|
|Foundation||Simple design, easy to construct and light weight.||Extensive, heavy foundation required.|
|Erection and 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.|
|Erection Time and Cost||The erection process is faster and much easier with very less requirement for equipment||Typically, conventional steel buildings are 20% more expensive than PEB in most of the cases, the erection costs and time are not estimated accurately.|
Erection process is slow and extensive field labour is required. Heavy equipment is also needed.
|Seismic Reistance||The low weight flexible frames offer higher resistance to seismic forces.||Rigid heavy frames do not perform well in seismic zones.|
|Over all Cost||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.|
|Future Expansion||Future expansion is very easy and simple.||Future expansion is most tedious and more costly.|
|Safety and Responsibility||Single source of responsibility is there because the entire 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.|
Advantages of Pre-Engineered Steel Building
1. Reduction in 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. In India, the use of PEB will reduce the total construction time of the project by at least 50%. This also allows for faster occupancy and earlier realization of revenue.
2. 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.
3. Flexibility 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.
4. Larger Spans
Buildings can be supplied to around 80M clear spans.5.
5. Quality Control
As buildings are manufactured completely in the factory under controlled conditions the quality is assured.
6. 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 costs.
7. Energy-Efficient Roofing and Wall Systems
Buildings can be supplied with polyurethane insulated panels or fiberglass blankets insulation to achieve required “U” values.
8. Architectural Versatility
The building can be supplied with various types of fascias, canopies, and curved eaves and are designed to receive precast concrete wall panels, curtain walls, block walls and other wall systems.
9. Single Source Availability
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 pre-engineered building systems.
Applications of Pre-Engineered Steel Buildings
The major application of PESB is found in the following-
- Houses & Living Shelters
- Sports Halls ( Indoor and Outdoor)
- Aircraft Hangers
- Office Buildings
- Labor Camps
- Petrol Pumps/Service Buildings
- Community centers