Let’s get technical and understand the real value of pre-engineered steel buildings.
What is the Difference between PEB and Conventional Steel Frame design?
The Primary Framing System
In conventional steel buildings, mill-produced standard-sized hot rolled sections are used for beams and columns. The size of each member is selected on the basis of the maximum internal stress in the member.
That means each part of the member has a constant depth. Hence, areas of low internal stresses are in excess of design requirements (represented by the shaded area). (Moment forces are represented in pink.)
On the other hand, pre-engineered building (PEB) frames can be cut from an extensive inventory of standard plates. We are able to match the frame geometry with the shape of the internal stress diagram. Hence, PEB frames are normally tapered and have flanges and webs of variable thickness along the individual members, minimizing material waste and reducing the total weight of the structure.
The Secondary Framing System
Z-shaped roof purlins and wall girts are used for the secondary framing. They are lighter than the conventional hot-rolled C-shaped sections in conventional steel buildings.
Nesting of the Z-shaped members at the frames allows them to act as continuous members along the length of the building. This doubles the strength capacity of the Z-shaped members at the laps, where the maximum internal stresses normally occur.
What is the Difference between PEB Steel Buildings and Concrete Buildings?
When it comes to PEB steel buildings versus concrete buildings, there are added advantages brought about by steel qualities, in addition to ease of construction, and flexibility of expansion and industrial applications.
1. Design and Building Dimensions
PEB Advantage: Compared with concrete buildings, PEB can have wider spans and cantilevers at more affordable costs.
Concrete Building
A concrete building is suitable for short spans of 5 to 8 metres. It becomes complex and heavy when the span increases. Heavy concrete buildings will require sizeable foundations, and closer column spacings means more footings are needed. Cantilevers are also expensive to build because it demands extensive formwork to hold the concrete until it cures.
PEB Steel Building
PEBs are suitable for clear spans of 20 to 30 metres, and it can be designed for even larger spans such as 90 metres and over. Due to its lightweight design, the building requires reduced foundations. With greater spans, columns are further spaced and requires less footings. Cantilevers are easy to design and construct at no additional costs.
2. Flexibility in Design or Change
PEB Advantage: Ease of change and lower modification or expansion costs
Concrete Building
Unless the concrete building has originally been designed to enable modular additions, it is almost impossible to modify a concrete building to meet changing needs.
To expand, the contractor has to build a new structure with foundations and columns, and may need to break part of the old structure as part of the modification works.
PEB Steel Building
Expansion is easy with PEB. Expanding the length of the building simply means adding more bays, and connecting new secondary members and cladding to the old building.
After erection, if modification is necessary, it can be done by cutting, welding or attaching steel members.
3. Industrial Applications
PEB Advantage: Ease of installing industrial equipment, resulting in lower maintenance costs.
Concrete Building
Heavy equipment usage such as cranes is limited. Precision installation can be an issue so steel I beams and platforms are used for such installation.
PEB Steel Building
PEB can easily handle equipment and multiple cranes are possible within a building. Sways can be controlled and precision can be achieved during installation.
4. Quality, Consistency and Reliability
PEB Advantage: Guaranteed quality and Longer Life Expectancy
Concrete Building
Many factors can lead to quality deterioration in a concrete building. As concrete is not a homogenous product, the concrete mix, quality of water, temperature variances, adequate use of vibrators, proper curing methods can all affect the concrete quality. In addition, concrete strength cannot be guaranteed without testing, and concrete properties change over time with environmental conditions.
PEB Steel Building
Steel is a homogeneous product, and it is not affected by site weather conditions. Coupled with precision fabrication according to shop drawings, quality can be guaranteed by the PEB factory. Steel strength is also assured from design, and steel properties remain stable with time.
5. Fabrication, Logistics, Construction and Cost
PEB Advantage: Faster, easier and lower site costs
Concrete Building
Fabrication must be done on site. In addition, the construction process has to be sequenced (e.g. building the reinforcement cage and shuttering work prior to pouring), leading to time-consuming erection. The contractor waits for the previous cast to harden (14 to 28 days) to attain strength before casting another batch. With the lengthy project time and tedious process at site, construction cost is higher. If the site is secluded, a batch plant may have to be built on-site, raising capital costs. On-site noise, dust and water pollution will be expected during construction.
PEB Steel Building
For PEB, members are precisely fabricated in a controlled environment, leading to a 90% savings in fabrication time on site. The precisely fabricated members can then be delivered anywhere and used immediately for erection. Fabricated members can also be delivered in sequence on-time, assisting with the project schedule, a clean worksite and less site storage. Concrete foundations can be executed in parallel with member fabrication in the factory, shortening overall schedule of the project. Erection of exact members according to plan is quick, and hence PEB has a faster and shorter mobilization and demobilization. As a result, erection cost is low at site. Construction is also dust free utilising dry techniques.
6. Safety
PEB Advantage: Steel is a safe choice and requires less costly safety measures.
Concrete Building
Concrete has poor flexibility under seismic conditions, and heavy structures will exacerbate the seismic effect on the structures. Steel reinforcement is needed to prevent brittle failure.
PEB Steel Building
Steel’s strength and ductility makes it a safe choice for earthquake-prone or volcanic vibration areas. Steel framing has excellent performance under high lateral wind loads because it is ductile i.e. the ability to bend without breaking and can absorb that kind of energy. Ductility also provides early signs of failure when overloaded, allowing the problem to be noticed and fixed.
