Conventional steel construction could be considered the parent to pre-engineered steel buildings; both are still used in the industry to develop everything from small steel sheds to skyscrapers and wide, open-span facilities.
Let's compare the two methods.
Conventional steel building construction
Each conventional steel building is individually designed from the ground up, from scratch for each project. Often the architect and engineer have few design tools. Any change or addition to the design, such as a specialized projection or another design outside of a strictly geometric shape (usually square or rectangle) requires customized work.
Because each design is created for a single project, no two buildings are constructed the same way. There is no engineer stamped plan to present for permitting.
Conventional steel building design uses selected rolled "T" sections which are standardized in length but must be cut, punched, and bolted up onsite. Standardization can create cost savings at the time of purchase; however, customizing them onsite requires skilled labor and time.
These T-sections are heavy and generate metal scrap that must be removed from the jobsite and taken for recycling. The rest of the building materials are typically sourced from multiple vendors, creating complications in logistics and potential quality control problems.
It can take as much as 20 to 26 weeks to receive all the materials.
Because the overall weight of a conventional steel building is quite heavy, you need a robust concrete foundation to support it. Additionally, there is no way to predict the final weight of the building, so the foundation may wind up being overestimated for the actual, completed building.
Of course, overestimating is better than an insufficiently strong foundation.
As mentioned above, the primary frame is built from rolled T-sections that have been cut onsite to the needed length. Secondary members are also selected from standard hot-rolled sections that can be heavier than needed. These members do not come with flanges, and any bolt-holes must be punched onsite as well.
Field-cutting and punching these members takes a lot of skill so the holes will match up and be the correct size for the bolts to fit, complicating the connection process. Punching holes creates more scrap to be hauled off as well as specialized equipment to perform the work and safety precautions to prevent injuries, especially to the eyes.
Custom architectural detailing is often designed and built onsite as well, with access to few design tools. Any flashing and trim are of unique design as well.
Expansion and repair
Building additions or making repairs to conventional buildings can be a difficult undertaking, especially when the original frame details and quality are unknown. Expansion and repair is a labor-intensive undertaking. However, the bolt-up design does make it possible to remove and replace members more easily than if they were welded permanently.
Bolt-up or conventional steel building construction is highly durable. Structures can last for decades if not centuries with the appropriate maintenance of the envelope and additional materials.
In regions of high seismic activity, conventional construction design must take into account the need for specialized connections and other safeguards.
Pre-engineered steel buildings
A pre-engineered metal building, also known as a pre-manufactured or pre-fabricated metal building, is designed to specification at the manufacturer. There are numerous designs available, all of which can be customized as needed.
Specialized software and other design tools are readily available.
Since these buildings are not created until the design is complete, the members and panels are created as needed, minimizing the amount of steel required and resulting in a lighter-weight building. Every piece is sourced from the manufacturer.
Each piece is precision rolled, cut, punched, and marked to make assembly as easy as possible once the kit reaches the jobsite. Everything is included in the kit: members, panels, and fasteners, which have all been tested for fit before shipping.
The building kit arrives in about six to eight weeks.
A pre-engineered building has the advantage of a known weight, simplifying foundation design. Also, since pre-engineered buildings use customized members, less steel is needed to create them and results in a lighter building that needs a less complex or heavy foundation.
Pre-engineered primary and secondary framing members are custom-made for each building designed. Instead of standard T-sections, tapered members that are sturdy yet light-weight can be used in the primary frame. Secondary members are steel Z and C shapes; all girts and purlins are lightweight steel as well.
No field cutting is needed to create frame members to fit; they simply bolt together as designed as punched in the factory.
Expansion and repair
Pre-engineered steel buildings are eminently expandable and easily customized to new uses. New sections are readily bolted onto any side or added to the top of an existing structure.
Original, engineer-stamped documents assist future redesign work and streamline the permitting process. If a section of the building is damaged, repairs can be performed easily, often using replacement parts from the original manufacturer.
Pre-engineered steel buildings have come a long way from the simple sheds you see along the side of the road. A multi-story or wide-span building can be pre-engineered as can anything in between, built to last for decades and able to be disassembled and moved if needed.
Every pre-engineered building is designed to meet the local building standards and requirements. Specialized connections and framing are designed in for seismically active regions or any other special environmental concern.
Conventional and pre-engineered steel buildings share a history, and both are highly durable structures. Conventional buildings require different skills to construct than pre-manufactured, with the need for metal cutting and punching onsite. Each building is designed individually, unlike a pre-manufactured structure where every hole and fastener has been planned and included.
This does not mean conventional or pre-fabricated buildings all look alike or must look different. The difference comes in when the design work is done, and the type of materials used to bring it to life. Both methods are successfully used to construct many types of structures that will last and last.