The U.S. structural steel industry serves all design and construction project delivery methods, but it is especially well-suited to thrive with design-build. But to do so, it behooves any design-build practitioner to develop an understanding of the structural steel supply chain function to enable those within the chain to serve the design-build process in the best and most efficient manner.
The structural steel industry is comprised of four distinct components: producers, service centers, steel fabricators and erectors. This highly automated and highly efficient supply chain provides fabricated and erected structural steel framing to more than 50,000 buildings each year.
Fabricators typically have the closest relationships with the design and contracting community and receive the steel contract from the general contractor. They then orchestrate the supply chain to fulfill the contract.
The fabricators become responsible for acquiring, fabricating and shipping the structural steel to site. They also need to subcontract with a steel erector and where necessary subcontract the steel detailing.
In addition, the fabricator ensures any other materials or requirements to complete the steel contract are purchased, contracted or supplied. These may include such things as painting, galvanizing, fireproofing and any specialized services such as bending and rolling. The fabricator is responsible for providing all these items to suit the construction sequence and schedule.
From the general contractorfs point of view, there is just one major specialty contractor to deal with, and that contractor supplies and installs the structural steel frame as efficiently as possible by taking advantage of the entire structural steel supply chain.
So, what happens within this supply chain?
Genesis Phase
It all starts with steel mills and hollow structural shape (HSS) manufacturers. Steel mills directly produce wide-flange beams, channels, angles and plate, and HSS manufacturers produce square, rectangular and circular hollow structural sections out of flat steel plate from the mill.
More than 8 million tons of hot-rolled structural steel was produced in the United States in 2007, nearly 6 million of which was wide-flange sections. Every piece of steel is produced to conform to precise American Society for Testing and Materials standards.
Material strengths and dimensions are checked and verified several times before the material leaves the mill. This ensures a reliable, predictable product that structural engineers can design more easily, confident of its strength and characteristics.
Todayfs modern steel production mills can be thought of as huge scrap metal recycling facilities ? scrap metal being the primary component in structural steel manufacturing. Steel is North Americafs number one recycled product. The recycled content of structural steel beams and columns produced in the United States averages in excess of 90 percent, with wide-flange beam production often having recycled content of more than 98 percent, making structural steel the model of sustainable material production.
On the broader sustainability scale, the iron and steel industry reduced carbon emissions by 47 percent between 1990 and 2005, according to the Environmental Protection Agency. By comparison, initiatives such as the Kyoto Protocol would have required U.S. industries to reduce emissions by 5.2 percent by 2012.
The steel industry has also continually pursued methods for reducing energy consumption and has reduced energy usage by nearly a third over the past three decades. Following the course toward continual improvement, the industry has also committed to the Climate Vision program, which seeks to reduce energy usage by an additional 10 percent by 2012.
Meet the Need
Steel mills produce material according to pre-planned rolling cycles and do not generally keep a significant amount of inventory. A rolling cycle is the time between the same product (size and shape) being rolled twice by the same mill. The cycle (and the amount of material rolled in that cycle) can vary according to the product and market requirements at the time, but it can be as little as four to eight weeks for commonly used sections.
Fabricators are tuned into the millsf rolling schedules and order material from each cycle according to their forthcoming projects. Design-build projects that involve fabricators early in the process gain the advantage of close coordination between the design engineer and fabricator. By coordinating information, the team can narrow the range of shapes utilized in the project based on availability, place mill orders earlier and adjust designs utilizing material already on order. This additional time can be crucial when mill rolling schedules are extended.
Buying steel directly from the mill however, is a relatively small part of the equation. Most structural steel ? around 70 percent ? is supplied to fabricators directly by steel service centers.
While four domestic mills provide structural steel to the U.S. market, hundreds of steel service centers are strategically located across the nation. Steel service centers buy steel from each rolling cycle at every mill and keep it as inventory to sell to fabricators. They keep a full range of steel products in multiple lengths and also provide value-added services to fabricators, such as first-stage, pre-fabrication processing (cutting beams to length, tee splitting, cambering, plate burning) and meeting staged delivery requirements (e.g. delivering multiple shapes from various producers according to the project sequence).
Service centers typically maintain about a three-month inventory, ensuring steel is always available by acting as a gshock absorberh for any unexpected peaks in demand.
Raw Material
The steel that arrives at the fabricator from either the mill or the service center is raw product. In terms of cost, the material represents only about 20 to 30 percent of the total steel package, the remaining value coming from fabrication, detailing and erection. Material price fluctuations have a limited effect on the overall cost of the project.
Before the fabricator can fashion this raw steel into the finished pieces erected and bolted together at the job site, the structural steel detailer interprets the construction drawings and breaks them down into fabrication shop drawings of individual pieces and assemblies that can be made on the shop floor and shipped to the job site.
Detailing is a specialized area of expertise that utilizes some of the most advanced technology in the construction industry. A fabricator will either have this capability in-house or will subcontract to an outside firm. Detailers take the construction drawings and prepare detailed plans, shop drawings and other production documents so that each individual column, beam, brace, truss and handrail can be made in the fabrication shop and then assembled at the job site.
Steel detailers have utilized sophisticated 3-D Building Information Modeling (BIM) systems for two decades. This technology allows them to build a virtual model of the building in the computer ? often using the engineerfs model to start with ? apply connections among members and make sure everything fits together and there are no clashes in the steel frame or between the steel frame and other disciplines such as Manufacturing Extension Partnerships.
The steel industry leads the way in the BIM application where it reduces schedules, improves communication among team members and minimizes requests for information and change orders. In addition, the BIM model contains massive amounts of information that the fabricator can use throughout its shop, to control machinery and to feed other information management systems for planning, scheduling and shipping.
Next Steps
Fabrication itself consists of tasks such as cutting, drilling, punching, shearing, welding, piece assembly and assembly of complex geometry and trusses. Fabricators have invested in advanced computer-controlled (CNC) machinery and material-handling equipment to perform the more common tasks such as cutting to length, drilling and shape burning. CNC machines are extremely fast and efficient and are fed automatically from the BIM systems used by the detailers.
Once the steel arrives and the drawings are complete, the fabrication process begins. There are around 2,500 fabricators in the U.S., serving every corner of the nation.
The fabricator works to a predetermined schedule developed in consultation with the project team. This schedule controls everything, from how the detailers release information, to when material is sent to the shop, to the order of trucks shipping fabricated steel to the job site.
One of the major advantages of building with structural steel is the quality of the fabrication process. Off-site fabrication allows for a quality controlled environment unaffected by climate and weather changes or by adverse site conditions. The nature of the material allows it to be fabricated to very close tolerances, and at every stage of fabrication the steel is inspected to help guarantee a quality product and eliminate mistakes and costly site work.
Delivery Details
Once fabrication is complete, the steel is delivered to the job site for installation. Depending on the contract, the fabricator will normally arrange any necessary finishes, such as priming, painting or galvanizing. Paint may be applied in-house or by a specialty contractor. Galvanizing also is done by a specialty contractor, typically en-route to the job site. Whichever the case, the steel is on the way to the job site, having been shipped in the sequence required by the erector.
Early in the project, the fabricator, erector and general contractor meet and assess project site conditions to determine crane positioning erection sequence. This sequence drives the whole project from the fabricatorfs point of view and must also fit in with the general contractorfs master schedule and that of all the other disciplines at the site.
The erector is the most visible entity in the structural steel supply chain and thus maintains a close relationship with the general contractor while working alongside all the other disciplines on the site.
The fabricated steel arrives on the site and is normally unloaded to a storage area prior to erection. Erection managers can use the BIM model, determine difficulties and erection methods in advance and save valuable field time.
Steel erection does not require a large labor force; erectors work in small skilled crews of four to six people. In addition, equipment requirements are minimal, and because the process is so rapid, assembling a steel frame is extremely economical.
Whether a project uses design-build or a typical design-bid-build delivery method, building teams who show the foresight to involve the steel specialty contracting team early on in the design phase to leverage the advantages of the highly efficient structural steel supply chain find they have made the sustainable, available, fast and economical ? and safe ? choice.
Chris Moor is the industry mobilization director at the American Institute of Steel Construction.