You might ask why an architecture firm working predominately in single-family residential is interested in steel. Looking around your house you might say, “I don’t even see any steel here.” But the reality of home construction can be deceiving. The wood framing members are joined by steel nails and nailer plates. You may have steel windows depending on the age and budget of your house. Some of your homes may even have steel structural members at particularly large openings, heavily-loaded columns in your basement, or if you have a large cantilever hanging out past the line of your foundation. These elements are all covered and concealed. Additionally, there is one major steel component unseen by most unless you kick around the job site while your foundation is being poured, rebar.
Steel rebar allows us to rely on our concrete foundations, slabs, and walls. Concrete is a wonderfully strong material in compression (think crushing) but fails quickly and easily in tension (think pulling apart). Since building are subjected to constantly fluctuating conditions—whether moisture, temperature, or loading—things move. We like to use concrete in compression but because of fluctuating conditions and some principles of structures concrete elements are sometimes stretched, pulled, or bent, and then we need steel!
Steel rebar can be found in almost all modern applications of concrete. Round bars are bound to one another with wire and assembled into cages that are floated within the concrete while it hardens. After the concrete has cured, the steel is permanently set. Ribbing or texture on the outside of the bars acts like teeth to bite into the hardened concrete and keep it from cracking apart while subjected to pulling and bending.
An invaluable resource for architects and other professionals in the construction industry is to physically handle materials and see how they are made. Luckily for us, we have a top-notch steel plant in West Seattle producing over 800,000 tons of steel products annually, of which 85% is rebar. Knowing this, a crew from Board & Vellum took a trip to tour Seattle’s NUCOR Steel plant recently to understand what goes into this critical building material that keeps our buildings standing up while almost never being seen.
Just over the West Seattle Bridge in an area affectionately called Little Pittsburgh, NUCOR has been rolling out steel products since 1904. Since then, this NUCOR location has grown and evolved to produce steel with the most current processes and technologies. Another thing we like about what they do is almost everything from the plant is 100% recycled!
In certain industries, like automotive, requirements are such that only newly produced steel can be used. This is not the case in the building industry. The grade of steel is very high in building products but not so high that it requires virgin steel. In addition, there is so much steel being produced and used in cars, buildings, cans, and other applications that there is a constant supply of scrap steel. Train cars and truckloads drop off heaps of scrap metal all day long every day of the week at NUCOR, and this is where it begins.
Loads of scrap coming from all over the region, including across the border in British Columbia, are delivered to the plant and scanned for radioactive materials or other such contaminants that would make handling dangerous. The safety requirements at NUCOR are so stringent that if there is any radioactive material detected within a train car or truck load, that whole shipment is sent back to where it originated. The safety manager giving us the tour tells us this can happen sometimes multiple times in a day, but it’s all part of keeping workers, end users, neighbors, and the environment safe.
After passing contamination inspection, the scrap metal is hauled to the on-site scrap yard. The scrap yard is an open-air covered region of the plant (one of three covered steel plants in the world) spanning multiple acres. Here large spools of spent cable, car chassis, maritime sprockets, and enormous steel plates are sorted into piles based on metallurgical properties. The yard is managed by a giant gantry crane equipped with two round, pickup-truck-sized electromagnets. From here the material is gathered to start making new rebar and other rolled steel products.
For any given order, a recipe is devised dictated by the requirements of the end product. Each product requires a specific grade of steel and a maximum allowable amount of added alloys. These standards are critical so that we know how structures will perform and can design for those conditions. In the end, this makes our buildings more efficient in terms of material and also in the final price to our clients. The gantry crane operator gathers whatever is needed from the scrap yard and drops the recycled material into a large bucket on its way to the furnace. The furnace is where the real fun begins.
Somewhere between a post-apocalyptic Matrix nightmare and an enormous welding booth, the furnace is almost always running. Our guide puts in perspective the energy required to run this process saying that the monthly electrical bill at NUCOR Seattle is close to $2 million. From behind blast-proof glass we hang out with Phil, the most senior employee at the plant who has been working his way up from the floor for 45 years. Phil is now the senior furnace operator. He sits perched above the melt-house floor in the control station with blue and green plastic shields placed strategically to keep his retinas from burning out the back of his eyes. Here, he uses what looks like a modified fighter plane control to deliver 40,000 lbs. of scrap at a time to the furnace pot. After three payloads are added to the vat, Phil maneuvers a three-headed electrode into the pile to start the melt. The furnace works on the same principle as an arc welder. An electrical current travels to the electrode head and is held off of a conducting material just enough to create an electrical arc which superheats and melts the metal, but in this case there are three electrodes and each is larger than a Seahawks linebacker. Delivering a high dose of electricity and heat to the vat, Phil keeps the furnace around 3200°F. At this temperature, the scrap metal melts completely and can be fully mixed to produce a consistent mixture. During the process Phil pulls levers and hits touch screens that also add various metals and oxygen to purify the mixture. Slag, a byproduct made of impurities is then dumped off the top before the steel mixture is poured into billets in the next step.
The molten steel is formed into billets, large, square-shaped bars cut to different lengths depending on weight needed for a specific order. In order to keep the process continually moving, the cutting mechanism actually travels with the steel as it is being pushed out of the furnace. This way it can take its time cutting accurately while the product is moved out of the furnace, making room for the next superhot batch of steel. Once the billets are formed and cut they have to cool, but not because they are too hot, but because they are not magnetic at high temperatures. Billets are about eight inches square and 32’ long, meaning they weigh roughly 9000 lbs. EACH. To handle these pieces of steel the plant once again needs to use electromagnets, but until the billets cool to a modest 1100°F they cannot be attracted to the magnets, so they sit on a steel track that has cold water lines running through it to keep the entire setup from deforming and dropping all the newly formed billets off the rails. At this point, the billets are also marked with an order number that codes them for what product will be rolled from them in the final stages of the process.
When the billets have cooled to temperatures that allow them to be handled by another set of magnets, they are brought to the finishing building. Here, another furnace reheats the steel to temperatures that make it pliable for forming into end products. Once the billets are glowing a bright orange they are sent through a series of rollers that gradually take the square forms down to round rebar, all the way from 8” squares to rebar that is 3/8” in some cases. We watch this process from another control room that sits overlooking the roller assembly. Behind the controls on this side of the plant is Charlie, Phil’s brother and the second most tenured employee at NUCOR Seattle. Charlie pulls a different set of switches and touchscreens to control the shape change, feed speed, and cutting of the rebar that comes off the line. He tells us the glowing steel is traveling fast and that when this process was worked manually it would sometimes catch a worker and send him clear across the warehouse. This is another point where our guide reiterates the safety measures taken at the plant which include getting workers as far away from hot, moving parts as possible.
In the final steps, the rebar is bundled with coils of wire and tagged for shipping and end use. At this point, the rebar is finally at a temperature that you can touch with bare hands or even stand near without fear for losing your eyebrows as it leaves the plant.
The Board & Vellum trip to NUCOR Steel was fun and valuable. So often in this profession we discuss building materials, lifecycles, and holistic understanding of what we do but are not often able to see the cycle in action or watch the processes that go into what we receive on site. One take-away from our NUCOR visit is that we can all be more committed to understanding the entire lifecycle of our materials and buildings. The supply chain for building steel is almost entirely recycled from the waste stream. In addition, the byproducts from processing the steel are either recovered and disposed of safely (particulates are collected in large dust-hoppers) or collected and used in other industries (slag is solidified and crushed to be used as a higher-performing road pavement alternative to asphalt). These big-picture ideas are ones to consider in making better performing buildings.
We thoroughly enjoyed our afternoon at NUCOR and suggest that if you are at all interested in seeing the process for yourself that you schedule a free tour as well!
(photo credit: Mike Siegel/Seattle Times)