I’m not very familiar with steel beams, but I would guess they have to be cut on site. Obviously, many will be stock lengths but not every building is going to be stock length widths, which means measuring that final, non stock width, and cutting the steel to fit. Personally, I wouldn’t want to order that in advance on such a massive scale as these buildings are. A math error, or a problem with the steel placement for whatever reason, could turn into a very costly mistake.
Edit: Ok so after 2 mins of research, apparently the steel is ordered to size and only cut on site when there is ordering mistakes. Eek.
Ah Erector Sets were one of the most educational toys ever… A older cousin gave me his supper sized (do not recall name of it but was a 3’ X16" X 6"deep box of 1000’s if parts. I even used one of the motors to demonstrate that a spinning disk of back and white stripes, at correct speed, will make you see colors for HS biology project. So even even educational for other people.
Yup. Steel is custom fabricated in my experience, and cutting and welding steel onsite adds cost to the project. I’m working on a fast-tracked hospital where sitework and structure was permitted through early release packages, before we’d even finished all of the interior design and documentation. Steel has already been fabricated and stored on site, but we’re still moving roof equipment around, coordinating elevator requirements, etc. because of some unforeseen conditions. Every departure from the contract documents will cost thousands.
Seems like concrete is extremely slow to go up. Been watch Kanes Autoparts tower in N. Hills go up for almost a year now and they still haven’t topped it out. I think with steel it would have been up in a matter of weeks vs. months.
Not sure why anyone would use concrete. But I guess if it’s not a schedule driven project there must be some good cost savings.
Not sure why that’s been the case here, because concrete is generally seen as being equal to or faster than steel, although I’ve seen some studies that put the cut-off at around 10 stories (i.e. below ten, steel is preferable. Above 10, concrete is faster).
People also often forget that while steel may rise quickly on site, the procurement, fabrication, and delivery of steel may require 6 to 10 months of lead time. Concrete structures can go up without that lead time and essentially start work immediately. Steel also needs spray-on fireproofing whereas concrete doesn’t, and since the floors are part of the concrete structure, the contractor can install electrical/mechanical/plumbing/etc. in lower floors while the upper floors are still being poured. Concrete can also lessen the floor-to-floor height significantly, because you’re not layering a slab over decking over joists over beams/girders. Over the length of a high-rise, that means less cladding, less HVAC and elevator run, more floors fitting within the same overall building height. And lastly, concrete is more structurally efficient for clear spans, which is really attractive for office buildings that usually want unobstructed open space.
There is a very standardized set of steel sizes (a kit of parts if you will) that we (structural engineers) choose from, and we talk to fabricators to stay up to date concerning which sizes are most readily available in which market. Fabricators then take the design drawings and “custom” detail every single piece on the job with each cut, bolt hole, connection plate, etc laid out with precise dimensions. They then submit these “shop drawings” to us through the contractor for us to review and approve (on sizable jobs, these submittals can easily be in the thousands of pages). Then they are released to be “fabricated” and delivered to the site ready to erect. On a very fast track job, a steel sub can go from receiving a contract to beginning erection in about 15 weeks.
This has become more and more of an industry standard unfortunately. However, while costing thousands of dollars is certainly a bad thing, in some ways concrete buildings are even worse, providing less flexibility during construction.
These days pretty much every job is schedule driven in order for the GC to make any money. However, many times structure is only on the critical path near the beginning of construction. Concrete is slower floor to floor, but once it gets a head start, there is so much other scope to follow at the lower floors that it is not a real problem. In other words, steel might be able to jump out way ahead, but it wouldn’t speed up completion of all the finishes.
I was running (walking) by Phase 2 and noticed 3 things. The elevator shafts are quite prominent now for the apartment section that doesn’t wrap around the deck. Definitely putting wood framed units there. Also, the concrete ceiling/columns seem to have been poured for the entire ground floor now. More surprising is that there seems to be a second story of concrete for the section wrapping the deck. I’m guessing it has to do with making it level and connecting over “Tucker St” to the section closer to Phase 1 that is downhill.
