Which structural framing systems and materials are most commonly used in the United States for residences? For office buildings?
◦ What factors explain why those dominate?
◦ Why did you choose your system, and what did it cost you?
You sized members by judgment rather than analysis.
◦ What did you base your first guess on?
My first design driver was lateral stiffness. I focused on stiffening the exterior perimeter to strictly control inter-story drift. The main goal was to guarantee the serviceability and integrity of the architectural envelope—specifically preventing the glazing and windows from failing under seismic loads. By utilizing a highly rigid concrete system, structural deformations are minimized, effectively protecting these brittle non-structural components.
However, I fully acknowledge that this stiffness-driven approach led to over-sized elements, leaving significant room for optimization in the beam-column joints and overall member cross-sections. Because the US seismic framework permits much larger inter-story drifts and total roof displacements compared to Chilean standards, the structure can afford to be considerably more flexible. Assuming the floor slab behaves as a rigid diaphragm transferring lateral shear, we can significantly scale down the framing members. Rather than resisting seismic forces purely through massive elastic stiffness, the system can be optimized by relying on structural ductility and energy dissipation, which perfectly aligns with the local code's philosophy.
◦ Why is it safer to guess large and shrink than to guess small and grow?
From an engineering view, it is much better to design in large spaces, closing the gaps between the different disciplines. When you have small spaces, the specialties must adapt the engineering to those spaces, increasing the probability of error when you are designing and when you are in the construction phase.”
◦ At what point in a real project does the engineer take over from the guess?
The structural engineer must be involved in the project from the beginning. The most important decisions are made at the start of the project. The longer you wait to make a decision, the more time and money it will cost you
Design teams link and share models rather than working in one file.
◦ What are the advantages of linking?
Linked models optimizes the team's decision-making and saves time in the overall process. It also provides clear change control, making it much easier to track and analyze the modifications made by each discipline independently.
◦ What errors does linking make possible that a single model would not?
Speaking from my own experience (which might not be the case for everyone), I found it difficult to work in the software because the structural environment doesn't always easily recognize the linked architectural elements. The physical integration of the structural framing with the architecture was one of the main problems I faced—an issue that probably wouldn't happen if everything was built inside a single file
◦ Why is getting shared coordinates right at the start so much cheaper than fixing it later?
I learned this the hard way. By mistake, I shifted the architectural model away from the structural one. I was trying to turn on the linked model, but it wouldn't appear, and the elements I wanted to copy didn't work. In that moment, I realized exactly how important it is to work with shared coordinate systems from day one. Fortunately, fixing it this time was quite easy and intuitive by simply aligning them origin-to-origin, but in a real massive project, fixing misaligned models later would cost a lot of time and money
Not every clash is a problem.
◦ On what basis did you classify a clash as an issue versus not an issue?
◦ Who should have authority to close a clash on a real project?
Your beam depths just constrained next week's ductwork.
◦ Where in your building is the ceiling plenum now tightest?
Actually, I am not planning for all utilities to go up and down through the main shafts. For example, potable water will run through the baseboards in bathrooms and kitchens, and wastewater will drop directly within each apartment. The key is to keep the floor layouts identical to collect the wastewater easily.
This leaves only electricity and HVAC for the ceiling plenum. Since the building will use A/C, the plenum will be tightest where the main HVAC equipment goes. I need to wait for the real dimensions of the extractors and injectors before making a final decision on the ceiling. However, I left enough clearance initially so that any future adjustments won't be too expensive.
If I need to get space back, I have a Plan B: for fire protection (NFPA), the piping will run up through the stairwells, and I can also open additional vertical shafts in those stairwells to free up the ceiling.
◦ What would you give up to get it back?
I feel I am making good decisions early on to avoid taking a step back. My main concern is related to the exact sizes of the HVAC equipment. However, if I really need some extra space in the ceiling, I know my concrete beams are currently oversized and the floors are metal decks. I would give up some of that beam depth to get the space back.
◦ Should the structural engineer have consulted the mechanical engineer before setting spans?
Absolutely. All MEP disciplines must be involved during the early architectural design phase. This is the stage where the main entrances and vertical shafts for all levels are created. The mechanical engineer needs to work alongside the architect and the structural engineer from the very beginning to support and coordinate these critical decisions.