Which structural framing systems and materials are most commonly used in the United States for residences? For office buildings?
For residences, platform wood framing is the most common structural framing system and they typically use wood materials, like lumber or engineered wood products (OSB, plywood, etc.) For US office buildings, the most common structural framing systems are steel frames (i.e. steel skeletons) or reinforced concrete frames. This building type typically uses materials like structural steel, reinforced concrete, or mass timber.
◦ What factors explain why those dominate?
The reason these factors dominate is due to the loads carried by each building type, material availability, and building code regulations, among other things. Steel and concrete structural framing systems dominate office buildings, which are typically quite tall. These materials can span much longer distances and carry much heavier live loads than wood framing structures. In addition, fire concerns in building code regulations restricts the use of highly combustible materials (such as wood), in tall buildings with high occupancy levels. On the other hand, for residences, which are typically much shorter and have fewer occupants, wood is an easily accessible, abundant material, making it ideal for residential framing systems.
◦ Why did you choose your system, and what did it cost you?
I chose a steel structural framing system because of my building type. Since my building is a office building with a ground retail space, based on industry standards, a steel structural framing system is recommended. However, steel framing structures are typically much more expensive (high material cost) and have a much higher embodied carbon cost, which also increases the carbon emissions of the building. This could be a potential cost depending on if there are any sustainability/carbon metrics that the building needs to meet as part of its design.
You sized members by judgment rather than analysis.
◦ What did you base your first guess on?
My first guess was based on industry standards and typical sizes for structural members.
◦ Why is it safer to guess large and shrink than to guess small and grow?
It’s safe to guess large and shrink, since having structural framing that is too large is easier to change than framing and columns that are too small. Oversizing ensures that there is enough space for various structural members, whereas undersizing can result in conflicts with other architectural elements if members need to be increased in size.
◦ At what point in a real project does the engineer take over from the guess?
The engineer takes over from the guess once loads are fully defined and project extends beyond the schematic design. Engineers take over when structural members actually need to be detailed and sized via analysis rather than judgement; this typically occurs during the design development phase.
Design teams link and share models rather than working in one file.
◦ What are the advantages of linking?
The advantages of linking models is that different design teams can work on their individual models without having to worry that others might actually delete or alter their work. This is also useful since the linked models can be underlaid and updated every time the file is opened. This allows different teams to work on the design concurrently.
◦ What errors does linking make possible that a single model would not?
Linking can result in clashes between models due to alignment issues (i.e. incorrect shared coordinates, different origins/basepoints), double-modelled elements from copying over from a linked model, etc. In addition, if not refreshed/saved on a consistent basis, the design team may not be working on the most updated linked model, which can also cause some clashes between different models.
◦ Why is getting shared coordinates right at the start so much cheaper than fixing it later?
Getting the shared coordinates right at the start is much cheaper than fixing it later because the error multiplies once other features and structures are placed in the model. If you build a model using the wrong coordinates, this can cause alignment issues and potential new clashes once the models are realigned. Additionally, this could cause coordination issues for other design teams working off the linked model.