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?
Wood frame over podium is most common for urban mid-rise residential or mixed use developments. This is because it is the cheapest option, meaning that developers can turn the biggest profit. It is also the lowest carbon option, which is increasingly a statistic that developers are using to attract investment into their operations, and it can help comply with legislation designed to limit carbon emissions. Although it constrains height, spans and floor plate depth, these are often limitations that already exist due to local regulations.
For office buildings, concrete or steel are common. This is because they have good acoustic separation, which is helpful for dividing multiple businesses operating under one roof. It has longer schedules and higher embodied carbon, but companies developing offices can typically deal with these variables.
I choose a concrete ground floor and a timber food frame structure for the upper residential floors. This led me to have a grid with smaller spacing in the upper residential floors, meaning I had more columns that will likely fall into some of the residences. However, I choose this system for the lower price and the climate-friendly impact. The concrete ground floor is optimal for separating the different stores that will occupy the mall on that level.
You sized members by judgment rather than analysis.
◦ What did you base your first guess on?
◦ Why is it safer to guess large and shrink than to guess small and grow?
◦ At what point in a real project does the engineer take over from the guess?
Design teams link and share models rather than working in one file.
◦ What are the advantages of linking?
◦ What errors does linking make possible that a single model would not?
◦ Why is getting shared coordinates right at the start so much cheaper than fixing it later?
By linking the models, each team can control what pertains to its own discipline across different offices and software. The models sync across everyone’s system, so each team can publish and update others on what they have done. It also divides responsibilities clearly, and tools such as clash detection can be helpful in reconciling the different models in a way in which everyone is aware of the differences/disagreements in between the different teams’ work.
This opens the potential for a team to forget to reload or republish, so teams end up coordinating against outdated geometry. Models can be misaligned, or have drifting grids, levels, units, and origins. Links can break when files are renamed or moved without everyone being in agreement. Differences in software versions can also alter geometry or drop data.
Getting shared coordinates right at the start is cheap because nothing yet depends on them, whereas fixing them later is costly. If different teams develop different coordinates, then a team’s sheets, views, dimensions, tags, and clash reports could potentially be built on the wrong position. In the worst case scenario, this inconsistency can carry into an offset discovered during construction.
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?
Sometimes a clash was simply a difference in detail between the two models; for example, one clash was between the generic floor outlined in the architectural model and the joists laid down in the structural model. Both are the same floor and they don’t clash with one another: one is simply more detailed. Other instances were the two models having different elements in the same place. For example, a column in the structural model stands in the place of a window in the architectural model - that is a legitimate clash that will need to be resolved.
Closing a clash means someone is accepting a condition or changing the design. Thus, each discipline should have the authority to close clashes that are relevant to it. The structural engineer has the authority to close the structural design clashes, the architect has the authority to close the architectural clashes, the mechanical engineer has the authority to close the mechanics clashes, etc.
Your beam depths just constrained next week's ductwork.
◦ Where in your building is the ceiling plenum now tightest?
◦ What would you give up to get it back?
◦ Should the structural engineer have consulted the mechanical engineer before setting spans?