Isolated Structural System Overview:
3D Structural:
Plan (level 1, shows columns and foundations):
Plan (level 2, shows more of the framing systems):
Since the majority of my building design consists of just the one floor, I’ve only shown level 1 and 2 in plan. Level 1 shows most of the column spacing and foundation layout pretty well, and level 2 shows most of the framing above the first floor. It does not show the sloped framing used for the pitched roofs and does not show a section of the north exhibit, which has higher ceilings and is not visible at the level 2 cut plane. These aspect are best seen in the 3D model shown at the top.
Grid strategy:
Since my building consists of many distinct geometric forms all interconnected, I split the building into sensible components and created five distinct grid systems to help place columns in each respective area. The two ‘corner’ regions were difficult to create grids for and resulted in some interesting grid systems that kind of followed angular and rectangular logic at the same time.
Structural System Strategies:
Overall objectives I followed are:
- Maximize mass timber usage for structure because of the material’s biogenic storage capacities and minimal embodied carbon to material strength ratio
- Minimize column placements in exhibit areas (counteracts the above objective!); maximize openness and flexible circulation in exhibit areas
- Use mass timber in areas with exposed structure for aesthetic and psychological (lol) purposes
This resulted in the following design strategies:
- The administrative wing was able to use a more closely spaced column grid, so mass timber columns and beams were used
- The two glass walkways were also able to make use of mass timber columns and beams because of the columns intimate spacing and the beams short spans — these structural elements would also be visible to the public, and since I fancy the appearance of timber, I’d like the exposed elements to be timber
- Exhibit areas all use steel columns and largely use steel framing; steel is used to capitalize on the material’s span length potential, and all the exhibit spaces demand column spacing that is longer than 30’, thus mandating the use of steel.
- The sole exception to the above is the pitched roof in the lobby area; the spans were short enough that timber beams were used in conjunction with steel girders to support the roof
- Foundations are largely just column footings, no piles are used as I’m not too familiar with the condition of the soil at the site, but considering it might be kind of moist because of the proximity to a body of water maybe these might be necessary (?); closely spaced columns are placed on raft foundations
- I only have one stair and elevator shaft system, and these were appropriate accommodated in the framing system
All of these design decisions can be seen in the 3D structural model image shown above.
Material and Sectional Choices:
The section sizes I chose for most of my framing was relatively light/small in light of the fact that I don’t expect gravity loads to be significant for my largely 1 story structure.
Material:
- Steel - A992 (50/65 ksi)
- Concrete - cast-in-place (foundation only) (3.5 ksi)
- Mass timber - glulam Western species (I never took a timber engineering class unfortunately :( so not gonna elaborate much more)
Sections:
- Steel columns up to 1.5 stories tall: W12x40
- Steel columns 2 or more stories tall: W18x76
- Steel girders: W12x40
- Steel joists supporting an enclosed roof assembly: W12x26
- Steel joists supporting a non-enclosed canopy: W8x10 (tiny)
- Interior timber columns: 8.75x18
- Walkway timber columns: 8.75x9
- Timber beams: 6.75x12
- Foundations under timber columns: 6’x4’x1.5’
- Foundations under steel columns: 8’x6’x1.5’
- Raft foundations: size varies
Coordinated Model Views:
Glass walkway with timber framing, I should cover the upper framing with a ceiling:
Admin wing with timber framing:
Seminar room:
Southern exhibit (again I need to add a ceiling):
Challenges with the Structural System:
- I didn’t have an elegant way of attaching many of the framing elements to the pitched roof because the roof was part of the linked model and could not be copied (since it’s a roof?) into the structural model; I ended up having to manually readjust column heights for many of the columns that did not align with a particular floor level at their top end
- I was not sure about where exactly the foundations would sit relatively to the ground floor plane; I ultimately extended each column 2 feet deeper than the level 1 plane and situated the footings below ground there — I’m not sure whether this is an appropriate elevation for these
- I had a lot of issues in the BIM 360 clash detector with the pitched beams and many of the interior walls I had created in the architectural model which extended to the roof; I need to adjust these interior wall heights back to the top of level 1
- I am not too sure about how the structural columns relate to the interior, nonbearing walls; I noticed that in our practice exercise (module 8.5A), that many of the models created (mine included) situated columns in line with the interior walls; and this was a strategy I also used for my project structural model (as you can see above), because it would conveniently keep the columns out of the room space. However, I’m curious about how this would actually be built — would the column just be embedded in the wall, or would it protrude out of or separate the wall?
- There is an area of my model where I have a second floor terrace that is continuous with the first floor roof of another part of the building, and the framing system I used for that whole area is also continuous. Since the framing was continuous, I was struggling with how to create that 6-8” offset you need for steel beams in order to accommodate the next floor level, because the roof that the floor was continuous with was already situated above those beams (not sure if this makes sense, might bring it up in a check-in). I might consider raising the floor by 6-8” to accommodate the framing system instead of the lowering the beams in this case….