Glenn KatzYour Design Journal entries this week should highlight your design thinking that influenced your decisions about:
- your overall strategy and the features of the structural system
- the material and framing system selected
- the locations of structural columns and major framing elements
- any special structural challenges
For the structural system, since this is where my background is I have been trying to consider it from the beginning. Unfortunately creativity and structural practicality don’t mesh super well, so it was still a challenge to come up with a layout that made sense.
I went with a steel structural system. This allows the use of a steel moment frame lateral system, which lets me have larger openings for windows. Additionally, using steel sections allows for more slender sections than concrete. Lastly, I chose steel over timber because I am more familiar with it and can come up with a more realistic system.
View from bottom that shows the beam system
Here are the plan views. (I can’t seem to get rid of the stairs and doors).
Level 1
Level 2
Level 3
Level 4
Roof
In the end my result has some pretty long spans which will require pretty deep beams, however for this building it should work if the floor system is considered and the beams are designed to utilize composite action. The modeled floor is concrete over metal deck, with the current depth in the model being 2” deck and 3” concrete topping. The location of the deck was offset up 3” and the beams were offset down 3” to accurately model them.
The sizes are all W14s for the columns. For the beams, the typical sizes are W24s for the middle span and W21s for the top and bottom spans. The typical girders (spanning left to right) are all W24s.
Another consideration were the other openings for elevators, shafts, and stairs. I made sure to add some extra bracing to all of the smaller opening locations. For the elevators (top left opening) a beam is showing to be running through it, however in the coordination view it is by a wall between the elevators. The only change that will have to be made is adding a little bit more space between them.
The main clash is with the main stair. I could not get this to work nicely, and ultimately decided that I will have to move the stair up a few feet.
I also considered a lateral system. Here I wanted to use a moment frame, and have some deeper beam elements in the areas highlighted below. All of these elements are modeled as W33s (some of which can be seen in the 3D view). Columns were also rotated accordingly and footings at these locations were sized up, which is shown in the Level 1 floor plan above.
Moment Frame Locations
Below are screenshots in coordination view with the architectural model showing where the columns will be located. This gives an idea of things I will have to go back and modify.
Level 1
Level 2
Level 3
Level 4
My next steps for this project is to go back to my architectural model and make a few adjustments where there are clashes. Here are the main ones I am looking to address:
- There is a beam intersecting the top of the main stair. The main stair will have to move up a few feet.
- In line with that, on Level 4 there are awkward columns in the middle of rooms. These walls will also be moved along with the stairs.
- There is a column right outside the restroom on level 1
- The column intersecting the elevator opening is okay, but there should be a gap between the elevators to accommodate this.