Link to Student
Journal Entry For
Module 7 - Study Your Options
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Step 1 - Generative Design Framework
Motivated by the AEC global teamwork project, I believe that employing generative design for buildings can bring significant benefits. This approach necessitates collaborative efforts, engaging professionals with diverse expertise, including architects, structural engineers, construction managers, MEP engineers, and life cycle financial managers to create a comprehensive and optimal final design.
In this module's initial phase, I will focus on outlining three pivotal design decisions for a typical three-story engineering building on campus within the domain of structural engineering. These decisions interconnect closely with other disciplines, ensuring a holistic and synergistic solution.
- Design Decision 1: Structural Grid Subdivision
- Objective: to achieve an optimal grid subdivision for structural elements, ensuring acceptable deformation and safety under specific gravity/lateral load while also facilitating prefabrication and construction convenience.
- Design Variables
- Horizontal grid spacing
- Vertical grid spacing
- Evaluators
- Element total volume
- The maximum deflection of structural elements
- The maximum lateral drift
- Most Important Tradeoffs to Consider
- Building code standards
- Financial budget
- Design Decision 2: Structural Material Selection
- Objective: to select a building material to construct a sustainable building while simultaneously reducing its carbon footprint and adhering to specific financial budget and benefit requirements.
- Design Variables
- Structural materials: timber/steel/concrete
- Scale for building: element size and numbers
- Evaluators
- Carbon footprint
- Life Cycle Cost
- Most Important Tradeoffs to Consider
- Financial budget
- Local context: labor and environment constraint
- Design Decision 3: Construction Planning
- Objective: to devise a construction plan for structural design that determines the percentage of elements to be prefabricated and establishes the timeline for completion, while adhering to a limited construction cost budget and maximizing the quality and value of the building.
- Design Variables
- Prefabrication percentage
- Construction timeline
- Evaluators
- Building quality and deconstruction value
- Construction cost: transportation, manufacture, assembly
- Most Important Tradeoffs to Consider
- Financial budget
- Local context: labor expertise and element size in the market
Overall Generative Design Study Graph:
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Step 2 - Generative Design Study
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Description of Chosen Design Decision
The design decision chosen for examination in this module focuses on the subdivision of the structural grid. A comprehensive and in-depth description is provided below:
- Objective: For a building with fixed height and scale, find the number of stories and grid spacing that will maximize the net benefit (market value - construction cost) and minimize the force in structural elements
- Modal: Assuming the fixed volume building has a square base area and specific height, select one typical section view and idealize it as a simple frame structure
- The frame can have a different number of story (n), larger n provide more usable area and therefore more market value; however, larger n would also decrease the column height and increase the base shear at the bottom.
- The frame can have different grid spacing, i.e., grid spacing * (#columns - 1) = frame width. Larger spacing indicates fewer columns and less construction cost, while also increasing the structural element deformation as well as the base shear.
- The reaction force can be calculated with domain knowledge in structural engineering:
- Design Variables (2 inputs)
- Number of stories
- Number of spans
- Constants
- The scale of the simplified frame structure (width and height)
- Structural element effective strength
- Load condition
- Construction cost per length
- Market value per length
- Evaluators (outputs)
- Reaction forces in the sub-frame structure
- Construction cost
- Market Value
- Net benefit (market value - construction cost)
- Interpretation
- In the optimal structural design, we want to minimize the base shear in structural elements to prevent large deformation/drift, and also maximize the net benefit. These two objectives conflict with each other therefore a trade-off is required.
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Study Graph
- General: each block represents a specific function node group:
- Inputs: the two design variables are #story and #span, from which the height and width of the simplified sub-frame structure can be accordingly calculated. The constants are also input, including the building scale, load condition, as well as values required for construction cost and market value computation.
- Functions: the construction cost and market value are computed similarly to the process in module 6, and the structural element is calculated as shown:
- Outputs: the main evaluators are structural reaction force and net benefit (market value - construction cost), while the market value and construction cost are also outputs for reference.
- Geometry: the frame model is built for visualization:
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Step 3 - Generative Design Study Results
- Inputs and Goals: the inputs are the number of spans and the number of stories, and my goal in this module is to minimize the reaction force in structural elements as well as maximize the net benefit (minimize the construction cost and maximize the market value).
- Parallel Coordinates Graph
- Overall result
- Set constrain: reaction force < 5000
- Scatter Plot and Optimal Structure
- The parallel coordinate graph illustrates the relationship between the outputs (construction cost, market value, net benefit, reaction force) and inputs (#story and #span).
- It demonstrates that the number of stories is positively correlated with both construction cost and market value. On the other hand, the number of spans has a smaller impact on the net benefit within each #story condition. Generally, a higher net benefit is achieved with more stories and fewer spans, which is desirable.
- In terms of structural performance, fewer stories and more spans result in lower reaction forces in the structural elements, which is preferable.
- When considering the conflicting preferences for the two main outputs, a tradeoff is required.
- The scatterplot provides a clearer representation of the relationship between the two main outputs. It shows that higher market values are generally associated with larger reaction forces. However, it is evident from the plot that the structural reaction force does not vary significantly when it is below 5000, but it differs substantially when it exceeds 5000 (where the benefit does not increase significantly).
- Based on this observation, we conclude that the optimal solution would be the maximum benefit achieved while keeping the reaction force limited to 5000, as highlighted in the plot.