Today we look at providing a framework for comparing two different structural design schemes.
We will examine the example case study shown below.
Case Study #1
You are working on a residential 12-storey development in a rural area of a developing country with low design wind speeds and low seismic risks. Construction is typically done in Reinforced Concrete (RC). The Client has asked you to consider two different floor framing options:
- Steel floor framing
H-700 primary steel beams and H-400 secondary beams with a composite deck slab. - RC flat slab floor framing
Flat slab (t=300 mm) with drop panels (t=450 mm) at column locations.
Can you think of some advantages and disadvantages to present?
I have listed some below.
| ◍ Great 〇 Good △ Not Ideal ✖ Not Feasible | ||
| Steel Floor Framing | RC Flat Slab Floor Framing | |
| Flexibility (MEP planning) | 〇 Beam openings can be provided. | ◍ Easy to route MEP pipes under the slabs. However, floor openings may require RC beams. |
| Flexibility (architectural planning) | 〇 Steel beams will impact the clear height. | ◍ Can have more storeys for a given height. |
| Flexibility (future) | ◍ Can be easily modified in the future. | △ Difficult to modify |
| Constructability | 〇 Steel can be quickly assembled on site using bolted connections. | ◍ Local contractors well accustomed to RC construction. |
| Quality / Appearance | ◍ | △ Susceptible to cracking. |
| Construction schedule | ◍ Steel can be quickly assembled on site using bolted connections. | △ Concrete pouring takes time and could extend the project schedule. |
| Structural Performance | 〇 No cracking/creep. Can provide longer floor spans. However, requires fireproofing. | 〇 Requires no additional fire-resistance measures. Generally the deflection is quite small. |
| Cost | △ Steel costs are considerably higher compared to concrete costs. | ◍ Concrete and rebar are available in large supply and a relatively cheap price. |
| Vibration Performance | △ If long span, susceptible to footfall vibrations. | ◍ No vibration concerns. |
| Acoustic Performance | △ Must be careful when choosing composite deck slab and slab thickness. | 〇 Good vibration performance. |
By using such a table, we can easily convey the pros and cons of two different structural systems and help the Client or architect make a more informed decision.