RC Structure or Steel Structure? My answer as a Construction Manager.

Steel construction has increasingly gained prominence due to its efficient erection methods and well-established systems for ensuring quality and craftsmanship. Furthermore, structural steel has the advantage of supporting higher loads with smaller member sizes, making it an attractive option for various engineering applications. However, when compared to reinforced concrete (RC) structures, steel constructions are typically more costly in terms of material expenses.

Reflecting on my experience as a Design & Cost Engineer in 2017, I worked on a skyway project in the Philippines, where the primary structure was originally designed as an RC system. Due to the necessity of passing over a congested highway intersection, the deck required a long span design to minimize traffic disruption. This constraint led to the decision to transition to a steel structure, as it better suited the project's requirements.

While the use of RC structures is widely known to be more cost-effective than steel, a detailed evaluation was necessary to fully understand the financial implications. To assess the cost differential, I conducted a comprehensive analysis, comparing three design options:

Option 1: Reinforced Concrete (RC) Structure
Option 2: Full Steel Structure Frame
Option 3: Composite Structure (RC and Steel)

The results of the cost analysis confirmed that Option 1, the RC structure, was the least expensive. However, it was evident that labor costs associated with the construction of an RC system would be significant. To mitigate this, a potential solution was to incorporate precast elements into the skyway frame design. This would not only reduce labor costs but also minimize the on-site construction risks and hazards associated with in-situ casting.

Option 2 entailed using a complete steel structure for the main frames. While this approach had an initial material cost three times that of the RC structure, it offered a major advantage in terms of reduced installation time, thereby potentially reducing overall project duration and related overhead costs.

Option 3 combined both RC and steel components in a hybrid configuration. In this case, RC was utilized for the shorter spans, while steel was employed for the longer spans crossing the highway intersection. While this option was more expensive than Option 1, it was significantly less costly than Option 2, offering a balanced solution in terms of material and labor costs.

Ultimately, the choice between these options cannot be based solely on material pricing. A holistic approach is essential, factoring in critical elements such as the project timeline. Specifically, we must ask: Can the RC structure meet the required deadlines?

In addition to project duration, the risks and hazards inherent in each design must be thoroughly assessed. RC construction poses challenges due to the handling of rebar, the use of heavy equipment, and the associated risks of concrete pouring and casting, including exposure to hazardous chemicals. Conversely, steel construction introduces risks related to the use of heavy materials, specialized equipment, and hot work operations.

Beyond these primary considerations, other factors such as site conditions, available space, labor costs, material availability, installation methods, and logistics must also be evaluated. These elements can significantly impact both the cost and feasibility of the project.

In conclusion, the decision-making process for selecting between RC, steel, or composite structures requires a detailed and multidimensional analysis. The interplay between cost, timeline, risk, and operational efficiency must be carefully balanced to determine the most suitable solution for the project's unique requirements.