Steel frameworks are suitable for tall structures, while concrete frameworks can only support a limited number of floors.
The durability and high strength of steel allow for a long operational lifespan, a condition that cannot be easily claimed for concrete frameworks.
Constructing a steel structure is relatively easy, and the execution speed is high. In contrast, the curing time required for concrete and the subsequent phases of construction demand a lot more time for concrete frameworks.
The weight of a structure built with a steel framework is significantly lower than that of a concrete framework, which is a major advantage and contributes to the overall reduction of the building’s weight.
Steel is a homogeneous material manufactured under strict supervision in factories, whereas concrete is produced on-site and lacks the same level of homogeneity.
Because steel has elastic properties compared to concrete, steel structures are highly resistant to large compressive forces, such as explosions, as well as lateral forces like earthquakes.
Stages of Constructing a Two-Story Steel Framework
Here, we provide information on the process and stages of constructing a steel framework in multi-story buildings.
Excavation
Excavation is a step that must be carried out in both steel and concrete structures. Generally, excavation continues until reaching solid ground, and for buildings with a basement, deeper excavation is required.
Concrete Pouring (Blinding Concrete)
After excavation and soil sampling, along with conducting geotechnical tests, the next step is concrete pouring. This concrete work is intended to protect the foundation concrete and create a smooth surface for the continuation of construction.
Blinding concrete, as mentioned, provides a flat surface for further work. It contains a lower cement ratio to ensure easy flow and coverage, ultimately yielding a smooth finish.
Reinforcement
After executing the blinding concrete and allowing it to cure, the next step is reinforcement. Reinforcement is necessary in both concrete and steel structures.
Following reinforcement, the locations for installing column bases and formwork are identified. This step does not differ between the two types of structures. It’s important to ensure that reinforcement is done according to national building regulations.
Concrete Pouring (Foundation Concrete)
Once reinforcement and formwork are in place, the concrete pouring process begins. This stage is specifically for the foundation. The concrete used can either be prepared on-site due to its small volume or purchased from concrete suppliers. Regardless, the mixer must thoroughly blend the concrete to ensure homogeneity before application.
At this stage, the concrete should be poured close to the reinforcement, and after each pouring phase, it should be vibrated to ensure proper mixing and homogeneity. To prevent concrete from cracking and deteriorating, the surface must be kept moist during the curing phase. After initial curing, the formwork is removed, but the curing process continues.
Plate Placement
Plate placement is the process in which steel plates, which will support the beams, are firmly secured onto specific reinforcement bars. A part of this operation, called venting, occurs while the concrete is still not fully cured.
During venting, a large amount of loose concrete is poured beneath the steel plates, and then the plates are tightly bolted down to eliminate any voids beneath them.
It’s crucial to note that voids beneath the plates can lead to settlement in the columns due to increased weight. Thus, loose concrete is used for venting purposes.
Column Installation
To install columns, I-beams are ordered from the factory. Initially, the height of the columns is measured, and the required I-beams are cut to size. Then, smaller beams are welded to the first-floor beams for the second floor to reduce the building’s dead load and column thickness.
Once the beams are prepared, they are lifted vertically using a crane and secured in place on the steel plates prepared during the reinforcement and plate placement phases. The connection of columns to the plates is typically achieved through welding or bolting. It’s worth noting that angle brackets for better connection are often pre-bolted to the plates.
Beam Installation
Beams are long steel components that connect the columns, and the flooring or ceiling structure is then supported on these beams. The I-beams used for the beams differ from those used for the columns.
To enhance resistance, the beams are often made in a honeycomb shape. During this phase, hexagonal cuts are made on the beam’s body at specified intervals using templates and gas cutting machines to increase beam strength. The remaining hexagonal pieces are then used to connect the beams to the columns.
Bracing Installation
The final stage of constructing the steel framework involves installing bracing. Typically, both paired and single channels are used for bracing, connecting from the column and beam joints to the next column and beam joints in a cross pattern.
Lastly, metal plates are used at the intersection points of the braces to enhance the framework’s resistance against lateral forces. It’s important to mention that the installation of braces involves detailed steps and specific guidelines that are beyond the scope of this discussion.
Conclusion
Once the bracing is installed and the intermediate stairs are put in place, the construction of the two-story steel framework is complete. The process continues with the installation of floor beams, ceilings, and then wall framing, marking the start of the finishing phase.
