Steel frame structures are essential in modern construction due to their strength, flexibility, and ability to withstand heavy loads. They are commonly used in high-rise buildings, industrial facilities, and large commercial spaces. The construction of these structures involves various key phases, including the foundation, column installation, beam erection, and the integration of floor systems. This article provides an in-depth look at the construction process of steel frame structures, from the foundations to the cladding.
1. Introduction
Steel frame structures play a vital role in modern architecture and construction. These structures provide the framework for large buildings and are prized for their durability, strength, and ability to support heavy loads. The steel frame is made up of interconnected columns, beams, and floors, and its construction follows a systematic process that ensures stability and safety. This article explores the various phases involved in constructing steel framed structures.
2. Construction Phases of Steel Frame Structures
The construction of a steel frame structure typically occurs in several distinct phases:
- Foundation Construction
- Column Construction
- Erection of Steel Beams
- Floor System Installation
Each of these phases is critical for the overall stability and safety of the building.
3. Construction of Steel Frame Structure Foundations
The foundation is the first critical phase in the construction of a steel frame structure. The foundation’s purpose is to transfer the load of the building to the ground and ensure the structure’s stability. The type of foundation used depends on several factors, including soil conditions and the building’s load requirements.
Foundation Types and Selection
The type of foundation chosen for a steel frame structure depends on the soil’s bearing capacity. A soil investigation is typically conducted, involving both surface and subsurface exploration, to determine the soil’s ability to support the structure. Based on these findings, different foundation types may be chosen:
- Reinforced Concrete Bearing Pad Foundation: Used when the soil has moderate or low bearing capacity and can support the transferred loads. This foundation is suitable for lighter buildings or structures with moderate load requirements.
- Pile Foundation: In cases where the soil strength is poor or the structure imposes a large load, pile foundations are recommended. These foundations transfer the building’s load to deeper, stiffer layers of soil. Piles are driven deep into the ground to ensure adequate load transfer.
Construction Process
The foundation construction process begins with preparing the site, followed by excavation and laying the foundation. Reinforced concrete is often used for bearing pads, and pile foundations may require the installation of steel bearing piles driven into the ground.
4. Steel Column Construction
Once the foundation is set, steel columns are installed. The column design is determined based on the anticipated load that the column must bear.
Column Design and Selection
Steel columns are fabricated in different sizes, and their selection is influenced by the load-bearing requirements of the structure. Typically, steel columns are prefabricated and produced in advance to streamline the construction process.
Installation Process
The next step is the placement and installation of the columns. The most critical aspect of column installation is the connection between the foundation and the column. A base plate is welded to the bottom of each steel column, ensuring a strong and secure connection to the foundation. The most common base plate shapes are square and rectangular, as they allow for optimal spacing between bolts.
Column Splices
Column splices, or the joining of two sections of columns, are commonly placed every two to three stories. This facilitates easier erection and simplifies column fabrication and delivery. The splice is typically positioned about 60 cm above each floor. In cases where circular steel columns are used, welded connections are employed to join the sections.
5. Erection of Steel Beams
After the columns are in place, the next step is the erection of steel beams. These beams are essential for transferring the load from the floors and roof to the columns.
Steel Beam Selection
Steel beams come in various sizes and spans. While steel beams can span up to 18 meters, the most common span ranges from 3 to 9 meters. The type of steel beam selected depends on the design requirements and load considerations.
Column to Beam Connections
Column-to-beam connections play a crucial role in the stability of the structure. Various types of connections are used based on the types of loads the joint will experience. For joints subjected to vertical loads, simple connections like flexible end plates, fin plates, and double angle cleats are commonly used.
For joints exposed to both vertical loads (shear force) and torsion forces, more robust connections like full-depth end plates and extended end plate connections are preferred.
Beam to Beam Connections
When connecting secondary beams to primary beams, end plate beam-to-beam connections are typically used. These secondary beams support the floor system, so they must be aligned with the top flange of the primary beams. This can be achieved by notching the top flange of the secondary beams, or alternatively, a projected bracket can be welded to the primary beam, allowing for the attachment of secondary beams without the need for notching.
6. Floor Systems Used in Steel Frame Structure Construction
Once the beams are erected, the floor system is installed. The floor system is essential not only for supporting the vertical loads but also for providing lateral load resistance.
Floor System Types
There are several types of floor systems that can be used in steel frame construction:
- Short-span composite beams and slabs with metal decking
- Slimdek and cellular composite beams with slabs and steel decking
- Slimflor beams with precast concrete units
- Long-span composite beams and slabs with metal decking
- Non-composite beams with precast concrete units
Each floor system is designed to meet specific load requirements, and the choice depends on the building’s design and function.
Floor Functionality
In addition to bearing vertical loads, floor systems also serve as diaphragms that resist lateral forces. Bracing within the floor system ensures that the structure can withstand wind and seismic loads, contributing to the overall stability of the building.
7. Construction of Bracing and Cladding
Once the primary structure is in place, the next phase involves adding bracing and cladding to the steel frame.
Bracing
Braces are used to resist lateral forces, such as wind or seismic loads, which could otherwise cause the structure to sway. These braces transfer lateral loads to the columns and, ultimately, to the foundation. The bracing system is essential for ensuring the structural integrity of the building under various load conditions.
Cladding
Cladding serves as the outer layer of the building, providing protection from the elements and enhancing the structure’s appearance. Common types of cladding include brick cladding and sheet cladding. These materials help shield the interior of the building and can also contribute to energy efficiency by providing insulation.
8. Conclusion
The construction of steel framed structures involves several phases, each of which contributes to the overall strength and stability of the building. From the foundation to the final cladding, each step is essential for creating a safe and durable structure. By understanding these construction phases—foundation, columns, beams, floor systems, bracing, and cladding—construction professionals can ensure that steel frame buildings are built to withstand heavy loads and environmental forces. With the proper materials, techniques, and planning, steel frame structures continue to be a vital part of modern construction.