Steel column reinforcement techniques for seismic resistance
Product22 Apr 2024
Steel columns play a crucial role in the seismic resistance of buildings, particularly in regions prone to earthquakes. The below techniques can be employed individually or in combination, depending on the structural requirements, seismic hazards, and building design objectives.
Increased cross-sectional area: improving the cross-sectional area of the steel column can enhance its capacity to withstand seismic forces. This can be achieved using thicker steel sections or increasing the number of steel plates welded together to form a composite column.
Composite columns: composite columns combine steel with concrete to take advantage of both materials' strengths. Concrete can provide additional mass and stiffness, while steel offers ductility and strength. This combination enhances the column's ability to dissipate seismic energy.
Buckling-restrained braces (BRBS): BRBS are devices installed within the steel column to enhance its lateral stiffness and strength. These braces restrain buckling under seismic loads, thus improving the column's performance during an earthquake. They have a steel core surrounded by a casing filled with a low-ductility material such as concrete or grout.
Concentric bracing systems: Concentric types of bracing are opposite V-bracing, X-bracing, 2-story X-bracing, diagonal bracing, V-bracing, and K-bracing, connected to the steel column at both ends. They are designed to carry seismic loads by dissipating energy through yielding and plastic deformation, thus reducing the forces transferred to the column.
Added shear reinforcement: lateral reinforcement, such as stirrups and crossbars welded to the column flanges, can enhance the column's ability to resist shear forces during an earthquake.
Prequalified connections: using prequalified connection details, such as moment-resisting or concentrically braced frame connections, ensures that the connections between the steel columns and beams are designed to withstand seismic forces.
Base isolation: base isolation systems decouple the building from the ground motion by introducing flexible bearings or isolators between the foundation and the superstructure. While this technique primarily applies to the entire structure, it indirectly benefits steel columns by reducing the seismic forces transmitted to them.
Damping systems: damping devices, such as viscous or tuned mass dampers, can be installed within or adjacent to steel columns to absorb and dissipate seismic energy, reducing the structural response to earthquakes.
Performance-based design: utilising performance-based design approaches allows engineers to tailor reinforcement techniques based on the structure's specific seismic hazards and performance objectives, optimising the seismic resistance of steel columns.
Structural steel beams commonly used in construction for structural reinforcement:
Indian standard medium beams (ISMB): They have a standard 'I' shape with relatively narrow flanges and a tapered web. They are commonly used in construction for various applications, such as building frames, bridges, and industrial structures. ISMBs are preferred for medium-span structures where moderate loads are anticipated.
Narrow parallel beams: narrow parallel beams typically refer to beams with narrow flanges and a parallel web. These beams are suitable for applications with height restrictions, but the load-bearing capacity is still essential. They are often used when space is limited, such as in mezzanine floors or roofing structures.
Wide parallel beams: wide parallel beams have broader flanges than narrow parallel beams but maintain a parallel web. They are used in applications where a higher load-bearing capacity is required compared to narrow parallel beams. Wide parallel beams are often employed in heavy-duty industrial buildings, bridges, and other structures where significant loads must be supported over long spans.
Universal beams: universal beams, also known as UBS or I-beams, have a distinctive 'I' shape with broad flanges and a tapered web. They are versatile and widely used for various purposes, including building frames, bridges, columns, and other structural elements. Universal beams offer excellent load-bearing capacity and are suitable for small and large-scale construction projects.
In reinforced concrete buildings, vertical columns have two types of steel reinforcement: long bars running vertically and horizontal loops of smaller bars. During earthquakes, these columns can bend or break apart. To prevent this, horizontal loops must be placed closely together, holding vertical bars in place and preventing concrete from bulging. Loop bars should have end hooks to prevent concrete from pushing out and vertical bars from bending. These techniques can be employed individually or in combination, depending on the building's structural requirements, seismic hazards, and design objectives.