Tall structures frequently have tubular structures. Frame tube, braced tube, tube in tube, and bundled tube constructions are examples of tubular structures. With a tubular structure, lateral loads can be resisted by designing the building to resemble a hollow cantilever that is perpendicular to the ground. Because they have less storey shear, storey displacement, and storey drift than other tubular systems, tube in tube structures are preferable. According to IS1893:2016 (Part 1), the influence of bracing type and position has been investigated in this study for a 20-story building in zone IV. Seismic metrics for braced and unbraced buildings are compared. The study at the building\'s corner and centre uses bracing made of angles and tubular sections. Seismic parameters are compared for unbraced and braced building. Angle and tubular section bracing are designed and used for the study at centre and corner of the building. From the study a comparative statement has been made for the use of bracing at different locations of tube in tube building. Comparative analysis will ease the designer to select the proper bracing type and location for high-rise tube in tube buildings.
Tall buildings frequently use tube in tube structures. It is made up of an outer tube and an inner tube. The outer tube is made up of heavy columns and deep beams that support gravity and lateral stresses, while the inner tube is a shear wall designed for lifts. Due to its substantial structural depth, the outer tube is crucial. The inner tube provides a column-free surface because it has a shear wall. These kinds of buildings are also known as hull and core constructions. Bracing is a construction method used to stabilize the building structure against lateral forces. It improves a building's capacity to withstand lateral loads imposed by wind and earthquakes. Buildings designed to withstand earthquakes must be braced in order to remain stable. In a frame structure, the bracing supports the horizontal loads while the beams and columns support the vertical loads. The main goal of bracing is to strengthen the building and prevent collapse due to an earthquake, wind gusts, or the effect of moving loads like cranes. It ensures the building's safety. Tube in tube structural form bracings provides additional resistance and stiffness in the building, making the system more effective than framed tube constructions. Tube in tube constructions with bracing models performed better than frame tube constructions. X braced framed tube structures and tube in tube structures with V bracing outperformed all other structural models that were tested . The Time Period for Tubular structures reduced considerably when compared with the Tall RC Moment Resisting Frame Structure. The Base shear for Tall Tubular structures increased when compared to Tall RC Moment Resisting Frame Structure under the seismic loading. Story displacement and Storey drift got reduced in Tubular Structures compared to Tall RC Moment Resisting Structure and the value of top story displacement and storey drifts are well within the limits. Storey accelerations increased for Tubular structures over the Tall RC Moment Resisting Structure . The main objectives of this study are to compare the seismic response of braced and unbraced structure against lateral loads in seismic zone IV as per IS 1893:2016.
In this study 20 storey building having 3m storey height is taken for study. The geometry of the building is rectangular. The buildings are modelled on Etabs 2018 software. The code used for designing these buildings is IS 456:2000 “Code of practice for plain and reinforced concrete”, IS 1893:2002 “Criteria for earthquake resistant design of structures”. Following models and nomenclature have been used in the model to categorise different models used in this study.
Regular - 20 storey rectangular tube in tube structure without bracing.
Bracing 1 - 20 storey rectangular tube in tube structure with angle section bracing at centre in all four faces of building.
Bracing 2 - 20 storey rectangular tube in tube structure with angle section bracing at corner in all four faces of building.
Bracing 3 - 20 storey rectangular tube in tube structure with tubular section bracing at centre in all four faces of building.
Bracing 4 - 20 storey rectangular tube in tube structure with tubular section bracing at corner in all four faces of building.
Following are the conclusions of the study –
1) It has been concluded that by selecting proper bracing section, the effect of the seismic parameters reduces significantly.
2) From the two-location decided for bracing i.e., centre and corner for the study, it has been found that centre bracing system with angle section performs well as compare to other bracing systema and location.
3) Storey drift and storey stiffness results validated that on incorporating bracing system, drift reduces, and stiffness increases.
4) It has been also concluded that bracing system in new as well as old tube in tube buildings will enhance the seismic performance of the building. Although no major change has been marked on comparing effect of angle section and tubular section.
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