PSI - Issue 70

Ajisha T T et al. / Procedia Structural Integrity 70 (2025) 27–34

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1. Introduction After the millennium, with the fast development of Computer Modelling technique and Finite Element analysis and new construction technologies numerous tall buildings were built around the world. Many tallest buildings were built at that time (Brunesi et al. 2016). Taipei 101 with a height of 509.2m became the tallest building in the world in 2004. Laterin 2010, Burj Khalifa became the world tallest building with are mark able height of 829.8m. In 2016, China built its tallest building Shanghai Tower with the height of 632m (Dennis et al. 2011). Due to catastrophic events such as earthquake and cyclones, the demand for the design of high-rise buildings as earthquake resistant structure became mandatory especially in high seismic zones (Patil et al. 2015; Patil et al. 2016). The key design feature of the high- rise buildings is its lateral stability system, therefore many lateral loads resisting system were developed for tall buildings such as bracing system, shear wall system, tube system, core-outrigger system, diagrid system and mega frame system. In terms of outrigger design, most of the studies are related to finding out the optimum locations for the outriggers (Alok Rathore et al. 2017). It is preferred to use multiple numbers of outriggers in a structure. The bracing system for core should be analyzed separately. In the outrigger structural system, it is observed that lateral stiffness of the structure increases along with its base shear. Application of belt truss is efficient in resisting inter storey drift. To predict the behaviour of the outrigger structural system nonlinear dynamic analysis is preferred. The relative stiffness of the outriggers greatly influences the storey displacement. This present study considers the evaluation of three 40 storey braced-core steel frame 3-Dimensional high-rise structure by varying the positions of different types of outrigger system with fixed base condition. The models considered for the seismic analysis are designed as per IS 800: 2007 and IS 1893 (Part 1): 2016. Equivalent static analysis is efficient for low to medium high-rise structure and it provides the response of the structure is based on their fundamental natural period of vibration. Response spectrum analysis ( RSA) is a linear dynamic analysis is used widely in the field of seismic analysis to obtain the peak response of the SDOF system through the contribution of mode shapes, frequencies, and modal participation factors. Time history analysis provides the response of the structure at regular time increments for given total time steps. NLTHA provides real time response of structure under actual earthquake loading (Taranath 2012). Earthquake magnitude selected ranges from 6 to 8 Richter, Shear wave velocity ranges from 0 to180m/s for the soft soil condition. To get the significant seismic response of the structure greater magnitude of ground motions are selected, shear wave velocity selection is conservative to represent the clay soils (Hi Sun Choi et al. 2017). The selected ground motion databases are used familiarly for dynamic analysis among the researcher’s community and to attain the similarity of structural response in comparision with the literatures. SAP2000 software it can model, assign properties of material, loading of the structure, analysis, design and output can be obtained in representation (Premalatha et al. 2018). Under this software a linear or nonlinear dynamic analysis is carried out based on equivalent static method response spectrum method, push over method and time history method. Yes, SAP softwares are most widely used for the dynamic analysis of structures (Al-Subaihawi et al. 2020). 3. Design approach and details 3.1. Design approach Three models of 40 storey 3D outrigger braced – core steel frame structure with plan dimensions of 30X30m, namely Model 1, Model 2, Model 3 in fig. Each model has a typical story height of 3.5m and a plan layout of 6 bays of 5m symmetrically on both axes. The core having an area of 10X10m is braced with Chevron type bracing on all sides symmetrically and the total height of the building is 140m. The foundations are assumed to be fixed and the connections in the frames and braces are fully restrained (Fang et al. 2019). The class of the section is designed as a plastic The models are designed as per IS 800: 2007 and IS 1893 (Part 1): 2016 for the seismic zone III and soil type as soft soil. The structure was assumed to be in the moderate seismic zone The grade of steel material used for frame 2. Technical specification 2.1 Numerical approach