Performance based Wind Analysis of Diagrid Structural Systems

Abstract

The rapid growth of urban population and subsequent pressure on limited space lead to the vertical development of buildings. Favoured by Ministry of Housing and urban affairs under smart city development, this trend is expected to accelerate in future. Design of Tall buildings are sensitive to lateral load, specifically wind load. For resisting lateral load various structural systems are used. Shear wall core system, tubular system, outrigger & belt truss system, braced frame system, diagrid structural systems etc. are widely adopted structural systems. Diagrid structural system is used in many tall buildings due to better aesthetics, high redundancy and high lateral stiffness. Diagrid structural system consists of diagonal columns on periphery of building and resists lateral load. There is no vertical column, as it is common in other structural system. Generally, steel tubular sections are used in the construction of diagrid buildings. Concrete filled steel tube (CFST) can also be used in formation of diagrid for better efficiency.

Recently many destructive cyclone such as Cyclone Vayu (2019), Cyclone Fani (2019), Cyclone Gaja (2018), Cyclone Nilofar (2014), Cyclone Phailin(2013) and others have affected major cities with heavily occupied residential or commercial areas. Due to these natural calamities buildings are affected to great extent causing major loss globally. Current wind design approach is inefficient to provide accurate and reliable method for computing the performance of the buildings during extreme wind events. The primary objective of code based approach is to keep the structural system within elastic condition. But more efficient design can be achievable by allowing some controlled inelasticity in structural components. Such inelastic design require use of dependable wind design and building performance assessment approach which describes performance of the building when it is subjected to expected level of wind hazards.

The main objective of the present study is to evaluate the performance of Diagrid structural system under wind loading. For the study, G+50 storey Diagrid building with plan dimension of 36 m × 36 m is considered. Performance of building is evaluated by carrying out static, dynamic and time history wind analysis and by adopting suitable performance criteria available in various literature. For time history analysis, wind time history data are acquired using TPU (Tokyo Polytechnic University) Aerodynamic database. Modelling and nonlinear analysis is carried out using SAP2000 software for evaluation of performance of diagrid structural systems. This report includes procedure to derive wind time history for actual building based on data acquired from TPU. Wind time history varies along the height as well as on various faces of building with reference to wind direction. The parametric study is also carried out by varying angle of diagrid columns of structural systems. For this purpose G+50 storey building is considered with different angle of diagonal columns on periphery of the building like 74.47 ̊, 78.23 ̊ and 80.53 ̊ with 6,8,10 storey modules respectively. Performance of the buildings are evaluated using static wind analysis, dynamic wind analysis and time history wind analysis by adopting suitable performance criteria. Two types of performance under wind loading are evaluated i.e. based on structural component performance and Serviceability performance in terms of human comfort. Structural component performance level is evaluated as function of basic wind speed and Serviceability comfort performance level is evaluated in terms of allowable floor acceleration range for evacuation of people during wind storms. Analysis results in terms of time period, base shear, store drift ratio, lateral displacement and floor acceleration are compared for various diagrid structural system. Based on comparison of analysis results it is found that G+50 storey diagrid building with angle of column 74.47 ̊ and 80.53 ̊ gives better performance as compared to 78.23 ̊ angle of column.