Study of Behaviour of Eccentric Diagrid Structural System

Abstract

The behaviour of concentric and eccentric diagrid structural systems in tall buildings is studied in present major project. The study involves a comprehensive review of existing diagrid structures worldwide, highlighting their application in high-rise construction. As building heights increase, the influence of wind loads surpasses that of earthquake forces. Given that current building codes only address certain height and slenderness ratios, this research utilizes the Tokyo Polytechnic University(TPU) aerodynamic wind pressure database to calculate dynamic wind loads. A comparison is made with the gust factor method outlined in Indian Standards, offering insights into the effectiveness of each approach for evaluating wind loads in tall buildings. The findings reveal that dynamic wind loads calculated from TPU data base present a more accurate representation as compared to the gust factor method of IS 875. The gust factor method gives 35% to 40% of the base shear observed in static wind load analysis. The study specifically examines the analysis and design of a 40-storey steel-concrete composite building with a 48 m × 48 m floor plan, incorporating well-distributed structural walls system(WDS), concentric diagrid system(CDS), and eccentric diagrid system(EDS). Both the static and dynamic wind load analyses are conducted as per IS 875 (Part 3): 2015, while seismic loads are evaluated using equivalent static analysis and dynamic response spectrum analysis according to IS 1893 (Part 1): 2016. The modeling, analysis, and design of buildings are performed using ETABS Software, with load combinations selected based on applicable Indian standards. The design of composite structural members adheres to AISC 360-16, ensuring robust structural integrity. The results indicate that both the diagrid systems exhibit distinct structural responses, each with its advantages and challenges. The evaluation of structural behaviour of buildings encompasses key parameters such as natural time period, base shear, storey shear, storey displacement, inter-storey drift ratio, and lateral and gravity load participation among frame and shear wall. Comparative analyses demonstrate that the composite EDS has a greater natural time period (7% to 18% higher than WDS and 30% to 35% higher than CDS), reflecting increased flexibility due to shear links. Base shear results show that the composite CDS exhibits the highest lateral load resistance, indicating superior performance in earthquake conditions. Furthermore, the analysis of maximum storey displacements highlights that composite CDS performs exceptionally well, with displacements 4.5% to 23% lower than those of WDS under various loading cases. The lateral and gravity load participation reveals that 90% of lateral load and 60% of gravity load in WDS are resisted by walls. In CDS, 93% lateral load and 50% gravity load are resisted by periphery diagonal column. While in EDS 95% lateral load and 50% gravity load is resisted by diagonal columns on periphery. The study concludes that overall, the diagrid systems (CDS and EDS) demonstrate superior performance in terms of stiffness, weight efficiency, and lateral load resistance compared to the well distributed structural wall system (WDS). This emphasizes the effectiveness of diagrid systems as optimal choices for high-rise buildings subject to seismic loads. Non-linear static (pushover) analysis is also performed on both the concentric and eccentric diagrid systems with varying numbers of storey (12, 16, 20, and 24). Different shear link lengths (0.3 m, 0.4 m, and 0.5 m) are employed in the eccentric diagrid systems to assess their impact on behavior of building. This analysis focuses on displacement monitoring until the buildings reach their collapse state, and examines the pushover curves and collapse mechanisms of both the systems. Through a detailed pushover analysis, it is further observed that the introduction of shear links in the EDS enhances its ductility, while the CDS demonstrates a higher capacity to resist lateral loads. The findings underscore the importance of further exploration into diagrid systems for future high-rise buildings, particularly in seismic-prone regions.