Comparison of Lateral Load Resisting Systems in Steel-Concrete Composite Tall Buildings

Abstract

The rising urbanization of the world's population, the high cost of land, and the competition to build smart, sustainable, and distinctive skyscrapers have contributed to a surge in tall building development. Designing and constructing a skyscraper is a challenging task. Along with architectural design considerations such as core planning, slenderness ratio, and building forms, structural design considerations such as structural materials and structural systems play a significant role in making tall buildings smart, sustainable, and resilient. The evolution of structural systems, materials, and construction technology has pushed the height barrier of skyscrapers over the last few decades. In general, the stiffness of tall structures is equally important as their strength because the lateral stiffness requirements for tall structures to resist lateral loads induced by wind or earthquakes governs as the structure's height increases. So, the selection of suitable structural systems and materials becomes essential. Due to natural phenomena like wind storms and earthquakes, buildings are affected greatly, causing significant loss globally. Building authorities are constantly taking measures against such severe hazards. In the last few years, the Bureau of Indian standards has brought revisions in the wind and seismic codes such as IS 875 (Part 3): 2015 and IS 1893 (Part 1): 2016 along with IS 16700: 2017 for design criteria of tall structures. One of the objective of present project work is to understand various approaches for evaluation of wind loading on tall buildings. The evaluation of along and across wind forces acting on tall buddings is carried out utilizing the gust factor method from IS 875 (Part 3): 2015. In addition to codal specifications, wind time history data based on wind tunnel studies available at Tokyo Polytechnic University (TPU) Aerodynamic database is used. The present study considers nine different tall buildings with different number of story and aspect ratios for comparison of wind load obtained from IS 875 (Part 3): 2015 and wind tunnel study based TPU database. Three distinct methodologies are used to calculate along and across wind forces using the TPU database's wind time history data: maximum sum of pressure coefficients at particular time instant, peak pressure coefficients and mean pressure coefficients. It is observed that along wind forces calculated from pressure coefficients using the TPU database match with the wind forces evaluated from the gust factor method from IS 875 (Part 3): 2015, while for across wind forces, difference is observed between wind forces calculated from IS 875 (part 3): 2015 and TPU database. The main objective of the present study is to gain a better understanding about the behaviour and design of steel-concrete composite tall building structural systems, including the impact of lateral loads induced by wind and earthquakes. The present study analyses and designs tall buildings with four basement floors, ground floors and 19, 39 and 59 upper stories with different lateral load resisting structural systems such as Structural Wall-Moment Frame system, Tubular system, and Outrigger and Belt Truss system. The location of tall buildings is considered as Ahmedabad (Seismic zone III and basic wind speed 39 m/s). Response Spectrum analysis in accordance with IS 1893 (Part 1): 2016 as well as Site-specific Response Spectrum and Time History analysis are performed for seismic lateral load analysis. For analysis and design purposes, both along and across wind forces in accordance with IS 875 (Part 3): 2015 are considered concurrently. All building models are modelled, analysed and designed in line with applicable Indian standards, including IS 16700: 2017, IS 875 (Part 3): 2015, IS 1893 (Part 1): 2016, IS 456: 2000, and IS 13920: 2016, as well as the composite design code AISC 360-10 using ETABS software. Excel sheets are also developed for design of various composite structural elements like composite slab, composite beam, composite columns etc. The Structural Wall-Moment Frame, Tubular and Outrigger, and Belt Truss systems are compared in terms of building response characteristics such as time period, base shear, modal mass participating ratio, top story displacement, inter-story drift ratio, design forces, contribution of structural walls in resisting lateral loads, and structural weight. For 24 story buildings, the design governed either by the strength parameters of structural members or the torsional mode time period values, but for 44 and 64 story buildings with any structural system, the design is governed by the top story displacement in all structural systems. Based on concrete and steel quantity estimates, the structural wall-moment frame system and tubular system are correspondingly more cost-effective structural system for 24-story tall building. Outrigger structural system can become cost-effective by altering location of outrigger from mid-height to the optimum location of outrigger in the building. The outrigger system is the cost-effective and efficient structural system for 44-story and 64-story tall buildings considered in the present study.