International Research Journal of Engineering and Technology (IRJET) e-ISSN: 2395-0056 Volume: 10 Issue: 06 | Jun 2023 www.irjet.net p-ISSN: 2395-0072 © 2023, IRJET | Impact Factor value: 8.226 | ISO 9001:2008 Certified Journal | Page 1279 Backstay Effect Due to Podium Structure Interaction Riddesh Naik 1 , Roshni John 2 , Dinesh Joshi 3 1 ME Student, Dept. of Civil Engineering, Saraswati College of Engineering, Kharghar, Maharashtra, India 2 Associate Professor, Dept. of Civil Engineering, Saraswati College of Engineering, Kharghar, Maharashtra, India 3 Associate Professor, Dept. of Civil Engineering, Saraswati College of Engineering, Kharghar, Maharashtra, India ---------------------------------------------------------------------***--------------------------------------------------------------------- Abstract - Marvels of the modern world cannot be imagined without the involvement of enormous superstructures which form the very core of visual attraction for metropolitan cities. Modernization and urbanization have led to migration to a vast extend, causing scarcity of land. Economical and efficient use of land is the need of the hour as horizontal expansion of cities is a complicated task. So, to overcome this scenario the vertical expansion of cities in the form of Highrise structures is to be undertaken. To enhance the efficiency of a particular land, developers and architects have come forward to include below storey podium structure to Highrise buildings. These structures prove to be more efficient as they can be used for various commercial purpose. Focus of current work is to study the effects of these augmented portions of structure in the form of podiums, on the structural aspect of the entire structure. A 40 Storey RCC structure is been considered situated in the IV th seismic zone of India. Various effects of inclusion of podium are studied by comparing structures with and without the inclusion of below storey podium. Effect of the increased stiffness due to podium is studied by considering various structural parameters like Lateral Displacement, Storey Shear, Storey Drift, Time Period. Studies regarding Backstay Effect due to below storey podium structure are made and its effects are observed at the podium structure interaction level. Sensitivity analysis is been carried out as per IS 16700 to study effect of crack formation. Key Words: Highrise buildings, Backstay Effect, Storey Shear, Storey Drift, Time Period, Sensitivity Analysis, Below Storey Podium, Podium Structure Interaction. 1.INTRODUCTION Increased job availability in major cities as a result of urbanisation has indirectly increased migration to these areas. The population of these cities grows as a result. The effects of population growth are directly related to the liveable area of a specific city. Population growth, urbanization, and the need for diverse infrastructure all contributed to the scarcity of adequate land for development. Because there is a lack of land, it is difficult to expand cities horizontally; therefore, tall buildings are constructed as a solution to this problem. Consequently, in order to gain leverage and satisfy the need for larger commercial space close to the road level, architects and developers have come up with a plan to provide a below storey podium to an existing structure. At the base of medium-rise and tall structures, podiums are expanded floor surfaces. Metropolitan areas with low to moderate seismic activity prefer this type of construction since a structure with this configuration can support a variety of functionalities. (i.e., retail space in the podium's lower levels and housing or office space in the tower). Moment resistant frames and shear walls make up the lateral load-resisting system for such building constructions. Many tall structures have an arrangement in which the lower few storeys have a wider floor plan than the tower above. Any lower component of a tall structure with a wider floor plan and much higher seismic force resistance than the portion above it can be viewed as a podium structure. This sort of architecture is typical in multi-story buildings where the lower section of the storeys is commonly utilised for commercial spaces, retail stores, parking lots, etc. 1.1 Setback/Backstay Effect In comparison to the above structure, the surface area of the below storey podium structure is significantly larger. This larger shift in stiffness occurs across the entire structure due to the podium structure's different dimensions. As a result, the podium structure's rigidity is substantially higher than that of the tower structure above. As a result, the podium structure helps in resisting lateral loads that act on the entire structure. At these levels, lateral load resistance within the podium level with a guaranteed load transfer path through the floor diaphragms, aids in the overall structure's ability to withstand lateral stresses. This aspect of the structure's resistance to lateral loads is known as the Backstay effect or shear reversal because shear forces in the structure tend to change direction at the podium structure interaction level. To equilibrate the lateral forces and moment of a tower projecting above a podium structure, a set of lateral forces are developed within the podium structure, which helps to resist the external lateral forces, this is termed as the backstay effect. 1.2 Sensitivity Analysis When cracks are formed in a member the moment carrying capacity or stiffness of the member tends to reduce. Exact extend of these cracks cannot be determined. Once a crack is formed in a member, its stiffness reduces. Thus, different stiffness modifiers are applied to different structural elements in order to account the effect of cracking on stiffness of section and there by on the behaviour and