International Research Journal of Engineering and Technology (IRJET)
e-ISSN: 2395-0056
Volume: 12 Issue: 05 | May 2025
p-ISSN: 2395-0072
www.irjet.net
IMPACT OF BACKSTAY EFFECT ON TALL STRUCTURE WITH PODIUM. MAHETA RAJ V., MR. AAKASH SUTHAR 1 M.Tech Student, L.J. University, Ahmedabad
2 Assistance Professor, Structural Engineering Department, L.J. University, Ahmedabad, India.
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Abstract - This research examines the seismic response of
high-rise multi-functional buildings with attached podium structures, emphasizing the backstay effect as outlined in IS: 16700 (2017). A structural model was developed using ETABS to study the behavior of a tower-podium configuration subjected to lateral seismic forces. Two analytical approaches equivalent static analysis and response spectrum analysis were applied. The findings reveal that the presence of the podium significantly influences shear force distribution and induces differential displacements among structural walls, underlining the importance of meticulous design strategies to reduce potential negative impacts on overall structural integrity. Key Words: Backstay Analysis, podium, sensitive analysis, Etabs, High Rise, Shear reversal
FIGURE-2: SHEAR EFFECT WITH PODIUM The "backstay effect" refers to the transfer of lateral seismic forces from the tower’s primary seismic-resisting elements into additional structural components located within the podium. This force transfer typically occurs through one or more floor diaphragms. The podium contributes to resisting seismic overturning moments by distributing lateral forces through these diaphragms, which enhances the overall stability of the structure. This mechanism is analogous to the back-span in a cantilever system and is sometimes referred to as "shear reversal," since the direction of shear forces in seismic-resisting elements may invert at the podium levels. A common example involves a structural system with a reinforced concrete core wall above ground and a subterranean podium structure. The interaction between the tower and the below-grade floor diaphragms and perimeter walls is what gives rise to the backstay effect. This phenomenon is common in many high-rise building designs.
1. INTRODUCTION In high-rise construction, the lower section of the structure is commonly known as the podium. This portion typically features a larger floor area and offers greater resistance to seismic forces compared to the tower it supports. Critical to the podium’s performance are the floor and roof slabs, which function as diaphragms by transmitting shear and flexural forces to the vertical structural elements. Within these diaphragms, collector elements operate under axial tension and compression to gather and direct the seismic forces toward walls and frames, facilitating effective load transfer. SHEAR REVERSAL:
1.2 Objectives
FIGURE-1: SHEAR EFFECT WITHOUT PODIUM © 2025, IRJET
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Impact Factor value: 8.315
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Study how the top of multi-tower buildings moves when lateral forces act on them, using different podium heights, based on IS 16700:2017.
Find the best place to position towers on the podium by checking how the structure behaves when towers are in the center or off to the side.
Check how different tower and podium setups handle side forces and wind loads, and see if they improve building stability.
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