º£½ÇÊÓƵ

Sesen

Mumbai, India

Taking the name ‘Sesen’ from the term used for the ancient Egyptian hieroglyph of a Lotus flower – the culture’s eternal symbol of the sun, creation and rebirth – Mumbai’s newest residential tower is rising up in one of the city’s most sought-after locations.

The imposing 285m-tall tower will take its place on the southern skyline of the business capital of India, with views across the Arabian Sea. 

The project, developed by Sesen Realty Private Limited, offers high-end duplex units, where residents can enjoy the green parks, exclusive clubs and cultural landmarks in this fashionable district of the city.  

Sesen is a luxury residential tower on the southern edge of Mumbai, with views across the Arabian Sea. 

The 285m-tall tower will include 30 levels of duplex apartments. 

The project was originally conceived with a shorter design. Our structural engineers revised the plans to accommodate five additional duplex floors. 

To achieve the addition of floors, a series of technical mitigations were devised to ensure an overall reduction in the weight of the structure. 

Challenge

The project comprises six podium levels, four service levels and 30 levels of duplex apartments. The 24m-high podium structure, which incorporates residents’ parking spaces, sits adjacent to the main tower.  

The tower was first conceived more than a decade ago, with an intended overall building height of 248m. Wind tunnel structural response analysis was conducted for a height of approximately 263m and the building was partially built to 120m.  

Construction will now recommence with the intention of increasing the number of duplex levels from 25 to 30, which will boost the financial viability of the project and will result in an increase in building height of almost 40m.

º£½ÇÊÓƵ has been engaged to provide expert structural engineering consultancy, to take the initial base design and develop it, working to current best practice. The foundation and the lower portion of the tower (up to 120m above ground) have been constructed as per the original tower design.  

The gravity load resisting system (GLRS) consists of the perimeter framed structure and internal columns. The lateral load resisting system (LLRS) of the tower consists of a reinforced concrete framed structure, outriggers bracings at four levels, with limited contribution from the small core walls.

This, along with the fact that the lower portion of the tower and the entire foundation are already constructed, has provided a challenge in accommodating the additional duplex units along with the revised architectural form, without changes to the existing structure in the lower levels.   

Solution

Our experts decided to take a parallel approach, focusing on LLRS and GLRS simultaneously to ensure that we were on the right track, keeping the project’s time constraint in mind. To achieve the addition of floors, an overall reduction in dead weight of the structure was essential.

To achieve this a structural steel composite deck was proposed on conventional reinforced concrete slabs on upper floors, column sizes at upper floors were optimised and a higher grade of concrete and concrete encased steel sections was proposed for columns.   

We also advised that landscape garden filling at typical lower levels could be reduced from 600mm to 200mm.  

By reducing column sizes and the use of composite deck slabs at higher levels, the overall self-weight of the tower was reduced and the overall loading intensity of the structure for the new design of 285m was brought close to the original design of 248m.  

The tower was first conceived more than a decade ago, but was only partially built to 120m.  º£½ÇÊÓƵ has been engaged to take the initial base design and develop it to achieve a structure that is 285m in height. Image: º£½ÇÊÓƵ.

Due to the height and the planned dimensions of the tower, wind loads govern the structural design of the LLRS. The moment capacity of structural beams is influenced by the presence of shear (internal stresses) within the beam. A few already cast link beams within the core at the lower levels were found to be critical and exceeding the shear and moment capacities.

Our experts devised a solution to strengthen these beams by closing some of the openings in core walls at lower levels, increasing the width of some of the link beams by encasing rebars and concrete, and adding steel plates on one or both sides of the beams to increase the shear capacity. 

Preliminary wind tunnel studies indicated that wind-induced accelerations were high. Various mitigating options were developed to reduce the wind loads and wind accelerations, including changing the overall extent of upper floors, tweaking the shape of the building design, and proposing chamfered, stepped and rounded corners for balconies and terrace levels.  

Other suggested interventions included the use of 50% porous screens on the southern facade, increasing the mass of the top five floors, and the integration of discontinuous edges in the design to disturb wind flow around the building. 

Value

As one of the tallest residential developments in the country, Sesen will be a landmark development in the heart of the city of Mumbai.

The project exemplifies º£½ÇÊÓƵ’s commitment to ensuring such landmarks have a robust and elegant structural system based upon a carefully balanced approach to the principles of sustainability, efficiency, economy and innovation.