05 April 2020

Interaction-Ar.Pranav Desai, Partner, IAG Consultants

Structural design of Supertalls, as much an art as science


An integrated architectural firm, IAG Consultants is a comprehensive practice engaged in contemporary design, planning, and development of the built environment. In an exclusive interview to CONSTRUCTION OPPORTUNITIES,
AR. PRANAV DESAI, PARTNER, IAG CONSULTANTS, discusses the iconic character of Supertalls, and elaborates on the five iconic residential towers designed by his Practice.



As an Architect, what is your take on Supertall buildings. Are they mere icons of 21st Century architecture or do they also have utilitarian value in terms of containing the urban surge.
Super Tall Buildings are undoubtedly the most dominating symbol of cities that they are in, to an extent that sometimes they put that city on the world map, thereby signalling and prompting its significant economic progress and advancement. These cities compete on the global stage to have the title of the tallest building with which to announce the confidence and global stature of their economic growth. As cities continue to expand horizontally, the super tall building – as a building type – is a possible solution by way of conquering vertical space through densification. Land prices have always been a prime driver for constructing tall buildings. In large cities, properties are very expensive and buildings logically grow upwards. A tall building can be defined as a machine that makes the land pay.
Undoubtedly, there are some inherent drawbacks of tall buildings from an economic point of view.
Construction of these buildings requires an extra cost premium because of their need for sophisticated structural systems, and high-tech mechanical, electrical, elevator, and fire-resistant systems. In addition, a large core area is needed to accommodate elevators and building services systems. While about 60 per cent of a skyscraper’s floor plate is generally usable space (remainder being the building’s elevator core, stairwells, and columns), compared to a low-rise or mid-rise buildings where 80 per cent of the space is useable. Tall buildings also suffer from higher operational costs, such as high-energy consumption, elevator maintenance, emergency response preparedness, etc.



Your design philosophy for tall buildings.
The biggest influence on design of tall buildings is to create a structure that is ‘timeless’ – Timeless design is functional and sensible, it’s a style that suggests quite confidence, its not over the top, nor is it boring. It is perfectly scaled and proportioned. Timeless design is enduring, economical, sustainable, and has the power to stay, it is not created to be temporary, nor is it a fad or a trend. That’s the design philosophy we try to follow in all our projects, especially tall buildings.
Due to the advancement in design and construction, architects and designers have more form freedom than ever before.
While complex forms would often result in an increase in construction cost, a careful and thoughtful engineering approach is required to achieve the architectural vision without unnecessary cost overruns.



What kind of paradigm shift in structural engineering, design, and technology, made construction of Supertall buildings possible.
The structural design of tall and super tall buildings is as much an art as a science. First and foremost, a profound respect for forces of nature is required. These forces, induced by gravity, wind, seismic effects, thermal conditions, and settlements, are extraordinary and must be carefully managed. To achieve an efficient structural design, close collaboration with the architect and mechanical engineers is required. Although it may be possible to simply ‘apply’ a structural design to a set architectural vision, the resulting building will likely be inefficient in the management of forces and distribution of materials. Close collaboration with the design team, so that the structural concepts become integral with the architectural and functions of the building, will lead to best overall outcome.
Preferences and economic viability of structural materials used in tall buildings’ construction are also changing. In 1970, 90 per cent of the 100 world tallest buildings were all-steel buildings. Today, all-steel buildings account for less than 15 per cent in favor of concrete or composite structures. The cost of material, technological expertise, and the way that tall buildings are being built, all influence this change in material selection of tall buildings.



How do Indian tall buildings compare with the global Standard.
India has still a long way to go as far as ‘tall buildings’ are concerned. The definition of ‘tall’, however, has changed over time. According to the definition given by CTBUH, a 200 m+ building is ‘tall’, 300 m+ is ‘supertall’ and 600 m+ is ‘mega tall.’ India has only few buildings that are 200m to 300m tall, most of which are in Mumbai. These buildings do compare with global standards as far as architectural and structural design is concerned, but are quite behind in terms of mechanical design and sustainability parameters.


Your comments on the tall buildings wave in urban India. What factors are fuelling a rise in their population.
The increasing rate of urbanisation in India has seen an accelerated trend in the construction of high-rise and tall buildings, particularly in the metro cities.
A fundamental economic driver for the growth of tall (particularly residential) buildings is the scarcity of land in densely populated cities. The competition for constructing the tallest building in a city, country, region, has acted as another driver for growth of tall buildings in India. In the last decade or so, the race for constructing the tallest has been extended to include the contest for constructing the most iconic and spectacular high-rise buildings, often characterised by complex geometries and leaning/twisting forms.



Exploiting the sheer scale and size of Supertall buildings, is it possible to design and build a close system ecosphere which is self-sustaining, with a Zero-Discharge quotient.
Sustainable structural design goals can be achieved by addressing the following three objectives: reduce, reuse, and recycle. Advanced analysis and design methodologies allow us to design increasingly more efficient structures (with just the required amount of material and no more). Also, new material technology is opening the way for the reduction of embodied energy per unit of material (in terms of transport energy, sustainable supplies, and the like). The use of industrial by-products such as fly-ash, slag, and silica fume, as a cement substitute can drastically reduce the embodied energy of concrete.
While the trend in development of higher strength steel and concrete is not stopping, use of new material with superior performance (like fibre reinforced concrete) and/or superior sustainability (such as engineered wood) is gaining significant momentum.



Impact of wind loads on Supertall buildings.
Wind loads affecting design and construction of high-rise buildings are intrinsically dynamic and random in nature. There is a third component of wind load, namely the resonant component that dominates the structural behaviour. Wind has always been an important consideration when erecting tall buildings and it becomes more important and complex as the height increases. Wind loading on tall buildings can have a direct impact on the serviceability of the building as well as the comfort of occupants, as they will be able to perceive building motion (acceleration) due to the Resonant component of wind, if appropriate design measures aren’t used to mitigate excessive building vibrations.



The most challenging tall building designed by your Studio.
Raheja Vivarea complex consists of five iconic residential towers;


Tower 1-2-3   45 floors, (185m) Completed
Tower 4 47 floors, (195m) Completed
Tower 5 58 floors, (225m) Under Construction

The towers are carefully positioned and oriented to maximise views to the racecourse and Arabian sea, whilst minimising overlooking between the towers. The ‘Y’ shaped floor plan was conceptualised such that three wings are the apartments, i.e., 4 BHK unit in the front and 3 BHK units on the other two flanges, with centre consisting of lift and staircase core. The tower floor plan with lift core in the centre maximises structural efficiency and reduces wind forces on the tower. The structural system can be described as a ‘buttressed core, and consists of high performance concrete for torsional resistance to the structure.
The perimeter columns participate in the lateral load resistance of the structure; hence, all of the vertical concrete is utilised to support both gravity and lateral loads. The result is a tower that is extremely stiff laterally and torsionally. The structural design is extremely efficient, in a way that the gravity resisting system has been utilised so as to maximise its use in resisting lateral loads.
The towers are constructed using Mivan Aluminium formwork system. In this system, cast-in-situ concrete walls, columns, beams, and floor slabs are cast monolithic in one pour. Early removal of forms was achieved by hot air curing due to which we could achieve only a 9-day slab cycle and target faster project completion.
RahejaVivarea is environmentally sustainable and rated Gold certified building by LEEDS.

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