COVER STORY

Prestige Kingfisher Tower, Bangalore

The majestic Kingfisher Tower located in Bangalore has been built by Prestige Construction and United Breweries to serve as a luxury residence. Architects Thomas Associates and Structural Engineers Sterling Engineering Consultancy led proficient design teams to the completion of this urban edifice.

Client Brief
Client brief was simple, when it comes to a complete analysis of structural safety, the magnitude of the task at hand can be assessed. It’s not the first time that the team was asked to design a penthouse for a client, but it was the first penthouse designed that sat atop a thirty-three storey mega-structure with cantilevered landscaped gardens, an infinity pool, and a helipad!

Architectural Features
The residential structure was planned for three towers of twenty-seven floors each, which share common basements, parking levels and entry levels.

Two basements levels and four additional floors above the ground provide parking for the triplet. From the fifth floor is the residential suits which continue till the thirty-third storey. From the south face of the structure, five distinct levels house recreational floors at five storey intervals to house swimming pools, landscaped gardens and gymnasiums.

At these floors, the individual towers connect to create a large base plate. From the north face of the structure, at the thirty-third floor a swimming pool rests on top of the tower and a cantilevered garden projects 18 meters beyond the structure on either side.

The designed scissor shape inclined struts support this structure which stands out as a unique feature in the north elevation of this structure. The complexities in design started as early as the foundation, but the enthusiastic and every-ready design team considered all challenges as opportunities for innovation and learning.

The foundation of the structure was designed as per the soil investigation reports as isolated footings. An unexpected finding after excavation showed the loss in bearing capacity of the soil around the bore holes taken for testing. This led to redesign of the isolated foundation under the west tower. The variation of floor plan from parking to residential suits to intermittent recreational floors and subsequently the penthouse required floating of major columns.

The southern elevation shows five prominent recreational levels which have restricted beam depths and floating columns. The structure designed as a R.C.C framed structure benefited from the use of Composite Construction in specific large load carrying members. The connecting areas are supported using a metal deck slab spanning between a network of structural steel beams and girders to create a large base for the recreational level. The use of structural steel not only helped in avoiding shuttering but also minimized construction time. Composite construction reduces the cost of the structure as compared to construction in solely R.C.C or Steel and significantly reduced structural member sizes and considered aesthetics of indoor spaces.

 

With an eye for aesthetics as well as structural integrity, Sterling Engineering proposed the use of inclined scissor-shaped struts to support the cantilevers at the penthouse. These unique features as compared to simple-inclined struts makes the structure stand out. As seen in the north elevation a single strut establishes itself from the 27th floor column and splices into two members. This junction uses a steel mechanism embedded into the slab to distribute the loads. Precast R.C.C. brackets were fitted with steel plates for bolted connections to the hollow steel sections of the struts. The splices terminate at the base of the cantilever at the 33rd floor and are fixed using a steel plate and bolt mechanism. Two such identical scissor arrangements under each cantilever along with the help of cross bracings provide lateral stability. Provision of a secondary bolt fitted under the primary bolt ensures safety in case of failure or slip until repairs are carried out.
Amit Shantanu Shinde
Project Leader, Sterling Engineering Consultancy Services Limited

 

Geometrics
Space constraints in and around the construction site due to surrounding structures and roadways restricted the location of construction cranes on the south end. Communication between the structural consultant and contractor regarding crane loading, moment calculations and safety is essential to ensure that cranes provided on site are adequate to lift members and deliver equipment.

This structure made use of two cranes placed on the south side of the structure which outstretched their arms to provide support to the northern end of the structure during construction of the scissors and cantilevered girders.

To provide enough stability to the cranes, slabs of two floors under the crane base were supported using props which were removed post-construction. The structure did not require provision of a central core with shear walls as the stiffness of the towers was enough due to its intermittent connections at recreational levels.

The unique aspect and a design challenge of this structure was the two-storey Penthouse. An additional transfer level at 33rd floor was required to support the penthouse at 34th and 35th level. As seen in plan, the penthouse cantilevers in three regions, two on the north end carrying landscaped areas and one at the south supporting the penthouse.

The penthouse is supported on thirty-three-meter-long and five-meter-deep structural steel trusses which are resting on southern peripheral columns. Within the penthouse area we have achieved a column free space spanning fifteen meters which is supported on one-meter-deep rib beams all skilfully placed to consider aesthetics.

With an eye for aesthetics as well as structural integrity, Sterling Engineering proposed the use of inclined scissor-shaped struts to support the cantilevers at the penthouse. These unique features as compared to simple-inclined struts make the structure stand out.

As seen in the north elevation a single strut establishes itself from the 27th floor column and splices into two members. This junction uses a steel mechanism embedded into the slab to distribute the loads. Precast R.C.C. brackets were fitted with steel plates for bolted connections to the hollow steel sections of the struts.

The splices terminate at the base of the cantilever at the 33rd floor and are fixed using a steel plate and bolt mechanism. Two such identical scissor arrangements under each cantilever along with the help of cross bracings provide lateral stability. Provision of a secondary bolt fitted under the primary bolt ensures safety in case of failure or slip until repairs are carried out.

Using Steel
The variation of floor plan from parking to residential suits to intermittent recreational floors and subsequently the penthouse required floating of major columns. The southern elevation shows five prominent recreational levels which have restricted beam depths and floating columns. The structure designed as a R.C.C framed structure benefited from the use of composite construction in specific large load carrying members.

The connecting areas are supported using a metal deck slab spanning between a network of structural steel beams and girders to create a large base for the recreational level. The use of structural steel not only helped in avoiding shuttering but also minimized construction time. Composite construction reduces the cost of the structure as compared to construction in solely R.C.C or steel and significantly reduced structural member sizes and considered aesthetics of indoor spaces.

Sterling Engineering’s design team at the head office in Kurla, Mumbai performed all design related calculations and drawing submittals and all site inspection visits and reporting was carried out from Sterling’s Bangalore office to ensure fast response to our clients. The project was completed in 2018 and has been a landmark project for the city of Bangalore and all disciplines associated with it.

Learnings & Technology
ETABS software was used to model the building’s RCC and Composite members. To design the unique scissor-struts STAAD Pro was used. All outgoing drawings are drafted using AutoCAD.

Sterling Engineering has worked with Prestige Developers of Bangalore in the past and has always pushed for a call for innovation and efficiency in our designs and submissions. They value all their relations with all disciplines that thoroughly enjoy the work.

The city of Bangalore has many upcoming landmark developments which we hope to be part of soon. As all construction projects are concerned, coordination and managed are key to successful and timely completion. The project was competed in four years.

Fact File

Client: The UB Group
Developer : Prestige Estates Projects Ltd
Architect: Thomas Associates
Structural Consultant: Sterling Engineering Consultancy Services Pvt Ltd
MEP Consultant: Design Tree Service Consultants Pvt Ltd & Cerebration Consultants
Steel Fabricator: Eversendai Construction Pvt Ltd
Steel Tonnage: 1850MT
Status: Completed