The Zaha Hadid Architects-designed Generali Tower is just one of the high-rise masterworks that grace Milan’s skyline

Travelling back into the not so distant past, many may recall Daniel Libeskind’s vertical state-of-the-art PwC Tower for Milan’s CityLife masterplan that adorned the news pages of FC&A’s third edition of 2018. Adjacent to Libeskind’s impressive structure, informally known as ‘The Curved One’, proudly soars Zaha Hadid’s helical, striking Generali Tower. Collectively, the houses of Libeskind, Hadid as well as Arata Isozaki and Andrea Maffei, who designed the third tower in Milan’s CityLife high-rise tripartite – CityLife Tower – have all delivered a majestic addition to Milan’s skyline.

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enerali Tower is within the CityLife masterplan that has redeveloped Milan’s abandoned trade fair grounds following the fair’s relocation to Rho Pero in 2005.

Located above the new Tre Torri station on Line 5 of the city’s metro system, CityLife opens the 90-acre site to year-round public use for the first time; providing new civic spaces, public parks and residential areas, in addition to shopping districts and corporate offices.

When fully complete in 2020, CityLife will be the largest new civic space and public park created in the city since Parco Sempione opened 130 years ago; welcoming more than seven million visitors, workers and residents each year. CityLife will include 1000 new homes, offices for more than 11,000 staff, the new 42-acre public park, piazzas as well as kindergarten.

Aligned at ground level with three of the city’s primary axes that converge within CityLife, the 170m (44-storey) Generali Tower connects with its surrounding public piazzas and park; the curvilinear geometries of its podium defined by the perceived centripetal forces generated from the staggered intersection of these three city axes at the tower’s base.

This vortex of centripetal forces at ground level is transferred vertically through the tower by realigning successive rhomboid-shaped floorplates to twist the tower about its vertical axis. This helical twist reduces incrementally with the height of each floor above street level, giving all floors a fractionally different relationship to the floors above and below.

As the tower rises offering broader views across Milan, the twist orientates the tower’s higher floors to the primary south-east axis leading to Bramante’s 15th-century tribune of Santa Maria della Grazie, and beyond to the centre of the city. With its interiors to be completed this summer, Generali Tower will house up to 3900 employees to meet their continued growth as one of the world’s largest financial institutions.

The tower excels in all international benchmarks for efficiency while respecting Milan’s rigorous local building codes. Its double facade of sun-deflecting louvres flanked by glazing provides extremely efficient environmental control for each floor and ensures excellent energy performance, contributing to Generali Tower’s LEED ‘Platinum’ certification by the US Green Building Council.

Inclined perimeter columns follow the twisting geometry of the tower to mirror the inclined alignment of its external facade units. These perimeter columns also maximise usable office space within the tower’s coherent formal envelope.

An integral element of the CityLife redevelopment that has created a new civic, residential and business district near the centre of Milan, Generali Tower is defined by its surrounding urban fabric to connect directly with the city.

The architecture of the tower is visible, what we don’t see but makes such a peculiar building physically feasible, are the structures, visible only when the construction is growing. This is the result of the structural design by Redesco (Research-Design-Consulting), a true Italian excellence in the engineering sector that has authored the structures of some of the most important buildings of the recent modernisation of Milan.

Conceiving and developing the structures for the Generali Tower has been the perfect example of structure-architecture interaction. Starting from a complex set of problems, the Redesco team applied a holistic approach based on the premise that “simplicity is complexity resolved” (K. Brancusi), thus imagining and implementing a structural system that did match with architecture, safety, economy, functionality and buildability in the most efficient way.

From the beginning of the project, some main challenges had to be addressed: above all, how to cope with the torsion of the tower, induced by the warping of the columns around the core, while choosing the most efficient materials, shapes and construction methods. Once set the conceptual basis of the project in terms of structural members layout, Redesco decided, after a thorough evaluation of structural alternatives, to go for a reinforced concrete structure, being the one that maximised the benefit/cost ratio. A more efficient structure, albeit extremely more complex to design and calculate than any solution made of steel. Concrete means a highly non-linear material: the structure’s deformations are evolving during and after construction. To control and forecast with precision the evolutive behaviour of the structure has been the key to success, not only in order to understand how internal forces and stresses changed in the structural organism but moreover to allow the facade, internal elements, installations to be designed to strict tolerances and no waste. The complexity of the spatial resisting phenomenon of the tower required to dwell into the most advanced structural engineering tools and methods, and to perform a substantial amount of research. The leading of ZHA proved to be a key factor to success since the strict and creative cooperation with the architects led to a clean, simple, extremely optimised layout of the structure and a deep coherence of all the building’s elements.

Similar to the challenge of structural physics, the innovation of this project consisted in implementing a method that would pair with the parametric approach of Zaha Hadid Architects. All structural simulations, analysis, drawings and detailing were developed with advanced tools and in-house software that followed the mathematical method set by the architects in designing the tower’s shape. The whole structural design, from concept to final construction documentation, has been created by means of parametric tools. The final stage of the design has also been implemented in BIM, in full coordination with other design disciplines.

Redesco’s role in the Generali Tower structural design has been extended from the initial conceptual stages all the way through to the construction phase, so that we had the chance to follow the design until the tiniest detailing, rebar scheduling, steelwork joints and details and moreover to cooperate with the contractor in defining construction methods, sequences, monitoring of the structural behaviour and checking of results.

The podium

Redesco has been in charge of the structures of the ‘free form’ volume of the podium, which is the visible part above the upper plaza level. The complexity of this structure arises from the coexistence of an extremely high number of constraints; from one side, the columns could only rest on the regular grid of the parking structures below; on the other side, the freedom of form, internal arrangement, density of functions of the podium asked for an extremely sophisticated structural strategy. The structural arrangement was born by parametrically coupling of the external surface to be respected and the internal constraints: the whole structural frame was generated automatically by combining all the constraints in a graphic algorithm. Based on this frame, that includes very long spans, column deviations and cantilevers, optimisation and recurrent operations have been carried on the structural members in order to achieve the maximum cost-efficiency and structural soundness.

All the structures are in steel, including the facade substructure that consisted of many hundreds of different frames. Finally, one of the most challenging aspects of the structure is it’s being built across a series of structural joints: joints between different parts of the underground parking structure and joints between the tower base and the surrounding systems. A sophisticated study of details and structural behaviour, that allows each different part to settle independently, has been carried on. Also for the podium, Redesco has been appointed to design and follow the structures from the conceptual stages down to the detailing and construction phase.

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