Client:UnipolSai Assicurazioni s.p.a.
Location:41, Via Fara – Milan
Architects: BG&K, Maurice Kanah
Completion: work in progress – expected end: 2017
Engineering services provided
Built at the end of Fifties, Torre Galfa is one the most important building in the historical financial district of Milan and one of the first high rise building in Italy. It has 31 above ground stories and reaches the height of 109 m. The will of the Property is to requalify the building with a complete retrofitting involving functions, layouts, structures and façade in order to assign half of the floors to residence and half to hotel.
The building has reinforced concrete structures, composed by a system of shear walls supporting concrete ribbed lightened slabs.
The aim of the structural design was the assessment of existing structures toward vertical dead and imposed loads and toward horizontal actions induced by wind and earthquake, with the evaluation of the appropriate structural interventions needed to obtain a strength enhancement of weak elements, improving the global behaviour of the tower according to the current structural Code. The project envisages also the constructions of a new 31 stories steel and glass staircase on the North-West elevation, of a new façade and the requalification of ground level highlighted by the presence of a glass cube.
Accurate 3D FEA was performed with the creation of different model to investigate the actual structural behaviour of both existing and new structures.
The analysis of slabs revealed an adequate behaviour for residential and hotel functions also due to the design choice of using light and dry flooring systems.
On the other hand, the analysis of vertical structures shown a considerable lack of resistance for wind and seismic actions, due to a generalized reduced amount of shear reinforcing bars.
Once the target resistance ratio was fixed to 75% of the design action, different reinforcement strategies and methods was analysed. Among FRP plating and wrapping, steel reinforcements and concrete jacketing it was chosen the concrete jacketing. In order to combine rapidity of execution, absence of temporary formwork, small covering thickness and fire protection the better technology to use is represented by thixotropic concrete mortar reinforced with inorganic fibre and steel reinforcement bars (total thickness 5 cm). The concrete jacketing involves the majority of RC shear walls. Structural analysis demonstrate that there is no need of flexural and axial strengthening of vertical elements.
Torre Galfa was one of the first tall building in Italy with a total glass façade. The design of the existing façade is considered a very representative example from an historical, architectural and technological point of view. For this reason the project of the new façade had to be respectful of the existing pattern of aluminium frames. At the same time, the new envelope must satisfy the current requirements in terms of thermal, hygrometric and acoustic performance. The design solution for matching all these needs leads to a triple glazed unitized façade. Being this kind of façade heavier than the existing one, it was envisaged the introduction of a new steel box shaped beam along the perimeter of the building, directly constrained to transversal concrete beam, in order to by-pass the existing concrete “L” edge beam and to support the loads transferred by the façade (self weight, wind action, personnel load) to the concrete structures of the tower.
The project of the façade also includes: ventilated façade with ceramic tiles, stick system for the store front, glass fins for the steel and glass new staircase, glass fins and glass beams for the cube in front of the South East elevation at ground floor.