Cruz del Sur Building

Cruz del Sur Building

Architect
Izquierdo Lehmann Arquitectos
Location
Santiago, Chile | View Map
Project Year
2009
Category
Offices
Stories By
Izquierdo Lehmann Arquitectos

Architectenweb Magazine
Cristóbal Palma

Cruz del Sur Building

Izquierdo Lehmann Arquitectos as Architects

The project consists of an office tower with a commercial complex in the base, located at the intersection of Apoquindo Av, Santiago’s main axis, and Vespucio Av, the capital’s circular beltway. Despite its urban importance this place is poorly laid out as a cloverleaf intersection surrounded by several buildings of varying height and quality. The site has immediate access to a Metro station, which has the highest daily traffic flow in the entire subway network. The roughly square site is opened on three fronts. Given its location, the tower faces Apoquindo Av coming east from a mile away, as an iconic mark at it’s vanishing point.


The regulations allowed a tower of 21 floors; a buildable area of 18,738 m2, with square shaped plants averaging 1,000 m2 each, and a core containing a battery of eight elevators and two enclosed double stairwells; plus 4,000 m2 of built area in a two storey commercial complex, and 18.000m2 in five underground floors for 600 parking lots. The volume of the building is quite constrained by the maximization of the built area within these regulations.


Given the high pedestrian density of the area, our first decision was to clear the ground level as much as possible, freeing up the site as an extension of the public space. This was made possible by hiding underground a major part of the program’s commercial area and withdrawing the rest of the complex’s structure to the borders at the back of the property, so as to allow an interior corner square. Furthermore, it was possible to structure the tower in such a way that only the shaft core rests on the ground, as it is capable to resist by itself all vertical loads as well as shear stress and flexion at the base, considering the proportion between the height of the building and the width of this base, and that, because it is centered in the square floor plans, torsion of the structure under seismic stress is avoided. Moreover, in this solution, matching tower and underground columns is unnecessary, so, an optimum result of 27m2 per car was achieved on parking floors. Floor plan surface gradually increases from floors 4 up to 21 to attain the total built area. This section allows to: - Reduce the shaded area produced by the bottom floor suspended over the ground; - Reduce the angle of diagonal bracing supporting the series of floors; - Column-free floor plans with increasing sellable area at upper floors, which price rise as well; - And finally, to define the outline of a memorable landmark facing the axis of Apoquindo Av.


Continuous floor to ceiling windows are shaded by columns and a perimeter eave at all floors, standing upright 90cm. behind the edge of the slabs, thus leaving the supporting structure expressed at the outside of the tower. Glazing setback plus screen printing and differentiated reflectivity according to lighting and thermal requirements for each different area of the facades together resulted in a reduction in energy consumption of up to 25% in comparison to nearby buildings of the same category. Building costs turned out to be inferior than the initial estimates related to towers of similar characteristics. This is important because we believe that economy in design purifies the rhetoric of architecture; after all, the efficient use of available resources is an infallible condition for achieving beauty.


Towers are seen from below. Their perception varies as one approaches them. In this building, its trapezoidal shape with the distorted structural grid of its facades counteracts the fugue of lines in perspective, rendering an orthogonal volume as one gets closer while still framing the object completely, and as one looks up shifting the visual angle with respect to the vertical direction given by the sense of gravity, an equivocal sensory adjustment is produced. This balance plays with the relativity of the perception of volume and weight, making conscious the quest of stability as a decisive matter of architecture.

Cruz del Sur

Architectenweb Magazine as Publishers

A load bearing outer wall and a vertical circulation core form the basis of the Cruz del Sur office building in Santiago, Chile. Izquierdo Lehmann Arquitectos have realised a building that fans out towards the top and thus frees up the ground level in order to improve public space. This effective structure also helped to keep the construction costs within budget.


In the north east of Santiago, where the main axis of the city meets the ring road, is the city’s busiest subway station – the Metro Escuela Militar. This is where the Chilean firm Izquierdo Lehmann Arquitectos purchased five plots of land. Together they form a roughly square shaped site of about 4,000m² which faces three streets. In spite of its importance to the city, the area is badly laid out. Furthermore, its busy streets and narrow pavements are lined with a large variety of buildings of a questionable architectural nature.


Given the high pedestrian density and scarcity of public space in the area, the decision was made to free up as much of the ground level as possible so it can be used as an extension of the public space. The office space was elevated and the parking hidden underground. The construction consists of a core and load bearing outer wall. From the fourth floor upwards, diagonal bracing transmits the load from the façade to the core. With its tree like construction, the building is better equipped to resist earthquakes. The limited size of the core ensures that torque reactions of the structure are avoided under seismic stress. Also, the square floor plan is equally stable in any direction.


The 15m by 15m core features eight elevators, two double staircases and services, creating a vertical street. The relatively compact core is an advantage to both the flexibility of the office layouts and the car park floors: the tower structure allows each parking space to be 27m², most underground car parks are approximately 25m². This resulted in five floors of parking with a total of 600 parking lots.


The wish to free up the ground level was contradictory to the need to maximise office space. The loss of floor space on the bottom floors was compensated by allowing the building to fan out towards the top. The structure profits from this construction as any vertical forces are automatically directed towards the core, maximising the size of the floor plate. The increment of the floor plate also benefits the architecture, urban planning and finances.


The strong shape of the building is reinforced by the lines in the façade. Columns contrast with the windows which have been set back 90cm from the columns. The façade is shaded by the columns and a full perimeter eave, tempering the interior climate. The reflectivity of each façade is differentiated according to its situation.


With the Cruz del Sur office building, Izquierdo Lehmann Arquitectos have created a clever construction which meets the economic demands of the region and at the same time stimulates urban quality.

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