The Concrete Exposed of Casa de Alisa
The capacity of concrete as a building material is unquestionable, especially for structural purposes. This is agreed upon by Stu/D/O, although they also believe that concrete holds more potential to support architectural development.
Casa de Alisa is a two-story house project by Stu/D/O that optimizes the potential of concrete in its design concept.
In a two-story house project in Nonthaburi, Thailand, Stu/D/O decided to use concrete as its design concept. The goal is to prove that exposed concrete materials can form an architecture that shelter the lives in it from the surrounding context.
The series of exposed concrete planes on the Casa de Alisa design form a relationship with nature vertically.
Casa de Alisa was designed by Stu/D/O by utilizing several structural concrete walls (planes) to form its spaces while framing and accommodating the house’s interior. Furthermore, because of cast concrete planes in its design, Casa de Alisa has the potential to acquire the desired natural scenery while maintaining privacy in it. Thus, Stu/D/O indirectly increases Casa de Alisa’s sense of austerity through the bond between concrete, water, and the garden with the sky above it.
The threshold between the interior and the exterior of the house, especially on the ground floor.
Casa de Alisa offers an excellent visual and sound barrier from the surrounding environment as a two-story house with a clear division of programs. The lower floor of a semi-public nature consists of various thresholds that obscure the house’s interior and exterior dividing lines: garden-pond-living space. Meanwhile, the upper floor, which accommodates the family room and bedrooms, expresses more private internal programs and functions due to the help of concrete planes. The planes divide each space to maintain the comfort of privacy and provide a difference in functionality.
The main façade of the Casa de Alisa shows a 37-meter-long plane cantilever.
For example, the 37-meter-long plane cantilever on the second floor creates space for the master bedroom and children’s room so that it gets closer to nature without compromising privacy and comfort. This cantilever plane also acts as the main façade of the house as the ‘background’ for the spaces behind.
View from the master bedroom formed behind the plane cantilever.
Family room upstairs with the ‘background’ of the plane cantilever in front of it.
To add to the character of the cast concrete planes to the Casa de Alisa, Stu/D/O deliberately retained the texture of the wooden frame used during the construction process. As a result, the texture of the wood attached to the concrete will be more radiated when sunlight passes through the upper openings of the house or existing skylights.
The process of house formwork is one of the challenges, so many experiments are carried out by Stu/D/O to erect concrete fields perpendicular to the ground and intersect with each other at the upper level. The intersection point between two opposing planes supports the main structural system of the Casa de Alisa.
Cast concrete details retain the wood texture of the house formwork process.
Each concrete plane intersects to form the spaces of the house and supports the main structural system.
In the end, the Casa de Alisa can stand as a purely structural composition that allows for the efficiency of construction time. Furthermore, by highlighting exposed concrete materials, this house also managed to become a monolithic architecture that can provide protection and a sense of security for life in it.
First floor plan.
Second floor plan.
Tube structural system
The tube is a structural engineering system that is used in high-rise buildings, enabling them to resist lateral loads from wind, seismic pressures and so on. It acts like a hollow cylinder, cantilevered perpendicular to the ground.
The system was developed in the 1960s by the engineer Fazlur Rahman Khan, and has been used to construct most high-rise buildings since then.
The tube system can be constructed using concrete, steel or a composite of both. In its simplest form, closely-spaced columns are tied together with deep spandrel beams through moment connections as part of the external perimeter of the building. The rigid frame that this assembly of columns and beams forms results in a dense and strong structural ‘tube’ around the exterior.
Since lateral loads can be resisted by this stiff exterior framing, interior columns can be located at the core and are fewer in number. The interior can be simply framed for gravity loads and floor space is left free from columns.
The first building designed by Khan using a tube frame was the DeWitt-Chestnut building, Chicago, in 1963. The first skyscraper to use the system was Chicago’s Willis Tower.
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Types of system
The most common of variations are as follows:
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Framed tube
This is the simplest form of the tube system and can be used on a variety of floor plan shapes, including square, rectangular, circular and freeform. This type is reasonably efficient from 38-300 m (125-1,000 ft) in height. It was the initial system type developed by Khan.
Khan defined a framed tube structure as “a three dimensional space structure composed of three, four, or possibly more frames, braced frames, or shear walls, joined at or near their edges to form a vertical tube-like structural system capable of resisting lateral forces in any direction by cantilevering from the foundation.”
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Trussed tube
Trussed (also known as braced) tube systems are similar to the framed tube but have fewer exterior columns space further apart. To compensate for the fewer columns, steel bracing or concrete shear walls are introduced to tie the columns together.
By interconnecting all the exterior columns, it forms a rigid box which is capable of resisting lateral shears by axial in its members rather than through flexure (bending or curving).
By having relatively broad column spacing, it is possible to have lots of clear space for windows.
The diagonals that are introduced on each façade should intersect at the same point on the corner column. These diagonals interact with the perpendicular face trusses to make the structure ‘tubular’ and equalise the gravity loads of the exterior columns.
This system is also known as ‘hull and core’ and consists of a core tube inside the structure which holds services such as utilities and lifts, as well as the usual tube system on the exterior which takes the majority of the gravity and lateral loads.
The inner and outer tubes interact horizontally as the shear and flexural components of a wall-frame structure. They have the advantage of increased lateral stiffness.
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Bundled tube
The bundled tube system involves, instead of one tube, several individual tubes interconnected to form a multi-cell tube. Together they work to resist the lateral loads and overturning moments. When the tubes fall within the building envelope, interior columns are positioned along their perimeters.
Not only is this system economically efficient but it also allows for more versatile building designs, adopting interesting shapes and bundled in dynamic groupings rather than being simply box-like towers.
The first type of building to use this system was the Willis Tower in Chicago.
A hybrid system is often used where the building design has a slenderness such that a single system cannot provide adequate strength or stiffness. It combines two or more basic structural forms, either by direct combination or by adopting different forms in different parts of the structure. As high-rise building designs become more complex, hybrid systems are increasingly common.
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