The direction of evolution of the tall building’s structural systems has been toward efficiently increasing the lateral stiffness against lateral loads – primarily wind loads.
In order to obtain the necessary lateral stiffness, introduced first were braced frames followed by tubular structures, core-supported outrigger structures, and more recently diagrid structures.
On this basis, various forms of high rises have been evolved.
STRUCTURAL EVOLUTION AND ARCHITECTURAL EXPRESSION
The natural monumentality of skyscrapers resulting from their scale makes their ARCHITECTURAL EXPRESSION very significant in any URBAN CONTEXT where they soar.
Thus, constructing any tall building requires careful studies on AESTHETIC ADEQUACY of the new structure within the existing urban context.
TRADITIONAL BRACED FRAMES: the braces – the main lateral stiffness provider – were generally limited within the interior cores, and serve only for structural performance:- SO NO AESTHETIC EXPRESSIONS
But the emergence of the exterior-braced tubular structures such as the John Hancock Center in Chicago gave an external architectural expression to the facade
TUBULAR & DIAGRID STRUCTURES,
Locate their major lateral load-resisting components at the building perimeters where building facades are, creating structural domination in the expression of the buildings.
Therefore, in tall buildings that employ these types of structural systems, technological components and architectural components of building facades are inseparable, one complementing the other.
These circumstances require very intimate cooperation between architects and engineers.
Form of a high rise is governed by the following factors:
The purpose for which the building is to be used.
Economics connected with it.
Requirements of the client.
Effect on the surrounding built-ups in the urban context.
Aesthetics.
Accordance with the site.
Heat Transmittance according to orientation.
Town planning motive
Type of structure system adopted
BROADLY – Two main shapes of high rise buildings have emerged:
The Point Block
The Slab
The Point Block (The Monolith Tower)
The Slab (Lipstick Building)
THE POINT BLOCK
Accessible by central circulation.
Plans can be in many variations: Square(the original plan of the point block), rectangle, star, twin arrangement, etc.
The tower effect of the point block forces comparison with the surrounding building heights.
Height comparison is immediate in a tower block.
Point blocks frame and highlights the view
The linear shape of the block casts shadows on the lesser surface area of lower levels, which are less disturbing and annoying.
Permit their neighbours a wide view
Can be used to produce real exterior space only if surrounded by large lower development.
More suitable for mixing into the development of distinguished heights.
Being the vertical spatial element it creates sufficiently large surrounding neutral areas and leaving the task of horizontal shaping to the horizontal development.
May be suitable for a residential highrise from the point of the user as it incorporates the optimal layout for privacy.
THE SLAB FORM:
Accessible by additional access balconies.
Plans can be in many variations.
The slab used with variations with staggered or curving facades as well as contrasting heights.
Slab from high rises attracts attention not so much by its height but by its mass.
Slab form dominates the environment, eliminating an appreciable section from the range of vision.
The dominating mass shadows nearby areas to an extent which may prove to be bothering &disturbing.
Slab form may be suitable for offices, hospitals or hotels, etc.
Further, they could be classified as:
Aerodynamic Forms
The emergence of Twisted Forms
Free Forms
AERODYNAMIC FORMS
In conjunction with increasing lateral stiffness against winds, a recent trend in tall building design practice is to ….
IMPROVE AERODYNAMIC PROPERTIES OF TALL BUILDINGS TO REDUCE WIND FORCES CARRIED BY THEM.
Aerodynamic forms, in general, REDUCE the along-wind response as well as across-wind vibration of the buildings caused by vortex-shedding by “confusing” the wind.
While irregular forms pose challenges to structural engineers for developing the structural framework, they can be advantageous in reducing wind load effects and building responses.
Like in Buckminster Fuller’s Dymaxion project, the aerodynamic shield rotates about an axis according to the direction of the wind to minimize the impact of the wind force.
In addition to today’s pluralistic architectural styles promoting diversity, this logic of rational aerodynamics has led twisting, tapering, or other building forms with discontinuities and multi-planar facades that are emerging in urban skylines.
The Shanghai World Financial Center
Kingdom Center in Riyadh
Both the forms employ a large through-building opening at the top combined with a tapered form.
THE 71-STORY, 2.2-MILLION-SQUARE-FOOT PEARL RIVER TOWER, GUANGZHOU, CHINA,
The building’s form guides wind to a pair of openings at its mechanical floors. The winds drive turbines that generate energy for the building’s heating, ventilation, and air conditioning systems. The openings also provide structural relief, by allowing wind to pass through the building instead of pressing against it.
Pearl River Tower, Guangzhou, China
EMERGENCE OF TWISTED FORMS
Twisted forms employed for today’s tall buildings are comparable to twisted forms of Mannerism architecture at the end of Renaissance architecture. For example, at Palazzo Ducale in Mantua, Giulio Romano designed twisted columns.
This twisted form can be found in today’s tall building as well.
Turning Torso, apartment & office tower, in Malmo, Sweden
Chicago Spire Project in Chicago -Santiago Calatrava
In general, twisted forms are effective in reducing the vortex-shedding-induced dynamic response of tall buildings by disturbing vortex shedding.
FREE FORMS
The number of free-form tall building projects has been rapidly increasing these days.
Within the context of tubular design, however, the free-form structure is exemplified by the Sears Tower and One Magnificent Mile Building, both in Chicago, which employed a bundled tube system.
Daniel Libeskind’s Fiera Milano Tower
Even though the supporting structural systems behind the free forms vary depending on the project-specific situations, DIAGRIDS are often employed as primary structures for free-form tall buildings as can be observed from Daniel Libeskind’s Fiera Milano Tower
Hadid Dancing Tower in Dubai
Other contemporary free-form (poetic, cinematic, and tilted) tall buildings include Hadid’s Dancing Tower in Dubai.
