ct@2 strctural system

MASTERS OF BUILDING ENGINEERING & MANAGEMENT 2013-15SPA, NEW DELHI

Study of a Structural System

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Bundel Tube Structure

GROUP 6MOHIT GUPTA NIKITA VARMA PRIYANKA SINGH SAMEERA SIMHA T.P SULAGNA CHAUDHURI


Bundeled Tube Strcture

The underlying principle to achieve a bundled tube response is to connect two or more individual tubes into a single bundle.

The bundled tube system can be visualised as an assemblage of individual tubes resulting in multiple cell tube. The increase in stiffness is apparent. The system allows for the greatest height and the most floor area. This structural form was used in the Sears Tower in Chicago. In this system, introduction of the internal webs greatly reduces the shear lag in the flanges. Hence, their columns are more evenly stressed than in the single tube structure and their contribution to the lateral stiffness is greater.

The first person to implement the bundled tube structural system was Fazlur Rahman Khan

Sears Tower Chichago


Advantages of Bundled tube system

• Decrease shear lag effects.• Sufficient lateral stiffness • Building acts as a unified system of

stiffened tubes• Aesthetically appealing • The interaction between the individual

tubes and the belt trusses at mechanical levels allows the building to attain its extreme height

• These trusses take the gravity loads from above and redistribute them evenly onto the tubes below

Carnegie hall tower, new york city


Disadvantage

• The bundle tube design was not only highly efficient in economic terms, but it was also "innovative in its potential for versatile formulation of architectural space.

• Internal Space PlanningConstraints were obsereved in Bundel tube Syestem


Case Study Four Allen Tower

Site Plan

Type of Structure:SteelConstruction Height : 210.52 mLength :37.85 mWidth : 89.01 mFloors (above ground) : 50Floors (below ground) :2Year of Completion :1983Floor-to-floor-height :3.96mTotal Floor Area: 133,920 m2Total Project Cost : $160,000,000


FourAllenTower


• The building plan shape, an elongated rectangle with semi-circular ends, has overall plan dimensions of approximately 33.35 x 79.07 m• The curved ends of the building in conjunction with a 12.20 m lease space depth from curtain wall.• Perimeter frame aspect ratio in excess of 6.85 and the constraint of a central shear truss core depth of only 7.85 m

The perimeter framed tube system typically consisted of two-story high"tree column" modules located approximately 4.57 m on center Of the 42 perimeter column shaft locations, 36 were of an Hshapeconfiguration while the 6 columns located at junctures


•A four-celled bundled tube system is adopted •The perimeter frame was assembled from twostory high "tree column" modules located at 4.58 m•The cross frames which subdivided the plan into its four-celled plan were formed by horizontal "treebeam" modules interacting with diagonalized trusses in the shallow central core area


The first step in the system development was to add several lines of diagonal bracing (inverted K-truss type) within the core of the building. Even though flexurally weak due to the short truss depth of7.85 m

To enhance the stiffness and strength of the wind girder concept, the tree beam concept was adopted, whereby short vertical stub columns at midspan were added to heavy horizontal wind girders

The stub columns forced an intermediate inflection point in the member thus greatly increasing its stiffness and strength


Key Dimnesion of Strctural Elements

Strctual Element Sizes

H- Column 114.3 x 609.6 mm to 44.45 x 508.0 mm

Spandrel beams 63.5 x 406.4 mm to 9.5 x 304.8 mm

Tree beam 2.92X95.25 X 508 mm to 44.45 x 457.2 mm

Composite metal deck slab 158.8 mm

Typical Deck Span 4.57 m

Core columns W14 ASIC Section

The mat foundation underlying the Four Allen Center Tower approximates the plan shape of the tower and has an overall length of approximately 91.44 m and a width varying from 45.72 m - 47.00 m . Mat thickness varies from a basic dimension of 2.59 m - 5.87 m

ct@2 strctural system

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