Structural system of tall building can also be divided into two broad categories:

• Interior Structure
• Exterior Structure

This classification is based on the distribution of the components of the primary lateral load-resisting system over the building. A system is categorized as an interior structure when the major part of the lateral load resisting system is located within the interior of the building. Likewise, if the major part of the lateral load-resisting system is located at the building perimeter, a system is categorized as an exterior structure.

 

Interior Structures

By clustering steel columns and beams in the core, engineers create a stiff backbone that can resist tremendous wind forces. The inner core is used as an elevator shaft, and the design allows lots of open space on each floor.

 

1. Rigid Frame

• A rigid frame in structural engineering is the load-resisting skeleton constructed with straight or curved members interconnected by mostly rigid connections which resist movements induced at the joints of members. Its members can take bending moment, shear, and axial loads.
• Consist of columns and girders joined by moment resistant connections.
• Can build upto 20 to 25 floors.

 

2. Shear Wall Structure

• Concrete or masonry continuous vertical walls may serve both architecturally partitions and structurally to carry gravity and lateral loading. Very high in plane stiffness and strength make them ideally suited for bracing tall building.
• Usually built as the core of the building.
• Can build upto 35 floors.

 

3. Outrigger Structures

• The core may be centrally located with outriggers extending on both sides or in some cases it may be located on one side of the building with outriggers extending to the building columns on the other side.
• The outriggers are generally in the form of trusses in steel structures, or walls in concrete structures, that effectively act as stiff headers inducing a tension-compression couple in the outer columns.
• Belt trusses are often provided to distribute these tensile and compressive forces to a large number of exterior frame columns.
• A built upto 150 floors.

 

Exterior Structures

In newer skyscrapers, like the Sears Tower in Chicago, engineers moved the columns and beams from the core to the perimeter, creating a hollow, rigid tube as strong as the core design, but weighing much, much less.

 

1. Tube System

• The tube system concept is based on the idea that a building can be designed to resist lateral loads by designing it as a hollow cantilever perpendicular to the ground. In the simplest incarnation of the tube, the perimeter of the exterior consists of closely spaced columns that are tied together with deep spandrel beams through moment connections. This assembly of columns and beams forms a rigid frame that amounts to a dense and strong structural wall along the exterior of the building.
• The different tubular systems are-

# Framed Tube

# Braced Tube

# Bundled Tube

# Tube in Tube

 

2. Diagram Systems

• With their structural efficiency as a varied version of the tubular systems, diagram structures have been emerging as a new aesthetic trend for tall buildings in this era of pluralistic styles.
• Early designs of tall buildings recognized the effectiveness of diagonal bracing members in resisting lateral forces.
• Efficiently resists lateral shear by axial forces in the diagonal members but have complicated joints.

 

3. Space Truss

• Space truss structures are modified braced tubes with diagonals connecting the exterior to interior. In a typical braced tube structure, all the diagonals, which connect the chord members- vertical corner columns in general, are located on the plane parallel to the facades.
• However, in space trusses, some diagonals penetrate the interior of the building.

 

4. Exeo Skeleton Structures

• In exoskeleton structures, lateral load-resisting systems are placed outside the building lines away from their facades.
• Due to the system’s compositional characteristics, it acts as a primary building identifier- one of the major roles of building facades in general cases.
• Fire proofing of the system is not a serious issue due to its location outside the building line.

 

5. Super Frame Structures

• Super frame structures can create ultra high-rise buildings upto 160 floors.
• Super frames or Mega frames assume the form of a portal which is provided on the exterior of a building.
• The frames resist all wind forces as an exterior tubular structure. The portal frame of the super frame is composed of vertical legs in each corner of the building which are linked by horizontal elements at about every 12-14 floors.
• Since the vertical elements are concentrated in the corner areas of the building, maximum efficiency is obtained for resisting wind forces.