Building Structure Issues in Tall Edifices

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Table of Contents

Abstract
Introduction
History of tall buildings
Comparison between the Old and New Tall Building Structures
Problems concerning tall buildings and their possible solutions
Conclusion
References

Abstract

The history of the tall building is very old. According to the Old Testament, in the City of Babel, people made a tower with bricks to save themselves from the flood. The tall buildings are the symbol of any countrys pride. This paper first tells about the historical background of tall buildings and discusses some famous high rise buildings. It further compares the structure of the buildings created in the past and present. The paper analyzes the problem in tall buildings and then discusses the rectification of those problems. It concludes that the advancement in computer and material science has made it possible to make high rise towers efficiently.

Introduction

The modern-day tall buildings symbolize national pride rather than being the embodiment of corporate wealth. The erection of super-tall structures in the Middle East and Asia that supersede the famous high-rise structures like the Empire State Building and the American Towers etc. denotes the idea of projecting the status of a country at the global level.

A building is a structure of walls, floors, roofs, and windows. A tall building is a multi-story structure in which most occupants depend on elevators [lifts] to reach their destinations. The most prominent tall buildings are called high-rise buildings in most countries and tower blocks in Britain and some European countries. The terms do not have internationally agreed definitions (High-Rise Building: Definition, Development, and Use, 2009, p.1).

Generally, a high-rise structure is considered to be one that extends higher than the maximum reach of available fire-fighting equipment. In absolute numbers, this has been set variously between 75 feet (23 meters) and 100 feet (30 meters), 5 or about seven to ten stories (depending on the slab-to-slab distance between floors) (High-Rise Building: Definition, Development, and Use, 2009, p.2).

Thesis Statement: Structure issues have been present in tall buildings for ages. This paper is an attempt to examine these structure issues under the following points:

History of tall buildings
Comparison between the old and new tall buildings structures with respect to the methods of construction, the material used, and their architectural designs
Problems occurring in tall buildings and possible solutions to minimize such problems

History of tall buildings

It is mentioned in the Old Testament that after the Flood, people at that time wanted to create a new city by the name of Babel. They wanted a tower to be made which could reach heaven. That tower was made with bricks, stones, and tar (High-Rise Building: Definition, Development, and Use, 2009).

During the era of the Roman Empire and in the reign of Julius and Augustus Caesar, many apartment buildings were constructed. Collapsing buildings became a frequent story due to structural failure. As a result, the laws were passed, and the heights of the buildings were limited to first 70 feet and then to 60 feet.
The history of such buildings says that there have been many other tall structures like towers, pyramids, cathedrals, and castles, but skyscrapers were created only by the end of the 19^th century. One hundred and fifty years ago, the structure of the buildings in which people used to live or work was very different from todays buildings. The height of such buildings used to be rarely over a flagpole.
In the middle of the 19^th century, two major developments took place that encouraged the construction of skyscrapers at a large level throughout the world:

1. Elisha graves Otis, an American, invented the first elevator in 1853. This helped people to travel upwards speedily and without much effort as required in walking.
2. The steel frames were introduced as a substitute for cast iron and wood in the 1870s.

The two of the tallest buildings were constructed in 1930 and 1931. They were Chrysler Building (319 meters) in New York City and Empire State Building (381 meters). After this 40, 50, 60 story structures were constructed in the whole of the United States. In the late 19^th century, most of the buildings structure was based on steel frames (Moon et al., 2007).

Comparison between the Old and New Tall Building Structures

There have been many changes in the structure of the tall buildings since the very first high-rise building appeared. Presently, the structure and design made of glass, steel, and concrete is followed everywhere internationally. One of the main differences in the tall structures of the 1970s and 1980s is that the structural and architectural elements avoid regular repetition. In spite of the complexity involved in constructing the non-prismatic shapes, the past few decades have witnessed practicable use of products that are quite unusual in building the superstructures. Most of the non-orthogonal tall structures are erected with the purpose of marking them on the world map. These buildings generally have curved or organically shaped facades and distorted elevation. Architects have CAD modeling tools on hand, which is quite useful in constructing tall structures. In place of the conventional box form with rectilinear shape, modern architects are constructing many exciting and unexpected new shapes (Taranath, 2011)

The comparison can be made on the basis of the following three categories based on three generations of high-rise buildings:

First-generation: The external walls of these buildings were made of mainly stones and bricks. The use of cast iron was also prominent for decorative purposes.

The columns were made of cast iron, beams were made of steel or wrought iron, and floors were made of wood.
In the event of a fire explosion, floors could collapse, and the iron frame would not be that strong to hold anything.
A single stairway could be used for escaping from the floor.

Second generation: The Metropolitan Life Building (1909) and the Empire State Building (1931) belong to this generation. These buildings are the frame structures.

Riveted-steel columns and beams are used in the whole building.
These structures are considered extremely strong, but their floor space is not much attractive.

Third generation: Buildings which were constructed after World War II till today are the most current high-rise buildings.

Steel-Framed Core Construction: In such type of building construction, lightweight steel and concrete frames are used. In the center of these buildings, an inner load-bearing core is created. With this central code, the utilities and services of the buildings are attached.
Steel-Framed Tube Construction: Tube structures changed the design of steel-framed buildings. They are so strong that they can control the lateral forces of wind and the effects of the earthquake.
Reinforced Concrete Construction: Concrete, which is made tough against embedded metal, is known as reinforced concrete. It is very strong for any construction.

Problems concerning tall buildings and their possible solutions

A building has to be a secure place for working or living. Therefore, it is very important to focus on the probable tribulations that may arise during the construction of a tall structure and find their possible solutions.

Wind excitation: The most important factor in the construction of tall buildings is to choose the structural system that would defend against the lateral load. Tall buildings, being supple structures, need extra attention with respect to their response to wind excitation. Therefore, their dynamic response to wind excitation is critical in assessing their loading and performance particularly with respect to buildings deflections and accelerations at the top occupied floors (Taranath, 2011,p.452). There can be a cross-wind response and along-side response in this situation. However, the across-wind response is more pervasive in this background. The present-day computer-based geometric designing of tall buildings have transformed the shaping of tall structures perpetually (Taranath, 2011). Improving aerodynamic properties of tall buildings can lessen the effect of wind forces carried by them (Ali & Moon, 2007).

Comfort: The wind load can cause vibrating sway in the tall buildings. If the load is strong and constant, it may result in the development of cracks in the concrete and consequently make the structure fragile to further sway. There is a possibility of people to feel motion sickness in such buildings. Therefore, it is important to create aerodynamic structures to make them stronger against sway. While creating such tall structures, the frequency range should be kept under consideration (between 0.1-1.0HZ).
Load distribution: In a tall structure, load transfer from the surface to the foundation is influenced by all the significant stabilizing components of that building. The floor slabs are firm and unbending. Their bond with the vertical stabilizing components is helpful in dispensing the load between the mechanism that makes the tall structure firm and stable. However, it is important that the assumed solidity of the floor slabs should correspond with the real slab. The uncertain correspondence of slabs combined with the uneven load leads to force distribution, specifically in tall buildings.
Twisting and open cross-connections: To stabilize tall buildings, engineers use various stabilizing coordination in their construction. Generally, there is a stabilizing tower in the middle of the tall buildings. However, it is difficult to calculate problems related to load distribution at the center in cases of changes. The open cross-sections like U-shape and L-shape experience unbalanced pressure and are subject to unexpected distortion in the opened towers. The tall structures have an adverse effect due to larger rotation along the elevation. The twisting effect can lead to the displacement of the edges and overhanging in the axial and on the sides of the structure. However, the floor slabs work as supporting beams to avert this displacement.
Interaction between the soil and the foundation: The connection between the soil quality and tall structures is significant in view of the stability of the structure. Solid bedrock provides an entirely fixed foundation to a tall building. Foundations resting on the layer of clay are not considered as a permanent base for tall structures. In tall buildings, the piles are subject to move in a lateral direction and compress the soil due to their vulnerability to the vibrating sway. In such cases, it is important to maintain a stable bond between the soil and the piles to stabilize the structure.
Pierced shear wall: Shear walls are the firm stabilizing components of a tall building. It is evenly stiff, and it is easy to set up forces and moments and assume the linear pattern throughout the wall. However, the assumption of force distribution is not simple in pierced shear walls. Hence, it is wise to use an elastic method applicable to all types of pierced walls in common (Gustafsson & Hehir, 2005).

Conclusion

On the whole, the structure of tall buildings has been analyzed from many perspectives. It has been established that the advancement in computer and material science has given the solution for making taller and lighter buildings. Tuned Mass Damper is a very good solution for excessive wind-induced vibrations. The use of TMD has been beneficial for Taipei 101, and it has reduced the acceleration in the tower by 40% (Kourakis, 2005).

Except this, it is advisable that the structure should be able to bear the weight of the building in cases of accidents like fire. Other components of the building should protect it from collapsing immediately after the failure of any significant component (Taranath, 2011).

References

Ali, M.M. & Moon K.S. (2007). Structural Developments in Tall Buildings: Current Trends and Future Prospects, Architectural Science Review, 50 (3), 205-223

Gustafsson, D & Hehir, J. (2005). Stability of tall buildings.Department of Civil and Environmental Engineering, Web.

High-Rise Building Definition, Development, and Use (2009). Web.

Kourakis, L. (2005) Structural systems and tuned mass dampers of super tall buildings: Case study of Taipei 101, Massachusetts Institute of Technology. Web.

Moon, K.S., Connor, J.J. & Fernandez, J. (2007) Diagrid structural systems for tall buildings: Characteristics and methodology for preliminary. Struct. Design Tall Spec. Build. 16, 205230.

Taranath, B. S. (2011). Structural Analysis and Design of Tall Buildings: Steel and Composite Construction, CRC Press: New York.

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