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INTRODUCTION
1.1 General
Tall buildings emerged in the late nineteenth century in the United States of America.
They constructed a so-called " America Building Type " meaning that most important tallbuildings were built in the U.S.A. Today, however, they are aworldwide architectural phenomenon. Many tall buildings are build worldewide, especially in Asian countries, such as China, Korea, Japan and Malaysia. Based on data published in the 1980s, about 49% of the worlds tall buildings were located in North America
Table 1-1: Tall Buildings in Regions (ca.1982).
REGION COUNTRIES(NO) PRECENT(%) BUILDINS (NO.)
North America 4 48.9 1,701
Europe 35 21.3 742
Asia 35 20.2 702
South America 13 5.2 181
Australia 2 1.6 54
Middle East 15 1.5 51
Africa 41 1.3 47
Mid-America 20 O.1 4
TOTAL 165 3,482
The distribution of tall buildings has changed radically with Asi now having the largest share with 32% and North America's at 24% ( Table 1-2 ). This data demonstrates the rapid grouth of tall building construction in Asian during this period while north American construction has slowed. In fact, eight of the top ten tall buildings are now in Asia and only two, the Sears Tower and the Empire State building, are in Nourth America
Table 1-2: Tall Buildings in Regions (2006,based on most active cities in the regions reported in imporis.com).
REGION COUNTRIES(NO) PRECENT(%) BUILDINS (NO.)
Asia 20 32.2 35,016
North America 18 23.9 26,053
Europe 20 23.7 25,809
South America 10 16.6 18,129
Oceania 7 2.6 2,839
Africa 20 1.0 1,078
TOTAL 95 108,924
1.2 Definition of a tall building
The term, "high-rise ", is defined in webster's dictionary as a " building of many stories ". This serves to illustrate the term's subjectivity. Do any clear and precise definitions exist , and on what basis are they founded?
Many local fire codes in the USA base their definition of atall building on that which is not attainable with their fire fighting equipment.Some plumbing engineers would argue that only when abuilding has more than 25 stories do design concepts require modification for plumbing systems ; therefore, only buildings taller than 25 stories are high-rise (steele,1979). Other professionals can argue from their perspective. Who is bright?
The definition of a tall building was one of the first topics to com under discussion by the Council on Tall Buildings and Urban Habitat, an international group sponsored by engineering, architectural, and planning professionals, that was established to study and report on all aspects of the planning, design, construction, and operation of tall buildings.
As described in its Monograph ( Council, 1978-1981 ), no minimum height is specified. "The important criterion is whether or not the design is influenced by some aspect of tallness. Asuggested definition, then, might be " a building in ehich tallness strongly influences planning, design and use ; or " abuilding whose height creates different conditions in the design, construction, and use than those that exist in common buildings of a certain region and period ".( for purpose of standardization, in connection with its survey of tall building characteristics, the Councile collects information on buildings that are nine stories and more in height .)
And other references defined the high rise building ( tower ) as the building which has total height exceeds 36m or more than 12 floors and its use varies between residential, administrative or as ahotel. Except for height is always a relative matter and abuilding can't be defined using the term of height only, where judging on a building depende on the conditions of the surrounding environment, so it's not possible to set a precise definition to high rise buildings. But fro the structural point of view it can be defined as the building that its height will be affected by lateral forces resulting from earthquakes & wind forces to the extent that such forces will play a major role in the process of design.
1.4 Reasons for taking the trend of constructing high rise buildings (Tower ):
There are many reasons to establish a high rise building investment project. And they are as follows:
- Rapid grouth of population in urban communities, and therefore the constant pressure of the limited land area affected the evolution of building.
- Expensive land prices.
- Restriction of random expansion in major cities adjacent to agricultural land.
- The high cost of setting up infrastructure for new cities.
- Expression of progress and civilization.
And there are many other factors, for example the city of Rio de Janeiro & Hong Kong, they had other specific reasons such as terrain's conditions or the lack of land area like the United Arab Emirates and others.
1.5 Elements that affected the buildings height & grouth:
There are many elements that encourage the construction of high rise buildings, and they are as follows:
- Available construction materials and structural technology to implement the construction.
- The advancement of the required services for building uses such as mechanical systems ( Elevators,HVAC, etc. ).
1.6 High rise buildings (Towers) Economics:
Economic feasibility studies are considered one of the most important success elements in the ivestment projects. These studies focus on all the affecting elements in the project and all funding capabilities. Buildings economic studies have developed greatly especially after the technological progress and the advancement of construction materials variety, and construction methods.
Feasibibility studies have achieved an advanced level of precision in directing investments in terms of providing the necessary credits and completing goals within scheduled time limits and definitive investments with the lowest amount of modification to the project and its different component
- High rise buildings (Towers) are projects with huge investments and many varying components and systems. So its feasibility must be studied carefully through the application of value engineering in order to choose the most appropriate elements to use order to achieve the best outcome with the best construction materials, construction system and operation systems, without any compromises to the general outline or the objective of the project.
- So value engineering is considered an organized methodology aims to remove the unnecessary components that increases the cost and in the same time increases quality of the final product.And through the value analysis that can be applied on all services & operations and materials related to the building in order to reduce the construction cost and increase the quality in the same time, without compromising the building's efficiency.
LITERATURE REVIEW
2.1 General
In high rise structures, the behavior of the structure is greatly influenced by the type of lateral system provided and the selection of appropriate lateral structural system plays an important role in the efficient analysis of the structure. Few of the lateral structural systems Shear wall system, Braced Framed system, Framed tube system, Tube in Tube system and so on.
2.2.1 Alpa Sheth (2008) " Effect of perimeter frames in Seismic performance of Tall concrete buildings with shear wall core and Flat slab system " presented the effect of perimeter frames for structural systems with flat slab structure and shear wall core for different location of the shear wall and for different heights and spans of concrete towers. It is concluded that for tall buildings of compact size, regular shape and distributed shear wall core, there is very marked improvement in performance of the structure with flat slab system and shear wall core when a perimeter frame with closely spaced columns is added to the structure. Farther spaced perimeter frame has a relatively less impact on reducing drift. Further it is concluded that building with a central shear wall core and with length to width ratio exceeding 2, the performance is enhanced by adding outrigger and perimeter frame. A perimeter frame without outriggers does not help significantly in resisting lateral loads . For shorter towers of non compact size and with distributed cores, the perimeter frame does not greatly impact the structural behavior.
2.2.2 A.L.SALAMA et al ² suggested the structural repair and seismic upgrading of severely damaged bearing wall structures. A dwelling apartment building was converted into industrial, administrative facility. This implied the removal of various bearing walls and the opening in others. Such serve modifications were conducted in the absence of any engineering judgment and controle. Severe structural cracks, damage to beams & slabs were recorded. Seismic resistance was totally hindered. The building was judged to be unsafe and needed full structural assessment of damage along with professional repair and seismic upgrading scheme. Load concentration at wall edges necessitated enlargement of footing at these specific areas, newly cast enhancement was achieved by means of newly added shot-created slab at the soffit of existing beam-slab system. Seismic upgrading was achieved by adding four shear walls at external periphery of existing structure.
2.2.3 X.G.HE24 studied the behavior of concrete frame-corewall structure with non-continuous exterior frame beams by considering aconcrete frame wall tall building with inner balconies with 3-story-height at the two opposite corners on some floors, the corresponded edge beams cannot be connected to the two corner columns which are in adiagonal line. The layout affects the lateral stiffness of the structure. The behavior of the structure is compared with the ordinary frame- corewall structure which has continuous exterior frame beams, and in another way, comparison of behaviors of similar structures, in which inner balconies are with different-story heights, is carried out. It is concluded that the lacking of some corner beams of the introduced structure has little influence on its overall behavior. The influence is only about 3-4% and the seismic behavior of the structure is quite well.
2.2.4 Khan et al 18-20 discussed the analysis and design of framed tube structure for tall concrete buildings. The behavior of framed tube structures is discussed from an overall structural system point of view. The influence of various structural parameters is emphasized for achieving better tubular behavior. The concept of the equivalent reduced plane frame modeling technique is used for developing aseries of influence curves for the preliminary analysis and design.
2.2.5 A.M.CHANDLER et al3 suggested the application of strut-and-tie method on outrigger braced core wall buildings. This is to enhance practicing engineers to understand the general structural behavior of outrigger braced core wall system. Strut-and-tie method is applied to analyze the whole lateral structural system.The complete load transfer mechanism between the outrigger brace the core wall is displayed Many practical concerns in design including the structural behaviors of different configurations of outriggers, the effect of openings through the core wall adjacent to the outrigger brace, the arrangement of shear studs on outrigger brace and the shear link arrangement in core wall are briefly discussed.
2.2.6 JIEMIN DING et al 15 introduced the design and research for a tall building of concrete filled square steel tube. The braced-frame system was adopted to reduce the torsion effect brought by architectural irregularities of plan and elevation. The modal analysis, response spectrum analysis and history analysis was carried out by several software. The period, displacement and story shearing force etc. were obtained and compared with each other.
2.2.7 Xillin Lu et al 16 proposed modeling of coupled shear walls and its experimental verification. A nonlinear macro model is proposed to simulate the behavior of coupled shear walls.This model is composed of multi-vertical-element model for wall piers and a combined model for coupling beams. In the model for wall piers. Some key characters, such as shifting of neutral axis within wall section, interaction among flexure, shear and axial force, can be taken into account. In the model for coupling beams, the deformation of flexure and shear, and the interface bond-slipaction are considered by using different element. Experiments of coupled shear wall specimens with different size of coupling beams are carried out to verify the proposed model. The comparison of the analysis with the test results shoes that the model is an efficient one in nonlinear analysis of coupled shear walls.
2.2.8 AYSIN SEV 4 conducted afeasible study on tubular systems for tall office buildings with special cases. The building skeleton was considered with closely T aced perimeter columns that provide much greater lateral resistance than is obtained with conventional systems because of the three-dimensional response of the building to lateral loads. This paper gives a brief explanation of tubular systems with a number of case studies from Turkey and abroad. In this context, the historical development of tubular systems is given firstly. Then, the tube concept is identified from the structural point of view as well as architectural point of view, and types of tubular systems-such as framed tubes, trussed tubes, and bundled tubes-are considered.
2.2.9 BO LI et al5 conducted an analysis on displacement-baced seismic design of shear wall structure in tall buildings. According to the characteristic of shear wall structure, its performance level is divided into three levels, which are serviceability, life-safety, and collapse prevention. The three levels are qualified with story drift ratio. For the serviceability and collapse preventation performance levels, it is assumed that the curvature at the bottom cross section of the first story of the shear wall structure reaches yield curvature and ultimate curvature, respectively. Then, the target displacement mode of the two performance levels can be obtained. Based on the target displacement mode of shear wall structure in the serviceability performance level, the effective parameter, the base shear Vb and horizontal earthquake force Fi at each floor of the building can be determined, and then the structural members can be designed to satisfy strength demand and details of seismic design. Finally, the designed structure is analyzed with nonlinear static analysis procedure and is adjusted by the pushover analysis result until it is satisfied.