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When designing high-rise reinforced concrete buildings, length changes of vertical members caused by time-dependent effects must be considered. For design purposes, long-term deformations of columns, walls, and caissons may be considered to consist of instantaneous deformations, shrinkage deformations, and creep deformations. In most cases these are non-reversible deformations. Short-term time-dependent deformations are caused by temperature changes and lateral loads. These are generally reversible. Instantaneous deformations depend largely on vertical load, cross-sectional dimensions of member, and modulus of elasticity of steel and concrete at the age when the load is applied Creep deformations depend on concrete stress, size of member, amount of reinforcement, and creep properties of concrete at different ages. Shrinkage deformations generally depend on concrete materials, quantity of water in the mix, size of the member, and amount of vertical reinforcement. When the above factors are considered together with the actual stress histories and realistic material properties, it is possible to predict with reasonable accuracy the shortening of vertical members in high-rise buildings. Temperature changes occur on a daily and seasonal basis. The exposed portions of a building respond to these changes with induced forces or deformations that depend on degree of expo-sure and boundary conditions of the structural members.

This paper deals with developments in caisson and high-capacity pile design and construction that have assumed importance during recent years and is heavily influenced by the writer's personal experiences which carry a decidedly U.S. perspective and in the case of caissons, a decidedly Chicago perspective. The developments covered include: In situ testing for better soil property information to use in design. Testing and instrumentation to facilitate caisson construction. 3 0 Use of large diameter, very high-bearing-pressure,belled caissons on both cohesive and non-cohesive soil.Developments in high-capacity piling and increased use of dynamic measurements during pile driving. Development of high-capacity friction caissons and design of rock sockets. 6 0 Construction of caissons under water or slurry. 7 0 Development of high-strength concrete for high-capacity caissons.

The optimum design of high-rise buildings should satisfy architectural and engineering performance criteria according to codes and local regulations at the most economical cost. The large variety of construction materials and structural systems makes the task of obtaining the optimum solution difficult for the designers. This study is related to the structural variables influencing the economical choice of materials and systems in cast-in-place multi-story construction. An efficient and economical structural system can evolve only through an understanding of the significant factors affecting the design of a tall building. This optimization study has considered a number of these factors in order to evaluate their in-fluence on the optimization process. These factors can be summarized as follows: Design lateral force (wind) Height-to-width ratio of building, Ratio commonly known as Aspect 30 Criteria for lateral stiffness (Drift Ratio) 4 l Type of occupancy (office vs. apartment) Influence on foundation system Fire rating considerations Local availability and cost of primary construction materials The final choice of a structural system depends upon the factors mentioned above. It should be obvious that there cannot be any single structural system that is valid for all cases. It is this philosophical attitude that is essential for the architect and engineer in evaluating the best possible structural system for a particular project, time. for a particular location, at a particular The most common types of multi-story construction are residential and office buildings. Architectural layouts for residential' buildings have their maximum performance from spans of 15 to 24 eet, and for office buildings from spans of 24 to 30 feet. Be-sides the column, caisson, and floor system considerations for these two types of buildings, the lateral load consideration is an important concept in the design of high-rise structures. A maximum recommended drift of l/500 of the height of the building allows the buildings without shear walls (frame buildings) to be built to a certain number of stories depending on the slab thickness and column sizes. When shear walls are added to the frame buildings, they can be built still taller, satisfying the maximum drift limitations.

Developments in concrete high-rise buildings have undergone a dramatic evolutionary change in the last twenty-five years. Simple systems, such as shear wall buildings that were exclusively used prior to the 1960’s, have been transformed to a considerable number of systems suitable for commercial, residential and mixed uses up to 80 stories or more. In many cases, the reinforced concrete elements have been combined with structural steel to produce a more effective mixed system. The progressive development of higher-strength concrete together with advancement in mechanization of formwork and placement methods have fueled this systems development. The advantages offered by concrete, with respect to moldability for shaping as well as massivity and rigidity for structural purposes, have been exploited to the fullest. This paper is developed somewhat as a review of the systems developments that have occurred in the past twenty-five years together with discussion of some current appl icat ions.

SP97 This publication is a collection of 12 papers detailing the new and definitive techniques that have made possible the construction of milestone buildings in high-rise construction. The "Chicago style" of construction and the concepts developed by the Chicago design and construction teams in the science of high-rises are covered in this publication. Topics covered include: high-rise system developments in concrete; prestressed concrete in high-rise construction; recent developments in deep foundations for high-rise buildings; and simplified design of slender unbraced columns. Analysis and Design of High-Rise Concrete Buildings offers a wealth of information on concrete technology such as high strength, lightweight, fiber reinforced, corrosion-resistant, and impermeable concretes that have been utilized to make possible some of the tallest buildings in the world.