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.

Stability of tall frames has been studied for elastic structures by a number of authors. A few references are: (5, 8, 9, 10) 3 . These methods have usually considered the elastic buckling of structures. Most structures have been found to buckle in a lurching mode at some story, usually near the bottom. Plastic design of multi-story frames considers the beams to yield, with a resultant loss of stiffness. When these hinges form, the structure may buckle in its entirety within a region several stories high. Stability of structures with nonlinear stiffness has been studied for structures of a limited size (2, 3, 7, 8). For large structures, it is usually hoped that adequate required strength is predicted by accounting for the geometric nonlinearity in the analysis and by including a load factor on the vertical load (11). This paper presents a theory which can be applied to structures which have sufficient drift to cause yielding of their bracing elements. Large structures with a large number of sequentially yielding elements can be readily solved using this method.

The ready-mix concrete for high-rise structures in Chicago is unique in reference to the special concretes that have been developed for this type of construction. However, the overall picture of the ready-mix industry is similar to what is happening to the ready-mix industry in other areas of the world. The ready-mix concrete business is a dynamic resource for the construction industry, which must periodically reevaluate its position in relation to the economy, the nation, local industry, and especially with the customer. Highly-developed economies bring changes in market conditions. A change which has been occurring is the change from a product to a service-related market. This change occurs earlier in mass consumer products and lags behind in more static products like those in the construction industry. This conversion from product to service is taking place now in the construction industry. The ready-mix industry has traditionally made its profit in the volume of regular concrete with strengths from 3000 to 5000 psi. This is a product that does not require special quality control or special technology, consequently it can be handled by concrete technicians and salesmen with limited technical knowledge. This is also a product which does not require special promotion, is simple for code compliance, has abundant analysis and design information for the users, and does not require special mixing and transportation equipment. It is not difficult to sell when the price is right. It is usually sold with a questionable margin of profit which will continue diminishing until management makes the decision to make some changes. Management realizes that the ready-mix industry cannot survive in the mature economy of large metropolitan areas where the large concentration of ready-mix producers and their geographical proximity has brought their profit to a minimum return on their investment. Consequently, the search for changes becomes imperative to survive in a highly technological and competitive economy. However, changes are expensive in this high capital industry. The changes required to bring the ready-mix industry to high-technology levels are expensive because they involve management, equipment, quality control and marketing concepts. Aside from being expensive, they are difficult to accomplish because they require a total commitment from management and a clear understanding of a long range plan for its proper implementation.

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.

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.