The Chicago Department of Inspectional Services, otherwise known as the Department of Buildings, has the same mission as any other Building Department in the country--namely, to protect public safety, health, and property. As a department, it is not small in size or force, but not too large either. It is no more wasteful than any other government office. It is, however, rather effective in its mission. It does provide valuable services to the public with courtesy and speed and does have some progressive fea-tures both in its organizational makeup as well as in the manner of providing its services.

This text is the product of a collaborative effort by the concrete construction services staff of Ceco Industries, inc. Many staff members contributed their findings and recommendations, which were organized and integrated by William R. Anthony, PE, Manager, Market Development. Through its subsidiaries, Ceco Industries is a national formwork subcontractor, and provides the preconstruction services of value engineering, systems analysis and budget pricing. In a growing number of markets, Ceco also provides a total concrete building frame contracting service.

A simplified method to calculate the moment mag-nification factor and the critical buckling load for a laterally unsupported story of a building is discussed. The method is a hand calculation technique which has nearly the same results as a computerized P A method. The method is a substitute for the effective length method. A practical designer% definition of a braced frame is given. A practical designer's definition of frame instability is given. Several design examples are given toillustrate the application of the procedures.

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.

As the speed of construction of concrete frame structures has increased and the sophistication of design has improved, there has been an increased need for a more thorough understanding as to the way construction loads are disbursed into the structure. During the 60's and 70's, several designers and researchers proposed methods of analyzing the loads in multi-story structures during construction. A computer program employing one of these methods has been developed. In the 1982 PCA conference,the author used the results of this program to show how the number of levels of equipment, cycle time, and attained concrete strength affected the number of levels of reshores required. This paper describes in detail the process used to calculate the reshoring requirements for a 359-story flat plate structure built using a three-day construction cycle. The discussion includes the practical implications of providing reshoring for a mild steel structure. The hand calculation procedure presented parallels the computer program and is sufficiently detailed to provide the reader a practical procedure that can be used on the next project.