International Concrete Abstracts Portal

The concepts of capacity design philosophy, which aims to ensure a desirable sequence in the plastification of ductile frames during severe seismic excitation, are introduced, In the establishment of desirable strength hierarchies the relationship between beam load inputs and ideal column strengths are examined in detail. Simple procedures, that recognise relative strength values and general characteristics of dynamic behavior, are proposed for the evaluation of moments, axial and shear forces for columns of frames. The proposals intend to ensure a high degree of protection against premature damage to columns, and to eliminate the possibility of concentrated energy dissipation in storey mechanisms in frarnes that may be subjected to unidirectional earthquake attack or to concurrent orthogonal seismic excitations. Because hinging is not expected in upper storey columns, the re-quirements for confining reinforcement in the end regions of these columns can be greatly relaxed.

This paper describes the structural earthquake design of a 28 story reinforced concrete Office Building located in Caracas, Venezuela, which is a very heavy seismic area. The structure has special features, such as its cross-shaped plan and four 'U' shaped shearwalls placed at comers of the building. It was designed to resist a total shear at the base of building of .08g, distributed over the height according to its dynamic response. Soil site properties, represented by a measured alluvial deposit 160 meters deep (525 ft.), were considered to select an appropriate response spectrum for the structural design. The structural analysis underlined the excellent behavior of the lateral load resisting system used in this structure. This system consists of longitudinal frames interacting with 'U' shearwalls. The structural system complies with limits on lateral deformations imposed by the Venezuelan Seismic Code MOP-1967 (1). The shearwalls proved to be extremely efficient in limiting lateral deformations and in resisting additional shear forces due to Code requirements in connection with torsion. The Wide column-frame analogy was used to model shearwalls, and the analysis considered full frame-shearwalls interaction, axial strainin all structural elements and infinitely rigid haunches at nodal points of frames in order to take account of the relative effect of the actual dimensions of the structural elements. The design of the shearwalls was achieved by means of ultimate strength computer interaction diagrams for combinations of axial loads and uniaxial bending moments.

Numerous computer analysis techniques for use in the seismic design of reinforced concrete structures are available to the design engineer and are finding general use. Unfortunately, these techniques are not "exact". Rather, they are forced to make a large number of questionable assumptions about earthquake characteristics and building behavior. To the practicing engineer, whose complex structures and structural elements defy symmetry, regularity and simplicity, the valid use of such technique depends on a complete understanding of the analysis limitations and inaccuracies and requires constant review of the results for analysis generated errors. This paper, while presenting a practical analysis application, addresses the serious difficulties and the inherent inaccuracies encountered in applying the most commonly used computer analysis techniques to concrete shear wall buildings. It is based on the actual computer analyses of a variety of middle-rise concrete shear wall buildings performed over the past few years at H. J. Degenkolb & Associates. This paper, while it addresses and identifies the invalid results that can be easily produced, believed and designed for, in concrete shear wall building analysis, also provides usable techniques for identifying, adjusting and correcting the problems that are encountered. As such, it provides the practicing engineer with additional insight and understanding of his computer analysis techniques.

The lateral force stiffness characteristics of structures cannot be represented by a single set of modeling assumptions. Measured data obtained from the study of full-sized buildings subjected to various sources of lateral displacements are compared to calculated results based on various modeling assumptions used in determining the stiffness characteristics of structures. Tentative recommendations are presented for use in the lateral force design of reinforced concrete buildings subjected to winds and/or earthquakes. Stiffness properties associated with effective concrete sections, concrete slab participation, and nonstructural materials are discussed. For both wind and earthquake design, it appears that the assumptions that apply to low amplitude motion should be different than the assumptions that apply to high amplitude motion. Therefore, it is recommended that modeling techniques and the cal-culation of stiffness characteristics be based on some form of a two-level approach.

A five story reinforced concrete building which collapsed during the Mindanao, Philippines Earthquake of August 1976 is studied. The building experienced a twisting motion dur-ing its collapse. The damages to the building are described, and design calculations which consider the twisting are performed. The calculation results show that a number of columns were understrength but that other factors such as reinforcement detailing and material quality influenced the seismic performance of the building.