Earthquake Spectra

Several earthquake ordinances have been enacted requiring owners of pre-1934 unreinforced masonry buildings either to upgrade their seismic strength or to demolish them. In this paper some of the factors which an owner must consider, including the relative costs of rehabilitation and reconstruction, are reviewed and specific examination of the after-tax returns for a hypothetical California building is made. It is shown that whereas there may be little direct income benefit gained from upgrading a particular building, tax shelter advantages may well provide sufficient financial inducement to justify a decision to upgrade rather than to demolish.

We examine here the costs and benefits of reinforcing some existing buildings in Boston at the time of remodelling with significant change of use. The buildings of interest are the unreinforced masonry warehouses and the reinforced concrete manufacturing buildings that are remodelled into apartment or office buildings. Given some estimates of the Boston seismicity and of the performance of these buildings in earthquakes with and without additional reinforcement, we evaluate three possible levels of reinforcement that the Masssachusetts Seismic Advisory Committee could recommend as part of the building codes. For the unreinforced masonry buildings, the first upgrading level is the addition of floor and roof diaphragms, and the two subsequent levels involve addition of internal walls and reinforcement of the existing ones. For the reinforced concrete buildings, the first level involves increase of the shear walls' size, and higher upgrading levels involve addition of shear walls and increase of the columns' size. We introduce in our study the market effects of the additional costs. We conclude that only the first levels of reinforcement that we considered could be adopted as regulations, and that higher standards should be left to the choice of the buildings' occupants.

This paper, through description and analysis of the performance of underground facilities during the magnitude 7.8 Tang-Shan earthquake of 1976, indicates that, in the area of strong surface shaking, damage to underground facilities decreases exponentially with depth to 500 m (1640 ft). Below this depth, damage remains constant. In addition, the rate of reduction of earthquake shaking away from the source fault is greater in the subsurface than on the surface.

Research on strong ground-motion characteristics conducted in the United States within the last 10 years (1974-1984) forms the basis for a detailed discussion of important factors to be considered when selecting or developing strong-motion attenuation relations for use in earthquake engineering and seismic hazard studies. While emphasis is placed on the empirical prediction of ground-motion amplitudes, a brief discussion of procedures is presented that can be used when insufficient strong-motion data are available to perform an adequate statistical analysis. The discussion is followed by a tabulated summary of selected strong-motion attenuation relations proposed and developed in the last 10 years (1974-1984) to acquaint the reader with the types of relationships currently available.

A number of methods have been developed with the aim of estimating the damage or effects of future earthquakes. As this field continues to rapidly expand, it is valuable to gain some perspective by comparing a representative sample of methods to see in what respects they are similar or different. The most significant conclusion of this review is that the use to which a damage estimation may be put is the single most important factor and, while there is already an extensive array of methods, there has been relatively little in the way of practical application.