Showing papers on "Earthquake resistant structures published in 1978"

Eccentrically Braced Steel Frames for Earthquakes

Abstract: A unique, practical structural steel system that possesses many advantages in the seismic design of structures is described The system employs diagonal bracing with large eccentricity between the brace-beam connection and the beam column joint The eccentricity provides a ductile fuse that yields in shear and prevents brace buckling Static and dynamic analyses indicates that this system can perform well during earthquakes, because it combines the stiffness of a braced frame with the excellent energy dissipation of a moment-resisting frame One-third-scale experiments showed that the system behaves as predicted in the analyses It dissipates large amounts of energy while maintaining a very stiff structure, and it offers many potential applications in the seismic design of structures

Determining models of structures from earthquake records

Abstract: The problem of determining linear models of structures from seismic response data is studied using ideas from the theory of system identification. The investigation employs a general formulation called the output-error approach, in which optimal estimates of the model parameters are obtained by minimizing a selected measure-of-fit between the responses of the structure and the model. The question of whether the parameters can be determined uniquely and reliably in this way is studied for a general class of linear structural models. Because earthquake records are normally available from only a small number of locations in a structure, and because of measurement noise, it is shown that it is necessary in practice to estimate parameters of the dominant modes in the records, rather than the stiffness and damping matrices. Two output-error techniques are investigated. Tests of the first, an optimal filter method, show that its advantages are offset by weaknesses which make it unsatisfactory for application to seismic response. A new technique, called the modal minimization method, is developed to overcome these difficulties. It is a reliable and efficient method to determine the optimal estimates of modal parameters for linear structural models. The modal minimization method is applied to two multi- story buildings that experienced the 1971 San Fernando earthquake. New information is obtained concerning the properties of the higher modes of the taller building and more reliable estimates of the properties of the fundamental modes of both structures are found. The time-varying character of the equivalent linear parameters is also studied for both buildings. It is shown for the two buildings examined that the optimal, time-invariant, linear models with a small number of modes can reproduce the strong-motion records much better than had been supposed from previous work using less systematic techniques.

Tapered steel energy dissipators for earthquake resistant structures

Abstract: The paper describes the testing and design of tapered-steel cantilevers used as energy dissipating devices, manufactured from either round bar or plate, which can be used in isolation systems to protect buildings or bridge decks against earthquake attack. The steel cantilever energy absorber is a simple device which can be manufactured from steel supplies normally available in an engineering stores using standard engineering practice.

Retrofitting bridges to increase seismic resistance

Abstract: The 1971 San Fernando, Calif., earthquake was a turning point in the seismic design of bridges. It disclosed a number of deficiencies in the bridges designed according to AASHTO specifications and common practices at that time. California initiated a program of identifying seismically deficient bridges and retrofitting them to make them more seismically resistant. Retrofit philosophy, prioritizing systems, retrofitting details, concepts, hardware and costs are considered.

Simple models for computing dynamic responses of complex frame structures

Abstract: Prohibitive costs of analyzing large frame structures using the finite element method have led researchers to investigate simpler procedures of analysis The development of a simple shear beam and a Timoshenko base model for dynamic analysis of complex frame structures is described Formulas are derived for computing the equivalent shear and bending rigidities of the structure Simple models are evaluated by comparing simple model solutions with solutions obtained from using full scale finite elements in free vibrations of plane frames It was found that the simple models yield very accurate frequencies as well as mode shapes for the lower modes, and the Timoshenko model is more superior to the shear beam model when diagonal bracings are present When the shear beam model was employed to compute the natural frequencies of a TVA fossil fuel power plant at Paradise, Kentucky, the first two frequencies were found to be in good agreement with the finite element solutions The simple models were also used to compute transient dynamic responses of structures subjected to earthquake disturbances Evaluative examples and dynamic internal force and moment computations using simple models are included

Approximate Design for Three Earthquake Components

Abstract: The seismic analysis of complex structures is often carried out by the response spectrum method. A method was presented by which the simultaneous variation of various responses can be postulated using the results from the response spectrum analysis under each of the three components of earthquakes.

Modern Concrete Structures Survive Romanian Earthquake

Abstract: On March 4, 1977, 35 buildings collapsed during a severe earthquake (7.2 on the Richter scale) in Bucharest, Romania. Thirty-two of the 35 were older structures, erected before World War II, before seismic design was considered. After World War II, construction began with cast-in-place concrete, rigid frame structures having clay masonry infill walls and partitions; some have since been stiffened with shear walls. With few exceptions, multistory cast-in-place concrete structures built during the past 25 years had enough strength and stiffness to withstand the earthquake, More recently, 70,000 dwelling units have been built using precast large-panel construction in buildings up to nine stories high. Precast buildings designed for earthquake resistance withstood the earthquake with little distress.