Showing papers on "Earthquake resistant structures published in 1975"

Torsional response of high-rise buildings

Abstract: Ambient and earthquake response records obtained in several southern California high-rise buildings are analyzed. Building translational and torsional natural periods are estimated and compared. Ambient response is found to be an important indicator of earthquake response. Torsional building response resulting from ambient and earthquake excitation was found to be significant. A design spectrum is developed representing a standardized torsional ground motion of El Centro 1940 Earthquake Intensity.

Earthquake Design of Buildings:Damping

Abstract: A Fourier spectra analysis of the recorded February 9, 1971, San Fernando earthquake response of 12 southern California high-rise buildings was conducted and damping in building normal modes of vibration was estimated. Obtained damping values were correlated with building basement 0% damped pseudovelocity response spectrum and empirical equations were derived for damping estimation. A procedure utilizing these equations was developed for the selection of damping values for use in building design.

Seismic field methods for in situ moduli

Abstract: : The design and evaluation of the response of engineered structures to earthquake excitation have increased the current use of seismic field studies to determine soil properties at low strain levels for in situ materials. Buildings, nuclear power plants, major earth structures, locks, and concrete dams are now being studied using finite element techniques and modal or time- step analyses. The validity of these studies and the interpretation of their results depend on a reliable assessment of input values for in situ foundation properties. This report presents procedures for planning seismic field investigations for the determination of soil properties. Emphasis is placed on the selection of appropriate seismic techniques to obtain sufficient redundant data with which to establish internal consistency for reliable assessments of determined properties.

Design Aspects of Shear Walls for Seismic Areas

Abstract: This presentation, taking the form of a state of the art report, considers several aspects of the behavior of tall and squat shear walls In particular the problems of brittle and ductile failure modes, diagonal tension, construction joints, alternating plasticity, sliding shear, stiffness degratation, and strength loss under reversed cyclic loading are discussed The behavior of coupled shear walls is examined in some detail and the problems related to the components of this structure are reviewed The principles rather than techniques of design for earthquake resistance are stated Wherever possible the issues are studied against the background of experimental evidence The material presented indicates that carefully detailed shear walls, designed to possess an intelligent hierarchy in their failure mechanisms, can be made to possess the properties so desirable in earthquake resistant structures

Earthquake Resistant Design of Intake-Outlet Towers

Abstract: The problem of designing reinforced concrete intake-outlet towers, partially submerged in water, to withstand earthquake ground motion is examined in general terms. It is shown that water, surrounding as well as inside, significantly affects the response to ground motion and these hydrodynamic effects should be considered in the design of towers. A rational method for elastic design including the hydrodynamic effects is proposed. It is recommended that towers be designed to elastically resist ground motions which they may experience several times during their useful life. The ductility requirements that would be imposed on code-designed towers by the intense ground motions expected near the causative fault during high magnitude earthquakes are evaluated; they appear to be rather large. It is recommended that forces for elastic design be increased so that the lateral displacement ductility requirements imposed by the most intense ground motion that can occur at the site would be no larger than a ductility factor of two.

Dynamic behavior of a submerged tunnel during earthquakes

Abstract: The authors have conducted model tests for the purpose of clarifying the dynamic behavior of the submerged tunnel and the interaction between the tunnel and the surrounding soil during earthquakes. The earthquake observations have been carried out on an actual submerged tunnel in order to obtain information on the real behavior of deformation of the submerged tunnel during earthquakes. By making reference to the data thus obtained, a method of earthquake response analysis is proposed for this type of tunnel using a new mathematical model in which the ground around the tunnel is represented by lumped masses along the tunnel axis. The tunnel is assumed as a beam on an elastic foundation. Several problems regarding the earthquake resistant design of the submerged tunnel are discussed including the effects of the ground conditions and of joints, etc., on its earthquake response and a preliminary earthquake resistant design method is proposed. /Author/

Seismic Behavior of K-Braced Framing Systems

Abstract: Three 10-story three-bay structures having K-braced framing systems are designed for seismic loads according to building code requirements. Members are proportioned by standard allowable stress procedures. The frames are subjected to strong ground motion and the inelastic response of the three systems is evaluated and compared. Results show that increased ductility requirements occur in regions adjacent to discontinuities in lateral stiffness. The addition of an outrigger truss at the top of the frame tends to force more of the inelastic deformation into the girders and bracing rather than the columns. The fully braced systems are very effective in controlling lateral displacement.

Effects of soil deposits on seismic behavior of prefabricated highway tunnels

Abstract: A comprehensive study was made of the earthquake resistance of prefabricated highway tunnels embedded into soft undersea soil deposits to establish design methodology for providing adequate structural resistance to seismic disturbances. Measurements of seismic motions were carried out employing downhole accelerometers at three sites around Tokyo Bay, and dynamic analyses were conducted by utilizing seismic records obtained and applying the multi-reflection theory. Model experiments and dynamic analyses on the dynamic response of a highway tunnel embedded in soft soil deposits were also conducted. The following conclusions were drawn: (1) accelerations at deeper locations of soft soil deposits are small in comparison with the surface accelerations, and shapes of vertical distribution of maximum accelerations are different among various earthquakes; (2) the multi-reflection theory may be employed satisfactorily in estimating seismic response of multi-layered subsoils, provided that soils properties, primarily elastic moduli, are appropriately evaluated; (3) for estimating three-dimensional behavior of long structures embedded in soft subsoils during earthquakes, model experiments would be effective, and in the model experiments gelatin can be advantageously used as soft soil; (4) dynamic analyses by means of the finite element method would be also effective in obtaining seismic response of underground structures; and (5) deformation of soft soil deposits has significant effects on the dynamic behavior of the embedded structures, and soil deposits in resonance to seismic motions might exert the structures into critical state, and furthermore, the structures would be affected extensively in the vicinity of a site where depth of soft soil deposits varies steeply due to the fact that the deformation of deeper soil deposits is larger than that of the other section.

Seismic studies of the articulation for the dumbarton bridge replacement structure. volume 2. numerical studies of steel and concrete girder alternates

Abstract: The influences of various girder types and joint articulations on the seismic responses of long multi-span highway bridges are reported. The girder types are of cast-in-place and precast concrete constructions and steel twin-box sections. Various types of expansion joints and girder to pier-cap connections are considered. A 7400 feet long bridge, that is to cross the lower arm of San Francisco Bay, is studied. The bridge is composed of 43 spans founded on various soil conditions, including Thick-Mud and Deep-Water sections. Response characteristics are determined for light, moderate, and severe ground motions of both sections. Time-history and spectral analyses based on design and response spectra are performed for two- and three-dimensional models. Interactions of water mass, soils, footings, and piling groups are considered. Volume 2 considers the following topics: Numerical results for the effects of longtiudinal and vertical ground motions; and Numerical results for the effects of transverse ground motions.

Determination of seismic design criteria for the dumbarton bridge replacement structure. volume 1. description, theory, and analytical modeling of bridge and parameters

Abstract: This report deals with the first phase of an extensive seismic investigation that is being made of a long multi-span bridge proposed for a crossing of the lower arm of San Francisco Bay. In this phase, a preliminary design is investigated and a set of seismic design criteria are established. The bridge is 7400 feet long and is composed of 43 spans founded on various soil conditions, including Thick-Mud and Deep-Water sections. Parametric studies are performed (a) to determine and explore the critical questions of design, (b) to define the parameters that need be considered in the analyses, and (c) to establish seismic design criteria for the final phase of design. Among the parameters studied are those associated with five different quakes, two soil columns, the interaction of the various footings and piling groups with varying water and soil conditions, and the properties of the structural elements along the bridge. Based on these studies, seismic design criteria are established in the form of design spectra for both strong and moderately strong earthquake motions.

Structural analysis and retrofitting of existing highway bridges subjected to strong motion seismic loading

Abstract: The objective of this project was to determine cost effective means for modifying existing intermediate size bridges so as to better withstand the damaging effects of intense earthquake ground motions. Research studies were performed to identify and define, through structural analysis, practical techniques and criteria for retrofitting the bridges selected during the program. The need for retrofitting is based on the philosophy that damage should be limited so that collapse does not occur and traffic can be restored after minimum repairs. Seven different bridge structures were selected throughout the United States in high risk seismic regions. Seismic loads were determined for each bridge based on the soil conditions and seismicity at its site. A simplified analysis procedure was defined during the project and validated by selective comparisons with nonlinear response analyses. Each bridge was analyzed for horizontal seismic loads. Failures and potential weaknesses are indicated for several of the structures and retrofit measures are recommended. All known retrofit concepts which are of potential value in reducing seismic bridge damage are described and illustrated. Based on this study, many bridges located in high seismic risk zones may be subjected to severe damage and potential failure during the life of the structure.

Protecting buildings against ground-borne vibration

Abstract: The principal of protection of buildings against earthquakes is to design so that the lowest natural frequency should be above the highest frequency of significant excitation by an earthquake. For protection against traffic vibration, the building is mounted on springs so that its dominant natural frequencies are less than the frequencies of the excitation. The latter technique can also be used against earthquake vibration. Properly designed buildings in earthquake zones are constructed to withstand the full horizontal acceleration load produced by a design earthquake. This method has the disadvantage that occupants and fittings in the building also experience the full force of the motion. It has been found that natural rubber is the most suitable material for mounting of buildings. The cost and engineering of a typical building is illustrated by the example of a building designed to the Mexico Code of Practice. A large number of buildings have been protected against traffic induced vibrators by being mounted on springs.

Modal analysis methods in seismic design for buildings

Abstract: : This report is the first step in preparing a change to the tri-services manual TM 5-809-10, Seismic Design for Buildings. Changes in this manual are necessary to provide guidance for the design of critical military facilities which must remain functional after subjection to strong earthquakes. This report describes and discusses modal analysis methods used in the dynamic analysis of structures in conjunction with the earthquake response spectra and time history methods. Elastic and inelastic conditions are discussed, as well as structural damping and assumptions and limitations of the methods. Example calculations are included.