Showing papers on "Earthquake resistant structures published in 1987"

Analytical Modeling of Hysteretic Behavior of R/C Frames

Abstract: A theory for an enhanced mathematical model of R/C frame members is presented and its accuracy is verified by simulating various laboratory experiments for which data were available in the literature. New member and global damage parameters are defined. These damage parameters are useful for subsequent reliability analysis of damaged concrete frames.

Seismic design of bridges on lead-rubber bearings

Abstract: A number of time-history dynamic analyses are reported for structures where the following parameters are varied: bearing height, dissipator strength, pier and foundation flexibility, deck flexibility, and earthquake record. The research described in the report was completed in four stages: (1) evaluation of the response of sdof (single-degree-of-freedom) structures, using a model equivalent to the response of a bridge on rigid foundations; (2) investigation of the response with piers of differing flexibility; (3) study of the response of bridges with various combinations of pier and abutment flexibility and bearing arrangements. The final stage (4) reviews the work to establish an alternative design procedure. The new procedure is more straightforward and conceptually clearer than the present design procedures. (TRRL)

Reliability of Concrete Frames Damaged by Earthquakes

Abstract: A methodology that permits an assessment of the reliability of concrete frames, which may have been damaged in previous earthquakes, is presented. Using Monte Carlo simulation, damage probability matrices are constructed that take into account the variability of building strength parameters in addition to the randomness of ground motions. This methodology can serve owners and public officials as a decision aid for strengthening strategies and repairs.

Parametric Study of Earthquake‐resistant Coupled Walls

Abstract: A parametric investigation was conducted to determine the significance of selected structural and ground motion parameters on dynamic inelastic response of coupled wall structures. Structural parameters include: fundamental period, wall strength, beam-to-wall stiffness and strength ratios, coupling arm, clear beam span, gravity loads, and structure mass. Ground motion parameters include: earthquake frequency characteristics, duration, and intensity. A computer program and a moment-rotation hysteretic model, including the effects of axial force-flexure interaction, was used to conduct nonlinear dynamic analyses. Significance of each parameter on maximum force and ductility response is shown. The most significant parameters are identified as design variables. Relationships between design variables and response quantities are established.

Probabilistic Design of Moment‐Resistant Frames Under Seismic Loading

Abstract: This is the second part of a two‐part paper on the development and preliminary testing of a methodology for the optimal probabilistic limit states design of seismic‐resistant steel frames. Part two illustrates the design of a three‐story, single‐bay, moment‐resistant steel frame using a computer‐aided design system called DELIGHT.STRUCT. Linear and non‐linear time history analyses are built into the design procedure itself rather than serving as a check at the end of the design process. The frame's performance is assessed on the basis of its statistical response to gravity loads alone, gravity loads plus a family of moderate earthquakes, and, finally, gravity loads combined with an ensemble of rare severe earthquake ground motions. Design objectives include the frame volume, minimum story drifts and maximum hysteretically dissipated energy. The Phase I–II–III Method of Feasible Directions is used to solve the constrained optimization problem for an optimal design that balances the attributes of minimum vo...

Probabilistic Design of Earthquake‐Resistant Structures

Abstract: This is the first of a two‐part paper on the development and preliminary testing of a methodology for the optimal probabilistic limit states design of seismic‐resistant steel frames. A mechanism for allowing a designer to include the effects of uncertainties and multiple design objectives in the design process is described. The concept of [GOOD, BAD] and [HIGH, LOW] preference pairs is explained. Scaling procedures for combining the aforementioned effects and the statistics of frame response in a single design entity called designer dissatisfaction are developed. The features of the proposed design method are demonstrated via the design of a simple one‐story shear building.

Evaluation of Performance of Concrete Buildings Damaged by the September 19, 1985 Mexico Earthquake

Abstract: As a part of a general evaluation of the structural behavior of buildings during the 1985 earthquake in Mexico City, a detailed study of 8 damaged concrete buildings has been performed. The paper contains a general description of the buildings, of their damage and of its possible causes. An approximate method of evaluation of seismic strength is proposed and applied to the eight buildings. General conclusions about the causes of damage and about changes needed in the design practice are proposed.

Benefits and Costs of Earthquake Resistant Buildings

Abstract: The benefits of constructing earthquake resistant buildings are the savings in property damage, injuries, and lives that accrue in the event of an earthquake. The costs are the additional resources required to ensure that buildings are resistant. In certain regions of the U.S., particularly in California, earthquake resistant buildings are commonplace. As we will show, the cost of adding this resistance to buildings is about seven billion dollars in Los Angeles County alone. The purpose of this paper is to present a methodology for estimating these costs as well as the benefits of resistance. The methodology draws upon the economic approach to valuing risks to life, as well as recent engineering and geological studies of earthquakes and the damage they cause. Our results should be useful both to policy makers concerned with whether the current level of precautions taken to mitigate earthquake losses are adequate, and to economists confronted with evaluating the precautions taken by society against natural hazards in general. Currently, the level of resistance to buildings in most of California is dictated by seismic building codes. The justification for mandatory codes as opposed to a market oriented

The Mexico Earthquakes-1985: Factors Involved and Lessons Learned

Abstract: This publication reports initial results of study of the 1985 Mexico earthquake, one year after the event. The findings present sufficient depth of analysis to provide an understanding of the causes and effects of earthshaking within Mexico City that resulted in extensive damage to some buildings and structures. Also reported are the assessment of damage caused by the earthquake and emergency response including recovery operations. Buildings of different construction types and materials were subject to the earthquake. Performance of their response is analyzed and evaluated. Topics presented include seismicity associated with the Mexico earthquake of 1985. General engineering topics include dynamic soil response, foundation failure, performance of structures and analysis of building failure, analysis of lifelines performance, and emergency response including building code regulations. Specific practical problems addressed include: modeling of soil motion, modeling of structural behavior, analysis of drift in frame structures, structural pounding, structural stiffness softening due to long duration motion, soil-structure interaction, influence of local soil conditions on building performance, dam behavior, and repair and strengthening of buildings.

Safety margins of suspension bridges under seismic conditions

Abstract: The American Association of State Highway and Transportation Officials (AASHTO) 1983 code, "Seismic Design of Highway Bridges," does not cover explicitly suspension bridges. Nevertheless, if AASHTO earthquake excitation is applied to some existing suspension bridges, even those of strategical importance, for example, the Golden Gate bridge, the structural safety of these bridges cannot be proven. The need for new standards is also widely recognized in Japan. Analyses that have appeared in the literature are reviewed. A criterion to select the design earthquake is proposed and its relevance on the previous safety analyses is shown.

A Comparative Study of Different Base Isolators

Abstract: A comparative study of the effectiveness of four different base isolators is carried out. The structure is modeled as a rigid mass and the accelerograms of the North-South component of El Centro 1940 earthquake and the N90W component of Mexico City 1985 earthquake are used. The performances of the isolation devices under a variety of conditions are evaluated and discussed.

Performance of Steel Structures

Abstract: A description of the various types of steel structures built in Mexico City is made, including comparisons of the older types of steel construction with more modern buildings. Performance of steel buildings in the September, 1985 earthquake are discussed and related to the local geotechnical conditions including foundation behavior. The Edificio 21 Atlas and Conjunto Pino Suarez buildings are discussed in more detail.

Cyclic Behavior of Concrete-Filled Tubes

Abstract: This paper presents the results of tests on hollow and concrete-filled rectangular tubes subjected to cyclic bending and buckling. It is shown that concrete infill greatly improves the performance of these members by reducing the effects of local buckling and increasing their ductility and energy dissipation capacity. Use of such composite members appears to have great potential in earthquake resistant structures.

Code Designed Steel Frame Performance Characteristics

Abstract: Three similar steel ductile moment-resisting frame structures designed in accordance to the Uniform Building Code (1976-1985) are evaluated for their performance characteristics during severe earthquake motion. The framing systems allow comparison for variations in two alternate designs in the same seismic zone and two similar designs in different seismic zones. The capacity spectrum method, which approximates the inelastic behavioral characteristics of the building, is used in the analyses. The results of the study present the relative abilities of the structures to resist the effects of maximum postulated earthquake motion.

Earthquakes Will Not Damage This Bridge

Abstract: A California pipeline bridge has been retrofitted with isolation bearings that damp earthquake shocks. The bridge over Southern California's Santa Ana River carries the Upper Feeder Pipeline of the Metropolitan Water District of Southern California and is the second in the U.S. to be fitted with isolation bearings. These bearings isolate the bridge superstructure and the 116 in. steel pipeline from earthquake shaking and damp much of the shaking energy that does get through. The vendor claims that replacing the existing rocker bearings with isolation bearings costs only 10% as much as the alternative solution which was to make the bridge stiff enough to withstand the shaking by increasing the lateral stiffness of the columns above the piers and below the superstructure. This article describes the bridge, the isolation bearings, the dynamic analyses done to determine the magnitude of the shaking forces and displacements, and the size of the bearings selected to handle them.

Development of structural design procedures for earthquake resistance in new zealand

Abstract: Structural design procedures for earthquake resistance in New Zealand have gradually evolved since the 1931 Hawkes Bay earthquake. A good deal of New Zealand research and development has led to the current philosophy for the design of structures for earthquake resistance, as expressed by current recommendations of study groups of the New Zealand National Society for Earthquake Engineering and in provisions of recent codes of the Standards Association of New Zealand. These recommendations and codes emphasize the importance of structural detailing to achieve satisfactory performance of structures during severe seismic loading.

Methods for Improving the Seismic Response of Concentrically Braced Steel Frames

Abstract: This paper briefly reviews various factors contributing to the poor performance occasionally observed in concentrically braced steel frame structures during recent earthquakes. Several alternative systems for improving this behavior are described for chevron (K) braced frames. The relative effectiveness of these variants is evaluated on the basis of results of analytical simulations. Guidelines for the design of such frames are identified from these studies.

Performance Characteristics of Structures, 1985 Mexico City Earthquake

Abstract: The 1985 Mexico City earthquake caused major damage to buildings, but not other structures, in the center of Mexico City, located approximately 400 km. from the epicenter. Due to soil conditions in this area, ground motions were especially amplified at a frequency of about 0. 5 Hz. Due to this unusual amplification, damage was inordinately concentrated in buildings in the 6 to about 12 story range. Based on measurements in 1962 and 1986, average natural periods for buildings in that story range are estimated and, together with an existing mid-rise building seismic damage estimation methodology, are used to estimate building damage for the 1985 ground motions. These estimates are compared with data on observed damage and reasonable agreement is seen to result, within the limits of the available data on observed damage.