Showing papers on "Earthquake resistant structures published in 1992"

Seismic Design of Viscoelastic Dampers for Structural Applications

Abstract: Some practical issues associated with the application of viscoelastic (VE) dampers to building structures for seismic performance enhancement are studied in this paper. A sequential procedure is developed for optimally placing VE dampers to structures, based on the concept of degree of controllability. This optimal placement procedure is then experimentally verified using a five‐story steel model structure. Economical use of the VE dampers is made possible by adding them to the optimal locations found by this procedure, as is clearly demonstrated by the numerical examples and experimental results presented in the paper. A design procedure is also presented by which damper dimensions, number, and locations needed to achieve desired level of additional damping can be determined in accordance with the structural parameters and structural‐response reduction requirement. Design of VE dampers for a 24‐story steel frame is presented as an example, showing the complete design procedure for applying VE dampers to ...

Influence of ADAS Element Parameters on Building Seismic Response

Abstract: Supplemental damping devices have been used to decrease the dynamic response of buildings subjected to wind and earthquake inputs. These devices can be generalized into the following three major types: friction devices, viscous or viscoelastic devices, and material yield devices. Lead dampers would be included in this last case, even though its characteristics do not involve yielding. A study of one of the metallic yield devices, the steel‐plate added damping and stiffness (ADAS) device, is presented. Yield force, yield displacement, strain‐hardening ratio, ratio of the device stiffness to the bracing member stiffness, and ratio of device stiffness to structural story stiffness without the device in place have been identified as the most important parameters to characterize the performance of this device. The influence of these parameters on earthquake response of building structures is analyzed. The results show that these devices can substantially increase the energy dissipation capacity of a structure ...

The Seismic Design of Waterfront Retaining Structures

Abstract: : This technical report deals with the soil mechanics aspects of the design of waterfront retaining structures built to withstand the effects of earthquake loadings. It addresses the stability and movement of gravity retaining walls and anchored sheet pile walls, and the dynamic forces against the walls of drydocks and U-frame locks. The effects of wall displacements, submergence, liquefaction potential, and excess pore water pressures, as well as inertial and hydrodynamic forces, are incorporated in the design procedures. Several new computational procedures are described in this report. The procedures used to calculate the dynamic earth pressures acting on retaining structures consider the magnitude of wall displacements. For example, dynamic active earth pressures are computed for walls that retain yielding backfills, i. e., backfills that undergo sufficient displacements during seismic event to mobilize fully the shear resistance of the boil. For smaller wall movements, the shear resistance of the soil is not fully mobilized and the dynamic earth pressures acting on those walls are greater because the soil comprising the backfill does not yield, i.e., a nonyielding backfill. Procedures for incorporating the effects of submergence within the earth pressure computations, including consideration of excess pore water pressures, are described.... Dynamic earth pressures, Hydraulic structures, Earthquake engineering, Soil dynamics, Earth retaining structures.

Hysteretic Response of Reinforced-Concrete Infilled Frames

Abstract: Strengthening of framed reinforced concrete structures by cast‐in‐place reinforced concrete infills is commonly used in practice. The objective of this study is to investigate the behavior of such infilled frames under seismic loads. For this purpose, 14 two‐story, one‐bay infilled frames are tested under reversed cyclic loading simulating seismic action. The variables investigated are the effect of type of infill reinforcement, the connection between the frame and the infill, and the flexural capacity of columns. Test results are evaluated to estimate the effects of infill on stiffness, strength, energy dissipation, lateral drift, and ductility. The feasibility of different analytical methods is also investigated. The results obtained using such analytical methods are compared with the experimental observations. Using the test results, a simple dynamic evaluation is made to predict the dynamic behavior of infilled frames under seismic action.

Fundamentals of earthquake-resistant construction

Abstract: A concise summary of practical methods that provides insight for earthquake safety in construction is conspicuously missing from the copious literature on earthquakes. This book was conceived to fill that void. It examines and recommends procedures for earthquake resistant construction and provides rationales for their use. The contents are presented in three parts. Part One, Causes and Characteristics of Earthquakes, contains the following chapters: (1) Basics; (2) Concepts and Definitions; (3) Seismological Evaluation; (4) Geological Evaluation; (5) Forms of Ground Motions; and (6) Selecting Design Motions. Part Two, Selection of the Design Motions for Earthquakes, includes the following chapters: (7) Maps of Seismic Zones and Seismic Ground Motions; (8) Procedures for Selecting Earthquake Ground Motions; and (9) Role of Codes and Empirical Procedures. Part 3, Designs for Earthquakes, consists of the final nine chapters which are: (10) Acquisition and Evaluation of Geotechnical Data; (11) Landslides and Slope Stability; (12) Liquefaction; (13) Foundation Design; (14) Structural Design; (15) Retaining Structures; (16) Dams; (17) Construction over Active Faults; and (18) Strengthening Existing Structures. There are two appendices: (1) Definitions and (2) Intensity- and Magnitude-Related Earthquake Ground Motions. An Index is provided.

Sliding Isolation System for Bridges: Experimental Study:

Abstract: A seismic isolation system for bridges has been tested on a shake table. The system consisted of Teflon disc bridge bearings and displacement control devices. These devices provided restoring force for re‐centering the bridge during earthquake excitation, additional energy dissipation capacity and rigidity for service loading. The tests were carried out with a 51‐kip model which was subjected to strong recorded earthquake motions with a wide range of frequency content and to simulated motions compatible with CalTrans 0.6g design spectra. In all tests the isolated deck responded with peak acceleration less than the peak table acceleration and peak bearing displacement less than the peak table displacement. Results from an analytical model show very good agreement with experimental results.

Sliding Isolation System for Bridges: Analytical Study

Abstract: This paper reports on a parametric study of the response of bridges supported by an isolation system consisting of sliding Teflon bearings and displacement control devices. The isolated bridges are subjected to simulated earthquake motions which are compatible with CalTrans design spectra. The effects of isolation system properties, deck flexibility, pier flexibility, pier strength, distribution of isolation elements and earthquake type are investigated. Results are presented in a form that is useful in the design of sliding isolation systems for two‐span continuous deck bridges. Comparisons with the response of conventionally built bridges demonstrate the significant benefits of seismic isolation. Finally, simplified code‐type analysis procedures are presented and evaluated.

Evaluation of Seismic Vulnerability of Highway Bridges in the Eastern United States

Abstract: For high risk seismic zones such as California, the state-of-the-art in earthquake resistant design for new highway bridges has been well advanced, especially since the damaging 1971 San Fernando earthquake. The catastrophic failures in the 1989 Loma Prieta earthquake brought a new awareness to the vulnerability of existing non-seismically designed bridge structures, particularly those in the eastern U.S. Instead of applying code-based formulations as an inverse to the design process to determine the vulnerability of existing bridges, this paper presents an energy-based evaluation methodology. Results are presented for a one-quarter scale model gravity load designed pier, which show that in spite of poor detailing, gravity load designed structures can possess a high degree of intrinsic lateral strength and ductility capacity.

Design Considerations for Using Adhesives in Shear Walls

Abstract: The results of earthquake tests of light-frame, wood shear walls conducted by several researchers are reviewed. The effect of using adhesives to attach the sheathing material to the framing is considered, specifically, potential problems due to the adhesive strengthening and stiffening of the wall system when subjected to an inertial loading such as an earthquake. None of the current design and building codes used in the United States address the use of adhesives, and engineers may design unsafe structures. Change in probable failure modes from the traditional ductile yielding of the nail connections between the sheathing and the framing to the anchorage connections or adjacent structural components is highlighted. Recommendations for changes that should be made to the building and design codes are suggested. Changes to the seismic design procedures only are recommended and the improved performance of adhesives in shear walls subjected to wind or other applied loads is acknowledged.

Masonry as a structural material

Abstract: Four case studies are presented which illustrate the use of masonry as a structural material Results of laboratory studies for unreinforced piers subjected to in-plane lateral forces, and infill panels subjected to out-of-plane pressures, are discussed Measured dynamic response of a two-story, unreinforced masonry building subjected to the Loma Prieta Earthquake and parallel analytical studies are presented Design of a post-tensioned concrete masonry reaction wall structure is discussed in terms of its measured behavior under lateral loads Performance of these structural elements and systems is used to document that masonry can indeed be considered as a structural material

Sharing california's seismic lessons

Abstract: The article describes how municipalities in earhtquake-prone areas can learn important lessons from Caltrans' (California Department of Transportation) experience. In Califronia, examination of damage to structural steel bridges after recent earthquakes demonstrates the need for continuous bridges or for seismic retrofit details to tie superstructure joints together, as well as tieing together the superstructures to the supporting substructures. Examples from the 1971 and 1989 earthquakes are described. While structural steel is a ductile material, it must tbe designed to resist the highest expected seismic forces or retrofitted to resist those forces. The performance and damage in the San Francisco-Oakland Bay Bridge is described, as well as elevated viaducts, and the Eel River and Van Duzen River Bridges. The inadequacies of the pre-1971 column designs are pointed out.

Three‐Dimensional Nonlinear Dynamic Analysis of Complex High‐Rise Building Structures

Abstract: The authors have developed a three-dimensional (3-D) dynamic analysis system, 'Super DYNAMICS', which considers the nonlinear behavior of each structural member in order to analyze the structural behavior of such complex steel buildings under severe earthquakes. This paper first describes the general concepts of the system and the 3-D dynamic response analysis methods, based on the nonlinear behavior of each structural member under axial force and biaxial bending moments, and then examines the precision of the multispring models which have been adopted to trace the behavior of steel members or steel structures after yielding and the stability of the system. Lastly, it shows some application examples for actual designing.