Showing papers on "Earthquake resistant structures published in 1989"

Experimental Study of Active Control for MDOF Seismic Structures

Abstract: Active control of building structures has been extensively studied theoretically, using a variety of control schemes showing varying degrees of efficiency. The demand for experimental evidence of feasibility of control of structures subjected to severe transient loads leads to the present study. Structural control experiments are carried out in the laboratory using a 1:4-scaled model structure simulating a three-story frame building. The control experiments are performed using a system of prestressing tendons connected to a servo-hydraulic system and linear optimal control algorithms. The model is subjected to base options produced by a 12×12 ft (3.6×3.6m) shaking table, which include banded white noise and earthquake accelerograms. Results of the experiment show clearly that traditional algorithms can be implemented when proper adjustments are made. These include compensations for time delay and error accumulation in the online computation. Several new algorithms based on instantaneous optimal control are experimentally verified in this study, following new developments based on previous experiments of single-degree-of-freedom structures. The efficiency of various algorithms is discussed along with comparisons of analytical and experimental results.

Lateral Displacement Ductility of Reinforced Concrete Flat Plates

Abstract: It is presently unclear whether the reinforced concrete flat-slab connection possesses sufficient lateral displacement capacity to survive the lateral deformations that can be expected during a strong earthquake. The objective of this paper is to examine the available data from present and past research and from there develop an understanding of the major parameters that influence the lateral displacement capacity and ductility of reinforced concrete flat plates. The significant effects of gravity load and biaxial lateral loading are presented together with the implications of the findings with regard to seismic design and performance. An expression of the gravity level shear stress acting on the slab critical section to which it must be limited to insure adequate displacement ductility under extreme earthquake loading is given.

Response Modification Factors for Earthquake Resistant Design of Short Period Buildings

Abstract: Most recent seismic codes include response modification factors in the definition of the equivalent lateral forces that are used for the design of earthquake resistant buildings. The response modification factors (R) are used to reduce the linear elastic design spectrum to account for the energy dissipation capacity of the structure. The evaluation of these response modification factors for various sets of earthquake records and ductility factors is presented herein. Special attention is given to the short period range where the reduction of linear elastic response spectra is smaller than the values for intermediate and long period structures. An idealized and simple variation of the response modification factor as a function of the period of vibration, suitable for seismic codes formulation, is also presented.

Earthquake Load for Structural Reliability

Abstract: An ultimate limit state criterion is developed for the seismic reliability assessment of single-story structures. This criterion is: when the structural precollapse energy absorption capacity is greater than the earthquake energy input, the structure can survive. Thus, the load effect is the maximum earthquake energy input which the building is expected to encounter during its lifetime. For the determination of this load effect, the seismic hazard potential as well as the dynamic characteristics of the structure and the ground motion are considered in this study. The seismic hazard term is determined from seismic source and attenuation models, and the dynamic characteristic term is determined from the energy input spectrum of inelastic single-degree-of-freedom (SDOF) systems. The uncertainty involved in these terms is also investigated in order to calculate the failure probability.

Brace Fractures and Analysis of Phase I Structure

Abstract: Bracing members in concentrically braced structures may be subjected to large cyclic deformations in post-buckling range during a severe earthquake causing possible early fractures. This paper investigates the phenomenon and presents an empirical criterion to predict the fracture of rectangular tubular bracing members. The criterion includes two parts: normalizing axial deformation cycles into standard cycles, and predicting the fracture life of the bracing members in terms of the standard cycles. The criterion is incorporated into DRAIN-2DM, a general purpose computer program for dynamic analysis of inelastic structures. The U.S.-Japan Phase I test structure, a six-story, two-bay by two-bay steel structure with concentric bracing, is analyzed using the criterion and analytical results are compared with the test results.

Seismic Design of Bridges on Lead-Rubber Bearings

Abstract: This paper reports on a parametric study of the response of bridge superstructures supported on lead‐rubber bearings when subjected to the 1940 El Centro earthquake (N‐S component) and the 1966 Parkfield earthquake. The effect of parameters such as lead‐plug size and aspect ratio, bearing thickness and yield strength, pier, abutment, and superstructure stiffnesses, and different earthquake records were investigated. The results of the time‐history analyses by Turkington (1987) produced clear trends that are used in the design procedure proposed by Turkington et al. (1987, 1989). The trends showed that the presence of lead shifts the natural period of the structure and increases the amount of damping. The magnitude of the period change and damping decreases as the natural period of the structure increases or as the pier height increases. Lead‐rubber bearings are most effective when used in conjunction with stiff substructures and can be used to redistribute seismic forces between piers and abutments.

Earthquake Response of Torsionally Coupled, Frame Buildings

Abstract: The earthquake response of torsionally coupled buildings is presented for a wide range of system parameters. Based on these results, it is demonstrated that the building response depends significantly on the static eccentricity ratio e/r, the uncoupled torsional to lateral frequency ratio Ω, the beam‐to‐column stiffness ratio ρ, and the uncoupled, fundamental, lateral vibration period Ty1. It is concluded that the response contributions of the higher vibration modal pairs increase with increasing Ty1. and decreasing ρ. However, if Ty1. is in the accelerationor velocity‐controlled regions of the earthquake design spectrum, the first two vibration modal pairs are sufficient to estimate the response to a useful degree of accuracy; the fundamental vibration modal pair suffices if Ty1. is in the acceleration‐controlled region of the spectrum.

Design Method for Bridges on Lead‐Rubber Bearings

Abstract: This paper presents a design method based on a parametric study by Turkington (1987) of the response of bridge superstructures supported on lead-rubber bearings and subjected to the 1940 El Centro (N-S component) and Parkfield earthquakes. The study showed trends of both period shift and additional damping brought about by the inelastic behavior of the lead core in the lead-rubber bearings, although the two earthquakes introduce different amounts of period shift and additional damping. Two design examples of four-span bridges with different pier, abutment, and bearing arrangements are presented. The arrangements of lead-rubber and elastomeric bearings are used as examples to show how seismic forces can be distributed between piers and abutments.

Lateral-Torsional Coupling in Earthquake Response of Frame Buildings

Abstract: The earthquake response of torsionally coupled buildings is presented for a wide range of the system parameters. By comparing these responses with those of corresponding torsionally uncoupled syste...

The Application of Seismic Isolation to Bridges

Abstract: Unlike a building application the primary intent in a bridge is to protect the structure below the plane of isolation - the superstructure being relatively rigid to in-plane loads and of adequate strength to resist these loads. Bridges are particularly suitable for isolation and literature surveys indicate that more than 90% of the world's isolated structures are, in fact, bridge structures. Applications include both new construction and retrofit work. Implementation within the United States has only occurred within the last few years and then predominantly as a retrofit measure rather than in new construction. This activity is reviewed in this paper.

Recent research on repair and strengthening of reinforced concrete structures

Abstract: As part of the research effort organized following the 1985 Mexico City earthquake, a series of tests were conducted at the University of Texas at Austin to assess the performance of redesigned structures. Two techniques basic to many of the repair and strengthening schemes in Mexico City were studied. The objective of the program was to evaluate the procedures which appear to have particular applicability to U.S. practice. In this report, tests on structures or subassemblages redesigned using (a) infill walls to strengthen and stiffen non-ductile frames, and (b) jacketing of damaged or inadequate columns to improve strength, stiffness, or ductility are described.

Experimental Behavior of Dual Steel System

Abstract: A six-story eccentrically chevron-braced dual steel system (EBDS) was subjected to 24 earthquake ground motions with effective peak accelerations of up to 0.55\dg on the earthquake simulator at the University of California at Berkeley. The design, construction, dynamic characteristics and experimental behavior of this eccentrically braced system is discussed in this paper. The EBDS was analyzed for its compliance with current earthquake-resistant regulations that include the 1985 Uniform Building Code (UBC) 1984 Applied Technology Council (ATC) 3–06, and 1986 Structural Engineers Association of California (SEAOC). A substantial overstrength of this dual system with respect to its nominal yielding strength was observed and this is discussed in terms of the response modification factors currently adopted by the ATC and SEAOC. The lateral force distributions for the elastic level tests corresponded to the code-base design lateral force distributions but varied considerably for the collapse level tests. The role of the ductile moment-resisting space frame (DMRSF) in the EBDS is discussed in light of its performance during the testing program. Conclusions are drawn regarding the suitability of the EBDS for regions of high seismic risk and the response modification factors and lateral forces distributions currently used or implied in the UBC, ATC, and SEAOC.

Detection of Seismic Structural Damage

Abstract: Damage analysis models based on equivalent modal parameters are used to identify the serviceability limit state for structures subjected to earthquake loads. A model for the analysis of seismic structural damage consists of a number of numerical indicators (damage indices) and of a procedure for their computation. A structure exhibits a nonlinear behavior when it experiences an earthquake. Nonetheless a time variant equivalent linear structure can be defined. Damage indices can be defined from the vibrational parameters of the equivalent linear structure considered. It is shown that the problem of identification of the serviceability limit state is equivalent to the problem of detection of seismic structural damage. A limit state can be defined as a surface in the space of the damage indices relative to the model considered. Experiments on small-scale models are analyzed to obtain an analytical definition of the serviceability limit state. Additional aspects of the subject are discussed.

Concrete-face rockfill dam: i. assessment

Abstract: This is a discussion of a paper of this title by J.L. Sherrard published in the October 1987 (Vol. 113, No. 10) issue of this journal. The discussers focus attention on the importance of the statement: "Since the entire CFRD (concrete-faced rockfill dam) embankment is dry, earthquake shaking cannot cause pore pressures in the rockfill voids." The discussers proceed to expand on the significance of this statement. The absence of pore pressure is a major factor in accepting the CFRD to be inherently safe against strong earthquake shaking, and complex design theories (dynamic seismic analysis) are not needed for design. The basic concept of trying to keep structures in a "dry" state comparable to that existing in the embankments of the CFRDs is one of the most important concepts in the design of all civil engineering structures exposed to the intrusion of water. The discussion is followed by the author, J.B. Cooke's comments on dynamic seismic analyses, seismic loading and seismic design, and the zoning of rockfill for the CFRD.

Seismic Damageability Assessment of R/C Buildings in Eastern U.S.

Abstract: In the eastern United States, reinforced concrete building structures, medium- to high-rise construction, are usually designed for gravity loads only. A damage evaluation was done in this study for typical structures of medium height using inelastic dynamic analysis and artificially simulated earthquake motion. An empirical relation was developed to provide quick assessment for the expected damage in medium-high, reinforced concrete structures. The paper presents the methodology used for this evaluation, including the simulation of artificial ground motion from eastern United States data, and describes the major factors influencing damageability.

Shaking Table Tests of Pinned‐Base Steel Gable Frame

Abstract: In the United States, design of steel gable frames normally follows the guidelines prescribed by the American Institute of Steel Construction for assumed wind and gravity loadings. In this study, a pinned‐base steel gable frame structure composed of prismatic members is constructed, and the dynamic characteristics of that structure are investigated using the shaking table. The tests are carried well into the inelastic range so that ultimate lateral strength under seismic excitation can be quantified. It is observed that for such structures the response modification factor adopted by the Applied Technology Council (ATC) should be assumed with caution. In addition, the excessive elastic and inelastic story drifts, which are attributed to the pinned‐base condition, require careful evaluation to ensure structural safety against large sidesways. The excessive story drift is likely one of the major reasons for the severe nonstructural damage of steel gable frames during the 1985 Chile earthquake and the 1987 Ed...

Building Frames Subjected to 2D Earthquake Motion

Abstract: Inelastic response of a simplified model of a 10-storey building frame was analyzed to assess the effects of bi-directional seismic loading. Interaction between the strengths in the two orthogonal directions was accounted for.

Reply: Force reduction factors for the seismic provisions of the National Building Code of Canada

Abstract: A derivation of force reduction factors for the seismic provisions of the National Building Code of Canada (NBCC), 1985, is presented This includes the following: classification of seismic actions, applicable limit states, change in load factor, derivation of force reduction factors, and classification of structural configurations Quantitative comparisons are made between the derived force reduction factors and the response modification factors of the Applied Technology Council and good agreement was found It is suggested that seismic requirements should be considered as accidental actions with a load factor αQ = 10 These results can form the basis for possible modifications to the 1985 NBCC seismic provisions Key words: earthquake resistant structures, building code, loads, load factors

Experiments on active structural control under seismic loads

Abstract: Two control systems, an active tendon system and an active mass damper system are selected for study for possible real structural implementation. Presented in this paper are simulation results when these systems in simple configurations are applied to a scaled-down six-story frame building in the laboratory. These results show that a simple active control system can be effective in response control of complex structures under earthquake loads. Relative merits of the two active systems are compared together with a discussion of some general control requirements expected in performing the experiments.

Postearthquake Safety Evaluation of Buildings

Abstract: Procedures for the safety evaluation of buildings in earthquake damaged areas have been developed. Two evaluation techniques, Rapid Screening and Detailed Inspection, are described. Rapid Screening is used for the quick assessment of buildings in the damaged area and can be used by building inspectors and others familiar with building construction. Detailed Inspection is a more thorough evaluation technique and is intended to be used by structural engineers.

Simplified earthquake analysis of gated spillway monoliths of concrete gravity dams

Abstract: : The simplified procedure for earthquake analysis of concrete gravity dams developed earlier for nonoverflow monoliths is extended in this report to gated spillway monoliths. Standard data are presented for the vibration properties of such monoliths and for all parameters that are required in the analysis procedure. The use of the simplified analysis procedure and of a computer program that facilitates implementation of the procedure is illustrated by examples. Keywords: Concrete, Dams (gravity), Design, Dynamics, Earthquakes, Earthquake resistant structures, Foundation interaction, Hydrodynamic pressure, Spillway.

Study of the Seismic Behavior of Retrofitted Reinforced Concrete Buildings

Abstract: Over ten years experimental research in Japan on the seismic behavior of retrofitted reinforced concrete buildings is reviewed. Emphasis is put on the improved strength and/or ductility of frames and columns retrofitted with various construction techniques. The effectiveness of each technique is discussed based on existing test data. Analytical studies on the seismic behavior of an extensively retrofitted four-story building is also described.

Seismic Engineering : Research and Practice

Abstract: This volume of Seismic Engineering: Research and Practice contains papers from twenty-two sessions of the 1989 ASCE Structures Congress. These papers represent a wide-ranging interest in this field of seismic engineering. Papers were contributed not only by both ASCE's Structures and Engineering Mechanics Divisions; but, by the Structural Engineers Association of California; the International Structural Consultants Association; the Japan Structural Consultants Association; and by professionals in Taiwan. This variety of sources enable the coverage of a broad range of seismic engineering topics including: lessons learned from past earthquakes, evaluation and upgrade of existing structures, dynamic testing and monitoring of structures, design and analysis of special structures including bridges, dams, and liquid storage tanks and new approaches to earthquake-resistant design including base isolation.

Impact of earthquakes on cantilever retaining walls

Abstract: Cantilever retaining walls are required to retain earth at a change in ground elevation. As the nonseismic design of cantilever retaining walls is well discussed elsewhere, this paper deals mainly ...

Recent Developments in Testing Base Isolation Systems

Abstract: One of these developments has been the ability to test large scale isolation systems using simulated seismic loads. These tests have not only proven the performance and reliability of the isolation systems and hardware, but have enabled correlation studies to be undertaken which have confirmed the accuracy of analytical methods and the acceptability of current design procedures. Component tests on single isolators are described. Tests on plain and filled natural rubber bearings, lead-rubber bearings, sliding bearings and bearings incorporating uplift resistance mechanisms have been performed. High shear strain tests on large (up to full-scale) elastomeric bearings have been conducted to determine the stability characteristics and limit states of the isolators. Performance evaluation studies using the earthquake simulator to test large scale model isolated structures have been carried out for a variety of isolation systems and structures. Uplift studies of slender base isolated buildings and the investigation of the behavior of base isolated skew bridge decks have been studied. This paper aims to highlight those areas where progress has been made.

Dynamic Response Prediction for Earthquake Resistance Design of Bridge Structures

Abstract: Newly developed nonlinear analysis procedures for assessing the earthquake resistance of bridges have been incorporated into the computer program SEISAB (SEISmic Analysis of Bridges). The new version SEISAB-II, which includes the nonlinear capabilities, was developed under the sponsorship of the National Science Foundation as part of their earthquake hazard mitigation program. The analytical model to predict the complex interaction of abutments, pile and superstructure under longitudinal earthquake excitation is presented. Preliminary results based on a simple test structure indicated several advantages of allowing abutment backwall to fail. These include: period elongation and therefore reducing the earthquake loading, multiple pounding between abutment and deck is reduced significantly, and reduced ductility demand on the column. Additional aspects of the subject are discussed.

Seismic Response of Flexibly-Connected Steel Frames

Abstract: The response of typical low-rise steel building frames designed by the 'Type 2 Construction' method to moderate earthquakes is examined. Such frames are often identified by large girders, small columns, and semi-rigid connections. The simple methods underlying the Type 2 design approach do not permit realistic consideration of the frame response to either static or dynamic loads. In this paper, typical flexibly-connected Type 2 frames are analyzed for seismic resistance with the methods recommended by the 1988 Uniform Building Code. The results indicate that these Type 2 frames possess adequate strength, but may not have adequate lateral stiffness for moderate seismic loads.

Seismic Strengthening of a Historic Unreinforced Masonry Building

Abstract: The building involved is a four-story unreinforced masonry structure. Considerations related to development of design criteria are presented along with retrofitting strategies. The building was seismically upgraded using a combination of stotcrete and center-core drilling techniques for the walls. A variety of elements were utilized to form structural diaphragms at floor and roof levels.

Earthquake Resistant Design Using Friction Pendulum Connections

Abstract: The Friction Pendulum System (FPS) offers a simple approach for increasing a structure's earthquake resistance. The approach uses steel connections which absorb earthquake vibrations using small amplitude pendulum motions. The FPS connections can permit the building frames to resist severe seismic forces on an elastic strength basis, with only minimal impact on the construction cost. This paper discusses the design approach, FPS performance, an example design, and design details.