NATIONAL CENTER FOR EARTHQUAKEENGINEERING RESEARCH

State University of New York at Buffalo

Pi393~1?7512

Active Bracing System:A Full Scale Implementation of Active Control

by

A. M. Reinhorn, T. T. Soong, R. C. Lin and M. A. RileyDepartment of Civil Engineering

State University of New York at BuffaloBuffalo, New York 14260

Y. P. WangDepartment of Civil EngineeringChung-Hwa Polytechnic Institute

Hsin-ChuTaiwan

and

S. Aizawa and M. HigashinoTechnical Research Laboratory

Takenaka Corporation2-5-14 Minamisuna Koto-Ku

Tokyo 136Japan

Technical Report NCEER-92-0020

August 14, 1992

This research was conducted at the State University of New York at Buffalo, Chung-HwaPolytechnic Institute, and Takenaka Corp., and was partially supported by the

National Science Foundation under Grant No. BCS 90-25010 and the New York StateScience and Technology Foundation under Grant No. NEC-91029.

NOTICE

This report was prepared by the State University of New Yorkat Buffalo, Chung-Hwa Polytechnic Institute, and Takenaka Corp.as a result of research sponsored by the National Center forEarthquake Engineering Research (NCEER) through grants fromthe National Science Foundation, the New York State Scienceand Technology Foundation, and other sponsors. NeitherNCEER, associates of NCEER, its sponsors, the State Universityof New York at Buffa~o, Chung-Hwa Polytechnic Institute, andTakenaka Corp., nor any person acting on their behalf:

a. makes any warranty, express or implied, with respect to theuse of any information, apparatus, method, or processdisclosed in this report or that such use may not infringe uponprivately owned rights; or

b. assumes any liabilities of whatsoever kind with respect to theuse of, or the damage resulting from the use of, any informa­tion, apparatus, method or process disclosed in this report.

Any opinions, findings, and conclusions or recommendationsexpressed in this publication are those of the author(s) and donot necessarily reflect the views of the National Science Founda­tion, the New York State Science and Technology Foundation,or other sponsors.

II, a..,

III111 11--------

Active Bracing System:A Full Scale Implementation of Active Control

by

A.M. Reinhorn1, T.T. Soong2

, R.C. Lin3, M.A. Rilel,

Y.P. Wang5, S. Aizawa6 and M. Higashino7

August 14, 1992

Technical Report NCEER-92-0020

NCEER Project Numbers 89-2201, 90-2201 and 91-5121

NSF Master Contract Number BCS 90-25010and

NYSSTF Grant Number NEC-91029

1 Professor, Department of Civil Engineering, State University of New York at Buffalo2 Samuel P. Capen Professor, Department of Civil Engineering, State University of New York

at Buffalo3 Research Associate, Department of Civil Engineering, State University of New York at

Buffalo4 Graduate Research Assistant, Department of Civil Engineering, State University of New

York at Buffalo5 Associate Professor, Department of Civil Engineering, Chung-Hwa Polytechnic Institute,

Hsin-Chu, Taiwan, R.O.C.6 Senior Research Engineer, Technical Research Laboratory, Takenaka Corp., Tokyo, Japan7 Research Engineer, Technical Research Laboratory, Takenaka Corp., Tokyo, Japan

NATIONAL CENTER FOR EARTHQUAKE ENGINEERING RESEARCHState University of New York at BuffaloRed Jacket Quadrangle, Buffalo, NY 14261

..)/

PREFACE

The National Center for Earthquake Engineering Research (NCEER) was established to expandand disseminate knowledge about earthquakes, improve earthquake-resistant design, and imple­ment seismic hazard mitigation procedures to minimize loss of lives and property. The emphasisis on structures in the eastern and central United States and lifelines throughout the country thatare found in zones of low, moderate, and high seismicity.

NCEER's research and implementation plan in years six through ten (1991-1996) comprises fourinterlocked elements, as shown in the figure below. Element I, Basic Research, is carried out tosupport projects in the Applied Research area. Element II, Applied Research, is the major focusof work for years six through ten. Element III, Demonstration Projects, have been planned tosupport Applied Research projects, and will be either case studies or regional studies. ElementIV, Implementation, will result from activity in the four Applied Research projects, and fromDemonstration Projects.

ELEMENT IBASIC RESEARCH

• Seismic hazard andground motion

• Soils and geotechnicalengineering

• Structures and systems

• Risk and reliability

• Protective andintelligent systems

• Societal and economicstudies

ELEMENT IIAPPLIED RESEARCH

• The Building Project

• The NonstructuralComponents Project

• The lifelines Project

• The Bridge Project

ELEMENT IIIDEMONSTRATION PROJECTS

Case Studies• Active and hybrid control• Hospital and data processing

facilities• Short and medium span

bridges• Water supply systems in

Memphis and San FranciscoRegional Studies• New York City• Mississippi Valley• San Francisco Bay Area

ELEMENT IVIMPLEMENTATION

• ConferenceslWorkshops• EducationlTraining courses• Publications• Public Awareness

Research in the Building Project focuses on the evaluation and retrofit of buildings in regions ofmoderate seismicity. Emphasis is on lightly reinforced concrete buildings, steel semi-rigidframes, and masonry walls or infills. The research involves small- and medium-scale shake tabletests and full-scale component tests at several institutions. In a parallel effort, analytical modelsand computer programs are being developed to aid in the prediction of the response of thesebuildings to various types of ground motion.

iii

Two of the short-tenn products of the Building Project will be a monograph on the evaluation oflightly reinforced concrete buildings and a state-of-the-art report on unreinforced masonry.

The protective and intelligent systems program constitutes one of the important areas ofresearch in the Building Project. Current tasks include the following:

1. Evaluate the perfonnance of full-scale active bracing and active mass dampers already inplace in tenns of perfonnance, power requirements, maintenance, reliability and cost.

2. Compare passive and active control strategies in tenns of structural type, degree ofeffectiveness, cost and long-tenn reliability.

3. Perfonn fundamental studies of hybrid control.4. Develop and test hybrid control systems.

NCEER's research efforts in the active control area has led to the development of a full-scaleactive bracing system, which was installed in an experimental structure in Tokyo. This reportdescribes design, fabrication, and operational aspects of this system, together with its observedperformance under three actual earthquakes and other artificial loadings. We note that, whileseveral active mass dampers have been implemented in full-scale structures over the last fewyears, the active bracing system described here represents thefirstfull-scale active system of thistype developed and tested under actual ground motions. The experience gained through thedevelopment of this system can serve as an invaluable resource for the development of activestructural control systems in thefuture.

iv

ABSTRACT

An active bracing system has been designed, fabricated, and installed in a full-scale ded­

icated test structure for structural response control under seismic loads. This report

presents (i) a description ofthe constructed system, (ii) design specifications forthe control

system along with simulation studies for the design earthquake, and (iii) observed per­

formance of the system under three actual earthquakes and other artificial loadings.

Detailed design and analysis of the active system are carried out with respect to hardware

development, control force constraints, and power and energy requirements. It is shown

that a full-scale efficient active structural control system can be developed within limits of

current technology. Simulation results provide information on performance bounds that

can be expected of active systems in structural control under seismic loads and under

constraints imposed by practical considerations. Installation details of the system in the

building structure are presented along with the selections for fail-safe shutdown operations

in case of malfunctions. Also presented are the procedures for proper maintenance and

self testing which ensure continuous control with minimal resources. The observed per­

formance under artificial loadings and actual ground motions is compared with the esti­

mated analytical response. It is shown that the performance of the active bracing system

is predictable by simple analytical procedures and efficient within the design limitations.

v

ACKNOWLEDGEMENTS

This work is a product of a series of analytical and experimental research projects which

began in 1980, funded by the National Science Foundation. This continuing support is

gratefully acknowledged. The full-scale development phase was supported in part by the

National Center for Earthquake Engineering Research, Grant Nos. NCEER-89-2201,

NCEER-90-2201, and NCEER-91-5121.

Industrial participation and contributions were also important to the success of this research

effort. It is apleasure to acknowledge support received from the MTS Systems Corporation,

the Takenaka Corporation, and Kayaba Industry, Ltd.

Special acknowledgements are due to many engineers and technicians who assisted and

dedicatedly developed many components of the system. Among those it is a pleasure to

acknowledge the major assistance of Mr. Mark Pitman, Mr. Daniel Walsh,

Mr. Xiao-Qing Gao (SUNY/Buffalo), Mr. Niel Peterson (MTS Corp.), and Mr. Haniuda

(Kayaba Industries).

vii

Preceding page blank

TABLE OF CONTENTS

SECTION TITLE PAGE

1 INTRODUCTION 1-1

2 TEST STRUCTURE AND ACTIVE BRACING SYSTEM 2-1

2.1 Full-Scale Test Structure 2-12.2 Active Bracing System (ABS) 2-12.2.1 Braces 2-72.2.2 Hydraulic actuators 2-72.2.3 Hydraulic power supply 2-12

2.3 Analog/Digital Controller 2-152.4 Digital Microcomputer 2-152.5 Sensors 2-17

3 CONTROL ALGORITHM DEVELOPMENT 3-1

3.1 Basic Considerations 3-13.2 Velocity Feedback with Observer 3-43.3 Three-Velocity Feedback Control 3-103.4 Time Delay 3-12

4 DESIGN OF ACTIVE CONTROL 4-1

4.1 Design Earthquakes 4-14.2 Analysis and Design 4-14.2.1 Determination of weighting factor f3 4-14.2.2 Design of passive power resource 4-3

4.3 Verification 4-54.4 Power and Energy 4-5

5 EXPERIMENTAL STUDY 5-1

5.1 Control Algorithm 5-15.2 Automatic Control Operation 5-15.3 System Reliability and Maintenance 5-25.4 Control Software 5-3

6 SYSTEM PERFORMANCE 6-1

6.1 Identification of Dynamic Properties 6-16.2 Free and Forced Vibration Response 6-26.3 Response to Earthquakes 6-2

7 ANALYTICAL PREDICTION OF OBSERVED RESPONSE 7-1

ix

Preceding page blank

SECTION

8

9

10

TABLE OF CONTENTS (cont.)

TITLE

COMPARISON OF PERFORMANCES OF ABS AND AMD

CONCLUDING REMARKS

REFERENCES

APPENDiX I

x

PAGE

8-1

9-1

10-1

A-1

LIST OF FIGURES

FIGURE TITLE

1.1 Experimental Stages of Active Bracing Control

2.1 View of Building

2.2 Configuration of Active Bracing System (a) Side View; (b) Top View

2.3

2.4

2.5

2.6

2.7

2.8

2.9

2.10

2.11

2.12

2.13

2.14

3.1

3.2

Active Brace System

Details of First Story Active Braces

Block Diagram of Control System

Member of Active Brace

Joint Configuration of Active Brace

Actuator and Connected with Brace

A Set of Actuators with a Servovalve

Details of Control System for Active Bracing System

Manifold and Accumulators

Digital Microcomputer System

Servovelocity Seismometer

LVDT Installed Actuator

Control Parameters as Functions of ([3)

Structural Response Under 32% EI Centro Earthquake ([3 = 4)

xi

PAGE

1-2

2-2

2-3

2-4

2-5

2-6

2-8

2-9

2-10

2-11

2-13

2-14

2-16

2-18

2-19

3-7

3-8

LIST OF FIGURES (cant.)

FIGURE TITLE

3.3

4.1

5.1

6.1

6.2

6.3

6.4

Control Requirements Under 32% EI CentroI Earthquake (fj = 4)

Cumulative Oil Flow During 32% EI Centro Earthquake

Block Diagram of Control System Software

Typical Acceleration of AMD During Harmonic Loading Tests

Sixth Floor Response During Harmonic Loading Tests

Ground Accelerations During Earthquakes

Comparison of Controlled (Observed) vs. Uncontrolled (Estimated

Responses

PAGE

3-9

4-4

5-5

6-6

6-7

6-8

6-9

6.5 Acceleration Transfer Functions With and Without Active Braces 6-11

7.1 Comparison of Analytical and Observed Responses During Har- 7-2

monic Loading Tests

7.2 Comparison of Analytical and Observed Responses During April 14 7-3

Earthquake

8.1 Full-Scale AMD 8-2

8.2 Observation Results of AM D 8-3

8.3 Acceleration Transfer Functions With and Without Active Mass 8-4

Damper (From Aizawa et ai, 1990)

xii

UST OF TABLES

TABLE TITLE

3.1 Performance Comparisons with Different Control Algorithms

4.1 Design Earthquakes

4.2 Summary of Response Analysis Under Design Earthquakes

([3 = 4)

5.1 Control System Software

6.1 Uncontrolled Dynamic Properties of Structure

6.2 Characteristics of Harmonic Loading Tests

6.3 Peak and RMS Response During Earthquakes

8.1 Comparison of AMD and ASS

A1 Actual Earthquakes During the Operation Period of ASS

xiii

PAGE

3-11

4-2

4-6

5-6

6-2

6-4

6-5

8-1

A-1

SECTION 1

INTRODUCTION

The possible use of active control systems as a means of structural protection against

seismic loads has received considerable attention in recent years. It has now reached the

stage where active systems have been installed in full-scale structures (Soong 1990). The

focus of this report is on the development of an active bracing system and it's imple­

mentation to a full-scale dedicated test structure whose performance could be assessed

under actual ground motions.

Active control using structural braces and tendons has been one of the most studied control

mechanisms. Systems of this type generally consist of a set of prestressed tendons or

braces connected to a structure, their tensions being controlled by electrohydraulic ser­

vomechanisms. One of the reasons for favoring such a control mechanism has to do with

the fact that tendons and braces are already ~xisting members of many structures. Thus,

active bracing control can make use of existing structural members and thus minimize

extensive additions or modifications of an as-built structure. This is attractive, for example,

in the case of retrofitting or strengthening an existing structure.

Active tendon control has been studied analytically in connection with control of slender

structures, tall buildings, bridges and offshore structures. Early experiments involving the

use of tendons were performed on a series of small-scale structural models (Roorda 1980),

which included a simple cantilever beam, a king-post truss and a free-standing column

while control devices varied from tendon control with manual operation to tendon control

with seNo-controlied actuators.

More recently, a comprehensive experimental program was designed and carried out in

order to study the feasibility of active bracing control using a series of carefully calibrated

structural models. As Fig. 1.1 shows, the model structures increased in weight and

1-1

Stage 1:

Stage 2:

Stage 3:

Stage 4:

1DOF

2.84 tons

~

3DOF

2.84 tons

~

6DOF

19.1 tons

~

Full-Scale6DOF

600 tons

Fig. 1.1 Experimental Stages of Active Bracing Control

1-2

complexity as the experiments progressed from Stage 1 to Stage 3 so that more control

features could be incorporated into the experiments. At Stages 1and 2, the model structure

was a three-story steel frame modeling a shear building by the method of mass simulation.

At Stage 1, the top two floors were rigidly braced to simulate a single-degree-of-freedom

system. The model was mounted on a shaking table which supplied the external load and

the control force was transmitted to the structure through two sets of diagonal prestressed

tendons mounted on the side frames.

Results obtained from this series of experiments are reported in (Chung et al. 1988, Chung

et al. 1989). Several significant features of these experiments are noteworthy. First, they

were carefully designed in order that realistic structural control situations could be inves­

tigated. Efforts made towards this goal included making the model structure dynamically

similar to a real structure, working with a carefully calibrated model, using realistic base

excitation, and requiring more realistic control force. Secondly, these experiments per­

mitted a realistic comparison between analytical and experimental results, which made it

possible to perform extrapolation to real structural behavior. Furthermore, important

practical considerations such as time delay, robustness of control algorithms, modeling

errors and structure-control system interactions could be identified and realistically

assessed.

Experimental results show significant reduction of structural motion under the action of the

simple tendon system. In the single-degree-of-freedom system case, for example, a

reduction of over 50% of the first-floor maximum relative displacement could be achieved.

This is due to the fact that the control system was able to induce damping in the system

from a damping ratio of 1.24% in the uncontrolled case to 34.0% in the controlled case

(Chung et al. 1988).

1-3

As a further step in this direction, a substantially larger and heavier six-story model structure

was fabricated for Stage 3. It was also a welded space frame utilizing artificial mass sim­

ulation, weighing 19.1 metric tons and standing 5.5 m in height. In this series of experiments,

multiple tendon control was possible and the results again show that simple tendon

arrangements can produce significant motion reduction under simulated earthquake

excitations (Reinhorn et al. 1989).

Another added feature at this stage was the testing of a second control system, an active

mass damper, on the same model structure, thus allowing a performance comparison of

these two systems. Furthermore, control requirements and control efficiencies realized in

this series of experiments were extrapolated to the full-scale case, leading to a preliminary

design of the full-scale active bracing system for Stage 4. The feasibility of implementation

was analyzed, followed by the design and simulation study in order to assess its per­

formance capabilities when installed in an actual structure (Soong et al. 1991).

The active bracing system has since been fabricated, installed in a full-scale test structure,

tested using artificial excitations, and subjected to actual ground motions (Reinhorn et al.

1992). The objectives of the full-scale implementation are (i) to verify the complex

electronic-digital-servohydraulic system under actual strong motions, (ii) to verify the

capability of the system to operate or shutdown under prescribed conditions, and (iii) to

validate simplified analytical procedures used to predict actual system performance. This

report provides information on the detailed design and analyses of the full-scale active

bracing system. The performance of the system under simulated excitations and actual

ground motions is described and compared with predicted performances using simple

analytical procedures.

1-4

SECTiON 2

TEST STRUCTURE AND ACTIVE BRACING SYSTEM

2.1 Full-Scale Test Structure

A dedicated full-scale test structure was erected for performance verification of the active

bracing system under actual seismic ground motions. Located in Tokyo, Japan, the

structure is a symmetric two-bay six-story building as shown in Figs. 2.1 and 2.2. It was

constructed of rigidly connected steel frames of rectangular tube columns and W-shaped

beams with reinforced concrete slabs at each of the floors. Having rectangular columns,

the two orthogonal directions are not structurally identical. Weighing 600 metric tons, the

structure was designed as a relatively flexible structure with a fundamental period of 1.1 sec

in the strong direction and 1.5 sec in the weak direction, in order to simulate a typical

high-rise building. The structure was constructed without claddings exceptfor the top story

(sixth floor), which houses an experimental active mass damper (AMD) (Aizawa et ai, 1990).

Side access stairs were built without connection to the main structure to preserve the

symmetry of the system for sake of simplicity. Due to lack of cladding and the simple

connections, the structure has very low damping in the dominant modes (between 0.5%

and 1% of critical).

2.2 Active Bracing System (ASS)

As shown in Figs. 2.2 and 2.3, solid diagonal tube braces were attached at the first story

of the building after the main structure was constructed (see details in Fig. 2.4). The control

system enables longitudinal expansion and contraction of the braces by means of hydraulic

servocontrolled actuators, inserted between the brace elements and forming an internal

part of the bracing system. The control system includes also a hydraulic power supply, an

analog and digital controller, and analog sensors as shown schematically in Fig. 2.5.

2-1

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2-3

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2-6

2.2.1 Braces

The design of the braces was based on the maximum control force and the anticipated

stiffness with the assurance that buckling will not occur under actuator actions. The active

brace and the joint configuration are shown in Figs. 2.6 and 2.7. Circular steel tubes were

used as bracing members with the following specification: length = 360.5 em,

diameter = 165.2 mm, thickness = 4.5 mm, and strength = 564 kN. The measured

stiffness of the braces is 98.4 kN/mm in the x-direction and 73.8 kN/mm in the y-direction.

2.2.2 Hydraulic Actuators

Four units of Parker, heavy-duty hydraulic cylinder series 2H--style TC (NFPA style Mx2)

were selected as actuators with the following specifications: length = 735 mm, piston

diameter = 152.4 mm, rod diameter = 63.5 mm, stroke = ± 50 mm, and average

capacity = 344 kN. Figure 2.8, shows the manner in which the actuator is connected with

the brace. Although the expected movement in the actuators is only ± 12 mm, larger size

actuators were chosen to enable length corrections during construction. In future appli­

cations, a much shorter actuator would be sufficient.

The average capacity of the actuator is based on the working pressure [20.68 MPa

(3,000 psi)] of the hydraulic oil and the average piston area, Le., the average of the piston

area on one side and the same area minus the rod area on the opposite side of the piston.

The capacity can be improved by increasing the working pressure of the hydraulic oil.

Two hydraulic actuators are coupled in series in each direction and are monitored by one

servovalve, which is shown in Fig. 2.9, and one servovalve-controller of type

2-7

Reproduced frombest available copy.

Fig. 2.6 Member of Active Brace

2-8

Fig. 2.7 Joint Configuration of Active Brace

2-9

Fig. 2.8 Actuator and Connected with Brace

2-10

Reproduced frombest aveilable copy.

Fig. 2.9 A Set of Actuators with a Servovalve

2-11

MTS 458. The inner control loop for the hydraulic actuators is used for position feedback.

The servovalve MTS252.2x can supply up to 55 liter/min (15 gpm) at a pressure drop of

6.89 MPa (1000 psi).

2.2.3 Hydraulic power supply

The final design of the hydraulic system allows the active system to remain ready for full

power controlled operation, while requiring the hydraulic pump to operate for only a few

seconds each hour, to keep the system fully charged. As shown in the simplified block

diagram of the control system hardware (see Fig. 2.10), hydraulic accumulators, which are

shown in Fig. 2.11, are placed between the pump and a hydraulic manifold, and are kept

charged by the hydraulic pump. This stored power is used when the active control is first

started so that full hydraulic pressure is instantly available. The accumulators can supply

enough power to allow the hydraulic pump to reach full pressure operation, and can drive

the actuators for approximately one minute, longer than most major earthquakes, in the

event of a power failure.

The actuators use oil at pressures varying between 19 and 21 MPa (2700 - 3000 psi). The

hydraulic pump with a capacity of 120 liter/min (-30 gpm) operates between the upper

and lower pressure limits. The hydraulic power system was designed to operate almost

passively, i.e., the accumulator battery of 38 liters (10 gallons) is inserted in the line to

maintain continuous pressure and to supply the required oil for an event of up to 60 seconds.

The hydraulic manifold (an electrically controlled valve) opens the hydraulic system in case

of an event, while the accumulators supply the required oil. When the pressure on the

hydraulic lines drops below the lower operating pressure limit, the hydraulic pump starts

its operation to restore the pressure and charge the accumulators. According to this design

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2-14

it is expected to have the hydraulic pump operating only after (and not during) a seismic

event. The schematic of the hydraulic system is shown in Fig. 2.10 coupled to the necessary

controllers and actuators.

2.3 Analog/Digital Controller

An analog/digital controller was chosen based on the requirements that the analog con­

troller must be compatible with the hydraulic service manifold and with the servovalves, and

be capable of simultaneously controlling the two sets of servovalves. The controller is

capable of fully controlling the state of the hydraulic service manifold, and driving the ser­

vovalves; moreover, the controller has a series of fail-safe circuits designed to properly shut

down the entire system if any problems are detected. As built, the controller was designed

to allow a digital computer to monitor the status of the controller and the hydraulic system

linked to the controller, and to adjust some operating parameters of the system, including

triggering the fail-safe circuits. More detailed discussion of the fail-safe system is presented

in Section 5.3. To allow the computer to control all aspects of the system, afield modification

was made to the digital logic circuits of the controller, which allows the hydraulic system to

be remotely controlled through an external digital connection.

2.4 Digital Microcomputer

The microcomputer executes the control algorithm, monitors the status of operation of

various hydraulic components and monitors the status of the structural system. The

software algorithm is designed to start operation upon detection of an event or shutdown

in case of malfunctions. The system consists of a PC computer with an

INTELTM 80386/25 MHz processor equipped with an INTELTM 80387/25 MHz math­

coprocessor, which are shown in Fig. 2.12. Two analog-to-digital (A/D) and digital-to­

analog (D/ A) conversion boards provide interface for up to 16 channels of differential inputs

from sensors and four channels of analog outputs to controllers. In addition, 16

2-15

Fig. 2.12 Digital Microcomputer System

2-16

lSlTl digital logic channels are available on the computer boards. The analog channels

are used to interface with the sensors (conditioners) and with the analog servoloop. The

digital logic channels are used to monitor the state-of-the-controller and adjust its opera­

tions. An RGB monitor is connected to the system to enable visual monitoring of operations.

2.5 Sensors

The control system has four servovelocity seismometers of type Tokyo Sokushin VSE11,

which is shown in Fig. 2.13, for each principal direction of the building with an output range

of ±100 em/sec. The velocity sensors are located on the ground, at the first, at the third,

and at the sixth floors of the building. Same sensors can provide acceleration information

up to ± 1000 cm/sec2. Additional transducers are mounted at each floor to monitor

building behavior. Each actuator is equipped with a displacement transducer (lVDT) which

is shown in Fig. 2.14 having a range of ± 12 mm which is used to adjust the length of the

brace via the servovalve loop.

2-17

Fig. 2.13 Servovelocity Seismometer

2-18

Fig. 2.14 LVDT Installed on Actuator

2-19

SECTION 3

CONTROL ALGORITHM DEVELOPMENT

The control algorithms developed for the full-scale test were based on classical linear

optimal control laws previously discussed by Chung et al. (1988,1989) and Reinhorn et al.

(1989). However, unlike in the laboratory, the use of displacement measurements as

feedback state variables in conventional control design is not feasible in the field. Under

the constraintthat only three velocity sensors are available, two alternative control strategies

were developed. They are (1) velocity feedback with observer which provides full­

dimensional state feedback with the aid of a state-estimator and (2) three-velocity feedback

which treats the full-state as an equivalent reduced-order system. These control algorithms

are described below following a brief summary of the classical linear optimal control theory.

3.1 Basic Considerations

The classical linear optimal closed-loop control algorithm which is the basis of the control

design is reviewed herein. The equation of motion of a discrete-parameter structure, under

earthquake excitation x 0 (t) and active control force which is expressed in terms of

actuator displacement u (t) ,is described in the state-space representation as:

z(t)

where

A z Ct) + b u(t) + w xoCt) (1)

lx(t)J [ 0z(t) = -. , A = _ M -I K- x(t) - __

3-1

where z (t) is the state vector of order 2 n consisting of vectors x (t) and x (t)

which are the relative displacement and relative velocity vectors of order n, respectively,

n being the number of degrees offreedom (DOF) of the structure (n = 6 in the present

case); u(t) is the actuator displacement that characterizes the control force. Matrices

M ,C and K are the mass, damping and stiffness matrices, respectively, which- d

can be estimated through identification tests. Vector b is the control force location- I

vector of order n, whose elements are 2 k c cos a for the corresponding floor where

the active braces are attached and zero otherwise, k c being the stiffness of the active

brace and a the brace inclination angle from the horizontal; w is a vector of order- I

with all elements equal to - 1, ,indicating the contribution of the ground acceleration.

Based on the classical quadratic performance criterion, u (t) is found by minimizing the

integral:

(3)

for the duration t f of ground excitation. In Eq. (3), Q is a positive semi-definite

weighting matrix for the response and r is a positive weighting factor for the control.

In the present case, matrix Q is chosen to be:

3-2

Q [~ ~J (4)

so that the first term in Eq. (3) characterizes the potential energy of the structure, and

(5)

such that the second term in Eq. (3) characterizes the contra! energy. r? is a control

parameter which determines the relative importance between safety and economy;

r? = 00 represents the uncontrolled case. It is noted from the above derivation that r?

is the only parameter that needs to be specified in the control design.

Under linear feedback control, u (t) is obtained to be linearly related to the state vector

z (t) as (Sage 1977, Chung et al. 1988,1989):

u(t) = G z(t) r-1bTPz(t) (6)

where G is the feedback gain of order 2 nand P is obtained from the approximated

time invariant Ricatti matrix question:

PA + ATp - Pbr-1bTp + Q o (7)

It can be seen from the above that information of all state variables, i.e., displacements and

velocities, is required in order to calculate the feedback control force. This requirement,

however, is impractical in field applications either because all the state variables are not

3-3

accessible for direct measurement or because the available sensing devices are limited.

In the present full-scale structural test, only three velocity sensors are provided in each of

the principle directions which necessitates modifications.

3.2 Velocity Feedback with Observer

Suppose the state variables of a dynamic system are not fully accessible. In order to apply

the state feedback strategy, a state observer can be used if the system is completely

observable (Chen 1984).

Consider a dynamical system whose state equation is given by Eq. (1) and the associated

output or observation equation is expressed as:

yet) C z (t) (8)

where y (t) is the observed vector of order m (m ::; 2 n) and C is the m x 2 n

measurement matrix. Assuming that z(t) is an estimator of z (t) , then the state

observer equation can be written as (Chen 1984, Soong 1989):

z(t) (9)

where L is the 2 n x m observer matrix.

Let z (t) , be the error between the actual state vector z (t) , and the estimated state

vector z(t), i.e:

3-4

z (t) z(t) -z(t) (10)

Substituting Eqs. (1) and (9) into Eq. (10), one obtains:

z (t) ( 1 1)

It is seen from Eq. (11) that, if the observer matrix L is properly selected so that the

eigenvalues of matrix (1 - ~ ~ )have negative real parts smaller than - (J, then all

elements of the error vector z (t) will die out at rates faster than e -at. Consequently,

even if there is large error between z(t 0) and z (t 0) at initial time to' the vector

z(t ) will approach z (t) rapidly.- -

Once the full-dimensional state vector is established, the state feedback control can be

accomplished by substituting the observed state z(t) forthe real state z (t) in Eq. (6),

giving:

I T -u(t) = -,- b Pz(t) (12)

In an effort to reduce on-line computation, an approximation is introduced in solving Eq. (11)

by using finite differences. Equation (9) then becomes a difference equation in the

discrete-time form:

3-5

L~ty(t)] ( 13)

It is noted that, in order to predict the state vector at time instant t, , the knowledge of

ground acceleration x 0 at time t and the estimated state vector at the previous time

step are required along with the available output measurements. As a consequence, an

increase in on-line computation is inevitable with a potential increase in time delay, which

is critical in real time control.

In the present study, two velocity transducers located at the first and third floors are selected

for output measurements of the system. To illustrate the effectiveness of the proposed

control algorithm, a series of numerical simulations were performed with various [3 values

using the 32% EI Centro earthquake as input. The observer matrix is L determined in a

way that the poles of matrix (1 - ~ ~ )are assigned to be three times of those of matrix

A so that the error term will diminish rapidly. The correlation between the control force

requirement with the weighting factor [3 is shown in Fig. 3.1 (a), where the associated

control efficiency in terms of reductions in maximum structural relative displacement,

maximum absolute acceleration and maximum base shear is given in Fig. 3.1 (b). It is seen

that, as expected, the smaller the [3 value, the better the performance. The case of

[3 = 4 is determined for the design of ASS as will be explained in the next section. As

an illustration, time histories of the top floor response and base shear corresponding to

[3 = 4 are shown in Fig. 3.2. The associated control force requirement is shown in

Fig. 3.3(a).

3-6

321684l3

210-+--­

0.5

1200(a)

1000

~ 800-.....;..

~

~<:';) 600~......<::>;...~- 400=--~

\..,)

200

60'",--~,-------------------,

(b)

50

10

0,+---0.5 1 2 4

138 16 32

_ Relative Dis. _ Absolute Acc. _ Base Shear

Fig. 3.1 Control Parameters as Functions of ( f3 )

3-7

~V [t. - . _.n~ J p

. . .. _ .. -iIJ ~

'"V

~

~

o0.4-r----------------~

0.3-;::--~_ 0.2-c~ 0.1

1~ 0.0+4·

~ -O.lj~ -0.2]

-0.31

~.4' Io 1 2 3 4 5 6 7 8 9 10 11 12 13 14 151200..,....------------------.

-800

-120 1+-,'~:--;,r_r___;_.---r,---r,--;-,---;,---:.----:----:.--'''-.,---1

o 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15TIME (sec)

- Uncontrolled. -- Controlled

Fig. 3.2 Structural Response under 32% EI Centro Earthquake ( f?>

3-8

4)

uvv

6(a)

~ 4~

~ 2~c~-e -200~-....c

-400U

-600

-8000 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

25.(b)

20.

5.0

0.00 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

(c)

1;' 6.0-c§ 5.0~E. 4.0

~ 3.0~

~ 2.0

1.0

0.0 0 1 2· 3 4 5 6 7 8 9 10 11 12 13 14 15TIME (sec)

Fig. 3.3 Control Requirements under 32% EI Centro Earthquake ( ~ 4)

3-9

3.3 Three-Velocity Feedback Control

Since three velocity sensors are available at the first, third and sixth floors, an alternate

control design is one using direct three-velocity feedback. In this development, the full-order

system is first reduced to a 3-DOF system and the mode shapes of the reduced order

system are constructed from the first three modes of the frequency response functions of

relevant floors. It is noted that orthogonality between the mode shapes does not hold here

because a part of the modal displacement information has been discarded. A mode

smoothing procedure to improve the modal orthogonality is therefore conducted for a more

comprehensive dynamic analysis whereby the masses are redistributed to three nodal

points and the equivalent stiffness and damping matrices are derived, respectively, by pre­

and post-multiplying the diagonal generalized stiffness and damping matrices by the inverse

modal matrix. Accordingly, the natural frequencies of the reduced order system are close

to the first three modes of the full-order system.

The control design is now developed using velocity information only. The effectiveness

of this strategy is confirmed by simulation. The difference between the control efficiency

of using both displacement and velocity feedback and that of using velocity feedback alone

is insignificant as can be seen in the last two columns ofTable 3.1. However, it is interesting

to see that less control force is required in the velocity feedback case but more power is

required.

Control requirements and structural performance using different control strategies are also

compared in Table 3.1. While the control algorithm with observer gives the best result as

expected, its implementation requires more on-line computation time, as mentioned earlier,

implying greater increase in time delay and reduction in control efficiency.

3-10

Table 3.1 Performance Comparisons with Different Control Algorithms

Full-state Velocity

Control Algorithm uncontrolled Observer Feedback Feedback

Control Based on Based on

3DOF 3DOF

Top fl. ReI. Disp.

Maximun (em) 7.9769 4.6673 5.0406 5.0480

Reduction (%) 41.5 36.8 36.7

Top fl. Abs. Ace.

Maximun (g's) 0.3678 0.2340 0.2555 0.2576

Reduction (%) 36.4 30.5 30.0

Base Shear

Maximun (leN) 1019.7 606.6 632.7 650.3

Reduction (%) 40.5 38.0 36.2

Control Force (kN) 629.1 565.5 563.4

Power Requirement 20.47 24.1 28.8

(kW)

3-11

3.4 Time Delay

In real time control, time delay is contributed mostly by signal processing, on-line com­

putation, and control execution using the hydraulic system. These time delays accumulated

in the control loop can cause deterioration of control performance or even system instability

if they are not properly compensated (Soong 1990).

Time delay can be determined from the phase lag measured between the signal input and

signal output for a given system component. In an identification test, the phase lag angle

is determined from the imaginary and real parts of the input and output frequency transfer

functions. The delay time for each component of the system is in turn determined by:

T =d

e3601

(14 )

where T d is the time delay in seconds, e is the phase lag in degrees and 1 is the

frequency in Hertz.

A preliminary assessment of time delay of the hydraulic actuators used in this test was

carried out in the laboratory. Using banded white noise as input, the delay time between

the command signal and the achieved actuator response was estimated to be about

12 msec. The required on-line computation time was also estimated in a similar manner

to be about 14 msec for the observer control algorithm and 5 msec for the three-velocity

feedback algorithm.

Among various time delay compensation methods, phase compensation that was first

discussed by Roorda (1980) and verified effective in laboratory experiments (Chung et al.

1988, McGreevy et al. 1988 and Chung et al. 1989) is one of the most attractive strategies.

This method is adopted in the present stUdy as briefly described below.

3-12

If the displacement feedback force lags the displacement by L x in time while velocity

feedback force lags the velocity by Lx,their corresponding phase lags for the i-th mode

are Wi L x and Wi Lx' With the phase shift, the displacement feedback force may be

resolved to produce positive active stiffness and negative active damping while the velocity

feedback force may be resolved to produce positive active stiffness and positive active

damping. Due to the existence of negative active damping, control effects are diminished

for the real system as compared to the ideal one. Even worse, time delaywill cause instability

if the resultant damping force is negative. Since phase lag is proportional to the delay time

and modal frequency, the effect of time delay can become serious for higher modes even

with small amounts of time delay.

The control force contributed by the i-th mode can be expressed as (Chung et al. 1989):

ui(t) = -9Ii11i(t) - g2i~i(t) = -9'li11i(t - Lx)

-g'2i~i(t - Lx) (15)

where g' I i and g' 2i are the modified displacement and velocity feedback gains,

respectively, with time delay compensation. The modified feedback gain factors are

determined so that the same control effect can be achieved.

Due to phase shift, the displacement feedback forces contributed by the mode can be

resolved into (g' Ii cos W i Lx) 11 i as a displacement component and

(-g' lisinwiLx)~JWi as a velocity component. Similarly, the displacement and

velocity components of the velocity feedback force contributed by the i-th mode are,

respectively, (g' 2isinwiLx)wi11i and (g' 2iCOSWiLx)~i' In order to make the real

system equivalent to the ideal one, the relationship between feedback gains for the real

3-13

system and those for the ideal system can be established such that both systems have

the same active stiffness and active damping. Thus, the modified feedback gains are

obtained as :

- (1 /Wi)SinWi'tX]-1

coswi't x(16 )

For multi-degree-of-freedom systems, the control gain correction due to time delay as

indicated in Eq. (16) can be applied to each mode in the modal domain and transformed

into the physical domain through modal transformation. More detailed derivation can be

found in (Reinhorn and Soong et al. 1989).

3-14

SECTION 4

DESIGN OF ACTIVE CONTROL

4.1 Design Earthquakes

For design purposes, the peak velocity of the design earthquakes was taken to be

10 em/sec based on local seismic records over the past seven years

(maximum = 9.5 em/sec). Accordingly, the scaled (32%) EI Centro earthquake with

98 cm/sec2 (0.1 g) peak acceleration was determined as the design earthquake which

corresponds to the criterion of 10 em/ sec maximum velocity. Response analyses were also

carried out using a series of recorded earthquake time histories to verify the adequacy of

the design specifications. Table 4.1 tabulates the earthquakes considered in the verification

of the control system with their maximum accelerations scaled to 0.1 g.

4.2 Analysis and Design

4.2.1 Determination of weighting factor f3.

A series of numerical simulations with different f3 values have been presented in the

preceding section. While the best reduction in displacement was observed in the case of

f3 = 0.5 , f3 = 4 was used for control system design from the practical standpoint since

it gave satisfactory structural performance (approximately 40% reduction) while requiring

reasonable amount of control force (665 kN), just within the capacity of the selected

actuators. The associated maximum actuator displacement and velocity are (± )0.5 em

and 6.6 em/sec, respectively, also within the performance limitation of the specified device.

The following analysis for design of the power resource is based on this f3 value.

4-1

Table 4.1 Design Earthquakes

Earthquakes Component Scale Duration Sampling

factor (sec) time (sec)

E1 Centro NS 0.32 20 0.02

Hachinohe NS 0.60 20 0.01

Miyagioki. 0.68 30 0.01

Taft N21E 0.715 20 0.02

Mexico N90W 0.65 100 0.02

Mexico SOOE 1.115 100 0.02

Pacomia Dam S16E 0.095 20 0.02

PacomiaDam S74W 0.104 20 0.02

Tokyo 1.48 10 0.02

4-2

4.2.2 Design of passive power resource.

The required flow rate q(t) of the hydraulic cylinders can be determined approximately

in terms of the piston area A p and the actuator velocity u(t) as:

(17)

in which u(t) is calculated based on the selected f3 value and the assumed brace

stiffness.

Equation (17) is a first-order approximation in which compressibility of the hydraulic fluid

and leakage around the valve and piston are neglected, which is adequate only when the

load reaction is small. In general, maximum values are the criteria of design specification.

The design capacity of the flow rate, however, is not based on the extreme value; it is rather

determined in accordance with the average flow rate from an economic point of view. The

servo-controlled system pumps the hydraulic oil with a constant speed during the control

action. The difference of the oil flow between the required and the supplied is then adjusted

through the hydraulic accumulators.

Figure 4.1 illustrates the cumulative flow accumulated during an earthquake, which is

obtained by integrating the time history of the flow rate. The slope of this curve represents

the instantaneous flow rate required to achieve the control goal. It is observed from

interpreting the slope of the curve that system demand is the highest between 2 and 5

seconds and less so over the rest of the time history, a property apparently resulted from

the nonstationary nature of the earthquake motion and the control effect contributed in the

previous time period. The linear curve represents the cumulative volume of a constant flow

which is obtained by minimizing the difference between the demand and supply

4-3

0.70...-----------------------.,

'2 0.60

0,.....-.4,.....-.4 0.50cjb1)

'--'~ 0.40eM0

4--1a 0.30 Size of AccumulatorQ)

S 0.20~~

0

>- 0.10

0.00 -t",'---~___r-.,____r--,.,-_,.______r-_:_I --,.--____r-...-~I---.---,.-_l

o 2 3 4 5 6 7 8 9 10 11 12 13 14 15

TIME (sec)

Fig. 4.1 Cumulative Oil Flow During 32% EI Centro Earthquake

4-4

of oil using the least-square criterion. The largest difference between the cumulative flow

and the average flow indicates the minimum volume of the hydraulic accumulator to be

considered in design.

A summary of simulated results under representative earthquakes is given in Table 4.2.

The ABS design specifications are determined accordingly.

4.3 Verification

From the analytical data shown in Table 4.2, it was found that the design was appropriate

for almost all earthquake records used except for the case of Hachinohe earthquake. In

that case, it requires a maximum control force of 696.5 kN which is far beyond the design

capacity of the system if the same control strategy is to be used. Investigation was made

by restricting the output control force within the design capacity of the actuator while using

the same feedback gains. Results show less reduction of structural response (about 30%

in displacement and 47% otherwise) when the control force is restricted to 333 kN per

actuator whereas stability of the mechanical system is preserved.

This situation should also be taken into account in the on-line control practice due to erratic

nature of earthquake ground motions.

4.4 Power and Energy

In order to generate the required control forces, large power supply may be required to

effectively activate the actuators. Power requirement, p (t) , of the hydraulic system can

be evaluated in terms of the control force F (t), and actuator velocity zl (t) as:

pet) = F(t)zl(t)

Energy consumption, E (t) , can be obtained from:

4-5

(18)

~ I 0>

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Figures 6(b) and 6(c) illustrate the time histories of power and energy resources required

under the 32% EI Centro earthquake.

4-7

SECTION 5

EXPERIMENTAL STUDY

5.1 Control Algorithm

As discussed in Sections 3.1 through 3.3, the three-velocity feedback control algorithm is

the simplest of those available based on the sensor configuration. It is, thus, used in the

experimental study discussed in this section.

Using the three velocity feedback control, the movement of the actuators which provide

the control force is calculated by:

u)(Ct) = G~ xCt) and

in which u)( and u yare the actuators displacements, G)( and Gyare control gain

vectors, and x and yare vectors of sensed velocities in the x - and y - directions,

respectively.

The uncompensated feedback gains used in this case are 0.02166,0.01031 and 0.00595

for the first, third and sixth floor velocities in the x- direction, respectively. The gains in the

y-direction are 0.02476,0.01400 and 0.00706.

The implementation of this algorithm in real-time requires adjustment of gains to enable

quick integer operations. The program is compiled to execute modules that allow for a

computational cycle of 4.2 msec.

5.2 Automatic Control Operation

As discussed in Sec. 2.2.3, the hydraulic power for the full-scale active bracing system

needs to be continuously available, yet, unlike in a laboratory, it is not practical to have the

hydraulic system operating constantly. Consequently, the system had to be designed so

that the hydraulic system remains in a ready, but dormant, state, with the control software

5-1

capable of bringing the system to full operation. In addition, the hydraulic system had to

be capable of almost instantly supplying full power to the active braces, and keeping the

braces supplied with power for the duration of the event, even if the hydraulic pump loses

power. To accomplish this, the control software monitors the status ofthe control hardware,

and adjusts the state as necessary. These requirements are met by subroutines added in

the control program, which monitors system status, starts or stops the control operations.

5.3 System Reliability and Maintenance

While occasional minor glitches in operation of a control system may be acceptable in a

laboratory, any problems or errors in the full-scale control system, operating without

continuous human guidance and monitoring, have the potential to cause damage or cat­

astrophic failure. To properly protect the system and the structure from damage in the

event of a full or partial failure of the control system, fail-safes were added to both the

hardware and the software.

The long-term maintenance of the system poses an additional series of challenges. If strict

tolerances are not met, the continuous wear can lead to degradation in the system per­

formance, and even to failure. The standard maintenance must include manual inspection

and verification of the system components on a regular bases.

As a safety feature, the computer can latch the servovalve commands, such that the

actuators are held in a rest position. When the latching command is sent to the controller,

all external servovalve commands are immediately disabled, and the actuators are adjusted

from their current position to the rest position. During rapid adjustment to the rest position,

the actuator displacement decays exponentially, such that neither the structure nor the

control system is stressed by the adjustment, and so that the natural frequencies of the

structure are not excited. This latching circuit is designed to be activated either by an

external signal from the computer, or by the fail-safe circuitry of the controller.

5-2

To improve safety and reliability ofthe entire system, an external electrical circuit was added

to the system's fail-safe chain. This circuit is directly connected to the controller, the

hydraulic pump, the control computer, and the top floor velocity transducers. The circuit

monitors both the signals from the velocity transducers and an analog signal from the

control computer. If the velocity signals exceed a preset limit or if the computer sends a

large signal, the circuit will trigger the fail-safe interlocks of both the controller and the

hydraulic pump. The connection to the hydraulic pump is a redundant safety feature, since

when the controller's interlock circuit is triggered, the controller will automatically trigger

the pump's interlock circuit.

5.4 Control Software

The design and development of the control software for the full-scale active bracing system

posed a variety of challenges. The control program is required to monitor the system and

the structure, start and stop the control system operation, and intelligently handle any

problems that might occur; moreover, the software must be able to handle these tasks

reliably for a long period of time. In addition, the software must be able to perform these

tasks efficiently; while the operating speed is not critical during the routine monitoring and

maintenance operations, the program must operate extremely fast during the actual control

operation. The major features ofthe control software are shown in ablock diagram (Fig. 5.1)

outlined in Table 5.1. A detailed description is given below.

(a) Normal Operation. During normal operation the control software deals with three

operations, Le., "stand-by," "control," and "shut-down."

(i) During the "stand-by" operation the control program monitors both the status of the

control system and the motion of the structure. The controller is continually moni­

tored for system interlocks and problems with the hydraulic system, both of which

could either reduce the effectiveness of, or prevent altogether, any active control

5-3

operation. All of the instruments are constantly monitored for zero drift; any offsets

in the zero position of the instruments' signals are removed, first when the program

is started and then on a regular basis during the normal operation. The base and

top floor instruments are monitored for seismic and wind induced motions,

respectively, and the active control system is started ifa significant motion is detected.

An averaging technique is used to minimize the possibility that signal noise will

unnecessarily trigger the control.

(ii) "Control" starts when a seismic ground motion or high wind is detected, the control

program first turns on the hydraulic power and releases the servovalve command

latch, before beginning the controlled operation. During the controlled operation,

the program uses the signals from the instruments to calculate control signals

according to the previously detailed control algorithms. The program checks both

the control signal and the top floor velocity, to see that neither exceeds preset limits.

If the control signal exceeds the limit, the output is clipped at the limit level.

(iii) If the top floor velocity exceeds the limit, the software performs an emergency

"shutdown." In addition, the program monitors the controller for any problems. If a

problem is detected in the system, the program will either attempt to correct the

problem, if possible, or will perform an emergency shutdown of the system. When

the motions of both the ground and the structure have returned to reasonable levels,

the program will latch the servovalve command, turn off the hydraulic power, and

return to the normal waiting state until the next event is detected.

(b) System Self-Maintenance. Besides the normal operating routines, the control pro­

gram contains several routines for testing and verifying the integrity of the system. A self

excitation test is used to verify that the control system is working properly, and to check

the efficiency of the control. A self identification test is used for verifying the natural

5-4

NO

RM

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ER

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are

Table 5.1 Control System Software

Module / )urpose Notes(1 (2)

Normal operations

Monitor ground and individual floor velocitiesAdjust instrument offsetsStart / stop control The software can identify signal noise to

• Turn hydraulic power. on / off eliminate false starts.• Release /Iock servovalve commands

Generate control signalSee system/software reliabilityMonitor system status

System maintenanceSelf excitation testSelf identification testEmerqency stop test

System / software reliability

Servovalve command locked when control is off Command locked at zeroTraps and properly handles software errors Critical errors cause an emergency stopMonitor status of computer hardware Uses intelligent error handlingMonitor status of digital controller (Monitor Uses intelligent error handling

hydraulics and electronics through controller)Monitor top floor velocity Large velocity causes emergency stopIntelligent error handling

• Recovery from certain non-critical errors• System protected from some operator errors• Excessive errors trigger emergency stop

Emergency stop Actuators are smoothly returned to the• Redundant interlock triggers resting positions, such that the natural fre

Digital si~nal to controller quencies of the structure are not excited.Analog signal to remote relay/trigger

• Servovalve command instantly locked• Hydraulic power stopped• Control siqnal "ramped" to zero ,

5-6

frequencies of the structure and comparing the uncontrolled response of the structure to

the controlled response from the self excitation test. A third test is used to verify that the

emergency stop procedures and the fail-safe systems are working properly.

(c) Safety and Reliability. To protect the integrity of the control system, the software

contains many features designed to improve safety and reliability. As a general safety

feature, the servovalve command is kept latched, with the actuators in the rest positions,

whenever the program is not running either the control or a test routine. In addition, the

control is started automatically daily to prevent stick of the sensitive servovalves. Besides

extensive debugging and beta testing, the software is programmed so that a defect in the

program code or the occurrence of an unpreventable software error during operation will

not cause an outright failure of the program. Instead, when such an error is detected, the

program will trap the error and attempt an emergency shutdown of the system. Finally, the

program extensively monitors the status of the system hardware. The software constantly

checks the computer's data acquisition boards for any problems. The program can clear

most of the data acquisition board errors; however, if an excessive number of errors occur,

or if an error cannot be cleared, the program will perform an emergency shutdown. The

software monitors the status of the controller in a similar way, and monitors the top floor

velocity as mentioned above.

When the control program detects a problem anywhere in the system hardware or software,

it will determine if the error is critical or not. If the error can be identified as a non-critical

error, an attempt is made to correct the problem. If the program is unable to correct the

error, or if an excessive number of correctable errors occur, the system is immediately

halted through an emergency shutdown. The emergency stop sequence consists of

sending two redundant interlock triggers; a digital signal to the controller, and an analog

signal to the external fail-safe circuit. The servovalve command is latched, and the hydraulic

5-7

power stopped. As an added redundant safety feature, the program will return the analog

control signal to zero through an exponential decay similar to the seNovalve command

latch.

5-8

SECTION 6

SYSTEM PERFORMANCE

The building structure was subjected to a series of excitations to identify its dynamic

properties and to verify the performance of individual components as well as of the overall

system. Forthe identification studies, the structure was monitored during ambientvibrations

created by heavy traffic and during self excitation tests. Free vibrations and forced vibrations

were generated using the 6 mton AMD located at the top of the test structure operated in

reverse action of its usual function. Note that the presence of the AMD in the same test

structure allows also a performance comparison with the active bracing system as further

explained. The "actual test" ofthe system was observed during three strong ground motions

that occurred on April 10, April 14, and May 11, 1992. The three earthquakes of magnitude

4.95.0, and 5.6 (respectively) had peak accelerations of approximately 10 cm/sec2 (ap­

proximately 1% of gravity).

6.1 Identification of Dynamic Properties

The dynamic properties of the uncontrolled system are determined from frequency

response functions obtained from ambient vibration tests or sweep tests produced with

the bracing system. The dynamic properties, listed in Table 6.1, did not change during the

observation period of 20 months except for small variations within the measurement

accuracies. It is interesting to note the lower damping ratios in the y-direction as compared

with the ratios in the x-direction. It should be remembered that the x-direction is reflecting

the strong axis of the columns and that connections are different in both directions. The

mode shapes were orthonormalized for the computation of the control gain coefficients.

The difference between the orthonormalized and the unmodified

6-1

Table 6.1 uncontrolled Dynamic Properties of Structure

(...) Values In parantheses could not be precisely venfled due to excessive nOise.

Direction Mode I II 1\1 IV V VI(1 ) (2) (3) (4) (5) (6) (7) (8) (9)

Frequency Hz 0.98 2.88 4.93 7.18 9.79 13.23Damping % 1.00/< 2.00/< 4.00/< 8.00/< (>10%) (>10%)

6 0.0264 -0.0248 0.0181 -0.0130 -0.0019 0.00015 0.0224 -0.0030 -0.0204 0.0287 0.0003 0.0006

X Modal 4 0.0185 0.0163 -0.0176 -0.0252 0.0130 -0.0051Shapes 3 0.0125 0.0230 0.0104 ··()'oOOO -0.0264 0.0161

2 0.0069 0.0170 0.0212 0.0119 0.0102 -0.02671 0.0022 0.0063 0.0117 0.0063 0.0279 0.0274

Participation 50.82 19.94 13.40 4.97 13.20 7.09Factors

Frequency 0.69 1.91 3.18 4.39 5.81 8.30Damping 0.5% 0.30/< 0.70/< 1.50/< (>15%) (>15%)

6 0.0268 -0.0234 0.0210 0.0065 0.0001 -0.00045 0.0230 -0.0040 -0.0275 0.0196 -0.0077 0.0029

Y Modal 4 0.0183 0.0187 -0.0088 -0.0196 0.0227 -0.0097Shapes 3 0.0114 0.0229 0.0085 -0.0095 -0.0262 0.0158

2 0.0063 0.0171 0.0190 0.0265 0.0030 -0.01861 0.0018 0.0043 0.0068 0.0122 0.0219 0.0325

Participation 50.01 20.34 10.88 20.42 7.90 12.84Factors ..

6-2

normal modes is almost negligible in the lower four modes and more substantial in the

higher two. However, this difference is less important in these higher modes since natural

damping in these modes is relatively high.

6.2 Free and Forced Vibration Response

The AMD was activated in both directions using harmonic excitations that produced

vibrations in the building. Free vibration observations were obtained from measurements

of the structural response made after abruptly stopping the mass damper movement.

Typical excitations ofthe AMD are shown in Fig. 6.1. The responses ofthe sixth floor shown

in Fig. 6.2 indicate large increases in damping, more pronounced in the decay in the

y-direction, and a successful brake in the buildup in the resonant response

[Fig. 6.2(e) and (f)]. The performance of the structure, summarized in Table 6.2, shows a

substantial increase in the equivalent damping ratio [Col.(?) and (8)] and a substantial

reduction of the resonant amplitude [Col. (5) and (6)]. Control results from nonresonant

forced vibrations indicated good amplitude reductions in all affected modes.

6.3 Response to Earthquakes

The structures response was recorded while the control system was automatically activated

during the earthquake episodes mentioned earlier. The ground motion was simultaneously

recorded (as shown in Fig. 6.3) and is used with an analytical model to estimate the probable

response of the structure in the uncontrolled mode. The analytical model was carefully

calibrated prior to its use for earthquake response estimates by comparing the structural

response in various tests with the ones computed (Aizawa et a11990, Wang, et aI1992).

Some typical response histories of the sixth floor are shown in Fig. 6.4 for the controlled

(observed) and the uncontrolled (estimated) cases. The peak response and the RMS are

tabulated in Table 6.3 for the sixth floor and for the base of the structure.

6-3

Table 6.2 Characteristics of Harmonic Loading Tests

Response Maximum EquivalentVibration Control Frequency Velocity DampingSource Status (Hz) (em/sec) (%)

X Y X Y X Y(1 ) (2) (3) (4) (5) (6) (7) (8)

Free Vibrations OFF 0.98 0.68 6.26 5.64 1.04 0.55ON 0.98 0.68 6.86 6.86 3.34 3.47

Resonant OFF 0.95 0.70 (12.78) (23.42) 1.04 0.55Force Vibrations ON 0.95 0.70 3.98 3.84 3.34 3.47

OFF 0.80 0.80 2.57 2.57 1.04 0.55Nonresonant ON 0.80 0.80 1.22 1.71 3.34 3.47

Force Vibrations OFF 2.00 2.00 0.63 2.53 1.04 0.55ON 2.00 2.00 0.52 0.89 3.34 3.47

() Estimated values (actual values exceed allowable In structure)

6-4

Tab

le6.

3P

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and

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SR

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(1)

(2)

(3)

(4)

(5)

(6)

(7)

(8)

(9)

(10)

(11

)(1

2)(1

3)(1

4)

(a)

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61

1.3

615

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330

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15.6

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17.8

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716

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7

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/sec

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ase

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67.

368.

938.

937.

577.

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11.7

79.

249.

249.

949.

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741.

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551.

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ocity

30.

600.

730.

751.

151.

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261.

150.

961.

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(em

/sec

)1

0.54

0.61

0.87

0.92

0.29

n/a

0.42

0.81

0.48

0.69

0.30

n/a

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e0.

230.

230.

370.

370.

64n

/a0.

740.

740.

490.

490.

62n

/a6

1.0

01.

511.

451.

973.

676.

071.

701.

701.

962.

443.

454.

70

Dis

plac

emen

t3

0.50

0.82

0.86

1.05

2.26

2.96

1.00

1.10

1.15

1.28

1.83

2.23

(mm

)B

ase

0.30

0.30

0.40

0.40

0.94

0.94

0.78

0.78

0.55

0.55

0.79

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1.79

%

(b)

RM

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spon

se

61.

893

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2.28

3.51

3.75

.6.

791.

974.

671.

914.

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465.

68

Acc

eler

atio

n3

3.1

72.

663.

513.

012.

865.

372.

964.

573.

525.

133.

225.

37

(em

/sec

/sec

)B

ase

1.04

1.04

1.30

1.30

1.28

1.28

1.02

1.02

1.11

1.11

1.17

1.17

60

.19

n/a

0.26

n/a

0.53

n/a

0.20

n/a

0.25

n/a

0.55

n/a

Vel

ocity

30.

12n

/a1.

44n

/a0.

27n

/a0.

16n

/a0.

17n

/a0.

30n

/a

(em

/sec

)1

0.11

n/a

0.15

n/a

0.05

n/a

0.10

n/a

0.10

n/a

0.06

n/a

Bas

e0.

04n

/a0.

06n

/a0.

10n

/a0.

05n

/a0.

06n

/a0.

11n

/a

60

.29

0.77

0.42

0.69

0.85

1.62

0.33

1.08

0.46

0.86

1.09

1.31

Dis

plac

emen

t3

0.15

0.36

0.21

0.33

0.43

0.77

0.25

0.52

0.26

0.41

0.51

0.62

(mm

)B

ase

0.11

0.11

0.12

0.12

0.18

0.18

0.06

0.06

0.08

0.08

0.17

0.17

Co

ntr

ol

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17.2

21.7

39.1

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29%

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%0.

65%

0.27

%0.

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0.77

%

o· .

(b)200 Ivl' . . IL::J \ ! ! FOR~ V1BRATlO~ TESTS I

:: ::::::::::::::::1:::::::::::::'::1:::::'::::':::::1:::'::::::::::::j"::::::::::::::r:::::::":::"::ro i .1 L j ..

2510 15 20TIME (seconds)

5

-50 ~ ,. '" ..·r·· ..

::: :::r=j::j::::[:::t:-2OOf---;.---+---+-----i----i----l

o2510 15 20TIME (seconds)

5

Fig. 6.1 Typical Acceleration of AMD During Harmonic Loading Tests

6-6

(a)

2510 15 20TIME (seconds)

5

(b)8rr=,--,--,...,---;===========n[] . !! I UNCONTROLLEO FREE VIBRATIONS I

:-:=:t:'r!:~:r::r=::g i :!"? 2······ '.: ' ' .

i -:~... :I·-ll_I- .• ·:·_.·· .. ·.•·.• ·.• ·-~ i:: i

-4 ···..··· ··..1· I· .. i· , ~ .: I : ; !

~--i---~rWpI--I----B+---;---~;----;----;r---;-----l

o2510 15 20TIME (seconds)

5

8~

-2 . .

-4 ················1.······· . . .....; .... ········j················t················: : :

~ ················1············ ··n·StDP······I················t················-8

o

(c)8rr=::;-----,--,-----,==========jl~: I I ~NTROLLE~ FREE VlB~nONs I

" :~_T······r-r=:I:::l:-:I:... .... ..·-~;~~~r:g -2 . i ·············T··············r···············

~ -4 .. f ... . 1.. 1... 1. .

:-\ .....,:m}swp-l-+-o 5 10 15 20 25 3J

TIME (seconds)

(d)

8li~r=y=1-:.'-'-:'i-"I==CO=NTR==OLLE==O=FR=E=E=VI=S=RA=TI=O=N=S:=:::jl

6 .~ ;..- -.._. ~ ················t················i················i-··· .: I : : !

··....l················l················~······ ..········1 ! ~

'1: ::! l

-4 !: ~.:, ····i··..··..········i············ t········ ····: : :

: ················!·············Pf·StDp·..·\················t················

o 5 10 15 20 25 3JTIME (seconds)

25

(f)

10 15 20TIME (seconds)

5

8 ~! ! I CO~OLLEO F~RCEO VlB~noNS I

-B+---'!---ri __-i~ +-1-_-i1__--J

o2510 15 20TIME (seconds)

5

.. .-4 ·········:······\················t················,················,················t················

~ ················j················i················!················j················t················~ ~ ~ ! ;-8+---;----;----;----;----;------l

o

(e)

Fig. 6.2 Sixth Floor Response During Harmonic Loading Tests

6-7

-- --0 0Q) Q)(f)

~-0 0Q) Q)

~ ~E E0 0-- .........Z Z0 0

~ ~a: a:w w-' -'W W0 00 0oct: -15 oct: -15

0 5 10 15 20 25 30 35 40 0 5 10 15 20 25 30 35 40TIME (sec) TIME (sec)

5 10 15 20

TIME (sec)25 35 40

zo~a:w-'woo< -15

0 5 10 15 20 25 30 35 40

TIME (sec)

40353015 20 25

TIME (sec)

(f)

105

fl-lmIJM~Y 1:. 1~921: i ~ : : : :: : : : : : :·,t--- ..: -.- :- - -:--- ~---.: -:- ; .: . ; j 1 1 j

; . : : ~zo~ .....IT: r··· ~ r·········T·········-;--·········T·········-;--··········w-' iii i ~ ! !W -1 ....•.••..+ -+ + + + + + .~ -15 I I I I I I I

o403530

(e)

15 20 25

TIME (sec)105

o

. . . .--_.: ;- __ -:- _-..; ,! ----..: : ! : !~ i ; i ~

-10 ( ( --t- --t- -t-- -t-- --!- .

1 i ~ 1 j ~ 1~ ; ; 1 ~ ~ ~

-15+--;----ir----;---+---;---+---;---1o

o 15 : : : : : : :

~ 10 .~I ./.mm L L.lM~Y 1 ~ J 1~921.~ i I Iii I iE :: i : : ! :.: "r· t·· , ·-···········r·········r·········-r··········

..2- :; ~ ;!:zo~a:w-'woo<

Fig. 6.3 Ground Accelerations During Earthquakes

6-8

2.8-rr=========,.--,,.-----,-----,-----,----,----,----r=:'c=i.6thR.OOR

I 1.

I :i :'8

'1.

02­02-e+----+------:1~0------:1:i:8----±20:------::!I!ll=------;3Ot-----,38±-------40J

Tt.CE(....

(b)2.8-r-;=========;--:------:-----,-------,,.-----,...----,---,....~,.-,

31dFLOOA2.

10

2.8-nr----::'~~:-'-....,---,;----,...----,-------;----:----,--r==::="11

-1.

(d)

-1.

10 20Tt.CE(....

30 38

Fig. 6.4 Comparison of Controlled (Observed) vs. Uncontrolled (Estimated) Responses

6-9

The peak responses are generally reduced in the x-direction, but are less affected in the

y-direction. The RMS responses are, however, reduced in all cases which indicate an

overall reduction of vibration amplitudes throughout the motion.

The reason for small or no reduction of peaks in the y-oirection is the inability of the control

algorithm used to reduce substantially the first amplitude, which is the largest. Alternative

control algorithms can handle this problem. It should be noted also, that the RMS is more

indicative of the energy transferred into the structure, and therefore energy reductions

obtained with active control are substantial.

The transfer functions of the structural response with respect to the excitation input are

indicative of the change of dynamic properties during control as shown in Fig. 6.5. The

controlled response has lower peaks and wider distributions around the peak, indicating

damping increase. The active bracing system produces a somewhat uniform reduction of

modal responses as indicated in the transfer functions in Fig. 6.5. The controlled peaks

are somewhat shifted from the uncontrolled ones, although the control algorithm used is

supposed to affect only the damping and not the stiffness. This shift is likely due to the

imperfect compensation of time delay, which creates "leaks" in the stiffness components

and, therefore, the frequency shifts.

6-10

(c)

3~3

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ces

SECTION 7

ANALYTICAL PREDICTION OF OBSERVED RESPONSE

The analytical model was calibrated based on initial observations during the identification

studies. Two models were used: (i) A discrete model based on modal time analysis (Soong

et a11991) and (ii) an approximated continuous model (Wang et aI1992). Both models

produced similar results for the simulations used for the design of the bracing system. The

approximated continuous model was used to predict the uncontrolled and the controlled

responses of the sixth floor of the structure during the nonresonant forced vibration tests

as shown in Fig. 7.1. Some discrepancies occur at the beginning of the motion presented.

These discrepancies are due to the transient response, which appears in the analysis, while

the observed structural response was recorded during the steady state.

The actual earthquake response was predicted using the time step analysis and the

identified properties of the system. The control forces were estimated using the uncom­

pensated gains. The analysis was performed using the recorded acceleration time histories

shown in Fig. 6.3. Thetime histories ofthe analytical and observed responses are compared

in Fig. 7.2 for the April 14th earthquake. The differences in the maximum peaks are less

than 10%, while the RMS differences are less than 2%. Considering inherent imperfections

in the structural system, the analytical predictions seem to be adequate for interpreting the

structural response and for designing new systems.

7-1

(a)

I OBSERVED (UNCONffiOLLED) I: !~..··..··r:·:·r:::J:··:::::r:::I::::::r::::::r::::::r::::::r::::::

ru,.. t i"

• •.j. •••••••••,. .i. ••••••••.j.••••••••J .i. l ..;. .! iii i i ~ ~ ~........+·•.·····~········4· ..·····..4..·....··-J.·..-·..·.;.· ..··•••..} .••••.••.." .•••..•..;.•.••...•! i ~ ~ i ~ ~ ~!

~i+--{--j1bo--:\16~--,20±-----;211t--------::!3O;:---±36;---4O±:-----;4i;;-6-;!5O

TP.E lMOOnd<l

(c)

••••••••.j. .j.••••••••l -i. •••.••••.;.•••••••• -1.••• --- •• ..}••••.•••..;.._-•.•.•.;..•••••••

.........L .l .l L l. l. .1 .1 1. .! ! ! ! l ! ! ! !

~i+--+--1+,0--1+,6---:20b---:211i::------:3Oi::-------::i36::--,;4O=---j.6=----:l5O

TW:E lMOOndol

(e)

(g)

OBSERVED (CONffiOLLED)

.........;. .;. .;. .; .;. .;. .;. .;. .;. .

.......J L l l. .l l. 1..u J 1. .! ~ ! l ~ ! ~ ! !

~1-I--+--1:i:0---,1:i:6---:20b---:211'=----:3O'=---:!315i:---j4O=---i.5----:l5O

Tt.AE1~

(0)

~1I1J,...,....,..S_IM_U..,..LA_TE.....,.D.;.(U_N..,C"..O_NT_R..,..O_l.L.E......,.D;..).......,,..lI ~ L.~

r"U--ll-IIHtlHM1 ·i.· tT)r+ 1-

-2- .. J ..;. J j J .;. .;. J .

.~ ········1········1········1········1········t········t········t········t·········f········~/l 10 15 20 2'l 30 35 40 .5 50

lIVE lMO<Xld4

(d)

••••••••4. ••••••••..;. 4. 4. -1. 4.•..••.•• .;. 4. .;. .

~ ~ ~ i ~ i ! ! !·3 ·········j.···..····y·····....·~ ..·..····..-}········~··· ..···4······.. ·4·..···.···$0·········$0··..·····! ~ ~! ~ ~ ~!!

~+---r--1*=0--:1*=5---:l!Ob---:211b----:3Ob----:35i::-----:4Oi:---.i:-6--J5OThIE (MO<Xld4

(f)

II SIMULATED (UNCONTROLLED) I i j.:J

I~ .:1'i~T· jl;~~1~.+tl.~;'. m:

;-2- ••••••••••••••..;. ..;. ..;. ..;. ..;. ..;. ..;.•••••••• ..;. .

.~ ········t········t········t········t········t········t········t········t·········I········• 10 16 l!O ... :io 35 40 40 50

ThIE(~

(h)

I:... :~~~j(:::=)11~j:=tf~ ·1 . . . . .::

: : : ! i i ! f !

: ::::::::r::::::r::::::l::::::::r::::::r::::::r::::::l::::::::r::::::l::::::::

Fig. 7.1 Comparison of Analytical and Observed Responses During Harmonic

Loading Tests

7-2

(a)

20TME(""'l

(b)

" ..1 3 rd FLOOR 1..·......·....···...·+...··...····.......·..+·····...·····...····..·1····.....·····...··...··I··Q:=J··..:::::::::::::::::::::::r::::::::::::::::::::::r:::::::::::::::::::::r:::::::::::::::::::::r:::::::::::::::::::::r:Q6.$.iB~P.:::::::::::::::::::::r::::::::::::::::::::::... "'."'.'" "r .. .. . 1<1: ··················:······················..r······ , .,. -r- .

10 15 30 40

403020nv:E(M4

1510

"!i-rr====+=='~====='3=====t:----,-------;----...,.------;--.====Jl

E.s~ 1.

Zw:2: 0.W

~9> ,1.

(5

(d)"~r==============;-------,--------:----:-----,r==:=:====j-,

I " :}::::::::::::::::::::[:::~~:;:~~~~::::::::::::::::::::::}::::::::::::::::::::::I:::::::::::::::::::::::t~~~~~~~:::::::::::::::::::::t:!:::::~::::::~:::~ 1........•.......... ; .•...••......•....~•....••..•......•..••.1 1 f··.· l i .

~ . "' "..' '..: ·:1 . ;..: -+ ~ + + + .::s : : : : : : :9> ::: ::::::::::::::::::::··:r:::::::::::::::::::::r:::::::::::::::::::::r:::::::::::::::::::::r::::::::::::::::::::::f.NA.~Y.TI:G.8F::::::::::::::::::::r::::::::::::::::::::::(5 ." ························t························t························~························f········ [ [ ············r························

: : : : : : :10 15 30 40

Fig. 7.2 Comparison of Analytical and Observed Responses During April 14 Earthquake

7-3

SECTION 8

COMPARISON OF PERFORMANCES OF ABS AND AMD

As a active control devise, an Active Mass Damper system (AMD) has been installed on

the top floor of the same test building with ASS (Fig. 2.1) to compare their performances.

The top view of the AMD system is shown in Fig. 8.1. A complete description of the AMD

system and some observed results are given by Aizawa, S., et al. (1990). In the AMD

system, a six-ton moving mass is suspended (T=3.1secs) so that it can respond instan­

taneously. The structural response can be controlled in two directions by the two elec­

trohydraulic servo actuators, which are installed along orthogonal directions.

While both systems were installed in the same building, the structural control is performed

by only one at a time. The control effect of the AMD system was examined during the

lzu-Oshima earthquake on October 14,1989 and on February 20,1990. The observation

results are shown in Fig. 8.2. The structural response in the frequency domain is shown

in Fig. 8.3.

Summarizing the observation results for both control systems, a rough performance

comparison of AMD and ASS is shown in Table 8.1.

Table 8.1· Comparison of AMD and ASS

AMD ABS

Average Reduction of Peak Displacement 56% 29%

Structural Response Acceleration 22% 26%

Maximum Actuator Movement (em) 10.51 0.194

8-1

Fig. 8.1 Full-Scale AMD

8-2

6F DISP (UNCONTROLLED) - ANA. MAX - - 0.98

SF ACC (UNCONTROLLED) - ANA. MAX - 35.26

6F DISP (UNCONTROLLED) - ANA. MAX - 0.69

- AN";' MAX - - 0.29- OBS. MAX - 0.40

.....,iolliJII,iA\I\lyM~rt/'"..~I"'li/\!I'~/ ...~W~"rJ.'i!"fVi~

GF ACC (UNCONTROLLED) - ANA.. MAX - 29.69

6F DlSP (CONTROLLED)

CM1.

ol---""",,..,...,..-'tMl\fJ\fVVlI!Wf/V'>'~W~:I+i'-.Af\.¥J\AJl-1.0

CM1.~ •

_1.~L---"""·'''''·v"''"'''t~'''·'-'J·'IJ~'r''''''''''t'''1'''A.''.''''''''-'''''';''''-'''''''''''"" 1"','/'0."' .

GAL

-:rrGAL 6F Ace (CONTROLLED) - OB$. t,lAX - 21.19

_:1----.Jo,,/.it....."'~'tI"'IIIW,'ill~ll11ii~'t/'~',~!••~t.lr-'jf'o.I,.., ....,.,.boJ,o',...".........;-..., ....."'.......,.............,.",...._..-

cM1.0

o!---J.M''''INif.'v'.--'''MVNNWN.wJi-1.0

CM 6F DISP (CONTROLLED) - ANA. MAX -- 0.27

1'~[ -""'''''''~'¥\''''''''JY''''''''''''''''''Y''''''''~~''''''_-''''~~rv~....::,."....~",AX...."~""0_.3~0__...,,,,.......

-1.0

GAL50

OI----f!l!wMNy.,..~~MfflWMWNN'M'fM''f'HI'wWNf- 50

GAL 6F ACC (CONTROLLED) - OBS. MAX - - 35.56

5X--ff:<rl:,'irN~I'Jt~.,r.!/'o"'" ~-5~[

70

MAX~-7.10

·tJ,~¥IY~'Ir~Y - direction'

, I ,

TIME (SEC)o

GAL BASE ACC ·a9.10.1~. -OBS.

~~~~I!lf'''''''''''''I 'f,fi'rl fJ ,11111 i ..-8

• I

70

_ OBS. MAX - 13.39

TIME (SEC)o

I~AL BA~E ACC '69.10.14.

_1~~'lflfV.'''/J.~j,j,Jr\,ft'i~II'I,...I>t''''~\'I''''''~'WoI''fll'I~~I'-'"'-~''''d''''ir-e-c''''''ti'''~'''''n'''''''', I

- ANA. MAX - - 13.n- OBS. MAX - - 15.89

x - directionI I

70nME (SEC)

6F ACC (UNCONTROLLED) -ANA. MAX--41,67

o

GAL5

O~-"h¥J'NMfN(-JWMWM~WMFNH~w.--.~f'/W'IW- 50

GAL SF ACC (CONTROLLED) - ANA. MAX - - 17.84_:1----·"i,'V\/ l"''''''Y'''....~-..ofo......"'...'f'(.~.........,.,.------.......",-........"'"

GAL SF ACC (CONTROLLED) - 085. MAX - - 35.39

,-_........,..~.,~'f*Jw.y. ~1'.'t~-WN ..tJ.~ "....,-5~[

;"L BASE ACC '90. 2.20. - oas. MAX - - 7.11S

O~IJAJ1A1JJJu.l~,.I!I,.Il>J,. ,I ••• 1\~ ... J...... rw_8~~T·,'1'rrrW'·l 'I ;'i'n 'X' :::d~-;~ti~n

I I I , I I I I

70

6F DISP (CONTROLLED) - ANA. MAX - - 0.39_ oas. MAX - - 0.44

SF DISP (UNCONTROLLED) - ANA. MAX - 1.05CM1.

ol----wI/IrwtI'fN/WM~w{fWWWN'N/'>t'-wv-"""""\N'MN'/V-1.5

eM

I.~o -----w'Yo +.'~."A"'''''•.- '''''.''''' _--- ,.. ,.....~ ..-1.S

CM CYLINDER STROKE - ANA. MAX - 9.04

1S

t. . - OBS. MAX - 10.51

o _"""---I~A~~~'!'rM~ --lia ..A~-IS 'I~' -r ~

Fig,8.2 Observation Results of AMD

8-3

......

.....

'89.

10,1

0.--

'89.

10.1

4.-

'90

.2.2

0'8

9.10

.10.--

'89.

10.1

4.-

'90

.2.2

0

50Iiii

iiiI

IX~

dir~

citi

~~i110

0Iiii

iiiI

Iy~

dir~

cti~

~iI

ol;.

L£h:

:D%J

f~¥~

1.0

10.0

FRE

QU

EN

CY

(Hz)

lru~

o'-'

-C:~~

1.0

10.0

FR

EQ

UE

NC

Y(H

z)

ex>

i ~

w Cl

::;) too :J 0.. :E «

:' :~ :i I j ! I

:

w Cl

::;) too :J 0.. :E «

II fI I,

~ i\

Fig.

8.3

Acc

eler

atio

nT

rans

fer

Fun

ctio

nsW

ithan

dW

ithou

tA

ctiv

eM

ass

Dam

per

(Fro

m

Aiz

awa

etai

,19

90)

Note that the AMD system has a better reduction of displacement response and a lesser

reduction of accelerations. This implies a more comfortable response using the ASS and

lesser base shear

using the AMD. The maximum actuator movement is an indicator of the required input

energy. It is very large for the AMD system and is quite small for the ASS indicating sub­

stantially less energy needed by the ASS. Comparing the response transfer functions

shown in Fig. 6.5 and Fig. 8.3, it is noted that the AMD reduces the structural response

substantially in the first and second modes in the y-direction and only in the first mode in

the x-direction (Fig. 8.3). The ASS system reduces the structural response in all modes,

as can be observed in Fig. 6.5. The main reasons of this behavior are (i) the ASS has better

ability to redistribute earthquake energy in higher modes and suppress their influence, as

noted also by Yang (1982) and (ii) the AMD constructed in this building was designed to

suppress only the lower modes. A change in the control algorithm can produce even better,

performance in the higher modes for the ASS.

8-5

SECTION 9

CONCLUDING REMARKS

The design, installation, and operational characteristics of a full-scale ABS for earthquake

resistance of a building have been presented in this report. The control algorithms were

developed based on the classic optimal closed-loop control theory. As required by sensor

limitations, two modified control algorithms were used. They are (1) velocity feedback with

observer, and (2) three-velocity feedback. Both alternatives have been proven to be

effective through numerical verification.

Based on the recognition that it is more efficient to control a structure by applying a force

rather than a moment, (Yang et al. 1978, Reinhorn et al. 1989), horizontal control forces

were applied to the first floor through the action of diagonal active braces. While it is

conceivable that extra column axial forces are introduced by the vertical component of the

bracing forces when the control system is activated, the P - 6. effect, which is a problem

in structures with large deformations, be less pronounced since the braces are connected

to the first floor where the displacement is relatively small.

While several active mass dampers have been implemented in full-scale structures over

the last few years, the active bracing system reported here represents the first full-scale

active system of this type developed and tested under actual ground motions. The results

presented in this report demonstrate that:

(a) The concept of an active tendon or bracing system, originated almost 20 years ago,

has led to the successful development of the device for civil engineering structural

control.

9-1

(b) The success of the full-scale ASS performance is the culmination of numerous ana­

lytical studies and carefully planned laboratory experiments involving model struc­

tures.

(c) The ASS can be implemented with existing technology under practical constraints

such as power requirements and under stringent demand of reliability.

(d) The use of ASS in existing structures can be a practical solution for retrofit as dem­

onstrated by this full-scale experiment. Note that the active braces were added only

after the structure was completed.

(e) The full-scale ASS performs, by and large, as expected, and its performance can be

adequately predicted through simplified analytical and simulation procedures.

(f) The experience gained through the development of this system can serve as an

invaluable resource for the development of active structural control systems in the

future.

9-2

SECTION 10

REFERENCES

Aizawa, S., Hayamizu, Y., Higashino, M., Soga, Y., Yamamoto, M., and Haniuda, N. (1990).

"Experimental Study of Dual Axis Active Mass Damper." Proceedings of the U.S. National

Workshop on Structural Control Research, (Housner, G.W. and Masri, S.F., eds), University

of Southern California, Los Angeles, 68-72.

Chen, C.T. (1984) Linear System Theory and Design, Holt, Rinehart and Winston, NY.

Chung, L.L., Lin, R.e., Soong, T.T. and Reinhorn,A.M. (1988), "Experimental Study of Active

Control of MDOF Structures Under Seismic Excitations," Report NCEER-88-0025, National

Center for Earthquake Engineering Research, Buffalo, NY.

Chung, L.L., Lin, R.C., Soong, T.T. and Reinhorn, AM. (1989), "Experimental Study ofActive

Control for MDOF Seismic Structures," ASCE J. Engr. Mech. Div., Vol. 115, No.8,

pp.1609-1627.

Chung, L.L., Reinhorn, AM. and Soong, T.T.(1988), "Experiments on Active Control of

Seismic Structures," ASCE J. Engr. Mech. Div., Vol. 114, No.2, pp. 241-256.

Clough, R.W. and Penzien, J. (1975), Dynamics of Structures, McGraw-Hili, NY.

McGreevy, S., Soong, T.T. and Reinhorn, AM. (1988), "An Experimental Study of Time

Delay Compensation in Active Structural Control," Proceedings of 6th International Modal

Analysis Conference and Exhibits, Vol. I, pp. 733-739, Orlando, FL.

Reinhorn, AM. and Soong T.T., et al. (1989), "1:4 Scale Model Studies of Active Tendon

Systems and Active Mass Dampers for Aseismic Protection," Report NCEER-89-0026,

National Center for Earthquake Engineering Research, Buffalo, NY.

10-1

Reinhorn, A.M., Soong, T.T., Riley, M.A., Lin, R.C., Aizawa, S., and Higashino, M., (1992).

"Full Scale Implementation of Active Control - Part II: Installation and Performance,"

ASCE!J. of Structural Engineering, (in print).

Roorda, J. (1980), "Experiments in Feedback Control of Structures, in Structural Control,

H.H.E. Leipholz (ed.), North Holland, Amsterdam, pp. 629-661.

Soong, TT. (1990), Active Structural Control: Theory andPractice, Longman, London and

Wiley, NY.

Soong, TT, Reinhorn, A.M., Wang, Y.P. and Lin, R.C. (1991). "Full Scale Implementation

of Active Control- Part I: Design and Simulation," ASCE/Journal of Structural Engineering,

ASCE, Vol. 117, No.11, 3516-3536.

Wang, Y.P., Reinhorn, A.M. and Soong, T.T. (1992). "Development of Design Spectra for

Actively Controlled Wall Frame Buildings," ASCEjJournal of Engineering Mechanics,

ASCE, Vol. 118 No.6, 1201-1220.

Yang, J.N. (1982). "Control of Tall Buildings Under Earthquake Excitations," ASCE/Journal

of Engineering Mechanics Division, 18 No.1, 50-68.

Yang, J.N. and Giannopoulos, F. (1978), "Active Tendon Control of Structures,"

ASCEjJournal of Engineering Mechanics Division., Vol. 104, No. EM3, pp. 551-568.

10-2

APPENDIX I

EARTHQUAKE OBSERVATIONS - - TIME HISTORIES

OF OBSERVED MOTIONS AND ESTIMATED RESPONSES

Table A1 provided the description of the three earthquakes that considered in this report.

This is followed by the display of a more complete set of the structural response time histories

(observed and simulated) related to this earthquakes.

Table A1 - Actual Earthquakes During the Operation Period of ASS

Time of Occurrence Epicenter Location Depth (KM) Magnitude

April 10, 1992 North latitude 35" 14'/ 89 4.9

(23:31) East longitude 139' 38'

April 14, 1992 North latitude 3E> 10'/ 62 5.0

(12:03) East longitude 139' 50'

May 11,1992 North latitude 3E> 32'/ 56 5.6

(19:07) East longitude 14<Y 32'

A-1

1. Earthquake on April 10, 1992:

1) Response of 6th Floor in X-Direction

TIME (SEC)o 10 20 30 40 50I I I i I I I I I iii I I I I I I I I I I I Iii I I I I I I I I iii I I i I Iii I I I I i I

0.2 CM 6F Dis X Controlled CObs.) MAX.= 0.105 CM (9.9505ECl

Of , .• A V' A" 0 AAA "~" " AAAAA". 'cr • • • A A Y' AA A A An A A.,[ - ~"V 0 'VV V "i[V ~VV vl(J VVW¥lflTvVl) VVv\lv V4;J OJUV' ITQ\}V • vv\jITV\I.

-0.20'o2~CM 6F Dis X Uncontrolled (Ana.) MRX.= 0.152 CM (l!7.9405ECl

_ • AAAAV dAAA ~~!V:"~A rn AA ""'4" AAd AA~AMlAAAAAflIlf1<JljYr~ VV VI[I.JW VVV'VUv"~ v v VVvlj IJ \TV VIJ'V \['{VlJlJ VIJ\Jl

-0.21.5KIINE 6F Vel X Controlled CObs.) MRX.= 0.7l!7 KINE (14.3905ECl

O ,"' ... - .. \/( 11' 1\ ~ tA.,Jo.,!, ¥d A!If' II (\ Af\ f\ f\ ~.II 6~.1\. Lor>. A....~./o.. '" '" f\ u!\ "f\ 1\ fL 1\ A-\j• q ov i vlfVloulj'YiI I"c'V VVl Vv \TVV' V'" r4JnvnrV"'V~V'r'""4>'i4O>0 V VY°4/"

-1.51.5K~INE 6F Vel X Uncontrolled (Ana.) MRX.= 1.161 KINE (17.2B05ECl

O •• A" 1-4/IIr}UM~ &JJ, j kAd._ ~J>,J-A' ~ ~,j AAV" (I AAAAnA~•• .., I'( ~ \i Ill'~ ~ ~\~ 1 \l' VVVV f'C prrv n,l\' 'TV'\f'V VV VVlJlJlJlJVlJ

-1.5

200L. ":"'~J:IC~ ,( ~:~"I :':'~ll:I~~d ~ ~o

~:.: A, < ..~:::,~ .1,~,:,', ~~:,. :~ • 'v ~ A s~ :8~:E:)-20rr ,~lf'ill"liti V1'iI'«ljl 'vlli1ilTI' IOYvry y 'i'1J "I yp", "(ttll' fyhil'yn "inn'" ..... In. JrI/1'"

20GRL 6F Acc X Uncontrolled (Ana.) MRX.= 15.300 GRL (9.950SECl

O~llldliJh~UII~ILdl~hlnt~L~II~~,n'\I1'll..~ /wJW"4 .~ ..~ .},.4.!~ /y, tt. " 11. l\. " '" " A II t\ !i~~ IV yn~ ,Wl (. r'fllVTI1 V'~"i °pf' Vi Vi If 'r'T'lrVIIV"I V

-20

A-2

2) Responses of 6th Floor in V-Direction

TIME (SEC)o 10 20 30 L!O 50I I I I , I I I I I I I I I I I I I I I I I iii iii I I Iii I I I I I i I Iii I I I I i I I

-20

-1.5GAL 6F Acc Y Controlled (Obs.) MAX.= 15.666 GAL (5.5110SECl

::~..~~VyJt{vIV~~;Jr~-r;,~.-GAL 6F Acc Y Uncontrolled (Ana.) MAX.= 15.467 GAL (5.570SECl

20

0.2[" 6F Dis Y Con troll ed (Obs.) MRX." 0.171 CM (6. 290SEC(

O ~ 0 JiA M~fl.1I1\ AA .AdA.!' ~.., I-. A ~ ,,<A 'Mil ,.~_o¥o M -, ~ "<~v v ~1 V IJ V\l4J1r'V I) ~ IJ"TVW- Y '9 or V V 11,,'" v~v orv V V v

-0.2. (A )0.2[" 6F D15 Y Uneon tro II ed na. MRX. = 0.170 CM (8.120SEC(

., nA ~ r!l &A t'I A ~o.~ ~ ~ .~ ~ ~ A. r!Io· • °rMn ijJ Ifw~mNWr'~ IffVvJ'1

-0.2l.lNE 6F Vel Y Controlled CDbs.) MRX.= 1.272 KINE (5••60SECI

AM;' ~ j, A.I"\ JAl.rqMIMJ r.l\ •• AA A,.., ..... fI ~n.A~Of""o.d "'~"""--,.,." .".01\ A" ",'o. '... '~~VW]"l"VU'V'l'V'''"l~V V"·"~V"V'VV"" ..""" • ~W'V"T ~ ....,

-1.5 .KINE 6F Vel Y Uncontrolled (Ana.) MAX.= 1.555 KINE (8.270SECl

1.5

A-3

3) Responses of 3rd Floor in X-Direction

I I I I I Iii I i I I I J I J I. Ii I I i Io 10 20I I I I I I I I I lit I I i I I l I I I I I I I Iii

30 LIDTIME (SEC)

50

o.lOr 3F Dis X Controlled (Obs.) MAX.= 0.051 CM 110.a;;OSECI

, ~ ~,,.,,,.., f\ Af\ h, r'\ Ii M1'\ A~ II 11 A(\ {\ A" fie 1\ • A • • ,.r .. Jo ,,(', /I ,.." ...." 1\ f\ AA1\ou. w .... lV'YJ ~ ~-lJr(>rr,,'P'V 'IIi V'f"il V Vl[V Vl/I(v"iIVV "V' \T1"I"IIr'V v~ ~nJ\ru~

-0.10o.lOr 3F Dis X Uncontrolled (Ana.) MAX.= 0.077 CM I Y7.910SECI

_ J~~~~AAntAk ~A~~~6~~ Dn~~~AAAAAAAA AAow • 1J111J yVJIJ #Hv roVvrqw-; 'Q rlV V vvvvvvv VVVvVvlJ N1

-0.10KINE 3F Vel X Controlled (Obs.) MRX.= 0.596 KINE (9.720SECl

0' f,,,. d" u. MILII .I' 'j .,,,Iu,,lwuM ''fit •AII, , J"jlo. ""'11'" "<1'" ""''''''''I'"......... ••, 'Y''''"/~~1'\ i\ WHTrV'I\'fl\~ . II\TvY'pr I'V ,qt' Iffv 'pm y. "n" -jnn" ~ ,

-1KINE 3F Vel X Uncontrolled (Aria.) MRX.= 0.729 KINE ( 13.020SECl

0' ~" ..>' .1'~Yl"I!~~W·'~.liIL' i .~.,.•. •~.t'",yU' /, I " ~ ~ ~ 'If A'If AI. AA"".. "'11~ )i'r I ~ ~I f'V'lJ .... VI ~"V' 'irt ril' ... 'rrun~ w~ ~ vv VVVV\[~

-115GRL 3F Acc X Controlled (Obs.) MRX.= 13.952 GAL (5.L!30SECl

o~1Ii1~~tl~;:t~iii~\~I\If.~f~I~'~~h~~~It~IU~1%W~~t~~11~~~tttJ-15

1SGRL 3F Acc X Uncontrolled (Ana.) MAX.= 10.911 GAL (5.L!L!OSECl

o~U".cJ,~,lh03!AI~IJ.llli!hM~illMili.U1lW'L~I~Wlh"'~tJW~lAlhHWtJ<' NI~ ~..fJVi.J/IlI1<!l'1' 11~'WI11l~.~1VVYYFnl~pHH1VpWll'PYHrrTll/'~Y' y liiiy' r"i~ ~Yt '"

-15

A-4

4) Responses of 3rd Floor in Y-Direction

TIME (SEC)o 10 20 30 L!o 50I I I I , ( I I I I I I I I I i I I I I I I I II I I I , I I Ii' I I Iii I I I , I I I Iii I

0.15 eM 3F Dis Y Controlled (Obs.) MAX.= 0.099 eM (7.700SECl

•~.IJ wi. !11M." 1'\,M.lvi,M'&jJ.,"",!I,el.r·"","'tM ""'''',eo '" 6., '" " • • . vVur~ V r'~V"YV \ r r v' ~ i ~ r or vir V'T"I/' \JJ"

-0.15O. [Sr 3F Di s Y Uncon tro 11 ed (Ana.) MRX. = O.11U CM ( ~O. ~9DSECI

O •• ! '~"W·'! M n, hL~,tn~,~h~'B!'~lM~V!tl,,~Un'!.M An.A,,~no.~, "'1 1 V' V IT'VV rv'vv vfVrW~V vr1r r~ ,TV YVfijl[vij~1J~1JVlnrlvvv

-0.15l.lNE 3F Ye1 Y Controlled (Obs.) MRX.= 1.26~ KINE (S.91DSECI

.... 'n ~JA~I~ .. jJ~ AlCn~,L .. nLl\!.A ......},h~~A","" •• b'~ ",.""1.,,.1 ••.o1< ".~~'l ',r~""~Uiy""<''''''r·.,J,,."."m",", ~. ,n ..~"",.~~~-1.5

KINE 3F Ve 1 Y Uncon t ro 11 ed (Ana.) MAX. = 1. 153 KINE (B. 540SEC)1.5

-1.5GRL 3F Ace Y Controlled CObs.) MRX.= 16.L!7Ll GRL (7.690SEC)

2:YM~~~~IM'I~,\ ,lfJJ~~~~~~~-2ot~20r",....,.".~I~,~~~:c Y Uncon tro lied (Ana.) MRX. = 19.287 GRL (B. ~8DSECI

°r~~-20

A-5

2. Earthquake on April 14, 1992:

1) Response of 6th Floor in X-Direction

o 10 20I I I Ii' I i I I I I I I I I I I I Iii I I

TIME (SEC)30 ijO 50

I I I ii' I I I I I I I Iii I I Iii I

0.3 CM 6F Dis X Controlled (Obs.) MAX.= 0.1ij8 CM (9.2405ECl

Or "~ ·A" AAA AA • A00 •• 'if ~ " " Ae ,,' " ~ " .. .."' "' ". , " 4v- "". VIT'Vlj Vl) VIIV \TG WI?" "VV"Q VVVV VV VI.JVVV~VVvvv vv v VVif·ro

-D.3eM 6F Dis X Uncontrolled (Ana.) MAX.= 0.302 CM ( 12. 1205ECl

o~:r .. A A1\ WN ~ ~~ ~ ~ AAAAAA¥A8rvwn nnAA8AAAAfJjq ·VVV r~~VVVl)VOVVV \[V~ ~~VVlJl)VlJVVlJV

-D.3KINE 6F Vel X Controlled (Obs.) MAX.= 1.063 KINE (8.9505ECl

20 f .0 .... ~;.f'AtA~.OA !.,.. ..;,.,~.;;dA ••• ",. "_"1/'" '"" '00'-;, "'T v y ~\I V \J \JV V'iJ' \'l VV1 •i 'Ii \I ni'lVV crv "iI v· U 'In,;,",\)'" V'V~'TVV\T VQ v \h

-2KINE 6F Vel X Uncontrolled' (Ana.) MAX.= 1.857 KINE ( 12. 360SECl

2

-220GRL 6F Acc X Controlled (Obs.) MAX.= 15.245 GAL (6.000SECl

O[d'IU'W.~.l.J,~~.LIM hllu L ,ft,~A 1.., """ " ~A .. '"~ VMw' .'001~~,,~ l1'r~I~,rfI111Irllv''Ii~,ryY'VYl'I'vyr'i 1"'" V' '(Frrf"r WPi(F'( v "Ii if' 'n" y ~ ~ ... "1"

-20 )GRL 6F Ace X Uncontrolled (Ana. MAX,= 19.509 GAL ( 11.1.990SECl

2: r""Lu.....l}~~A~ W.lJJ A6A~ D~ ~ ~ AA" " ~ A n A '"1l'1''"'''III'4l~'1 i· III ~ 'If '{iJ I f~ rVl/ ViJ iJ '{~ V\(VY"i) ~ iii IJIJ'tl

-20

A-6

2) Response of 6th Floor in Y-Direction

o 10 20 30TIME (SEC)

40 50I I I I I I ill I I j I / I I I I j / I ' I I i j J I I I j I I S I i j I i j , j I I

( 9.31.10SEClCM0.198MRX.=CM 6F Dis Y Con t r 011 ed (0bs. )

O':l~~::tCM 6F Dis Y Uncontrolled (Ana.) MAX.= 0.220 CM (8.880SECl

" .0 0 fI 1\ ~ ~ • A H h .f\. tv. 'V' f\ 06 (\ 1\ f\ I~ ~ f\ A0 ~ 1\1' '" f\ /\ r'\ f\ ~0;, .., •v • V'JlJl)'JOY' vIi1Jv VV "Vv~ V "iJ W \fV CJl) \TV V '{ WI} V'Tv V

-0.3KINE 6F Vel Y Controlled CObs.) MAX.= 1.533 KINE (8.970SECl

:f..", -4~V'I/'V-Mv,*J'fvJ'~"'V"'~I11J'V";A,'"V'"-"""'I1~t .

2K[INE 6F Vel Y Uncontrolled CAna.) MAX.= 1.588 KINE (9.060SECl

O-'-~~N0MV'~i~G-2

~:F:;;;;;;=~~:~~:l~:~~=1GRL 6F Acc Y Uncontrolled (Ana.) MAX.= 15.032 GAL ( 11.1.530SECl

20

-20

A-7

3) Responses of 3rd Floor in X-Direction

TIME (SEC)o 10 20 30 40 50I I I I I I I I I I I I I I I i I I I I I I I i I I I I I I I II I Ii I I I I I I I I I I I I I I I

-115GRL 3F Acc X Controlled (Obs.) MRX.= 12.708 GRL (11.920SECl

Lh"C.l'J-ill~J'~ ~~f~lJ)~11_~d)!!~'I~!JL!II.JYJ~d/ldl!l1.IJlhULJlJ'}J~llt.l,1'l!1 JIlt.- ~ -U~lll rL.; .J.~LJJI,Jl~.~~!, ~11)lto t~·llThWIl ~I~M 'vfr rll"~1iIPilt'l\\\~ltH."qll'J\I'lliljll';~~I\~'ll"fh;~lWTlf tl~ If'tMn·.~l.l\p·ti\I1i''~''II'''''''r·~I'r·lti

-15ISGRL 3F Acc X Uncontrolled (Ana.) MRX.= 14.402 GRL (5.860SECl

t Ji!L~)lAJWl.~ WJ!llJ.\.lM~Mf &AU~ Ai.~ AI U~ ~J..u.M\o ~illi:l~t~ljl~ Wr 'f ~ II 'lIT 'Vj'r1'llrrr, I ,'fffrlfYV ~ " firyTr T'If y ,Ill

-15

0.15 eM 3F Dis X Controlled (Obs.) MRX.= 0.085 CM [9.720SECI

OL~~ J\ AhnIi ~oO"AA'-M." ••. d ." A""•.. d • 'If • '"t I,JIrV V'\ITO n rr~ n n V ITvv vvvo vVV vvvv \/'VVvvv VV

-D.15 . 11 ( )0.15 CM 3F DIS X Uncontro ed Ana. MRX.= 0.165 CM [12.110SECI

at - . r\6n~.~rJiAAAAAAnn~AAAA~~AAnnAA~AAAAi[ U b QVV~ VVVlJ VV VrVlJ V VIJ\[~ ij ~ ~ ~ VVVlJl) VV'J\} V

-D.15l KINE 3F Vel X Controlled (Obs.) MRX.= 0.751 KINE [ 14.820SECI

a ~~Iift#~'/{I,f*~~'fv'''~-1

KINE 3F Vel X Uncontrolled (Ana.) MRX.= 1.145 KINE (11.370SECI1

A-B

4) Response of 3rd Floor in V-Direction

TIME (SEC]o 10 20 30 LID 50I I I I I I I I I I I I I I I I I I I I I I I I Iii I i I I I I Iii Ii' I Iii I I I I I I I I

A-9

3. Earthquake on May 11, 1992:

1) Response of 6th Floor in X-Direction

oI I I

10I I I I , I I I I I I I I

20I I I I I I I

30I i I I I I I I I

LIDI I i

TIME (SEC)50

i , I I Iii I

( 3Ll. 8LlOSECl

( 27. 0505EC IMAX.= 19.169 GRL6F Ace X Controlled (Obs.)

6F Acc X Uncontrolled (Ana.) MAX.= 25.181 GALGAL30

CM 6FDis X Controlled (Obs.) MAX.= 0.365 CM (27.1705ECl

0·08[__~_~Ilfr.A.AA.+J.-l+A-I+++A+H-+-I+f>--A-A-A~~~_ ~~ Orq",/lfI,,{\{\f\I\AAf\{\f\/\ "f\Ao ;0 -0 0"" Ir- ITV,IlV" V\{\T'iTV VVVV\)--VV v ........ vv '<,)\) v v VV\J

-0.8CM 6F Dis X Uncontrolled (Ana.) MAX.= 0.672 CM (3L.!.8505ECl

o.o8l-- ~ --vn"'v"O__r:A,1I..q.,..,t"AJrA"-.....t-1f\r++Af-\-I-IOfI1J f\ A AAAfI1lflJlJlJl.A AAAf\ f\ f\ 1\ "0

10

0 " o~v'V'J~'TVlJ v~1J'V VlJIJ V~ VV\[VVV VIJ\JV Vi

-0.8KINE 6F Vel X Controlled (Obs.) MRX.= 2.827 KINE (27.L!705ECI

05 [ ..-...-_..-.A1tr----.....-.....AAJ"'.......M-,,'Jrf',A't>I6~~-\-If\'-\+\A -Hf\+1A+1I1f,JA-\lIJl+f\-A-An,...-A-,0f+{\p..A..,..,o.............-I.Jl1"'~'tt'A~~ ,p."_4"AfI.p."~"1• • "to "'0T"'/ Irv vlJlJIJ VVtvV VV u • v r iJ v IJV -0<> "'lTV v

-5

JM'

-:r-30

A-i0

2) Response of 6th Floor in Y-Direction

oJ I

10 20[ I I I I I I ' , I I , I I I , I I , I I

TIME (SEC)30 ~O 50

I , I I i I I I I I I I i I I I I I I I

6F Vel Y Uncontrolled CAna.) MRX.= 3.539 KINE ( 38.510SECl

. - .... -... .. • ••.~ ~ .n ~ oJ YAAAAfVUJl Aill..~ w v n n ~V' 'V1WI] ViI VVV VVlj VVVVVV I

6F Acc Y Controlled CObs.) MRX.= 17.840 GRL (25.370SECl

• .... 'j.' .. •.• ~.A!~~!.I~ .!l!~d!!!w .6" ,M. 6'0'\. ,I,01 ¥ ~ A <\ " b"Aj·f· P' 'or o. "f'r' ""W{f "V~VV~ yliifll\{iVvrVV VViVV'Vi VITVV y~

6F Acc Y Uncontrolled CAna.) MRX.= 19.390 GRL (39.590SECl

6F Dis Y Uncontrolled CAna.) MRX.= 0.799 CM (39.630SEC)

.-'-'~ '~~WJ

-20

eM 6F Dis Y Controlled CObs.) MRX.= 0.347 CM (41.840SECl

0'0

8

f-~~~~A++-f>JlrIJr~~-ffi-t+-I+f--Jr++++++l--J,_ /I l\ f\. f\ I\. A f\f\ 1\ f\, 1\ 1\ /\ '" f\ f\ f\ fI f\ 1\ 1\ f\ a A-~~vFVOv~_~v"" vV!'V V"rVVVVVVU v v\J\I u'JiVVVV V V V

-0.8

D'r-0.8

KINE 6F Vel Y Controlled CObs.) MRX.= 2.153 KINE (41.620SECl

-4

l!o f-----..........,..,--,----.......,.-rF-1rtHrlllUo;f\tTt''t;t'''rA+t+tttft;+\;;R;r,fLr.IUrmf-'.;;rJ-b'-\:++t-+t-'''rf-JI--f-'rf-l-r-/C-\i_ n J>. -t _ 0'" - • .1\ fiN! ~AM fuMA!I"~ "oM fit" A A 1\ /\f\f'\f\..1\. f\ f\ f"\jo - V .. - v - -~ ITvnQ~ ~Y\fI[V V'J1..~WIjJ'VV"i)"V \TV VV '\TV-'V~

~r2:["'

~JGAL

20

A-11

3) Responses of 3rd Floor in X-Direction

TIME (SEC)o 10 20 30 ~O 50I I I r I I I I I I i I I I I I I I I I I I I I I I I I I I I I I I I I I I I i I I I I

3F Vel X Uncontrolled (Ana.) MRX.= 2.18l! KINE (34.620SECI

• H _ .... .,. .,. ."!~ ~ ,fI 11M h~ ~ Ali AA!lfJMA~ AAAAAll A I\j..~~ • ~n • v V" vr~ r ~ if'9 \J~V VVVlJV m'{V l[VW'J "i/VV

3F Dis X Uncontrolled (Ana.) MRX.= 0.348 CM (35.350SECI

• a '1 • • • • " ., - /\ ~ t\ A AAAAAA~ AAAnJl~ {lilltA AAAf\ f\ (\ (\ A• V V v. 0 Q V\i~~ V 'vv V'J ~ VV\[V vvmmv VVl) veTO V

( 27.21OSECI

( 25. 170SECIMAX.= 16.6l!8 GAL

MRX.= 15.897 GRL3F Ace X Controlled (Obs.)

O'OYr_CM~~_3_F_D_l~'S~_x_c_o_n_tr_o_I_I~ewd~-~~OAb~S.~)~~M~R~X~·=~~AO.~2~2~6~~CM~~~(2~7A'A22~O~S~ECI_ L • ~ "" II -"" f\ A fI AA0/1 fI A. ,,1\ ~" t". 0 c. 0" f\ /\ '"

.... '" 0 v p 0 .... "'.... V\TVV4JVV VI) VV"TV VV=v VV"' ..... v v v V v v V VV'

-O.Y

"r-0.14

KINE 3F Vel X Controlled (Obs.) MRX.= 1.335 KINE (27.840SECI

.2'0

5

r----....-~~_............-...,t.,.Jlorf'Vt,J-'rAf\++t+f+++Hr-J'lrlJ-itt+-H:fl<.,....J\j'-\-f\\~~oTV''w'''<~......tf+A,.p,I- • " v" ......... , ,',' ~\,~MAJvrl\lb¥NIfIMlfj"'''' 6JfI~'-'''''''''''w''v'\;."",6J\.f\;R

-2.5

2':r-2.5

2f-20 tJ_RL_-......,N.;:w.,)/grJV':""':¥:,UJ.:l;,/....,W;,:M-:~w.:_,n .......t rtw°~ll ed (An a. )

A-12

4) Response of 3rd Floor in Y-Direction

oI I

10 20i I I I i I I I I I I I I I I J iii I

TIME (SEC)30 ~o 50

I I I I I I I I iii I Ii' Iii i I I

( 25.840SECI

( 30. 9605EC I21.21H GAL

MRX.= 20.656 GAL3F Acc Y Controlled (Obs.)

3F Dis Y Uncontrolled (Ana.) MRX.= 0.393 CM (1l9.S90SECI

•••- ..... - •...".,rvA,~3F Ve 1 Y Con t ro 11 ed (Obs.) MRX. = 1. 71.J:2 KINE ( 25. 760SECI

"~'<"-1'---""'~~~WV\>o,3F Vel Y Uncontrolled (Ana.) MAX.= 1.912 KINE (1l7.130SECI

-2GAL

2S

eM 3F Dis Y Controlled (Obs.) MRX.= 0.194 CM (41.300SECI

O'o~[_~~~~~~~~~~ • v ~ r ~. v A_ A ~ 'vv~!rI'vJ'tv.)l~vfvf"vtv..O V' c"\j\,h/\"'vAA!fJ\fVV\j\f\/i

-0.11

o'r-o.~

~r

A-13

NATIONAL CENTER FOR EARTHQUAKE ENGINEERING RESEARCHLIST OF TECHNICAL REPORTS

The National Center for Earthquake Engineering Research (NCEER) publishes technical reports on a variety of subjects relatedto earthquake engineering written by authors funded through NCEER. These reports are available from both NCEER'sPublications Department and the National Technical Information Service (NTIS). Requests for reports should be directed to thePublications Department, National Center for Earthquake Engineering Research, State University of New York at Buffalo, RedJacket Quadrangle, Buffalo, New York 14261. Reports can also be requested through NTIS, 5285 Port Royal Road, Springfield,Virginia 22161. NTIS accession numbers are shown in parenthesis, if available.

NCEER-87-oo01 "First-Year Program in Research, Education and Technology Transfer," 3/5/87, (PB88-134275/AS).

NCEER-87-oo02 "Experimental Evaluation of Instantaneous Optimal Algorithms for Structural Control," by R.C. Lin, T.T.Soong and AM. Reinhorn, 4/20/87, (PB88-134341/AS).

NCEER-87-0003 "Experimentation Using the Earthquake Simulation Facilities at University at Buffalo," by AM. Reinhorn andR.L. Ketter, to be published.

NCEER-87-oo04 "The System Characteristics and Performance of a Shaking Table," by 1S. Hwang, K.C. Chang and G.C. Lee,6/1/87, (PB88-134259/AS). This report is available only through NTIS (see address given above).

NCEER-87-0005 "A Finite Element Formulation for Nonlinear Viscoplastic Material Using a Q Model," by O. Gyebi and G.Dasgupta, 11/2/87, (PB88-213764/AS).

NCEER-87-0006 "Symbolic Manipulation Program (SMP) - Algebraic Codes for Two and Three Dimensional Finite ElementFormulations," by X. Lee and G. Dasgupta, 11/9/87, (PB88-219522/AS).

NCEER-87-0007 "Instantaneous Optimal Control Laws for Tall Buildings Under Seismic Excitations," by J.N. Yang, AAkbarpour and P. Ghaemmaghami, 6/10/87, (PB88-134333/AS).

NCEER-87-0008 "!DARC: Inelastic Damage Analysis of Reinforced Concrete Frame - Shear-Wall Structures," by YJ. Park,A.M. Reinhorn and S.K. Kunnath, 7/20/87, (PB88-134325/AS).

NCEER-87-0009 "Liquefaction Potential for New York State: A Preliminary Report on Sites in Manhattan and Buffalo," byM. Budhu, V. Vijayakumar, R.F. Giese and L. Baumgras, 8/31/87, (PB88-163704/AS). This report isavailable only through NTIS (see address given above).

NCEER-87-001O "Vertical and Torsional Vibration of Foundations in Inhomogeneous Media," by AS. Veletsos and K.W.Dotson, 6/1/87, (PB88-134291/AS).

NCEER-87-0011 "Seismic Probabilistic Risk Assessment and Seismic Margins Studies for Nuclear Power Plants," by HowardH.M. Hwang, 6/15/87, (PB88-134267/AS).

NCEER-87-oo12 "Parametric Studies of Frequency Response of Secondary Systems Under Ground-Acceleration Excitations,"by Y. Yong and Y.K. Lin, 6/10/87, (PB88-134309/AS).

NCEER-87-0013 "Frequency Response of Secondary Systems Under Seismic Excitation," by J.A. HoLung, J. Cai and Y.K. Lin,7/31/87, (PB88-134317/AS).

NCEER-87-0014 "Modelling Earthquake Ground Motions in Seismically Active Regions Using Parametric Time SeriesMethods," by GW. Ellis and AS. Cakmak, 8/25/87, (PB88-134283/AS).

NCEER-87-oo15 "Detection and Assessment of Seismic Structural Damage," by E. DiPasquale and A.S. Cakmak, 8/25/87,(PB88-163712/AS).

B-1

NCEER-87-0016 "Pipeline Experiment at Parkfield, Califomia," by l Isenberg and E. Richardson, 9/15/87, (PB88-163720/AS).This report is available only through NTIS (see address given above).

NCEER-87-0017 "Digital Simulation of Seismic Ground Motion," by M. Shinozuka, G. Deodatis and T. Harada, 8/31/87,(PB88-155197/AS). This report is available only through NTIS (see address given above).

NCEER-87-0018 "Practical Considerations for Structural Control: System Uncertainty, System Time Delay and Truncation ofSmall Control Forces," IN. Yang and A. Akbarpour, 8/10/87, (PB88-163738/AS).

NCEER-87-0019 "Modal Analysis of Nonclassically Damped Structural Systems Using Canonical Transformation," by J.N.Yang, S. Sarkani and F.x. Long, 9/27/87, (PB88-187851/AS).

NCEER-87-0020 "A Nonstationary Solution in Random Vibration Theory," by J.R. Red-Horse and P.D. Spanos, 11/3/87,(PB88-163746/AS).

NCEER-87-0021 "Horizontal Impedances for Radially Inhomogeneous Viscoelastic Soil Layers," by AS. Veletsos and K.W.Dotson, 10/15/87, (PB88-150859/AS).

NCEER-87-0022 "Seismic Damage Assessment of Reinforced Concrete Members," by Y.S. Chung, C. Meyer and M.Shinozuka, 10/9/87, (PB88-150867/AS). This report is available only through NTIS (see address givenabove).

NCEER-87-0023 "Active Structural Control in Civil Engineering," by T.T. Soong, 11/11/87, (PB88-l87778/AS).

NCEER-87-0024 "Vertical and Torsional Impedances for Radially Inhomogeneous Viscoelastic Soil Layers," by K.W. Dotsonand A.S. Veletsos, 12/87, (PB88-187786/AS).

NCEER-87-0025 "Proceedings from the Symposium on Seismic Hazards, Ground Motions, Soil-Liquefaction and EngineeringPractice in Eastern North America," October 20-22, 1987, edited by K.H. Jacob, 12/87, (PB88-l88115/AS).

NCEER-87-0026 "Report on the Whittier-Narrows, California, Earthquake of October I, 1987," by 1.Pantelic and A Reinhorn, 11/87, (PB88-l87752/AS). This report is available only through NTIS (see addressgiven above).

NCEER-87-0027 "Design of a Modular Program for Transient Nonlinear Analysis of Large 3-D Building Structures," by S.Srivastav and J.F. Abel, 12/30/87, (PB88-187950/AS).

NCEER-87-0028 "Second-Year Program in Research, Education and Technology Transfer," 3/8/88, (PB88-219480/AS).

NCEER-88-0001 "Workshop on Seismic Computer Analysis and Design of Buildings With Interactive Graphics," by W.McGuire, J.F. Abel and C.H. Conley, 1/18/88, (PB88-187760/AS).

NCEER-88-0002 "Optimal Control of Nonlinear Flexible Structures," by IN. Yang, F'x. Long and D. Wong, 1/22/88, (PB88­213772/AS).

NCEER-88-0003 "Substructuring Techniques in the Time Domain for Primary-Secondary Structural Systems," by G.D. Manolisand G. Juhn, 2/10/88, (PB88-213780/AS).

NCEER-88-0004 "Iterative Seismic Analysis of Primary-Secondary Systems," by A Singhal, L.D. Lutes and P.D. Spanos,2/23/88, (PB88-213798/AS).

NCEER-88-0005 "Stochastic Finite Element Expansion for Random Media," by P.D. Spanos and R. Ghanem, 3/14/88, (PB88­213806/AS).

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NCEER-88-0006 "Combining Structural Optimization and Structural Control," by F.Y. Cheng and C.P. Pantelides, 1/10/88,(PB88-2138l4/AS).

NCEER-88-0007 "Seismic Performance Assessment of Code-Designed Structures," by H.H-M. Hwang, J-W. Jaw and H-J. Shau,3/20/88, (PB88-219423/AS).

NCEER-88-0008 "Reliability Analysis of Code-Designed Structures Under Natural Hazards," by H.H-M. Hwang, H. Ushibaand M. Shinozuka, 2/29/88, (PB88-229471/AS).

NCEER-88-0009 "Seismic Fragility Analysis of Shear Wall Structures," by J-W Jaw and H.H-M. Hwang, 4/30/88, (PB89­102867/AS).

NCEER-88-001O "Base Isolation of a MUlti-Story Building Under a Harmonic Ground Motion - A Comparison of Performancesof Various Systems," by F-G Fan, G. Ahmadi and I.G. Tadjbakhsh, 5/18/88, (PB89-122238/AS).

NCEER-88-0011 "Seismic Floor Response Spectra for a Combined System by Green's Functions," by F.M. Lavelle, L.A.Bergman and PD. Spanos, 5/1/88, (PB89-102875/AS).

NCEER-88-0012 "A New Solution Technique for Randomly Excited Hysteretic Structures," by G.Q. Cai and Y.K. Lin, 5/16/88,(PB89-l02883/AS).

NCEER-88-00l3 "A Study of Radiation Damping and Soil-Structure· Interaction Effects in the Centrifuge,"by K. Weissman, supervised by J.H. Prevost, 5/24/88, (PB89-144703/AS).

NCEER-88-00l4 "Parameter Identification and Implementation of a Kinematic Plasticity Model for Frictional Soils," by J.H.Prevost and D.V. Griffiths, to be published.

NCEER-88-0015 "Two- and Three- Dimensional Dynamic Finite Element Analyses of the Long Valley Dam," by D.V. Griffithsand J.H. Prevost, 6/17/88, (PBS9-144711/AS).

NCEER-88-0016 "Damage Assessment of Reinforced Concrete Structures in Eastern United States," by A.M. Reinhorn, MJ.Seidel, S.K. Kunnath and YJ. Park, 6/15/88, (PB89-122220/AS).

NCEER-88-0017 "Dynamic Compliance of Vertically Loaded Strip Foundations in Multilayered Viscoelastic Soils," by S.Ahmad and A.S.M. Israil; 6/17/88, (PB89-102891/AS).

NCEER-88-00lS "An Experimental Study of Seismic Structural Response With Added Viscoelastic Dampers," by R.C. Lin,Z. Liang, T.T. Soong and R.H. Zhang, 6/30/88, (PB89-122212/AS). This report is available only throughNTIS (see address given above).

NCEER-8S-0019 "Experimental Investigation of Primary - Secondary System Interaction," by G.D. Manolis, G. Juhn and A.M.Reinhorn, 5/27/88, (PB89-122204/AS).

NCEER-88-0020 "A Response Spectrum Approach For Analysis of Nonclassically Damped Structures," by J.N. Yang, S.Sarkani and F.x. Long, 4/22/88, (PB89-102909/AS).

NCEER-SS-0021 "Seismic Interaction of Structures and Soils: Stochastic Approach," by A.S. Veletsos and A.M. Prasad,7/21/88, (PB89-122196/AS).

NCEER-88-0022 "Identification of the Serviceability Limit State and Detection of Seismic Structural Damage," by E.DiPasquale and A.S. Cakmak, 6/15/88, (PB89-122188/AS). This report is available only through NTIS (seeaddress given above).

NCEER-88-0023 "Multi-Hazard Risk Analysis: Case of a Simple Offshore Structure," by B.K. Bhartia and E.H. Vanmarcke,7/21/88, (PB89-145213/AS).

B-3

NCEER-88-0024 "Automated Seismic Design of Reinforced Concrete Buildings," by Y.S. Chung, C. Meyer and M. Shinozuka,7/5/88, (PB89-122170/AS). This report is available only through NTIS (see address given above).

NCEER-88-0025 "Experimental Study of Active Control ofMDOF Structures Under Seismic Excitations," by L.L. Chung, R.C.Lin, T.T. Soong and A.M. Reinhom, 7/10/88, (PB89-122600/AS).

NCEER-88-0026 "Earthquake Simulation Tests of a Low-Rise Metal Structure," by 1.S. Hwang, K.C. Chang, G.C. Lee and R.L.Ketter, 8/1/88, (PB89-102917/AS).

NCEER-88-0027 "Systems Study of Urban Response and Reconstruction Due to Catastrophic Earthquakes," by F. Kozin andH.K. Zhou, 9/22/88, (PB90-162348/AS).

NCEER-88-0028 "Seismic Fragility Analysis of Plane Frame Structures," by H.H-M. Hwang and Y.K. Low, 7/31/88, (PB89­13l445/AS).

NCEER-88-0029 "Response Analysis of Stochastic Structures," by A. Kardara, C. Bucher and M. Shinozuka, 9/22/88, (PB89­174429/AS).

NCEER-88-0030 "Nonnormal Accelerations Due to Yielding in a Primary Structure," by D.C.K. Chen and LD. Lutes, 9/19/88,(PB89-131437/AS).

NCEER-88-0031 "Design Approaches for Soil-Structure Interaction," by A.S. Veletsos, A.M. Prasad and Y. Tang, 12/30/88,(PB89-174437/AS). This report is available only through NTIS (see address given above).

NCEER-88-0032 "A Re-evaluation of Design Spectra for Seismic Damage Control," by C.J. Turkstra and A.G. Tallin, 11/7/88,(PB89-145221/AS).

NCEER-88-0033 "The Behavior and Design of Noncontact Lap Splices Subjected to Repeated Inelastic Tensile Loading," byV.E. Sagan, P. Gergely and R.N. White, 12/8/88, (PB89-163737/AS).

NCEER-88-0034 "Seismic Response of Pile Foundations," by S.M. Mamoon, P.K. Banerjee and S. Ahmad, 11/1/88, (PB89­145239/AS).

NCEER-88-0035 "Modeling of R/C Building Structures With Flexible Floor Diaphragms (IDARC2)," by A.M. Reinhom, S.K.Kunnath and N. Panahshahi, 9/7/88, (PB89-207153/AS).

NCEER-88-0036 "Solution of the Dam-Reservoir Interaction Problem Using a Combination of FEM, BEM with ParticularIntegrals, Modal Analysis, and Substructuring," by C-S. Tsai, G.C. Lee and R.L. Ketter, 12/31/88, (PB89­207146/AS).

NCEER-88-0037 "Optimal Placement of Actuators for Structural Control," by F.Y. Cheng and C.P. Pantelides, 8/15/88, (PB89­162846/AS).

NCEER-88-0038 "Teflon Bearings in Aseismic Base Isolation: Experimental Studies and Mathematical Modeling," by A.Mokha, M.C. Constantinou and A.M. Reinhom, 12/5/88, (PB89-2l8457/AS). This report is available onlythrough NTIS (see address given above).

NCEER-88-0039 "Seismic Behavior of Flat Slab High-Rise Buildings in the New York City Area," by P. Weidlinger and M.Ettouney, 10/15/88, (PB90-145681/AS).

NCEER-88-0040 "Evaluation of the Earthquake Resistance of Existing Buildings in New York City," by P. Weidlinger and M.Ettouney, 10/15/88, to be published.

NCEER-88-0041 "Small-Scale Modeling Techniques for Reinforced Concrete Structures Subjected to Seismic Loads," by W.Kim, A. E1-Attar and R.N. White, 11/22/88, (PB89-189625/AS).

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NCEER-88-0042 "Modeling Strong Ground Motion from Multiple Event Earthquakes," by G.W. Ellis and A.S. Cakmak,10/15/88, (PB89-l74445/AS).

NCEER-88-0043 "Nonstationary Models of Seismic Ground Acceleration," by M. Grigoriu, S.E. Ruiz and E. Rosenblueth,7/15/88, (PB89-l896l7/AS).

NCEER-88-0044 "SARCF User's Guide: Seismic Analysis of Reinforced Concrete Frames," by Y.S. Chung, C. Meyer and M.Shinozuka, 11/9/88, (PB89-174452/AS).

NCEER-88-0045 "First Expert Panel Meeting on Disaster Research and Planning," edited by J. Pantelic and J. Stoyle, 9/15/88,(PB89-l74460/AS).

NCEER-88-0046 "Preliminary Studies of the Effect of Degrading Infill Walls on the Nonlinear Seismic Response of SteelFrames," by C.z. Chrysostomou, P. Gergely and J.F. Abel, 12/19/88, (PB89-208383/AS).

NCEER-88-0047 "Reinforced Concrete Frame Component Testing Facility - Design, Construction, Instrumentation andOperation," by S.P. Pessiki, C. Conley, T. Bond, P. Gergely and R.N. White, 12/16/88, (PB89-174478/AS).

NCEER-89-000l "Effects of Protective Cushion and Soil Compliancy on the Response of Equipment Within a SeismicallyExcited Building," by lA. HoLung, 2/16/89, (PB89-207179/AS).

NCEER-89-0002 "Statistical Evaluation of Response Modification Factors for Reinforced Concrete Structures," by H.H-M.Hwang and J-W. Jaw, 2/17/89, (PB89-207187/AS).

NCEER-89-0003 "Hysteretic Columns Under Random Excitation," by G-Q. Cai and Y.K. Lin, 1/9/89, (PB89-l965l3/AS).

NCEER-89-0004 "Experimental Study of 'Elephant Foot Bulge' Instability of Thin-Walled Metal Tanks," by Z-H. Jia and R.L.Ketter, 2/22/89, (PB89-207195/AS).

NCEER-89-0005 "Experiment on Performance of Buried Pipelines Across San Andreas Fault," by l Isenberg, E. Richardsonand T.D. O'Rourke, 3/10/89, (PB89-218440/AS).

NCEER-89-0006 "A Knowledge-Based Approach to Structural Design of Earthquake-Resistant Buildings," by M. Subramani,P. Gergely, C.H. Conley, I.F. Abel and A.H. Zaghw, 1/15/89, (PB89-218465/AS).

NCEER-89-0007 "Liquefaction Hazards and Their Effects on Buried Pipelines," by ToO. O'Rourke and P.A. Lane, 2/1/89,(PB89-2l848l).

NCEER-89-0008 "Fundamentals of System Identification in Structural Dynamics," by H. Imai, C-B. Yun, O. Maruyama andM. Shinozuka, 1/26/89, (PB89-2072l1/AS).

NCEER-89-0009 "Effects of the 1985 Michoacan Earthquake on Water Systems and Other Buried Lifelines in Mexico," byA.G. Ayala and MJ. O'Rourke, 3/8/89, (PB89-207229/AS).

NCEER-89-ROlO "NCEER Bibliography of Earthquake Education Materials," by K.E.K. Ross, Second Revision, 9/1/89, (PB90­125352/AS).

NCEER-89-0011 "Inelastic Three-Dimensional Response Analysis of Reinforced Concrete BuildingStructures (IDARC-3D), Part I - Modeling," by S.K. Kunnath and A.M. Reinhom, 4/17/89, (PB90­114612/AS).

NCEER-89-0012 "Recommended Modifications to ATC-14," by C.D. Poland and J.O. Malley, 4/12/89, (PB90-108648/AS).

NCEER-89-00l3 "Repair and Strengthening of Beam-to-Column Connections Subjected to Earthquake Loading," by M.Corazao and AJ. Durrani, 2/28/89, (PB90-109885/AS).

B-5

NCEER-89-0014 "Program EXKAL2 for Identification of Structural Dynamic Systems," by O. Maruyama, C-B. Yun, M.Hoshiya and M. Shinozuka, 5/19/89, (PB90-109877/AS).

NCEER-89-0015 "Response of Frames With Bolted Semi-Rigid Connections, Part I - Experimental Study and AnalyticalPredictions," by PJ. DiCorso, A.M. Reinhorn, J.R. Dickerson, J.B. Radziminski and W.L. Harper, 6/1/89, tobe published.

NCEER-89-0016 "ARMA Monte Carlo Simulation in Probabilistic Structural Analysis," by PD. Spanos and M.P. Mignolet,7/10/89, (PB90-109893/AS).

NCEER-89-P017 "Preliminary Proceedings from the Conference on Disaster Preparedness - The Place of Earthquake Educationin Our Schools," Edited by K.E.K. Ross, 6/23/89.

NCEER-89-0017 "Proceedings from the Conference on Disaster Preparedness - The Place of Earthquake Education in OurSchools," Edited by K.E.K. Ross, 12/31/89, (PB90-207895). This report is available only through NTIS (seeaddress given above).

NCEER-89-0018 "Multidimensional Models of Hysteretic Material Behavior for Vibration Analysis of Shape Memory EnergyAbsorbing Devices, by E.J. Graesser and FA Cozzarelli, 6nJ89, (PB90-164146/AS).

NCEER-89-0019 "Nonlinear Dynamic Analysis ofThree-Dimensional Base Isolated Structures (3D-BASIS)," by S. Nagarajaiah,A.M. Reinhorn and M.C. Constantinou, 8/3/89, (PB90-161936/AS). This report is available only throughNTIS (see address given above).

NCEER-89-0020 "Structural Control Considering Time-Rate of Control Forces and Control Rate Constraints," by F.Y. Chengand C.P. Pantelides, 8/3/89, (PB90-120445/AS).

NCEER-89-0021 "Subsurface Conditions of Memphis and Shelby County," by K.W. Ng, T-S. Chang and H-H.M. Hwang,7/26/89, (PB90-120437/AS).

NCEER-89-0022 "Seismic Wave Propagation Effects on Straight Jointed Buried Pipelines," by K. Elhmadi and M.J. O'Rourke,8/24/89, (PB90-162322/AS).

NCEER-89-0023 "Workshop on Serviceability Analysis of Water Delivery Systems," edited by M. Grigoriu, 3/6/89, (PB90­127424/AS).

NCEER-89-0024 "Shaking Table Study of a 1/5 Scale Steel Frame Composed of Tapered Members," byK.C. Chang, J.S. Hwang and G.C. Lee, 9/18/89, (PB90-160169/AS).

NCEER-89-0025 "DYNA1D: A Computer Program for Nonlinear Seismic Site Response Analysis - Technical Documentation,"by Jean H. Prevost, 9/14/89, (PB90-161944/AS). This report is available only through NTIS (see addressgiven above).

NCEER-89-0026 "1:4 Scale Model Studies of Active Tendon Systems and Active Mass Dampers for Aseismic Protection," byA.M. Reinhorn, T.T. Soong, R.C. Lin, Y.P. Yang, Y. Fukao, H. Abe and M. Nakai, 9/15/89, (PB90­173246/AS).

NCEER-89-0027 "Scattering of Waves by Inclusions in a Nonhomogeneous Elastic Half Space Solved by Boundary ElementMethods," by P.K. Hadley, A. Askar and A.S. Cakmak, 6/15/89, (PB90-145699/AS).

NCEER-89-0028 "Statistical Evaluation of Deflection Amplification Factors for Reinforced Concrete Structures," by H.H.M.Hwang, J-W. Jaw and A.L. Ch'ng, 8/31/89, (PB90-164633/AS).

NCEER-89-0029 "Bedrock Accelerations in Memphis Area Due to Large New Madrid Earthquakes," by H.H.M. Hwang, C.H.S.Chen and G. Yu, llnJ89, (PB90-162330/AS).

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NCEER-89-oo30 "Seismic Behavior and Response Sensitivity of Secondary Structural Systems," by Y.Q. Chen and T.T. Soong,10/23/89, (PB90-l64658/AS).

NCEER-89-oo31 "Random Vibration and Reliability Analysis of Primary-Secondary Structural Systems," by Y. Ibrahim, M.Grigoriu and T.T. Soong, 11/10/89, (PB90-161951/AS).

NCEER-89-oo32 "Proceedings from the Second U.S. - Japan Workshop on Liquefaction, Large Ground Deformation and TheirEffects on Lifelines, September 26-29, 1989," Edited by ToO. O'Rourke and M. Hamada, 12/1/89, (PB90­209388/AS).

NCEER-89-oo33 "Deterministic Model for Seismic Damage Evaluation of Reinforced Concrete Structures," by 1M. Bracci,AM. Reinhom, J.B. Mander and S.K. Kunnath, 9/27/89.

NCEER-89-oo34 "On the Relation Between Local and Global Damage Indices," by E. DiPasquale and A.S. Cakmak, 8/15/89,(PB90-173865).

NCEER-89-0035 "Cyclic Undrained Behavior of Nonplastic and Low Plasticity Silts," by AJ. Walker and H.E. Stewart,7/26/89, (PB90-183518/AS).

NCEER-89-oo36 "Liquefaction Potential of Surficial Deposits in the City of Buffalo, New York," by M. Budhu, R. Giese andL. Baumgrass, 1/17/89, (PB90-208455/AS).

NCEER-89-oo37 "A Deterministic Assessment of Effects of Ground Motion Incoherence," by AS. Veletsos and Y. Tang,7/15/89, (PB90-164294/AS).

NCEER-89-oo38 "Workshop on Ground Motion Parameters for Seismic Hazard Mapping," July 17-18, 1989, edited by R.V.Whitman, 12/1/89, (PB90-l73923/AS).

NCEER-89-0039 "Seismic Effects on Elevated Transit Lines of the New York City Transit Authority," by C.J. Costantino, C.A.Miller and E. Heymsfield, 12/26/89, (PB90-207887/AS).

NCEER-89-0040 "Centrifugal Modeling of Dynamic Soil-Structure Interaction," by K. Weissman, Supervised by J.H. Prevost,5/10/89, (PB90-207879/AS).

NCEER-89-0041 "Linearized Identification of Buildings With Cores for Seismic Vulnerability Assessment," by I-K. Ho andA.E. Aktan, 11/1/89, (PB90-251943/AS).

NCEER-90-0001 "Geotechnical and Lifeline Aspects of the October 17, 1989 Loma Prieta Earthquake in San Francisco," byT.D. O'Rourke, H.E. Stewart, F.T. Blackburn and T.S. Dickerman, 1/90, (PB90-208596/AS).

NCEER-90-oo02 "Nonnormal Secondary Response Due to Yielding in a Primary Structure," by D.C.K. Chen and L.D. Lutes,2/28/90, (PB90-251976/AS).

NCEER-90-oo03 "Earthquake Education Materials for Grades K-12," by K.E.K. Ross, 4/16/90, (PB91-1l3415/AS).

NCEER-90-oo04 "Catalog of Strong Motion Stations in Eastern North America," by R.W. Busby, 4/3/90, (PB90-251984)/AS.

NCEER-90-oo05 "NCEER Strong-Motion Data Base: A User Manual for the GeoBase Release (Version 1.0 for the Sun3),"by P. Friberg and K. Jacob, 3/31/90 (PB90-258062/AS).

NCEER-90-oo06 "Seismic Hazard Along a Crude Oil Pipeline in the Event of an 1811-1812 Type New Madrid Earthquake,"by H.H.M. Hwang and C-H.S. Chen, 4/16/90(PB90-258054).

NCEER-90-oo07 "Site-Specific Response Spectra for Memphis Sheahan Pumping Station," by H.H.M. Hwang and C.S. Lee,5/15/90, (PB91-108811/AS).

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NCEER-90-0008 "Pilot Study on Seismic Vulnerability of Crude Oil Transmission Systems," by T. Ariman, R. Dobry, M.Grigoriu, F. Kozin, M. O'Rourke, T. O'Rourke and M. Shinozuka, 5/25/90, (PB91-108837/AS).

NCEER-90-0009 "A Program to Generate Site Dependent Time Histories: EQGEN," by G.W. Ellis, M. Srinivasan and AS.Cakmak, 1/30/90, (PB91-108829/AS).

NCEER-90-00lO "Active Isolation for Seismic Protection of Operating Rooms," by M.E. Talbott, Supervised by M. Shinozuka,6/8/9, (PB91-110205/AS).

NCEER-90-0011 "Program LINEARID for Identification of Linear Structural Dynamic Systems," by C-B. Yun and M.Shinozuka, 6/25/90, (PB91-110312/AS).

NCEER-90-0012 "Two-Dimensional Two-Phase Elasto-Plastic Seismic Response of Earth Dams," by AN.Yiagos, Supervised by IH. Prevost, 6/20/90, (PB91-110197/AS).

NCEER-90-0013 "Secondary Systems in Base-Isolated Structures: Experimental Investigation, Stochastic Response andStochastic Sensitivity," by G.D. Manolis, G. Juhn, M.C. Constantinou and A.M. Reinhom, 7/1/90, (PB91­110320/AS).

NCEER-90-0014 "Seismic Behavior of Lightly-Reinforced Concrete Column and Beam-Column Joint Details," by S.P. Pessiki,C.H. Conley, P. Gergely and R.N. White, 8/22/90, (PB91-108795/AS).

NCEER-90-0015 "Two Hybrid Control Systems for Building Structures Under Strong Earthquakes," by J.N. Yang and ADanielians, 6/29/90, (PB91-125393/AS).

NCEER-90-0016 "Instantaneous Optimal Control with Acceleration and Velocity Feedback," by J.N. Yang and Z. Li, 6/29/90,(PB91-125401/AS).

NCEER-90-0017 "Reconnaissance Report on the Northern Iran Earthquake of June 21, 1990," by M. Mehrain, 10/4/90, (PB91­125377/AS).

NCEER-90-0018 "Evaluation of Liquefaction Potential in Memphis and Shelby County," by T.S. Chang, P.S. Tang, C.S. Leeand H. Hwang, 8/10/90, (PB91-125427/AS).

NCEER-90-0019 "Experimental and Analytical Study of a Combined Sliding Disc Bearing and Helical Steel Spring IsolationSystem," by M.C. Constantinou, AS. Mokha and AM. Reinhorn, 10/4/90, (PB91-125385/AS).

NCEER-90-0020 "Experimental Study and Analytical Prediction of Earthquake Response of a Sliding Isolation System witha Spherical Surface," by A.S. Mokha, M.C. Constantinou and A.M. Reinhorn, 10/11/90, (PB91-125419/AS).

NCEER-90-0021 "Dynamic Interaction Factors for Floating Pile Groups," by G. Gazetas, K. Fan, A Kaynia and E. Kausel,9/lO/90, (PB91-170381/AS).

NCEER-90-0022 "Evaluation of Seismic Damage Indices for Reinforced Concrete Structures," by S. Rodriguez-Gomez andA.S. Cakmak, 9/30/90, PB91-171322/AS).

NCEER-90-0023 "Study of Site Response at a Selected Memphis Site," by H. Desai, S. Ahmad, E.S. Gazetas and M.R. Oh,10/11/90, (PB9l-196857/AS).

NCEER-90-0024 "A User's Guide to Strongmo: Version 1.0 of NCEER's Strong-Motion Data Access Tool for PCs andTerminals," by PA Friberg and CAT. Susch, 11/15/90, (PB91-171272/AS).

NCEER-90-0025 "A Three-Dimensional Analytical Study of Spatial Variability of Seismic Ground Motions," by L-L. Hongand AH.-S. Ang, lO/30/90, (PB91-170399/AS).

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NCEER-90-0026 "MUMOID User's Guide - A Program for the Identification of Modal Parameters," by S. ROdriguez-Gomezand E. DiPasquale, 9/30/90, (PB9l-l7l298/AS).

NCEER-90-0027 "SARCF-II User's Guide - Seismic Analysis of Reinforced Concrete Frames," by S. Rodriguez-Gomez, Y.S.Chung and C. Meyer, 9/30/90, (PB9l-171280/AS).

NCEER-90-0028 "Viscous Dampers: Testing, Modeling and Application in Vibration and Seismic Isolation," by N. Makris andM.C. Constantinou, 12/20/90 (PB91-190561/AS).

NCEER-90-0029 "Soil Effects on Earthquake Ground Motions in the Memphis Area," by H. Hwang, C.S. Lee, K.W. Ng andT.S. Chang, 8/2/90, (PB9l-l90751/AS).

NCEER-91-000l "Proceedings from the Third Japan-U.S. Workshop on Earthquake Resistant Design of Lifeline Facilities andCountermeasures for Soil Liquefaction, December 17-19, 1990," edited by T.D. O'Rourke and M. Hamada,2/1/91, (PB91-l79259/AS).

NCEER-9l-0002 "Physical Space Solutions of Non-Proportionally Damped Systems," by M. Tong, Z. Liang and G.C. Lee,1/15/91, (PB91-179242/AS).

NCEER-91-0003 "Seismic Response of Single Piles and Pile Groups," by K. Fan and G. Gazetas, 1/10/91, (PB92-174994/AS).

NCEER-9l-0004 "Damping of Structures: Part 1 - Theory of Complex Damping," by Z. Liang and G. Lee, 10/10/91, (PB92­197235/AS).

NCEER-91-0005 "3D-BASIS - Nonlinear Dynamic Analysis of Three Dimensional Base Isolated Structures: Part II," by S.Nagarajaiah, A.M. Reinhorn and M.C. Constantinou, 2/28/91, (PB91-190553/AS).

NCEER-91-0006 "A Multidimensional Hysteretic Model for Plasticity Deforming Metals in Energy Absorbing Devices," byE.J. Graesser and F.A. Cozzarelli, 4/9/91.

NCEER-91-0007 "A Framework for Customizab1e Knowledge-Based Expert Systems with an Application to a KBES forEvaluating the Seismic Resistance of Existing Buildings," by E.G. Ibarra-Anaya and S.J. Fenves, 4/9/91,(PB91-210930jAS).

NCEER-91-0008 "Nonlinear Analysis of Steel Frames with Semi-Rigid Connections Using the Capacity Spectrum Method,"by G.G. Deierlein, S-H. Hsieh, Y-J. Shen and J.F. Abel, 7/2/91, (PB92-113828/AS).

NCEER-91-0009 "Earthquake Education Materials for Grades K-12," by K.E.K. Ross, 4/30/91, (PB91-212142/AS).

NCEER-91-0010 "Phase Wave Velocities and Displacement Phase Differences in a Harmonically Oscillating Pile," by N.Makris and G. Gazetas, 7/8/91, (PB92-108356/AS).

NCEER-91-0011 "Dynamic Characteristics of a Full-Size Five-Story Steel Structure and a 2/5 Scale Model," by K.C. Chang,G.C. Yao, G.C. Lee, D.S. Hao and Y.C. Yeh," 7/2/91.

NCEER-91-0012 "Seismic Response of a 2/5 Scale Steel Structure with Added Viscoelastic Dampers," by K.C. Chang, T.T.Soong, S-T. Oh and M.L. Lai, 5/17/91 (PB92-1108l6/AS).

NCEER-91-0013 "Earthquake Response of Retaining Walls; Full-Scale Testing and Computational Modeling," by S. Alampalliand A-W.M. Elgamal, 6/20/91, to be published.

NCEER-91-0014 "3D-BASIS-M: Nonlinear Dynamic Analysis of Multiple Building Base Isolated Structures," by P.C. Tsopelas,S. Nagarajaiah, M.e. Constantinou and A.M. Reinhom, 5/28/91, (PB92-113885/AS).

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NCEER-91-0015 "Evaluation of SEAOC Design Requirements for Sliding Isolated Structures," by D. Theodossiou and M.C.Constantinou, 6/10/91, (PB92-114602/AS).

NCEER-91-0016 "Closed-Loop Modal Testing of a 27-Story Reinforced Concrete Flat Plate-Core Building," by H.R.Somaprasad, T. Toksoy, H. Yoshiyuki and A.E. Aktan, 7/15/91, (PB92-129980/AS).

NCEER-91-0017 "Shake Table Test of a 1/6 Scale Two-Story Lightly Reinforced Concrete Building," by A.G. EI-Attar, R.N.White and P. Gergely, 2/28/91.

NCEER-91-0018 "Shake Table Test of a 1/8 Scale Three-Story Lightly Reinforced Concrete Building," by A.G. EI-Attar, R.N.White and P. Gergely, 2/28/91.

NCEER-91-0019 "Transfer Functions for Rigid Rectangular Foundations," by A.S. Veletsos, A.M. Prasad and W.H. Wu,7/31/91, to be published.

NCEER-91-0020 "Hybrid Control of Seismic-Excited Nonlinear and Inelastic Structural Systems," by J.N. Yang, Z. Li and A.Danielians, 8/1/91.

NCEER-91-0021 "The NCEER-91 Earthquake Catalog: Improved Intensity-Based Magnitudes and Recurrence Relations forU.S. Earthquakes East of New Madrid," by L. Seeber and J.G. Armbruster, 8/28/91, (PB92-176742/AS).

NCEER-91-0022 "Proceedings from the Implementation of Earthquake Planning and Education in Schools: The Need forChange - The Roles of the Changemakers," by K.E.K. Ross and F. Winslow, 7/23/91, (PB92-129998/AS).

NCEER-91-0023 "A Study of Reliability-Based Criteria for Seismic Design of Reinforced Concrete Frame Buildings," byH.H.M. Hwang and H-M. Hsu, 8/10/91.

NCEER-91-0024 "Experimental Verification of a Number of Structural System Identification Algorithms," by R.G. Ghanem,H. Gavin and M. Shinozuka, 9/18/91, (PB92-176577/AS).

NCEER-91-0025 "Probabilistic Evaluation of Liquefaction Potential," by H.H.M. Hwang and C.S. Lee," 11/25/91.

NCEER-91-0026 "Instantaneous Optimal Control for Linear, Nonlinear and Hysteretic Structures - Stable Controllers," by IN.Yang and Z. Li, 11/15/91, (PB92-163807/AS).

NCEER-91-0027 "Experimental and Theoretical Study of a Sliding Isolation System for Bridges," by M.C. Constantinou, A.Kartoum, A.M. Reinhorn and P. Bradford, 11/15/91, (PB92-176973/AS).

NCEER-92-0001 "Case Studies of Liquefaction and Lifeline Performance During Past Earthquakes, Volume 1: Japanese CaseStudies," Edited by M. Hamada and T. O'Rourke, 2/17/92, (PB92-197243/AS).

NCEER-92-0002 "Case Studies of Liquefaction and Lifeline Performance During Past Earthquakes, Volume 2: United StatesCase Studies," Edited by T. O'Rourke and M. Hamada, 2/17/92, (PB92-197250/AS).

NCEER-92-0003 "Issues in Earthquake Education," Edited by K. Ross, 2/3/92.

NCEER-92-0004 "Proceedings from the First U.S. - Japan Workshop on Earthquake Protective Systems for Bridges," 2/4/92,to be published.

NCEER-92-0005 "Seismic Ground Motion from a Haskell-Type Source in a Multiple-Layered Half-Space," A.P. Theoharis,G. Deodatis and M. Shinozuka, 1/2/92, to be published.

NCEER-92-0006 "Proceedings from the Site Effects Workshop," Edited by R. Whitman, 2/29/92, (PB92-197201/AS).

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NCEER-92-0007 "Engineering Evaluation of Permanent Ground Deformations Due to Seismically-Induced Liquefaction," byM.B. Baziar, R. Dobry and A-W.M. Elgamal, 3/24/92.

NCEER-92-0008 "A Procedure for the Seismic Evaluation of Buildings in the Central and Eastern United States," by C.D.Poland and lO. Malley, 4/2/92.

NCEER-92-0009 "Experimental and Analytical Study of a Hybrid Isolation System Using Friction Controllable SlidingBearings," by Q. Feng, S. Fujii and M. Shinozuka, 2/15/92, to be published.

NCEER-92-0010 "Seismic Resistance of Slab-Column Connections in Existing Non-Ductile Flat-Plate Buildings," by AJ.Durrani and Y. Du, 5/18/92.

NCEER-92-0011 "The Hysteretic and Dynamic Behavior of Brick Masonry Walls Upgraded by Ferrocement Coatings UnderCyclic Loading and Strong Simulated Ground Motion," by H. Lee and S.P. Prawel, 5/11/92, to be published.

NCEER-92-0012 "Study of Wire Rope Systems for Seismic Protection of Equipment in Buildings," by G.F. Demetriades, M.C.Constantinou and A.M. ReinhorD, 5/20/92.

NCEER-92-0013 "Shape Memory Structural Dampers: Material Properties, Design and Seismic Testing," by P.R. Witting andF.A. Cozzarelli, 5/26/92.

NCEER-92-0014 "Longitudinal Permanent Ground Deformation Effects on Buried Continuous Pipelines," by MJ. O'Rourke,and C. Nordberg, 6/15/92.

NCEER-92-0015 "A Simulation Method for Stationary Gaussian Random Functions Based on the Sampling Theorem," by M.Grigoriu and S. Balopoulou, 6/11/92.

NCEER-92-0016 "Gravity-Load-Designed Reinforced Concrete Buildings," by G.W. Hoffmann, S.K. Kunnath, J.B. Mander andA.M. ReinhorD, 7/15/92, to be published.

NCEER-92-0017 "Observations on Water System and Pipeline Performance in the Limon Area of Costa Rica Due to the April22, 1991 Earthquake," by M. O'Rourke and D. Ballantyne, 6/30/92.

NCEER-92-0018 "Fourth Edition of Earthquake Education Materials for Grades K-12," Edited by K.E.K. Ross, 8/10/92.

NCEER-92-0019 "Proceedings from the Fourth Japan-U.S. Workshop on Earthquake Resistant Design of Lifeline Facilities andCountermeasures for Soil Liquefaction," Edited by M. Hamada and T.D. O'Rourke, 8/12/92.

NCEER-92-0020 "Active Bracing System: A Full Scale Implementation of Active Control," by A.M. ReinhorD, T.T. Soong,R.C. Lin, M.A. Riley, Y.P. Wang, S. Aizawa and M. Higashino, 8/14/92.

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