NAT l INST. OF STAND & TECH i

Ainob atoasb

NBSIR 84-2879

The NBS Tri-Directional Test

Facility

U.S. DEPARTMENT OF COMMERCE

National Bureau of Standards

National Engineering Laboratory

Center for Building Technology

Washington, DC 20234

May 1984

UATIC'TAL Bt;?"AU CF STANDARDS

LIBRARY

LX U

NBSIR 84-2879

. (X5 Co THE NBS TRI-DIRECTIONAL TEST

FACILITY

Kyle Woodward

Frank Rankin

U.S. DEPARTMENT OF COMMERCE

National Bureau of Standards

National Engineering Laboratory

Center for Building Technology

Washington, DC 20234

May 1984

U.S. DEPARTMENT OF COMMERCE, Malcolm Baldrige. Secretary

NATIONAL BUREAU OF STANDARDS. Erimt Ambler. Director

ABSTRACT

A general description of a unique structural testing apparatus is presented.

The apparatus is called the NBS Tri-directional Test Facility (NBS/TTF) . The

NBS/TTF can subject large structural elements to a wide variety of threedimensional loadings including both translations and rotations in three orthogonal

directions. The facility is computer based with all aspects of data acquisition,

reduction, and display coordinated and controlled by a minicomputer. The

minicomputer also controls the loading of test specimens as directed by the

operator. The loads are applied by a closed-loop hydraulic system having seven

independently servo-controlled hydraulic actuators. Test specimens having

dimensions as large as 3 m long by 3 m deep by 3.5 m high may be installed and

tested in the facility. Lateral forces of up to +900 kN may be imposed on

the test specimen in combination with vertical forces of up to +1800 kN.

i
TABLE OF CONTENTS

Page

ABSTRACT . i

LIST OF FIGURES ..... iii

1. INTRODUCTION 1 1.1 BACKGROUND ..... 1 1.2 OVERVIEW 1 1.3 GENERAL CAPABILITIES 2 1.4 NBS/TTF COMPONENTS ........ 3

2. REACTION SYSTEM ......... 9

3. LOADING SYSTEM 13

4. LOAD DISTRIBUTION SYSTEM AND ACTUATOR POSITIONING BEAMS .... 15

5. CONTROL SYSTEM HARDWARE 17

5.1 MINICOMPUTER AND PERIPHERALS 17

5.2 ANALOG-TO-DIGITAL CONVERTER (ADC) 17

5.3 DIGITAL-TO-ANALOG CONVERTER ( DAC) 18

5.4 SERVO- CONTROLLER 18

6. CONTROL SYSTEM SOFTWARE 19

6.1 ORGANIZATION 19

6.2 DATA ACQUISITION AND STORAGE 19

6.3 HYDRAULIC ACTUATOR CONTROL 20

6.4 DATA DISPLAY 20

7. REMARKS 22

8. ACKNOWLEDGEMENT 23

APPENDIX A: A PICTORIAL DESCRIPTION OF THE CONSTRUCTION OF THE

NBS/TTF 24

ii
LIST OF FIGURES

Page

Figure 1.1. Crosshead-test specimen arrangement 4

Figure 1.2. Simplified sketch of NBS/TTF 5

Figure 1.3. NBS/TTF 6

Figure 1.4. Hydraulic actuator arrangement 7

Figure 1.5. Control system schematic 8

Figure 2.1. Components of reaction system . 10

Figure 2.2. Floor slab anchorage detail 11

Figure 2.3. Buttress detail 12

Figure 3.1. Hydraulic actuator components 14

Figure 4.1. Actuator positioning system 16

Figure A.l. Laboratory prior to construction 25

Figure A. 2. Drilling holes in tie-down floor for rock anchors .... 26

Figure A. 3. Proof-testing an installed rock anchor 27

Figure A. 4. Rock anchor after removal from tie-down floor 28

Figure A. 5. Roughened outline of buttress cross-section 29

Figure A. 6 . Arrival of steel crossheads 30

Figure A. 7. Fabrication of buttress flange reinforcment 31

Figure A. 8. Erection of buttress flange 32

Figure A. 9. Buttress reinforcement in place 33

Figure A. 10. Pumping of buttress concrete 34

Figure A. 11. Placement of buttress concrete

Figure A. 12. Removal of buttress forms 36

Figure A. 13. Installation of lower crosshead

Figure A. 14. NBS/TTF nearing completion

iii

1. INTRODUCTION

In support of the National Bureau of Standards’ (NBS) legislated mission to

assist in the development of improved design procedures for buildings subject

to earthquakes, the NBS Center for Building Technology has constructed a unique

structural testing apparatus. The apparatus, referred to as the NBS Tridirectional Test Facility (NBS/TTF), is capable of applying controlled

displacements and/or forces in three orthogonal directions simultaneously.

1 . 1 BACKGROUND

Structures which are subjected to seismic disturbances undergo displacements

which include components in three orthogonal directions. As a result, the

structural elements which make up the load resisting framework of the structure

are also subjected to three-dimensional actions, including both translations

and rotations in all three orthogonal directions. However, much of the research

on structural component behavior, including ultimate resistances, has been done

using two-dimensional representations of the actual imposed conditions. (Such

representations generally impose translations and rotations in only two orthogonal

directions.) It is necessary to validate the results from such simplified test

procedures with data obtained from tests which better represent the threedimensional nature of the seismic response of structures.

One currently used testing technique is the shake table test. A shake table

is a platform on which test specimens are constructed and then vibrated using a movement pattern modeled from some previously recorded seismic event. While

shake table tests include dynamic effects (inertial effects and damping) they

rarely, if ever, include motions which incorporate translations and rotations

in three orthogonal directions.

Another technique currently used in structural testing is the "quasi-static"

test. Here, loads are imposed on the test specimen slowly, thereby eliminating

dynamic effects. However, a compensating advantage is the ability to closely

observe test specimen behavior during the test. The elimination of the dynamic

requirements simplifies the application of forces in all three dimensions.

For these reasons, the "quasi-static" approach was selected by the NBS

researchers as the basis for the development of the NBS/TTF.

1 .2 OVERVIEW

The general concept of the NBS/TTF is straightforward, but its actual implementation

is complex. At its most basic level the NBS/TTF is an apparatus which controls

the actions of two opposite ends of a test specimen. The test specimen is

placed between and attached to a pair of loading surfaces (crossheads) as shown

in simplified form in figure 1.1. The lower crosshead is attached to a structural

tie-down floor and is stationary. The upper crosshead is maintained in position

by seven hydraulic actuators. Lateral (horizontal) forces are resisted by

vertical buttresses and vertical forces by the tie-down floor. A simplified

1
depiction of the arrangement is shown in figure 1.2 and the actual NBS/TTF is

presented in figure 1.3.

The loading apparatus of the NBS/TTF is composed of a moving (upper) crosshead

and a stationary (lower) crosshead. The actions of the seven hydraulic actuators

(figure 1.4) directly control all six degrees of freedom (dof) of the upper

crosshead o The six dof consist of translations vertically and along each

crosshead arm and rotations about each of the translational axes. The upper

crosshead can impose any combination of values for the six dof on a test specimen,

within the limits of the hydraulic actuator capacities (see section 1.3).

A schematic of the equipment associated with the control system is shown in

figure 1.5. The schematic illustrates the primary information necessary to

the operation of the control system. The control system equipment is interfaced

with the operator by means of computer programs (software) which coordinate

the activities of the facility hardware to accomplish the user specified objectives.

The NBS/TTF is completely computer based permitting complex tasks to be directed

by simple instructions and, thereby, greatly improving the overall efficiency

of a test program. The data acquired during a test are stored by the computer

for future use. Much of the data reduction and display can be done automatically

with little direct operator intervention. The philosophy of the software is

to minimize direct user interaction with the NBS/TTF hardware during its operation.

The software commands are tailored for convenient use and generally make use

of English word commands and worksheet display entry.

1.3 GENERAL CAPABILITIES

The NBS/TTF is contained in a three-story open bay room serviced by two

overhead bridge cranes each having a capacity of 90 kN. The room is environmentally controlled, but has direct outside access through an overhead garage-type

door, 5 m wide and 4 m high. Normal laboratory facilities are available including compressed air to 850 kPa, hot, cold, and chilled water, and low- and

high-pressure steam.

The NBS/TTF can accomodate test specimens which have dimensions less than 3 m

long by 3 m deep by 3.5 m high. The vertical height of a test specimen includes

any attachments necessary to connect the specimen to the crossheads.

The force and displacement limits are not readily defined since actual test

conditions have a significant effect. As a guide, however, the displacement in

each of the three translational directions is limited to + 50 mm. The force

limits are + 1800 kN vertical, + 900 kN in one lateral direction, and + 700 kN

in the other lateral direction.

The rate of displacement change is slow (less than 20 mm per second) since the

NBS/TTF is designed to test specimens slowly, but with well-defined applied

actions. The NBS/TTF as currently configured is not intended for use where

fast loading rates or a large number of loading repetitions is required.

2
1.4 NBS/TTF COMPONENTS

For purposes of discussion, the NBS/TTF is divided into five major systems.

They include: the reaction system, the loading system, the load distribution

system, the control system hardware, and the control system software. The

remainder of this report is organized on the basis of these systems. A pictorial

description of the construction of the NBS/TTF is presented in an appendix.

The purpose of this report is to provide a general description of the NBS/TTF.

The discussion is devoted to an understanding of the concept, capabilities,

and sophistication of the NBS/TTF.

3
Figure 1.1. Crosshead-test specimen arrangement

4
Figure 1.2. Simplified sketch of NBS/TFF

5
Figure 1.3. NBS/TTF

6
Note: Actuator load capacitlas

ara shown in paranthaaaa

Figure 1.4. Hydraulic actuator arrangement

7
NBS/TTF CONTROL SYSTEM SCHEMATIC

Figure 1.5. Control system schematic

8
2 . REACTION SYSTEM

The reaction system is composed of two parts, a structural tie-down floor and

two vertical buttresses (figure 2.1). The structural tie-down floor is a 1.8 m

thick heavily reinforced concrete slab. The slab contains an embedded grid of

steel beams to resist lateral forces. Anchorage points for connecting test

fixtures to the slab are located in a grid 1.5 m on center. The anchorage

points (figure 2.2) are flush with the slab surface and have two threaded

sleeves which accept threaded high strength steel rods. Each anchorage point

(using both sleeves) has a working capacity of 900 kN in both the vertical and

horizontal directions. The horizontal resistance is not provided by the threaded

rod, but by direct bearing of shear sleeves which are concentric with the

threaded rods.

The buttresses are vertical reinforced concrete structures which are post-tensioned

both vertically and horizontally (figure 2.3). The orientation of the buttresses

with respect to the loading system is shown in figure 1.2. The buttresses are H-shaped in plan view and are 4.9 m tall. There are through holes in each

buttress at four heights to permit fastening of attachments. Each buttress

has a design lateral load capacity of 1300 kN applied 4.3 m above the slab

surface. The capacity is based on a criterion of no vertical tension in the

buttress. The moment resistance is principally provided by the twenty-eight

vertical post-tensioned rods in each buttress. Each post-tensioned rod is

terminated in the tie-down floor with a rock anchor. The rock anchors are made

of a length of high strength steel rod embedded in an epoxy material with a coupler at the top to receive the buttress rod. Each rock anchor/buttress rod

assembly was proof tested to a load 30 percent greater than its design working

load.

9
Figure 2.1. Components of reaction system

10
CAPPED HOLE

-I’-l”—

±0.00S”

HOLE USED FOR

SHEAR RESISTANCE

AND HOLD DOWN

Removable plus

Finish floor

1-1/4” x IS

continuous otool plato

Wold both sides

Wrap surfaces to

prevent bonding

to concrete

Dimensions arc shown in English units because

construction dimensions

were specified in English

units. 1 m = 3.20 1 ft.

Figure 2.2. Floor-slab anchorage detail

11
Figure 2.3. Buttress detail

12
3. LOADING SYSTEM

The loading system consists of seven double-ended hydraulic actuators which

are part of a general closed-loop, servo-controlled hydraulic system. Support

equipment includes a hydraulic power supply (pump), servo-controllers (discussed

in section 5.4), and miscellaneous wires, hoses, and other items necessary to

interconnect the different parts of the system.

A hydraulic actuator, in its simplest form, is a hydraulic cylinder with a piston which can extend and retract. The movement of the piston is controlled

by the volume of oil in the cylinder. A servo-controlled hydraulic actuator

has an electrically controlled hydraulic valve to regulate the volume of oil in

the cylinder. The hydraulic actuators used in the NBS/TTF have additional

components not found on simple hydraulic actuators. A typical hydraulic

actuator used in the loading system is shown in figure 3.1 with the major

components identified. The major components are the servo valve, service

manifold, piston, load transducer (load cell), internally mounted displacement

transducer (LVDT-linear variable differential transformer), and swivel end

fittings. The servo valve has a flow rating of 3.36 cubic meters per second.

The service manifold performs several functions. It filters the oil, controls

oil volume fluctuations, permits operation of the actuator in a low-pressure

condition and, when needed, prevents the piston from moving even in the absence

of an external hydraulic pressure source. The load transducer measures the

load applied to the actuator as a result of piston action. The displacement

transducer is rigidly mounted inside the body of the actuator and measures the

piston movement relative to the actuator body. The swivel end fittings permit

relatively unrestrained rotation over an angle of 270 degrees in the plane of the

swivel and approximately 10 degrees in the other planes. In short, the swivel

can rotate in all three dimensions.

Each of the four vertically installed hydraulic actuators has a total piston

movement range of 300 mm. The load capacity of each vertical actuator is 670

kN in either tension or compression. Each of the two horizontal actuators

which are parallel to the north-south axis of the NBS/TTE has a stroke of 300 mm and a load capacity of 380 kN in either tension or compression. The single

horizontal actuator installed along the east-west axis of the facility has a stroke of 150 mm and a load capacity of 975 kN in either tension or compression.

The hydraulic power supply is a 4.5 cubic meters per second, variable volume pump

rated at a pressure of 34 MPa but used at a pressure of 20 MPa.

13
Figure 3.1. Hydraulic actuator components

SWIVEL END FITTING

DISPLACEMENT!

TRANSDUCER lj

(INTERNAL LVOTi

swim end fitting

SERVICE MANIFOLD

SERVOVALVE

: iS ON mmsm

£e&. . ; vj

LOAD TRANSDUCER

14
4. LOAD DISTRIBUTION SYSTEM AND ACTUATOR POSITIONING BEAMS

The load distribution system consists of upper and lower steel crossheads.

Each crosshead is formed by two approximately 4 m long beams bisecting

at a 90 degree angle. Each beam has a cross section in the shape of a flanged

box. This shape was made by welding two heavy wide-flange structural shapes

(W21 x 132) together along their butted flanges. Each crosshead surface is

approximately 635 mm wide and is pierced along its length with holes through

which test specimens can be bolted to the crosshead. Each crosshead is heavily

stiffened by vertical plates 6 mm thick welded to both the top and bottom flanges

and the web of each wide-flange beam. The lower crosshead is bolted to the

tie-down floor and held stationary

The horizontal hydraulic actuators are attached to the reinforced concrete

buttresses by means of steel positioning beams. A typical beam is shown in

figure 4.1. The use of slotted holes and an incremental round hole spacing

permits a continuously variable height adjustment. The limits of the adjustment,

however, are dictated by the hole pattern of the buttress and are approximately

1.2 m and 4.3 m above the slab surface.

15
Figure 4.1 Actuator positioning beam

16
5. CONTROL SYSTEM HARDWARE

The control system coordinates the activities of the NBS/TTF including hydraulic

actuator piston movements, test specimen data acquisition, and data display.

The control system consists of a minicomputer with the usual peripherals, an analog-to-digital converter, a digital-to-analog converter, seven servo con- trollers, and computer software. A schematic of the system is shown in figure 1.5. This section discusses the hardware while the next section discusses

the computer software.

5.1 MINICOMPUTER AND PERIPHERALS

The minicomputer system is based on a moderately powerful, 16-bit word length,

central processing unit (CPU). Enhancements to the CPU include memory management with 18-bit addressing, hardware floating point operations, and hardware

integer multiply and divide. The main memory contains 256 kilobytes (kb) of

MOS memory which is the maximum possible for 18 bit addressing. Permanent

mass storage is provided by three hard media disk drives and one tape drive.

There are currently about 18 megabytes (Mb) of disk storage with all but 5 Mb

contained in removable media disk drives. The tape drive is an industry com- patible nine-track unit supporting both 800 and 1600 bit per inch writing

densities. Storage capacity on a tape is affected by several factors but, as

a guide, 40 Mb (10 million data points) can be recorded on a single 730-m reel

of tape.

The user interface includes several video display terminals, high-speed printing

terminals, video graphic devices (including color), a flat-bed digital plotter,

and a high-speed (300 line per minute) line printer. The video terminals are used for data display in both tabular and graphical form. The printing terminals are primarily intended as user input devices during a test so that a copy

of all user instructions is obtained. The flat-bed plotter is mainly used for

post-test data plotting and the line printer is used to obtain a listing of

all acquired data immediately after a test.

5.2 ANALOG-TO-DIGITAL CONVERTER (ADC)

The ADC is a high speed multiplexed converter with a sampling rate of 50,000

samples per second. It is connected to the minicomputer by Direct Memory

Access such that the total system throughput is equal to the 50 kHz converter

sampling rate. The current system has provisions for 192 separate data channels.

The ADC has two levels of internal signal amplification (gain) to maximize the

conversion resolution. The first gain is determined by interchangeable chips on the circuit boards with each channel being individually adjustable. The

second gain is selected by computer instruction and can be set for each channel.

The total gain applied to each channel prior to conversion is the product of

the two gain levels. The total gain is variable in discrete steps between 1 and 20,000. Active signal filtering is performed on each channel with tin

cutoff frequency selected by interchangable chips on the circuit boards. The

converter has a full-scale range of 10 volts with a digital representation

17
provided by a 12-bit word. The resolution (not error) is 1 part in 4096

( 1 /2 12 - 1/4096).

5.3 DIGITAL-T0-ANAL0G CONVERTER (DAC)

The DAC can be accessed at CPU machine speed, but the rise and settle time is on the order of 5 microseconds. There is a total of eight DAC channels, seven

of which connect to the servo-controllers. The DAC has a full-scale range of + 10 volts with a resolution of 1/4096.

5 . 4 SERVO- CONTROLLER

Each hydraulic actuator requires a servo-controller to manipulate the actuator's

servo valve. The servo-controller is basically an analog comparator. Its

function is to constantly compare an analog command signal with an analog

feedback signal and to manipulate the action of the hydraulic actuator's piston

such that the difference between the command and feedback signals is zero.

The difference between the command and feedback signals is called the error

signal. The servo-controller uses the error signal to determine how the servo valve should be directing oil flow. The feedback signal is usually from a load transducer (load control) or a displacement transducer (stroke control).

The command signal may be produced internally by the servo-controller and

varied manually by the operator at the servo-controller itself or the command

signal may be externally generated and varied such as through a DAC. For ease

of operation, the servo-controller is calibrated such that the full-scale

range of the command signal is equal to the full-scale range of the two feedback

transducers. This procedure produces a direct one-to-one correspondence between

a given command signal and the resulting feedback signal.

A simple example of servo-controller operation is described below. Assume that

stroke (displacement) is the control feedback and the relation between piston

movement and feedback voltage is 5 mm per volt with piston extension producing

a positive change in voltage. Consider that the actuator's piston is extended

10 mm from its fully retracted position and that this extension corresponds to

a feedback signal of +2 volts. If the command signal is set to +2 volts then

there is no piston movement. If the command signal is changed to +1 volt then

an error signal of -1 volt is produced. The error signal is translated by the servo controller into a current signal to the servo valve which causes oil to

flow into and out of the actuator such that the piston retracts 5 mm. There

is no further piston movement until the command signal in changed and an error signal generated. Within the load capacity of the actuator the piston will

move to satisfy the command signal regardless of the load developed as a result

of the movement. The load produced by piston movement is determined by the

stiffness of the objects attached to the actuator. If load control is used

then the piston moves to whatever position is required (within its stroke

limits) to produce the desired load.

18
6. CONTROL SYSTEM SOFTWARE

All functions associated with hydraulic actuator control and data acquisition,

manipulation, and display both during and after a test are computer-based. A

large collection of computer software has been developed by NBS researchers to

perform the various tasks. In general, all software is user oriented, making

it possible for relatively inexperienced operators to use the NBS/TTF. However,

the complexity and sophistication of the overall NBS/TTF (both hardware and

software) require that a trained and experienced operator must oversee the

planning and execution of any test.

6.1 ORGANIZATION

The software which actually supports the performance of a test is all that will

be discussed in this report. Post-test data manipulation and display software

is of a general nature and not exclusive to the NBS/TTF. It is worthwhile to

note, however, that there is extensive software available to support the posttest analysis of data produced by tests in the NBS/TTF.

The software which supports the actual testing of a specimen in the NBS/TTF is

called TEX which is an acronym for J?est Executive. TEX is not a single program,

but a collection of separate executable programs (tasks) which operate concur- rently in a multi-task environment. The specific needs of a test determine

which programs are actually used, but the selection and operation of the various programs is controlled by the software and not by the operator. The use

of multi-tasks permits fast response to changing test conditions by enabling

the various tasks to be prioritized. The assignment of priorities enables TEX

to allocate more computer resources to those tasks which require them and to

do it on a real-time basis. There are also pre-test computer programs which

support the use of data bases necessary to the execution of TEX. In addition,

there is software tailored to the manipulation of the NBS/TFF during test

specimen installation.

The functions of TEX can be divided into three main categories: 1) data

acquisition and storage, 2) hydraulic actuator control, and 3) data display.

In actual practice the functions are not as distinct, but for purposes of the

subsequent discussion the division is a convenient classification.

6.2 DATA ACQUISITION AND STORAGE

The function of data acquisition and storage is common to all laboratory testing.

TEX requires several separate data acquisition processes, but this discussion

is limited to that which pertains to data acquired by user request. The operitor predefines the ADC channels which will be sampled during the test but the

channel definition may be changed during the test. The same data base can he

used for many tests. The operator specifies acquisition rate and can turn tin- acquisition of data on and off. The acquired data are stored as decimal

voltages and the amount of data which can be acquired is limited only by t Im- permanent storage space (disks and tape) available. The user does not have

19
access to the stored decimal voltage during a test, but to permit data

plotting and display during a test a second form of data storage is provided.

A certain amount of permanent storage is allocated to a data pool. The same

pool is used for each test so the information in the pool exists only during a test. TEX processes the acquired data on a time available basis to produce

data in engineering units (reduced data) and stores these data in the data pool.

The user may access the data pool to produce graphical or tabular displays of

the acquired information. The data in the pool can be algebraically manipulated

and edited to produce data displays using almost any possible combination of data.

6.3 HYDRAULIC ACTUATOR CONTROL

The computer software which controls the individual hydraulic actuators is

complex, but the use of the software is simple. The operator

need not consider the individual actions of the actuators. Instead, the operator

defines global actions of the upper crosshead. The global actions are defined

in terms of three easily visualized global directions which are north-south,

east-west, and vertical. The lateral directions, north-south and east-west,

are aligned with the two intersecting arms of the crosshead prior to crosshead

movement. Each of the six degrees of freedom of the upper crosshead is defined

by the operator by simply specifying values for the dof in terms of either a force (moment) or displacement (rotation). The specified value denotes whether

a particular degree of freedom is displacement or load controlled. The method

of control can be changed by simply specifying the desired control value. For

example, the vertical translation degree of freedom may be defined as load

control with the software required to maintain 50 kN of vertical compressive

force on the test specimen. The vertical displacement of the crosshead is then

automatically varied by whatever amount is required to maintain 50 kN. Simultaneously, the translation in the north-south direction could be defined as 2 mm in displacement control. The software would then direct the hardware to

move the crosshead 2 mm in the north-south direction while still maintaining 50

kN vertically. The software accounts for the effect of geometry changes caused

by crosshead movement and resolves all actuator piston displacements and imposed

forces into components acting in the global directions.

6.4 DATA DISPLAY

The data display function described in this section is the real-time data

monitor. The display capabilities associated with user specified data acquisition

were discussed in section 6.2. It is important that the operator have certain

test specimen data available on a continuously updated basis. The operator can more readily verify proper test conduct and alter loading conditions if required.

It would be extremely wasteful of permanent storage space to acquire and store

all of the information needed to produce updated data display. For this reason,

TEX includes a monitor capability which provides a real-time display of user specified data channels. The data are not stored, but only updated on a video

display terminal. The data displayed by the monitor are reduced data and include

corrections for excitation voltage fluctuations, gage factor, and temperature

effects as specified by the operator. The data channels actually displayed may

20
be selected by the operator prior to the test and changed at any time during

the test. An alternative to the reduced data format is the display of uncorrected

decimal voltage values. This format is useful to verify that transducers are operating properly.

21
7 . REMARKS

The NBS/TTF is an addition to the existing structural testing laboratories

and complements the currently available capabilities. The primary enhancement to structural testing provided by the NBS/TTF is its ability to control the

movements (translations and rotations) of a test specimen in three orthogonal

directions. While the NBS/TTF is primarily devoted to research on improving

the resistance of structural elements subjected to earthquake loadings, its

usefulness extends into other areas of structural research including the effects

of wind loadings on structural elements.

22
8 . ACKNOWLEDGEMENT

The authors wish to thank Dr. John Gross, Dr. Spencer Wu, Dr. E. V. Leyendecker,

and Dr. Len Mordfin for their careful review of this report and their constructive

comments

.

23
APPENDIX: A PICTORIAL DESCRIPTION OF THE CONSTRUCTION OF THE NBS/TTF

Figure A. 1

Figure A.

2

Figure A. 3

Figure A.

4

Figure A. 5

Figure A.

6

Figure A.

7

Figure A.

8

Figure A. 9

Figure A. 10

Figure A. 11

Figure A. 12

Figure A. 13

Figure A. 14

Laboratory prior to construction

Drilling holes in tie-down floor for rock anchors

Proof-testing an installed rock anchor

Rock anchor after removal from tie-down floor

Roughened outline of buttress cross-section

Arrival of steel crossheads

Fabrication of buttress flange reinforcement

Erection of buttress flange

Buttress reinforcement in place

Pumping of buttress concrete

Placement of buttress concrete

Removal of buttress forms

Installation of lower crosshead

NBS/TTF nearing completion

24
Figure A.l. Laboratory prior to construction

25
I

Figure A. 2. Drilling holes in tie-down floor for rock anchors

26
Figure A. 3. Proof-testing an installed rock anchor

27
Figure A. 4. Rock anchor after removal from tie-down floor

28
Figure A. 5. Roughened outline of buttress cross-section

29
Figure A. 6. Arrival of steel crossheads

30
Figure A. 7. Fabrication of buttress flange reinf orcenen

31
Figure A. 8. Erection of buttress flange32
Figure A. 9. Buttress reinf orceraent in place

33
Figure A. 10. Pumping of buttress concrete

34
/

Figure A. 11. Placement of buttress concrete

35
Figure A. 12. Removal of buttress forms

36
* *& *

» • *

ff

Figure A. 13. Installation of lower crosshead

37
Figure A. 14. NBS/TTF nearing completion

38
NBS-II4A REV. 2*®C i U.S. DEPT. OF COMM.

BIBLIOGRAPHIC DATA

SHEET (See instructions)

1. PUBLICATION OR

REPORT NO.

NBSIR 84-2879

2, Performing Organ. Report No. 3. Publication Date May 1984

4. TITLE AND SUBTITLE

The NBS Tri -Directional Test Facility

5. AUTHOR(S)

Kyle Woodward and Frank Rankin

6. PERFORMING ORGANIZATION (If joint or other than N BS, see instructions)

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

7. Contract/Grant No.

8. Type of Report & Period Covered

9. SPONSORING ORGANIZATION NAME AND COMPLETE ADDRESS (Street, City, State, ZIP)

same as 6 above

10.

SUPPLEMENTARY NOTES

_ Document describes a computer program; SF-185, FIPS Software Summary, is attached.

11.

ABSTRACT (A 200-word or less factual summary of most significant information. If document includes a significant

bi bl iography or literature survey, mention it here)

A general description of a unique structural testing apparatus is presented. . he

apparatus is called the NBS Tri-di rectional Test Facility (NBS/TTF). The NBS/TTF

can subject large structural elements to a wide variety of three-dimensional loadings

including both translations and rotations in three orthogonal directions, the

facility is computer based with all aspects of data acquisition, reduction, and display coordinated and controlled by a minicomputer. The minicomputer also controls

the loading of test specimens as directed by the operator. The loads are applied by

a closed-loop hydraulic system having seven independently servo-controlled hydraulic

actuators. Test specimens having dimensions as large as 3 m long by 3 m deep by 3.5

high may be installed and tested in the facility. Lateral forces of up to ±900 kN - ay

be imposed on the test specimen in combination with vertical forces of up to :18C0 kN

12.

KEY WORDS (Six to twelve entries; alphabetical order; capitalize only proper names; and separa * -

. , --in Actuators; computer based; hydraulic; seismic; servo-control led ; structural testir , test facility; three dimensional.

13. AVAILABILITY

YY Unlimited For Official Distribution, Do Not Release to NTIS —

Order From Superintendent of Documents, U.S. Government Printing Office, Aashingto' . D.C. 20402. XX Order From National Technical Information Service (NTIS), Springfield, VA. 22161

14. NO. OF

PRINTEO PAGES

44

IS. Price

$8 . 50