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A 11 ID 3 fi M 6 L T

3

NBSIR 85-3126

Monitoring of Dynamic Response

of Floor in "D" Wing of the Main

Building, Bureau of Engraving and

Printing

Felix Y. Yokel

U S. DEPARTMENT OF COMMERCE

National Bureau of Standards

National Engineering Laboratory

Center for Building Technology

Gaithersburg, MD 20S99

and

Paul W. Mayne

Law Engineering Testing Company

P.O. Drawer QQ

McLean, VA 22201

March 1985

Prepared for

. au of Engraving and Printing ^

and C Street, SW

100 iington, DC 20228

. U56

85-3126

1985

NATIONAL BUREAU OF STANDARDS

LIBRARY N8SIR 85-3126

9 4 4 MONITORING OF DYNAMIC RESPONSE

OF FLOOR IN "D" WING OF THE MAIN

BUILDING, BUREAU OF ENGRAVING AND

PRINTING

Felix Y. Yokel

U.S. DEPARTMENT OF COMMERCE

National Bureau of Standards

National Engineering Laboratory

Center for Building Technology

Gaithersburg, MD 20899

and

Paul W. Mayne

Law Engineering Testing Company

P.O. Drawer QQ

McLean, VA 22201

March 1 985

Prepared for Bureau of Engraving and Printing

1 4th and C Street, SW

Washington, DC 20228

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

NATIONAL BUREAU OF STANDARDS, Ernest Ambler. Director

ABSTRACT

In December 1981, the National Bureau of Standards investigated structural

vibrations induced in the first floor of the "D" wing of the main building of

the Bureau of Engraving and Printing. In January 1985, additional measurements

were performed to check whether there are any changes in the response characteristics of the floor systems which might indicate structural degradation. The

results of these measurements are presented and it is concluded that the results

of the vibration measurements give no indication of structural degradation.

Key Words: Floor vibrations; structural dynamics; structural engineering.

1. BACKGROUND

Following the installation of two new coiling machine perforators on the first

floor of the "D" wing of the main building of the Bureau of Engraving and

Printing, floor vibrations were observed. In December 1981, the Center for

Building Technology of the National Bureau of Standards (NBS) conducted vibration

measurements in order to determine whether potential structural damage could

resul t.

In an analysis of the December 1981 vibration data [1], NBS concluded that

future structural damage as a result of these vibrations would be unlikely.

However, it was recommended in the NBS report that machine web speeds which were

observed to produce peak displacement responses in the floor systems be avoided.

It was also recommended that vibrations be periodically monitored in order to

detect potential signs of structural deterioration.

It was recommended to check the natural frequency and damping characteristics

of the floor systems in these vibration tests and to compare measured values

with those observed in December 1981.

In accordance with the above NBS recommendation, vibrations were monitored on January 7, 1985. The results of this investigation are reported herein.

2. TEST EQUIPMENT

A SINCO S-3i/ vibration monitor with an oscillographic recorder was used.

Vertical vibrations were measured with a geophone which measures velocities

and has a flat response from 6 Hz to 150 Hz frequency. Velocities are measured

to an accuracy of 0.25 mm/ si/. Measurements were graphically recorded to a scale of 4 • 10"3 g's per mm for accelerations, 0.1 mm/s per mm for velocities,

and 0.001 mm per mm for displacements. The time scale for most measurements

was 4.21 ms per mm.

Reference to a specific make of equipment does not imply endorsement of

this equipment by the National Bureau of Standards.

U Information provided by the manufacturer 1 s representati ve.

1
3. TEST SCHEDULE

The objective of the tests was to obtain natural frequencies and damping ratios

(percent of critical damping) at two critical locations near the machines on the south and north floors, and to duplicate some of the December 1981 measurements at locations and machine speeds which produced the greatest displacement

response.

Data were taken for vertical acceleration (a), veclocity (v), and displacement (<5) of the floor at the point of measurement as a function of time

(t). Since the equipment used measures velocities and since the acceleration

records of the steady-state machine induced vibrations tend to exhibit many

discreet spikes while the velocity and displacement records are relatively

smooth sinusoidal curves, RMS values for comparison with the December 1981

measurements were estimated from velocity and displacement records only.

Critical machine web speeds which produced peak displacement response amplitudes

in the December 1981 tests were 117 fpm (feet per minute) and 160 fpm for the

south floor, and 125 fpm and 155 fpm for the north floor. In the present test

the machine on the south floor would not run faster than 150 fpm. Consequently,

the south floor readings for the fast machine speed were taken at 150 fpm,

rather than the 160 fpm for which there are data from the December 1981 tests.

This may have resulted in a reduced dynamic response.

The time scale of 4.21 ms per mm used in the recording of data was obtained by

advancing the recording tape at a rate of 0.275 m/s. The manufacturer specified

the speed of paper advance to be 0.25 m/s +3 percent. The speed of 0.275 m/s

which was used to calculate response frequencies was obtained by calibrating

the speed of advance of the recording tape against time intervals measured

electronically to an accuracy of +_ 2 percent^/ and marked on the tape.

Measurement inaccuracies may be responsible for slight discrepancies between

frequencies measured in the present and the previous test. However, since

changes in the magnitude and distribution of floor loads could also lead to

slight changes in frequency response, the accuracy of the equipment used was judged adequate for the intended purpose.

Table 1 shows the test schedule. Refer to figure 1 for test locations.

2
(HID

COLUMN

HimifOS

tOVTrt

Figure 1. Grid of test points (dots indicate grid points)

3
Table 1. Test Schedule

1

1

1 Floor | Location

Row/Col .*

Free

Vibration

1 Steady-State Vibration 1

1 117 fpm** 150 fpm 1 125 fpm | 155 fpm|

T

1

r South | 7/4 (1)***1

1 (2) (3)

n r

i i ri

1 1 4/4 ! (4) (5) 1 1 1

1

i

1

i 9/4 1

i (6) 1 11 i

1

1

i

1

l North | 6/5 (7)i

1 1 (8) | (9) |

1 1 8/5 1 ! do) | (ID |

1

1

1

I 10/5 1

•

1 1

1 1

(12) |

1

* Refer to figure 1. ** Machine web speed, feet per minute. *** Number in parentheses designates test number.

4. TEST RESULTS

4.1 FREE VIBRATIONS

Free vibrations were generated by a 190 lb person jumping once near the point of

measurement. Figure 2(a) shows a plot of vertical velocity (v) versus time (t)

for a free vibration at point 7/4 on the south floor. The damping ratio is

approximately 5 percent of critical damping. This compares with a damping ratio

of 6 percent measured in December 1981 at the same location. The fundamental

natural frequency is 13.0 Hz, which compares with a 13.3 Hz frequency measured in

December 1981.

Figure 2(b) shows a plot of vertical velocity for the north floor. The damping

ratio is approximately 6 percent and the fundamental natural frequency 13.5 Hz.

This compares with a 14 Hz natural frequency observed in December 1981. The

damping ratio of the north floor was not measured at that time.

4.2 STEADY-STATE VIBRATIONS WHEN MACHINES ARE OPERATING

Typical traces of vertical velocity and displacement vs. time are shown in

figure 3 for point 7/4 on the south floor at a machine speed of 117 fpm. The

results of the measurements are summarized in table 2 and compared with RMS values

of the December 1981 measurements. Figure 4 shows a comparison of primary

vibration frequencies at different machine speeds measured in the present tests

with average values obtained in the December 1981 tests.

4
>

H

O

o

HI>

<

o

DC

III >

(a) Trace of vertical velocity

on the south floor

vs. time for a free vibration at point 7/4

>

K

O

o

_JHi>

_J<

o

DC

Hi>

TIME (s)

(b) Trace of vertical velocity vs. time for a free vibration at point 6/5

on the north floor

Figure 2. Free vibration record

5
VERTICAL

Figure 3. Traces of vertical displacement and velocity vs. time at point

7/4 on the south floor measured at 117 fpm machine speed

6
Induced

by

Different

Machine

Speeds

s/: cXZi0) uX£

fcT XOuX

CN

0) —x

£-

uouxox—I uXEcu 7
PRIMARY

FREQUENCY

OF

FLOOR

VIBRATION

(Hz)

MACHINE WEB SPEED (fpm)

Figure 4. Comparison between primary frequencies of steady-state vibrations

as a function of machine speeds measured in December 1981 and

January 1985.

8
5. DISCUSSION OF RESULTS

Any structural degradation of the floor system would tend to increase the

damping ratio. It also would tend to decrease the stiffness of the system and

thus lower its natural frequency, however, this effect may be more difficult to

observe, since the frequency will also be affected by the magnitude and

distribution of floor loads which is likely to change from test to test.

The test results indicate that the damping ratio of the south floor observed in

the January 1985 test is somewhat lower than that observed in December 1981.

Thus, there is no indication of any structural degradation (no data were taken

for the north floor in December 1981, however, future tests can be compared

with the results of these tests.)

The natural frequencies of the south and north floors observed in these tests

are somewhat lower than those observed in December 1981, however, in view of

the fact that the natural frequency is also affected by the magnitude and

distribution of floor loads, this minor difference is considered to be

insignificant.

The comparison of the steady-state displacement responses in table 2 shows that

the responses are of the same order of magnitude. For the lower machine speeds

the RMS displacement responses measured in the present tests ranged from 44 to

61 percent of those measured in December 1981. For the larger machine soeeds,

most RMS diplacement responses in the present test tended to be larger than

those in the December 1981 test. The RMS displacement responses measured in

the present test ranged from 0.7to 1.52 times those measured in December 1981.

It can be seen from figure la in reference [1], that the response is- sensitive

to the machine speed and a larger (or smaller) response could conceivably have

been produced by slightly different machine speeds.

It is important to note that, as the analysis in the 1982 report shows,

displacement responses of the order of magnitude observed in the December 1981

tests and those observed in the present tests are associated with stress levels

which are unlikely to produce any structural deterioration [1].

9
It is concluded from the data presented in this report that the results of the

January 1985 vibration measurements do not give any indication of structural

degradation of the floor system.

6. REFERENCES

[1] Reinhold, T. A., Yokel, F. Y., Rudder, F. F., "Investigation of Floor

Vibrations in the "D" Wind of the Main Building of the Bureau of Engraving

and Printing," NBSIR 82-2599, National Bureau of Standards, October 1982.

10
U.S. DEPT. OF COMM.

BIBLIOGRAPHIC DATA

SHEET (See instructions)

1. PUBLICATION OR

REPORT NO.

NBSIR 85-3126

2. Performing Organ. Report No. 3. Publication Uate

March 1985

4. TITLE AND SUBTITLE

MONITORING OF DYNAMIC RESPONSE OF FLOOR IN "D" WING OF THE MAIN BUILDING,

BUREAU OF ENGRAVING AND PRINTING

5 . author(S) Felix Y. Yokel

Paul W. Mayne

6 . PERFORMING ORGANIZATION (If joint or other than NBS, see instructions) 7. Contract/Grant No.

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE 8. Type of Report & Period Covered

WASHINGTON, D.C. 20234

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

Bureau of Engraving and Printing

10. SUPPLEMENTARY NOTES

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

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

bi bliography or literature survey, mention it here)

In December 1981, the National Bureau of Standards investigated structural

vibrations induced in the first floor of the "D" wing of the main building of

the Bureau of Engraving and Printing. In January 1985, additional measurements

were performed to check whether there are any changes in the response characteristics of the floor systems which might indicate structural degradation. The

results of these measurements are presented and it is concluded that the results

of the vibration measurements give no indication of structural degradation.

12. KEY WORDS (Six to twelve entries; alphabetical order; capitalize only proper names; and separate <ey words : / tern c; ;

Floor vibrations; structural dynamics; structural engineering.

13. AVAILABILITY 14

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Order From Superintendent of Documents, U.S. Government Printing Office, Washington. D.C. 20402. 15.

NO. OF

PRINTED PAGES

13

Price

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