FLOWER CONSUAPTION TES'

:)OUi:31.J:: i31;:;CK BASCULE ORll

OR] DC

V. A. CROWN L. C^ BuSM

19 13

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;rown, V. M.

?ower consumption tests of double deck bascule bridge

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Power Consumption Tests of a Double Deck Bascule Bridge

A THESIS

PRESENTED BY

V. M. Crown and L. C. Bush

TO THE

PRESIDENT AND FACULTY

OF

ARMOUR INSTITUTE OF TECHNOLOGY

FOR THE DEGREE OF

BACHELOR OF SCIENCE

IN

CIVIL ENGINEERING

MAY 29, 1918

APPROVED:

,/?

ILLINOIS INSTITUTE OF TECHNOLOGY ^jj ^^^

PAUL V. GALVIN LIBRARY /^ nSS^^T^r^i ^^^^^

35 WEST 33RD STREET ' ^. T?t .C?^__„_„

CHICAGO, IL 60616 ~ Dea^^^BineenngSmdies

Dean of Cultural Studies

POWER CONSDMPTION TEST OP A DOUBLE DECK BISCDLE BRIDGE

Lake Street Double Deck Bascule Bridge

28108

F OEEWORD

In May 1917 a thesis similar in cbar- acter to this one was written by two students of Armour Institute pertaining to a power con- sumption test on the Webster Av. bascule bridge of Chicago* Mention was made therein that under conditions existing at that time a test on the new Lake St • double track bascule bridge would be very difficult to meke. However, the bridge department of the City of Chicago was very de- sirous of having a test made on this bridge* So, through the co-operation of Mr* Chas * Harrington of the electrical department, who personally directed the test, the writers are able to pre- sent this thesis*

The authors also wish to express their sincerest thanks to Mr. John C. Bley of the Divi- sion of Bridges, Prof* John C. Penn and Mr* Falk of Armour Institute of Technology, for their valuable assistance and co-operation and to A* L,

Scbreiber and Stuart K . Miller of the class of 1917 from whose thesis the authors obtain- ed valuable information pertaining to a simi- lar test.

The City of Chicago has in view the erection of several bridges of this type. It is hoped that the results of this investiga- tion will furnish data by which present diff- iculties in the operation and control of a bridge of this kind may be overcome.

May 1st, 1918

COHTBHTS

Page

Frontispiece Z

Foreword Z

Introduction 7

Operation of Bridge 10

Obj'ects of Teats 15 Apparatus

Wattmeter and Auxiliary Equipment 16 Apparatus for Eecording Angular

Position of the Bridge Leaf £1 Anemometer and Determination of

Torque 26

Eesults 30

Conclusion 44

Curves 46

LIST OF ILLUSTKATIOIIS

Frontispiece 8

West Leaf in Open Position 9

Operating Machinery IZ

Eecording Apparatus in Plan 2&

Side View of Bridge 4£

POWEE COM SUMPTION TEST OF A DOUBLE DECK BASCULE BRIDGE IKTEODUCTIOH

The Lake Street bridge is a double leaf, double deck, trunnion bascule bridge spanning tbe Junction of tbe two branches of the Chicago River, at Lake Street. It replac- ed a single deck, three truss, swing bridge built in 1888, and in 1893 was strengthened to carry the Chicago and Oak Park Elevated R.R.

On March 31st, 1914, work was begun on the sub-structure. The sub-piers rest on rock at an elevation of 106 to 110 feet, Chic- ago datum, and were spaced to allow future sub- way construction. At tbe anchor piers, the sub- piers are 8 feet in diameter. About 2000 cubic yards of concrete were used in tbe sub-piers, 5200 cubic yards of mortar were used in water- proofing the main piers and abutments, 392 cu- bic yards of mortar in waterproofing the tail-

pits and about 4,112,000 potinds of steel were used in reinforcing the piers.

On Jan. 13tb, 1915, work on the sup- er-structure was comnienced and on Jan. 1st, 1916, the bridge was practically ready for the initial lowering. The east leaf was the first in place and was lowered on Feb. 28th at 4:10 P.M. The west leaf was lowered March 1st at 6:55 A. M.

The total weight of steel in the bridge is 2025 tons. Each movable leaf weighs about 670 tons and the fixed portion 685 tons. The counterweight in each leaf weighs about 1075 tons, making a total counterweight of 2150 tons.

The length of steel work over all, abutment to abutment, is 355 feet. The dis- tance from center to center of trunnions is 245 feet 3 inches. The width of steel work ov- er all is 70 feet.

The lower deck has a clear roadway

width of 38 feet and two 14 foot sidewalks* The upper deck provides for the elevated railroad tracks*

10

POWER COHSIMPTIOI TEST OF A DOUBLE DECK BASCULE BEIDGE OPERATION OF BRIDGE

Sote:- Ntunbers refer to points on wiring diagram blueprint .

Eaob leaf is controlled by a bridge operator, who is stationed in an operating bouse at the East and West ends of the bridge respectively. The power required to operate the bridge may be taken from either the ele- vated or the street railway source of direct current supply. Both are 600 volt circuits, which are connected to the bridge motor load by means of a single pole double throw switch (1) in the main operating bouse. The street railway supply is generally used, as other bridges in the city also use this source of energy. Each leaf may be opened independently of the other, but on starting, the bridge oper- ators exchange signals so that succeeding oper-

IX

ations may occur as nearly simultaneously as possible.

Then each one rings a large band operated bell which warns the oncoming traffic that the bridge is about to be opened. Follow- ing this, each one throws a switch which starts the warning bell and flasher lights (2). To one approaching the bridge the lights appear and disappear in the form of a ware; even in daylight showing up quite distinctly, and to date, have proven very effective in warning the oncoming traffic of danger.

The West side operator now signals the elevated signal tower. Each operator puts down bis on-coming roadway gate, sidewalk gates and finally the off-going gate which when shut clos- es contacts in gate bases which are in series with the car checker switches. The switch in the West house takes care of the West bound trains, and the switch in the east house, the east bound.

12

A car between "barriers, however, would open their respective switches, but when away from these barriers, both switches are closed. This interlocking circuit is completed on both sides by means of a submar- ine cable across the river*

Now the barriers are lowered which close one contact in the interlocking circuit. The signals on the elevated structure when set at danger, operate a relay and close the 600 volt bridge control circuit after which the center and then the rear locks may be opened. As the barrier and the bridge leaf are interlocked in series, the opening of the bridge leaf is dependent upon the occurence of both the aforementioned events, thereby pro- tecting traffic on both the elevated and the street railway right ©f way.

Signals are now exchanged between the operators and the two leaves are raised by means of two 100 H. p., 550 V. 530 r.p.m, General

as

Electric series motors operating in parallel through a train of gears, the current being

admitted to the main motors through controllers which are so arranged that their resistances in circuit are decreased by cutting in addi- tional resistances in parallel (6). Should a heavy wind be blowing against either face when up, it would begin rolling down again, but this is prevented by a magnetic brake (4) which is

u

energized by a circuit not in series with the main lift motors. Should this fail, an emer- gency hand brake may be used.

In coming down, signals are exchanged between operators so that both leaves may be lowered at the same time for convenience. Tbe brakes are now released ( by point 1 on control- ler ) and the bridge is lowered. When the bridge is down the auxiliary leaf switch (5) is closed to permit operation of the rear locks, which when in, permit the center lock to be operated and circuits S and Sg, which give in- dications to the elevated signal tower that the center locks are in and elevated trains may cross. After this, each operator raises bis barrier roadway and sidewalk gates as rapidly as possible. The bell and flasher mechanisms are stopped and the bridge is again ready for traffic .

1&

P0TI7EE COUSUMPTIOU TEST. OF A. DOUBLE DECK BASCULE BEIDGE OBJECTS OF TESTS

In studying the conditions and tbe de- sired results, six distinct problems presented themselves for solution, namely:

1. The relation of tbe power consumed at any instant to the angle of tbe leaf with tbe horizontal at that instant.

2 . The relative power consumed by tbe two leaves under similar conditions.

3. The features of the parallel oper- ation of tbe two motors on each leaf .

4. Tbe effect of wind upon tbe maximum power consumption.

5* Tbe accuracy of tbe balance of each leaf .

6. The spacing of resistance steps in tbe controllers.

16

POWEE CONSUMPTION TEST OF A DOUBLE DECK BASCULE BRIDGE APPARATUS

Tbe apparatus used vas:

1. A recording wattmeter and auxil-

iary equipment •

2. A mechanical device to record tbe

motion of tbe bridge leaf* 3* An anemometer to measure tbe ve- locity of tbe wind.

4. A Weston Voltmeter ( 0-600 ) Ho.

5. A G. E. Ammeter ( 0-500 ) No. THE WATTMETER ABD AUXILIARY EQUIPMENT.

Tbe wattmeter used was a portable type, recording meter, manufactured by tbe Esterline Company of Indianapolis^ Indiana. It was designed to take a mazimiun current of 5 am- peres with a maximum potential of 200 volts through the respective coils, and will operate

17

on either direct or alternating current cir- cuits. The drop over each current coil and its leads was given at 100 milivolts . The recording mechanism consisted of an inking needle swinging over a moving paper operated "by clockwork. The paper was ruled with para- llel lines so that it would register any pow- er from zero to one kilowatt. The paper move- ment could be controlled by means of a catch which started or stopped the clockworks .

In order to adapt the meter to work- ing conditions of the test, it was necessary to provide shunts of the proper size to reduce the current over the coils to less than 5 am- peres . It was found upon examination that one of the elements of the meter had been burned out and so the one coil was used in recording the power of both motors. In order that the power to each motor could be recorded with the instrument, it was found most convenient to

18

plaoe one sbunt in line with the soutb motor and one in line with the north motor/ and the power taken first with one connected to the meter and then the other* In order that both motors could be connected to the meter at one time, it was necessary to provide a single shunt and place it in series with both motors*

From preliminary runs made in the operation of the bridge, an estimate was bad as to the probable maximum current at any time, and was found to be 300 amperes for motors op- erating in parallel. [Two 200 ampere, 100 mil- ivolt shunts were provided, and one placed in line with the soutb motor and the other in line with the north motor. ( The meter was cali- brated with these shunts before and after in- stallation, and these calibration curves are shown on pages ) For both motors op- erating together, a 300 ampere, 100 milivolt shunt was used. Curve B is the calibration

19

with the 200 ampere shunt and C with the 300 ampere .

It was also necessary to reduce the voltage from 580 to 200 volts, the allowed voltage over the coils. This was done by plac- ing a resistance in series with the coil. The resistance of the coil was given at 4407 ohms. and the external resistance was then computed from the formula:

V s Eel^ 4- Rcli » Eeli <• Vc Re = Y - Vc

II » Vc Re

Re « V - Vc X Ec Ve

lere Ee = required external resistance

20

The total voltage was estimated at 600 volts and tbe necessary resistance to re- duce 600 volts to 200 volts is 2 x 4407 = 8814 ohms. The resistance used was measured and found to be 8830 obms» and when the voltage was checked it was found to be 580 instead of 600. With an external resistance of 8830 ohms, and an impressed voltage of 580 volts, there was impressed upon the coil of the instrument 193 volts . In calibrating the instrument a con- stant voltage of 193 volts was used and the cur- rent varied. The calibration curves B and B^ were prepared from the results of the meter cal- ibrations . The abscessae are the recorded power as given by tbe meter and tbe ordinates are the true power or tbe product of tbe currents through the shunts, tbe voltage over tbe coils and the

ratio of 580 » 193

21

APPARATUS FOB RECOEDIKG THE AHGDLAE POSITIOH OF BRIDGE.

It was necessary to find a means whereby the movement of the leaf could be re- corded on the moving paper which, at the same time, was recording the power.

The wattmeter stand was placed in the operating bouse and at an elevation of about five feet above the end of the trunnion. A braided steel picture wire was wound aro^lnd the portion of the trunnion protruding from the bearing nearest the operating house, one end was fastened securely and the other end led off to a set of pulleys which were held at the same elevation and in line with the top of the trunnion by means of a bracket fastened on the wall. From this smaller of the two pulleys the wire was led up into the operating house and around the disk, placed horizontally and direct- ly over the wattmeter. A coTinter weight was hung on the free end of the wire in order to

2S

keep tbe wire taut as the bridge moved. The photographs on page show bow tbe apparatus was arranged. A pencil was dropped through a closely fitted hole in tbe disk, so that tbe pencil described an arc on tbe paper when tbe disk revolved.

Tbe radius of the arc described by the pencil was made the same as that described by tbe meter needle. However, tbe center of this arc was placed about 3/8 of an inch be- yond that of the needle to avoid any inter- ference of the two .

By this arrangement, when any move- ment of tbe leaf occurred, the wire unwound from the trunnion and in so doing turned the disc through an angle proportional to tbe angu- lar position of tbe leaf.

In order to find tbe instantaneous power corresponding to any angle of leaf, it was necessary to move tbe leaf-angle curve a distance of s/s of an inch to the left, and

23

read the corresponding ordinates of the two curves. In drawing up the final curves, this was taken into account and the whole trans- fonned into rectangular co-ordinates with time as abscissae and power as ordinates .

The necessary diameters of the pul- leys to transmit the motion of the leaf were determined as follows:

The diameter of the trunnion equals 25.875 inches. The leaf turns through a max- imum angle of 79 , the linear motion of the

wire is 25.875 x 5.1416 x 79 ~ 17.83" 360 It was desired to use the same watt- meter stand and disc that had been used in a previous test. The radius of the disc is 6.875 inches and as the swing of the wattmeter needle is 60° and a radius of 4 7/l6 inches, the motion

of the needle is 4.4375 x 2 x 3.1416 x 60 r 4.64"

360 This linear motion of the wire must be reduced

from 17.83" to 4.64" and this was done by the

S4

two pulleys on the same shaft, supported by a "bracket.

The second reduction In motion must

"be equal to 4.64 x 6.875 = 7.19", and &s the

4.4375 smaller of the two pulleys was made 4" diam- eter, the larger must be

17.85 X 4 . 9.906 = 9 29/32". 7.19

2&

S6'

MEMOMETER MD DETEBMIEATIOH OF TOKQUE DUE OJO WIND PEESSIXRE. The anemometer used was a Tyoos in- strument # 11431 made by Short and Mason . It is of the vertical plane, revolving vane type. Accompanying this instrument was a correction chert for all possible ranges of wind velocity we might have occasion to determine* Anemometer Corrections:

Velocity	Correction
feet per	min.
100
200		+ 40
300		f 28
400		<- 16
500		+ 4
600		- 9
700		- 22
800		- 35
900		- 50
1000		- 68
1250		- 86
X500		-104
1750		-122
2000		-140
2250		-158
2500		-176
2750		-186
3000		-210

S7

Tbe pressure of the wind against a flat surface depends upon tbe velocity and direction of tbe wind, and upon tbe inclina- tion of tbe surface. Nomenclature:

P = pressure in pounds per square foot

on a flat normal surface. V = velocity in miles per bour aa deter- mined by anemometer. X.\^ experimental constant, found by Eiffel tbe noted expert on aeronautics to be 0.0032 for our conditions. PqS normal component of wind pressure . " = angle of bridge leaf witb borizontal

in degrees. M]_" moment due to any uniformly distri- buted load. 1 - balf span of bridge, b = breadth of bridge in feet. M = total moment due to wind^ for any angle of bridge leaf.

28

The wind is assumed to move hori- zontally and the pressure against a flat sur- face, normal to the direction of tbe wind, may be found from tbe formula P = K^V^ = 0. 00327^

As before mentioned tbe normal wind pressure varies as tbe inclination of tbe sur- face to tbe borizontal; and several formulae beve been derived for finding tbe normal com- ponent. Tbe formula of Ducbemin is based upon carefully conducted experiments, and was se- lected by tbe writers to be the most reliable. _ 2 sincC

P S P M mill ■' ■ V '

^n T. ♦ sin^

also , ^.,

Ml « ( Pnl ) 3c 1 for a cantilever span.

M s ( Py,l ) X b X i X sinc^ 2 s p2sin5<y-^ = TLi^slnyi'br' 2 (Usin^ Ifsi^^C

S9

The velocity of the wind as determined lay

the anemometer was 1500 ft. for 30 seconds or 3000

ft. per minute. Applying the correction factor

corresponding to this velocity gives

3000-210 - 2790 ft. per minute.

This is equivalent to a velocity of

^1 « 2790 X 60 • 38 miles per hour. 5280

As the bridge lies in an east and west direc- tion and the wind was blowing from the northeast, the component parallel to the direction of the bridge leaf would be

V = 32 sin 45° = 32 x 0.707 = 2E m.p.h. and

M = 0.0032 X ~g^ X sin(<x 70 x Tog Z ^' "l . sin^

1.543,000 sin

1 t sin^<3e

Curve "C" gives values of this moment

in Kip feet plotted against angle of lift with

horizontal as absc(^ssae.

30

POWER COKSTMPTION TEST OP A DOUBLE DECK BASCULE BRIDGE RESULTS

In a test of this kind tbe results are only relative ones, due not only to the small inaccuracies in the apparatus, but large- ly to the nature of the problem.

A check was made on the power curves for both motors operating in parallel by plac- ing a calibrated voltmeter and ammeter in the line* This was also done to check the instru- ments in the operating house. The power re- corded varied from two K. W. less than the ac- tual power on one side, to four K. W. greater than that on the other/ or a maximum variation of 4 in 174 K. W. This error was probably due to tbe variation in wind pressure and the small inaccuracies in the apparatus itself, due to temperature changes*

The original curves give the total power at the switch board, and this is great- er than the actual power delivered to the motors, because there is power lost in the grid resistances due to the rise in temperature. A thermometer was placed between two grids in or- der to obtain the rise in temperature during the run. When the first point on the controller is in the resistance, the circuit is 3.6 ohms., for the second it is 1.8, and for the third it is 1.0 ohm. The usual run is made upon these three points, and the power corrections for these resistances were applied. This correction was made by noting what resistance was in and then obtaining the power at that instant from the calibration curve for the wattmeter. The power divided by the total voltage gave the current at that instant from which the IE drop due to the rise in temperature was computed.

The grids have a temperature coefficient

32

of about .004 and using the formula R = R|.(l-k£t) where H-t; Is the resistance at normal temperature, << is the coefficient and t is the rise in tem- perature, the actual resistance in the circuit . was obtained at each point. The loss in power due to the difference in resistance was computed and found to be appreciable for the first two resistance steps. For the other steps, this loss became so small that it was impossible to show it accurately on the scale to which the final curves were plotted.

The maximum rise in temperature for the lift shown by curve Ic was 38°C. When the first resistance of 3.6 ohms, was in, the actual resistance in circuit as computed by the formula was 4.04 or a difference of 0.44 ohm. The power was 35 £. W. and from this the current was

35000 _ 60.2 amps. The power lost was 60.2x0.44x60.2 580 ' 1000

1.57 K. W. The actual power to the motor at this

point would be 35-1.57= 33.43 E. W.

35

In the following paragraphs a dis- cussion is given of each problem as it was en- countered.

1. The relation of the power consTjmed at any instant to the angle of the leaf with the horizontal at that instant •

Curves lA to Ic inclusive show this relation on the east leaf, and curves £A to 2c inclusive, show the seme relation on the west leaf. These curves have been corrected and transferred to rectangular co-ordinates .

Referring to curve Ic, it is seen that the power jumps from 0 to 0.34 K. W. in one half second, then to 24 in the next half second. During the next second and a half, the power rises to 92 K. W. where it remains constant for one and a half seconds, then grad- ually drops to 64 at 11 seconds, and then rises to 86 at 24 seconds. The angle curve shows that the bridge does not start to rise until one and one half seconds after the power is applied.

After 11 seconds, the curve has assumed a uni- form slope and continues this slope until 27 seconds after the power is applied, when it begins to flatten out. At 30 l/2 seconds, the power rises to 118 K. W. and then falls to 72 K.W. at 35 1/2 seconds and rises to 112 Z. W. at 37 seconds. It is at this point where the "bridge leaf has come to rest, and it is seen that for only part of the distance, that is, from about 11 seconds to 22 seconds, the leaf had a xmi- form velocity. When the leaf comes to rest the power drops instantly to 20 K. W. and then grad- ually to zero .

At 46 seconds the power is again applied and the leaf begins to move downward about 2 sec- onds later. At 60 seconds the power drops again to 0 and remains there for 13 seconds, when it is again applied to bring the leaf to rest. Just before the leaf comes to rest, there is a large jump in the power curve, that is, during the last

35

few degrees. Tbis large amount of power is applied as a braking action to "bring tbe leaf to rest at tbe proper point, in order that tbe central locks may "be operated.

Curves lA and IB sbow tbe relation between power and angle of leaf for eacb motor and are practically the same. Curves 2A and 2B sbow tbis relation for tbe respective motors on tbe west leaf, and these two curves also a- gree very closely.

One of tbe most notable properties of tbe angle curve is that the angular velocity of tbe leaf can be obtained from it. Tbis is done by taking the difference between tbe two ordinates, between which tbe velocity is desired, and di- viding by tbe elapse of time between them. This, however, will give only average velocities where the bridge leaf is being accelerated, but along tbe straight part of tbe curve, where tbe velocity is uniform, tbe actual velocity may be computed.

36

2. The relative power consumed by the two leaves mider similar conditions •

It is very difficult to obtain any satisfactory data upon this relation because the results may be very easily hidden by tbe effect of tbe wind. It was impossible to get a lift on each leaf, during tbe time these tests were made, with the wind velocity down to zero. By comparing the various curves ob- tained, it is seen that the power for either leaf averages about tbe same, but the details vary in so many ways that no definite con- clusions can be drawn from them.

In order to make a definite compari- son of the power consumed by tbe two leaves, the curves to be compared should be taken at exactly tbe same time. This would necessitate a duplication of tbe recording apparatus . On a bridge where there is very little traffic, approximate results may be badf ^y using tbe

37

one recording set and making a lift on eaoh side, one iaimediately after the otber and comparing tbe curves for these runs.

3. Parallel operation of tbe motors.

Curves 3A and 3B show the action of the motors for the east leaf, and curves 4A and 4B show the same relation for tbe west leaf.

These curves were obtained by making a lift with only one motor recording at a time . The two lifts for each side were made as near the same time as possible, in order to obtain the action of the two motors, running under like conditions.

Tbe curves for each leaf, in order to prove that the motors take the same power, should enclose equal areas. In either case, however, the curves do not represent exactly identical conditions because lifts were made at least 6 minutes apart, for the west side and 10 minutes apart for the east side. It is seen, however, that in each case the areas are almost exactly

36

equal wbicb proves that the motors operate effi- ciently in parallel.

If both elements of the wattmeter bad been intact, a further test of the action of the two motors under parallel operation, could have been made by connecting both motors to the in- strument and then allowing first one and then the other to record the power used. This method is fully described in the results of a series of tests made upon the Webster Avenue bridge by A. L. Scbreiber and S. H. Miller •

4. The effect of wind on the maximum pow- er constimption.

It so happened that upon the days the tests were made, the wind blew from a northerly direction. The first day, however, the wind blew from the north-east with a high velocity, and its effect was obtained upon the east leaf only. During the other days the wind blew from the north and its effect was neglected. This, of

39

course, made it Impossible to test botb leaves under wind pressures constant in volmne and dir- ection*

In curve 5, it has been attempted to show tbe relation of the power consumed at any instant to tbe overturning moment due to tbe wind. These curves were obtained for the east leaf with a normal wind velocity of 22 miles per hour.

Tbe values of the overturning moment were obtained from curve "c" which was plotted for the given wind velocity of 22 miles per hour. The values on this curve corresponding to each 10 degree interval of lift were taken and plotted against the time at which the open- ing of tbe bridge corresponded to each of these 10 degree intervals *

The overturning moment curve shows a maximum value of 720 » 000 ft. lbs. at an angle of 69 degrees, and a wind velocity of 22 miles

40

per hour. This is equivalent to a force of 6850 lbs. acting normal to the leaf on the off shore end. The overturning moment curve and the angle of leaf curve show clearly the relation for the effect of wind as the leaf is raised or lowered. These two curves agree very closely except for the smaller angles. The moment curve and the power curve do not show the theoretical relation which they should, but as the wind pressure is only a small per cent of all the forces tending to retard the bridge, this relation would naturally be great- ly obscured in such a test.

The data obtained has shown the writ- ers that attempts to measure the effect of the wind give only vague results, where actual val- ues are considered. However, the general ef- fects may be shown and from a set of curves such as curve 5 some very interesting results may be had.

41

From the angle curve, the time taken

to lift the "bridge from 18 degrees to 50 degrees

is about 12 seconds. This was along the straight

part of the curve and hence the bridge leaf was

moving with a tmiform velocity of:

n - 60 X (50-16) s 0.44 r.p.m. 12 X 360

From the overturning moment curve the

average moment between these two positions of

the leaf is:

M ' 180.000 * 500.000 « 340,000 ft. lbs.

Then the horse power required to keep the bridge

moving, against the wind, with a uniform velocity

of 0.44 r.p.m. is

H. P. = 340.000 X 22 X 2 X 0.44 = 27 H.P. 33.000 X 7

The K. W. consumption for this position averages 72 K. W. or 96 H. P. and the power to move the leaf in still air at a uniform velocity of 0.44 r.p.m. would be 98-27 = 71 H.P. However, it is seen that the greatest power is used in acceler-

48

atlng tbe bridge and braking it down upon closing. At tbe latter point tbe maximum instanteous K* W* input is 170, which gives a maximum horse power of 2E6. This value, however, is only maintained for a small fraction of a second and the point where the greatest steady K. W. input is obtained gives the power as 168 K. W. or 210 horse power.

5. Tbe accuracy of the balance of each leaf.

Due to a lack of accurate data regard- ing the designers calculated power required to lift the bridge, we were unable to make any com- parisons in regard to tbe balance of tbe leaf.

6. Tbe spacing of resistance steps in the controllers .

A lift was made on both sides in order to obtain some idea in regard to way tbe current was admitted to the motors and bow it was con- trolled. Tbe leaves were raised and lowered by throwing in tbe resistances, which are in para-

43

llel, very slowly, tbus showing the current jumps distinctly. Curves 6A and 6B give these steps*

On the controller on the east leaf for a high run of 303 amps., the first point gave 96.5 amps., the second 110, and the third 96.5 amps. For the same run, on lowering the "bridge, the first point gave 51.8 amps., the second 102.5 and the third 158.7. This shows that resistance steps are just about right . The first point cut in is rather low and is, there- fore, about correct.

44

POWER CONSTMPTIOK TEST OF A DOUBLE DECK BASCULE BRIDGE COBCLUSIOH

In conclusion the writers wish to state that very reliable information was ob- tained pertaining to the operation and control of this bridge. Of course, it was not to be expected that very accurate data could be ob- tained due to many factors over which the writers bad no control. However, the tests show that, could a similar test be made on the bridge during erection, better bridge op- eration would result .

The problems mentioned and discussed herein, are those which will always present themselves in any test of this kind. Each individual bridge will bring forth difficul- ties which are characteristic of that bridge alone. In a general way, the method of pro- cedure will be the same as that outlined in

4&

tbis thesis*

It is hoped that the results of this investigation may contribute their quota to the solution of the problems of bridge op- eration which will be encountered in the fut- ure, and that they will assist in solving the problems which may present themselves in the design and erection of the two similar bridges which the city contemplates building.

V\?W

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