1、DAEN-ECE-D Engineer Technical Letter No. 1110-2-285 W 3515789 0022378 639 W Q.- 20-573 DEPARTMENT OF THE ARMY U. S. Army Corps of Engineers Washington, D. C. 20314 ETL 1110-2-285 29 July 1983 Engineering and Design TILT MEASURING INSTRUMENTS -. 1. Purpose. This letter provides information on differe
2、nt types of in- struments available to measure tilt of structures. This information will be included in- the next revision of EM 1110-2-4300. 2. Applicability. This letter is applicable to all field operating ac- tivities having civil works responsibility. 3. References. a. EM 1110-2-4300, “Instrume
3、ntation for Concrete Structures.“ b. EM 1110-2-1908, “Instrumentation of Earth and Rock Fill Dams.“ c. “Calibration and Installation of Electronic Measuring Devices - and Wall Deflection Pipe - Port Allen Lock,“ Miscellaneous Paper MP-3-432, U. S. Army Engineer Waterways Experiment Station, Vicksbur
4、g, MS, Jun 1962. d. Robertson, K.; “An Instrument to Monitor the Tilt of Large Struc- tures,“ Report ETL-0313, U. S. Army Engineer Topographic Laboratories, Fort Belvoir, VA 22060 (ATTN: ETL-TD-EA). e. Robertson, R.; “Manual for an Instrument to Monitor Tilt in Large Structures,“ U. S. Army Engineer
5、 Topographic Laboratories, Fort Belvoir, VA 22060 (ATTN: ETL-TD-EA). 4. Background. The tilting or deflection of concrete structures result- ing from external loads, temperature changes, or deformation of the founda- tion is a vital piece of information for evaluating structural safety and stability
6、. The instrumentation for measuring tilting or deflection de- scribed in Reference 3a. includes plumb lines, inverted plumb lines, op- tical plummets, electrolevel, and Terzaghi water level meter. This ETL provides additional information on other types of instruments that are available, both commerc
7、ially and by special construction, that are capable of measuring tilt in concrete structures. Some of these instruments were designed to measure tilt and some were designed for other uses but are adaptable to tilt measurement. Some measure surface tilt only, while others can measure tilt at various
8、elevations within a structure. 5. Instruments that measure tilt through a structure. These instruments, most generally, are devices that are lowered through some.sort of pipe, borehole, or channel that has been constructed in the structure. The - I iPtfI Provided by IHSNot for ResaleNo reproduction
9、or networking permitted without license from IHS-,-,-3535789 0022379 575 ETL 1110-2-285 29 Jul 83 instrument is not fixed to the structure, but moves through this channel taking readings at desired locations through the structure. . a. Digitilt inclinometer. This instrument, manufactured by Slope In
10、dicator Co. of Seattle, Washington, is mainly designed for measuring lateral movements in earth embankments and rock foundations (Reference 3b.). However, it can be installed in concrete structures to make tilt measurements. (1) Description. The sensor is shown in Figure 1 along with its digi- tal r
11、ead-out indicator. The sensor is 36.5 inches in length and has an outside diameter of 1.69 inches at the body. Two pairs of spring-loaded wheels at the top and bottom ofthe sensor guide the sensor when inserted into the casing which is either an aluminum or plastic tube having four lengthwise groove
12、s spaced 90 degrees apart on its inside circumference. These grooves guide the sensor in two orthogonal directions of measurement. The electrical cable connected to the sensor is 0.42 inches in diameter, six-conductor cable with a l/l6-inch stranded steel center wire to sup- port any tension on the
13、wires. A water-prpof neoprene cover surrounds the wires and the cable lias external markings at each 1-foot increment. This inclinometer has the overall sensitivity of one part in 10,000 or - +0.0001-foot lateral movement per two feet of casing. Figure 1. Digitilt inclinometer and digital readout in
14、dicator. Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-3515789 0022380 297 = ETL 1110-2-285 39 Jul 83 (2) Installation procedures. The only portion of the instrument that is permanently installed in the concrete structure is the inclinom- eter casi
15、ng. This portion of the instrument is fitted into a borehole and then backfilled with a suitable supporting material (generally a ce- mentitious grout). The borehole should be approximately eight inches in diameter. This will accommodate all sizes of inclinometer casings. The borehole is drilled to
16、below the elevation where measurement is required. Both the aluminum and plastic casings are installed in either 5 or 10- foot sections. The sections are butted together and joined by means of a sleeve that is pop riveted to .the sections on each side of the joint. Care should be taken in the joinin
17、g process to minimize any possible spiral of the grooves in the casing. As each successive section of casing is added to the previous length, the grooves must be aligned with the grooves in the previous section. Care should also be taken to install and backfill the inclinometer casing so that it rem
18、ains vertical. This is not critical with respect to reading the instrument since the first set of readings produces a baseline condition, and all subsequent read- ings are relative to the baseline; however, the less vertical the casing is, the smaller the reading range becomes. (3) Method of Operati
19、on. The sensor consists of two servo- accelerometers, one with its sensing axis in the same plane as the spring- loaded wheels and the other at 90 degrees to the first. Changes in tilt with respect to the vertical move a servo-accelerometer. This circuitry produces a restoring current, the magnitude
20、 of which is a measure of the tilt. The voltage output from the circuit is proportional to the sine of the angle made between the longitudinal axis of the sensor and the vertical. Sensor elements housing the 0.5-gram accelerometers have a range of operation through 530 degrees from the vertical, whi
21、le 1.0-gram accelerometers can function through 590 degrees from vertical. The voltage output from the sensors is sent to a digital read-out indicator where the output is displayed on an illuminated digital display. A more sophisticated method of read-out is provided by means of a magnetic tape indi
22、cator (Figure 1) that will record the sensor voltage output directly on tape as well as display the voltage digitally. (4) Data collection. Output data are read with a four digit bipolar digital voltmeter. It is self-contained and runs on a six volt recharge- able battery which allows operation for
23、a period of eight hours before requiring recharging. a variation from the vertical through the equation: The output is given as a voltage that represents where O = angle, in degrees, made between the longitudinal axis of in- clinometer and the vertical. V = output voltage read on the indicator. The
24、inclinometer is lowered to the bottom of the casing by the connecting cable and readings are taken at intervals as the inclinometer is raised from the bottom o.f the casing. field data sheets for later computations. is available that eliminates the possibility of errors obta.ined by The voltage read
25、ing is transferred to An alternative read-out device i Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-W 3535789 0022383 123 ETL 1110-2-285 29 Jul 33 rhtsreading or miscopying the manual read-out. tape recorder that automatically records the output o
26、n tape. can then be read into a computer for automatic processing of the raw data. (5.) Care and maintenance. The .inclinometer and its indicator are not part of the permanent installation and, as such, .are not subjected to conti.riuous field weather conditions. They should be given the same cre th
27、at any sensitive field instrument is given. remains in the field at all times. By virtue of its construction, either placficor aluminum, it is generally maintenance free; however, the casing should be protected by a cap that is des2gned to prevent debris and water fr-om entgting when the casing is n
28、ot being used. The device is a magnetic This tape c- The indicator casing b. Slope i-ndicator. This instrument is similar to the Digitilt in- cl5nomeBer but is less sensitive to tilt due to its method of operation. I-t is a- less expens-ive instrument manufactured by the same company, but can be us
29、29 Jul 83 (2) Installation procedures. The instrument casing is the only por- tion of the instrument that is installed and its installation is the same as that described for the Digitilt inclinometer. (3) Method-of operation. The Slope Indicator instrument consists of a pendulum-actuated conventiona
30、l Wheatstone Bridge circuit within the sensor. The pendulum contacts a fixed resistance element which subdivides the element into two resistances forming one-half of the Wheatstone Bridge. The other half of the bridge is contained in the control case in the form of a 10-turn precision potentiometer
31、which is manually operated to balance the bridge. The 10-turn potentiometer is coupled to a counting dial read- ing from O to 1000. The inclination of the instrument is proportional to the potentiometer dial reading when the circuit is in balance. The instru- ment has a sensing range of 512 degrees
32、from the vertical. It has a sensi- tivity of 1 part in 1000, which means it cannot measure-tilt of less than three minutes of arc. (4) Data collection. Data are taken by balancing the Wheatstone. Bridge. A potentiometer in the bridge is coupled to a counting device registering from O to 1000. The nu
33、mber read from the counter when the bridge is balanced is proportional to the angle of tilt of the instrument. Raw data, of counter readings, are taken in the field.and later reduced to angle of tilt. t (5) Casing spiral. As mentioned earlier, spiral of the grooves in the inclinometer casing will ca
34、use errors in instrument readings. Conse- quently, inclinometer installation extending to depth greater than SO feet should be checked using the spiral meter developed by MRD Laboratory* or other proven devices to measure the angular change of grooves in the casing for the purpose of correcting the
35、displacement directionas mea- sured by tiltmeter data. c. Wall deflection pipes. Several instruments that fall under the category of instruments that measure tilt through a structure must be installed in the structure during its construction. rely on a shaft or casing that has been cast into the str
36、ucture in order to make their measurements. Two instruments requiring shafts are the plumb line and the optical plummet (Reference 3a.). The instrument that requires a cast-in-place casing is the wall deflection pipe. These instruments (1) Description of the instrument. The wall deflection pipes and
37、 de- flectometer (Figure 3) are designed and constructed at the U. S. Army En- gineer Waterways Experiment Station (WES). deflectometer, which is a compound vice and two dial deflection gages, a plumb bob attached to the deflectometer, and a casing which is made up of flanged sections of five inches
38、 inside diameter iron pipe. The casing extends from the top of the structure down to a point below where the lowest reading is to be taken. At each joint between pipe sections, The equipment consists of a * The equipment and an operator can be made available to Divisions and Districts upon request.
39、MRD Laboratory, 420 South 19th Street, Omaha, Nebraska 68102, phone Inquiries should be directed to the Director, (402) 221-3207, FTS 864-3207. _- - - 2521 I 5 Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-= 3535789 0022383 TTb = ETL 1110-2-285 29
40、Jul 83 y Palchrf /Pau/ - .-:- _ J II SECTION - DETAIL *A“ Figure 3. Details of wall deflection pipes and deflectometer. Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-W 3515789 0022384 932 ETL 1110-2-285 29 Jul 83 there are mounted four silver-plate
41、d brass contact rods oriented around the inside wall of the pipe with each rod at 90 degrees to the adjacent rod. They serve as contact points inside the pipe. (2) Installation procedures. Proper alignment and plumbness of the deflection pipe are important in the installation procedure. base plate i
42、nstallation is most important with respect to alignment. It is installed in the monolith at an elevation approximately five feet below the elevation of the first instrument reading point. Three anchor bolts are cast into the top of the previous concrete lift such that they will be properly aligned w
43、ith the three slotted holes in the base plate shown in Figure 4. The base plate is leveled by adjusting nuts on either side of the plate flange and serves to hold its alignment. to align the scribe c.ross hairs on the base plate parallel to the two orthogonal directions in which measurements will la
44、ter be taken. If the base plate is not properly aligned, none of the pipe sections will be properly aligned since they all key on the base plate. When the base plate has been properly aligned and leveled, the nuts on the anchor bolt are tightened. ening the nuts and the first pipe section then place
45、d on the base plate. Plumbness of each pipe section is achieved by leveling. A proper sized “O“ ring must be placed in the groove provided in the base plate before the first pipe section is installed. After Che first section of pipe is secured to the base plate with six machine bolts, it is stabiliz
46、ed by at- taching three anchor rods to the top pipe flange and secured to the con- crete lift below. Turn buckles should be installed in the rods just be- low the pipe flange. This is done by inserting eye bolts through three bolt holes in the flange and attaching the turn buckle to the eye bolts. A
47、 special temporary cover plate, machined to make its faces precisely parallel, is placed over the top of the pipe. The top surface of the temporary cover plate is then made level by adjusting the turn buckles. This, in turn, plumbs the pipe. When the deflection pipe section has been plumbed, the con
48、creting operation can begin. As the concrete lift is being placed, the level of the temporary plate should be checked and adjusted as the lift rises until it is no longer possible to manipulate the turn buckles due to the elevation of the fresh concrete. At this point the eye bolts should be removed
49、 from the flange. The top flange of the deflection pipe should emerge approximately six inches from the top of the completed.lift. The temporary cover plate should be replaced with a less expensive plate and be left on the top flange until the next pipe section is installed. tering the pipe. Each remaining section of pipe is installed in the same manner as that of the first. The top of the last pipe section should ex- tend no less than 2-5/16 inches above the top of the st
