Test Items : Instrumentation Plan

Installation of Instrumentation

The FAA Instrumentation Specialist was responsible for the installation of the sensors and the completion of the data acquisition system.  The system retrieved and processed data from dynamic and static sensors placed in, on, and near the concrete.  The test items were instrumented with a total of 282 sensors, grouped as follows:

  •                       Dynamic

1.                  54 Vertical Displacement Transducers (VDT))

2.                  24 Horizontal Displacement Transducers (HDTs)

3.                  116 Concrete Strain Gages (CSGs)

4.                  12 Joint Gages (Js)

  •                  Static

1.                  36 Thermistors (Ts) in 12 Trees

2.                  18 Relative Humidity Gages (RHs)

3.                  18 Thermistors in RHs (RH-Temps)

4.                  4 Soil Moisture Gages (SMs)

Temperature Control

Ambient temperature and humidity were also measured in the NAPTF building using sensors that had been previously installed.  The sensors were positioned in the test items as shown in Figures 1, 2 and 3.

The NAPTF Control Room contained a computer which archived the data retrieved from the sensors, and two computers which processed and displayed the data.  Hourly files were made of the data from the dynamic system.  Data from the static system were recorded on a continuous sequence file.  During the test item monitoring phase, dynamic data were retrieved every second, handled by signal processing units (SPU3 and SPU4), and relayed to the Control Room computers.  The static data were retrieved every 5 minutes, handled by multiplexers (MUX 2, MUX 3, and MUX 4), sent to a data logger, and relayed to the Control Room computers.  The static data were displayed in tabular form on a separate computer.

Dynamic Sensors

The dynamic system contained 206 sensors distributed about equally among the three test items.  The seats for the vertical displacement transducers (VDT) consisted of steel reinforcing rods, 3/8 in. diameter by 18 in. length, driven into the base material under MRC and MRG.  The seats for MRS consisted of 1/4 in. stainless steel plugs inserted and epoxied into holes drilled in the Econocrete subbase.  The plungers of the VDT were threaded to the seats, and the connection area was coated with grease.  The concrete, when placed, gripped the plunger housing.  The horizontal displacement transducers (HDTs) were placed in the first set of forms.  They became embedded in the first concrete placement.  After the forms were removed, galvanized steel plates were secured to the sides of the slabs and became the seats for the HDT plungers.  The steel plates became embedded in the second concrete placement.  The concrete strain gages (CSGs) located at the joints were secured to 1/4 in. by 8 in. plastic rods placed horizontally through drilled holes in the forms.  Once the concrete set up and the forms were removed, the rods supported a second set of CSGs, on the opposite sides of the joints, which became embedded in the second placement.  The CSGs located in the open areas were secured between slender aluminum angles which were anchored to the base materials.  The CSG installations involved either the placing of one gage near the bottom of the slab, two gages with one near the top and one near the bottom, or four gages (MRS only) with one near the top, one at the middle, and one near the bottom.  The fourth gage was set within the Econocrete subbase, near the top.  The “U”- shaped joint gages were secured to the sides of the outboard slabs, north and south, after the side forms were removed.  Metal fasteners were used.  They engaged small brass fittings which had been set in the forms and became embedded in the concrete.


Figure 1.  Sensor Locations in MRC


Figure 2.  Sensor Locations in MRG 

 

 

Figure 3.  Sensor Locations in MRS

Static Sensors

The static system contained 76 sensors distributed about equally among the three test items.  The thermistors were set on 3/4 in. by 18 in. plastic rods inserted at least 6 in. into the base materials. The set up formed trees of two thermistors near the joints and four thermistors at the slab centers.  Both installations included one sensor near the top and one near the bottom of the slabs.  The four-thermistor installation included two additional sensors set at intermediate levels.  Slabs from both concrete placements received thermistors.  Conduits (plastic tubes) for receiving the relative humidity gages and their associated thermistors were set along the south edge of the slabs during each placement.  The conduits came in assemblies of three extending to the top, middle, and bottom of the slabs.  The sensor assemblies were set in the conduits after the 28 day curing period of the concrete.  The soil moisture gages were set 1 ft. below the surface of subgrade lift 0 after the clay was excavated.

Sensor Placement Procedures

There were three procedures which helped to safeguard the sensors during concrete placement:

  1. The instrumentation system was designed such that the majority of the sensors, for each test item, were embedded in the concrete during the placement of the first set of ten slabs.
  2. The pump and boom deposited the concrete in open areas free of the sensor locations.
  3. The sensors were hand packed and covered with concrete prior to additional material being placed above them.

Eleven outages were experienced in the sensors as a result of the concrete placement.  An additional 11 sensors appeared to be affected.  Figures 4, 5, and 6 show typical sensor installations prior to the concrete being placed.

 

 

Figure 4. Vertical Displacement Transducer, Slab Corner, MRS

 

 

 

Figure 5. Concrete Strain Gage, Thermistor Tree, Slab Edge, MRS

 

 

 

Figure 6. Typical Relative Humidity and Thermistor Installation, Slab Edge, South Side of a Test Item


Click provided links for additional Instrumentation Sensor information :      CC2 Sensors      Sensor Table     SPUs     TestSlabSensor

Strain Gage Temperature Test

Test procedure for determining temperature effects on concrete strain gage measurements

1.      Strain measurements will be made on

                          i.      strain gage mounted on steel bar (Setup-1); and

                        ii.      strain gage mounted on concrete core (Setup-2).

 2.      Drill a hole in the concrete core (Setup-2) and place a thermocouple close to the strain gage. Fill the space between concrete core and thermocouple with epoxy.

 3.      The strain gages in two setups are connected to a laptop computer for data acquisition.

 4.      The temperature range used for testing will be representative of ambient temperatures inside the NAPTF test facility. A temperature range of 10 °F (12 °C) to 110 °F (43 °C) will be sufficient.

 5.      For the low temperature strain measurements, place the two setups (1 & 2) inside the test facility at NAPTF (pavement testing area). Record the strain values and temperatures.

 6.      For measurements at other temperatures, place the two setups in the oven. Outlet for cables of data acquisition system is provided in the oven.

 7.      Set the oven to desired temperature setting. Record the strain readings and the temperature readings as the temperature is rising to the desired level. Keep collecting strain readings for 15-minutes once the temperature stabilizes at the desired level.

 8.      Repeat step 7 for temperature settings of 50, 60, 70, 80, 90, 100, and 110 °F.

 9.      Steps 5 through 8 will be repeated with the two setups immersed in the water bath.

 

 Figure 7. First Series Strain Gage Test Results   

Click the links provided for additional First Series test data notes :      Note 1       Note 2      Note 3      Note 4     Note 5

 

 Figure 8. Second Series Strain Gage Test Results

 

 

 Figure 9.  Therma Strain Gage Test Results

Surface Strain Tests on Transition

 
Below describes the plan for strains measured by surface strain gages on transition five – 2005-01-07 to 2005-03-23

Objectives

  (1)               To investigate the variation of strains at the slab top under different gear locations;

(2)               To investigate the effects of axle number (2, 4 and 6 wheels) on the maximum strains;

(3)               To measure the strain distribution along the transverse joint;

(4)               To investigate the effects of slab thickness on the measured top strains.

Input data for the tests

(1)               Tests will be done by using both carriage 1 and 2, with single, two, four and six wheels;

(2)               The wheel load will be 55,000 lbs with 210 psi tire pressur for all except 400 psi for the single wheel;.

(3)               Slow rolling tests will be done by slowly moving the load from the east to the west, then moving back to the east. All responses information will be stored in a file.

(4)               Static tests will be done by adding the 55,000 lbs wheel load by two steps. The target load will be 27,500 lbs and 55,000 lbs wheel load. The load will be held for five seconds then to go to next step or unload.

    

Installation of Strain Gages

(1)               The slab surface will be grinded as smooth as possible, after the strain gage is placed and wire conneected, epoxy is applied to protect the straingage. 

(2)               A few days after the straingage installation, grease can be applied on the surface of each straingage to avoid it is torn by any friction force due a moving wheel load. Then each straingage should be covered by a piece of thin (» 1/16”) flat metal sheet.

Test Procedures and Results

  (1)              The slow rolling tests will follow the location shown in Figure 10.

(2)               The static tests will follow the location shown in Figure 11.

(3)               The file name, symbol and comments are listed in Table 10.

           

                                      Table 1            DETAILED CARRIAGE LOCATION AND FILE NAME          

TEST ID

Carriage 1

(North)

Carriage 2

(South)

Notes, File name

Slow rolling tests using carriage 1. From the West to the East, stop then move back to the West. One round trip data will be saved into one file.

D1-a (2 Wheels, East)

7.15 ft

Unload

DataFile032305082050-D1-a

D1-b (4 Wheels, East+Mid)

7.15 ft

Unload

DataFile032305082756-D1-b

D1-c (6 Wheels)

7.15 ft

Unload

DataFile032305083045-D1-c

Static Test. Y positions are the same to previous slow rolling tests

Each load is applied by two steps:

0 => 27,750 (hold 5 seconds) => 55,000 lbs (hold another 5 seconds => 0

S1-a (2 Wheels, East)

7.15 ft

Unload

DataFile032305083834-S1-a

S1-b (4 Wheels, East+Mid)

7.15 ft

Unload

DataFile032305084032-S1-b

S1-c (6 Wheels)

7.15 ft

Unload

DataFile032305084551-S1-c

Move Carriage 1 towards South 1.2 ft (14.4 inch)

Each load is applied by two steps:

0 => 27,750 (hold 5 seconds) => 55,000 lbs (hold another 5 seconds => 0

S2-a (2 Wheels, East)

8.35 ft

Unload

DataFile032305085037-S2-a

S2-b (4 Wheels, East+Mid)

8.35 ft

Unload

DataFile032305085334-S2-b

S2-c (6 Wheels)

8.35 ft

Unload

DataFile032305085554-S2-c

Above nine tests will not touch any gages. The following three slow rolling  tests will be rolling on gage 1 at the longitudinal joint. From the West to the East, stop then move back to the West. One round trip data will be saved into one file.

D2-a (2 Wheels, East)

8.35 ft

Unload

DataFile032305085847-D2-a

D2-b (4 Wheels, East+Mid)

8.35 ft

Unload

DataFile032305090141-D2-b

D2-c (6 Wheels)

8.35 ft

Unload

DataFile032305090434-D2-c

Static Test Using Carriage 2 (South), Manual control is needed to provide stable load. Load will be applied at corner without touching any gages

SS1 (Single Wheel)

Unloaded

9.4 ft

DataFile032305091634-SS1

SS2 (Single Wheel)

Unloaded

10.6 ft

DataFile032305092000-SS2

SS3 (Single Wheel)

Unloaded

16.4 ft

DataFile032305092413-SS3

SS4 (Single Wheel)

Unloaded

18.625 ft

DataFile032305093031-SS4

SS5 (Two Wheel)

Unloaded

16.4 ft

DataFile032305100006-SS5

SS6 (Four Wheel)

Unloaded

16.4 ft

DataFile032305100223-SS6

Slow rolling Single Wheel tests using carriage 2. From the West to the East, stop then move back to the West. One round trip data will be saved into one file.

D3-a (Single Wheel)

Unloaded

13 ft

DataFile032305094530-D3-a

D3-b (Single Wheel)

Unloaded

15.25 ft

Gage 3 damaged

Slow rolling tests Using Carriage 2 (South). From the West to the East, stop then move back to the West. One round trip data will be saved into one file.

Depend on the gage quality, Y could be 13 or 17.5 ft

D4-a (2 Wheels, East)

Unloaded

16.4 ft

DataFile032305100658-D4-a

D4-b (4 Wheels, East+Mid)

Unloaded

16.4 ft

DataFile032305100920-D4-b

 

 

 

Figure 10           SLOW ROLLING TESTS

           

 

FIGURE 11      STATIC TESTS

 

 Click the links provided for additional notes and examples for the Surface Strain Test on Transition :   Note 1      Note 2     Examples