Soil Instruments 1030 User manual

User Manual
1
Vibrating Wire Embedment Strain Gauge
User Manual
Man142
6.1.0
06/08/14
P. Day
Andy Small
Chris Rasmussen
Manual No.
Revision
Date
Originator
Checked
Authorised for
Issue

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Contents
Section 1 : Introduction.................................................................................................................................3
Section 2 : Equipment Supplied ..................................................................................................................4
Section 3 : Installation ...................................................................................................................................5
3.01 Installation in Concrete ................................................................................................................5
3.02 Installation in Pre-cast blocks.....................................................................................................7
Section 4 : Protection of the Installation................................................................................................8
Section 5 : Cable Routing and Protection ...............................................................................................9
Section 6 : Monitoring...................................................................................................................................10
Section 7 : Data Interpretation.................................................................................................................11
Section 8 : Temperature Effects ...............................................................................................................13
Section 9 : Troubleshooting Guide...........................................................................................................14
Appendix A. Vibrating Wire Data..............................................................................................................15
Appendix B. Troubleshooting Flowchart................................................................................................16
Appendix C. CE Declaration.........................................................................................................................17

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Section 1 : Introduction
Embedment Strain Gauges were developed by the British Transport & Road Research Laboratory to
measure the internal strain in concrete structures. These waterproof gauges were developed in
conjunction with Imperial College, London and incorporate the latest materials and techniques to make
these gauges suitable for use in hostile conditions.
The nature of the instrument dictates that it is used to measure changes in strain (i.e. change in
length per unit length).
The gauges are designed for use in installations where they are cast directly into the mass of the
concrete structure. The pre-casting of the gauges into briquettes is recommended only where it can't
be avoided.

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Section 2 : Equipment Supplied
Strain Gauges come supplied at pre-set readings dependent on the expected magnitude and direction
of strains to be recorded.
Each gauge is supplied with a user specified length of cable moulded to the gauge sensing coil and a
securing clamp. The cable can be spliced to other cables for routing to a terminal location. Cables can
be routed over distances in excess of 1000 metres without degradation of signal.
Each gauge is supplied with a thick walled silicon rubber sleeve over each barrel (see Figure1) to
protect the gauge barrel when it is tied to support bars during mounting.
Although gauges are checked prior to leaving Soil Instruments, damage can occur during transit. It
is suggested that the gauges are visually checked immediately upon receipt. Additionally it is
prudent to check the operation using a vibrating wire readout device to ensure steady readings, if
an audio signal is available on the readout device this can give a good indication of the quality of
the signal.
Prior to installation secure the coil assembly to the gauge using the securing clamp as shown
above.
Before installation, a note should be made of the batch factors for the Strain Gauges for future
data interpretation.

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Section 3 : Installation
The gauges are supplied sealed and pre-tensioned; no adjustment is necessary or possible. It is good
practice to connect a readout to the gauge and ensure that the reading in free-air is stable and around
the mid-range position. Gentle pressure applied to the gauge ends (i.e. small compression) should
cause the F²/1000 reading to decrease.
The approximate mid position reading of the strain gauge is as follows:
830 Hz
690 F²/1000 (Linear)
12038 Period units x 107
For sweep excitation readout units set the sweep range to 400 –1200 Hz.
3.01 Installation in Concrete
The gauge can be installed in concrete in one of two ways; either by direct casting following attaching
the gauge to, or between rebar, or by pre-casing into a concrete block which is then cast into the main
concrete pour.
When affixing gauges to rebar for direct encasing into concrete, care must be taken to avoid over
range forces being applied to the gauge end blocks by the speed and/or weight of concrete being
poured. Do not tie the gauge too tightly to the rebar as this can move during pour and or curing and
thus damage the gauge. If placing the gauge between rebar, please note the following:-
Wrap self-amalgamating or a few turns of plastic (insulating) tape around the gauge where the
soft wire ties will contact it to act as a shock absorber.
Use only soft iron wire (as used by rebar erectors) and make at most 3 turns around the
gauge, each 3-4 cm from the end blocks either side of the coil.
Loop the wire (by twisting) between the gauge and the rebar, either side to allow for some
expansion movement.
Above; soft iron wire used to secure the gauge between reinforcing bars.

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Above; soft iron wire used to secure the gauge between reinforcing bars, Plan View.
As an alternative to the above, small rebar sections, cut to length can be used to replace the soft steel
wire with cable ties attaching these short lengths to the gauge and the main rebar. If this method is
selected under no circumstances over tighten the cable ties so that no movement is allowed. An
indicative picture is below.

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3.02 Installation in Pre-cast blocks
An alternative to fixing to rebar, is to pre-cast the gauge into a block of concrete prior to this being
cast into the main concrete pour. This method takes more time, but does protect the gauges better
during the main pour.
To install in this way, follow the steps below:-
Fabricate a mould for the desired size of block
Mix the concrete, ensuring the mix is the same as that which will be used for the main pour.
Fill the mound and position the gauge in the middle of the fill.
Do not cure for more than 3 days, or less than one day
Place blocks in position in main pour –note comments on cable protection to follow in section
4
TABLE INDICATING SUGGESTED DIMENSIONS FOR SUPPORT BARS
Refer to Figure 1
Gauge Length
'A'
'B'
150 mm
90 mm
8 mm
INFORMATION If the reinforcement spacing exceeds 3 x “A” then bar size “B” should
be increased.
The gauge positions should be marked, if possible on the reinforcement cages, and the cable route
indicated.
IMPORTANT the final position of the gauge should be accurately recorded since this
detail will be required for interpretation of its readings.

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Section 4 : Protection of the Installation
All efforts must be taken to protect the gauge during concreting without significantly altering the
reinforcement performance.
Where the gauge is installed in a vulnerable position good practice is to spray the area with marker
paint as a warning and/or cover the area with fine wire mesh.
It may be necessary to fix additional reinforcement steel around the gauge position to offer protection
during concreting though this could affect subsequent gauge readings.

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Section 5 : Cable Routing and Protection
Having established and marked the preferred route of the cables and decided upon the type of cabling
arrangement to be adopted, begin running the cables from the gauges furthest from the readout
location.
Where cables are not to be ducted, they should be strapped to the reinforcement, in a position where
they are least likely to be damaged, using strong tape or cable ties. Cable should be supported every
400-500mm and care should be taken to avoid over stretching the cables, especially where
movement/loading could take place when placing the cage.
The reinforcement bars can be used to protect the cables; for example by running the cables under the
bars to reduce the risk of damage where vibrating pokers are to be used.
Where significant movement could take place, the cable ties should be left a little slack and sufficient
cable left free and positioned so that it cannot be damaged.
Where cables are to exit from a concrete structural element, they should be protected by a short
length of plastic duct. This will reduce the risk of the cable shearing off where it emerges from the
concrete.
Once the cables have been fixed a full set of readings should be recorded for each instrument.

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Section 6 : Monitoring
Since the gauges are used to record changes in data and not absolute data, the stage when the "Base"
or "Zero" reading is recorded is flexible.
The reading recorded after the gauge has been fixed and prior to concreting is useful for record
purposes only.
Where the effects of concrete curing are to be observed, the Base reading should be recorded soon
after the concrete has been placed and where necessary, compacted. All other operations, such as
removal of steel pile casing, should have been completed before the Base reading is recorded.
Where loading tests are to be performed, the Base reading for the test data should be recorded just
prior to the beginning of the test.
Data from Vibrating Wire instruments can be recorded in 3 formats; Period, Linear or Engineering
Units. The required format should be established prior to any test beginning and remain consistent for
the duration of the monitoring program.
The Soil Instruments Model 1030 & 1050 Readout/Loggers requires the Base reading to be recorded in
Period units for automatic calculation of the applicable Engineering units. (See the Readout/Logger
Operation Manual for full details).
A monitoring schedule should be established by the engineers responsible for the structure, so that the
monitoring personnel are aware of the data gathering requirements.