IBJ Technology / Structural Health Monitoring – Real Time Stress Measurement 
The acousto-elastical stress measurement - a...
IBJ Technology / Structural Health Monitoring – Real Time Stress Measurement 
al. 2001]. The instrumentation influence of ...
IBJ Technology / Structural Health Monitoring – Real Time Stress Measurement 
( 2 ) 
with the shear modulus . 
For the hom...
IBJ Technology / Structural Health Monitoring – Real Time Stress Measurement 
The acousto-elastic effect describes the inf...
IBJ Technology / Structural Health Monitoring – Real Time Stress Measurement 
Larger variations in temperature are concret...
IBJ Technology / Structural Health Monitoring – Real Time Stress Measurement 
time-critical in relation to the measurement...
IBJ Technology / Structural Health Monitoring – Real Time Stress Measurement 
appropriate temperature result temperature-d...
IBJ Technology / Structural Health Monitoring – Real Time Stress Measurement 
and b = = 0,000285 
correlation coeffizient ...
IBJ Technology / Structural Health Monitoring – Real Time Stress Measurement 
Laufzeit = f (Spannung) 
7780 
7775 
7770 
7...
IBJ Technology / Structural Health Monitoring – Real Time Stress Measurement 
length, 200 mm of depth 
and 100 mm height. ...
IBJ Technology / Structural Health Monitoring – Real Time Stress Measurement 
Fig. 11: experimental set-up Fig.12: Data Aq...
IBJ Technology / Structural Health Monitoring – Real Time Stress Measurement 
s = ( LT1 - LT0 ) / Ks ( 7 ) 
Hereunder appl...
IBJ Technology / Structural Health Monitoring – Real Time Stress Measurement 
4.2. Measurement with TDC 
The measuring ins...
IBJ Technology / Structural Health Monitoring – Real Time Stress Measurement 
At present only approx. 3 measured values/se...
IBJ Technology / Structural Health Monitoring – Real Time Stress Measurement 
Fig. 19: Preparatory hole Fig. 20: Sensor in...
IBJ Technology / Structural Health Monitoring – Real Time Stress Measurement 
Fig. 23: Sensors after load measurement Fig....
IBJ Technology / Structural Health Monitoring – Real Time Stress Measurement 
5.2. Dynamic stress measurement 
To measure ...
IBJ Technology / Structural Health Monitoring – Real Time Stress Measurement 
• Measurement in the heap of debris and frac...
IBJ Technology / Structural Health Monitoring – Real Time Stress Measurement 
can facilitate the management after disaster...
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The acousto elastical stress measurement - a new procedure for the geotechnical on-line monitoring

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With the new procedure for the permanent monitoring by the acousto-elastical stress measurement changes in the structures can be recognized in time into civil engineerings. The world-wide only on-line procedure permits the measurement of loads and stress situations directly in the building. With ultrasonic the stress in the building directly and in real time is seized. All changes can be transferred immediately on-line by Internet or radio. The sensors are brought either directly into the building or later attached to endangered places. Design features such as carriers or bridge bearings can be supervised particularly simply. The sensors are constantly at or active in the building. The simple structure and the small size permit comprehensive application at all buildings from steel or concrete. Into all engineering structures can be measured static loads and tensions and small dynamic changes. In the procedure many important civil engineerings could be supervised world-wide. The costs of such a monitoring are small. The collapse of buildings accompanies with a measurable change of the tensions and loads. These are correlated with the world-wide available stove data of seismic events and examined for plausibility. Thus also a monitoring of buildings of all kinds on damage is possible by disasters (earthquake, ground slips, mudslide etc.).

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The acousto elastical stress measurement - a new procedure for the geotechnical on-line monitoring

  1. 1. IBJ Technology / Structural Health Monitoring – Real Time Stress Measurement The acousto-elastical stress measurement - a new procedure for the geotechnical on-line monitoring F.-M. Jäger With the new procedure for the permanent monitoring by the acousto-elastical stress measurement changes in the structures can be recognized in time into civil engineerings. The world-wide only on-line procedure permits the measurement of loads and stress situations directly in the building. With ultrasonic the stress in the building directly and in real time is seized. All changes can be transferred immediately on-line by Internet or radio. The sensors are brought either directly into the building or later attached to endangered places. Design features such as carriers or bridge bearings can be supervised particularly simply. The sensors are constantly at or active in the building. The simple structure and the small size permit comprehensive application at all buildings from steel or concrete. Into all engineering structures can be measured static loads and tensions and small dynamic changes. In the procedure many important civil engineerings could be supervised world-wide. The costs of such a monitoring are small. The collapse of buildings accompanies with a measurable change of the tensions and loads. These are correlated with the world-wide available stove data of seismic events and examined for plausibility. Thus also a monitoring of buildings of all kinds on damage is possible by disasters (earthquake, ground slips, mudslide etc.). 1. Physical fundamentals of the acousto-elastical measurement Contrary to the stress analysis of construction units, where generally the change of speed of the transversals and longitudinal waves is seized and evaluated, in situ stress measurement regarded here uses only the change of the speed of the longitudinal waves within the thickness of a measuring body. Past direct measurements of the speed of sound in rocks or concrete are unsuitable for regulations of the stress ratios. Rock anisotropies, tears etc. affect saliently these measurements. Particularly different contents of pore waters make such measurements with difficulty comparable and unsuitable for a monitoring [Huang et
  2. 2. IBJ Technology / Structural Health Monitoring – Real Time Stress Measurement al. 2001]. The instrumentation influence of changing porosities and/or dampness contents can lie the far over stress-dependent portion of the measuring effect. For the broad use of the measurement of speeds of ultrasonic waves from there the influence of changing rock parameters must be if possible excluded. The new beginning for the evaluation of the acousto-elastical effect is based on the use of measuring bodies made of metal in the inhomogenous and anisotropic items under test. These new applications of the acousto-elastical effect for the interests of the geotechnics are described by several relevant patent specifications [Jäger, 2005,2006,2007,2008,2009]. The measured variable is in all applications the running time of an ultrasonic impulse in a homogeneous measuring body, for example made of metal. Favourable way is this measuring body for more-axial receivers a metal cube or for in-axial receivers a metal plate with several or a PVDF foil for each tension direction. The force application takes place on the measuring cube and/or on the metal plate and concomitantly via the PVDF foil. The force application changes also the mechanical stress in the measuring body. Since this mechanical stress is not directly measurable, one must select either the detour over a mechanical size or over further directly dependent variables. The ultrasonic speed is like that one, from the mechanical stress, dependent variable. However still further factors of influence exist: · For the measuring instrument practically as factors of influence (material constants), which can be accepted constantly: the modulus of elasticity , the density and the Poisson number n. · The most important variable measured variable, the temperature, which over other material-specific parameters the speed of sound directly (thermal dependence on c) or indirectly affects (thermal coefficient of expansion a). Contrary to liquids and gases the speed of sound c in the solid body hangs of the modulus of elasticity off. In addition, there is here besides a dependence on the density the solid body. For longitudinal waves in a long staff with a diameter smaller than the wavelength, under neglect, is valid for the lateral contraction: ( 1 ) For transverse waves arises:
  3. 3. IBJ Technology / Structural Health Monitoring – Real Time Stress Measurement ( 2 ) with the shear modulus . For the homogeneous and isotropic solids regarded here simplified without roll-direction- controlled constants are regarded here. Thus the speed of sound does not depend on the direction of propagation. The speed of sound then additionally still depends on the transverse contraction ratio (Poisson number) n: ( 3 ) this is valid for a longitudinal wave. For a transverse wave arises: ( 4 ) Ultrasonic waves have a frequency range of over 20 kHz. The transverse contraction ratio one calls also Poisson number and is defined as follows: ( 5 ) with the change of diameter and length variation the body. As measured variable for an embedded measuring body no mechanical measured variable is available. Interference-freely and without influence of the item under test however the running time is measurable, which (in the broadest sense) is in reverse proportional to the mechanical stress in the measuring body. Fig.1:The Acousto-elastical Effect
  4. 4. IBJ Technology / Structural Health Monitoring – Real Time Stress Measurement The acousto-elastic effect describes the influence of tensile stress on the speeds of ultrasonic waves in the measuring body. The out spreading speeds is described thereby in the following form, in that the material density, which elasticity and shear modulus (flexible constant of IITH order) as well as the flexible constants of IIITH order as material-specific characteristic values and the three components of the orthogonality pressure tensor and/or the three principal stresses as condition parameters of the measuring body are received. The running time of the ultrasonic waves, which spread within the measuring body, is measured highly reolution with a TDC circuit. The adaptation of the ultrasonic transducers into or to metallic bodies is easily possible. The acousto-elastic effect can take place both via the measurement of the longitudinal wave and via the measurement of the transversals wave or via evaluation of the change of both waves. It is valid the reversibitity between expansion and upsetting. The Hook law is valid only for the elastic range. s (tension) = E (elastic module) * e (stretch) The ultrasonic waveguide of metal fulfill the Hook law. The relative change of the wave velocity by the tension effect is very small. The change of speed of the ultrasonic waves is an approximately linear function. The change of the speed of sound depends apart from the dependence on the influencing mechanical stress also on the temperature. In practice the temperature equalizing places itself between measuring bodies and surrounding building sufficiently fast. Fig. 2: Acousto-thermal effect
  5. 5. IBJ Technology / Structural Health Monitoring – Real Time Stress Measurement Larger variations in temperature are concrete in the stationary installation in the mountains or in tunnels, in the annular space between Tübbing and mountains not to expect. With applications, where on a changing ambient temperature is to be counted, temperature measurements are capable of being implemented for compensation conceivably and easily in the measuring body. By the elastic behavior of the measuring section between the ultrasonic sensors also the length of the measuring section is changed. It is well-known that those speed of sound changes by the effect of a mechanical stress. [Split 2002] via the measurement of the speed of sound a sufficiently exact determination of the tension can take place within the measuring body. The change of the speed of sound is very small in relation to the absolute speed of sound. The direct instrumentation evaluation by a usual measurement running time is too inaccurate, since the dissolution is not sufficient here. A direct frequency counting over microprocessors separates, there the cycle time (computing clock) around the factor 1000 to 10000 is larger than the demanded usable dissolution. Metal plates of few centimeters result in running times of the ultrasonic impulse smaller 10 μs. If loads are to be measured by only some MPa, and/or Nmm-2, the dissolution must be below 10 ns. For the measurement of small changes (10 kPa) and smaller the increase of the dissolution must take place via calculation of average values of many single measured values. TDC circuits can dissolve with a measurement better than 50 ps. By the short measure-strain in the measuring body can problem-free by 10.000 measurements per second be made. In one second so a resolution is very fast and easily possible 1 ps for better by calculation of average values. In the alga meaning the stress measurement in the mountains or concrete is not a time-critical task. The resolution of the running time under 1 ns requires from there only sufficient measured values. Resolution-limiting the temperature influence affects the running time. Modern TDC circuits possess special measuring entrances for temperature measurement and permit a resolution of the temperature of 0.004 ° C. The temperature is to be determined if possible with high resolution. The changes of temperature in the rock and/or concrete take place in practice slowly and are not
  6. 6. IBJ Technology / Structural Health Monitoring – Real Time Stress Measurement time-critical in relation to the measurement of flying time. In principle nearly each highly soluble temperature measurement is suitable. A standard deviation of the temperature of 0,001 °K causes an additional deviation of the tension from 1,31 kPa. Technically is executable with different electronic construction units and by the principle different temperature sensors. Temperature measurement principle: • Pt-Resistors Evaluation in the TDC circuit; (0,002°C) • Digital temperature sensors • 1-Wire-Interface Dallas DS18S20, resolution: 12 Bit, (0,0625°C) • 2-Wire-Interface National Semiconductor LM76CHM, resolution: 14 Bit • SPI-Interface Analog Devices ADT7310, resolution: 16-bit; (0.0078 °C) Advantage of the digital temperature sensors: Clear addressing already in the sensor contain. The absolute accuracy can be brought by calibration in ice water on better 0,1°C. The resolution can be further increased by calculation of average values. Since the temperature sensor is a firm component of the load sensor, the influence of the absolute accuracy can be neglected. The zero-measurement without load and the current measurement under load take place always also and the same temperature sensor. 2. Sensitivity and factors of influence The measurement of the running time took place with 2 different laboratory superstructures with in each case a H8-Prozessor for the controlling of the TDC-GP2 with digital display and/or the TDC501 with serial interface. For the determination of the thermal dependence of the speed of sound the running time with the TDC501 was determined and handed over the serial interface to a PC with the DATA Aquisitions system DASYLab by national instruments. Further the temperature of the measuring body with a semiconductor sensor was determined. With a microprocessor determined were likewise serially handed over and with a DASYLab module in °C scaled. From the pair of the running time and the
  7. 7. IBJ Technology / Structural Health Monitoring – Real Time Stress Measurement appropriate temperature result temperature-dependent correction for the running time. These factor to the correction are specific a material constant and for the respective measuring body alloy. Thus the influence equal thermal coefficients of expansion with is considered. The measurements confirmed that for instance to 10 times influence of the thermal dependence of the speed of sound in relation to the influence the thermal length variation measure-strain on the result of a computational determination of the speed of sound. Fig. 3: Determination of the thermal dependence of the running time with DASYLab The speed of sound in solids, decreasing with rising temperature, is not linear. For the interesting temperature range hardly concrete values are to be found in the literature. The construction unit temperature changes the flexible behavior in linear kind and run time change per 10 K temperature difference can confirmed temperature coefficients be corrected due to one for many steel approximately 1.1 ‰ [Längler 2007]. Own measurements were accomplished by the author at inspection pieces from aluminum with a thickness of 10 mm. Became in the temperature range of - 25°C to +75°C the following dependence determines: linear regression: regression curve: Y = a + b*x ( 5 ) wih a = = 3079,314922 and b = = 0,886518 dimension X values = °C dimension Y values = ns number of measured values = 65 correlation coeffizient R = 0,998204 coefficient of determination R² = 0,996412 exponential regression: regression curve: Y = a * exp (b*x) ( 6 ) with a = = 3079,341260
  8. 8. IBJ Technology / Structural Health Monitoring – Real Time Stress Measurement and b = = 0,000285 correlation coeffizient R = 0,998401 coefficient of determination R² = 0,996805 For practical application for the correction of the running time the use of the linear involution is sufficiently exact. Fig. 4: Run time change as function of the temperature Following fig. 5 shows exemplary the run time increase in an aluminum body of 25 mm of thickness of approximately 15 ns during a rise in temperature of approx. 20°C to 32°C. The curve down shows the result of the numeric run time correction. Even during the dynamic change of temperature and the still taking place heat flow amounted to the deviation of the corrected running time from the computational reference running time (0°C) less than 100 ps. 18:22:30 18:27:30 18:32:30 18:37:30 18:42:30 18:47:30 18:52:30 h:min:s 7850 7840 7830 7820 7810 7800 45 40 35 30 25 20 15 1050 5,0 2,5 0,0 -2,5 -5,0 -7,5 -10,0 run time [ns] temperature [°C] deviation [ns] Fig. 5: Compensation of the temperature dependence of the running time functional dependence of the running time in a 25 mm of measuring bodies
  9. 9. IBJ Technology / Structural Health Monitoring – Real Time Stress Measurement Laufzeit = f (Spannung) 7780 7775 7770 7765 7760 7755 7750 7745 7740 7735 7730 0 10 20 30 40 50 60 Spannung MPa Laufzeit ns Fig. 6: running time as function of the stress In the case of use of a measuring body with 25 mm measuring distance a change of stress results in a change of the running time of 10 MPa of approx. 7800 ps. Each individual measuring with the TDC circuit TDC-GP2 brings a resolution of ca.50 ns, i.e. the resolution amounts to approx. 64 kPa without calculation of average values. Fig. 7: Dependence of the speed of the longitudinal wave of the tension 3. Measurements of concrete bodies and reinforces elastomeric bearings under the hydraulic press For the static loading tests that the acousto-elastical sensors were centrically concreted in concrete bodies with the dimensions with the dimensions of 300 mm of
  10. 10. IBJ Technology / Structural Health Monitoring – Real Time Stress Measurement length, 200 mm of depth and 100 mm height. The concrete bodies lay on bed made of powder and leed sheet. Fig. 8: equipment Fig. 9: hydraulic press The upper load introduction took place over elastomer camp (make Gumpa). Over this camp to the distribution of the load a steel plate with a thickness was put of 30 mm. In order to achieve at the sensor a higher stress concentration, the elastomer camp was made smaller on a surface von100 mm x 200 mm. With following experimental setup became within the range of 0… 12.5 MPa load lines of aluminium bodys with 10 mm up to 25 mm of edge length taken up to concrete. . For higher mechanical stresses the surface was reduced for force application. The surface of the reinforces elastomeric bearing was made smaller on 100 mm x 200 mm. Fig.10: Stress concentration over the sensor
  11. 11. IBJ Technology / Structural Health Monitoring – Real Time Stress Measurement Fig. 11: experimental set-up Fig.12: Data Aqusition System DASYLab 9 Order for load took place with a hydraulic press upto max. 25 tons without load control. The measurement the load took place with a ring torsion cell RTN C 47t from gives with a 24-Bit AD-transducer ADS1232. The PC program TIADS123X (LABVIEW) for it ran separately when running. The temperature measurement took place with a digital temperature sensor. The stress in MPa, measured in Fig.12, became after a calculation specification from the running times measured with the TDC and with DASYLab as “sigma measuring “represented. The comparison load measured with the load cell (resolution 10 g) as “sigma target” seized. The resolution of the tension took place in each case in 1 kPa-walked. Fig.13: DASYLab 9 computation “sigma is For the computation of “sigma measuring “simplified according to the following regulation one proceeded: The stress s results from the temperature-compensated running time LT1, the reference on time LT0 and that acousto-elastic factor of the measuring body material Ks too
  12. 12. IBJ Technology / Structural Health Monitoring – Real Time Stress Measurement s = ( LT1 - LT0 ) / Ks ( 7 ) Hereunder applies for LT1 the measuring temperature T1 of the measuring body and for LT0 the reference temperature T0 = 0 °C and the reference stress s = 0. Whereby the temperature-compensated running time LT0 from the measured running time LT and the correctur factor KT is determined after LT0 = LT * KT ( 8 ) The thermal factor KT is for a large temperature range a nonlinear function KT = f ( T ) ( 9 ) The thermal factor KT of the running time determines itself according to (5) with the linear regression for the selected sensors too KT = 0,94684 ns°C-1 ( 10 ) . On the sensor test stand the acousto-elastical factor Ks, intended for the selected metal alloy and sensor thickness, too Ks = 4,4585 Mpa ns-1 and/or Ks = 4,4585 Nmm-2 ns-1 ( 11 ) 4. Field measurements at a building of the federal motorway 4.1. Sensor In order to permit the installation into boreholes under the elastomeric bearings, as low an overall height of the sensors as possible was selected. The installation of the sensors takes place into boreholes from approx. 25 mm in diameter. The sensors possess a 1-Wire-Interface DS18S20 von Dallas with a resolution of 12 bit. Each sensor is clearly identifiable with the sensor coding in the ROM. Fig. 14:stress sensor BBS_10_DS
  13. 13. IBJ Technology / Structural Health Monitoring – Real Time Stress Measurement 4.2. Measurement with TDC The measuring instrument with TDC is accommodated in a GFK box as well as the processor for temperature measurement. The ultrasonic impulse is generated by an ultrasonic thickness-measuring meter CL204 von Krautkrämer Branson. The announcement of the thickness is not evaluated and serves only for control of the operating condition. The starting and stop impulse for the measurement of running time with the TDC are inferred from the CL204 and supplied to the TDC board. The control TDC board takes place with a batch-program Fig. 15: Measuring box with TDC and CL204 The running time, those with the TDC board is determined over a serial Interface with a Windows program seizes. The tax and evaluation programs run multitasking on Panasonic a Toughbook CF-M34. 4.3. Measurement of the running time with ultrasonic material testing set With a further independent the running times of the sensors under the loaded bearings additionally with the ultrasonic material testing set USP1 one seized. The measurement of running time takes place with this measuring instrument only with a dissolution of 1 ns. The run time data were seized with a further notebook. The visualization of a-picture and the measurement of the echo amplitude make the estimate for the operability possible of each sensor. 4.4. Stress and load measurement The data at running time and the temperature, as well as the sensor number are processed serially over a USB stroke in Panasonic the CF-M34. The representation of the data takes place in a special program for the data evaluation under DasyLAB.
  14. 14. IBJ Technology / Structural Health Monitoring – Real Time Stress Measurement At present only approx. 3 measured values/second can be evaluated with the batch-program for the selection of the TDC. The TDC is to be implemented able at appropriate software 1000 to 10000 measurements/second. The measurement act of the ultrasound measurements with the CL204 amounts to 1 ms, i.e. 1000 measurements/second are accomplished at present. The TDC queries however only 3 measurements/second, since it is limited over the serial interface by the data transmission rate of 9600 Baud. Fig. 16: (Screen of the Windows program for the sigma determination) 4.5 Taking measurement Fig. 17: BAB 9, Munich-Berlin Fig. 18: bored hole for sensor After the hydraulic raising of the bridge and removing the elastomeric bearings the mounting holes for the sensors were bored for bearing load measurement if possible dare quite and centrically and/or close of the center of the surface of the elastomeric bearings. The drillings were slit with diamond gumption sheets. The sensors must be embedded actuated in the concrete under the elastomeric bearings. As mortar for actuated imbedding construction mortar of Pagel served.
  15. 15. IBJ Technology / Structural Health Monitoring – Real Time Stress Measurement Fig. 19: Preparatory hole Fig. 20: Sensor inserted Fig. 21: Before using the elastomeric bearing Fig. 22: Elastomeric bearing assigned After using the sensors the zero-measurement without load influence took place. The accomplished temperature measurements could not determine a rise in temperature by exotherm tying the mortar. The concrete was heated altogether still of the day before clearly. The air temperature on the day using the sensors was by a cooling break-down approx. 12°C to 13°C clearly under the concrete temperature from 17°C to 23°C. After sticking the elastomeric bearing together lowering the bridge took place.
  16. 16. IBJ Technology / Structural Health Monitoring – Real Time Stress Measurement Fig. 23: Sensors after load measurement Fig. 24: Sensor row direction the west After the bridge sinking take place the measurement of the load admission after 6 days. Apart from the measurement with the TDC board for each sensor the pertinent temperature was determined. After a further week the sensors with the USP1 were additionally examined. 5. Results of measurement 5.1. Static stress measurement If one lays on the stress measured under the elastomeric bearings as bar chart transverse to carriageway width, one receives the following representation: bearing location 1 is west (motorway center), the bearing location 27 is east (standing tires). With the TDC board no usable signal could be measured with bearing 4. The examination with that USP1 resulted in, which is still functional the sensor to generate the signal amplitude is too small over in the CL204 a stop signal for the running time. With a changed hardware this sensor is further evaluable. stress in concrete 100 80 60 40 20 0 1 3 5 7 9 11 13 15 17 19 21 23 25 27 bearing number stress MPa Fig. 25: stress and bearing number
  17. 17. IBJ Technology / Structural Health Monitoring – Real Time Stress Measurement 5.2. Dynamic stress measurement To measure despite the slow data transmission rate the attempt undertaken at a camp the load entry dynamically. The time axis in the continuous line recorder Windows program was adjusted to shorter time units. Fig. 26: Dynamic load measurement bearing 20 The break in fig. 26 possibly is on work on the opposite counter bearing to lead back. At the same time work in the hydraulics section. at the opposite bearings were accomplished. The fluctuations of the running time are induced by traffic on the motorway. The amplitude of the changes over 10 ns. That is 3 to 4 times more than the statistic noise of the zero-measurement. The next generation with improved controlling of the TDC will make 1000 measurements per second. 13:36:00 13:36:10 13:36:20 13:36:30 13:36:40 13:36:50 13:37:00 h:min:s Fig. 27: Sensor at the bearing 20 with a resolution time of 60 seconds. 6. View on applications The advantage of the acousto-elastical stress measurement is recordable with the following criteria: • Low cost on-line measurement • Practically indestructibly • No measuring range delimitation upward 50 45 40 35 30 25 20 15 10 5 0 Schreiber 0
  18. 18. IBJ Technology / Structural Health Monitoring – Real Time Stress Measurement • Measurement in the heap of debris and fracturing zone • Measurement in the water • Inexpensive lost probe From this concrete applications result how: The monitoring of all possible effect and structural parameters during the building phase and the enterprise of buildings is the basis for the condition and safety analysis of the building. The data seized with different geotechnical methods represent the basis for numeric and mechanical concept. On-line measuring procedures to stress measuring, do not have to be replaced in its force of expression and topicality. With on-line stress measurement the so far only modelful parameters at small expenditure can be measured and thus the verification of all past models be substantially improved. Fig.28: fracturing in rock By the use of expansive cements can be manufactured an analogy to the hydraulic frac. During a longer period such an equilibrium must adjust itself to the minimum ground pressure. Statements to the time performance of expansive ones to be cement in fig. 29 described [Mehta and Monteiro, 1993]. Fig. 29:Compressive stress in expansive cement From instrumentation view also the employment of RFI technology is conceivable. So measuring bodies with planar antennas or induction pick-up coils could be attached for the power supply of the ultrasonic units behind the Tübbings. Thus the installation is made possible for on-line stress measurement in the tunnel tube. Special meaning can attain the monitoring of buildings. So the in-situ stress sensors in the concrete could measure the load changes and stress changes with a building damage after earthquake immediately on-line. The alert with GPS item data is spread world-wide over the Internet. The combination also for everyone accessible maps of the world
  19. 19. IBJ Technology / Structural Health Monitoring – Real Time Stress Measurement can facilitate the management after disasters substantially. Material costs of a measuring system amount to less than 50 €. By networking of several measuring systems with modern systems to the data communication, how Internet, mobile or Satelite know thereby a kind of secondary low cost array Seismometer are developed. 7. Results Xiaojun Huang, Daniel R. Burns und M. Nafi Toksöz, ERL, MIT „The effekt of stress on the sound velocity in Rocks.Theory of Acoustoelasticity and Experimental Measurements“, Consortium Reports 2001, Earth Resources Laboratory, Cambrigde, MA 02142. Jäger, F.-M., Vorrichtung zur Ermittlung der Gebirgsspannung in einem Bohrloch - DE102005047659B4, Verfahren und Vorrichtung zur Früherkennung von Bauwerksschäden - DE102006053965A1, Vorrichtung und Verfahren zur Lastmessung an Lagern von Bauwerken - DE102007014161B4, Verfahren und Vorrichtung zur Bestimmung der Gebirgsspannung – DE102008037127.0, Verfahren und Vorrichtung zur Überwachung und Bestimmung der Gebirgsspannung – PTC/DE102009/001105 Längler,F., Wissensbasierte Automatisierung und kontinuumsmechanische Erweiterung der Ultraschall-Eigenspannungsanalyse zur Beschreibung des Spannungszustands im gesamten Bauteil, Dissertation 2007,Universität des Saarlandes, Saarbrücken, S.10 Splitt, G., Schraubenspannungs-Messung mit Ultraschall - moderne Messtechnik für sichere Schraubenverbindungen, Agfa NDT GmbH, DGZfP-JAHRESTAGUNG 2002 Mehta and Monteiro. (1993) Concrete Structure, Properties, and Materials, Prentice- Hall, Inc., Englewood Cliffs, NJ Author: Dipl.-Ing.(FH), Dipl.-Ing.Ök. Frank-Michael Jäger IBJ Technology Ingenieurbüro Jäger GBR Colkwitzer Weg 7 04416 Markkleeberg

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