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Testing is possible by the reference piece method. For different ground anchoring bolt types (different length, diameter and form of the ending) reference bolts were made. In different sound path distances reflectors (grooves, transversal borings) were introduced into the reference bolts. By sounding against the backend and against the reflectors of different size, what we call ,,reflector-comparison-diagrams" were plotted for the single bolt types, see figure 1.
Figure 1: Reflector comparison diagram
With decreasing anchoring bolt diameter we recorded assemblies of amplitudes at radial reflectors and especially at the back end because of the constrained guide of the sound ray and the side-swiped incidence, figure 2.
 Figure 2: Measurement of real diameter of ground anchoring bolts |
d = anchoring bolt diameter s = sound path c1 = sound velocity-longitudional c2 = sound velocity-transversal" a = sound angle |
For the evaluation of the reflector distance to the sound ray entrance these effects are to be considered among others when making the approximative echo height comparison.
Construction details/achor dimensions
Different designs and dimensions was arrived at. The bolts were partly sheathed or placed without sheating in the base. All anchoring bolts up to now tested had threads and spring nuts on the upper end. Anchoring bolts of 25 mm up to 140 mm in diameter and about 3 m up to 8 m in length were tested. The threaded ends were up to 300 mm long. The other end exhibited two different design features. The anchoring bolts were provided with threads and spring nuts or with forged hammer heads.
Testing data Problem
For testing purposes digital mode as well as frequency variable narrow-band sound transmitters are available with DMT's Testing Laboratory for Nondestructive and Destructive Testing (DMT-ZfP) . The selection of the testing heads was made according to the special testing demands, the anchoring bolt dimensions, and the anchoring bolts material.
Reference bolt tests in the DMT-ZfP' s laboratory
Generally three testing aims are specified.
- a) Inspection of the bolt upper threaded length (support) and the tensioning
point (absence of flaws)
- b) Inspection of the middle length of the bolt (absence of flaws and
measurable corrosion) and
- c) Inspection of the bolts bottom threaded length (support) (absence of flaws)
The first testing aim was reached for known thread lengths and diameters with a high resolution measurement. We may suppose that damages on the upper tensioning points will be primed in the force induction zone nearly as radial flaws and not profile surrounding. The reference bolts (here 30 mm and 100 mm in diameter) were provided with artificial flaws of 1 mm in depth. From the failures clear signals were produced on the ultra sonic screen, figure 3.
Fig 3: Ultrasonic diagram of artificial reflector
(reflector 1mm in depth, bolt diameter 30 mm)
In the middle of the shaft radial flaws can start after cross section losses and pitting by corrosion. The cross sections losses can here start around the f ull profile or over segments of a circle. Such corrosion points were realiably detected with cross section losses greater than 10 % . Corrosion attacks In ground anchoring bolts can also be primed in form of pittings or needle shaped. The detection of such damages was provided on reference bolts on radial bore holes. The bore hole diameters and the radial depth were determined according to the required resolution and of course with respect to the detection possibilities In greater sound path distances.
The most demanding task for the available testing systems is to spot damages on the ground anchoring bolts in the lower length and the bottom end. figure 4
Fig 4: Ultrasonic diagram of reflector in 5020 mm distance
shows the echo amplitude of a reflector in cat 5000 mm distance, for more than 10 % cross section losses with a reference bolt of 80 mm in diameter, as recorded by the ultra-sonic device.
Attention must be paid to the comparability of the material properties of the reference bolts and those at the tested ground anchoring bolts, because they influence the ultra sonic signal. Tests were made with two reference bolts of the same geometry, the same reflectors, but different material characteristics.
The reference bolts test delivered as result pictures, that were worked out before the reference piece method for the testing of ground anchoring bolts was used in several bridge constructions. For different reflector sizes and sound path distances reflector reference diagrams could be referred to for the evaluation of findings in the field.
Results of field tests
Example 1 - River crossing, federal motorway
The anchoring of the bridge is assured by what we call ,,pylon anchoring bolts" (32 mm In diamter, cat 5 m long) for the vertical forces and by what we call ,,cross-wind anchoring bolts" (also 32 mm diameter, cat 3 m long) for the horizontal forces. The ultra-sonic tests identified no defects.
Example 2 - River crossing, federal
highway
The anchorig of the bridge is assured, for its four pylons (of an older design), by four ground anchoring bolts ( 140 mm diameter, ca 6 m long) per pylon. Two additional pylons (of a later design) are held by 16 anchoring bolts of 35 mm diameter per pylon. The testing of the 140 mm thick anchoring bolts on the pylons of the older design identified by ultra-sonic defects over the smooth length. The order of magnitude of the defects was below the statutory threshold. All tensioning points and abutments were found to be without damage. What we call ,,Preservice inspections" were carried out on the anchoring bolts of the two pylons of newer designs.
Example 3 - Canal crossing, federal railway bridge
The ground anchoring bolts' dimensions were of 65 mm to 12.0 mm in diameter and cat 3,5 and 8,0 m of length. The echo sizes of ultra-sonic reflector found in different distances should be compared with known reflector echo sizes of the reference bolt. The association was made dependent on the diameter. Damages on the ground anchoring bolts directly affecting the safety of the bridge were not found in any case. Indications of local corrosion damages were given. Possibly occurring further development of damages may be monitored by recurrent tests.
Summary
Examples for possibilities of non-destructive ultra-sonic testing of ground anchoring bolts in bridge constructions were shown. The tests were carried out by experts of the DMT-IFT with good results. The evaluation of reflectors found during the tests was made in comparison to known reflectors in reference bolts of identical geometry and similar material. The association of echo sizes of the reflectors found in the ground anchoring bolts to the echo amplitudes of known damage sizes in the reference bolts yields an appropriate percentage of cross section losses by flaws or corrosion so that the residual safety can be calculated in comparison to the as-new state.
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For testing purposes digital mode as well as frequency variable narrow-band sound transmitters are available with DMT's Testing Laboratory for Nondestructive and Destructive Testing (DMT-ZfP) . The selection of the testing heads was made according to the special testing demands, the anchoring bolt dimensions, and the anchoring bolts material.
Reference bolt tests in the DMT-ZfP' s laboratory
Generally three testing aims are specified.
- a) Inspection of the bolt upper threaded length (support) and the tensioning
point (absence of flaws)
- b) Inspection of the middle length of the bolt (absence of flaws and
measurable corrosion) and
- c) Inspection of the bolts bottom threaded length (support) (absence of flaws)
The first testing aim was reached for known thread lengths and diameters with a high resolution measurement. We may suppose that damages on the upper tensioning points will be primed in the force induction zone nearly as radial flaws and not profile surrounding. The reference bolts (here 30 mm and 100 mm in diameter) were provided with artificial flaws of 1 mm in depth. From the failures clear signals were produced on the ultra sonic screen, figure 3.
Fig 3: Ultrasonic diagram of artificial reflector
(reflector 1mm in depth, bolt diameter 30 mm)
In the middle of the shaft radial flaws can start after cross section losses and pitting by corrosion. The cross sections losses can here start around the f ull profile or over segments of a circle. Such corrosion points were realiably detected with cross section losses greater than 10 % . Corrosion attacks In ground anchoring bolts can also be primed in form of pittings or needle shaped. The detection of such damages was provided on reference bolts on radial bore holes. The bore hole diameters and the radial depth were determined according to the required resolution and of course with respect to the detection possibilities In greater sound path distances.
The most demanding task for the available testing systems is to spot damages on the ground anchoring bolts in the lower length and the bottom end. figure 4
Fig 4: Ultrasonic diagram of reflector in 5020 mm distance
shows the echo amplitude of a reflector in cat 5000 mm distance, for more than 10 % cross section losses with a reference bolt of 80 mm in diameter, as recorded by the ultra-sonic device.
Attention must be paid to the comparability of the material properties of the reference bolts and those at the tested ground anchoring bolts, because they influence the ultra sonic signal. Tests were made with two reference bolts of the same geometry, the same reflectors, but different material characteristics.
The reference bolts test delivered as result pictures, that were worked out before the reference piece method for the testing of ground anchoring bolts was used in several bridge constructions. For different reflector sizes and sound path distances reflector reference diagrams could be referred to for the evaluation of findings in the field.
Results of field tests
Example 1 - River crossing, federal motorway
The anchoring of the bridge is assured by what we call ,,pylon anchoring bolts" (32 mm In diamter, cat 5 m long) for the vertical forces and by what we call ,,cross-wind anchoring bolts" (also 32 mm diameter, cat 3 m long) for the horizontal forces. The ultra-sonic tests identified no defects.
Example 2 - River crossing, federal
highway
The anchorig of the bridge is assured, for its four pylons (of an older design), by four ground anchoring bolts ( 140 mm diameter, ca 6 m long) per pylon. Two additional pylons (of a later design) are held by 16 anchoring bolts of 35 mm diameter per pylon. The testing of the 140 mm thick anchoring bolts on the pylons of the older design identified by ultra-sonic defects over the smooth length. The order of magnitude of the defects was below the statutory threshold. All tensioning points and abutments were found to be without damage. What we call ,,Preservice inspections" were carried out on the anchoring bolts of the two pylons of newer designs.
Example 3 - Canal crossing, federal railway bridge
The ground anchoring bolts' dimensions were of 65 mm to 12.0 mm in diameter and cat 3,5 and 8,0 m of length. The echo sizes of ultra-sonic reflector found in different distances should be compared with known reflector echo sizes of the reference bolt. The association was made dependent on the diameter. Damages on the ground anchoring bolts directly affecting the safety of the bridge were not found in any case. Indications of local corrosion damages were given. Possibly occurring further development of damages may be monitored by recurrent tests.
Summary
Examples for possibilities of non-destructive ultra-sonic testing of ground anchoring bolts in bridge constructions were shown. The tests were carried out by experts of the DMT-IFT with good results. The evaluation of reflectors found during the tests was made in comparison to known reflectors in reference bolts of identical geometry and similar material. The association of echo sizes of the reflectors found in the ground anchoring bolts to the echo amplitudes of known damage sizes in the reference bolts yields an appropriate percentage of cross section losses by flaws or corrosion so that the residual safety can be calculated in comparison to the as-new state.
- a) Inspection of the bolt upper threaded length (support) and the tensioning
point (absence of flaws)
- b) Inspection of the middle length of the bolt (absence of flaws and measurable corrosion) and
- c) Inspection of the bolts bottom threaded length (support) (absence of flaws)
- b) Inspection of the middle length of the bolt (absence of flaws and measurable corrosion) and
| The first testing aim was reached for known thread lengths and diameters with a high resolution measurement. We may suppose that damages on the upper tensioning points will be primed in the force induction zone nearly as radial flaws and not profile surrounding. The reference bolts (here 30 mm and 100 mm in diameter) were provided with artificial flaws of 1 mm in depth. From the failures clear signals were produced on the ultra sonic screen, figure 3. |  Fig 3: Ultrasonic diagram of artificial reflector (reflector 1mm in depth, bolt diameter 30 mm) |
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In the middle of the shaft radial flaws can start after cross section losses and pitting by corrosion. The cross sections losses can here start around the f ull profile or over segments of a circle. Such corrosion points were realiably detected with cross section losses greater than 10 % . Corrosion attacks In ground anchoring bolts can also be primed in form of pittings or needle shaped. The detection of such damages was provided on reference bolts on radial bore holes. The bore hole diameters and the radial depth were determined according to the required resolution and of course with respect to the detection possibilities In greater sound path distances.
The most demanding task for the available testing systems is to spot damages on the ground anchoring bolts in the lower length and the bottom end. figure 4
|  Fig 4: Ultrasonic diagram of reflector in 5020 mm distance |
Attention must be paid to the comparability of the material properties of the reference bolts and those at the tested ground anchoring bolts, because they influence the ultra sonic signal. Tests were made with two reference bolts of the same geometry, the same reflectors, but different material characteristics.
The reference bolts test delivered as result pictures, that were worked out before the reference piece method for the testing of ground anchoring bolts was used in several bridge constructions. For different reflector sizes and sound path distances reflector reference diagrams could be referred to for the evaluation of findings in the field.
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Example 1 - River crossing, federal motorway
The anchoring of the bridge is assured by what we call ,,pylon anchoring bolts" (32 mm In diamter, cat 5 m long) for the vertical forces and by what we call ,,cross-wind anchoring bolts" (also 32 mm diameter, cat 3 m long) for the horizontal forces. The ultra-sonic tests identified no defects.
Example 2 - River crossing, federal highway
The anchorig of the bridge is assured, for its four pylons (of an older design), by four ground anchoring bolts ( 140 mm diameter, ca 6 m long) per pylon. Two additional pylons (of a later design) are held by 16 anchoring bolts of 35 mm diameter per pylon. The testing of the 140 mm thick anchoring bolts on the pylons of the older design identified by ultra-sonic defects over the smooth length. The order of magnitude of the defects was below the statutory threshold. All tensioning points and abutments were found to be without damage. What we call ,,Preservice inspections" were carried out on the anchoring bolts of the two pylons of newer designs.
Example 3 - Canal crossing, federal railway bridge
The ground anchoring bolts' dimensions were of 65 mm to 12.0 mm in diameter and cat 3,5 and 8,0 m of length. The echo sizes of ultra-sonic reflector found in different distances should be compared with known reflector echo sizes of the reference bolt. The association was made dependent on the diameter. Damages on the ground anchoring bolts directly affecting the safety of the bridge were not found in any case. Indications of local corrosion damages were given. Possibly occurring further development of damages may be monitored by recurrent tests.