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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Journal of nondestructive evaluation 18 (1999), S. 103-113 
    ISSN: 1573-4862
    Keywords: acoustoelasticity ; stress ; EMATs ; bridges
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: Abstract Pin and hanger connections are used in bridges to suspend an interior span from the outer spans. The connections can sometimes lock up due to corrosion. If lockup occurs the stresses in the connection are cycled due to thermal expansion and contraction of the bridge; fatigue cracking and failure may occur. We constructed an apparatus to simulate a locked-up pin and hanger connection. We performed proof-of-concept tests of a method to detect stresses in pin and hanger connections. The method uses the stress-induced changes in sound velocity of shear waves polarized parallel and perpendicular to the hanger axis. The birefringence is the normalized difference in these shear wave velocities. We measured the birefringence at opposite sides of the hangers, at midsection. We simulated three scenarios: continuous monitoring of hanger status; intermittent monitoring from a known initial state; measurement with no a priori knowledge of hanger status. Good agreement with strain gauge data was obtained for all three scenarios.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Journal of nondestructive evaluation 14 (1995), S. 83-98 
    ISSN: 1573-4862
    Keywords: Rayleigh waves ; electromagnetic acoustic transducers ; acustoelasticity ; stress ; bridges
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: Abstract Fatigue load monitoring is a useful tool for safety assessment of highway bridges. Monitoring has been conventionally done using strain gages. Installation of these gages is labor-intensive and requires safety precautions. Noncontact electromagnetic-acoustic transducers (EMATs) offer an attractive alternative. EMATs were used to transmit and receive Rayleigh Waves (RW). Changes in time of flight of RW due to the acoustoelastic effect can in principle be used to monitor stresses resulting from vehicular traffic. We have performed proof-of-concept experiments to demonstrate the feasibility of this approach. Specimens were subjected to bending to simulate the load environment in bridges. RW EMATs were used to measure the relatively low stresses (less than 14 MPa) typically experienced by bridge girders. The signal-to-noise ratio achievable with our system should allow adequate stress resolution for fatigue load monitoring. Factors which could impede technology transfer were considered. The primary obstacle appears to be variability in time of flight (TOF) due to magnetostriction. If the magnetic state is changed (e.g., by scanning of the EMATs) the TOF can change, even at constant stress. We have characterized this effect. If a proper installation procedure is followed, fatigue load monitoring with RW EMATs is feasible.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Journal of nondestructive evaluation 17 (1998), S. 141-152 
    ISSN: 1573-4862
    Keywords: Ultrasonic ; EMAT ; applied stress ; strain ; Rayleigh wave ; bridge
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: Abstract The measurement of applied stress on bridges can provide valuable information on the condition of the structure. The conventional technique for measuring applied stress is with a strain gage. However, strain gages can be time consuming to install because first the surface must usually be prepared. On a bridge, paint removal will most likely be necessary as part of this surface preparation. When dealing with lead-based paints, which are considered hazardous waste, many time consuming removal procedures are required. Because of these factors, a device that measures applied stress without requiring paint removal could be useful. While a “clamp-on” strain gage can also be used to measure applied stress without requiring paint removal, this type of strain gage can not be used on some bridge details, such as webs of I-beams and tops of box girders. An ultrasonic technique using non-contact electromagnetic transducers provides a possible method for applied stress measurement which is not limited by the same factors as those with conventional strain gages. The transducers operate through nonconductive and conductive (lead-based) paint and work on rusted, pitted surfaces. Our previous research developed a technique for measuring applied stresses on bridges with EMATs and included many laboratory tests. This paper describes field applications of the technique on actual bridge structures, as well as additional system testing and instrument calibration in the laboratory.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    Journal of nondestructive evaluation 17 (1998), S. 141-152 
    ISSN: 1573-4862
    Keywords: Ultrasonic ; EMAT ; applied stress ; strain ; Rayleigh wave ; bridge
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: Abstract The measurement of applied stress on bridges can provide valuable information on the condition of the structure. The conventional technique for measuring applied stress is with a strain gage. However, strain gages can be time consuming to install because first the surface must usually be prepared. On a bridge, paint removal will most likely be necessary as part of this surface preparation. When dealing with lead-based paints, which are considered hazardous waste, many time consuming removal procedures are required. Because of these factors, a device that measures applied stress without requiring paint removal could be useful. While a “clamp-on” strain gage can also be used to measure applied stress without requiring paint removal, this type of strain gage can not be used on some bridge details, such as webs of I-beams and tops of box girders. An ultrasonic technique using non-contact electromagnetic transducers provides a possible method for applied stress measurement which is not limited by the same factors as those with conventional strain gages. The transducers operate through nonconductive and conductive (lead-based) paint and work on rusted, pitted surfaces. Our previous research developed a technique for measuring applied stresses on bridges with EMATs and included many laboratory tests. This paper describes field applications of the technique on actual bridge structures, as well as additional system testing and instrument calibration in the laboratory.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
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