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Encyclopedia Home Nondestructive Testing (NDT)

Bridge Testing
Related Entries: Ultrasonic Testing (UT): Civil Engineering,Other Methods: Schmidt hammer,
Exhibitors Keywords: TSC..
Selected Articles:
- BRIDGE DECK CONDITION ASSESSMENT USING GROUND PENETRATING RA... (2006-11-01)
- NDT Methods for the inspection of highway structures... (2003-10-01)
Articles Articles Keywords: bridge958 bridges65 unknown bridge foundation40 Bridge decks37 Bridge inspection25 bridge monitoring23 steel bridge22 cable-stayed bridge20 SHM for bridges19 bridge deck18 cable stayed bridge18 bridge deck inspection15 concrete bridge14 road bridge14 Thomson double bridge14 railway bridge13 Stone bridges11 Cable-stayed bridges10 Prestressed concrete bridges9 cultural heritage bridge9 bridge special inspection8 bridge repair8 steel bridges8 bridge deck surface structure8 A572-G50 bridge steel7 Bridges Network7 PT concrete bridges7 bridge cable6 long-span bridge6 railway steel bridge6 bridge design5 orthotropic steel bridge deck5 Suspension bridge anchorage5 bridge pier5 bridge management system5 Masonry arch bridge5 Bridge Engineering5 Stockbridge damper5 bridge structure5 Concrete-NDT, Highway Bridge, ROB, Combination of methods5 multi wire steel strand bridge cable4 Bridge Performance4 Concrete bridge decks4 ECHOGRAPH Ultrasonic Steel Bar Testing Bridge2
Web Web Selected: ZfPBau-Kompendium ยท 2004 (2006-01-12)
The NDE Validation Center of the Federal Highway Administrat... (2001-04-19)
Web Web Keywords: bridge27, bridges1,
Description:

The increasing load on highway bridges due to increasing heavy goods vehicle traffic, aging and problems with the durability of structures may lead to obstructions of traffic with ensuing severe economic damages. Effective and reliable condition assessment tools are an important part of the ongoing efforts to evaluate and maintain bridge structures. In most of countries in the world, bridges and other concrete structures are regularly inspected, normally at least once every two years. However, the inspections are mainly carried out visually. Therefore, damages are only identified when the deterioration becomes visible. In Germany the interval for a simple test must be carried out every 3 years and a "deep" inspection every 6 years accordingly to DIN 1076.

Many bridges in the world collapsed every year and this not only in poor or underdeveloped nations. Many people lost their lives in recent disasters in August 2007 in Minneapolis and in September 2006 in Canada. A recent U.S. Department of Transportation survey found that 27% of the nation's bridges are structurally deficient. The U.S. has about 600,000 bridges, with 17,000 considered "scour critical". About 1,500 collapsed between 1966 and 2005, according to Jean-Louis Briaud. In the past most bridges have failed for a handful of known reasons: weak foundations, corrosion, metal fatigue, ship collision or design error.

Nondestructive testing can be an effective tool in the inspection and condition assessment of bridge structures. It can provide knowledge that may not be possible to deduce from visual observation alone. The integration of both visual and nondestructive inspection methods is key to complete bridge condition assessment and management. Some simple nondestructive techniques, such as hammer sounding, rebound hammer testing, dye penetration, and magnetic particle testing, can be easily integrated into visual inspections. The results of these integrated inspections will improve bridge data files, and will yield more technically based recommendations for further inspection and maintenance, and more accurate estimations of remaining service life. Once a full representation of the overall bridge condition is determined, appropriate and economical decisions regarding the possible rehabilitation or replacement of bridge members or the entire structure can be made.

In the case of concrete bridge decks the decks consist of a concrete slab covered by an asphalt coating. The concrete slabs generally have a thickness of approximately 25 cm and contain two mats of steel rebar reinforcements. The most serious form of deterioration in concrete bridge decks is the corrosion of steel rebars caused by the excessive use of chloride deicing salts during winter for the maintenance of the structures. As the reinforcement steel corrodes, it expands and creates a cracks or surface fracture plane in the concrete at, or just above, the level of the reinforcement. The fracture plane, or delamination, may be localized or may extend over a substantial area.

Recent advances in NDE techniques have improved the functional characteristics of many NDE methods and have led to systems that are more reliable. Increased use of NDE methods will depend on several factors including the ability of the systems to accurately detect deteriorated conditions, the ease of use and field portability of the systems, and the total cost of completing the NDE based inspections.

Since bridges are build in almost hundreds of different kind of types and using so many different materials of supporting components, so that it is not possible to use just one NDT method for all tasks. For instants, microwave or ground penetrating radar (GPR) may be used for reinforced concrete decks but is not suitable for weld testing of steel members. Also there are many tasks which need further research to make NDT methods suitable.

A lot of application reports of NDT methods for bridge testing are frequently published. Several methods are available, are in research or are used for further inspection after regularly inspections indicates their needs. They include:

  • Impact-Echo (IE) for checking integrity of concrete.
  • Impact-Echo (IE) is suitable to determine the thickness of the concrete.
  • Magnetic flux leakage (MFL) to detect corrosion in strands and bars in post-tensioned concrete structures.
  • The nuclear magnetic resonance (NMR) method can determine the presence and location of water. This enables the determination of pore size and pore distribution as the concrete cures.
  • Infrared imaging technologies to find defects in the concrete parts of bridges.
  • ASTM Standard E837 for determining in-situ stresses in structural steel members.
  • Strain Transducers to record the induced strains.
  • Potential mapping is the most simple electrochemical technique used for obtaining corrosion information on site. The technique informs qualitatively on the corrosion risk of the reinforcement in the reinforced concrete structures.
  • Acoustic emission monitoring can play a very effective role in enhancing safety, ensuring availability and reducing the repair/refurbishment costs of bridges.
  • A well-established and accepted application of GPR is the accurate condition assessment of bridge decks as well as other reinforced concrete structures. The ability of GPR to be used without requiring the removal of an existing asphalt.
  • Ultrasonic testing allows also the visualisation of perpendicularly arranged reinforcement bars, tendon ducts. UT can compensate deficits of the radar method.
  • The combined application of radar, impact-echo and ultrasonic echo for the assessment of post-tensioned concrete structures.
  • Liquid-penetration testing - Visual check of dye that penetrates hairline fractures in pavement.
  • Ultrasonic testing of welds, bolts and rivets steel members.
  • Divers inspect underwater concrete piers, which may have been damaged by erosion.
  • Magneto-inductive is used for evaluation of cables and wires.
  • Laser Measurement Technologies for numerous applications using laser-based distance measurements for highway infrastructure. Applications for this technology include measuring bridge deflections under calibrated load to evaluate structural behavior, calculating out-of-plane distortions in girder webs and flanges, and evaluating the as-built construction of large structures such as abutments.
  • Bridge Monitoring Systems using acoustic emission sensors or eddy-current sensor. Generally, these instruments are dedicated, remote data-acquisition systems that collect information on the behavior of a structure over time. The acoustic emissions detection system can evaluate sounds emanating from any materials, including steel cables, trusses and concrete in a bridge. Cracks can be recognized many months before they are visible on the surface.
  • Thermographic methods for evaluating composite bridges and composite bridge repairs.
  • Both ultrasonic and radiographic testing are used to inspect steel bridges during fabrication to ensure weld quality.
  • Automated Ultrasonic Testing (AUT) can be an effective inspection tool that could be used in place of radiography under certain conditions.
  • Ultrasonic velocity measurements can be used as a quality-control tool during construction and how ultrasonic testing may be used for in-service inspection of bridges constructed of reactive powder concrete (RPC).
  • Electromagnetic acoustic transducers could detect broken wires within a strand.
  • Electrochemical Fatigue Sensor (EFS) can be used to determine if actively growing fatigue cracks are present. An EFS sensor is first applied to the fatigue sensitive location on the bridge or metal structure, and then is injected with an electrolyte at which point a small voltage is applied. An algorithm automatically indicates the level of fatigue crack activity at the inspection location.
  • Brillouin fiber optic sensor technology is a promising technology for structural health monitoring (SHM) thanks to its unique feature of distributed strain and temperature measurement by means of low-cost optical fibers.
  • X-ray computed tomography for determination of crack propagation in concrete using.
  • X-ray computed tomography for determination of void percentage and distribution in concrete.
  • Prompt Gamma Neutron Activation Analysis for determination of chloride concentration and depth profiles in concrete.
  • Neutron scattering technique measuring cement hydration using.
  • Ultrasonic method for direct measurement of preload force of bolted connections. This is an innovative technique for direct measurement of actual bolt stresses
  • Robotic Tacheometry System (RTS) (Total Station) offers the capability to measure the spatial coordinates of discrete points on a bridge without having to touch the structure.
There is incredible technology out there to help monitor and diagnose problems, and research continues to develop new technologies to keep up with the infrastructure of bridges.

Older bridges need more than just a regular inspection. As bridge get older, it needs more tests. What is missing, experts say, is short-term cash and a long-term commitment by governments to fund more research into new technologies and innovations.

Illustrations:


GPR data collection


Deterioration Map of GPR Data of Bridge Deck


Testing with Impact-Echo (left) and GPR (right)


Crevice corrosion in layers of steel can bend plates, or strike between concrete and steel. Surface corrosion may be visible in routine bridge inspections, but non-destructive ultrasonic testing can yield information on the extent of unseen damage(WisDOT


Rolf Diederichs created: 2007-08-06 Login

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