Monitoring structural responses during load testing of reinforced concrete bridges: a review

Figures & data

Table 1. Overview of diagnostic load tests reviewed in this study.

Testing campaign	Goal of the test	Loading system	Instrumentation & measurements
Three RC slab bridges with deterioration (Saraf, 1998) USA	Improve rating factors	Dump truck	(A)- deck deflections profiles, (B) -strains at the top and bottom of the bridge deck
Four RC T-beam bridges (Catbas et al., 2005) USA	Transverse flexural.	Truck	(A)- deflections profiles, (B) – concrete strain, (C)- steel strain, (D)- dynamic responses
Six RC slab bridges (Jones, 2011) USA	Transverse flexural distribution	Truck	(E)- underside of the concrete slab
Two skew slab bridges on girders (Arockiasamy & Amer, 1998) USA	Transverse flexural distribution	Truck	(A)- deflections, (C) and (F) for strains
Pan girder bridge (Velázquez, Yura, Frank, Kreger, & Wood, 2000) USA	Transverse flexural distribution	Dump Truck	(A)- deflections, (C)- concrete strains and exposed reinforced bars
Composite concrete slab on steel girder bridge (Sanayei et al., 2016) USA	Transverse flexural distribution	Dump truck	(C)- instrumented during construction for strain measurements, (G)- rotations on abutments and piers, (H)- temperature, (D)- dynamic responses
Skewed prestressed concrete bridge (Diaz Arancibia & Okumus, 2018) USA	Transverse flexural distribution	Trucks	(A) & (C)- strains, (F)-embedded for shrinkage and temperature effects, (I)- displacement of bearings and girders
Reinforce concrete T-beam bridge(Al-Mahaidi et al., 2000) Australia	Transverse flexural distribution	Hydraulic jacks	(A)- beam deflections,(J)- applied load, (C)- strains in reinforcement, (G)- rotations of the superstructure, abutments, and pier
Reinforced concrete skewed slab bridge (Aktan, Zwick, Miller, & Shahrooz, 1992) USA	Evaluate of stiffness	Hydraulic jacks	(J)- applied load, (A)-deflections and slab rotations of the abutment and pier, (A)- concrete strains, (C)- steel strains
Deck slab bridge(Taylor et al., 2007) Ireland	Quantification of arch action	Hydraulic jack	(A)- deflected shape, (J)- applied load
Cast in place concrete deck bridge on girders of different concrete mixes (Hernandez & Myers, 2015) USA	Transverse distribution factors bridge with self-consolidating concrete	Dump truck	(I)- vertical deflections of girders, (F)- embedded for strain measurements with thermistors, (D)
Five bridges reinforce concrete T-beam bridges (Merkle & Myers, 2004) USA	Verification of FRP strengthening system	Dump trucks	(I) and (A) -deflections
Composite concrete slab on steel girder bridge (Wang et al., 2016) USA	Transverse load distribution of lightweight concrete bridge	Truck	(E)- strain on deck and girders
Skewed RC slab bridge (Colombani & Andrawes, 2022) USA	Load rating	Dump truck	(E)- strain on the slab
Precast concrete bridge (Abedin et al., 2022) USA	Development of FE models for damage detection	Dump truck	(A) and (I) – deflections

(A)-LVDT; (B)- Clip gauges; (C)- Strain gauges; (D)-Accelerometer; (E)- Strain transducers; (F)-Vibrating wire strain gauge; (G)- Inclinometer; (H)- Temperature sensors; (I)- Total station; (J)- Load cells.

Table 2. Overview of proof load tests reviewed for this study.

Testing campaign	Application	Loading system	Instrumentation & measurements
Two prestressed concrete bridges (Shahawy, 1995) USA	Insufficiently rated	Vehicles with concrete blocks	(A)- deflection and strain, (K) –dynamic responses
T-beam concrete bridge (Juntunen & Isola, 1995) USA	Large uncertainties on a 68-year-old bridge	Two unit vehicle	(A) and (G)-deflections, (I)- monitor of cracks
Single span prestressed bridge with T beams (Anay, Cortez, Jáuregui, Elbatanouny, & Ziehl, 2016b, Aguilar et al., 2015) USA	Lack of information (no structural plans)	Dump trucks	(C)- Detect and locate cracks, (M)- Strains on at the bottom of the beams
Four reinforced concrete bridges (Lantsoght et al., 2017a) Netherlands	Uncertainties due to ASR damage (Fennis, Hordijk, Yuguang, & Koekkoek, 2015, Koekkoek, Lantsoght, & Hordijk, 2015) and insufficient rating (Fennis & Hordijk, 2014, Koekkoek, Lantsoght, Yuguang, & Hordijk, 2016)	BelFa loading truck and system with hydraulic jacks, counterweights and load spreader	(A)-deflections, crack widths and strains due to load ;(B)-Deflection; (C)-Crack formation; (D)-Load
Four prestressed overturned T-beam concrete bridges (Schmidt et al., 2018)	Development of a testing method	Test rig with weights and hydraulic jacks	(A), (H)& (B)- deflections, degree of fixation at the supports and strains, (D)-applied load, (F)- deformation, crack initiation and strains, (E)-strains, (L)- to reproduce the test environment in virtual reality and to measure distances in the point cloud after the test and strain measurements from the surface
Skewed RC slab bridge (Colombani & Andrawes, 2022) USA	Update load rating	Dump truck	(M)- strains, (A) and (O) - deflections

(A)-LVDT; (B)-Laser distance sensor; (C)-Acoustic emission; (D)-Load cells; (E)-Electrical strain gauges; (F)-Digital image correlation; (G)-Electronic level; (H)-Total station;(I)- Spotting scope; (J)- (K)-Accelerometer; (L)-3D scaning; (M)- Strain transducers, (O)-Computer vision method.

Figure 1. The basic principle of LVDT transducer.

Figure 2. Typical LVDT sensor installed for measuring displacements.

Figure 3. Laser triangulation principle.

Figure 4. Application of laser distance sensor to measure the deflection.

Figure 5. Electrical resistance strain gauge.

Figure 6. Typical strain gauge.

Figure 7. Vibrating wire strain gauge.

Figure 8. Typical strain transducer.

Figure 9. Hydraulic load cell.

Figure 10. Capacitive pendulum inclinometer working principle.

Figure 11. Piezoelectric accelerometer.

Figure 12. Measurement of the distance and angles with the total station.

Figure 13. 2 D DIC setup for a reinforced concrete beam showing the random pattern.

Figure 14. Methodology to measure vibrations with VVS.

Figure 15. Working principle of interferometric radar. Δφ: phase difference.

Figure 16. Radar measurement equipment. Left: radar, and right: the reflector (target).

Figure 17. Scheme of calculation of actual displacements for bridge monitoring.

Figure 18. Scheme of light traveling and reflecting in an optical fiber.

Figure 19. Application of FBG sensors. Left: glued to steel rebar, and right: attached to a concrete surface.

Figure 20. Scheme of AE monitoring principle.

Figure 21. Installation of AE sensor in a proof load test in the Netherlands.

Figure 22. Operating principle of LiDAR scanner.

Figure 23. Structure of a smart aggregate.

Figure 24. Installation of SA sensors. Left: before casting, and right: inside a drilled hole in an existing structure.

Figure 25. Scheme of RFID tag.

Figure 26. Working principle of thermocouple.

Table 3. Summary of techniques and sensors.

Technique	Parameter	Mechanism	Suitable for dynamic measurements	Measuring range	Range of accuracy	Advantages	Disadvantages	Distance to structure
LVDT	D	Electro-mechanical	Yes	1 − 250 mm	10 − 100 µm	Reliable, accurate, simple, light, and easy to maintain	Sensitive to temperature, on-site setup, operating range	Direct contact^i
DIC	D, C, S	Photo-grammetry	Yes	Depends on the pixel resolution of the equipment	0.1-1 pixel	Full-field, and no reference	Noise, calibration, durability, and cost	0.1 − 10 m
Laser distance sensor	D	Optical	Yes	1 − 1250 mm	10 − 100 µm	Accurate, light, and easy to maintain	Sensitive to temperature, foreign materials, rain, and dust	0.1 − 1 m
Interfero-metric radar	D	Microwave	Yes	> 0.01 mm	0.01- 10 mm	Suitable for all environmental conditions, several measurements	Location, relative displacements, planning	Up to 1 km
Total station	D	EDM with electronic theodolite	No	> 0.1 mm	0.1 − 10 mm^ii	Rugged, widely available, remote	Data gathering time consuming, sensitive to vibrations and environmental conditions	Up to 2.5 km
Fiber optic sensors	S	Optical	Yes	1 − 5000 µε	1 − 10 µε	High sensitivity, no reference, cover long distances, immune to electromagnetism	Installation, sensitivity to temperature, careful handling	Direct contact
Strain gauge	S	Electrical resistance	Yes	1 − 50000 µε	1 − 10 µε	Integrated to structure, light, widely available, low cost	Installation, not reusable, sensitive to temperature	Direct contact ^i
Load cells	F	Several	Yes	1 kN to 40 MN	0.01 − 1000 N	Measure tension and compression, long term stability	Application to the structure	Direct contact
VWSG	S	Frequency of vibration	Yes (with vibrating wire analyzer)	1 − 10000 µε	1-10 µε	Immune to electrical noise, can be embedded	No dynamic measurements, data analysis, size	Direct contact^i
Strain transducers	S	Electrical resistance	Yes	1 − 2000 µε	1- 20 µε	No surface preparation, reusable, waterproof, commercialized	Short term, issues with temperature, range	Direct contact^i
RFID sensor	D	Electro-magnetic fields	Yes	> 0.1 mm	0.001-10 mm	No power supply, inexpensive, monitor larger areas	Calibration, sensitive to the environment and electromagnetic radiation, noise, not commercialized	Up to 0.6 m
Inclino-meters	I	Several	Yes	0.001 − 360°	0.001°-0.1°	Very sensitive	Attachment to the structure	Direct contact
Accelero-meter	A	Several	Yes	0.1 − 250 g	1-10 g	Widely commercialized and easy to install	Complex modelling for structural analysis, maintenance for long term	Direct contact^i
VVS	V	Photo-grammetry/ FFT	Yes	Depends on pixel resolution and frames per second of equipment	0.01-1 Hz	Monitor multiple targets	Noise, dependent on the equipment and distance to the structure	Up to 15 m
Acoustic emission	C	Electric wave	Yes	1 − 100 Hz	1- 20 cm^iii	Real-time measurements, very sensitive	Signal attenuation, noise, coupling	Direct contact
Smart aggregates	S	Electric wave	Yes	1 − 90 Hz	1 − 10 µε^iv	Source and receiver, less influence by environmental changes, internal	Hole drilling, sensors are not commercialized	Direct contact
LiDAR	D	Optical	Yes	> 0.1 mm	1-2 mm	Full field, unaffected by light condition	Limited to surface points, requires data processing methods	0.6 to over 30 m

(A) – Acceleration; (D) – Displacement; (C) – Identification of crack; (I) – Inclination; (S) – Strains; (V) – Frequency of vibration; (F) – Force

ⁱ A wireless transmitter is commercially available. The transmitter connects to the sensors and collects the data. Then via Bluetooth, the readings are sent to the electronic device.

ⁱⁱ Total Stations can measure deformation accurately to 0.1 or 0.2 mm at close range (less than 10 m).

ⁱⁱⁱ The range of accuracy of AEs refers to the localization error of cracking activity in the monitored area.

^iv The range of accuracy of SAs refers to the strain changes determined from the measurements after processing the signal.

Table 4. Goal of the diagnostic load test of a reinforced concrete bridge and measurements.

Goal of the test	Measurement
Neutral axis	Strain measurements at different heights in the beams or deck cross-sections
Transverse distribution	Strain or deflection measurements over the width of the bridge
Degree of fixity	Rotation measurements at supports
Deflection shape	Deflection measurements in the transverse and longitudinal direction of the bridge
Dynamic response	Acceleration measurements

Table 5. Stop criteria and measurements during a proof load test of a reinforced concrete bridge.

Stop criterion	Measurements
Nonlinear behaviour	Deflections at the loading point and supports; and the applied load
Stiffness	Deflections at the loading point and supports; and the applied load
Deformation profiles	Deflections at different positions along the transversal and longitudinal direction
Concrete strain	Average strain measurements of the bridge components at critical positions
Crack widths	Crack width measurements of new and existing cracks
Crack identification	Surface deformation or fracture process of the critical crack or type of failure.
Joint and settlements of the substructure	Displacement measurements

Figure 27. Measuring technique or sensor selection flow chart.

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