This paper proposes a new axle detection methodology using direct strain measurements. Initially, numerical analyses are carried out on a 1-D simply supported bridge structure to investigate the strain response of a bridge to a 2-axle moving vehicle. The strain response obtained from the numerical model is further studied and a new axle detection strategy, based on the second derivative of strain with respect to time, is proposed. Having developed the theoretical concept, field testing is carried out on a single span simply supported railway bridge to validate the proposed methodology and test its robustness of on a full-scale bridge.

1. Workshop
CERI, UCD, Dublin
Wednesday 29th August 2018

2. Farhad Huseynov, Eugene OBrien, James
Brownjohn, David Hester, Karen Faulkner
Nothing On the Road Axle
Detection System Using Direct
Strain Measurements – A Case
Study

3. Outline
• Importance of axle detection and available systems
• Analytical Study - Theoretical Basis
• Experimental Validation - Field Testing
• Results and Discussion

4. Axle Detection Systems
• Why Important?
• Bridge Weigh-In-Motion systems use axle detectors to
detect axles.
• Indispensable part of Bridge WIM - directly affecting
accuracy of weight predictions

5. Axle Detection Systems
• Traditional Axle Detection systems usually use pneumatic
tubes
• Requires road closures for installation and
maintenance
• Durability issues – exposed to traffic

6. Axle Detection Systems
• State-of-the-art axle detection systems now use strain
transducers to detect axles

7. Axle Detection Systems
• Measure local strain response
Strain response to (5-Axle Truck)
Axle 1
Axle 2
Tridem

8. Axle Detection Systems
• Great advantages
• no need for road closures for installation or
maintenance
• reduced congestion, improved safety

9. Axle Detection Systems
• However, have some limitations;
• Effectiveness of these slab sensors depends on where
the wheel is, overhead
• Fail to identify presence of axles if the load is directly
applied on the main girders
• Limited to certain bridge types
i.e. short span, integral bridges etc.

10. Objective
• Overcoming these existing shortfalls in literature is the
main objective of the proposed work
• A new axle detection methodology is proposed which is
based on the second derivative of the strain
measurements with respect to time

11. Theoretical Basis
3.5t 3.5t
2.6m
V=4m/s
E=210 GPa
I= 1.23 x 109 mm2
Methodology is based on
The 2nd derivative of the
strain signal with respect
to time

12. Theoretical Basis
Function of Strain(t)
is 1st order conditional polynomial
1st derivative of Strain(t) function
Signals are always continuous
constant discontinuous function
Not differentiable!!!

13. 2nd derivative of Strain(t) function
• Positive peaks: axles arrive and
leave bridge
• Negative peaks: axles arrive at the
sensor location
1st derivative of Strain(t) function
constant discontinuous function
Not differentiable!!!
Signals are always continuous
Theoretical Basis

14. Field Testing

15. Field Testing

16. Field Testing
British Class 115 Diesel Multiple
Unit (DMU)
Consists of three sets:
• 2 x Driving Motor Brake Second
(DMBS)
• 1 x Trailer Composite with
Lavatory (TCL) type carriage
Axle spacing in a bogie = 2.6m
12 axles in total

17. Results & Discussion

18. Theoretical Basis
• Magnitudes of peaks are small
3.5t 3.5t
2.6m
V=4m/s

19. Results & Discussion

20. The TRUSS ITN project (http://trussitn.eu) has
received funding from the European Union’s
Horizon 2020 research and innovation
programme under the Marie Skłodowska-Curie
grant agreement No. 642453
Thanks for your attention