1. Development of Live Load Model
for Road Bridges
Korean Expressway Corporation
Choi Hyeok-jin [HOOK]
(Structure Engineer, PE)

2. Development
of Live Load Model 1. Truck Load of Countries
For Road Bridges
2. Governing Factors
3. Specification Development
CONTENT
S

3. 1. Truck Load of Countries
1.1 Standard Truck Load of Various Countries
1.2 Live Load Effects of Various Countries

4. Standard Truck Load of Various Countries

5. Total Max
National Code 1st 2nd 3rd 4th 5th
Weight Axle load
Korea
USA
USA
Canada
Canada
Eurocode
USK
Germany
Japen

6. Live Load Effects of Various Countries
(Simple Span, Moment)

7. Span Length(m)

8. Span Length(m)

9. 2. Governing Factors
2.1 Goal of Live Load Model Development
2.2 Principal Factors of Live Load
2.3 Procedure for Development of a Design Live
Load Model

10. Goal of Load Model Development
 A constant safety rate across all span lengths
 Development of economically feasible safe load that
befits bridge life cycle.
 Load patterns that are easy to use in design process,
and are familiar to designers.
Korean Expressway Corporation

11. Principal Factors of Live Load
 Distance between vehicles (= 1.2m)
 Load distribution of axle load
Vehicle type [passenger car, truck]
 Vehicle weight [vehicle + load weight]
 Compounding affect of vehicles in tandem
Korean Expressway Corporation

12. Principal Factor of Live Load
Passenger car Truck
 Type/Weight of Vehicle
 Compounding affects of vehicles in tandem
Korean Expressway Corporation

13. Procedure for Development
Survey of vehicle loads and driving patterns
Determine the trend line by Probability Chart
Estimate maximum load effects by span length
Determine design live load
Korean Expressway Corporation

14. 3. Specification Development
3.1 driving patterns
3.2 Maximum load effect
3.3 Live load model
3.4 economical benefits
Korean Expressway Corporation

15. Survey of Vehicle Loads
• BWIM ; Weigh-In-Motion
- Use the Displacement of Bridge by Passing Car
WIM System
• WIM ; Weigh-In-Motion Loop Sensor Piezo Sensor
- Loop Sensor : measures axle
lengths
- Piezo Sensor : measures vehicle
speed, weight , and number of axles.
※ WIM system allows a more Data
Locker
accurate weight for smaller
vehicles.
Korean Expressway Corporation

16. Survey of Driving Patterns
Driving Pattern  Mixture rate
Survey  Tandem rate
※We must discover the passenger car/truck mixture when travelling
in tandem.
Korean Expressway Corporation

17. Estimating Max Load Effects (1)
Maximum Load Effects by Largest single vehicle
• using top 10%, 20% values Trend Line Sample
from weight survey data Chart
• using the Gumbel Probability
Chart
- an equation can convert
probability distribution to a one-
dimensional linear formula
• Trend Line(y=a+bx)
y=Gumbel probability
x=weight
Korean Expressway Corporation

18. Estimating Max Load Effects (2)
Maximum Load Effects by Vehicles in tandem
 Groups of vehicles running in tandem
- different types running in tandem
– same types of vehicles running in tandem
 Using a Marcov Chain
P T
P 0.84120
18,185 0.06018
1,301
T 0.06018
1,301 0.00893
193
Korean Expressway Corporation

19. Estimating Max Load Effects (3)
 Calculating load effects at variable span lengths (positive
moment, shear, and negative moment)
Largest single vehicle Vehicles in tandem
Vehicles in tandem
Korean Expressway Corporation

20. Bias Factor
Bias factor of positive moment
Constant
safety rate
In order to ensure a constant safety rate over variable span lengths we use
a Bias factor calculation(M75/MDESIGN)
Korean Expressway Corporation

21. Design Live Load
•uniformly distributed load + concentrated load.
※ span length 10m : 12ton vehicle allowable
※ span length 30m : 15ton vehicle allowable
Korean Expressway Corporation

22. Summary
 Estimating maximum load effects for both categories,
greatest load and groups of vehicles running in tandem, using
span lengths to 200 meters.
 The proposed design load includes two components :
(1) a uniformly distributed load, and (2) a concentrated load.
Korean Expressway Corporation