Development of Live Load Model

for Road Bridges

Korean Expressway Corporation

Choi Hyeok-jin [HOOK]

(Structure Engineer, PE)

CON-TENTS

1. Truck Load of Countries

2. Governing Factors

3. Specification Develop-

ment

Development

of Live Load Model

For Road Bridges

1.1 Standard Truck Load of Various Countries

1.2 Live Load Effects of Various Countries

1. Truck Load of Countries

Standard Truck Load of Various

Countries

Korea

National

USA

USA

Canada

Canada

EurocodeUSK

Germany

Japen

CodeTotal

Weight

MaxAxle load

1st 2nd 3rd 4th 5th

Live Load Effects of Various Coun-

tries

(Simple Span, Moment)

Span Length(m)

Span Length(m)

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

2. Governing Factors

Korean Expressway Corporation

A constant safety rate across all span lengths

Goal of Load Model Development

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

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

Passenger car Truck

Principal Factor of Live Load

Type/Weight of Vehicle

Compounding affects of vehicles in tandem

Korean Expressway Corporation

Survey of vehicle loads and driving patterns

Determine the trend line by Probability Chart

Estimate maximum load effects by span length

Determine design live loadDetermine design live load

Procedure for Development

Korean Expressway Corporation

3.1 driving patterns

3.2 Maximum load effect

3.3 Live load model

3.4 economical benefits

3. Specification Development

Korean Expressway Corporation

• WIM ; Weigh-In-Motion

- Loop Sensor : measures

axle lengths

- Piezo Sensor : measures

vehicle speed, weight , and

number of axles.

Loop Sen-sor

Piezo Sen-sor

Data

Locker

WIM System

Survey of Vehicle Loads

※ WIM system allows a more ac-curate weight for smaller ve-hicles.

• BWIM ; Weigh-In-Motion - Use the Displacement of Bridge by Passing Car

Korean Expressway Corporation

Driving Pattern Survey

Mixture rate Tandem rate

Survey of Driving Patterns

※We must discover the passenger car/truck mixture when

travelling in tandem.

Korean Expressway Corporation

• using top 10%, 20% values

from weight survey data • 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

Trend Line Sample Chart

Estimating Max Load Effects (1)

Maximum Load Effects by Largest single vehicle

Korean Expressway Corporation

Groups of vehicles running in tandem

- different types running in tandem

– same types of vehicles running in tandem

P

P

T

T

18,185 1,301

1,301 193

0.84120 0.06018

0.06018 0.00893

Using a Marcov Chain

Estimating Max Load Effects (2)

Maximum Load Effects by Vehicles in tandem

Korean Expressway Corporation

Largest single vehi-cle

Calculating load effects at variable span lengths (posi-tive moment, shear, and negative moment)

Estimating Max Load Effects (3)

Vehicles in tandem

Vehicles in tandem

Korean Expressway Corporation

Bias factor of positive mo-ment

In order to ensure a constant safety rate over variable span

lengths we use a Bias factor calculation(M75/MDESIGN)

Con-stant safety rate

Bias Factor

Korean Expressway Corporation

• uniformly distributed load + concentrated load.

※ span length 10m : 12ton vehicle allowable

※ span length 30m : 15ton vehicle allowable

Design Live Load

Korean Expressway Corporation

Estimating maximum load effects for both categories, great-

est load and groups of vehicles running in tandem, using

span lengths to 200 meters.

Summary

The proposed design load includes two components :

(1) a uniformly distributed load, and (2) a concentrated load.