Page 152 - Bridge and Highway Structure Rehabilitation and Repair

CHAPTER 3 BRIDGE FAILURE STUDIES AND SAFETY ENGINEERING 127

4. Influence lines method redefined in terms of maximum deflection, shear force, and reactions

for single span beam.
5. Application of theories of yielding in steel structures such as cantilever sign structures.
There is a need for continuing education in the specialized area of software development.
With the large variety of bridge structures and structural systems, there is a need to introduce
graduate level courses at universities, as well.
3.21.6 Risk Management

The probability of failure can be linked to the degree of risk. For example, designing a sus-
pension cable, cable stayed or a deep arch bridge located near an airport for direct impact from

a plane may increase significantly the bridge’s cost. With the probability of such an extreme
event occurring being extremely small, any risk reduction by making the bridge stronger is not
required. Three types of risk levels are considered:
1. Risk reduction is required.
2. Risk reduction is optional.
3. Risk reduction is not required.
Risk 3 Frequency 8 Severity of potential loss
Frequency is the probability of occurrence of an event such as once a year or once in 100
years. Severity of loss may be loss of life, injury, or a fi nancial loss.
Loss control is the controlling of conditions which contribute to loss.
Risk management consists of identifying risk, analysis of risk, minimizing or eliminating
risk, providing varying levels of resources, and administering the risk management process.
The objectives of risk management are to:

1. Fulfill social responsibility such as public service, public image, and public relations.
2. Maintain stability of benefits such as continued use of a bridge.

3. Ensure continuity of growth in commerce and industry from transportation.
Risk reduction is a function of the relative importance of a bridge. The higher the importance
of a bridge, the higher the importance of risk reduction.
The importance factor of a bridge is classifi ed as:
1. Bridge on a military route.
2. Bridge serving a hospital.
3. Bridge located on a school route.
4. Bridge located on a major highway.
5. A long-span or high-cost bridge.

Risk reduction requires increased monitoring, maintenance, and resource allocation for
correcting any defi ciency. Hence,
Risk Reduction 3 k 8 Importance Factor

The factor k is based on average daily traffic (ADT). By neglecting the condition of a defi -

cient bridge, the probability of the number of lives lost will increase.
Table 3.14 shows a matrix for the assessment of risk. No risk reduction is required for minor
damage or when probability is categorized as improbable.
A paper by Henry Petroski, To Engineer is Human: The Role of Failure in Successful De-
sign, American Society of Civil Engineers proceedings, 2003 addresses the role of assumptions
and oversight in analyzing failures. To quote a nineteenth century English poet describing the
famous Westminster Bridge in London,