Page 144 - Bridge and Highway Structure Rehabilitation and Repair

CHAPTER 3 BRIDGE FAILURE STUDIES AND SAFETY ENGINEERING 119

7. Future design code specifi cations or construction procedures need to consider reasons for
failures as guidelines in developing a comprehensive approach. When implemented, such
measures are likely to minimize the frequency of failures.
• Durability requirements need to be addressed on a scientifi c basis.
• AASHTO code provisions and other relevant codes need to be followed.
• The engineer needs to refresh his knowledge of dynamic analysis, hydraulics, and materials
science through continuing education. These disciplines would help to combat challenges
of an early failure.
8. Fatigue, scour, and seismic analysis should be carried out in detail. Design criteria must
include specialized subjects such as fragility analysis and ship collision analysis. All designs
should be refined to include fracture mechanics principles for fracture of steel, concrete, and

composites. Thermal analysis and bearing design to prevent malfunction are necessary.
9. Although the past studies in general were able to identify immediate causes of failures, their
diagnosis was restricted to case studies only. Most of the older bridges which failed did not
have as-built drawings to evaluate their strengths in bending and shear.
10. Results of failure studies are not easy to analyze due to a large number of variables contribut-
ing to failure. Comparisons made between failure types revealed similar trends of failures
occurring during the bridge’s service life. Also, lack of maintenance and human-induced
external events occurred frequently.
11. Forensic engineering investigations of failures are partly based on technical reasons and to
some extent they narrow down the blame either the designer or the contractor. However,
there may be reasons other than individual responsibility.
12. Design criteria used did not include scour of foundations or earthquakes. Design live loads
were lighter than the modern vehicles, resulting in less fatigue.
13. Mandatory insurance of bridges may induce highway agencies to take a greater interest in
research and development of safety procedures (Figures 3.17 to 3.19).

3.20.2 Regular Inspection of Transportation Facilities
Inspection is critical to public safety. A problem of growing damages to bridges identifi ed
over time has resulted in increasing the minimum designstress for H-20 loading.
1. Older bridges were not designed tomeet the new criterion.
2. More and heavier trucks are usingour roads every day, increasing the rates of deterioration
of bridges and pavements.

Figure 3.17 A truck falls in a river due to a bridge failure in 2004.