Page 108 - Bridge and Highway Structure Rehabilitation and Repair

CHAPTER 3 BRIDGE FAILURE STUDIES AND SAFETY ENGINEERING 83

2. Wardhana and Hadipriono studied over 500 bridge structure failures in the United States.
The age of the failed bridges ranged from one year (or during construction) to 157 years.
The most frequent causesof bridge failures were floods and collisions.

Bridge overload and lateral impact forces from trucks,barges/ships, and trains constitute
20 percent of the total bridge failures. In the U.S. alone, over 36,000 bridges are either scour
critical or scour susceptible.
3. Campbell R. Middleton of the University of Cambridge Engineering Department has orga-
nized comprehensive databases summarizing the failure records according to the chronology
of events, country of occurrence, reasons of failure, and bridge type.
4. Bjorn Akesson in his 2008 book “Understanding Bridge Collapses,” estimates scour as
responsible for about 50 percent of bridge failures. The book presents useful information on

structural details and deficiencies of 20 well-known bridges that failed between 1847 (Dee
Bridge on River Severn, England) and 2003 (Sgt. Aubrey Cosens VC Memorial Bridge in
Canada) through analysis of failures. Other causes of failures listed in his book are lack
of material strength and maintenance, accidents, fatigue, brittle fractures, buckling, wind

loading, aerodynamic instability, fire, and poor anchorage capacity. While failures of very
old bridges built before 1940 appear to be of academic interest due to a different level of
technology, (much lower intensity and frequency of truck live loads), the failures in the
past 75 years (erstwhile generation of bridges) are of practical interest. A 70-year life span
is the current minimum design life of each generation of bridges based on fatigue, as sug-
gested by AASHTO LRFD Specifications. Many of the bridges listed by Akesson failed

much earlier.

5. Jana Brenning in the Scientific American Journal was one of the earliest to address the
causes of failures in 1993. Since then more information has been compiled. Technological
advances in informationsystems have a great impact on data collection and analysis.

Water, salt, stress, and corrosion can make a bridge structurally deficient. A decrease in the
load rating will result in imposing weight limits.
3.4.2 Understanding the Multiple Structural and Fracture Causes
The mostcommon causes of bridge failure include:
1. Overstress of girders from section loss (Figure 3.4), design defects, and defi ciencies: See

Section 3.6, Design Deficiency and Preventive Actions, for historical events and recom-
mended preventive actions.

Figure 3.4 The deterioration of girders is a potential cause of bridge failures.