Civil Engineering Reference
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been maintained well enough; and whether bridge problems should have
been recognized and the bridge closed. The study should judge whether
unexpected or extremely rare external events disastrously stressed a bridge
that was, by accepted criteria, well built.
Without consistent forensic studies, we usually cannot know with con-
fidence what makes American bridges fail. Researchers have nonetheless
been able to review the evidence and come to plausible conclusions about
the most common causes of failure.
The study we have in mind (by one of us, George Lee, along with
colleagues Satish B. Mohan, Chao Huang, and Bastam N. Fard) found evi-
dence on 1062 bridge failures over 33 years, for an average of 32 per year
(table 6.1). “Failure” was here defined as collapse, partial collapse, or distress
sufficient to force reduction in traffic, including closure.
The authors attributed some failures to internal problems, including
deterioration, corrosion, construction problems, and faulty design. But they
found that the large majority of failures, altogether 88 percent, had external
causes (table 6.1). Most of these were extreme events, the subject to which
we now turn.
Table 6.1. Causes of Bridge Failure, United States, 1980-2012
Cause
Percentage
2000-
1990-
1980-
2012
2000
1990
Hydraulic
Flood
4%
15%
10%
28%
47%
Scour
5%
9%
5%
19%
Collision
5%
5%
5%
15%
External
Overload
3%
3%
6%
13%
causes
Fire
1%
1%
1%
3%
88%
Earthquake
0%
1%
1%
2%
Wind
1%
1%
0%
2%
Environmental
2%
2%
2%
7%
Degradation
Internal
Design, Construction,
3%
3%
5%
11%
11%
causes
Material, etc.
Other &
Misc.
—
—
—
—
—
1%
Total
—
24%
39%
36%
—
100%
Note:
Total bridges judged to have “failed” over 33 years: 1062
Source:
Lee, Mohan, Huang and Fard, 2013.
