Page 135 - Bridge and Highway Structure Rehabilitation and Repair

110 SECTION 1 ADMINISTRATIVE ISSUES

2. Interpretating the Tacoma Narrows Bridge failure: Cable supported bridges are subject to:
• Wind-induced drag (the static component)
• Flutter (the instability that occurred at the Tacoma Narrows)
• Buffeting (where gusts “shake” the bridge).
3. Adequate aerodynamic performance is required with respect to each of these effects:
• For modest span bridges, drag generally controls the strength required to resist wind.
• Flutter becomes critical when the wind acting on the structure reaches a critical velocity
that triggers a self-excited unstable condition. The task in design is to assure that it has
a very low probability of occurrence. This can be achieved by providing a stiff structure
and/or an aerodynamically streamlined superstructure shape.
• The magnitude of buffeting response under higher probability wind conditions must be

controlled. It influences fatigue of the bridge materials as well as users’ comfort.
4. Addressing these issues in an engineering context requires the use of wind tunnel models.
Current practice is converging on the use of such models for the aerodynamic properties of
the bridge shape only. The mechanical properties of the bridge, and the final wind evalua-

tion, are performed using computer models that incorporate the wind tunnel results.
3.16 LACK OF MAINTENANCE AND NEGLECT
3.16.1 Lack of Effective Inspection and Rehabilitation Systems

Regular inspection of transportation facilities is critical to public safety.
1. Older bridges were not designed tomeet the new design criterion.
2. More and heavier trucks are usingour roads everyday, increasing the rates of deterioration
ofbridges and pavements.

3. Growing traffic on our waterways is increasingthe probabilities of a barge/bridge collision
that canresult in a disaster.
4. Aging highway signage and high mast lighting (luminaries) are becoming structurally
unsound, usually due to failing connections, and are dropping to the roadways with large
potentialfor damages and the risk of loss of life.
5. While the federal government did establishminimum guidelines and requirements for bridge
inspections, it has notestablished similar requirements for signs or luminaries. As a result,
some states do not inspect signs or luminaries. Similar requirements for bridge pierprotec-
tion, highway signs, and luminaries should be in place.
Table 3.13 shows a list of failures caused by miscellaneous reasons including oversight or
neglect.

Table 3.13 History of bridge failures due to lack of maintenance or neglect (management issues).
U.S. Bridges Location Year Details of Failures
Bridge over King’s Slough River Near Fresno, California 1947 Overloading from agricultural train
3-span bridge in Lafayette Street St-Paul, Minnesota 1975 Brittle failure of new steel
Point Pleasant Bridge West Virginia 1967 Fatigue crack in eye bar chain suspension bridge
Fulton Yates Bridge Near Henderson, Kentucky 1976 Overloading during refurbishment
K&I Railroad Bridge Louisville, Jefferson County, 1979 Vehicle exceeding weight limit
Kentucky
Connecticut Turnpike Bridge Near Greenwich 1983 Corrosion of joint hangers (Gerber-joint), constraint stresses
(Mianus River) due to skew