Page 137 - Bridge and Highway Structure Rehabilitation and Repair

112 SECTION 1 ADMINISTRATIVE ISSUES

3.16.2 Preventive Action against Negligence and Lack of Maintenance
1. Increasing inspections and using Structural Health Monitoring (SHM) methods.
2. Performing rating analysis.
3. Adopting structural health monitoring methods.
4. Timely rehabilitation is required.
5. Using weathering steel to reduce maintenance and painting cost.

3.17 UNFORESEEN CAUSES LEADING TO FAILURES
3.17.1 Ice Damage of Piers with No Timber Fender Shielding

1. AASHTO equation for dynamic ice pressure: Timber fenders may be damaged by moving
ice sheets or crushed by compressive forces exerted by frozen layers of ice. A 50-year return
period may be considered.
F 3 C p t w
n
The author studied ice loads for timber fender design for bridges located on Delaware River
and Raritan River Bridges for the New Jersey Turnpike Authority.

where F is the ice force in lbs
C 3 Nose inclination coeffi cient
n
p 3 Ice pressure in psi
t 3 Ice thickness in inches
w 3 Pier width/projected fender width

AASHTO specifications give a range of values of ice pressure from 100 to 400 psi based

on the conditions of ice incidence (provided by the Department of the Army Cold Regions
Research and Engineering Laboratory (CRREL). Timber fenders and sheeting were modeled
as structural members for analysis and were designed as timber structures.

C 3 1.0 for inclination of nose to vertical 3 0 degrees to 15 degrees
n
C 3 0.75 for inclination of nose to vertical 3 15 degrees to 30 degrees
n
Thickness of ice, t 3 10 to 18 inches

w 3 width of pier
2. Static ice pressure (US Army Corps of Engineers): In 1995, Haynes suggested a minimum
thermal expansion force of 5.0 kips/ft.

3.17.2 Malfunction of Bearings/Thermal Stresses
1. For continuous spans a thermal analysis is required. Due to dirt accumulation, expansion
bearings may malfunction, generating thermal forces that increase with the length of the
span.
2. Piers are usually not designed for bending moments caused by the daily recurring longitu-
dinal thermal force.
3.17.3 Examples of Unexpected Failures and Suggested Preventive Actions

1. Repairing the fire damaged Notre Dame Bridge: Thomas A. French of Manchester, New

Hampshire describes that onApril 12, 2003 a fire ignited underneath an important bridge in

the City of Manchester, New Hampshire. In the year and a half since the fire, the investiga-
tion has determined the official cause to be arson.