Page 58 - Bridge and Highway Structure Rehabilitation and Repair

CHAPTER 1 OVERVIEW OF BRIDGE ENGINEERING 33

• Queensboro
• Manhattan
• Outer Bridge
• Goethals
• Bayonne
• Verrazano Narrows
• Bronx/Whitestone and Throgs Neck
• Hell Gate Railroad Bridges.

1.10.5 Other Major U.S. Bridges
Some of the major bridges in the U.S. which continue to survive environmental effects
through regular maintenance are:

1. Chesapeake Bay Mackinaw Straits, which separates the upper and lower peninsulas of
Michigan
2. Al Zampa Memorial over Carquinez Strait, which separates San Pablo and Suisun Bay in
the San Francisco Bay area
3. Bridge over Lake Pontchartrain in Southern Louisiana, one of the longest bridges ever
built
4. Steel City Pittsburgh, Pennsylvania known as the City of Bridges, with a wide variety of
bridges
5. Long span steel bridges in Louisville, Kentucky.

1.11 DEFICIENT STRUCTURES

1.11.1 Foundation Failures
The following causes of failures need to be rectifi ed:
1. For widened structures, differential settlements of new and old components in widening
shall be considered. It is possible that the existing foundation has settled. New footings may
need to be placed on piling or drilled shafts in an attempt to prevent differential settlement.
The widened section should be designed so that superstructure defl ection for the new and
old deck is identical.
2. Scour analysis: Foundations need to be investigated for scour. The investigation consists of
determining on what the substructures are founded and the foundation depth, and deciding
whether potential scour will endanger the substructure’s integrity. Local scour and stream
meander need to be considered.

1.11.2 Seismic Resistance
If an existing bridge does not meet current AASHTO or state design specifi cations, seismic

retrofit needs to be considered.
1.11.3 Hydraulic Inadequacy
Environmental or Coast Guard concerns may push the rehabilitation versus replacement
decision in the direction of rehabilitation while hydraulic inadequacies and poor stream align-
ment may push the decision toward replacement.

1.11.4 Soil Conditions
Any signs of foundation settlement may push the decision toward requiring the replacement
of structure.