Page 91 - Bridge and Highway Structure Rehabilitation and Repair

66 SECTION 1 ADMINISTRATIVE ISSUES

2.6 COMBINING OLD AND NEW TECHNOLOGIES FOR REHABILITATION
2.6.1 Preservation Design for Historic and Older Bridges
1. A specialized approach to design is required for effective maintenance of historic bridges

and may include a diagnosis of deficiencies. It is based on the findings of a fi eld inspection

and structural health monitoring. Selective reconstruction in the form of repair, retrofi t
(structural strengthening) is the result.
2. Preservation design is a special type of diagnostic design: Preservation design is required for
bridges that are listed on the National Historic Register. They have a high importance factor
since their preservation is a sentimental consideration, depicting past history or culture, and
cost is not usually a major factor. Their importance emanates from their ability to serve as
a living museum.
3. “Preservation” design generally applies to historic bridges. It maintains existing shapes and
sizes, and optimization is not a consideration. To maintain the historical integrity of each
bridge, help is needed from sophisticated technology and special design methods, in addi-
tion to those deployed for diagnostic design.
To develop retrofitting or reinforcing systems, the process involves advanced numerical

modeling and simulation of the loading regime. The same analysis-based computer programs
will compute both rating and redesign separately.
4. Federal law protects historic bridges. Special attention is required for their rehabilitation
or improvement. The director of the Division of Historical Resources (the Department of

State) serves as the State Historic Preservation Officer (SHPO). The SHPO and state DOT
are responsible for determining what effect any structural changes will have on a historic
bridge.
5. According to the National Park Service, the structures and places that are part of its Na-
tional Historic Landmarks Program “possess exceptional value or quality in illustrating or
interpreting the heritage of the United States.”

Historical bridges increasingly make significant impacts as community landmarks. They
can be as simple as freeway overpasses decorated with American fl ags. They are symbols
of local attractions as distinctive as the pedestrian bridges or as famous as the Golden Gate
Bridge. In a small way, they promote tourism and are depicted on postcards that are mailed
the world over by tourists.
6. Guidelines for historic bridge maintenance and rehabilitation based on the Secretary of the
Interior’s Standards for Rehabilitation may be quoted as follows:

• “The original character-defining qualities or elements of a bridge, its site, and its environ-
ment should be respected. The removal, concealment, or alteration of any historic material
or distinctive engineering or architectural feature should be avoided.

• Distinctive engineering and stylistic features, finishes, and construction techniques or
examples of craftsmanship that characterize an historic property shall be preserved.
• Deteriorated structural members and architectural features shall be retained and repaired,
rather than replaced. Where the severity of deterioration requires replacement of a distinctive
element, the new element should match the old in design, texture, and other visual qualities
and where possible, materials. Replacement of missing features shall be substantiated by
documentary, physical, or pictorial evidence.”
7. A historic bridge serves as a “landmark” and is subjected to obtaining the following permits
as applicable, which is a most time-consuming process:
• Construction impact
• Floodplain impact
• Wetlands impact