Page 96 - Bridge and Highway Structure Rehabilitation and Repair

CHAPTER 2 DIAGNOSTIC DESIGN AND SELECTIVE RECONSTRUCTION 71

developed to match existing concrete. A combination of visual inspection, nondestructive
methods, and coring followed by laboratory testing is used in all cases. NDT minimizes
invasive investigation anddisruption to bridge operations.

2.6.7 Some Well-Known Historic Bridges

1. The ancient Chinese bridge “Rainbow Truss” was built of timber logs and bamboo strings
in a fashion of interlocking arches and cross beams, it is unique in both design and con-

struction. The configuration of the arches causes it to induce much less shear force and
bending moment than a beam of the same span. Its construction with small diameter round
or rectangular timber logs is an advantage due to large quantities of small diameter logs
readily available. Various timber bridges following the model of Rainbow Truss were later
built with rectangular members as seen today in North America.
2. The Dragon Bridge of Li Chun (also known as An Ji Bridge) in Ancient China, an open
spandrel, segmental stone arch bridge, is probably the oldest surviving bridge dating back
to seventh century A.D. It was the first major segmental bridge when constructed and was

later refurbished.

3. The John A. Roebling Bridge constructed in 1867 was the first suspension bridge to span
the Ohio River near Kentucky. The main span is 1100 feet long. Based on load tests for four
truck types and three bus types and compared to element level analysis, the posted weight
limits on the bridge were 17 tons for two axle trucks and 22 tons for three or more axles.
4. A large number of extant lenticular (fish belly or parabolic) iron truss bridges were built in

New England by the Berlin Bridge Company prior to 1900. There are still 43 pony truss,
27 through truss, and three Warren truss bridges made of cast iron which have survived.
5. The Bear Tavern Road Bridge in Mercer County, New Jersey, located on a quiet street near

the author’s office, includes two king through trusses built in 1882. The steel shape is a pratt
truss. The floor beams have been replaced, and the bridge is functioning without a reduction

in the original live load.

Figure 2.15 An example of a historic pedestrian bridge in Hunterdon County, N.J.