Future Shock and Segmental Evolution

Editorial by Cliff Freyermuth, Manager, ASBI

Alvin Toffler’s notable book “Future Shock”, published in 1970, observed that the rapid rate of technological change requires changes in organizational structures and procedures in order to accommodate and realize the advantages of advances in technology.

Presentations at the October 29-30 ASBI Convention in St. Louis demonstrated that segmental technology continues to develop rapidly. The bridge on the island of Réunion in the Indian Ocean exemplifies the continuing evolution. The bridge structure is a single 280m (918ft.) span anchored in counterweight abutments. The deck is a composite truss structure comprised of two segmentally constructed concrete slabs linked by two planes of steel tube diagonals which are filled with concrete and post-tensioned. Only the upper slab is continuous at the mid-span joint. The average combined thickness of the top and bottom slabs is only 0.72m (2ft.4in.).

A convention presentation by Japanese engineers, cancelled due to travel concerns following the September 11 WTC tragedy, described the development of segmental and extradosed bridges with corrugated steel webs in Japan. This development reduces dead load and provides webs with high shear buckling strength. Since the corrugated steel plates have little stiffness in the longitudinal direction, nearly all of the tendon force is effective in prestressing the top and bottom slabs.

The results of segmental seismic research at the University of California at San Diego, described at the convention by Professor Frieder Seible, has demonstrated that segmental bridges with 100 percent external tendons provide improved ductility and other advantages for structures exposed to cyclic seismic loading. (See the newsletter item on this research). Use of 100 percent external tendons for structures in seismic zones is not currently permitted under the AASHTO Segmental Guide Specifications, or the LRFD Bridge Design Specifications.

Many other technological advances were included in convention presentations. These include: the use of backlit glass panels for aesthetic effect in the top 190ft. of the pylon of the new Maumee River Bridge in Toledo, Ohio; use of state-of-the-art touch pad computers with a special graphical user interface for preparation of inspection reports on the Zilwaukee Bridge; and fast-set expoxy resins for sub-freezing temperatures.

When the AASHTO LRFD Bridge Design Specifications are officially implemented in 2007, the development period will have been about 20 years. It would appear that a more rapid process in development and implementation of specifications will be necessary in the years ahead to keep pace with developments in construction technology, for segmental as well as other methods of bridge construction.