Page 29 - Bridge and Highway Structure Rehabilitation and Repair

4 SECTION 1 ADMINISTRATIVE ISSUES

3. Construction over water would also require:
• Deep foundation excavation
• Cofferdams
• Barges
• Special supports.

1.1.4 Environmental Issues

1. Thermal loads: They should be applied as daily recurrent cycles for long-term behavior of
structures. The method of construction should account for hot weather concreting and cold
climate concreting procedures. For each case, deck expansion joints and expansion bearings
are provided to release thermal stresses.
2. Wind loads, tornados, and hurricanes: Structures need to be modeled correctly, as and
where applicable.
3. Progressive collapse: Seismic zones have large variations. Dynamic analysis methods shall
use the classification of seismic zones and return periods. In the case of a collision, earth-

quake, or flood erosion, the total bridge should not be a write-off and most of the bridge
should be salvaged.
The old practice was to use two rows of bearings on the pier making each span simply sup-
ported or partially continuous over the piers. There is an in-built advantage in this approach
so that progressive collapse does not carry over to the adjacent span.

1.1.5 Mathematical and Computing Issues
Improved mathematical methods: Mathematical methods for every type of bridge are pres-
ently limited. They need to be systematically organized to simulate and compute short-term
construction conditions and long-term aspects of repeated loads. Mathematical methods shall
adjust for different geometry, substructure type, construction method, construction loads, and
all special design issues.

1.1.6 Constructability Issues
One of the practical difficulties in rehabilitation design is to incorporate the vast variation in

construction sites, materials of construction, geometry of the bridge, loads, access, topography
and location. Construction methods and construction-related analysis and design are linked to
bridging requirements. No two sites are alike. The topography may be flat or hilly. Connecting

ends of bridges may have very different elevations. The erection of precast bridges over busy
highways is a modern day challenge.

1.2 A FRESH APPROACH TO MAINTENANCE

1.2.1 Changing Technology
In order to maintain old and historic bridges, it is important to understand the transition of
structural development from old to new technology. For example, use of arch structures made
of stone, masonry, or timber was popular in the olden days. Covered timber truss bridges had
fewer maintenance problems.
Development of metallurgical processes produced wrought iron and cast iron in larger
capacities during the mid-1800s. It soon led to the use of metal trusses. Except in the areas of
plentiful and large timber trees, timber trusses quickly lost their popularity in the late 1800s.
The earlier use of trusses for small or medium spans has been overtaken with the current use of
composite slab-beam structures.