Besides the safety aspects, the economy is the single most important factor when bridges are designed. Lowering the life cycle cost of bridges means that less tax-money would be spent, and that should be in the interest of the general public. Today, bridges in Sweden are generally designed with movable joints and bearings. Leaking joints are a major reason to corrosion problems, and it would be preferable if bridges were designed without these. Integral abutment bridges are bridges without any movable joints. The superstructures are rigidly connected to the abutments, which generally are supported by a single row of flexible piles. The largest benefits of integral abutment bridges are the lower construction- and maintenance costs.
Movable joints and bearings are used in order to handle the expansion and contraction of the superstructure due to temperature changes. If these components are not used, then additional forces will be transferred to the abutments. Therefore, abutments in integral bridges will be laterally displaced as the temperature changes. The top of the piles will also be displaced and forces as well as moments will be induced in the piles. Pile stresses can locally exceed the yield strength of the pile material and plastic hinges can be developed. The development of plastic hinges in steel piles is allowed in the design of integral bridges in some states in the USA. The Swedish National Road Administration seems to be more hesitant about allowing pile stresses above the yield strength. And there seems to be a concern about whether or not there could be problems with fatigue involving plastic deformations, low-cycle fatigue. The aim of this thesis is to answer if, how and when low-cycle fatigue failures might happen in piles supporting integral abutment bridges.
Author: Hallmark, Robert
Source: Lulea University of Technology
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