Overview
Every year several bridges of the federal road network are demolished due to changed demands, if they are an obstacle to expansion or if are reaching the end of their service life. During the demolition of these bridges valuable information can be gained. This information would be obtained at great expense if the structure has to maintain its function. Destructive testing methods can be applied without restriction and the results of earlier investigations can be verified.
The aims of the research project are the creation of a framework for registration of demolished bridges, the central collection and processing of the data and the development of detailed procedures for registration of the condition.
In addition, the project should provide new knowledge about damage and failure mechanisms as well as new knowledge for checks of similar objects.
The research project allows coordinated collection of the gained information in the long term. This guarantees a uniform methodology and data structure. Therefore, the results are comparable and statistically processable.
Funding
Results
The final report contains following information:
The database of objects to be demolished, which finally contained 89 bridges with 82 of them
being dismantled within the project period, is explained in the report. The emphasis lies on
data formats, criteria and classifications, as well as the procedures to reach coverage as complete
as possible.
This is the basis for the statistical analysis of the database, which produced results. Analysed were the distribution with respect to involved carriers, longitudinal structural systems, construction types and materials, respectively, types of cross section and bridge age at time of demolition.
Concerning the condition of badly accessible, crucial and endangered structural elements, post-tensioning was a major concern and new insights could be gained. The post-tensioning systems used up to the present day have stood the test of time. Corrosion may occur, however, in cases where all barriers to the chlorides originating from the traffic space fail.
On the success of prior maintenance and rehabilitation methods some special but no general conclusions can be drawn. The documented cases of condition surveys of rehabilitated, replaced or added structural elements do not cover the whole range of possible remedial measures and look more at random.
From the wide range of non-destructive testing methods impact echo, half-cell potential measurement, ground-penetration radar and dynamic investigations were used. Most of them were applied as parts of independent projects to which references are made.
The coincidence of planned and executed dimensions was checked and interpreted especially for bridge girders that were used for loading tests up to failure. Dimensional deviations not only occur for cast-in-place structures but also for precast elements. For lack of actual as-built plans last project modifications often are not documented.
The report ends with ten recommendations for practice to be followed covering the examination, the remedial measures and the demolition phase. Another two recommendations deal with the adjustment of standards.