Stress corrosion cracking investigation of the bridge stock of Mecklenburg-Vorpommern
Table of contents
Project data
| Titel | Title Spannungsrisskorrosion bei Brücken – Untersuchung des Brückenbestandes des Landes Mecklenburg-Vorpommern | Stress corrosion cracking in bridges – Investigation of the bridge stock of Mecklenburg-Vorpommern Förderer | Funding Landesamt für Straßenbau und Verkehr Mecklenburg-Vorpommern Zeitraum | Period 10/2005 – 03/2011 Leiter | Project manager Dr.-Ing. Torsten Hampel Bearbeiter | Contributors Dr.-Ing. Torsten Hampel, Dr.-Ing. Silke Scheerer Projektpartner | Project partners Curbach Bösche Ingenieurpartner, Dresden | Saxotest Ing. GmbH, Dresden u. a. |
Report in the yearbook 2010
Probability of failure of older prestressed concrete bridges
Stress-strain curves of two different kinds of prestressing steel
Older prestressed concrete bridges often contain steel that no longer meets today‘s requirements because they are classified, for example, as particularly sensitive to stress corrosion cracking (SCC). To maintain these structures and assure a safe further use, a corresponding nationwide guideline (HAW) has been introduced 1993, which deals with these structures. Currently, this HAW will be revised, with the assistance of the Institute of Concrete Structures.
Since 2005 we investigated the bridge inventory of Mecklenburg-Vorpommern with regard to this particular issue. All structures were catalogued and evaluated. Depending on the bridge condition and urgency, static recalculation and material tests were conducted. The results were transferred to other bridges. In 2010 a main focus was the testing of a new calculation method for the structural analysis based on stochastics, which was developed at the Technical University of Munich. Subjects of current work are the shear force resistance and the coupling joint problem at selected bridges.
Reinforcing steel and prestressed steel usually deforms visibly before failure occurs. Therefore, if the structure was properly sized and designed, visible signs, like cracks in the concrete, indicate a change in the load bearing behavior before the steel will fail. Prestressing steels with SCC, however, can fail very brittle. In these cases it is also possible, that no externally visible cracks form before the steel fails.
The parts of a structure with negative announcement behaviour are determined analytically in a static recalculation. Using the new method based on stochastical principles, it is possible to estimate how likely it is, that the prestressing steel fails at first in a place where no cracks are visible from the outside. For prefabricated bridges manufactured in the former GDR, which represent a large percentage of the total bridge stock, this procedure could be applied usefully in many cases. In affected prefabricated bridges, critical areas represent only a small amount of all examined parts. The probability of an unannounced failure was usually less than the critical limit value. In this evaluation also weak points of the new calculation method were pointed out. For example, small bridges with a relatively small number of tendons are evaluated more critically than large bridges with longer tendons. Nevertheless, this new method is one possibility for a realistic assessment of the load bearing capacity of bridges with SCC-sensitive steels.