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Die Kunst der Diagnose
(2023)
Structural assessments of existing older prestressed concrete bridges according to the currently applicable standards and guidelines in Germany generally reveal significant deficiencies in shear reinforcement. Large-scale tests within the scope of research activities commissioned by the Federal Highway Research Institute (BASt) were carried out at TU Dortmund University to analyze the shear load-bearing behavior of continuous prestressed concrete beams in more detail. The Arch Action Model (AAM) was derived from the Simplified Arch Action Model (SAAM) to provide a possible analysis method for determining shear contribution from concrete. Thus, the shear capacity of prestressed beams can be determined in a more realistic manner than using the truss model underlying the current state of standardization. The paper at hand provides information and explanations about the SAAM and AAM with regard to their application to real-world structures for structural bridge assessments.
A reinforced industrial concrete chimney (height 150 m) was built for a power plant in the Middle East. The author co-produced the structural design of the chimney. During the construction of the windshield, an undesired cold joint was generated at approximately 41 m above ground. The author, at that time working for Constructure GMBH, was asked by the construction company to give an expert opinion on the cold joint construction. It was necessary to determine the extent to which the windshield had possibly been weakened in the area of the cold joint regarding its structural safety and durability, if additional measures were required to strengthen the chimney’s windshield. The relationship with the construction company was especially contentious, as it was both the subject of the investigations and the client commissioning. In the course of the inspections on site, it was revealed - contrary to the assurances of the construction company - that there were significant structural damages in the windshield. This paper, at hand, presents the key chimney investigation, principal findings, and the damage mechanism. As a result of the defects, the actual load-bearing capacity of the structure could hardly be quantified. Given the critical situation, it was suggested to strengthen the newly built chimney.