INVESTIGATIONS ON THE FAILURES IN KRUPMAN BRIDGE GIRDERS AND THEIR REPAIR

Abstract

An investigation has been carried out on the causes which lead to the failure of Krupman bridge girders. This included chemical analysis, tensile testing, hardness measure-ments and micro-structure study of the girder material. Failure mechanisms which are operative in causing these girders to fracture were investigated by micro-macro-examinations. Detai-led microscopic examination, the results of which were related .0* to specific mechanisms of failure included metallography using direct observation under the scanning electron microscope (SEM), as well as optical microscopic examinations of metallurgical . specimens cut from the KM girders having cracks. The other important aspect of the study was to suggest a suitable repair technique so that these girders can be succe-ssfully put to .further use. In order to suggest a suitable filler material for repair welding of KM girders, four filler metal alloy compositions were selected based on the available literature and these were made in the laboratory. Another type of filler rod was procured from West Germany. These filler rods were tested by welding samples made out of the girder material by using a.c. Tig process. For testing the weld quality, transverse tensile test, transverse and longitudinal bend test and.examination of cross-section were carried out iii as per the Indian Standard Specifications. The fracture in KM girders was found to be due to stress-corrosion-cracking. It was also observed that the filler alldy containing Zn=2.0%, Mg=3.9Z, Mn..66%, 'Ti=.196, Cr=.1% gave the best results bout of the five alloys selected for the study. It was also observed that for getting best results, some suitable post-weld treatment should be given to the KM girders.