Simple analysis on failure of high strength bolts in Chongqing Chaotianmen Bridge

Abstract

From 2009 to 2012, 14 failure high strength bolts were found in Chaotianmen Bridge,and 11 bolts were collected on site, of which 8 bolts were pitted and rusted. The chemical composition, metallographic structure, hardness and other mechanical properties of these 11 bolts were analyzed and tested to explore the reasons for fracture failure of high strength bolts. The results show that six failure high strength bolts' HRC values are of 40, 40.5 and 43 (4 bolts), which does not meet the technical requirement of GB/T1231-2006, and the unqualified rate accounts for 54.5%. Tempered martensite, which belongs to brittle structure, was detected in metallographic structure in samples with unqualified hardness. The failure of high strength bolts is not only related to the unqualified metallographic structure, but also related to the construction processs, operating environment and other aspects. Especially the influence of environmental corrosion on the quality, micro-structure and mechanical properties of high strength bolts should be paid more attention by bridge managers. It is necessary to further explore and clarify the influence of environmental factors on the corrosion fracture of high strength bolts and its mechanism, so as to provide a basis for the measures taken to prevent the breakage of high strength bolts.