Failure Analysis of Kutai-Kartanegara Bridge’s Hanger Clamps from Fracture Mechanics Viewpoint* Dionysius SIRINGORINGO 1 ,Yutaka KAWAI 2 and Yozo FUJINO 3 1 Member of JSCE, Research Assistant Professor, Dept. of Civil Eng., University of Tokyo (Hongo 7-3-1, Bunkyo-ku, Tokyo 113-8656, Japan) E-mail:dion@bridge.t.u-tokyo.ac.jp 2 Fellow of JSCE, Part-time Lecturer, Dept. of Civil Eng., Nihon University ( Izumicho1-2-1, Narashino, Chiba275-8575, Japan) E-mail:Yutaka-kawai@mue.biglobe.ne.jp 1 Fellow of JSCE, Project Professor, Dept. of Civil Eng., University of Tokyo (Hongo 7-3-1, Bunkyo-ku, Tokyo 113-8656, Japan) E-mail:fujino@sogo.t.u-tokyo.ac.jp On November 26, 2011 Kutai-Kartanegara Suspension Bridge in Indonesia collapsed. The collapse was triggered by failure of the clamp of cable band that connects hanger with main cable in the middle of the center-span. The national investigation team report cited the failure as a result of stress accumulation on the clamps that have been weakened by fatigue, initial fracture and corrosion. In this paper, we investigate more detail the possibility of shear brittle fracture of the clamp’s pin from a viewpoint of linear fracture mechanics by utilizing the measured Charpy absorbed energy. Several possible scenarios of defect sizes and combined stress conditions were assumed. The analysis shows that the shear brittle fracture could occur even under low shear stress level when several unfavorable conditions occur simultaneously. Key Words :cable band, clamp pins, shear failure, linear fracture mechanics, brittle fracture *) Japanese version of this paper was published on JSCE Structure Engineering A1 Vol.69,No.2, 410-415, 2013 1. INTRODUCTION The report of national investigation team on the collapse of the Kutai-Kartanegara Bridge, the longest suspension bridge in Indonesia, released in January 2012, reveals that accumulation of design faults, lack of maintenance and improper retrofit work have se- quentially cause the bridge collapse. In particular, the report emphasizes on the stress accumulation of the hanger clamps as the triggering mechanism of the collapse 1) . Post-accident investigation of the clamps has shown that they might have been weakened by corrosion or cracking and fatigue. The report also questions selection of high strength ductile iron FCD-600 that has low energy impact absorption and poor toughness as material of the clamps. Based on the bridge design document, accident investigation report and field survey conducted by the first author immediately after the accident, the authors share the view of the national investigation team that performance of clamp should be considered as possible cause of the collapse. However, in our opinion, such conclusion should be assisted by fracture surface analysis, and such analysis, to the best of authors’ knowledge, has not been performed. This is partly because the main part of the hanger clamp from the middle of center span that triggered bridge collapse fall into the river, while the other parts are still attached to the suspension cable and remained inaccessible for analysis. In this note, we investigate the possibility of brittle fracture of the clamp from linear fracture mechanics viewpoint. Fracture toughness of the clamp is esti- mated using results from the Charpy impact values obtained from material test of the remaining clamps. The possibility of brittle shear fracture is examined by assuming initial defects at the base of pins and by considering fracture toughness of the material under influence of combined tensile and shear stress on the clamp. 2. BRIDGE DESCRIPTION AND COLLAPSE INCIDENT 1