Failure analysis of a suspension bridge in Indonesia using the direct analysis method Wiryanto Dewobroto Professor, Department of Civil Engineering, University of Pelita Harapan, Tangerang, Indonesia (Orcid:0000-0002-9773-0581) (wiryanto.dewobroto@uph.edu) A 120 m pedestrian suspension bridge recently inaugurated in Pacitan, East Java, Indonesia, suddenly collapsed when it was empty. It was one of the hundreds of similar bridges constructed through a current government project. Although there were no casualties, finding the cause of the failure is essential to ensure the safety of other bridges that have been or are currently being built. Moreover, field investigations showed that the change in the cable orientation between the bridge tower and cable end point of the suspension bridge and the insufficient capacity of the bracing connection in the bridge tower triggered the failure. The analysis is usually conducted through a numerical simulation using a relatively complex non-linear finite-element analysis. However, this research adopted second-order elastic analysis using the direct analysis method of the American Institute of Steel Construction code, a common method for designing steel structures. This method is relatively more straightforward but applicable in proving that the carrying capacity of the bridge tower decreased drastically due to the bracing failure, which is possibly the explanation for the collapsed bridge under the minimum load condition. Keywords: bridges/direct analysis method/failures/footbridges/second-order elastic analysis/steel structures/structural analysis/ structural design/UN SDG 9: Industry, innovation and infrastructure/UN SDG 11: Sustainable cities and communities Notation A e net area of member (mm 2 ) A b area of the bolt A e effective net area of a member (mm 2 ) A g gross cross-sectional area of a member (mm 2 ) A n net area of a member (mm 2 ) d bolt bolt diameter d hole hole diameter E modulus of elasticity of steel = 200 000 MPa F e elastic buckling stress (MPa) F cr critical stress (MPa) F nv nominal shear stress of the fasteners (MPa) F u specified minimum tensile strength (MPa) F y specified minimum yield stress (MPa) KL effective length of a member for slenderness analysis KL/r min slenderness parameter of the column L c length of the column l c clear distance, in the direction of the force, between the edge of the hole and the edge of the material (mm) M n nominal flexural strength (kN m) M py plastic bending moment in weak axis (kN m) M r required flexural strength determined using LRFD load combination (kN m) M u required flexural strength using LRFD load combination (kN m) P 1 ultimate point load of the bridge tower with full bracing (kN) P 2 ultimate point load of the bridge tower with one bracing broken (kN) P 3 ultimate point load of the bridge tower with two bracing broken (kN) P 4 ultimate point load of the bridge tower with three bracing broken (kN) P c available axial strength (kN) P h horizontal point load that acts on top of the bridge tower (kN) P n nominal axial compressive strength (kN) P r required compressive strength determined using LRFD load combination (kN) P u required axial strength in compression using LRFD load combination (kN) P v vertical point load that acts on top of the bridge tower (kN) R ratio of required strength to the available strength of the member R n nominal strength of members according to LFRD design (kN) 1 Cite this article Dewobroto W Failure analysis of a suspension bridge in Indonesia using the direct analysis method. Proceedings of the Institution of Civil Engineers – Forensic Engineering, https://doi.org/10.1680/jfoen.21.00009 Research Article Paper 2100009 Received 06/05/2021; Accepted 28/04/2022 ICE Publishing: All rights reserved Forensic Engineering