Use of vibration ods for structural integrity assessment of large engineering structures

Abstract

Operating deflection shape (ODS) is a proven technique in vibration analysis - often used for machines and structures. This paper reviews practical difficulties in the use of vibration ODS in fault diagnosis and structural integrity assessment of large engineering structures. The challenges are inherent in the number of measurement locations over large distances for which phase matched measurements are required where the structure is often subjected to varying load conditions with multiple excitation sources at different locations. Using a case study of a large concrete structure supporting a polymerization rector in a petrochemical plant, the paper describes procedures used in site measurements to obtain ODS undertaken to identify likely causes of vibration. This was followed by structural integrity assessment of the structure using finite element analysis collaborated with the actual measured experimental modal analysis of the structure. The challenge was to identify root causes correlated to process operations, and assessment of structural integrity of the structure. Results of the ODS were used to validate Finite Element Analysis of the structure. Using the validated FEA model, dynamic response and stresses in the structure were obtained for structural integrity assessment. The FEA predictions showed likely locations of high stress which were consistent with actual damage and incipient failure locations in the real structure.