Finite element modelling and updating of a lively footbridge: The complete process

Abstract

The finite element (FE) model updating technology was originally developed in the aerospace and mechanical engineering disciplines to automatically update numerical models of structures to match their experimentally measured counterparts. The process of updating identifies the drawbacks in the FE modelling and the updated FE model could be used to produce more reliable results in further dynamic analysis. In the last decade, the updating technology has been introduced into civil structural engineering. It can serve as an advanced tool for getting reliable modal properties of large structures. The updating process has four key phases: initial FE modelling, modal testing, manual model tuning and automatic updating (conducted using specialist software). However, the published literature does not connect well these phases, although this is crucial when implementing the updating technology. This paper therefore aims to clarify the importance of this linking and to describe the complete model updating process as applicable in civil structural engineering. The complete process consisting the four phases is outlined and brief theory is presented as appropriate. Then, the procedure is implemented on a lively steel box girder footbridge. It was found that even a very detailed initial FE model underestimated the natural frequencies of all seven experimentally identified modes of vibration, with the maximum error being almost 30%. Manual FE model tuning by trial and error found that flexible supports in the longitudinal direction should be introduced at the girder ends to improve correlation between the measured and FE-calculated modes. This significantly reduced the maximum frequency error to only 4%. It was demonstrated that only then could the FE model be automatically updated in a meaningful way. The automatic updating was successfully conducted by updating 22 uncertain structural parameters. Finally, a physical interpretation of all parameter changes is discussed. This interpretation is often missing in the published literature. It was found that the composite slabs were less stiff than originally assumed and that the asphalt layer contributed considerably to the deck stiffness. This paper has been published under the following reference:Živanović, S., Finite element modelling and updating of a lively footbridge: the complete process.

A review on model updating of joint structure for dynamic analysis purpose

“…Therefore, FE predictions are often called into question when they are in conflicts with experimental result. Based on previous studies [1,2], the discrepancy between numerical and experimental results may exceed 10% or sometime even 40% error. Incorrect modelling of boundary condition, modelling of joints and difficulties modelling with damping that led to existing of difference between numerical and test result.…”

A residual-based Gaussian process model framework for finite element model updating

“…It can be known from the references [41,42] that even minimizing the small discrepancy between FEM derived modal frequencies and measured modal frequencies can lead to large parameter adjustment. Refs.…”

Updating Stiffness and Hysteretic Damping Matrices Using Measured Modal Data

“…As a result, a significant discrepancy may exist between the modal properties calculated by the constructed FE model and those identified from the vibration measurements of the actual structure. Many investigations show that the differences between the numerical and experimental frequencies may exceed 10% [7,8]. The problem of how to modify a numerical model from the dynamic measurements is known as model updating in structural dynamics.…”