Adam J Crewe

Finite element model updating of a small scale bridge

Abstract Although considerable experience has been gained in model updating, the critical issues that remain are the choice of parameters and how to deal with ill-conditioning. Although a number of theoretical tools exist to help with both of these tasks, the techniques are advancing by gaining experience with a diverse range of structures. This paper adds to this debate by updating an experimental bridge model with a geometric scale of 1:50 that represents a typical multi-span continuous-deck motorway bridge. The bridge has four identical straight spans and an irregular distribution of piers, and the central pier is shorter than the others. Four configurations corresponding to different pier stiffnesses and the inclusion of an isolation–dissipation device were considered. An initial test without the piers present was also performed. The measurement of data in these different configurations allows the model updating to be performed sequentially, where parameters identified in earlier configurations maintain their estimated values in subsequent configurations. This approach means that each configuration has a small number of uncertain parameters to be identified, leading to a set of well-conditioned estimation problems based on predicting four natural frequencies of the structure. The procedure was successful, and all of the measured natural frequencies were estimated accurately with a maximum error of under 2.5%.

The European collaborative programme on evaluating the performance of shaking tables

This paper describes a concerted performance appraisal of four of Europes large shaking tables. Three of the shaking tables were capable of controlled motion in all six degrees of freedom, while the fourth was constrained to move in the three translational axes only. The principal study was the fidelity of the input motion at the testpiece. At all four tables this was found to be satisfactory, but, in one case, the time taken for the tuning process was often more than one hour, and in all cases highly trained and experienced operators were required. Even so, the tuning process was ‘out of real time’, which required that the physical properties of the testpiece should not change during the tuning process. This meant that controlled nonlinear specimen behaviour could not be studied experimentally. This was a major drawback, since modern economic design requires use of nonlinear material properties, leading to progressive failure of redundant members, but not total collapse. The studies did, however, have a major beneficial effect in showing that existing control systems were out of date. Further research programmes were therefore started which have already had the major consequence of producing ‘real–time’ control of shaking tables.

Model Container Design for Soil-Structure Interaction Studies

Physical modelling of scaled models is an established method for understanding failure mechanisms and verifying design hypothesis in earthquake geotechnical engineering practice. One of the requirements of physical modelling for these classes of problems is the replication of semi-infinite extent of the ground in a finite dimension model soil container. This chapter is aimed at summarizing the requirements for a model container for carrying out seismic soil-structure interactions (SSI) at 1-g (shaking table) and N-g (geotechnical centrifuge at N times earth’s gravity). A literature review has identified six types of soil container which are summarised and critically reviewed herein. The specialised modelling techniques entailed by the application of these containers are also discussed.

Obtaining Spectrum Matching Time Series Using a Reweighted Volterra Series Algorithm (RVSA)

In this paper, we introduce a novel algorithm for morphing any accelerogram into a spectrum matching one. First, the seed time series is re‐expressed as a discrete Volterra series. The first‐order Volterra kernel is estimated by a multilevel wavelet decomposition using the stationary wavelet transform. Second, the higher‐order Volterra kernels are estimated using a complete multinomial mixing of the first‐order kernel functions. Finally, the weighting of every term in this Volterra series is optimally adapted using a Levenberg–Marquardt algorithm such that the modified time series matches any target response spectrum. Comparisons are made using the SeismoMatch algorithm, and this reweighted Volterra series algorithm is demonstrated to be considerably more robust, matching the target spectrum more faithfully. This is achieved while qualitatively maintaining the original signal’s nonstationary statistics, such as general envelope, time location of large pulses, and variation of frequency content with time.

Computational Modelling Strategies for Nonlinear Response Prediction of Corroded Circular RC Bridge Piers

A numerical model is presented that enables simulation of the nonlinear flexural response of corroded reinforced concrete (RC) components. The model employs a force-based nonlinear fibre beam-column element. A new phenomenological uniaxial material model for corroded reinforcing steel is used. This model accounts for the impact of corrosion on buckling strength, postbuckling behaviour, and low-cycle fatigue degradation of vertical reinforcement under cyclic loading. The basic material model is validated through comparison of simulated and observed responses for uncorroded RC columns. The model is used to explore the impact of corrosion on the inelastic response of corroded RC columns.

Nonlinear dynamic analysis and seismic fragility assessment of a corrosion damaged integral bridge

Purpose – The purpose of this paper is to explore the impact of corrosion of reinforcing steel in RC columns on the seismic performance of a multi-span concrete integral bridge. A new constitutive model for corroded reinforcing steel is used. This model simulates the buckling of longitudinal reinforcement under cyclic loading and the impact of corrosion on buckling strength. Cover concrete strength is adjusted to account for corrosion induced damage and core concrete strength and ductility is adjusted to account for corrosion induced damage to transverse reinforcement. This study evaluates the impact which chloride induced corrosion of the reinforced concrete columns on the seismic fragility of the bridge. Fragility curves are developed at a various time intervals over the lifetime. The results of this study show that the bridge fragility increases significantly with corrosion. Design/methodology/approach – This paper first, evaluates the impact which chloride induced corrosion of the columns has on bridg...

Shaking Table Experimental Programme

The graphite components in AGR cores are subject to degradation processes that are predicted to lead to greater numbers of weakened and cracked components. The reactor core models used to assess the tolerability of the cores to seismic events need to represent higher levels of degradation. A shaking table programme has commenced, with the primary goal to provide experimental validation of the existing AGR core models. This paper presents the proposed rig work with main aspects of physical model design, rig manufacturing and dynamic testing being addressed. The candidate instrumentation systems and the relevant rig outputs are also described.

A multi-mechanical nonlinear fibre beam-column model for corroded columns

Purpose – A new modelling technique is developed to model the nonlinear behaviour of corrosion damaged reinforced concrete (RC) bridge piers subject to cyclic loading. The model employs a nonlinear beam-column element with multi-mechanical fibre sections using OpenSees. The nonlinear uniaxial material models used in the fibre sections account for the effect of corrosion damage on vertical reinforcing, cracked cover concrete due to corrosion of vertical bars and damaged confined concrete due to corrosion of horizontal tie reinforcement. An advance material model is used to simulate the nonlinear behaviour of the vertical reinforcing bars that accounts for combined impact of inelastic buckling and low-cycle fatigue degradation. The basic uncorroded model is verified by comparison of the computation and observed response of RC columns with uncorroded reinforcement. This model is used in an exploration study of recently tested RC components to investigate the impact of different corrosion models on the inelas...

Considering Wave Passage Effects in Blind Identification of Long-Span Bridges

Long-span bridges usually experience different input excitations at their ground supports that emanate from differences in wave arrival times, and soil conditions, as well as loss of coherency in arriving waves. These spatial variations can drastically influence the dynamic response; hence, this phenomenon must be considered in any vibration-based identification method. There are numerous Multi-Input Multi-Output (MIMO) identification techniques that may be applied to data recorded at long-span bridges that experience spatial variations in their input motions. However, inertial soil-structure interaction effects severely reduce the accuracy of these techniques because the actual Foundation Input Motion (FIM) cannot be recorded during earthquakes. In this study, we present an extension to a novel blind identification method that we had developed earlier, which enables the method to handle multiple input motions. For the sake of simplicity, we only consider wave passage effects—that is, all unknown input motions are assumed to be identical except for a known/unknown phase-delay. This method comprises two steps. In the first step, the spatial time-frequency distributions of recorded responses are used for extracting the mode shapes and the modal coordinates. This is achieved through a Blind Source Separation (BSS) technique. In the second step, cross relations among the extracted modal coordinates are used for identifying the natural frequencies, damping ratios, modal contribution factors, along with the unknown input motions through a least-squares technique. Both simulated and experimental examples are provided, which suggest that the method is capable of accurately identifying the dynamic characteristics of long-span bridges from recorded response signals without the knowledge of input motions, even in the presence of wave passage effects due to phase-delays.

Autotuning of Isotropic Hardening Constitutive Models on Real Steel Buckling Data with Finite Element Based Multistart Global Optimisation on Parallel Computers

An automatic framework for tuning plastic constitutive models is proposed. It is based on multistart global optimisation method, where the objective function is provided by the results of multiple elastoplastic finite element analyses, executed concurrently. Wrapper scripts were developed for fully automatic preprocessing, including model and mesh generation, analysis, and postprocessing. The framework is applied to an isotropic power hardening plasticity using real load/displacement data from multiple steel buckling tests. M. J. D. Powellźs BOBYQA constrained optimisation package was used for local optimisation. It is shown that using the real data presents multiple problems to the optimisation process because (1) the objective function can be discontinuous, yet (2) relatively flat around multiple local minima, with (3) similar values of the objective function for different local minima. As a consequence the estimate of the global minimum is sensitive to the amount of experimental data and experimental noise. The framework includes the verification step, where the estimate of the global minimum is verified on a different geometry and loading. A tensile test was used for verification in this work. The speed of the method critically depends on the ability to effectively parallelise the finite element solver. Three levels of parallelisation were exploited in this work. The ultimate limitation was the availability of the finite element commercial solver license tokens.