Multi-scale model updating of a timber footbridge using experimental vibration data

Abstract

Purpose The purpose of this paper is to capture the actual structural behavior of the longest timber footbridge in Spain by means of a multi-scale model updating approach in conjunction with ambient vibration tests. Design/methodology/approach In a first stage, a numerical pre-test analysis of the full bridge is performed, using standard beam-type finite elements with isotropic material properties. This approach offers a first structural model in which optimal sensor placement (OSP) methodologies are applied to improve the system identification process. In particular, the effective independence (EFI) method is used to determine the optimal locations of a set of sensors. Ambient vibration tests are conducted to determine experimentally the modal characteristics of the structure. The identified modal parameters are compared with those values obtained from this preliminary model. To improve the accuracy of the numerical predictions, the material response is modeled by means of a homogenization-based multi-scale computational approach. In a second stage, the structure is modeled by means of three-dimensional solid elements with the above material definition, capturing realistically the full orthotropic mechanical properties of wood. A genetic algorithm (GA) technique is adopted to calibrate the micromechanical parameters which are either not well-known or susceptible to considerable variations when measured experimentally. Findings An overall good agreement is found between the results of the updated numerical simulations and the corresponding experimental measurements. The longitudinal and transverse Young's moduli, sliding and rolling shear moduli, density and natural frequencies are computed by the present approach. The obtained results reveal the potential predictive capabilities of the present GA/multi-scale/experimental approach to capture accurately the actual behavior of complex materials and structures. Originality/value The uniqueness and importance of this structure leads to an intensive study of its structural behavior. Ambient vibration tests are carried out under environmental excitation. Extraction of modal parameters is obtained from output-only experimental data. The EFI methodology is applied for the OSP on a large-scale structure. Information coming from several length scales, from sub-micrometer dimensions to macroscopic scales, is included in the material definition. The strong differences found between the stiffness along the longitudinal and transverse directions of wood lumbers are incorporated in the structural model. A multi-scale model updating approach is carried out by means of a GA technique to calibrate the micromechanical parameters which are either not well-known or susceptible to considerable variations when measured experimentally.

Seismic assessment of bridges through structural health monitoring: a state-of-the-art review

“…In this sense, the work by Castro-Triguero et al. ( 2017 ) is somewhat different since it aims at calibrating the micromechanical parameters of a multi-scale model. In detail, Castro-Triguero et al.…”

“…In detail, Castro-Triguero et al. ( 2017 ) elaborate a multi-scale model for a timber footbridge and employ a GA to update the numerical values of degree of cellulose crystallinity, volume fraction of cellulose, volume fraction of hemicellulose, length of cellulose crystallites, radial dimension of wood cell, tangential dimension of wood cell, cell wall thickness, cell angle and microfibril angle. Throughout an iterative GA-based procedure, a homogenization technique is performed to obtain the macroscopic data for the global FE model of the bridge starting from these micromechanical parameters.…”

“…It is interesting to highlight that in all these studies, GA and PSO are applied to identify or update relevant macroscale parameters in bridge structures. In this sense, the work by Castro-Triguero et al (2017) is somewhat different since it aims at calibrating the micromechanical parameters of a multi-scale model. In detail, Castro-Triguero et al ( 2017) elaborate a multi-scale model for a timber footbridge and employ a GA to update the numerical values of degree of cellulose crystallinity, volume fraction of cellulose, volume fraction of hemicellulose, length of cellulose crystallites, radial dimension of wood cell, tangential dimension of wood cell, cell wall thickness, cell angle and microfibril angle.…”

Water–structure interaction analysis of a segmental bridge using ambient vibration testing at different water levels

“…The black triangle corresponds to the location of the reference sensor (located at L/3 of the total length of the bridge measured from the north access). To minimize the influence of the number of sensors used in the AVTs, the mode shapes identified in AVTs 1 and 2 are selected to perform an OSP analysis using the Effective Independence (EI) method [23,24]. The blue rectangles correspond to OSP positions.…”

Experimental and Numerical Dynamic Properties of Two Timber Footbridges Including Seasonal Effects

“…However, the relatively low stiffness of timber bridges in combination with their low self-weight may result in uncomfortable vibrations for crossing pedestrians, and therefore, accurate dynamic analyses are often required in the design process. For this reason, the experimental and dynamic performances of timber bridges have been the purpose of several research works in the last decade [2][3][4][5], including structural health monitoring analyses [6], evaluation of natural frequencies variations with the time and use [7], etc.…”