Experimental Estimation of the Elastic Modulus of Concrete Girders from Drive-By Inspections with Force-Balance Accelerometers

Parametric identification of bridges using instrumented vehicles can be challenging, mainly due to the reduced length of the time series associated with the bridge span under test. This research discusses the practicability of a time-domain identification method based on the use of an instrumented vehicle. The highest cross-correlation between the bridge response from an elementary analytical model and the experimental one, acquired by a moving force-balance accelerometer, yields the unknown model parameter. The effect of vehicle-bridge interaction is removed by proper filtering of the signals. Specifically, the authors estimate the elastic moduli of seven prestressed concrete bridges and compare a subset of the results to the outcomes of static load tests carried out on the same bridges. There is a good correlation between the elastic moduli from the instrumented vehicle and those from static load tests: the method grasps the approximate value of the elastic modulus of concrete. Still, the data do not return an excellent match due to the bias in the estimation of the deflection shape—the paper remarks on the issues faced during the experimental tests and proposes possible enhancements of these procedures

The architrave a tasselli

The architrave a tasselli is a peculiar design shape of the traditional stone lintels, which are widespread in Abruzzo, Italy: stone lintels are not usually monolithic elements, being formed by three pieces, the block spanning the opening and the tasselli, two small rectangular pieces. In the current paper, by means of an elementary Wrinkler-type beam model, it has been attempted to capture the behaviour of stone lintels, chasing the mechanical reasons supporting this traditional construction technique. Keywords: Architectural heritage, Theory of elasticity, Masonry building, Traditional constructive technique

Ambient vibration testing and structural identification of a cable-stayed bridge

This paper presents the results of an experimental and theoretical investigation on the Pietratagliata cable-stayed bridge (Udine, Italy). Ambient vibration tests were performed in order to estimate the dynamic characteristics of the lower vibration modes of the bridge. Structural identification is carried out by means of a manual tuning procedure based on finite element models of increasingly accuracy. The analysis allows to improve the description of boundary conditions and mechanical interaction between the bridge components. Results from local dynamic testing are used to estimate the traction on the cables and to assess the integrity of the suspending system of the bridge

Experimental unfolding of the nonlinear dynamics of a cable-mass suspended system around a divergence-Hopf bifurcation

Systematic experimental investigation of the finite amplitude dynamics of a multiple internally resonant suspended cable-mass, subjected to anti-phase support motion at primary resonance, is accomplished. Upon getting hints from a basic system configuration assumed as reference setup about the multiple bifurcation event possibly governing transition to complex dynamics, an improved experimental apparatus is used to make it technically accessible. Results obtained by varying three control parameters, namely the frequency and amplitude of excitation and the temperature of a thermostatic chamber embedding the experimental system, allow us to characterize in-depth various occurring classes of motion ill terms of time and spatial complexity, to describe peculiar and/or persistent features of transition to nonregular dynamics, and to trace them back to a canonical scenario from bifurcation theory. Variable response paths are detected via bifurcation diagrams and spectra of singular values of measurement results, and overall behaviour charts are built ill the excitation parameter space. Considering the temperature as a controllable parameter shows to be fundamental for: (i) indirectly setting cable material properties to values for which the conjectured codimension 2 bifurcation becomes apparent, (ii) qualitatively referring the experimental unfolding of regular and nonregular cable dynamics to the theoretical unfolding of the divergence-Hopf bifurcation normal form, and (iii) determining system response not only in the strict neighbourhood of the organizing divergence-Hopf bifurcation but also in the ensuing postcritical regions where the dependence of material damping on temperature affects secondary bifurcations to low-dimensional homoclinic chaos. (C) 2009 Elsevier Ltd. All rights reserved

Spatio-temporal dimensionality in the overall complex dynamics of an experimental cable/mass system

An experimental model of an elastic cable/mass hanging at in-phase or out-of-phase vertically moving supports is considered. System parameters are adjusted to produce two different conditions of multiple internal resonance. Nonregular dynamics are analyzed in various frequency ranges including meaningful external resonance conditions. Attention is devoted to characterization of system dimensionality in terms of both time and spatial complexity. The aims of this paper are (i) to give a general overview of the richness and robustness of different (quasiperiodic and homoclinic) bifurcation scenarios to chaos in various regions of the control parameter space, (ii) to characterize steady nonregular response through delay-embedding technique for attractor reconstruction and proper orthogonal decomposition of spatio-temporal flow and (iii) to identify spatial configuration variables (experimental eigenfunctions) contributing mostly to nonregular dynamics, thus obtaining hints about possible reduced models for reproducing complex regimes. System dimensionality will be evaluated both by relating the dimension of attractors to the dimension of the linear phase space, and from the dominating proper orthogonal modes

Flexural-torsional post critical behavior of a cantilever beam dynamically excited: Theoretical model and experimental tests

ABSTRACT The 3D dynamics of a cantilever beam undergoing large displacements under a sinusoidally varying, concentrated, vertical force at its free end are analyzed in this paper. The Partial Differential Equations (PDEs) of the motion are obtained by using the Principle of Virtual Power. Then a reduced 4 degrees-of-freedom model is obtained using, in a Galerkin approximation, four eigenfunctions of the linearized model. The obtained four Ordinary Differential Equations (ODEs) of the motion are expanded by means of a 3 rd order Multiple Time Scales perturbation technique to obtain Amplitude and Phase Modulation Equations (APMEs). The role of the inertial-elastic nonlinear terms, responsible for the coupling of the mass matrix, and of the viscous-elastic nonlinear terms, both usually neglected in the literature, is discussed. A path following procedure applied to the APMEs is used to describe the global dynamical behavior in the plane of the excitation control parameters. The results obtained using the 4 d.o.f. analytical model are compared with those of an experimental aluminium model of the cantilever. The regions of instability of the 1-modal planar solution, in which the nonlinear modal coupling excites out of plane and/or torsional components, are studied

Physics-based models, surrogate models and experimental assessment of the vehicle–bridge interaction in braking conditions

The dynamics of roadway bridges crossed by vehicles moving at variable speed has attracted far less attention than that generated by vehicles travelling at constant velocity. Consequently, the role of some parameters and the combination thereof, as well as influence and accuracy of the modelling strategies, are not fully understood yet. Therefore, a large statistical analysis is performed in the present study to provide novel insights into the dynamic vehicle–bridge interaction (VBI) in braking conditions. To this end, an existing mid-span prestressed concrete bridge is selected as case study. First, several numerical simulations are performed considering alternative vehicle models (i.e., single and two degrees-of-freedom models) and different braking scenarios (i.e., soft and hard braking conditions, with both stationary and nonstationary road roughness models in case of soft braking). The statistical appraisal of the obtained results unfolds some effects of the dynamic VBI modelling in braking conditions that have not been reported in previous studies. Additionally, the use of machine learning techniques is explored for the first time to develop surrogate models able to predict the effect of the dynamic VBI in braking conditions efficiently. These surrogate models are then employed to obtain the fragility curve for the selected prestressed concrete bridge, where the attainment of the decompression moment is considered as relevant limit state. Whilst the derivation of the fragility curve using numerical simulations turned out to be almost unpractical using standard computational resources, the proposed approach that exploits surrogate models carried out via machine learning techniques was demonstrated accurate despite the dramatic reduction of the total elaboration time. Finally, the accuracy of the numerical (physics-based and surrogate) models is evaluated on a statistical basis through comparisons with experimental data

Dispersion Curves of Transverse Waves Propagating in Multi-Layered Soils from Experimental Tests in a 100 m Deep Borehole

The estimate of the velocity of shear waves (Vs) is essential in seismic engineering to characterize the dynamic response of soils. There are various direct methods to estimate the Vs. The authors report the results of site characterization in Macerata (Italy), where they measured the Vs using the seismic dilatometer in a 100 m deep borehole. The standard Vs estimation originates from the cross-correlation between the signals acquired by two geophones at increasing depths. This paper focuses on the estimate of the dependence of Vs on the wavenumber. The dispersion curves reveal an unexpected hyperbolic dispersion curve typical of Lamb waves. Interestingly, the contribution of Lamb waves may be notable up to 100 m depth. The amplitude of surface waves decrease rapidly with depth; still, their influence may be essential up to depths considered unusual for standard geotechnical investigations, where their effect is generally neglected. Accordingly, these waves may bias the outcomes of the standard Vs estimations, which ignore frequency-dependent phenomena. The paper proposes an enhancement of the accepted procedure to estimate Vs and addresses the importance of Lamb waves in soil characterization

Fragility estimate of railway bridges due to concrete fatigue

Railway concrete bridges are prone to fatigue collapse, being subjected to multiple cyclic loads during their lifetime. This paper proposes a probabilistic procedure for assessing the fatigue life of concrete railway bridges. The procedure includes the uncertainties related to the concrete fatigue model and the concrete strength by highlighting the relevant uncertainty of existing fatigue models. Therefore, it proposes an enhancement of the fatigue model proposed by the Fib Code 2010 to reduce the modelling error possibly. The model has been calibrated on an extensive data set of normal-strength concrete samples following a Bayesian approach. Parallelly, the parameters have been reduced using a Bayesian step-wise deletion process. The paper uses the proposed probabilistic model to estimate the fragility curves in general cases by considering appropriate ranges for the train velocity, stress ratios and the number of cycles per year. In the second step, the paper applies the procedure to the fragility estimate of a typical prestressed-concrete railway bridge. The bridge response has been estimated using a finite-difference (FD) model. The FD model, simulating train-track-bridge interaction, has been calibrated on the measured displacement response. The analyses have been referred to different scenarios when suitable ranges of train velocities and cycles per year are considered