Papers by Elias Dimitrakopoulos
This paper studies the effect of vehicle-bridge interaction (VBI) on the vibration of the support... more This paper studies the effect of vehicle-bridge interaction (VBI) on the vibration of the supporting bridge, and subsequently proposes a decoupled analysis scheme for the VBI problem with reference to high-speed railway systems. The study examines the VBI problem analytically and reveals the main coupling parameters between vehicles and bridges. It proves that, except for the stiffness ratio, the impedance ratio, defined as the ratio of the vehicle's damping and bridge's mechanical impedance, is also a dominant coupling parameter between vehicles and bridges. Following, the study shows that VBI alters the mechanical system of the bridge via an additional damping, an additional stiffness and a modified loading term. The coupling terms (i.e., the vehicle response) appear solely in the modified loading term. Assuming small stiffness ratio, which is realistic for practical train-bridge systems, the proposed decoupling scheme eliminates the vehicle response from the bridge's equation of motion in a systematic manner. With respect to the fully coupled system, the proposed method returns more accurate results compared to well-known decoupling methodologies, such as the moving load approximation.
Analysis And Assessment Of ASeismically Isolated Bridge
WIT Transactions on the Built Environment, May 5, 2005
Estimation of bridge frequencies from a passing vehicle
CRC Press eBooks, Jul 4, 2018
Earthquake Engineering & Structural Dynamics, Jun 1, 2009
In this paper the dynamic response of two and three pounding oscillators subjected to pulse-type ... more In this paper the dynamic response of two and three pounding oscillators subjected to pulse-type excitations is revisited with dimensional analysis. Using Buckingham's-theorem the number of variables that govern the response of the system is reduced by three. When the response is presented in the dimensionless-terms remarkable order emerges. It is shown that regardless of the acceleration level and duration of the pulse all response spectra become self-similar and follow a single master curve. This is true despite the realization of finite duration contacts with increasing durations as the excitation level increases. All physically realizable contacts (impacts, continuous contacts, and detachments) are captured via a linear complementarity approach. The study confirms the existence of three spectral regions. The response of the most flexible among the two oscillators amplifies in the low range of the frequency spectrum (flexible structures); whereas, the response of the most stiff among the two oscillators amplifies at the upper range of the frequency spectrum (stiff structures). Most importantly, the study shows that pounding structures such as colliding buildings or interacting bridge segments may be most vulnerable for excitations with frequencies very different from their natural eigenfrequencies. Finally, by applying the concept of intermediate asymptotics, the study unveils that the dimensionless response of two pounding oscillators follows a scaling law with respect to the mass ratio, or in mathematical terms, that the response exhibits an incomplete self-similarity or self-similarity of the second kind with respect to the mass ratio. Copyright
A Semi-analytical Approach to Approximate Chattering Time of Rocking Structures
Springer INdAM series, 2023
Zenodo (CERN European Organization for Nuclear Research), Aug 1, 2023
The dynamics of bridges and (traversing) vehicles are coupled through the contact forces at the i... more The dynamics of bridges and (traversing) vehicles are coupled through the contact forces at the interface between the two subsystems. This study proposes the concept of virtual sensing (response reconstruction) in bridges using information from on-board sensors installed on an instrumented vehicle with known dynamic characteristics. The premise of the proposed approach is that contact force estimation requires knowing solely the properties of the vehicle model and information from on-board sensors, and, subsequently, using the Augmented Kalman Filter (AKF) technique. Interestingly, the proposed contact force estimation scheme does not necessitate knowledge of the rail profile irregularities characteristics, even though the contact forces depend on them. The estimated contact forces become then input to a finite element model of the traversed bridge, which enables the reconstruction of bridge response (acceleration, displacement, strains, stresses, etc). The estimated strain/stress time histories on the bridge can provide valuable information on the health status of the bridge. The proposed approach is verified with the aid of simulated data from railway bridge-vehicle interaction analyses, examining a 10-degree-of-freedom vehicle model that is representative of realistic train vehicles. The railway bridge considered is a simply supported Euler-Bernoulli beam model. The results offer valuable insights into the effects of different factors (measurement and model errors, vehicle speed, and rail irregularities) on the accuracy of contact force estimation and bridge response reconstruction, and suggest an optimal sensor configuration based on the minimum number of sensors required and their location on the vehicle.
Journal of building engineering, 2020
This study experimentally investigates the axial response of bamboo to steel connections under qu... more This study experimentally investigates the axial response of bamboo to steel connections under quasi-static reversed cyclic loading. It examines three different connection configurations: (Type A) plain bolted; (Type B) transversely confined by hose-clamps; (Type C) transversely confined by hose-clamps and infilled with cement mortar. The study specifically evaluates the effects of loading history in terms of strength degradation, pinching and dissipated energy, and recommends equivalent viscous damping coefficients. In general, the Type B and C connections are superior to Type A; they develop higher strength, possess ductile failure modes and dissipate more hysteretic energy. Compared to the monotonic response however, their cyclic performance is limited by early bolt-fracture. Nevertheless, the examined connections show promise towards a capacity-based design as the ductile components (i.e., the bolts) fail before the brittle components (i.e., the culms). All members are composed of pairs of Bambusa pervariabilis (Kao Jue) bamboo culms.
Experimental characterization of multi-full-culm bamboo to steel connections
Lecture notes in civil engineering, Oct 11, 2019
The present research examines the performance of newly developed multi-full-culm bamboo to steel ... more The present research examines the performance of newly developed multi-full-culm bamboo to steel connections under monotonic axial loading. The culms are of Kao Jue (Bambusa pervariabilis) bamboo species. Findings reveal that the plain (unreinforced) connections fail early by undesirable brittle longitudinal splitting of bamboo culms. The confinement provided by hose-clamps inhibits this brittle failure mode, and with sufficient end-lengths, drastically increases the strength and ductility of the connection. Compared to the hollow-section connections with hose clamps, adding mortar infill further increases the strength. However, it also restricts bolt-deformation and thus diminishes the ductility. More importantly, the European Yield Model (which refers to dowelled timber connections) can analytically estimate the obtained experimental yield loads with satisfying accuracy. This is a promising direction towards a more rational and safer structural design of bamboo structures.
Earthquake Engineering & Structural Dynamics, Oct 24, 2022
The parametric representation of rocking fragilities is statistically investigated. Initially, th... more The parametric representation of rocking fragilities is statistically investigated. Initially, the potential normalization of the rocking parameters to reduce the problem's dimensionality is tackled by undertaking comparisons both on a singlerecord and a sample-of-records basis. It is found that the slenderness angle can be normalized out when probabilistically considering the rocking response of simple rocking blocks with the same semi-diagonal length. Then, the robustness of the lognormal distribution for characterizing the rocking motion is investigated. Sets of pulse-like and ordinary ground motions are employed to test the lognormal fit for the full range of rocking response when the peak ground acceleration or the peak ground velocity are employed as intensity measures. In both cases, the lognormal distribution offers an adequate, but often imperfect, baseline model of the rocking fragility curves. Instead, a shifted lognormal that accounts for the absence of response below the rocking initiation intensity is an enhanced solution that can form the basis for offering simplified response model surrogates.
Simulation and experimental verification of an original full-scale bamboo truss
Engineering Structures, Apr 1, 2022
Nonlinear Dynamics, Nov 20, 2020
This study examines the effect of vehiclebridge interaction (VBI) on the vibration of coupled tra... more This study examines the effect of vehiclebridge interaction (VBI) on the vibration of coupled train-bridge systems and proposes a consistent approach to decouple the VBI problem; the Extended Modified Bridge System (EMBS) method. This constitutes an extension of the formerly developed, for simply supported bridges, Modified Bridge System method. The analysis considers a generic, multi-degree of freedom (MDOF) vehicle-MDOF bridge configuration, representative of a wide class of practical train-bridge systems. This approach enables the MDOF representation of the constituent VBI mechanisms on the mechanical system of the bridge. Based on an asymptotic expansion analysis of the coupled system response, the study brings forward the dominant coupling parameters and their relative importance on the bridge response. The proposed decoupling EMBS method solves the bridge independently of the vehicle by changing its mechanical system via additional damping, stiffness and loading terms. The MDOF description of these terms makes the proposed scheme appropriate for involved bridge configurations, such as continuous and arch bridges. In addition, it allows the accurate estima
Subspace identification of bridge dynamics via traversing vehicle measurements
Journal of Sound and Vibration, Apr 1, 2022
Procedia Engineering, 2017
This paper examines the seismic safety of high-speed railway (HSR) trains running over bridges du... more This paper examines the seismic safety of high-speed railway (HSR) trains running over bridges during strong earthquakes. It develops an original seismic vehicle-bridge interaction (SVBI) analysis scheme to investigate the response of both the vehicle system and the bridge system. The study models the train vehicles as three-dimensional (3D) multibody assemblies. All components of a vehicle are assumed rigid bodies connected with springs and dashpots, representing the vehicle suspension system. The 3D bridge is simulated using the finite element method (FEM). To determine the contact point and the direction of the contact forces it considers the practical nonlinear profiles of wheels and rails. The normal contact forces are derived from kinematic constraints as Lagrange multipliers. Detachment occurs when a normal contact force becomes zero. The study formulates the contact-detachment transition along the normal direction of contact as a linear complementarity problem (LCP) and assumes impact follows Newton's law. The calculation of the tangential creep forces due to the rolling contact is based on a nonlinear Shen-Hedrick-Euristic creep model. The proposed wheel-rail contact model can capture directly different contact phenomena, including flange contact, detachment, uplifting, climbing, derailment, and re-contact. The results underline the importance of a realistic analysis of the SVBI during seismic shaking. They show that seismic induced vibration of the bridge reduces both the comfort and the safety of the vehicles travelling over the bridge, compared to same vehicles travelling on the ground. For most examined cases with different wheelsets, the detachment of a wheel happens when the other wheel belonging to the same wheelset is in flange contact. The derailment of the wheel takes place when the wheel rolls over the rail head.
Engineering Structures, Oct 1, 2017
The present paper compares two simulation methods of the deck-abutment pounding in bridges: the c... more The present paper compares two simulation methods of the deck-abutment pounding in bridges: the commonly adopted gap element (or compliance) approach and a nonsmooth dynamics approach. Specifically, the study evaluates these two approaches with respect to their ability to predict the measured response of a straight, large-scale bridge model from an independent experimental study. The paper also investigates the sensitivity of the deck response to critical assumptions of the compliance approach, i.e., the stiffness of the gap element, the presence of friction during contact, the occurrence of sticking during frictional contact, and the constitutive law of the contact elements. The results show that the deck rotation predicted by these two approaches might differ notably, and highlight the dominant role of friction and its modelling on the seismic response of bridges involving pounding at the deck level.
Construction and Building Materials, Mar 1, 2019
h i g h l i g h t s Plain bolted connections fail early by brittle splitting of bamboo culms. Hos... more h i g h l i g h t s Plain bolted connections fail early by brittle splitting of bamboo culms. Hose-clamps resist brittle splitting drastically increasing strength and ductility. Cement mortar infill further increases the strength but diminishes the ductility. Sufficient end-length inhibits culm-damage and allow higher bolt deformation. The European Yield Model accurately predicts connection yield loads.
Proceedings of The Royal Society A: Mathematical, Physical and Engineering Sciences, Dec 1, 2016
This paper characterizes the stability of a rigid rocking block subjected to a family of multi-lo... more This paper characterizes the stability of a rigid rocking block subjected to a family of multi-lobe pulse ground motions. It unveils a counter to intuition plurality of overturning (OT) modes despite the short duration and bounded energy of the examined ground motions. Accordingly, it describes with original closed-form expressions the critical conditions of all OT modes involving a finite number of impacts. It also proposes pertinent semi-analytical, exact analytical and approximate analytical solutions with respect to the determination of the (unknown) times of impact, as appropriate. The analysis reveals that the first, or lower bound, critical OT mode is in most cases toppling during free rocking after one impact specifically before the end of the pulse. For this case, it elucidates the physical mechanism behind the timing of impact that produces minimum amplitude and maximum amplitude critical OT, respectively, and proposes pertinent closed-form approximations. Finally, the study derives, in 'universal' terms, global 'safety walls' against rocking OT considering a large number of different pulse shapes.
Bulletin of Earthquake Engineering, Jun 9, 2016
Traditionally, the seismic response analysis of a bridge does not account for the concurrent vehi... more Traditionally, the seismic response analysis of a bridge does not account for the concurrent vehicle-bridge dynamic interaction. However, the behavior of a seismically excited bridge can jeopardize the safety of the vehicles running on it, even if the bridge itself remains undamaged. This study examines the seismic response of a vehicle-bridge interacting (VBI) system under vertical earthquake excitation, modelling the truck vehicles as rigid body assemblies. An application of the proposed scheme to a realistic case of (highway) bridge-(truck) vehicles shows that the earthquake ground motion and the road surface conditions are the main sources of excitation. The results show that the road surface conditions influence strongly the dynamics of the VBI system, even when the vertical component of the earthquake excitation is significant. Also, the study brings forward the influence of traffic parameters (namely the speed, the number and the distance between the running vehicles) and underlines the need to consider different positions of the vehicle/s (on the deck) during the earthquake shaking. Finally, it examines the tendency of the wheels of a truck vehicle to detach (jump) from the deck during the seismic response of the VBI system. Detachment tends to be more frequent as the road surface conditions deteriorate and/or the peak ground acceleration increases. However, detachment is a complicated phenomenon which depends also on many other ground motion and VBI system parameters and deserves further study. Keywords Vehicle-bridge interaction Á Truck modelling Á Earthquake engineering Á Seismic response Á Bridges Á Dynamic analysis Á Wheel detachment
Engineering Structures, Jul 1, 2017
The present study examines a new approach for low-cost footbridges as a remedy to the overwhelmin... more The present study examines a new approach for low-cost footbridges as a remedy to the overwhelming lack of bridges in underprivileged rural areas. The proposed truss footbridges can be rapidly assembled, by non-experienced personnel from prefabricated full culm bamboo members and steel gusset plate type connections. This paper addresses the challenges of the design and the construction, and highlights important knowledge gaps in the process. Firstly, it evaluates experimentally the physical and mechanical properties of bamboo culms from two species (namely, Kao Jue and Mao Jue). Then, it develops an analytical model and performs the structural design of the bridge. Importantly, the present study introduces a new three-dimensional gusset plate type truss connection for full culm bamboo members. The proposed connection overcomes the assembly problems due to the non-standardized bamboo geometry. The study also reports the construction of full scale bridge prototypes and their experimental testing. The measured deck deflections under vertical loads are reasonably well captured by the analytical model. However, the bridge collapse is due to a local mode failure peculiar to bamboo; longitudinal splitting. The results reveal that the connections and the associated local failure modes of bamboo, are the most sensitive part of the examined structures, and highlight several directions for further experimental and theoretical research.
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Papers by Elias Dimitrakopoulos