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CONTENTS
Volume 7, Number 2, April 2018
 

Abstract
A successful methodology for modelling controlled destruction and progressive collapse of 2D reinforced concrete frames is presented in this paper. The strategy is subdivided into several aspects including the failure mechanism creation, and dynamic motion in failure represented with multibody system (MBS) simulation that are used to jointly capture controlled demolition. First phase employs linear elasto-plastic analysis with isotropic hardening along with softening plastic hinge concept to investigate the complete failure of structure, leading to creation of final failure mechanism that behaves like MBS. Second phase deals with simulation and control of the progressive collapse of the structure up to total demolition, using the nonlinear dynamic analysis, with conserving/decaying energy scheme which is performed on MBS. The contact between structure and ground is also considered in simulation of collapse process. The efficiency of the proposed methodology is proved with several numerical examples including six story reinforced concrete frame structures.

Key Words
complete collapse; multibody system; plastic joint; geometrically exact beam; energy conserving/decaying scheme; contact

Address
Mourid El houcine and Mamouri Said: Universite de Tahri Mohamed-Bechar, Algeria
Ibrahimbegovic Adnan: Universite de Technologie Compiegne/Sorbonne universites, France

Abstract
This work presents a novel model for analysis of the loading rate influence onto structure response. The model is based on the principles of nonlinear system dynamics, i.e., consists of a system of nonlinear differential equations. In contrast to classical linearized models, this one comprises mass and loading as integral parts of the model. Application of the Kelvin and the Maxwell material models relates the novel formulation to the existing material formulations. All the analysis is performed on a proprietary computer program based on Wolfram Mathematica. This work can be considered as an extended proof of concept for the application of the nonlinear solid model in material response to dynamic loading.

Key Words
lattice material model; nonlinear dynamical system; dynamic loading; Kelvin material model; Maxwell material model; sensitivity

Address
Ivica Kozar: University of Rijeka Faculty of Civil Engineering, Radmile Matejcic 3, 51000 Rijeka, Croatia
Adnan Ibrahimbegovic: Sorbonne Universites / Universite de Technologie Compiegne, Laboratoire Roberval de Mecanique Centre de Recherche Royallieu, 60200 Compiegne, France
Tea Rukavina:
1) University of Rijeka Faculty of Civil Engineering, Radmile Matejcic 3, 51000 Rijeka, Croatia
2) Sorbonne Universites / Universite de Technologie Compiegne, Laboratoire Roberval de Mecanique Centre de Recherche Royallieu, 60200 Compiegne, France

Abstract
The ship hydrodynamics in static and dynamic states were investigated using 3-dimensional numerical simulations. The static case simulated a fixed ship, while the dynamic case considered a ship with free sinkage and trim using the mesh morphing technique. High speed was found to increase the wave elevation around the ship. Compared with the static case, the dynamic case seemed to generate higher waves near the bow and after the stern. The frictional resistance was found be to more dominant. However, the pressure resistance became gradually important with the increase of the ship speed. The trim and sinkage were also analyzed to characterize the ship hydrodynamics in the dynamic state.

Key Words
hydrodynamics; trim; sinkage; ship waves; advancing resistance

Address
P. Du and A. Ouahsine: Laboratoire Roberval, UMR-CNRS 7337, Sorbonne Universites, Universite de Technology de Compiegne, Centre de recherches Royallieu, CS 60319, 60203 Compiegne cedex, France
P. Sergent: CEREMA-134, rue de Beauvais, CS 60039, 60200 Compiegne, France

Abstract
Reinforced concrete buildings in a seismically active area can be designed as DCM (medium ductility) or DCH (high ductility) class according to the regulations of Eurocode 8. In this paper, two RC buildings, one with a wall structural system and the other with a frame system, previously designed for DCM and DCH ductility, were analysed by using incremental dynamic analysis in order to study differences in the behaviour of structures between these ductility classes, especially the failure mechanism and ultimate collapse acceleration. Despite the fact that a higher behaviour factor of DCH structures influences lower seismic resistance, in comparison to DCM structures, a strict application of the design and detailing rules of Eurocode 8 in analysed examples caused that the seismic resistance of both frames does not significantly differ. The conclusions were derived for two buildings and do not necessarily apply to other RC structures. Further analysis could make a valuable contribution to the analysis of the behaviour of such buildings and decide between two ductility classes in everyday building design.

Key Words
ductility classes; Eurocode 8; incremental dynamic analysis; reinforced concrete buildings

Address
Zeljana Nikolic, Nikolina Zivaljic and Hrvoje Smoljanovic: Faculty of Civil Engineering, University of Split, Architecture and Geodesy, Matice hrvatske 15, 21000 Split, Croatia


Abstract
Fiber-reinforced concrete (FRC) is a material with increasing application in civil engineering. Here it is assumed that the material consists of a great number of rather small fibers embedded into the concrete matrix. It would be advantageous to predict the mechanical properties of FRC using nondestructive testing; unfortunately, many testing methods for concrete are not applicable to FRC. In addition, design methods for FRC are either inaccurate or complicated. In three-point bending tests of FRC prisms, it has been observed that fiber reinforcement does not break but simply pulls out during specimen failure. Following that observation, this work is based on an assumption that the main components of a simple and rather accurate FRC model are mechanical properties of the concrete matrix and fiber pullout force. Properties of the concrete matrix could be determined from measurements on samples taken during concrete production, and fiber pullout force could be measured on samples with individual fibers embedded into concrete. However, there is no clear relationship between measurements on individual samples of concrete matrix with a single fiber and properties of the produced FRC. This work presents an inverse model for FRC that establishes a relation between parameters measured on individual material samples and properties of a structure made of the composite material. However, a deterministic relationship is clearly not possible since only a single beam specimen of 60 cm could easily contain over 100000 fibers. Our inverse model assumes that the probability density function of individual fiber properties is known, and that the global sample load-displacement curve is obtained from the experiment. Thus, each fiber is stochastically characterized and accordingly parameterized. A relationship between fiber parameters and global load-displacement response, the so-called forward model, is established. From the forward model, based on Levenberg-Marquardt procedure, the inverse model is formulated and successfully applied.

Key Words
fiber-reinforced concrete, inverse model, Levenberg-Marquardt procedure, fiber pullout, probability density function (pdf)

Address
Ivica Kozar and Neira Toric Malic: University of Rijeka, Faculty of Civil Engineering, Radmile Matejcic 3, 51000 Rijeka, Croatia
Tea Rukavina:
1) University of Rijeka, Faculty of Civil Engineering, Radmile Matejcic 3, 51000 Rijeka, Croatia
2) Sorbonne Universites – Universite de Technologie de Compiegne, Laboratoire Roberval de Mecanique, Centre de Recherches Royallieu, 60200 Compiegne, France

Abstract
In this work we present an upscaling technique for multi-scale computations based on a stochastic model calibration technique. We consider a coarse scale continuum material model described in the framework of generalized standard materials. The model parameters are considered uncertain, and are determined in a Bayesian framework for the given fine scale data in a form of stored energy and dissipation potential. The proposed stochastic upscaling approach is independent w.r.t. the choice of models on coarse and fine scales. Simple numerical examples are shown to demonstrate the ability of the proposed approach to calibrate coarse scale elastic and inelastic material parameters.

Key Words
upscaling; Bayesian updating; Gauss-Markov-Kalman filter; coupled plasticity-damage

Address
Sadiq M. Sarfaraz Bojana V. Rosic and Hermann G. Matthies: Institute of Scientific Computing, Technische Universitat Braunschweig 38106 Braunschweig, Germany
Adnan Ibrahimbegovic: Lab. de Mecanique Roberval/Centre de Recherche Royallieu, Universite de Technologie de Compiegne, 60203 Compiegne, France

Abstract
In order to reduce the dependency on fossil fuels, a policy to increase the production capacity of wind turbine is set up. This can be achieved with increasing the dimensions of offshore wind turbine blades. However, this increase in size implies serious problems of stability and durability. Considering the cost of large turbines and financial consequences of their premature failure, it is imperative to carry out numerical simulations over long periods. Here, an energy-conserving time-stepping scheme is proposed in order to ensure the satisfying computation of long-term response. The proposed scheme is implemented for three-dimensional solid based on Biot strain measures, which is used for modeling flexible blades. The simulations are performed at full spatial scale. For reliable design process, the wind loads should be represented as realistically as possible, including the fluid-structure interaction (FSI) dynamic effects on wind turbine blades. However, full-scale 3D FSI simulations for long-term wind loading remain of prohibitive computation cost. Thus, the model to quantify the wind loads proposed here is a simple, but not too simple to be representative for preliminary design studies.

Key Words
wind turbine; wind load; energy-conserving scheme; long-term simulation

Address
Adnan Ibrahimbegovic and Abir Boujelben: Sorbonne Universites, Universite de Technologie Compiegne, Laboratoire Roberval de Mecanique, Chair of Computational Mechanics, Centre de Recherches Royallieu, CS 60319, 60200, Compiegne Cedex, France


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