Energy conserving time integration scheme for geometrically exact beam

An energy conserving finite-element formulation for the dynamic analysis of geometrically non-linear beam-like structures undergoing large overall motions has been developed. The formulation uses classical displacement-based planar beam finite elements described in an inertial frame. It takes into account finite axial, bending and shear strains. A theoretically consistent approach is used to derive a novel and simple energy conserving scheme, using the unconventional incremental strain update rather than the standard strong form. Numerical examples demonstrate perfect energy and momenta conservation, stability and robustness of the scheme, and good convergence properties in terms of both the Newton-Raphson method and time step size. (c) 2006 Elsevier B.V. All rights reserved

The strain-based beam finite elements in multibody dynamics

We present a strain-based finite-element formulation for the dynamic analysis of flexible elastic planar multibody systems, composed of planar beams. We consider finite displacements, rotations and strains. The discrete dynamic equations of motion are obtained by the collocation method. The strains are the basic interpolated variables, which makes the formulation different from other formulations. The further speciality of the formulation is the strong satisfaction of the cross-sectional constitutive conditions at collocation points. In order to avoid the nested integrations, a special algorithm for the numerical integration over the length of the finite element is proposed. The midpoint scheme is used for the time integration. The performance of the formulation is illustrated via numerical examples, including a stiff multibody system. (c) 2007 Elsevier Ltd. All rights reserved

Geometrically exact dynamic analysis of elastic and reinforced concrete frame\ud structures

The dissertation deals with dynamics of geometrically exact elastic and reinforced concrete planar structures.\ud The main topic is the treatment of exact (Reissner’s) kinematic equations in problems concerning\ud dynamics of planar beams. The kinematic equations include axial, bending as well as shear strains. The\ud dissertation is divided into four themes. The first theme concerns solving the problem of dynamics of\ud elastic planar beams by taking the strains as the only unknown functions. It turns out that the direct approach\ud to solving problems, defined in this way, is numerically inefficient as it involves multiple nesting\ud of integrals. An enhancement of the approach is therefore developed and tested on numerical examples.\ud In the next theme we discuss the issue of time integration in kinematically exact dynamics. During the\ud analysis we restrict ourselves to displacement and rotation based finite elements, which is the standard\ud approach to solving problems in mechanics. The classical approach is presented first followed by the\ud detailed energy approach. As a part of the analysis of energy conservation based integrators, a new time\ud integration scheme is developed. It is based on the use of kinematic equations, which are differentiated\ud with respect to time. Conservational properties of all analysed integration schemes are analytically and\ud numerically tested. The schemes have been supplemented with numerical dissipation, which can be arbitrarily\ud turned on or off according to a special algorithm in order to affect the lower modes of response\ud as little as possible. This is also verified by the numerical examples. The third theme of the dissertation\ud deals with the optimization of kinematically exact elastic structures. This part of the dissertation\ud contributes to the development and the application of the sensitivity analysis for the newly developed\ud time integration scheme. A wide array of problems dealing with optimization of dynamical systems can\ud be solved. These problems include the optimization of shape and resistance of structures as well as the\ud loading regimes and the optimal shape of mechanical manipulators. In the final part of the dissertation,\ud the dynamics of kinematically exact reinforced concrete structures is discussed. A numerical procedure\ud is developed, verified by the Opensees program and validated by experimental results. The majority of\ud the numerical procedures presented in the dissertation have been developed in AceGen and AceFEM\ud computer programs, through the symbolic programming of the finite element computer code and the expression\ud optimization. These programs have been found to offer a versatile environment for testing and\ud using finite element based analyses

Seismic behaviour of porous concrete buildings

U radu je opisano ispitivanje provedeno na potresnoj platformi dvaju troetažnih i jednog četveroetažnog modela zgrada izrađenih od porastoga beton. Zabilježeno je tipično ponašanje posmičnog zida s dijagonalnim pukotinama u smjeru uzbuđivanja i katnim mehanizmom ponašanja pri rušenju. Analizirani su odnosu između oštećenja, otpornosti i katnih pomaka za pojedina granična stanja, dana je ocjena za proračunske parametre, kao što su kapacitet pomaka i faktor ponašanja konstrukcije.The testing conducted on seismic platform to determine behaviour of porous concrete buildings, using two three-storey building models, and one four-storey building model, is described in the paper. Typical behaviour of shear wall with diagonal cracks in the direction of excitation, and with storey-based mechanism of behaviour during collapse, has been noted. Relationships between the damage, resistance and storey drift are analyzed for individual limit states, and an estimation of design parameters, such as the drift capacity and structural behaviour factor, is given

Preliminary study on the influence of fibre orientation in fibre reinforced mortars

U radu se obrađuje utjecaj čeličnih vlakana u mikroarmiranim mortovima. Uzorci morta u svježem stanju, s nasumično raspoređenim vlaknima su smješteni u spiralnu zavojnicu i izloženi elektromagnetskskom polju u cilju postizanja usmjerenosti vlakana. Lokacija i orijentacija vlakana je određena rengenskom snimkom. Provedena su ispitivanja čvrstoće na savijanje uz kontrolu progiba ISC sustavom (engl. Digital Image Correlation System - ICS). S obzirom na orijentaciju vlakana, rezultati su pokazali poboljšanu disipaciju energije i veću energiju pri lomu kod uzoraka s usmjerenim vlaknima.The influence of steel fibres in fibre reinforced mortars is considered in the paper. Fresh mortar samples with randomly distributed fibres are placed in a spiral coil and exposed to electromagnetic filed so as to achieve orientation of fibres. The location and orientation of fibres is defined by x-ray images. The bending strength testing with deflection checking using the ICS system (Digital Image Correlation System) is conducted. Considering the fibre orientation and load applied, the results exhibit better energy dissipation and greater energy at fracture in case of samples with oriented fibres

modelling of deformable polymer to be used for joints between infill masonry walls and r c frames

Abstract In the paper an idea to use a deformable polymer material for the joint between R.C. frames and masonry infills is presented. As an early step of testing the idea, experimental tests of the polymer in monotonic uniaxial tension at different load rates are performed and analyzed. The load rates range from very fast (8.3 mm/s) to very slow (0.00083 mm/s). The material exhibits a very strong strain rate effect and viscous behavior. In the second part of the paper a numerical model is developed and implemented into a finite element to simulate the results of the tests. The model is based on a new family of strain measures, called the Darjani-Naghdabadi strain measures and a classical viscosity formulation. Almost perfect model predictions up to collapse at 50-150% elongation are obtained by using calibration based on minimization of error

Pushover analysis of confined masonry walls using equivalent diagonal strut models

Masonry structures are commonly used for building residential buildings throughout the Balkans and worldwide, in urban and rural areas and areas with seismic risk. For masonry construction in regions with seismic risk, confined masonry (CM) construction offers an appealing alternative to unreinforced masonry (URM) due to its better seismic performance. The numerical simulation of CM is often based on the Equivalent Strut Model (ESM). Such a model provides a very reasonable compromise between accuracy and efficiency and is simple enough for use in design. The purpose of this paper is to compare the results of an experimental shear compression test on a modern CM wall with different ESM models. Five ESM models proposed by various authors are compared. The numerical pushover analyses were performed in the SAP2000 software, and the reference points of the model that gave the best alignment with experimental results were estimated using regression analyses. The results show that the simple modelling of CM walls with an equivalent diagonal strut, which carries load only in compression, can accurately simulate the global seismic response and is suitable for practical applications

Experimental and numerical investigation of the seismic response of confined masonry walls

Confined masonry (CM) is one of the most popular and affordable earthquake-resistant con-struction technology for masonry structures. The reinforced concrete (RC) tie-columns in such construction play a crucial role in improving seismic response. However, their interaction with the masonry warrants a review due to recent changes in masonry construction, which are typical for Southeastern Europe. The modern masonry walls built from clay units are thick to achieve thermal efficiency. The tie-columns size has also increased, but they are narrower than the masonry. A part of masonry thus protrudes from the area confined by tie columns, which can lead to stress concentrations and early onset of damage of the protruding masonry, as was observed in recent tests on such masonry. This paper numerically analyzes this problem using a detailed three-dimensional (3D) finite element (FE) model that can capture this effect. The numerical model was developed in ABAQUS, and uses Concrete Damage Plasticity (CDP) material model to model the brittle response of clay blocks. All input data for the numerical model were obtained by dedicated tests. The results are compared to tests of walls in terms of damage propagation, strength and deformation response and show that damage to the protruding masonry can be successfully modelled. The results show a good alignment with the experiments and can be used for detailed modelling of seismic response of CM masonry structures and further research

RC frames with masonry infills with and without openings: experimental and numerical results

RC frames with masonry infills are a widespread construction form in seismically active regions. Under seismic loading, masonry infills are activated in in-plane direction due to the frame deformation. This leads to the complex frame-infill interaction which can cause the failure of masonry infills or whole RC frame structures. Therefore, the in-plane behaviour of in-filled RC frames was a subject of many research projects that aim to predict the seismic performance of infilled frame structures or prevent the damage in masonry infills. Among many parameters that affect seismic response of infilled frames, openings are recognized to play the most significant role as they can affect the stress fields and thus alter the failure mechanism of masonry infills. This paper presents results of the investigation of in-plane behaviour of masonry infilled RC frames with and without openings. In the study, experimental results are firstly presented, and they are afterwards used for validation of numerical model. Further, influence of different opening arrangements on in-plane response of infilled frames is studied in numerical simulations. Results of the study show that openings cause the extensive damage on masonry infills and thus lead to deterioration in in-plane behaviour of infilled RC frames. Additionally, the study reveals that even large openings affect the seismic response of infilled RC frames and that they cannot be easily neglected in design process, which makes the reliable prediction of the seismic response of infilled RC frames complicated. The study points at the urgency of development of innovative solutions that will be able to prevent the damage in masonry infills and simplify their seismic design

Methods and approaches for blind test predictions of out-of-plane behavior of masonry walls: a numerical comparative study

Earthquakes cause severe damage to masonry structures due to inertial forces acting in the normal direction to the plane of the walls. The out-of-plane behavior of masonry walls is complex and depends on several parameters, such as material and geometric properties of walls, connections between structural elements, the characteristics of the input motions, among others. Different analytical methods and advanced numerical modeling are usually used for evaluating the out-of-plane behavior of masonry structures. Furthermore, different types of structural analysis can be adopted for this complex behavior, such as limit analysis, pushover, or nonlinear dynamic analysis.Aiming to evaluate the capabilities of different approaches to similar problems, blind predictions were made using different approaches. For this purpose, two idealized structures were tested on a shaking table and several experts on masonry structures were invited to present blind predictions on the response of the structures, aiming at evaluating the available tools for the out-of-plane assessment of masonry structures. This article presents the results of the blind test predictions and the comparison with the experimental results, namely in terms of formed collapsed mechanisms and control outputs (PGA or maximum displacements), taking into account the selected tools to perform the analysis.info:eu-repo/semantics/publishedVersio