169 publications from this institution
Praca pierwszego z autorow (S.J.) byla cześciowo finansowana z Grantu KBN Nr 7 T07A 04318 oraz Grantu Rektorskiego PW pt.: ”Modele konstytutywne hipersprezystych materialow gumopodobnych w ramach teorii duzych odksztalcen. Identyfikacja parametrow materialowych i implementacja numeryczna w systemie ABAQUS.” Prezentowane w pracy wyniki obliczen zostaly uzyskane z wykorzystaniem zasobow komputerowych Centralnego Ośrodka Informatyki Politechniki Warszawskiej.
The present paper outlines the results of tests performed on bituminous mixtures made by applying WMA, typical and modified bitumens. The mixtures AC 16 and SMA 8 were tested in respect to the compactibility (in a gyratory press and PBS cylinder compactor), water resistance, fatigue resistance, resistance to low-temperature cracking (through the TSRST method), complex modulus in a broad scope of frequencies, and crack propagation in the SCB apparatus. The impact of the technological and long-term ageing was taken into account. All tests were performed on the reference specimens and the specimens with WMA bitumens compacted at the temperature lower than the standard compaction temperature for a given mixture by 20°C and 40°C respectively. It has been proved that reducing the compaction temperature by 20°C is possible without deteriorating the mixture parameters. Moreover, in case of reducing that temperature by 40°C the majority of requirements have been met as well. The tests have confirmed in broad scope good functional characteristics of warm mix asphalts.
When designing embankments on a soft ground improved with columns (rigid inclusions) and with a geosynthetically reinforced load transfer platform (LTP), the methods of determining strains in reinforcement reduce the spatial problem to a two-dimensional one, and analytical calculations are carried out for reinforcement strips in the directions along and across the embankment. In addition, the two-dimensional FEM models do not allow for a complete analysis of the behavior of the reinforcement material. The aim of this research was to analyze the work of the membrane in the 3D space modeling of the LTP reinforcement, depending on the interaction with the column, the shape of the column’s cap, the value of the Poisson’s ratio, the value of the stiffness of the elastic foundation (subgrade reaction k) modeling of the soft soil resistance between the columns and the load distribution over membranes that model the reinforcement. The membranes were modeled in the framework of the theory of large deformations using the finite element method and slender shell elements as three-dimensional objects. This modeling method allowed for the analysis of the behavior of the LTP reinforcement in various directions. The conducted analyses showed, among others, that in the absence of soil resistance between the columns, regardless of the shape of the cap (square, circle), the greatest strains are located near the edge of the cap in the diagonal direction between the columns.
Welding is the most important joining technique and offers the advantage of customizable plate thicknesses. On the other hand, welding causes residual stresses and deformations influencing the load carrying capacity. Their consideration in the design requires simple and fast models. Though welding simulation has contributed to accurately access to these values nowadays, their application to large components remains still in a less practicable range. Nevertheless, many studies emphasized the need to make corrections in recently available simplified models. Especially the influence of residual stresses seems somewhat overestimated in many cases if comparing conventional structural steel S355 and high-strength steel S690. In times of computer-aided design, an improved procedure to implement weld-inducted imperfections appears overdue. This will be presented in two parts. The first part illustrates the potential influence of post-welding imperfections exemplified for weak axis buckling in comparison with the general method in accordance with Eurocode 3. Residual stresses and initial crookedness were varied systematically in order to produce a scatter band of capacities. An approach to characterize the borders of these imperfections was untertaken before that. The excessive scattering of reduction factors for the load bearing capacity demonstrates the importance of these variables. Results were finally evaluated against advanced simulation models which will be further detailed in part two of this contribution.
The formulations of tasks modelling embankments on soft soil, improved with columns and with reinforced load transfer platform (LTP), differ significantly. One of these differences is the distribution of equivalent load modelling part of the load carried by the LTP reinforcement and soft soil. This article analyses the influence of the nature of the load-modelling linear function, i.e., inverse triangular, uniformly distributed and triangular, as well as intermediate distributions. In total, 41 distributions of equivalent load were considered, and the results of the obtained deflection functions were compared with the measurement results of reinforcement deflection for 5 cases of experimental research available in the literature. A measure of the accuracy of mapping the reinforcement deflection curve was proposed as a relative error in relation to the deflection curve resulting from experimental measurements. Based on the analysis of the mapping error, it was determined that among the three commonly used distributions, the inverse triangular distribution shows the best fit in most of the analysed cases. However, not in every single case this is the distribution leading to a solution that best describes the behaviour of the geosynthetic reinforcement.
No abstract is provided for this article.
In the paper a general approach to modelling of anisotropic linear viscoelastic material properties is presented. Rychlewski's (1983) spectral decomposition theorem is used and one dimensional relaxation functions of linear viscoelasticity model is adopted to eigenvalues of stiffness tensor and named Kelvin relaxation functions. Proposed model was implemented in the FEM system Abaqus on the example of transversely isotropic and isotropic material. On the basis of experimental data available in literature, models were calibrated and verified. Constitutive relations were used in the complex boundary value problem modelling standard rutting test used in road sector to assess the resistance of asphalt mixtures to rutting.
This article presents the results of a systematic comparison of predictions of the thin-walled beam theory and shell theory in the context of bending of elastic thin-walled beams with an open or closed cross-section. The results for shell theory were obtained using FEM and the ABAQUS/Standard program. The bending task of the thin-walled beam was decomposed into the task with a symmetrical and anti-symmetrical loading, so that the bending and torsion of the thin-walled element would be better visible. In order to objectify the comparison, two coefficients characterizing the mutual similarity of functions were introduced: root mean square deviation coefficient determined for the selected cross-section (in relation to the entire contour) and a coefficient determining the maximum relative difference of a given quantity. The comparison was made for both the stress and the displacement state.
This paper attempts to verify the Eurocode's buckling resistance criteria in case of rolled I‐ and H‐sections in monoaxial bending about their major axis using finite element simulations and two imperfection modelling techniques, namely a) using the equivalent geometric imperfection concept in which the effect of material and geometrical imperfections is represented by an equivalent minor axis bow amplitude and the lowest eigenmode imperfection profile, and b) the separate inclusion of material and geometrical imperfections. In the latter approach, material imperfections are based on the standard rolled residual stress patterns consisting of compression/tension peak values dependent upon the h / b ratio. Moreover, the geometric imperfections are included as the tolerance limit of steel I‐section rolled products. Common and higher grades of steel products are considered. The finite element shell model is utilized and built within the ABAQUS software. The Eurocode's resistance criteria are verified by using the results of FEM simulations. An impact of the moment gradient on the member buckling resistance as well as the plateau limit evaluation and the resistance increase as a result of large twist rotations accounted for are assessed. Remarks in relation to analytical formulations presented in Eurocode 3 are drawn.
No abstract is provided for this article.
W artykule przedstawiono wyniki badań zależności pomiędzy stanem technicznym nawierzchni, wyrażonym parametrem równości podłużnej IRI, a wynikającymi z niego zmianami nacisków osi pojazdów ciężkich. W tym celu wykorzystano wyniki pomiarów wykonanych ugięciomierzem laserowym TSD, który wśród mierzonych parametrów rejestruje m.in. profil podłużny nawierzchni oraz naciski osi pomiarowej. Na podstawie danych zgromadzonych podczas rutynowych pomiarów, wytypowano odcinki reprezentatywne do badań, a wyselekcjonowane dane poddano analizom statystycznym. Pod uwagę brano zarówno wyniki pomiarów równości jak i powiązane z nimi naciski osi pojazdu. Omówiono zagadnienie równości podłużnej w kontekście wymagań stawianym nawierzchniom drogowym, a także określono stopień korelacji wskaźnika IRI z zarejestrowanymi naciskami osi pojazdu pomiarowego. Określona została ilościowa ocena wpływu nierówności na wielkość nacisków pojazdów ciężkich, uzupełniona o analizę zmian trwałości nawierzchni asfaltowych opartą na uzyskanych danych.
An interaction of uniaxial bending and axial compression occurs very often in engineering practice and has been widely described in clause 6.2 of Eurocode 3.There are appropriate formulae given to verify the design cross-section resistance of steel structural members.Numerical aspects of constructing the cross-section resistance interaction curve of I-sections are presented in this paper through numerical modelling of the behaviour of stocky beam-columns with the relative slenderness ratio of 0.2 that distinguishes the range of characteristic values of the cross-section resistance and the member buckling resistance.Numerical study was carried out with respect to hot-rolled wide flange HEB/HEAA sections.The case of combined planar bending about one of the section principal axis (y or z) and axial compression was considered.The scope of numerical research includes different cross-section classes from class 1 to class 4. In case of cross-sections from class 1 to class 3, Geometrically and Materially Nonlinear Analysis (GMNA) is carried out.As far as class 4 cross-sections are concerned, Geometrically and Materially Nonlinear with Imperfections Analysis (GMNIA) is carried out in which geometrical imperfections due out-of-flatness deformations of section plate components are taken into account in the form of first local buckling mode.Plate section components are modelled using Finite Shell Elements (FSEs).FSE modelling technique using ABAQUS/Standard library is utilized.Numerical results in the form of interaction diagrams are compared with those of analytical ones presented in Eurocode 3. Differences occurring between the results from conducted FE analysis and those obtained with use of Eurocode's interaction formulae are discussed and factors causing these differences are outlined.Concluding remarks are drawn.
This paper analyzes the influence of geometrical and material imperfections on the buckling resistance of welded I-section columns subjected to axial compression through numerical and analytical models. The paper is divided into two parts. The first part recalls a FEM parametric study of members under compression taking into account different slenderness ratios, as well as different amplitudes of initial crookedness and different values of postwelding residual stresses. The formulation of analytical approach is the main issue of the second part of the paper. Analytical formulation of the buckling resistance is based on a statistical hypothesis of the minima value approach, called the Marchant-Rankine’s-Murzewski approach (M-R-M). Calibration of imperfection factors included in the analytical formulation is made using the results of FEM simulations performed in the first stage of research investigations.
In the presented paper the local instabilities occurring in compression test of perforated thin-walled bars of low slenderness are observed using digital image correlation system ARAMIS. The tested samples slenderness is so low, that from theoretical point of view we are dealing with compression tests of some perforated shells. The samples are made from typical low carbon steel, which has to be treated as elasto-plastic material. Because of that, the final geometry of the sample (after unloading) is also analysed giving a good data for calibration of the theory of elasto-plasticity for large deformations. In analysed cases the total strain values are not exceptionally large, while local rotation (and permanent deformations) have significant values.
No abstract is provided for this article.
