Marian Giżejowski

Finite element modelling of the behaviour of a certain class of composite steel-concrete beam-to-column joints

Abstract Beam-to-column end-plate joints can be classified as rigid (fully restrained), semi-rigid (partially restrained) or pinned, depending on their type, configuration and the connector arrangement. Fully restrained joints are needed for rigid frames in which there is assumed that the frame joints have sufficient rigidity to maintain - under the service state - the angles between the intersecting members, ensuring the full moment transfer. In contrast in semi-continuous frames, partially restrained joints are characterized by relative rotations occurring between the intersecting members so that the bending moment can only be transferred partially. In recent years, the idea of using partially restrained, unstiffened joints in building structures has gained momentum since this idea appears to be more practical and economical. Semi-continuous frames can resist actions by the bending moment transfer in partially restrained joints, allowing in the same time for a certain degree of rotation that enhances the overall ductile performance of these structures. One of the effective ways that affects ductility of end-plate beam-to-column joints is to use thinner end-plates than those used nowadays in practical applications. In the current study, a certain class of steel-concrete composite joints is examined in which the thickness of end-plates is to be equivalent to approximately 40-60% of the bolt diameter used in all the composite joints investigated in the considered joint class. This paper is an extension of the authors’ earlier investigation on numerical modelling of the behaviour of steel frame joints. The aim of current investigations is to develop as simple as possible and yet reliable three-dimensional (3D) FE model of the composite joint behaviour that is capable of capturing the important factors controlling the performance of steel-concrete end-plate joints in which the end-plate thickness is chosen to be lesser than that used nowadays in conventional joint detailing. A 3D FE model constructed for composite joints of the considered joint class is reported in this paper and numerical simulations using the ABAQUS computer code are validated against experimental investigations conducted at the Warsaw University of Technology. Comparison between the nonlinear FE analysis and full scale experimental results of the considered class of composite joints is presented which conclusively allows for the accuracy assessment of the modelling technique developed. Comparison between the FE results and test data shows a reasonable agreement between the numerical FE model developed and physical model of experimentally examined joint specimens. Finally, practical conclusions for engineering applications are drawn. Streszczenie Wezły w konstrukcjach ramowych mozna sklasyfikowac jako sztywne (o pełnej nosnosci), podatne (o niepełnej nosnosci) lub nominalnie przegubowe, w zaleznosci od ich typu, konfiguracji i rozmieszczenia łaczników. Wezły o pełnej nosnosci sa wymagane dla ram sztywnych, w których załozono, ze wezły zapewniaja pełne przeniesienie momentów zginajacych z rygli na słupy. Natomiast w ramach z wezłami podatnymi o niepełnej nosnosci, wezły sa charakteryzowane przez wzgledne obroty pojawiajace sie pomiedzy łaczonymi elementami tak, ze moment zginajacy moze byc przeniesiony tylko czesciowo. W ostatnich latach, idea wykorzystania bezzebrowych wezłów podatnych zyskuje coraz wieksze zastosowanie w praktyce inzynierskiej. Ramy niepełnociagłe moga przeciwstawiac sie oddziaływaniom dzieki wezłom podatnym o niepełnej nosnosci, które przenosza momenty zginajace przy jednoczesnym pojawieniu sie lokalnego obrotu elementów przerwanych w wezle. Jednym z efektywnych sposobów zwiekszajacych ciagliwosc wezłów typu rygiel - słup z blachami czołowymi jest zastosowanie blach o grubosci mniejszej niz stosowana obecnie w praktyce inzynierskiej. W niniejszej pracy, poddano analizie grupe wezłów zespolonych stalowo-betonowych, w których grubosc blachy czołowej stanowi około 40-60% srednicy srub. Praca stanowi rozwiniecie zagadnien opracowanych przez autorów w powoływanych pracach wczesniejszych i dotyczacych numerycznego modelowania zachowania sie wezłów stalowych w konstrukcjach ramowych. Celem rozwazan jest znalezienie prostego i jednoczesnie wystarczajaco dokładnego modelu 3D zachowania sie wezła zespolonego, uwzgledniajacego najistotniejsze czynniki wpływajace na zachowanie sie stalowo-betonowych wezłów doczołowych z blachami o grubosciach mniejszych niz stosowane w rozwiazaniach konwencjonalnych. Przedstawiono model 3D skonstruowany dla rozwazanego typu wezłów zespolonych, przy wykorzystaniu systemu ABAQUS oraz porównano wyniki symulacji numerycznych z wynikami badan doswiadczalnych przeprowadzonych w Politechnice Warszawskiej. Porównanie wyników nieliniowego modelu skonczenie - elementowego z wynikami badan doswiadczalnych wezłów zespolonych w skali technicznej, swiadczy o poprawnosci przyjetej techniki modelowania, jak równiez o zadowalajacej zgodnosci modelu numerycznego z modelem fizycznym elementów badanych doswiadczalnie. Na zakonczenie podano praktyczne uwagi dotyczace innowacyjnego kształtowania i projektowania rozpatrywanej klasy wezłów zespolonych.

Numerical Modeling of Composite Castellated Beams

In modern composite structures, higher steel grades are used for structural steel profiles in order to increase span capacity without an unnecessary increase in the composite floor depth. This tendency results in beams that are more vulnerable to the failure modes that involve either web LSB (local shear buckling) and/or compression flange RDB (restrained distortional buckling). The effects of shear stresses as well as web buckling and post-buckling behavior on the overall beam performance have been investigated both experimentally and numerically in order to resolve the most important behavioral issues of plain-webbed composite beams. Less attention has been paid to investigations of instability effects on the ultimate strength of steel profiles in continuous castellated composite beam systems. In this paper, different finite element techniques are used to investigate the in-plane behavior with use of geometrically linear analysis and the out-of-plane distortional behavior with use of geometrically nonlinear analysis, with both techniques applied to trace the performance of continuous composite beams.

The buckling resistance of welded plate girders taking into account the influence of post-welding imperfections - Part 1: Parameter study

Abstract 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.

Is Accreditation an Opportunity for Positive Change or a Mirage

Accreditation was originally conceived and applied as an assessment tool for the quality of university programs. However, its emphasis shifted to program objectives and learning outcomes from the original prescriptive focus on measurable inputs. Accreditation normally confirms that the institution/department offering a program has established suitable processes and resources to ensure that the required quality and standards are achieved. Through the years, it has become the fundamental quality assurance mechanism for engineering education (Prados et al. 2005; Sarin 2000; Woollacott 2009). Accreditation is an important step in the life of any professional program, especially for international benchmarking. In the case of engineering programs, accreditation by any signatory of the Washington Accord guarantees international recognition, a feature sought after by many colleges of engineering, especially those in developing countries. Accreditation confirms that graduates have attained a recognized academic standing and that they possess the professional competence to practice engineering. In a majority of developed countries, graduation from an accredited program is the primary step toward professional registration; however, in most developing countries, graduation from any engineering program confers sufficient license to practice engineering. In these countries, graduation from an internationally accredited program provides additional recognition and acceptance. The international recognition of an engineering program has become important in recent years and is likely to be promoted by the increasing mobility of engineering graduates. It is particularly important for graduates in developing countries, who aspire either to work in more developed countries or in multinational companies. Graduation from an accredited program assures possible employers of the quality of education of their entry-level professionals. Because employability of graduates is one of the primary indicators of success and ranking of engineering programs, the competition for talented students has inevitably created a strong tendency, almost a necessity, for engineering programs to be internationally accredited. The accreditation requirements of different accreditation bodies may differ in form and detail, but all expect a considerable amount of documentation as the basis for evaluation. The preparation of the documents can be extremely challenging for first-time program presenters; preparation for each revalidation of the accreditation is also a time consuming activity. This paper advocates that, although the accreditation process is very demanding, it provides a great opportunity for a comprehensive review of an academic program. Ideally, the accreditation process should not only improve the program itself, but should also promote the development of the faculty that delivers the program. However, neither of these two objectives is usually achieved in developing countries. The following argument is based on the authors’ extensive experiences in the management and delivery of engineering programs in different institutions and on their involvement in the preparation of accreditation documents. Unfortunately, the accreditation of a program is not, in itself, a guarantee that the spirit intended by accreditation bodies is captured and implemented in the program.

Beam-Column In-Plane Resistance Based on the Concept of Equivalent Geometric Imperfections

Abstract Assessment of the flexural buckling resistance of bisymmetrical I-section beam-columns using FEM is widely discussed in the paper with regard to their imperfect model. The concept of equivalent geometric imperfections is applied in compliance with the so-called Eurocode’s general method. Various imperfection profiles are considered. The global effect of imperfections on the real compression members behaviour is illustrated by the comparison of imperfect beam-columns resistance and the resistance of their perfect counterparts. Numerous FEM simulations with regard to the stability behaviour of laterally and torsionally restrained steel structural elements of hot-rolled wide flange HEB section subjected to both compression and bending about the major or minor principal axes were performed. Geometrically and materially nonlinear analyses, GMNA for perfect structural elements and GMNIA for imperfect ones, preceded by LBA for the initial curvature evaluation of imperfect member configuration prior to loading were carried out. Numerical modelling and simulations were conducted with use of ABAQUS/Standard program. FEM results are compared with those obtained using the Eurocode’s interaction criteria of Method 1 and 2. Concluding remarks with regard to a necessity of equivalent imperfection profiles inclusion in modelling of the in-plane resistance of compression members are presented.

A Consistent Ayrton-Perry Approach for the Flexural-Torsional Buckling Resistance Evaluation of Steel I-Section Members

Abstract Steel I-section members subjected to compression a monoaxial bending about the major axis are dealt with in this paper. The current Eurocode’s design procedure of such members is based on a set of two interpolation equations. In this paper a simple and yet consistent Ayrton-Perry methodology is presented that for beam-columns yields the Ayrton-Perry design strategy similar to that utilized in the steel Eurocodes for design of beams and columns but not used so far for the beam-column design. The results from developed design criterion are compared with those of Method 1 of Eurocode 3 and the Ayrton-Perry formulation of a different format that has been recently published.

Partial Factors in Modelling of Steel Structures Reliability According to Eurocodes / Współczynniki Częściowe W Eurokodowym Modelu Niezawodności Konstrukcji Stalowych

Abstract Problems associated with the estimation of partial factors for structural systems, subsystems and buckling of individual elements are dealt with in this paper. Aspects related to resistance factors for the section resistance and member resistance are in particular referred to. The Eurocode’s approach of resistance partial factor calibration assisted by experimental data for subframe systems is also summarized. Streszczenie Stan graniczny nośności konstrukcji, projektowanej w tradycyjnym podejściu na podstawie efektów oddziaływań jest oceniany z niezawodnościowego modelu szeregowego. Kalibrację współczynników częściowych do nośności przeprowadza się wówczas na podstawie analizy niezawodności pojedynczego elementu konstrukcji (pręta lub węzła). Eurokod stalowy [4] wprowadził zasady projektowania bazujące na bardziej złożonych modelach nośności niż w [8], gdyż stan graniczny można ocenić na podstawie warunku stateczności technicznej podukładu konstrukcji lub w ogólności, jak przedstawia to warunek (2.1) - na podstawie punktu granicznego na ścieżce równowagi wyznaczonej dla nieidealnego modelu całej konstrukcji. Pojawia się pytanie, czy stosowanie do nośności wyznaczonej na podstawie bardziej złożonych modeli mechaniki konstrukcji współczynników częściowych wyspecyfikowanych do oceny nośności pojedynczych elementów prowadzi do bezpiecznych oszacowań. Kalibracja współczynników częściowych w metodzie stanów granicznych może być dokonana przy różnych założeniach wyjściowych. Model niezawodności i ogólne zasady przyjętego w eurokodach rozdziału docelowego wskaźnika niezawodności na składowe odnoszące się do ustalenia obliczeniowych oddziaływań i ich kombinacji oraz do ustalania nośności obliczeniowej zostały podane w eurokodzie [1]. W artykule przedstawiono zagadnienia dotyczące przyjęcia współczynników częściowych do nośności układu lub podukładu konstrukcyjnego. Opisano eurokodową procedurę wykorzystującą wyniki badań doświadczalnych do kalibracji współczynników częściowych do nośności.

Numerical Study of Joint Behaviour for Robustness Assessment

The paper presents studies on numerical modelling of beam-to-column joint behaviour in typical service and exceptional design situations. The complexity of such investigations arises from highly nonlinear effects associated with the prediction of joint performance, such as structural imperfections, large displacements and rotations, inelastic properties of steel and concrete, bonding effects between steel and concrete, and slip between concrete and structural steel, among others. The paper addresses these problems and provides validation of numerical modelling techniques trough comparison with experimental data for joints under hogging and sagging moments.

Example Validation of Numerical Modeling of Blast Loading

This paper reports a follow-up feasibility study on different approaches for numerical modeling of blast loads, implemented recently in a few commercial programs based on finite element method and explicit time integration. Four approaches have been considered including: explicit blast wave representation using fluid-structure interaction (FSI) with 2D and 3D multi-material arbitrary Lagrangian-Eulerian (ALE) formulations, direct application of empirical explosive blast loads on structures, and the most recent, combined method, in which direct empirical loading is applied to a reduced ALE domain. Each of these approaches has its own strengths and weaknesses, although the last one seems to be the most universal. Based on the published experimental data, a benchmark problem was selected, which considers a pressure loading exerted by explosion of near field hemispherical charges on a rigid steel plate. The comparison is done in terms of pressure peaks (overpressure) and time histories of reflected pressure, and reflected specific impulses.

Double Butt, Bolted Connections-Influence of Prestressing

Publisher Summary This chapter presents a project to develop a 3D computational finite element method model of double butt prestressed bolted connections taking into account the effects of bolts, initial gaps, friction, and prestressing force. This model may be used especially for investigation of the connections deformability, also after first slip not taken into account in the method of structures analysis used in the everyday engineering practice. There are some design parameters that are considered: initial yield stress, hardening modulus, friction coefficient, and prestressing force magnitude. To deal with these effects, a finite element model is created. The computational model is developed in the framework of ABAQUS general-purpose program. The connection is discretized with about 7500 3D-isoparametric brick elements. All parts of the connection are separated. Initial gaps are assumed among all of the elastic bodies and later, during the loading process, non-elastic bodies, and the contact surfaces are established. The proposed model is verified by experiments. The 20 specimens that are the connections in technical scale are investigated. Comprising the results obtained theoretically, as well as in experiment, shows that the 20 specimens differ insignificantly; it means that the proposed model can take advantage in workout of simplified models used in everyday engineering practice.