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DUCTILITY AND LOAD CARRYING CAPACITY PREDICTION OF STEEL BEAM-TO-COLUMN CONNECTIONS UNDER CYCLIC REVERSAL LOADING

The economy and reliability of steel-framed buildings in seismic areas depend basically on the hysteretic behaviour of its individual components, such as members and joints. With reference to the latter, despite the recent semi-continuous frame approach (which appears generally very convenient for the design of low- and medium-rise steel buildings), the present state of knowledge does not allow for a complete understanding of the behaviour and the low-cycle fatigue life of beam-to-column connections under dynamic loads. This paper presents a criterion for the definition of the low-cycle fatigue strength of steel connections, and proposes two approaches for the design of steel frames in seismic zones via the assessment of the fatigue damage, which is evaluated alternatively on the basis of either the ductility or of the load carrying capacity.

Non-linear cyclic model of top and seat with web angle for steel beam-to-column conections

The use of steel connections is inherent of every structural steel building. Savings in connection costs as well as improved connection quality has an impact on all types of buildings. Several analytical models have been developed in the last years to represent the cyclic behaviour of beam-to-column connections. However very few models have been substantiated by test results under cyclic loading conditions. For that reason, the implementation of such models in general-purpose structural analysis programs for steel structures under seismic actions, is in some cases complex and in others impossible. This paper is concerned with a non-linear cyclic model of top and seat with web angle for steel beam-to-column connections, with damage accumulation and bolts in cyclic shear. Numerical results are compared with experimental tests in order to evidence the capabilities and the accuracy of the proposed numerical model.

Low cycle fatigue strength assessment of cruciform welded joints

Abstract This paper presents the results of an experimental study on the low cycle fatigue strength of cruciform welded joints. Tests were performed on 22 specimens of three different categories, namely full-penetration, partial-penetration and fillet welded cruciform joints. These tests consisted basically of imposing on each specimen a constant amplitude cyclic displacement history in the plastic range of the material behaviour. The experimental testing procedure is described and the results are presented. The unified approach for low and high cycle fatigue strength assessment proposed by Ballio and Castiglioni [1] is applied to the test results. Such approach leads to the conclusion that the same set of Wohler ( S – N ) lines [2] usually given in recommendations [3] for high cycle fatigue can be also applicable in the low cycle fatigue range. It is demonstrated that the proposed damage model allows prediction of the number of cycles to failure for the specimens, at each given cycle amplitude, with a notable accuracy.

Experimental response of top and seat angle semi-rigid steel frame connections

The current study is concerned with the structural response of typical semi-rigid steel beam-to-column joints. In particular, the behaviour of bolted cleat angle connections is investigated under different loading conditions, both monotonic and cyclic loading being considered. Besides, aiming at assessing the susceptibility of the analysed connection typology to low-cycle fatigue, the latter has been referred to both constant and variable amplitude deformations. Therefore, 15 full-scale tests have been carried out by comparing the performance of specimens with reference to three different sizes of column member as well. Obtained results are provided in terms of moment-rotation relationship, dissipated energy and strength degradation per cycle. As expected, outcomes show that the main sources of inelastic deformation are located into cleat angles, which constitute the most influential component. As a consequence, the column size has a limited effect on the whole hysteretic response of the joint, while results appear to be strongly dependent on the applied deformation history.RésuméDans cet article, on étudie le comportement structurel d’un type de liaisons poutre-poteau semi-rigides. La poutre et le poteau sont liés par des cornières. Les procédures de chargement que l’on a suivies incluent plusieurs cas de chargements monotones et cycliques. Pour déterminer le comportement de ces liaisons à la fatigue (petit nombre de cycles et grandes déformations plastiques), on a adopté plusieurs procédures de déplacements à amplitude constante. L’étude a été appliquée à trois types de poteaux. Comme on a considéré cinq liaisons différentes pour chaque type de poteau, un total de quinze liaisons ont été essayées. Les comportements étudiés ont été représentés sous forme de diagrammes moment—rotation, de l’énergie dissipée et de la dégradation de rigidité, et ont été comparés entre eux. Comme prévu, la déformation plastique a eu lieu surtout dans les cornières, lesquelles sont donc les éléments les plus importants de la liaison. La dimension de la section du poteau influence très peu le comportement histérétique de la liaison, lequel, d’autre part, dépend des déplacements précédemment appliqués.

A model for predicting the failure of structural steel elements

Abstract A numerical model for predicting the failure of structural steel elements subjected to cyclic loading is presented. The cyclic response is considered to be inelastic to seismic loading. The model for damage accumulation is expressed as a function of the inelastic strain and the dissipated hysteretic energy. It is shown that damage accumulation does not depend on the maximum strain but does depend on the inelastic deformation. The numerical model is used for the evaluation of the behavior coefficient of steel structures.

Analysis of rectangular‐shaped collar connectors for composite timber‐steel‐concrete floors: Push‐out tests

Abstract The paper deals with the experimental analysis of an innovative connection system for composite timber‐steel‐concrete floors. The connection device consists of a collar composed by two or more parts, astride the timber beam, bolted together at adjacent wings. A rubber layer is interposed at the collar‐beam interface. The slipping action transmission is guaranteed by the superior wings of the collar or by a steel stud, purposely welded to the collar in the upper part, which are immersed in the concrete cast. In this paper push‐out monotonic tests on several rectangular‐shaped configurations of the connection system are presented, being part of a more comprehensive experimental campaign, aimed at the system performance evaluation and optimization. First, the preliminary numerical analyses, meant to define both the best geometrical characteristics of the specimens and the configuration of the testing apparatus, are illustrated. Then the push‐out tests, considering subsequent improvements of the conn...

Hysteretic behaviour of steel members: Analytical models and experimental tests

Abstract The seismic performance of steel structures is highly dependent on the hysteretic behaviour of their members. The assessment of this behaviour cen be done by means of experimental tests and the use of analytical models that take into account the main phenomena involved in a non-linear response. An overview of experimental methodologies for cyclic tests, including a more detailed investigation of the ECCS recommendations, is presented. Analytical models for the simulation of hysteretic behaviour and comparisons with some experimental results are shown. Finally, it is demonstrated how a cumulative damage model for failure assessment allows for the evaluation of q factors for structural design.

Behaviour of bolted composite joints: experimental study

Abstract In this paper, an experimental program on bolted end-plate type column-base joints is reported. Composite base columns are investigated under cyclic loading to study and characterise the typical cyclic behaviour modes of these types of joints. Details of the specimens, test results and the evaluated experimental data of the tests are presented. The tests also had a scope of investigating the influence of several parameters (the application of different bolt grades, the thickness of the end-plate, the type of the column and the influence of the reinforcement). The cyclic behaviour of the joints is studied by the moment–rotation relationships, where cyclic curves are used to evaluate the cyclic parameters of each specimen. On the basis of the evaluation of the measured data and the calculation of the cyclic characteristics, the typical cyclic behaviour modes of the studied connection type are determined and presented.

Low cycle fatigue testing of semi-rigid beam-to-column connections

Publisher Summary A research is carried out to investigate the cyclic behavior of beam-to-column connections. Three different typologies were tested, which represent frequent applications in steel construction. The specimens are submitted, in a multi-specimen testing program, to constant amplitude displacement histories, in order to develop a cumulative damage model. Such a model is based on the Ballio-Castiglioni hypothesis and Miners rule, and lead to the assessment of possible classes of fatigue resistance for the examined typologies of beam-to-column connections. Based on the experimental results of this and previous research programs carried out, a general failure criterium is proposed for steel components under low-cycle fatigue. This chapter presents preliminar results of a research program on low-cycle fatigue of semi-rigid beam-to-column connections. After identifying a limited number of structural steel details, they were realized and tested under low cycle fatigue. The aim of the research is to try to establish classes of (low cycle) fatigue resistance for connections, similar to those existing for structural details under high cycle fatigue.

Behaviour of steel beam-to-column joints under cyclic reversal loading: an experimental study

An experimental study was carried out to investigate the low-cycle fatigue behaviour of beam-to-column joints. Several full-scale specimens were tested, in a multi-specimen testing program, using constant amplitude displacement histories, to develop a cumulative damage model. This model is based on S-N line approach and, although proposed here for low-cycle fatigue, was derived and is valid also for high cycle fatigue. Possible definitions of parameter S , as well as, failure criteria for the definition of N , are compared. The influence of the definition of parameter S on the value of the slope of the S-N line is discussed. A statistical method for the assessment of the S-N lines, based on a given probability of failure with reference to suitable levels of safety and reliability of the structural joints, is also presented.