Ioannis Vayas

On the rotation capacity of moment connections

Abstract The paper presents an analytical method for the determination of the rotation capacity of moment connections, based on the component method from prEN 1993-1-8. From test results and numerical simulations, simple analytical expressions for the deformation capacity of the components are derived. These values are subsequently used for the determination of the rotation capacity of the complete joint. Comparisons with tests on whole joints indicate a good agreement between analytical and experimental results. The method is fully consistent with the present rules of prEN 1993-1-8 and extends them to the numerical estimation of the rotation capacity.

Stability and ductility of steel elements

This paper presents a method for the simulation of the behaviour of steel structural elements both before and after the attainment of the ultimate load. It is based on a strain-oriented formulation of the governing relations usually applied to stability problems. Accordingly, the response of elements subjected to specific strain conditions is determined. Several types of elements, including single plate panels, transversely loaded beams, axially loaded columns and compressed stiffened plates with imperfections, are investigated. The analytical results are compared with experimental ones. Various modes of failure with different characteristics in the post-critical region are detected. The elements examined show that if bending and plate buckling prevail, the failure mode is ductile, while in the case of global buckling and lateral torsional buckling, a nonductile failure is expected. The method may serve for both stability and ductility evaluations of steel elements, which are needed if the design format includes a direct comparison between ductility supply and ductility demand for structural elements.

Fatigue Analysis of Moment Resisting Steel Frames

A procedure for the fatigue assessment of steel building structures subjected to earthquakes is presented. The procedure constitutes an extension of the present, high-cycle, fatigue assessment to cases of low-cycle fatigue. It may serve as a basis for the introduction of a fatigue limit state in the earthquake design of steel structures. It may be also used for the damage assessment of existing steel buildings subjected to past earthquakes. By means of parametric studies, the effects of various parameters on the fatigue susceptibility of several moment resisting steel frames are studied. The influence of a number of parameters such as the type of ground motion, type of structural typology, local fatigue behaviour, overall frame design and semi-rigidity of joints on the susceptibility to damage are investigated.

Design of steel frames with slender joint-panels

The behaviour of thin-walled slender joint-panels in knee joints of steel frames and its influence on the overall behaviour of moment-resisting frames is studied. The joint resistance is supplied by three different mechanisms. The first mechanism is the shear buckling strength of the joint-panel, which is dependent on its slenderness. The second mechanism is the tension field strength that is dependent on the relation between the dimensions of the joint-panel and its surrounding flanges. The last mechanism is the resistance due to the frame action of the joint-panels surrounding frame. Design formulae for the evaluation of the joint resistance are derived. Monotonic and hysteretic rules for the description of the joint characteristics are proposed. Frame analyses considering the joint deformability are performed. The analytical results are compared to experimental results of joints subjected to cyclic loading.

Behaviour of thin-walled steel frame joints

Abstract Welded thin-walled plate girders play an increasingly important role in steel structures. The provisions of modern codes with regard to design are restricted to the span region between supports. The design of the joint panel is still governed by the buckling load, thus making the application of costly stiffeners necessary. Experimental investigations on such joints have shown that their strength is well above this load, due to the development of a tension field action. To ensure an effective design, it is necessary to make allowance for the postbuckling reserve of strength and to identify possible collapse mechanisms. The present paper provides a method for calculating the carrying capacity and the deformation characteristics of the joints. Static and kinematic limit state models are presented which allow the ultimate strength to be determined from closed formulae. The predicted values are in reasonable agreement with experimental results.

Torsional rigidities of open stiffeners to compression flanges

Abstract A critical review of code provisions and other proposals concerning the requirements for torsional rigidities of flat stiffeners to compression flanges is made. The relevant rules are investigated by means of 65 tests on compressed, stiffened plates with various loading and supporting conditions. A new design rule for the determination of the dimensions of flat stiffeners, based on their ultimate stress and the ultimate stress of the stiffened plate, is proposed and relevant design charts are given.

Could Cod Serve as Fracture Criterion in Case of Marble

An experimental study is presented here related to the behaviour of U-notched prismatic Dionysos marble specimens subjected to either three- or four-point bending or to direct tension, in an effort to investigate the variation of the Crack Opening Displacement (COD) versus the externally applied load. The purpose of the study is the determination of an-easy-to-use and reliable tool that could serve as fracture criterion in the hands of engineers working for the restoration projects of various ancient monuments as well as in every day’s practical applications.

Influence of Joint Flexibility in the Seismic Performance of Moment Resisting Steel Frames

Semi-rigidity in beam-to-column joints of steel frames has increasingly attained attention during the last years. For braced frames it was repeatedly demonstrated that semi-rigid joints may lead to remarkable material savings compared to simple joints, mainly due to a beneficial moment distribution along the members and provision of higher rigidity to satisfy serviceability requirements. Such an evidence is still lacking for moment resisting frames, where joint flexibility may lead to higher lateral deformations and increased 2nd order effects.

Restoration and Strengthening Techniques for Ancient-Greek Monuments

ABSTRACT Beginning from the late 1970s, at the Acropolis of Athens, and from the 1990s, in many other significant archaeological sites around Greece (Epidaurus, Arcadian Bassai, Nemea, Olympia, Delos et al.), numerous restoration projects of ancient constructions have been carried out, mostly concerning classical cult temples. The projects were supervised and carried out by multi-disciplinary groups (archaeologists, architects, engineers, conservators, stone-masons etc.), on the basis of common principles. The combined effort of so many experts, as well as the talent of individuals in all rungs, often led to innovative intervention and strengthening techniques, which can be applied for the restoration of dry-stone monuments in general. Many of these techniques, and various scientific benefits derived as side-results from the restoration projects, are presented in this article synoptically. Despite the concise way of the subject presentation, and the diversity of nature of the aforementioned techniques, it is quite clear that all these techniques are firmly based on two common characteristics of the restoration projects: the multi-disciplinary approach of every intervention, and the respect and preservation of the original structural system of the monuments.

FUSEIS PIN LINKS: INFORMATION BROCHURES AND DESIGN OF CASE STUDY

Abstract. In the frame of the INNOSEIS research project, which is funded by RFCS, information documents for INERD-pin and FUSEIS-pin links have been produced by NTUA for dissemination to all partners of the construction sector such as architects, structural engineers, construction companies, steel producers and all potential decision makers of the construction sector. For each of the two systems, an approximately 40-page information brochure has been drafted in English. They contain a description of the main features of the system, overall dimensions, preferred structural materials, range of sizes, member shapes, typical cross sections and limitations, possible arrangements for conceptual design, recommended structural details etc. and indicative application examples of selected building structures. In addition, information is given regarding the non-linear force-deformation characteristics and ductility/strength capacities of the systems, the hysteretic behavior of elements under cyclic loading, including rules for stiffness and strength degradation. Finally, pre-normative q-factors are proposed and reference is made to application examples in design practice, previous publications and literature.