Abstract | The behaviour of cold-formed steel angle members with bolted connections under compression is usually complicated, whereas not significant number of experimental tests is found in the literature. This study offers a better insight on the issue, by comparing experimental tests with a thorough numerical study, both carried out at the Institute of Steel Structures of NTUA. Significant attention is paid for the elaborate measurement of initial geometric imperfections along the member’s length. An in-house built deformation plotter was designed and upgraded for this reason. The compression failure loads of the experimental tests are illustrated both in graphical and tabular form and compared with similar tests of the literature. The results denote a prediction of the EN 1993-3-1 towards the safe side, for the case of the examined bolted cold-formed angles. A simple formula is proposed for the accurate prediction of angle columns’ buckling deformation, wherein the rigidity of the connection is also included. Finally, interesting conclusions are derived for the numerical simulation of cold-forming effects, as well as the shape and amplitude of the initial imperfect geometry, on the basis of the critical buckling load. Further research is in progress, aiming to capture the stochastic buckling response for the case of bolted cold-formed steel angles.

Abstract | The “Dimitrios Vikelas” athletic center in Ermoupolis of Syros, Greece, consists of two buildings. Building B has a steel superstructure that was constructed approximately 35 years ago. It was initially used as a boat shelter and no design calculations were made. It contains steel columns with varying cross section heights. The spans are bridged via trusses and I-beams. Significant geometrical inconsistencies are noted among the existing steel connections and failures have been recorded as a result of buckling in several beams and bracings during the service life of the athletic center. The current study presents an investigation performed in order to diagnose building structural problems and propose strengthening and intervention measures. The goal of this study was to improve the load-carrying capacity of the structure in order to comply with the current design codes. Moreover, enhancement of the dynamic properties of the strengthened structure was demonstrated using modal analyses. The structural behavior was determined in a more precise manner via non-linear wind time-history and incremental static analyses. The analytical results explain the development of failures in the existing structure.

Abstract | Angle sections are commonly designed to bear only axial force, usually neglecting the additional bending moments resulting from the eccentric connection and the shift of the effective centroid. The current work deals with the capacity of single-bolted equal angle sections made from cold-formed steel. The experimental investigation presented herein includes tension and compression tests that subsequently are compared with the corresponding code provisions. Numerical analyses are also presented based on a detailed finite element simulation. Finally, a reliability analysis is implemented in order to demonstrate the reliability of the design rules for cold-formed steel angle columns. Results indicate a small discrepancy on the strength prediction in general by EN 1993-1-3, as well as by the AISI for slender columns and a more conservative one by EN 1993-1-1. A comparison of the above results is clearly illustrated herein in graphical forms.

Abstract | An extensive literature review of human induced vibrations that flexible footbridges experience is addressed in this study. Qualitative information is comprehensively included herein to provide common methods and code recommendations for the practicing engineers. The parameters affecting the dynamic response of footbridges excited by pedestrians are highlighted. In particular, the synchronous lateral excitation is addressed. This investigation can be valuable for the design criteria selection. In addition, this work contributes to the review of numerous case studies correlating important dynamic characteristics for various footbridge structural types, the variability of which confirms the complexity of the issue. Furthermore, vibration upgrading methods are described, focusing on applications of tuned mass dampers and remarkable conclusions are drawn.

Abstract | The New Faliron steam-electric station, the first one in Greece, is a listed historical building. The initial structure was constructed at the start of the 20th century but a number of interventions followed until the 1960s. The structure was built with natural stone masonry, steel trusses and floors (with jack arches and joist fillers) and concrete floors reinforced with twisted cold formed rebars. The 12.5m high masonries practically lack any lateral restraints while large openings (doors, windows) exist. This paper presents brief information on the history of the structure, phases of construction, description of structure (dimensions, types of structural systems, etc), material properties and pathology. In addition, detailed information is presented regarding the assessment performed in accordance with the current code specifications (Eurocodes), including seismic actions. Especially for the masonry, a detailed finite element model was developed, whereas the seismic forces were evaluated through alternative methodologies (modal response spectrum analysis per EC8 and time history analyses). For the assessment of the RC part a displacement based methodology was applied as it is restrained by the surrounding masonry walls. From the assessment analysis, useful conclusions are drawn regarding the seismic performance of high masonry structures without lateral restraints and the behaviour of similar industrial structures under seismic effects.

Abstract | This work deals with the static and dynamic stability analysis of imperfect partially-sway frames with non-uniform columns. The examined two-bar frames are elastically supported and subjected to an eccentrically vertical load at their joint. Through a linear stability analysis, the effect of the taper ratio of the column cross-section on the buckling capacity of the partially-sway frame is thoroughly discussed. Using a non-linear method an accurate formula has been established for determining the exact asymmetric bifurcation point associated with the maximum load carrying capacity. These findings have been re-derived more readily using Catastrophe Theory (CT) and considering the frame as a one degree-of-freedom (1-DOF) system through an efficient technique. A local analysis allows us to classify, after reduction, the total potential energy (TPE) function of the system to one of the seven elementary Thom׳s catastrophes (with known properties) and to obtain static and dynamic singularity as well as bifurcational sets. It has been found that geometrical and loading imperfections, which are always present in structural engineering problems, have a significant effect on the dynamic buckling loads. The efficiency of the present approach is illustrated via several examples, while results from finite element analyses are in good agreement with the analytical solution presented herein.

Abstract | A nonlinear static analysis is performed on an imperfect elastically supported two bar frame, which is subjected to a concentrated vertical load eccentrically at its joint. The column has a variable cross-section whereas the girder has a uniform cross-section. The variation ratio of the column cross- section is extensively investigated in combination with other geometric parameters (ratios of lengths and moments of inertia between column and girder) as well as loading parameters (loading eccentricity). Following a simplified procedure where the horizontal stiffness of the frame is modeled by a spring at the joint of the frame, it has been found that the developed axial force in the girder can be neglected (insignificant deviation of the exact results). Nonlinear finite element analysis is performed to verify the analytical results.