Tassos P. Avraam

Linear and nonlinear analysis of a nonconservative frame of divergence instability

Linear static, linear dynamic, and nonlinear static stability analyses are performed on a geometrically perfect two-member frame subjected to a compressive tangential load at its joint. On the basis of the linear analysis, the frame loses its stability through either a divergence or a flutter type of instability depending on the amount of joint stiffness. In the case of flutter-type instability, the static (linear or nonlinear) method of analysis cannot be employed. By using the nonlinear static analysis we establish that the frame loses its stability through a limit point. The nonlinear static analysis also sheds some light on the jump phenomenon in the critical load which is due to the application of the linear stability analysis. The displacements corresponding to that critical state are extremely large.

A new approach for loads moving on infinite beams resting on elastic foundation

The present work deals with the problem of the dynamic behavior of infinite beams resting on a Winkler-type elastic foundation under moving loads. The beam is subjected to a moving point load traveling with constant speed. Determining the effective length of the beam for a non-moving (static) load, and using the so-called quasi-stationary state of the beam, a solution is proposed with the aid of modal analysis and useful conclusions are obtained. Moving loads have a significant influence on the dynamic behavior of elastic or inelastic solid elements of an entire structure or parts of the structure, while they may produce strong vibrations on such systems, especially when high speeds are reached. The expressions obtained in this work allow the use of the same formulae for any values of speed or damping parameters. The analytical results obtained by the relations presented herein are compared to the ones given by Frýba in the relative chapter of his classic work. Finally, the possible speeds of moving loads that can be reached in the case of such types of beams are estimated and the application field of the gathered relations is determined.

Experimental and Numerical Study on Single-Bolted Cold-Formed Angles under Tension and Compression

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 which 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.

Elastica stability analysis of a simple frame under a follower force

Abstract An elastica stability analysis is applied to a geometrically perfect and elastically supported two-bar frame, which is subjected to a follower compressive load at its joint, eccentrically applied to its column centre-line. The individual and coupling effect of the loading eccentricity and the support elasticity on the stability and postbuckling response is discussed. It is found that for a slight change in the amount of support elastic stiffness, the static bifurcational mechanism disappears and the frame exhibits a monotonically rising equilibrium path.