John Ch. Ermopoulos

Mathematical modelling of column base plate connections

Abstract Based on classical methods a design procedure is proposed for the derivation of M-ϕ curves of column base connections. Besides, a new simple formula is also proposed, which describes with adequate accuracy the relation between moment and rotation, and all the necessary coefficients of this formula are given for each particular case. Introducing this formula into equilibrium equations of any frame and using the appropriate M-ϕ curves, a more accurate analysis of the frames can be carried out, with a better approximation for the support conditions, regarding the assumption of fully pinned or fixed supports.

Equivalent buckling length of non-uniform members

Abstract The non-linear equilibrium equations of framed non-uniform members under compression are established for non-sway and sway mode. The models considered are similar to those proposed by EC3 Annex E for uniform members. Using an iteration procedure the critical loads and the corresponding equivalent buckling lengths are calculated, while results are presented in tabular and graphical form, to make direct use from practising engineers easy.

Slope-deflection method and bending of tapered bars under stepped loads

Abstract The equations of the slope-deflection method for tapered bars compressed by concentrated loads applied at various locations along their axes are formulated, and analytical expressions of stiffness and carry-over factors are obtained. The variation law for the moment of inertia chosen covers mainly members of steel structures. For the same compressed bars considered with fixed ends or fixed-hinged ends, the analytical expressions of the multiplication factors of the fundamental bending moments due to transverse loads (distributed or concentrated) are established. Utilizing all these factors, varying stiffness members are introduced as whole linear elements to the equilibrium equations of plane or space frames, and there is no need to divide them into smaller parts.

Buckling length of non-uniform members under stepped axial loads

Abstract In this paper an axially compressed non-uniform column connected with beams at its two ends is studied. The stepped axial loads act eccentrically on the column at intermediate points. The non-linear equilibrium equations of this model are established in the case of non-sway and sway mode, respectively. Using these equations and following an iteration procedure, the equivalent buckling length coefficients and the corresponding critical loads are obtained and the results are presented in an easy to use graphical form.

Buckling length of framed compression members with semirigid connections

Abstract The system of nonlinear equilibrium equations in the deformed state of framed compression members is expressed and methodology for the computation of their corresponding buckling length is proposed. The connections of the bars are considered to be semirigid and this is done by means of nonlinear rotational and translational springs. The present analysis covers both sway and nonsway modes, and with the aid of a specially prepared computer program, one can plot diagrams of the buckling length of framed compression members for various typical forms of bolted or welded joints.

Stability of battened columns with and without taper

Abstract In this investigation built-up columns with a linear variation of depth under various support conditions are analysed as rigid-jointed frameworks. A rigorous analysis for determining critical loads allows formulae to be established for buckling load estimates of practical importance. The individual and coupling effects on the critical loads are assessed for a variety of parameters such as: degree of nonuformity, number of panels as well as stiffness and length ratios of component members. The proposed solution technique is demonstrated with examples.

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.

Stability Analysis of Curved Cable-Stayed Bridges

Publisher Summary This chapter investigates the stability behavior of a curved cable-stayed bridge with a variety of geometric parameters, including the radius of the curved bridge deck. In recent days, cable-stayed bridges have become more popular due to their pleasant aesthetic and their long span length. When the span length increases, cable-stayed bridges become more flexible than the conventional continuous bridges and therefore, their stability analysis is essential. A three-dimensional finite element model is used in which the eigen-buckling analysis is applied to find the minimum critical loads. The numerical results first indicate that as the radius of the bridge deck increases, the fundamental critical load decreases. Furthermore, as the radius of the curved bridge deck becomes greater than 500 m, the fundamental critical loads does not decrease significantly and they approach those of the bridge with straight bridge deck. The comparison of the results between the curved bridges with various radiuses and that of a straight bridge deck determines the curvature effects on stability analysis.

Stability analysis and interaction surfaces of frames carrying crane girders

Abstract The equilibrium equations of a frame, in the deformed state, with either hinged or fixed supports, carrying a crane girder, are established. The elastic critical combinations of a concentrated (travelling) and a uniform loading are calculated for the geometrical characteristics that are most often encountered, and the corresponding three-dimensional diagrams presenting the interaction surfaces are plotted. In order to minimize the time needed to calculate the frames elastic critical loads, a simple but very reliable formula is proposed.