Steel column buckling

Codes of practice rely on the effective length method to assess the stability of multi-storey frames. The effective length method involves isolating a critical column within a frame and evaluating the rotational and translational stiffness of its end restraints, so that the critical buckling load may be obtained.
The non-contradictory complementary information (NCCI) document SN008a (Oppe et al., 2005) to BS EN 1993-1 (BSI, 2005) provides erroneous results in certain situations because it omits the contribution made to the rotational stiffness of the end restraints by columns above and below, and to the translational stiffness of end restraints by other columns in the same storey.
Two improvements to the method are proposed in this paper. First, the axial load in adjoining columns is incorporated into the calculation of the effective length. Second, a modification to the effective length ratio is proposed that allows the buckling load of adjacent columns to be considered. The improvements are shown to be effective and consistently provide results within 2% of that computed by structural analysis software, as opposed to the up to 80% discrepancies seen using the NCCI (Oppe et al., 2005).

Laminated structures find many applications in various engineering fields namely aerospace, bio-medical, civil, marine and mechanical engineering due to easy handling, good mechanical properties and low fabrication cost. Laminated plates with round holes and other openings are extensively used as structural members in aircraft design. These holes are act sometimes as access holes, holes for hardware to pass through, or in the case of fuselage, windows and doors or simply used to reduce the weight of the structure. These laminated structures are often subjected to load in one or more direction in cycles or as intermittent load. Thus there is need to study the failure of these components under bi-axial loading with the view to optimize the shape and lay of the components so as they give maximum service and more life. In this paper bi-axial testing machine is developed to determine bucking load of different materials. Experiments are carried out on cross ply composite under various buckling loads on the bi-axial testing machine. The theoretical results, analytical and experimental results are compared with each other. It is observed that the strength of Bakelite composite plates is higher than glass epoxy laminated composite plate. So Bakelite is more suitable than glass epoxy.

Steel structural elements with variable cross section, made of welded plates, are largely used in the construction industry for both beams and columns in accordance with the stress and stiffness demand in the structure. These types of elements are mainly used for the design of singles storey frames with pitched roof rafters and pinned column base. Rafters and columns can be designed as tapered members made of steel welded plates, respecting the bending moment diagrams for gravitational load combination. Although they are partially restrained against out of plane buckling by side-rails and roof purlins cooperating with sheeting, in current design practice it is quite difficult to evaluate their influence.
This paper deals with nonlinear elastic-plastic analysis and experimental tests performed on tapered beam-columns, parts of portal frames, subjected to both bending moment and compressive axial force. Failure of such members may occur by in-plane bending, local buckling and combination between these two, for members with low non-dimensional slenderness. While for members with intermediate and high non-dimensional slenderness, flexural–torsional buckling, local buckling and combination of these two may occur in function of the web slenderness.
Numerical results will be compared with experimental tests, obtained for a relevant number of specimens, in order to check the reliability of the numerically determined ultimate capacity of the elements. The influence of both lateral and torsional restraints applied on the beam-column will also be discussed.

Fuel can be saved in transportation if vehicles are made from lightweight structural solutions. Web-core steel sandwich plates are such structures and they are also environmental friendly because it is possible to recycle them. However, before a larger use of sandwich plates in industry, a few design aspects need to be understood better. This doctoral thesis reveals the influence of the plate stiffness coefficients on the buckling strength and post-buckling stiffness of the sandwich plates. Furthermore, the influence of corrosion on the material, geometric and strength properties of the sandwich structure is studied. This is performed by experimental and numerical methods.