Horizontal Stiffeners Research Articles

On the Effect of Stiffeners upon the Buckling Strength of Ship Structures

The most ship structures are composed of plate elements. When appropriate stiffeners are furnished on plates, the buckling strength of the plates increase effectively, as well as their bending rigidities.The finite element method has been expanded to analyse the buckling strength of ship structures. While the finite element method is very useful, the size of equations obtained by the method is extremely large.In the paper, a powerful eigenvalue economizer technique was introduced, which reduces the degrees of stability problems. As a basic example of the application, the accuracy of the solution by the technique using the finite element method was examined for several kinds of stiffened plates in relation to the number of degrees of freedom. The authors discussed mathematical meaning of the eigenvalue economizer technique. Variable informations are obtained on variables which are eliminated from the characteristic equation.Finally, the buckling strength of transverse ring of large tanker was analysed, varying the location of stiffeners. It was found that the ship structure without any stiffener buckles under applied load. While, the structure with horizontal and diagonal stiffeners was found not to buckle under the load.

Effect of stiffner on the patch loaded plates

An elasto-plastic large deflection FEM analysis is made on plates subjected to a patch loading to study the strength and failure mechanisms of such plates. To stiffen a plate subjected to a patch load, a horizontal stiffener is often used. In this case, suitability to use a horizontal stiffener to provide the vertical stress must be discussed. This paper presents numerical results on such plates with taking notices to the contribution of the horizontal stiffener. From the analysis, strength and failure mode of the plates according to the plate thickness, existence of the stiffener and so on are found.

Problèmes de perte de charge et de stabilité des grilles de prise d'eau

Definitions of the various screen (trash rack) elements are reviewed, also the eight parameters governing loss of head across a screen. Five of these parameters are solid area s, open area b, length L (see Fig. 2), vertical angle e (Fig. 1) and bar cross-section (Fig. 3), which Thoma and Kirschmer [2] took into account at Munich Institute in 1926 The sixth parameter, horizontal angle θ (Figs. 1 and 4) was studied by Thoma and Spangler in 1928 [3]. Measurements in Situ gave very much higher head losses than in the laboratory, and the explanation for this was provided by Dulnyev [6] and Berezinski [4] and [7], namely the failure to allow for the considerable amount of obstruction due to horizontal screen stiffeners, bracing members, fittings, etc. The seventh parameter, p, is the solid, percentage of the total area, which varies between 20 and 40 % whereas the percentage accounted for solely by upright bars only makes up about 6 to 16 % of the total. The eighth parameter is the residual detritus Kd which indirectly expresses cleaning efficiency. The loss of head across a screen perpendicular to the flow is given reasonably well by formula (1), in which : Kd = 1.1 to 1.2, for a modern automatic screen cleaner (trash rack rake) ; Kd = 1.5, for older designs ; Kf = 0.51, for a rectangular cross-section ; Kf = 0.35, for a circular cross-section ; Kf = 0.32, for an clongated cross-section with semi-circular ends. The function f (L/b) is shown in Figure 2. A numerical example is worked out for an operational installation at the end of the article. Figure 3 gives first approximates for the head loss coefficient [9]. Figure 4 gives data required to calculate the above coefficient for oblique inflows to the screen, with an example of its application ([3], [6] and [11]). Screen stability, which was frequently at fault before 1955, is discussed at length. The author has shown [1] this to be due to resonance of the natural bar frequency and the frequency of alternating eddy wakes forming on the fear face of the bar. The natural frequency of long components in a vacuum (actually in air) was given by Timoshenko in 1950. The author's formula (5) allows for the fact that such bars vibrate in water [13]. The meanings of symbols in this formula are as follows r = radius of gyration of the section ; H = distance between bracing members ; E and Yb = elastic modulus and density of bar material ; y' = fluid density (0.001 kg/cm3) for water) ; M = Fixing factor resulting from (6) and (7) for fixed and articulated ends respectively. Figure 5 [13] gives f in cycles/sec. for b/s = 10, and f is found for other values in this report by a simple calculation, which is demonstrated in the final numerical example. Frequency is very much lower in water than in air (by a varying between 0.6 and 0.9). Formula (5) applies for b/L ≤ 0.7, but above this value the calculation is carried out with (b/L) = 0.7.

Stability Considerations in the Design of Steel Plate Girders

Results of tests conducted on large steel plate girders; stability requirements of webs and stiffeners of large-scale steel girders; different combinations of bending and shear are considered; design rules for determining thicknesses of webs and locations and dimensions of vertical and horizontal stiffeners.