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The Structural Engineer

The Loma Prieta earthquake at 5.04pm on 17 October caused extensive structural damage in San Francisco, in Oakland, and in smaller communities to the south. It measured 6.9 on the Richter scale, which is comparable to the event which devastated parts of Azerbajan nearly a year ago. A major difference was the scope of destruction. While the Armenian disaster caused disruption which resulted in a death toll of over 2000, the fatalities in California were less than one 10th of this.

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The Structural Engineer

This paper reports a study of the elastic buckling of the perforated webs of transversely stiffened steel plate girders. The finite element method was used in the analysis. The parameters varied were the panel aspect ratios and the shapes and sizes of centrally placed holes in them. For the major part of the study, the sizes of the flanges and transverse stiffeners were kept constant, but the effect of reducing the stiffness of these elements was briefly considered. The modelling used allowed the web plate to assume its natural boundary conditions. The results show that the buckling strength of a web panel bounded by flanges and stiffeners can be estimated by assuming that its edges are fixed. A simple formula which relates the elastic buckling stress of a perforated web plate to that of a similar intact web is proposed. The formula is applicable to web plates containing centrally placed circular, rectangular and elongated circular holes. M.M.K. Lee and A.G. Kamtekar

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Author – Lee, M M K;Kamtekar, A G

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The Structural Engineer

The Tyne Bridge Sir Ralph Freeman and Ralph Anthony Freeman (son and grandson of the first Sir Ralph) have provided us with most interesting comment on the association of the earlier Sir Ralph with this very well-known bridge, which was featured on the cover of The Structural Engineer for 5 September last: We were pleased to see the picture of the Tyne Bridge and to read the positive comments about this famous bridge, now almost 61 years old. Verulam

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The Structural Engineer

A finite element method is applied to the study of natural frequencies of electric transmission line structures. The tower has been modelled as a space truss consisting of 3-dimensional truss elements with three translational degrees of freedom at each node. The sagged conductor cable has been assumed to be composed of straight elements. Extensional characteristics of the cable element are fully considered. A parametric study is conducted to determine the influence of various parameters on the spectrum of natural frequencies of a conductor cable, and appropriate non-dimensional curves are presented. These non-dimensional curves give an insight into the general characteristics of a sagged cable, and can be used to predict inplane natural frequencies over a wide range of sagispan ratios. The first few natural frequencies of the transmission linesystem fall in the range 0.05 to 0.5 Hz. Professor M.L. Gambhir

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