Issue 3

In his paper, the author has modelled the behaviour of compression members by assuming that they will have a buckling load given by Rankine's formula, and that they can undergo unlimited contraction at this load. It is well known, however, that compression members generally show some drop of load-carrying capacity after the critical load has been reached. On the other hand, it is quite reasonable to assume that tension members will elongate plastically under a constant yielding load (ignoring strain-hardening effects), provided that premature joint failure is prevented. Results of experimental work on compression members with varying degrees of end restraint have been plotted in Fig Cl. These values were mostly taken from a paper published by Francis and Stevens1 describing work carried out at the University of Melbourne, but also include results from Paris and van den Broek. It can be seen from Fig C1 that the critical loads of compression members are more closely related to the squash and Euler loads than to the Rankine load.

Mr. J. H. H. Williams(F) : Mr. Thomas has mentioned the importance of wall ties in cavity construction, but he did not mention the question of durability. It is my concern that we should not build into structures members which may become dangerous in sixty or even one hundred years' time because of the failure of some small but vital part which cannot easily be seen by future surveyors. Wall ties in cavity walls fall into the category of a humble but essential part contributing to the stability of large panels of masonry and as they cannot easily be inspected I believe that they should be designed for a period well in excess of the anticipated life of the building. Some engineers and authorities insist that non-ferrous or stainless steel ties are used in cavity walls in high rise structures, while others, less informed, may be misled by the compliance of galvanized wire ties with the British Standard.

The President: This must have been a most exciting job with many problems to overcome. It was a congested site, with restrictions of allowable pressures on the ground. The factors which influence the engineering design are quite amazing; I think you said that it was imperative to obtain a uniform pressure on the ground and that that particular restriction to some extent led you to adopt the curve columns.

The Clean Air Act of 1956 stipulates minimum heights for industrial chimneys according to the size of the boiler plant and also requires higher flue gas exit velocities which consequently produce chimneys of smaller diameter. On a multi-boiler plant the multi-flue chimney permits the maximum flue gas velocity to be achieved at all boiler loadings since each boiler has its own flue, however the beneficial aspects of the small diameter flue can be offset by the practical construction difficulties of freestanding brick linings of small diameter. W.C.J. Workman

The cable net structure for the 1972 Olympics is the largest and most complicated of its kind. After a brief outline of its history and some basic remarks on the loadbearing characteristics of such structures, the fundamental problems which the engineer encounters during the design and detailing of these unconventional structures and the proposals for their solution are described, using the Olympic roof as an example. Professor Dr. Ing. Fritz Leonhardt and Dr. Ing J. Schlaich

A computerized finite difference method is presented for the analysis of slender reinforced concrete columns. The method is developed in detail for the particular case of columns fixed at the base and prevented from deflecting laterally at the top as compressive loading is applied. Symmetric bending is assumed. The columns may have a cross-section varying along the length. The effects of cracking of the concrete, initial lack of straightness, and of initial deflexion of the top of the column by cantilever action are allowed for. Reduction in the capacity of the column arising from creep of the concrete is examined. The method presented may be adapted to suit end conditions other than fixed base pinned top. Flow diagrams for the computer analysis are given.

In the behaviour of structures under earthquake, the most effective role is played by the fundamental period of vibration of structures because it is one of the main parameters to determine the earthquake forces applied to the structure and it specifies the dynamic stability of the structure. In this paper'a simple approximate formula is proposed to calculate the fundamental period of vibration. The calculation with this formula is very short and easy. No mathematical background is necessary to apply the formula. In addition to the derivation and discussion of the formula, several examples showing its application are given.

In this paper is presented a study on dynamic stability of thin-walled bars with open cross-section, subjected to compression by an axial force, composed from a static component and a variable one. The case of non-symmetric profiles is analysed in the first instance, to obtain general equations of vibratory motions; these are then particularized for profiles with an axis of symmetry, currently used in construction.