Issue 11

Professor Bolton gives an exposition of the stability of frames that may well commend itself to engineers seeking an elementary understanding of the phenomenon. Precisely for this reason it is a misleading and even potentially dangerous paper. Although far from the intention of the author, it in fact conveys the impression that frame stability is a local phenomenon, calculable from the stiffness of a single symmetrical joint in a 'no-shear' frame on the assumption that the remote ends of the columns are direction-fixed. To attempt to derive the sway stability of a frame by considering one joint is just as inadequate as the procedure common in Codes, and criticised by Bolton, of merely dealing with crudely calculated effective lengths of single members. By contrast, in discussing our approximate methods, Wood and the contributor both give explicit recognition to the fact that sway stability is an overall frame behaviour problem, thereby deriving more consistent results for derived critical loads. M.R. Horne, R.H. Wood and J.W. Bunce

Towards a unified stress grading for timber It is hoped that this correspondence on the above title will cover most of the interesting points raised by Mr. J. K. Sykes (M) in the Verulam column, June 1976, page 233. Dr. D.N. Nwokoye

Mr. Alan Shilston (Consulting Civil Engineer) : Insurance and the mechanism of insurance claims is a subject the consulting engineering side of the industry ought to know something about. If one tries to understand anything about insurance, it is important to find out what are the background controlling general principles and then to explore how those broad principles relate to that sector of the insurance world concerned with the construction industry. I will indicate my impressions: these should be regarded as tentative since it is far from easy to identify what broad unanimity does exist amongst insurers. I attribute this to the inherently specialized character of the various sectors within the insurance market. My contribution is confined to discussing the scope of the principles that are thought to apply. It would be helpful if the authors, supported by their colleagues in the industry this evening, could confirm or modify any of the tentative conclusions I have reached.

The President: Good evening, ladies and gentlemen, and welcome to this rather special meeting, which is a combined one with the the British Group of International Association for Bridge and Structural Engineering. As well as welcoming all those of you in the body of the hall, we have a number of special guests that I would mention. First and foremost, Professor Leonhardt and Frau Leonhardt, and of course of Professor Leonhardt more later. We have Baroness Sharp, Dr. and Mrs. Feilden, Sir Hugh Wilson, Sir Charles Husband, Mr. Philip Gooding, and Professor Baker.

Various means are commonly used to rectify lack of straightness in stiffened steel panels to bring them within working tolerances such as those stipulated in the Merrison Rules for box girders. The paper describes tests to establish whether panels straightened by various heating, jigging and over-loading procedures have the same strength as panels fabricated to meet those tolerances without resort to such procedures. The panel proportions and modes of testing were designed to produce in all cases collapse by failure of the outstand. It was found that, while straightening procedures which caused compressive residual stresses in the outstand left the panel with a decreased capacity in compression, procedures which left a tensile residual stress could restore the full carrying capacity. M.R. Horne and R. Narayanan

In this paper the behaviour of reinforced and unreinforced masonry is considered. Tests on eccentrically-loaded unreinforced walls and couplet specimens are reported and a simple theoretical approach for solid block masonry is derived. A method of predicting wall strength is presented. Additional tests are described on reinforced masonry sections subjected to lateral loading only and the simple ultimate load theory used for reinforced concrete is shown to give a good indication of the ultimate strength of the sections. The effect of employing different values of the partial factor of safety for strength of the masonry is considered. It is indicated that present design procedures using permissible stresses result in uneconomic design. W.B. Cranston and J.J. Roberts

Dr. Nwokoye has written in reply to Mr. Sykes' comments on timber grading and the relationship of strength to elastic modulus in timber (June 1976), comments which were stimulated by a paper by Dr. Nwokoye in the March 1976 issue. Dr. Nwokoye's observations are fairly lengthy by the standards considered appropriate to this column and we have been making rather an issue concerning brevity recently; neverthless what Dr. Nwokoye has to say is likely to attract the close attention of some members and may stimulate further discussion which could be of interest at a time when a new limit state code for timber is being formulated. So as to maintain a semblance of our real concern for brevity in contribution we are putting this one at the end of the column where it can masquerade as a separate article, or a reply to a discussion on a paper, which it is. Verulam