Tag
Author
Date published
Price

Contents page

The Structural Engineer

The Florianopolis Suspension Bridge, having a main span of 1,113 ft. 9 ins., and a versed sine of 120 ft., in addition to being the longest suspension .span in the world with eye-bar or link chains, is also of special interest as being the first executed example of a novel type of stiffened suspension construction, by means of which greatly increased rigidity and economy of material are realised. A further departure from usual practice is the employment of rocker towers, this being the first suspension bridge in the Americas to be so built. The only large bridges previously built with hinged towers are the Elizabeth Bridge at Budapest (1903) and the suspension bridge at Cologne (1915). Still further interest attaches to the employment for the eye-bars, of high tension, heat treated carbon steel having to satisfy a specification of minimum ultimate tensile strength of 105,000 lbs. per sq. in., minimum elastic limit of 75,000 lbs. per sq. in., and minimum elongation of 5 per cent. In 18 ft., the tests being made on full-sized bars. The intended working stress in these bars is 50,000 lbs. per sq. in. Further reference will be made h the tests of this material, but it may here be noted that the average results of thirteen tests of full sized bars gave an ultimate strength of 123,000 lbs. elastic limit,, 84,500 lbs. per sq. in. and percentage elongation of 6.8 in 18 ft. The tender for the eye-bar chains in this instance reduced the total cost to the lowest estimated cost of the bridge if constructed with wire cables. Finally, a new method was employed for the erection of the eye-bar chains and stiffening girders, using an overhead trolley line, thereby eliminating falsework and working platforms. The erection occupied one year and was accomplished without loss of life. J Husband

The Structural Engineer

The CHAIRMAN said it. did not need any words from him to express the appreciation they all owed to Colonel Moncrieff for his very lucid and interesting lecture, because the acclamation of the audience had indicated what they felt. But he asked them to accord Colonel Moncrieff a very hearty vote of thanks for the great kindness he had shown in presenting this lecture and giving them such very interesting diagrams to illustrate it. Colonel Moncrieff had crystallised a very large subject extraordinarily well, and to have given the audience the results in a very lucid form. He (the Chairman) would like to say a few words in reference to some remarks Colonel Moncrieff had made, and the first of these was in relation to the application of sand to the stuff that had been ca1led “porridge.” He happened to have at the present moment a rather interesting problem of somewhat similar material to what Colonel Moncrieff had found in Norway, where under certain circumstances the ground would stand at an angle of 90 degrees to the horizontal, but after a shower of rain it was turned to “ porridge ” and lay down to 1 in 12, or something of that order. The problem was to form open cuts 30 or 40 ft. deep of a considerable width, and to ensure that the sides would not fall in. He had been extraordinarily interested and flattered really to find that the experience of Colonel Moncrieff had coincided exactly with what he intended to do, namely to cover over the slopes with sand or quarry refuse, and in addition to make provision for draining the ground. He would not say more because he knew there were a number of members present who wished to speak, and he would like to hear them.

The Structural Engineer

In giving a title to this paper, I have referred to the terms “bulking” and “grits,” and I think as a preliminary an explanation of my meaning is due. J.E. Worsdale

The Structural Engineer

THE CHAIRMAN said the paper was a delightful record of work done and brought to a successful issue and provided an object lesson in regard to the surmounting of difficulties in the face of opposition. He himself had been responsible for the construction of a smaller building at the time of the general strike, when it was a very difficult matter to obtain steel, and one had to use just what one could get. Having regard to the fact that the amount of metal required in the construction of the Epsom Grand Stands was so enormous, the results attained were very creditable to everybody concerned. He did not know whether a time limit was imposed. The manner in which the large girders were raised was also very creditable. A girder weighing 33 tons was very difficult to manipulate, and to have raised such a girder into its position in less than 24 hours was a notable achievement. The method of using the triangular steps had also impressed him. He did not quite follow how the reinforced concrete part of the work was done, but the method adopted seemed to be an artful way of getting over the difficulties without putting a tie of reinforced concrete all the way up and having to bond it in. It was doubtful whether everybody would have thought of that method. The paper was full of “ meat,” and he was looking forward to succient criticisms of the methods of construction from the many experts whom he saw before him in the body of the hall.

The Structural Engineer

Case II-Resultant stress in tension over portion of section. We now come to the case in which the eccentricity is sufficient to cause at the edge of the section remote from the load point a tensile stress in excess of the direct compression stress. Ewart S. Andrews