No abstract

Works) said that the tests described in the Paper made an important contribution to knowledge of the fire resistance of encased stanchions and their load-carrying capacity in both the 'fired' and 'unfired' condition. The tests must first of all be viewed in terms of the present design requirements, as given in B.S.449, and appeared to indicate that some modifications were required.69. In terms of the present rules, the Paper showed that there was no reason to insist on a minimum of 2 in. of cover. A cover of only 1 in. seemed to provide a satisfactory protection for two hours of fire resistance. This was also confirmed in the group of tests with l-in. cover reinforced with a very lightweight mesh. Such a mesh would be easy to fix and relatively cheap as compared with the intricate arrangement of stirrups which was required at present under B.S.449.70. Another important contribution from these tests related to the lightweight casings which were made with expanded clay or slag aggregates. These tests appeared to show that the carrying capacity of an encased column in both the 'fired' and 'unfired' condition was not adversely affected when lightweight aggregates were substituted for gravel.71. Perhaps the most important contribution came from equation (l), the basic conception of which was used in the design of a reinforced-concrete column. This equation stated that the ultimate load-carrying capacity of a cased stanchion was calculated from the sum of the areas of concrete and steel multiplied by their respective yield stresses. In terms of fire resistance this gave a considerable flexibility in design to meet the requirements of aesthetics, fire resistance and carrying capacity not formerly possible by conventional rules.72. But surely the most startling contribution was the application of equation (1) to the ultimate load of a cased stanchion in the 'unfired' condition. In this series of tests the yield stress of the steel and concrete were 15 tonslsq. in. and 3000 Ib/sq. in. respectively 'before firing'. No reduction was required for the slenderness of the column since the LID ratio was less than 20.73. Taking the example of an 8 in. X 6 in. stanchion in a casing of 12 in. X 10 in. overall size and applying these yield values to the area of steel and total area of concrete, the ultimate carrying capacity of the cased strut was 300 tons approximately, equally divided between the steel and the concrete. This appeared to agree very closely with the test result in the 'unfired' condition. Similar agreement existed with the other examples and appeared to indicate that cased steel columns could be designed in the same way as for reinforced-concrete columns.74. At the present time hollow board casings were more economical than concrete