USE OF RUBBER MOUNTINGS FOR THE VIBRATION ISOLATION OF BUILDINGS.

Some results are reported of a seven-year durability study of the rubber mounting ( ″springs″ ) under a six-story London apartment house to isolate the building from the 22 Hz ″rumble″ of the Underground railway passing directly beneath it. First, the amount of creep that this building can confidently be expected to undergo over 100 years is completely acceptable. It will not take the building down on to its safety stops and indeed it is an amount of movement which could easily take place in other circumstances by differential settlement. Two other sources of possible problems were scrutinized: mechanical deterioration and stiffness changes. Mechanical deterioration could occur from various causes: ozone cracking, oxidative effects, attack by oils or solvents. None of these was observed. In particular, there is no sign of ozone cracking, a phenomenon which often seems to worry engineers. Indeed, even if such cracking had been observed, it would have been confined to the surface layer; conclusions drawn from the behavior of orthodox laboratory ozone test strips can be misleading. The reason why even superficial cracking was absent is that these mountings were properly protected by incorporation of chemical antiozonants during manufacture. Stiffness changes did not appear to be a problem; measurements of the surface hardness show that no significant change has so far taken place.