EARTHQUAKE RISKS

New Zealand Herald, Volume LXXII, Issue 22046, 28 February 1935, Page 14

EARTHQUAKE RISKS

BUILDING DESIGNS principles of resistance NECESSITY-IN DOMINION [BY telegraph—OWN correspondent] WELLINGTON, Wednesday "It is now definitely possible to design at a reasonable cost buildings which will xesist earthquake shocks of great, intensity, and not to do this is, in New Zealand at least, to invite disaster," said Mr. 0. R. Ford, of Auckland, speaking at the annual meeting of the New Zealand Institute of Architects this evening. Mr. Ford said the frequency of destructive earthquakes within the last few years in many parts of the world suggested that earthquakes were not rare phenomena. Records showed that in 1926, for example, there were nearly 32,000 earthquakes, nearly 100 of which wore destructive to life and property. While it was true that some parts of the world were more liable to earthquakes than othors, it would bo unwiso to assume that any particular area was not likely to be subjected to shock. " Natural as Rainfall " "Earthquakes aro as natural a phenomenon as rainfall, or any other worldbuilding force, and as such aro not to bo ignored, and not to be feared, but to bo accopted and prepared for in ft rational manner," added Mr. Ford. "The results of the Napier earthquake caused rather a mistaken idea as to the supposed failure of existent methods of building construction. Much of the damage caused was done to obsolete buildings or structures in which additions had been carelessly made or in which workmanship was culpably bad. "In ono particular a revolution in building construction in New Zealand is necessary. That is in the recognition of the very real possibility of buildings being subjected to horizontal vibrational stresses and the need in future construction for the abandonment of those methods of design which experience has proved to be dangerous under such conditions." Among the changes mentioned by Mr. Ford were the limitation in height of buildings with bearing walls of brick or other unit block masonry, and the discontinuance in this typ,e of building of the use of concrete floors, the necessity of securing all elements of a structure so that the whole would act as a unit, and the need for the abandonment of high, unsecured parapets and of the use of the brick or other masonry arch as a structural support. Calculating of Stresses / Mr. Ford outlined research work which led to the belief that a building constructed to withstand a horizontal thrust equivalent to one-tenth the weight of the structure would safely resist an earthquake -of high intensity. The task of calculating such stresses presented great difficulties to the architect, but it was nevertheless essential. To construct a building designed to withstand earthquakes would naturally cost rather more than if purely static stresses were taken into account. It was generally considered that the additional cost of designing a building to resist a horizontal stress of one-tenth of gravity was approximately 10 per cent of the total cost, of the building. "Correctly viewed, the idea of 'extra' cost is wrong, however," Mr. Ford concluded. "If a seismic design is necessary, then any cost involved is no more an extra than is the cost or resisting the force of gravity or of providing sanitation and hot-water heating."