EARTHQUAKE LESSONS

Taranaki Daily News, 24 February 1931, Page 3

EARTHQUAKE LESSONS

BUILDING PRECAUTIONS NEW STRUCTURAL FEATURES. RESISTING FUTURE SHOCKS. The lessons of the Hawke’s Bay earthquake were reviewed in a paper read before the civil engineer’s conference by Mr. J. R. Baird, assistant-borough engineer of Hamilton. "Everyone should realise that by living in New Zealand he takes a certain definite risk,” said Mr. Baird. “Oui” country lies on that part of the world where some of the tremendous energy stored up as the result of continual shrinking of the earth will be released from time to time. We cannot tell at what time nor in what places future shakes will occur, nor would it be of great advantage were this power given tp us. Therefore we should take the sane step of designing our cities to safely withstand such occurrences.” •<

Mr. Baird estimated that about 90 per cent, of the building Joss in Napier was due •to structural deficiencies. He suggested that in tha near future it might well become unlawful for a structure to be erected without the services of a competent engineer. In summarising the main principles to be. kept in view he considered that the fundamental condition was site. Sites at the foot of or on the sides of steep hills or on the tops of cliffs were insecure. Rock formed the best foundation ■ material, while swamp and .reclaimed land were the worst.

The second fundamental consideration was shape. The more closely a building approximately a square in plan the safer it would be. L and U types, commonly used for schools and hospitals, were particularly bad, but a closed rectangle, provided the hollow was not too large s was satisfactory. In elevation a building should also be as symmetrical as possible, and it was desirable that towers should be omitted. If used they should be placed on the axis of the •building. Foundations of a building should be carried down to a uniform depth over the entire site, and should on no account rest on dissimilar materials. Individual column footings should not be allowed, but all foundations should be connected in at least two directions at right angles. One large reinforced slab or “raft” under the entire building was the ideal foundation. Soil pressures should be kept,as low as possible.

STRUCTURAL PRECAUTIONS.

City buildings in one block should be made structurally one building, although outwardly they could appear as a number of separate buildings, or else a clear space of 3ft should be left between the. structural frames or walls of adjacent buildings. < The ground floor and shop windows could, however, be allowed to utilise the ■whole of the frontage, provided they were designed to “crumple” without transferring any serious stress from one frame to the next.

Every part or component of a building should be so tied together that none could fall away when f under the influence of the maximum acceleration expected. For this reason brick, tile or block curtain walls, partitions, parapets and facings, and brick chimneys, of the present design, should be absolutely prohibited. The too’ should preferably be 'designed as part of the structural frame, and in any case, should be so fixed that it could not slide off the walls, and in addition, should be braced diagonally on the plane of the ceiling. The distribution of weight up the height of a building should, when plotted, resemble hs far. as possible a right pyramid. Heavy stores should be kept’as low as possible, and the offices should be placed at the top. On the road frontage all floors above the ground floor should be set back at least 6ft to enable the necessary bracing to be carried down to the foundations at the rear of shop windows and to protect the main front foundations from otherwise unavoidable weakness caused by numerous street excavations. The use of wood as an earthresisting material could not be ignored, but fire-proof buildings should be compulsory in city blocks.

GOOD WORKMANSHIP NEEDED.

Every effort should be made to give the four outer walls as much stiffness as possible, particularly on the ground floor. Windows should be reduced to a minimum of the total area, and should not be placed near corners. _ Diagonal braces or reinforced partition .walls should be placed wherever practicable across a building, while floors should be designed to prevent distortions of the walls and columns. Good workmanship was of the greatest importance, for a building being subject to an alternating stress would soon lose rigidity if. bad workmanship existed and a loss of rigidity. would quickly lead to progressive failure. ~ “Every person in New Zealand must do his best to separate past ‘fashion from his mind, and be prepared to accept something entirely different,” said Mr. Baird. “He must realise that, safety comes before appearance, convenience, or mere financial gain. It will possibly lead to a type peculiar to this country, but the fact that in the past we have been slaves to a type popular in older and more stable countries is not typical or our national ability to adapt ourselves to the conditions in which we find ourselves. ’’ Mr. Baird suggested that, in spite of the financial difficulties of the present time, a permanent independent department should be created to conduct research work into the many structural problems, both in connection with buildings and engineering works, and to enforce the new law. He felt that, without a definite head, the new law, no matter how well prepared, would, as time dulled the memory of this year s warning, fall into disuse. The importance of its success to human life and to community life could not be stressed too strongly, and the difficulties to be faced were sufficient to require the concerted eaerfy of an impendent body.