PREVENTING ’QUAKE DAMAGE

Greymouth Evening Star, 13 March 1933, Page 8

PREVENTING ’QUAKE DAMAGE

TYPES OF FOUNDATIONS. In the following article Mr R. W. de Montalk. F.N.Z.1.A.. describes a i-jQy ( r type of “floating foundation, patented by him. which is calculated to minimise' (he effect ol earthquake shock:; on buildings of all descriptions. ILirt hqimkos shake, twist and raise the country: the forces exerted are so powerful that it is impossible Io cal cnlale them. Everything “fixed" in the ground receives the impact ol every earthquake, and damage occurs to buildings solely bceuti.se their foundations are “fixed.’’

Attempts have been made to minimise damage, but the mind of man lias become so saturated with the custom of “fixing” in the ground that they find it difficult to make a change. Therefore in correcting forces imposed by earthquakes, “resistance” has been adopted. 'This is carried out by adding strength to the structure which is “fixed” in the ground as formerly. Certainly by means of great strength it is possible by resistance to enable a building to pass through earthquakes • apparently undamaged or only slightly | damaged. Nevertheless much damage /does actually occur, but is hidden from iview under concrete and plaster. [ It can be definitely asserted that that there can be no resistance without corresponding strain anil that strain cannot be exerted without injury. Therefore, in the resistance method, no matter what strength is employed Io resist, every earthquake causes damage, ('very succeeding one increases flic damage first done. It. may be merely a. matter of time before the accumulated damage will cause collapse. Why make the building of great strength so as to “resist" the forces to which it has been subjected? The objective should be; prevention of damage by avoiding the shock in contradistinction to resistance by strength.

A life-time study hits cnaijied th-’, writer to formulate simple laws goterning earthquake damage prevention, and to work out means of adapting; them in a. practical manner. The hr is as follows: — fa) The design shall conform to low centre of gravity. th) r rhe site shall be. consolidate .or otherwise treated so as to cnabi it io properly support the building an its contents. (c) The structure shall rest on : severer or separator, held in suer manner that (he severer shall he retained permanently in th-' original position in which it. was placed. 11 is of course understood that th building is well balanced in plan, o good materials and workmanship, aim of strength required due io gravil;. No greater strength is necessary. By compliance with Ibis simple lav . damage by earthquake to building . bridges, etc., will be preve.nled. I i addil ion, vibrations set up from a I other riuircr. such as traffic. workir machinery, rushing waler, etc., affec - ing buildings, bridges, reservoirs, tu - bines, and the like, will be nullilie .. A I-’OCN DATION DESCRIBED. The following describes a loiind' lion in lull compliance with the abo\ i la w : I. A platform of reinforced cm • i roic on crim l , the area of I he build ing;. A rim is turned up around it’, edges forming the platform into a tray. Ihe purpose being- to contain ait I retain ihe bed of shingle referred to in 2. Tim platform may be supported

on t rench walls brought down to a hard bearing surface,, or may be supported on piles. It. can thus be made of a strength capable of properly supporting the weight of any building. The platform is “fixed” in the ground, forming an integral part with the latter; therefore it will move with the ground when an earthquake takes place. The platform is not the foundation of the building, though it is an absolutely necessary adjunct to it, hut is u consolidation of the site in conipiinnee with I’> of the law. 2. \ bed of shingle is spread over the surface of the platform and tilled io th,- height <>f the rim. The shingle. r< stiiir. on tho reiuforced concrete platform, is thereby prevented from being pressed into the soil by the weight of the building. Likewise the rim around the platform prevents the shingle from being displaced laterally. In this way the shingle is permanently held in position in accordance with C of the law. The shingle bed is the medium which separates the building from the country. The foundation of the building is a reinforced concrete slab (termed the soleplate), covering the area of the building, and is spread over the bed of shingle contained on the platform; this is otherwise an ordinary floating foundation out of which the building rises. This foundation slab has no attachment, whatever with the platform; a severance has been made by the bed of shingle.

Hence an earthquake occurs, the platform, which is “fixed” in the ground, shakes "under” the building, and the building avoids the shake because of the interposition of the bed of shingle between the platform and the building.

It. is better and more sensible to build so as to “avoid” powerful forces rather than endeavour to “resist” them.