SAFER BUILDINGS

Taranaki Daily News, 22 July 1929, Page 16

SAFER BUILDINGS

RESISTING EARTHQUAKES

ENGINEERS’ CONCLUSIONS.

LESSONS IN OTHER COUNTRIES.

One of the immediate psychological effects of a big earthquake is to cause one to consider in which type of budding one is safest in the case of seismic disturbance—in < thcr words, on what lines building construction should proceed to guard against damage and loss of life in the event of a big shake. A good deal of expert investigation has been made since the disasters in San Francisco’in 1906, in Japan in 1923, and in Santa Barbara in 1925, and while there is a certain amount of controversy on the subject the majority of architects and engineers' seem to incline to the opinion that the structure steel frame building is the most satisfactory type of earthquake-resistant structure, and that when properly constructed according to sound design it constitutes the best protection against earthquake damage. An interesting paper on earthquakeresistant structures, read before the Los Angeles section of the-American Society of Civil Engineers, is one of the latest contributions to the subject. The author was Mr. Wendell M. Butts, civil engineer, of San Diego, California, and he argues to the conclusion outlined above.

NO AREAS FREE FROM MENACE

“Everywhere,” he. says, “structures should be built with a view to minimising earthquake damage, for there are no areas which are free from this menace. The degree to which buildings should be made earthquake-resistant depends on four factors. First, the particular site and character of the sub-foundation; it has been definitely demonstrated that the intensity and de.structivity of an earthquake is dependent on the subfoundations almost entirely, i.e., that the impulses at the origin of destructive ’quakes have not been so varying in intensity, but the sub-foundations through which they have acted made their differences in destructivity. Second, the character of the structure, its use, and the consequences of collapse; on this basis, it seems reasonable that a school, a theatre, ox' other place of assembly, where large numbers of people might be trapped should be. better protected than a warehouse or a garage. Third, the seismic record of the territory should be investigated, although this'is not to , be taken too seriously; Kamakura, the home of the famous bronze Buddha some 20 miles from Yokohama, had apparently a firm foundation for its reputed immunity, after freedom from seismic disturbance of over 600 years, yet the most violent vibrations of the terrible disaster of September 1, 1923, demolished nearly every structure in the area. Fourth, the cost of making provision for earthquake stresses should be studied. It can be shown that an adequate allowance for office buildings, even with poor sub-foundations, is four or five per cent., and slightly more for buildings of long span and great storey heights. When the low cost of protection is known it will not be a stumbling block.” Mr. Butts says it can be shown that bearing-wall construction is surpassed by skeleton structural', steel or reinforced concrete structures in throe particulars —positive determination of seismic and all other stresses; general resistance to shocks even when not designed for earthquakes; and lower cost. The use of vertical diagonal bracing to strengthen the frame has been extensively ad- • vocated, and if it can be used without interfering with the layout of openings, is a ’definite and economical solution. The use of walls to give the required stiffness to a well-connected frame has been foufad economical and to work well in practice. If a building is to come off free of all damage it must have strong walls regardless of its frame. A good frame will certainly prevent collapse, and the ideal building has light floors sufficiently rigid to compel the same deflection in all vertical bents, wall panels, and columns, and the girders, columns, and walls designed and constructed of such materials as to ensure ample strength to provide for that portion of the total horizontal forces which their rigidity demands.

QUESTION OF TYPE.

The author of the paper then proceeds to discuss the question what type of building is beet for earthquake-re-sistant construction. He points out that there were no concrete buildings in Yokohama over four storeys high, and only one in Tokio (which collapsed) over six stories. There were several towers in Yokohama, and many, buildings in Tokio eight stories in height of structural steel frame construction, and none failed, although several were damaged. It might be incorrect to say that none of these was seriously damaged, but it was a fact that none had to be razed during reconstruction. Many buildings of both types passed the earthquake test with no damage whatever. In San Francisco there was very little structural damage to skeleton steel frame buildings as high as 18 stories. “The records show that no conciete structures over 75 feet high have escaped severe damage or collapse in an eaithquake,” says Mr. Butts, “while there are no failures chalked up against structural steel frame buildings 100 feet high in Japan or 300 feet in height in California. No lives have ever been lost in a steel frame building. Several hundred can be traced to the collapse of concrete structures. The record, even for the low concrete buildings which have been subjected to earthquakes,. is no good. For buildings over six stories it is very unfavourable. Weight is a disadvantage in design to resist shocks. Pound for pound, a steel frame building is stronger than one of reinforced concrete, and when it is added that a concrete building for the same purpose is much heavier, the advantage of the steel frames structure is . apparent. Actual comparison of two designs for a store 100 ft by 100 ft and 10 stories high showed the one of reinforced concrete to be 1600 tons heavier than the fire-proof-ed steel frame buildings. “Even as engineers,” he says, we have a feeling that a structural steel frame building is safe/ but wc would like to have a look at the tests of the cement, the eand, and the crushed rock, the amount of water used, and the methods employed in placing the reinforcing steel and the concrete before we feel an equal assurance in the concrete structure, for we know better than anyone else that if any of these are faulty the strength of the structure is seriously impaired/ 5