Sunday, February 5, 2012

April 21, 1888, Engineering News, The Defective Assembly Chamber Ceiling.

April 21, 1888, Engineering News, page 310

The Defective Assembly Chamber Ceiling.

The German Technical Society of New York has published the following resolution regarding the unsafe large groined vault in the Assembly Chamber of the new capitol at Albany, N. Y., supporting the views expressed by Mr. Fabian some years before the actual failure of the ceiling. Mr. Fabian, we apprehend, correctly diagnosed the difficulty in advance, and is entitled to great technical credit for doing so.

Whereas the German Technical Society of New York, after a careful examination of treatise published by its Corresponding Secretary, H. W. Fabian, in the "American Architect and Building News" (October 29, 1881, and March 29,1884), has been convinced that the dangerous condition of the large groined vault of the Assembly Chamber of the new capital at Albany was justly and correctly criticized by him already some years ago. and

Whereas a development of the monumental building art. keeping pace with modern technical researches should be striven for.

Be it Resolved that we indorse the following summary of Mr. Fabian's statements as fully corresponding with the facts, and submit the same to the public:

1. The main cause of the instability of the vault is based upon the form of the inner construction, the lines of pressure in the bearing ribs considerably deviating from the middle lines. Hence follows an exceeding unequal straining of material in the dangerous cross sections and the existence in the outer fibres of strains of pressure considerably exceeding the allowable maximum. The resultant of the normal forces in the weakest cross sections acting considerably outside of the central core, tensile strains are produced, which Involve the cause of enormous deformation. These facts are sufficient to fully explain the endangered stability of the vault.

2. The construction of flying buttresses, joined together by iron tie-rods in order to gain the balancing power between the horizontal thrusts of the smaller and larger arches, is not in accordance with the demands of sound vault architecture. Two arches will be in equilibrium if in both the product of the radius of curvature multiplied by the height of load, both taken in the summit, is equal. According to this law, the problem might have been solved without employing flying half-arches and tie-rods. This manner of construction is objectionable on account of the unequal expansion of iron and stone; every change in temperature will cause a vibration in the arch system, which vibrations in the course of time imperil the stability of the vault. It is not believed, however, that the essential causes of the present deformation are to be sought In this direction.
3. Nor can the stated unequal settling of the columns be seriously considered in judging of the deformation, it being in comparison insignificant with the great dimensions of the vault. Both faults, this as well as the beforenamed, might indeed contribute to the aggravation of the defective condition, but not of themselves cause of it.

4. The attempt of the architect to ceil the Assembly Chamber with a monumental stone construction can be but approved. The art of vault building, as it has come to us from the middle ages is, however, constructively impotent to cover areas of this size. The ceiling of our large modern halls with stone vaults can, therefore, only be attained, when in place of the historical vault-lines, there are employed mathematically developed arch-lines, which coincide with the lines of pressure. Then the material in all its parts would be strained quite uniformly and only influenced by pressure. The additional load as employed at Albany to improve the lines of pressure in the pointed arches could then be dispensed with, and thus the total load be considerably decreased. There is no doubt that a groined vault built on such principles of construction can be employed for the Assembly Chamber at the Albany Capitol, without fears as to its stability.

In the interest of progress in monumental architecture, which is indissolubly connected with the employment of stone as a building material, it is, therefore, to be desired that the Legislature should adopt a resolution to that end.

The adaptability of the old material in case of reconstruction of the vault undoubtedly deserves some consideration in the light of the foregoing.

Robert Strikes,
Augustus Kunth,
Max C. Budell,
F. Knauer.
A. E. Gieseler.
The Committee.

We entirely agree with the view here expressed that it is desirable, if possible, to preserve the original form of ceiling with its defects of proportion corrected. The building has cost too much to have anything out of keeping with its general magnificence introduced unnecessarily.

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