Excerpt from City of New York, Aqueduct Commission: Reports on Researches Concerning the Design and Construction of High Masonry, in View of the Proposed Building of Quaker Bridge Dam

Gentlemen: I herewith respectfully submit the Report called for by your Resolutions of March 24, 1886, and June 22, 1887, on the subject of High Masonry Dams, both curved and straight in form.

The plans presented for the straight Quaker Bridge structure were made after long study of the forces and strains to be sustained, allowing for large factors of safety against overturning, crushing and Sliding. The best proportions and form consistent with safety and reasonable economy were designed, with great care to meet all requirements of strength and stability.

The world's experience in the designing and construction of great dams, together with the investigations and opinions of the highest authorities, in Europe and America, were collected and considered in the plans prepared and presented to the Commission.

The strength and cost of a straight dam, resisting hydraulic pressure, ice, wind and wave action by its weight only, was compared by mathematical results with the stability and cost of a dam in the form of a horizontal arch, transmitting thrusts to the hill-sides. For the Quaker Bridge structure, the strength, economy, and safety, of the straight dam, so far exceeded what was obtainable by the curved form that 1 can only account for the construction on a curve of so many large modern masonry dams, from the fact that only within a few years has the question begun to receive the attention it deserves from trained and experienced hydraulic engineers and authors.

The popular belief in masonry arches to bear great weight or pressure, is justified when confined within reasonable limits. But no masonry bridge arch of over 300 feet span has been constructed.

Beyond that length of span, the crushing strain, sustained by voussoirs, exceeds safe limits on their mortar joints from the weight of the masonry alone, without the added load the bridge Should carry.

It would therefore be out of the question to construct a masonry bridge of the length of Quaker Bridge Dam (1350 feet long) as it would be over four times the limit of safety in a possible span. The arch of a curved dam, however, does not carry any part of its own weight (as in the case of a bridge), therefore its strength of arch will bear only the water pressure against it from a full reservoir.

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