LETTER

ON THE

PROPOSED BRIDGE ACROSS THE OHIO RIVER

AT CINCINNATI,

WITH A

Single Span of 1400 Feet, and an Elevation of 112 Feet

ABOVE LOW WATER,

BY CHARLES ELLET, JR., CIVIL ENGINEER.

NOTE.

The cost of the bridge discussed in the following letter, is estimated at $300,000; a sum intended to cover every expense incident to the actual construction of the work, but not to include the cost of procuring sites.

To R. Buchanan, Esq.; Dr. John Locke; Henry E. Spencer, Esq.; Wm. S. Johnson, Esq.; of Cincinnati: and Charles A. Withers, Esq.; John B. Casey, Esq.; P. S. Bush, Esq.; M. M. Benson, Esq.; of Covington.

GENTLEMEN: I proceed at once, without preface, to the consideration of the very important subjects on which you desire my opinion, viz. "The practicability and cost of constructing a bridge across the Ohio, at Cincinnati, without piers, and at an elevation sufficient to allow steamboats to pass under it at all ordinary floods, without obstruction or delay."

I do not hesitate to assure you, in reply to this question, that it is entirely practicable to span the whole breadth of the river with a single arch, which will leave the navigation unimpaired, be easy of access from both shores, and of which the cost will not be too great for the fair remuneration of the enterprise of the builders.

It is now nine years since I gave formal assurances to many of your citizens that it was quite within the present state of art and mechanical knowledge, to throw a bridge over the Ohio, which should

offer no obstruction to the current, nor appreciable impediment to the navigation.

I can not say that further experience has strengthened that opinion, for the fact was susceptible of absolute demonstration then ;-but the construction of other works, the multiplication of examples, and the elevation of the public faith in the competency of art, will perhaps make it easier to win confidence in such an enterprise at this day, than at that period.

I propose to discuss the question of practicability as briefly as possible, and at the same time give you an estimate on which you may safely rely, of the probable cost of the work. But there are some considerations which precede the naked question of feasibility.

The object of permitting a bridge to be put across the Ohio, under the protection of chartered privileges, is public accommodation; and the legislature, charged with the care of all the public interests, will require it to be so constructed as to fulfil that purpose. They can neither authorize any unnecessary obstruction to be placed in the channel of the river, opposite a great city, where a concourse of boats assemble, nor allow the flooring to be established at a height that will interfere with the ordinary navigation of the stream. Neither, on the other hand, will they require the roadway to be swung at an inconvenient or unnecessary elevation, to the serious prejudice of the land travel and all the interests concerned in the prosecution and success of the undertaking.

There is a river interest to be guarded as well as a land interest to be promoted, and it is the duty of the legislature to look faithfully to the protection of both.

They will therefore neither permit the navigation to be unnecessarily embarrassed by a low bridge and dangerous piers, nor the land travel to be wantonly subjected, for all time to come, to the expense and inconvenience of surmounting an unreasonable elevation without adequate cause. There is a division of inconveniences and a division of benefits to be regarded. Justice, and the common wealthe good of all the public-are the object and care of wise and faithful legislation.

These considerations must govern the plan which I submit to you; for it is by these tests that its merits must be tried when brought before the sworn arbiters of the public good.

The general conditions here laid down to be made the basis of your present application, require a bridge on a bolder and grander scale than any that has yet been attempted; but I can not hesitate to submit it, and you can not shrink from its contemplation, merely on that account. This is a period in history when all repudiate their obligation to be bound by the limits set by antecedent practice; when the boldest plans may challenge consent, if sustained by argument convincing to the reason and common sense of men.

The width of the Ohio opposite Cincinnati, is at low water, about 800 feet; and the buildings on the landing nearest to the water, are about 700 feet from the center of the channel.

I propose to place no masonry, or work of any sort whatever, nearer to the center of the channel than the stores now standing on the landing; or to keep the abutments 700 feet back from the center of the river on each side-thus spanning the whole stream with a gi gantic arch of fourteen hundred feet opening.

It is not professed that this limit is actually necessary for the protection of the river interest; but it has the advantage of overleaping all objections from that source.

The elevation to be given to the flooring is a question of equal moment; but legislation in other states has already established certain limits which will serve in some degree as a guide in this part of the inquiry.

There can certainly be no injury done to the navigation, if the boats that pass under the platform are obliged in their trips to pass beneath other bridges as low or lower.

All the boats that come through the canal at Louisville, are compelled to lower their chimneys in passing a little bridge at that point; and all that ascend above Pittsburgh are subjected to the same necessity in passing the several bridges over the Alleghany and Monongahela.

The charter granted by the legislature of Pennsylvania for a bridge across the main channel of the Ohio below the point at Pittsburgh, has prescribed the height of the flooring that shall there be considered sufficient for the protection of the river trade. This height is fixed at 80 feet above low water.

The legislature of Virginia has chartered the Wheeling bridge company, and that work is nearly completed, at a height of 92 feet above low water, or 50 feet above the highest known freshet at that point.

The legislature of Illinois has recently granted a charter for the construction of a bridge across the Mississippi at St. Louis. It is not known that any specified height for the bridge is prescribed in the act: but in the plan presented as the basis of the application, the flooring was placed at an elevation of 45 feet above the highest freshets.

The greatest height adopted in any of these cases is that prescribed for the Wheeling bridge, or 50 feet above the highest known flood. The level here assumed for the flooring of the Cincinnati bridge is yet higher than this, or 50 feet above the memorable freshet of 1832, or 112 feet above low water.

It is true that there are boats on the Ohio which carry chimneys more than 50 feet above the water line; but they do not ply during such floods as that of 1832, and but two such floods as that have occurred within the memory of man.

When the river is thus swollen the landings are all submerged; the very streets leading to the wharves of Cincinnati are traversed by skiffs; the warehouses are flooded, and trade and navigation are practically suspended. No useful object requires that they should move on floods like this; and the highest class of boats are compel

led to lie by with the others for their own security. They can find neither freight, landings nor fuel on the river.

But, admitting that some rare emergency should require a boat of this class to set out upon a perilous and profitless voyage at such times, there will be nothing about this bridge, as now proposed, to obstruct its progress. The largest and finest boats on the river have jointed chimneys; and the lowering of a few feet of the top of these chimneys is the work of a few seconds, and can be productive of no loss or delay.

It would be insulting to the common sense of men, to compare that momentary labor, incurred only by the crew of an occasional boat, and that but once, perhaps, in six or eight years, with the lasting inconvenience of forcing the vast throngs which will traverse this bridge by day and night, at high water and low water, in all seasons of the year, and for centuries to come, to haul their loads up an inconvenient ascent, and pay the additional charge required to remunerate the company for the cost of placing the work at that unnecessary elevation.

Probably not one boat in ten carries chimneys lofty enough to touch this bridge at the top of the very highest floods; and it is hardly to be doubted that nine out of ten of the remaining tenth will run their career, live out their time and perish without ever bending their chimneys to pass under this arch.

This inconvenience is in fact reduced to an inappreciable element; and a bridge of 1400 feet span and 112 feet high, is out of the reach of all reasonable cavil or objection. It fulfils every condition that can be laid down for the public protection; and probably surpasses the limits that will be prescribed by the appointed guardians of the public rights.

GENERAL DESCRIPTION.

The span of the single arch forming this bridge will be, as stated, 1400 feet.

The height of the flooring above low water will be 112 feet in the center, 100 feet over the borders of the river when at its summer level, and eighty-seven feet at the line of the stores on Water streetassuming that its location be at Main street.

The approaches will rise towards the bridge by a grade of four degrees, which is only about one-third the steepness of the ascent from the present ferry to Water street, and much less than the actual acclivity of many of the principal streets and greatest thoroughfares of the city of Cincinnati.

The thickness of the floor of the bridge will be two feet.

The droop or verse sine of the curve formed by the cables, will be 100 feet.

The height of the towers which support the structure, measured from low water level to the saddles, or bearing points of the cables, will be 215 feet.

The capital will be fifteen feet; and the total height of the towers will therefore be 230 feet above low water.

This is certainly a great height to lift stone; but the quantity to be raised over one hundred feet is very small, and the situation of the work, close by the edge of a navigable channel, is exceedingly favorable for its economical construction. The barges which bring the material to the site can approach close to the masonry, so that the blocks may be hoisted, by steam, directly from the boats to their place in the wall.

The width of the flooring will be twenty-six feet in the cleareighteen feet of which space will be appropriated to a carriage way, leaving spaces of four feet on each side for foot-ways.

The Fairmount bridge, which, leading from a populous district into the city of Philadelphia, is a great thoroughfare, is of this width, and has been found, after long experience, to furnish all desirable accommodation.

The Wheeling bridge, intended for the heavy teams and droves which traverse the National Road, is twenty-four feet wide,

A strand of No. 10 wire, weighing 1-20th of a pound per lineal foot, will sustain a weight of 1400 pounds. Such a strand suspended vertically by one end, must therefore be 28,000 feet, or more than five miles long, to be broken by its own weight.

If a wire cable be suspended from elevated points by its two ends, and allowed to assume the curve usually adopted for suspension bridges, these points of support must be removed more than three miles apart before the strain will be sufficient to part the strands.

If we reduce the distance between the points of support, the cable will be relieved of a portion of its own weight, and may be required to uphold in its stead some other more useful burthen.

This is not the place to introduce such computations, and results only need now be stated. But it is upon this capability of wire to be stretched between very distant points of support and sustain a load greater than its proper weight, that the whole question of practicability turns.

The estimated strength of iron is the result of experiment. The strain produced by the bridge and passing loads, is ascertained from the weight of the materials in the structure and that of such transitory loads, and the application of known mechanical principles to these facts.

OF THE WEIGHT TO BE SUSTAINED.

The bridge which has been described will be upheld by twenty wire cables, each of which will be four inches in diameter, and about 1,800 feet long. These cables rest on cast iron saddles, at the summits of the towers, which are calculated to move on iron rollers, so as to compensate for the contractions and elongations of the stays, due to changes of temperature.

From the tops of the towers they sink towards the center of the