[Second indorsement.] ́UNITED STATES ENGINEER OFFICE, Detroit, May 18, 1887. Respectfully returned to the office of the Chief of Engineers with report of this date. O. M. POE, Respectfully returned to the Secretary of War, through the acting Judge-Advocate-General, U. S. Army, inviting attention to the accompanying report of Lieut. Col. O. M. Poe, Corps of Engineers, dated the 18th instant, from which it will appear that he has given the subject full and careful consideration, and has reached the conclusion that the plans and location of the bridge satisfy the requirements of the act of July 20, 1886, and may therefore be approved. His views are concurred in by this office. J. C. DUANE, Brig. Gen., Chief of Engineers. [Fourth indorsement.] WAR DEPARTMENT, JUDGE-ADVOCATE GENERAL'S OFFICE, Washington, D. C., June 1, 1887. Respectfully returned to the Secretary of War, with formal instrument for his approval (prepared in duplicate) of the design and drawing and map of location of the bridge across the west channel of the Detroit River, to connect Belle Isle Park with the mainland. G. NORMAN LIEBER, Acting Judge-Advocate-General. [Fifth indorsement.] WAR DEPARTMENT, Respectfully returned to the Chief of Engineers for file in his office, one copy of the within instrument having been sent to Mr. John Campbell, Secretary board of public works, Detroit. By order of the acting Secretary of War. JOHN TWEEDALE, Chief Clerk. REPORT OF LIEUTENANT-COLONEL O. M. POE, CORPS OF ENGINEERS UNITED STATES ENGINEER OFFICE, SIR: In compliance with indorsement, dated office of the Chief of Engineers, April 21, 1887, on a communication of April 15, 1887, from the board of public works of the city of Detroit, Mich. (by John Campbell, secretary), submitting to the Secretary of War for approval, plans and specifications for a bridge over the west channel of Detroit River, to connect Belle Isle with the mainland, under act of Congress approved July 20, 1886, directing me to examine and report "whether the accompanying plans, etc., of the proposed bridge are in conformity with the requirements" of said act, and transmitting "a copy of the rule of the War Department 'to be observed when application is made pursuant to an act of Congress for approval by the Secretary of War of plans for a bridge,"" with instructions to furnish it to "the bridge authorities for their information and guidance," I have the honor to submit the following, viz: The papers referred to me were received on the 24th of April and the copy of the rule of the War Department was transmitted to the board of public works on the same day. The municipal government had not, at that time, formally accepted the conditions of the act of July 20, 1886, but the necessary action was then taken, and a certified copy thereof (in duplicate) is here with transmitted. The plans and specifications, with the action of the municipal authorities thereto attached, assigning charge of the work to the Board of Public Works (all in duplicate and duly attested) were furnished and are herewith transmitted; also a copy in duplicate of the charter of the city of Detroit. An examination of the plans and specifications for the proposed bridge reveals the following provisions to meet the requirements of the act: 1. Location.-Section 2 of the act requires that the bridge "shall be so located and constructed that the channel of said Detroit River shall not be unreasonably obstructed." The location proposed is from the river terminus of the so-called Boulevard to a point about 1,000 feet above the lower end of Belle Isle, the axis of the bridge to make an angle of about 76 degrees with the direction of the channel. The object of this appears to be to make the bridge an exact prolongation of the Boulevard, as well as to get the shortest bridge and the most convenient landing on Belle Isle. Ordinarily a bridge at right angles with the channel would occupy the shortest line, but in this case the shores on either side of the proposed line fall away from the channel in such manner that a bridge at right angles with it would be a little longer than in the position pro posed. The departure from a line at right angles with the channel is so slight (only 14 degrees) that I do not consider it a matter of much consequence; yet, in an engineering point of view, it would doubtless be better not to make any departure at all. If it be built on the inclined line there will be a slightly increased chance of deposits below the southern (or island) half of the bridge, but should such occur they will be in a locality which has never been used for general navigation, because such channel as exists there is too crooked for safe navigation, whilst the other channels are perfectly safe and easy. The difference in cost between a bridge located as proposed and one built on the other line would be something against the latter, and its southern (or island) terminus would be less convenient. The effect of a bridge on the proposed line in prolongation of a fine street, such as it is expected the boulevard will be, would certainly be more impressive and pleasing to the eye than if built with a change of direction, a fact which should be taken into account in this connection. Upon the whole, all questions considered, I think the arguments in favor of building the bridge on the proposed line outweigh those in favor of a line at right angles with the channel, and am of opinion that so located and constructed it will not unreasonably obstruct the channel of the river. I therefore recommend that the proposed location be approved. 2. Spans.-The second section of the act requires that the draw or pivot span shall be so constructed as to leave a clear opening of not less than 125 feet on each side of the pivot pier, and that the pivot pier shall be located over the channel of Detroit River in such manner that one or both of the openings of said draw or pivot span can be conveniently and safely reached and passed by boats navigating the ordinary channel. The pivot span proposed is 318 feet long, with a clear opening of 125 feet on each side of a pivot pier, located in the main channel in such manner that it may be conveniently reached and passed on either side of said pivot pier. The requirements of the act are therefore complied with in these respects. The act does not prescribe the length to be given the fixed spans. The specifications and drawings of the proposed bridge indicate 11 metal spans, measuring 156 feet each from centers of masonry. This length of span gives a clear water way of about 149 feet between adjacent masonry piers, and, in my opinion, is sufficient. The spans might have been designed for a sufficient width to have rendered necessary at least one pier less, probably at no considerably greater cost, and I think it would have been better, but do not raise this point as a serious objection to the span proposed. 3. Approaches.-The plans and specifications show approaches of timber pile-work, the northern one (next the city) being 497 feet long, and the other being 600 feet. Although in these localities the action of ice is much less destructive than in the channel, yet it is likely to be sufficiently so to render their early reconstruction necessary. However, as proposed they are not likely to injuriously affect the channel, and may be approved. 4. Height at which the bridge shall be constructed.-Section 3 of the act provides" that the height at which said bridge shall be constructed above the surface of the river shall be such as may be approved by the Secretary of War." The specifications place the top of the bridge floor at a height of 22 feet above ordinary water level. This fixes the top of the piers at a height of 20 feet above the same level. The variation in the water level of Detroit River is comparatively slight, seldom amounting in any one year to as much as 2 feet. In a long series of years it might amount to as much as 6 feet, that is to say, 3 feet above or below mean level, consequently the height seems to be sufficient for all practical purposes. 5. Operating draw-span.-Section 4 of the act requires that all draw or pivot spans shall be operated by steam or other reliable mechanical power. The plans and specifications provide for steam-power, with alternative hand-power. The whole arrangement is well designed, and in my opinion may be approved. 6. Position of piers with reference to current.-It is required by section 5 of the act that the "piers upon which said bridge is built shall be parallel with the current of the river." The specifications appear to be silent as to the direction which the piers shall occupy with reference to the current, but refer to the drawings which accompany and form part of the specifications. (Item 13, page 2.) The drawings show all piers, abutments, and trestles parallel to the current, thus making the bridge askew with reference to them. This seems to be sufficient to secure the proper position for these por tions of the structure. However, lest there should be misunderstanding upon the subject, I desire to say that in recommending approval of the location of the bridge I do so under the express condition that all con structions extending below the surface of the water shall be placed par allel with the thread of the current. Inasmuch as the specifications and drawings show that this is the in tention they may be approved in this regard. 7. Plans. The drawings are sufficiently in detail to show the pro posed location of the bridge and the general features of its construc tion. The strain sheets show the stresses to which the various parts o the bridge will be subjected, and these have been recomputed in thi office. The details of construction are not given, at least so far as concern the superstructure, but the specifications seem to provide all that necessary to secure a proper construction. However, detail sheet should be prepared after the contract is awarded to the end that ther be no serious departure from the general design, and particularly in the areas of cross-section and arrangement of parts entering into them, a well as the relations of the parts going to make up the trusses. It is proposed to found the masonry upon a timber grillage 6 feet in thickness, resting upon piles cut off at a depth below the surface o the water, generally of 16 feet, the spaces between and about the piles being compactly filled with riprap before they are cut off. This is the most objectionable feature of the whole design, and unless the work be done with absolute fidelity the results might be serious. The addi tional cost involved in founding the masonry at a considerably greater depth is so great that it is doubtful if the amount of funds available would suffice to construct the bridge, and if it be required that this additional depth be attained the condition may prevent its early con struction. The prevalent desire upon the part of the people of the city of De troit that the bridge be built as soon as possible is so great that I am reluctant to interpose such a condition. However, it is a design 1 would not personally propose, and I therefore find myself unable to rec ommend that it be specifically approved. If the city can nevertheless be permitted to proceed with the work, under the consideration that it is the money of the city and not that of the Government that is in volved, and that it is the city of Detroit and not the United States which takes all the chances, then the proposed foundation may be ap proved. I do not mean to assert that the foundations if built as pro posed would be sure to fail, or even that the chances are largely against their success, but I do not think they are designed with sulicient assurance of stability to justify me in making a specific recom mendation that they be approved, although if faithfully built as designed I think the chances are that they would prove to be sufficient. S. Specifications.-The specifications are general in their nature, but seem to be sufficient, if faithfully observed, to provide for all contingen cies. 9. Data.-Section 8 of the act provides that before commencing work on the bridge certain data shall be submitted by the municipal authori ties to the Secretary of War. These appear to have been furnished, and include A design and drawing of the proposed bridge and piers. A map of the location, giving for the space of one-half mile on each side of the proposed location the topography of the banks of the river, the shore line (which because of the freedom from freshets is always practically the same), the direction of the current in the navigable channel, and the soundings. A cross-section of the stream along the line of the proposed location. In addition to the foregoing, there is supplied from this office an extract from the published lake survey chart of Detroit River upon which is indicated in red the line of the prosposed bridge. 10. Finally. I have been in great doubt as to the amount of detail desired in this report, as well as concerning the character of the approval required by the act. Is it to be limited to the location of the bridge, the draw-span, its length, and mode of operating it; the height of the bridge above the surface of the river, and the location of the piers in their relation to the current, but without reference to any of the details of construction? Or is it to be more specific, and apply as well to all the details of construction? It seems to me that the law only contemplates the former, and with that understanding I recommend ap proval, leaving to the city of Detroit all responsibility for the details of construction. The papers referred to me are herewith respectfully returned. O. M. POE, The CHIEF OF ENGINEERS, U. S. A. Bvt. Brig. Gen. U. S. A. LETTER OF THE CHIEF OF ENGINEERS. OFFICE OF THE CHIEF OF ENGINEERS, SIR: Acknowledging the receipt of the papers in the case of the bridge proposed to be built by the city of Detroit under the provisions of "An act to provide for the construction of a bridge across the west channel of the Detroit River to connect Belle Isle Park with the mainland," approved July 20, 1886, which were returned to this office with approval of plans, etc., by the Acting Secretary of War, dated June 14, 1887, I beg leave to recommend that under provisions of section 10 of the act above mentioned Lieut. Col. O. M. Poe, Corps of Engineers, be appointed by the Secretary of War to supervise and personally examine the construction of said bridge. Very respectfully, your obedient servant, CHAS. W. RAYMOND, Hon. WILLIAM C. ENDICOTT, Secretary of War. [First indorsement.] WAR DEPARTMENT, June 18, 1887. Approved. By order of the Acting Secretary of War: JOHN TWEEDALE, Chief Clerk. |