ments; (2) for superstructure; and (3) for approaches-the total cost not to exceed the appropriation of $140,000.

The following proposals were received for the construction of the bridge:

For the site 500 feet above the Aqueduct Bridge but one proposal was made, as shown on the abstract of proposals for this site, here with inclosed. (Inclosure No. 2.) This bid was made by Messrs. Charles H. Bliss & Co., of Washington, D. C., who proposed to construct an iron bridge similar and equal to the Anacostia Bridge in substructure and superstructure, to be 1,350 feet long, with substantial approaches of wood or iron on each side of the river, for the sum of $183,600.

The proposal was not accompanied by a bond, nor by any plans or specifications of the proposed bridge, and was therefore informal, and as its amount exceeded the appropriation of $140,000 made by Congress, it could not, in any event, be entertained.

For the site at or near the "Three Sister" islands, about 3,100 feet above the Aqueduct Bridge, there were three bids, shown on the abstract of proposals at this site, herewith inclosed. (Inclosure No. 3.) These three bids, with the prices named, are as follows:

1. The Corrugated Metal Company, of East Berlin, Conn. For the piers and abutments, $36,000; for the superstructure, $100,000; for embankments and approaches, $4,000; total, $140,000.

2. The King Iron Bridge and Manufacturing Company, of Cleveland, Ohio: For the superstructure alone, $102,000.

3. Messrs. Charles H. Bliss & Co., of Washington, D. C.: For the entire bridge, $145,000.

The proposal of Charles H. Bliss & Co. was similar to their proposal for the Aqueduct Bridge, but as it was unaccompanied by either bond, plans, or specifications, and as it further exceeded the amount of the appropriation, it could not be considered.

The second proposal of the King Iron Bridge Company contemplates the erection of the superstructure alone, the general character of which is indicated on the abstract of proposals.

As no bid was submitted for piers or abutments this proposal could not be considered.

The proposal of the Corrugated Metal Company, of East Berlin, Conn., is the only one which, coming within the amount of the appropriation, provides at the same time for the construction of the entire bridge. I have therefore taken sufficient time to examine carefully the plans and specifications submitted by this company, and to make inquiries as to the strength and durability of bridges which they have already erected.

As the specifications which they submitted for the masonry and superstructure were very brief and indefinite, it was also necessary to prepare detailed specifications, in order that the character of the work proposed might be fully understood, and the delay in reporting upon the proposals received has been due to these causes.

The following is a brief abstract of the proposition of the Corrugated Metal Company:

The general plan proposed is a parabolic truss bridge of wrought-iron with pin connections, with spans of from 150 to 300 feet, the last being across the main-river channel.

Foundations.-Three classes of foundation were proposed, all starting from solid rock: 1. Courses of large stone laid in the water with a derrick, with the top concreted. 2. A timber crib filled with grouted masonry, the outside being protected with riprap. 3. A foundation

Tension

Compression

built with a coffer-dam, the courses of masonry starting from the solid rock, after the rock has been leveled to receive them.

This last foundation is clearly the only one admissible for this bridge. The class of masonry specified was coursed rock-faced masonry, of the stone quarried along the river, the courses to be from 18 to 36 inches high, with one-half inch joints, the beds to be one and a half times the rise, vertical joints 12 inches deep, one-fourth headers, and with suitable backing. The pier heads were to be dressed, the stones doweled together, and the whole laid with the best quality of cement mortar.

The width of the piers at the top, as proposed, was 6 feet for the shorter spans, and 7 feet on the 300 foot span, the height being but 24 feet above low-water, and the batter 1 in 12. The height should, however, be that of the centers of the trusses 45 feet above low-water, and the widths at this grade should be 7 feet for the 200-foot spans and 8 feet for the 300-foot span. With these, and some less important exceptions, the specifications for masonry, as modified, would probably meet the requirements of the work.

Superstructure.-For the wrought-iron superstructure of the bridge, full specifications were prepared covering the quality of iron, details of construction, workmanship, painting, &c., and the requirements in these particulars were substantially met by the bidders.

The capacity of the bridge and the corresponding unit strains on the iron, are, however, the most important and essential points to be considered.

Capacity. For the live load on the bridge the Corrugated Metal Company proposed, for all the spans, 80 pounds per square foot on the roadways and 60 pounds per square foot on the foot-walks, or an average of 73 pounds on the entire width. The live load specified for the Anacostia Bridge and the Little Falls Bridge is 100 pounds per square foot.

Inasmuch as the free bridge may in the future be subjected to severe strains by droves of cattle, by the passage and crowding of large bodies of people visiting government reservations or witnessing regattas upon the river, or by the passage of troops and heavy ordnance in time of war, I am satisfied that the capacity or live load of the bridge should not be less than the Anacostia Bridge.

Strains on iron.-The principal strains which the bidders propose per square inch of iron, and also the specified strains on the Little Falls bridges, are shown in the following table:

Anacostia

and

Shearing strain

8,000

The strains on wrought iron should not exceed 10,000 pounds per square inch in tension, 8,000 pounds in compression (reduced by Gordon's formula), and 7,500 pounds in shearing. The strains proposed by the

Corrugated Metal Company considerably exceed these amounts, and are clearly inadmissible. The bidders subsequently proposed to decrease the load and decrease the unit strain, but this would not increase the strength of the bridge.

While a structure such as they propose for the amount of the appropriation might be admissible as a country bridge, subject to light traffic, it would not possess the requisite strength for such loads as the free bridge might be called upon to sustain; and it seems evident that a bridge of the proper strength cannot be built for the appropriation.

The proposal of the Corrugated Metal Company fails to meet the evident requirements as to the capacity and strength of a bridge for this locality, and I would therefore respectfully recommend that this, together with all proposals received, be rejected.

Very respectfully, your obedient servant,

The CHIEF OF ENGINEERS, U. S. A.

S. T. ABERT, United States Civil Engineer.

CONSTRUCTION OF FREE BRIDGE ACROSS POTOMAC RIVER. NEAR GEORGETOWN, D. C.

Advertisement.

UNITED STATES ENGINEER Office,

No. 1907 PENNSYLVANIA AVENUE, Washington, D. C., September 14, 1881. Sealed proposals for the construction of a bridge across the Potomac River at "Three Sisters," about 3,100 feet above the present Aqueduct Bridge at Georgetown, D. C., to include approaches and right of way for same, as provided for in the act of February 23, 1881, will be received at this office until 12 m. on Saturday, October 29, 1881, and opened immediately thereafter.

Also sealed proposals for the construction of same bridge on a section of the river about 500 feet above the said Aqueduct Bridge, under the provisions of the act above named, will be received and opened at the same time and place.

General specifications, containing a copy of the act of Congress of February 23, 1881, together with blank forms of proposals, can be obtained at this office. The right to reject any or all proposals is reserved.

General specifications.

S. T. ABERT, United States Civil Engineer.

1. Locality. The locality of the work is on the Potomac River, at or near Georgetown, in the District of Columbia. Georgetown is near the head of tide-water. It has good harbor and wharf accommodations, and can be reached at ordinary high-tide by vessels drawing 18 feet. Range of tide about 3 feet.

2. General description of bridge.—The bridge is to be built upon piers and abutments of masonry founded upon solid rock. The superstructure is to be of iron with plank roadway and footways. Its width is to be sufficient for a double roadway, with footways on each side.

Proposals for its construction at either of the two sites, as described below, are solicited.

3. Proposed site at "Three Sisters."-At this section of the river (about 3,100 feet above Aqueduct Bridge) its width is about 1,050 feet, and the bottom is believed to be solid rock, or rock with a covering of a few feet only of sand and gravel.

Along the north bank, and 100 feet from it, runs the Chesapeake and Ohio Canal at an elevation of 38 feet above low-water of the river. The canal is 45 feet wide, and along its north bank there is a macadamized road 50 feet wide and 44.8 feet above low-water of the river.

The abutments are to be at the water's edge, and their faces will be about 1,050 feet apart. The bridge will be continued over the canal and road, where, at the north side of the road, it will terminate at a retaining abutment for embankment of approach. The distance between the faces of the larger and smaller north abutments will be about 200 feet.

The height of roadway above low-water will be 60 feet, though with a view of diminishing the cost of approach on the Virginia (south) side, it may ascend from this elevation at its north end toward the Virginia end on a grade not exceeding 1 foot in 100 feet. The clear headway at canal shall not be less than 14 feet.

4. Proposed site about 500 feet above Aqueduct, Bridge.-At this section the width of the river is about 1,500 feet, and the distance between main abutments would be about 1,500 feet, with a further distance of 200 to 225 feet to the smaller abutment at north side of road. The north half of the river width has hard bottom, the remainder being soft. The depth to rock is not known at any part of this section. The requirements for the structure at this site are the same as for the preceding, except as to the height of roadway, which may be less, and is to be taken at a convenient level as regards approaches, but shall not be less than that of the Aqueduct Bridge. The clear headway at canal shall not be less than 14 feet.

5. Funds available.-The amount appropriated for the construction of the bridge complete, with approaches and right of way, is $140,000, and proposals exceeding that amount, or which do not include all the work comtemplated in the act of appropriation, cannot be entertained.

6. Examinations and measurements.-Bidders are expected to examine the sites and ascertain for themselves the character of ground for foundations for piers and abutments, and for approaches, &c., and must inake their own measurements of distances, heights, and grades.

7. Further information.—Any further information in possession of this office will be given persons desiring to bid, on their application.

8. Explanations and corrections.-Any doubt as to the meaning of the specifications, and any obscurity in the wording thereof, shall be explained by the engineer, who shall have the right of correcting any errors or omissions in them when such correction is necessary for the proper fulfillment of their intention, the action of such correction to date from the time the engineer gives due notice thereof.

9. Extra work, &c.-No claim for extra work or for delay of any kind will be considered or paid, and the contractor will be held responsible for the entire work until every part of it is completed according to the specifications, and accepted by the Secretary of War as in accordance therewith and with the act of February 23, 1881.

10. Payments.-Estimates for payments will be made upon each pier and abutment as soon as safe from damage by freshets, and upon embankments as soon as riprapped above flood line. Thereafter monthly estimates will be made until the structure is completed. Ten per cent. will be reserved from all payments until the entire work is completed. At the end of six months after the entire work shall have been completed, if no fault of construction, use of improper material, or settling of foundations or embankments are apparent on an inspection of the work by the engineer, the reserved percentages will be paid; otherwise they will be retained until the contractor makes good the deficiency, together with all damage that may have been caused thereby. 11. Proposals.—Proposals must be in duplicate for each or either of the sites for which proposals are submitted, and must be on separate forms for each site. Proposals for each site must be accompanied by bidders' plans and specifications in detail. A single set of plans and drawings will suffice for each site bid for.

The proposals, plans, and specifications are to include the construction of piers and abutments with proper foundations, superstructure complete, approaches connecting with the most accessible road, and right of way for same, together with all other expenditures necessary for the covenient use of the structure by the public.

Each proposal must be accompanied by a copy of these general specifications, which, together with the special specifications, plans, and drawings submitted by the bidder, are to be referred to in the proposal as forming a part thereof.

Each bidder will submit for each or either site three prices as follows:

(A.) For constructing bridge with approaches, right of way, &c., as specified, at "Three Sisters":

(1.) For piers and abutments, as specified,..

(2.) For superstructure complete, as specified,..

(3.) For grading and embankments for approaches, as specified,

dollars.

dollars.

dollars.

(B.) For constructing bridge with approaches, right of way, &c., as specified, about 500 feet above Aqueduct Bridge:

(1.) For piers and abutments, as specified,.......

(2.) For superstructure complete, as specified,

(3.) For grading and embaukments for approaches, as specified,...

dollars.

dollars.

dollars.

These prices are to cover all costs whatever for labor, materials, appliances, &c., for the completion of the work as specified.

The right to reject any or all bids is expressly reserved. The right is also reserved to accep: a bid or bids for any one or two of the three classes of work at either site, rejecting the bids for the remaining class or classes made by that bidder, for accept

ance of corresponding bid or bids of another bidder or bidders, provided the bidder does not expressly state with the price for each class that it is conditioned upon the acceptance of the bid or bids for one or both of the other classes.

Bids will also be considered for one or more of the classes of work named at either or each of the sites; also, bids based on plans and estimates differing from those described in the specifications but made in accordance with the act of February 23, 1881, will be received and considered at the same time.

Proposals must be accompanied by a bond, with two sureties, in the sum of $5,000, in accordance with the act of Congress of April 10, 1878, and with the form prescribed. A proposal unaccompanied by such a bond will not be considered.

12. Contract.-The successful bidder will be required to enter into a written contract with the United States, with good and approved security, in the sum of $25,000, within ten days after being notified of the acceptance of his proposal.

These specifications will be attached to the contract and form a part of it.

Instructions to bidders.

S. T. ABERT, United States Civil Engineer.

No bids will be considered which are not made on blank forms furnished from this office.

Proposals and bonds must be in duplicate, and each accompanied by a copy of these specifications.

All the blank spaces in the proposal and bond must be filled in.

The duplicate proposal must be in a sealed envelope indorsed "Proposals for constructing bridge near Georgetown, D. C."

Bidders are requested to be present at the opening of the bids.

For further instructions see "General instructions for bidders."

A copy of the act of Congress referred to is appended for further information.