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3. Two bars 10 inches by 1 inch, and four bars 2 by 2 inches by 7-inch angle combined, section 9.00 square inches.

4. Two bars 12 inches by inch, and four bars 2 by 2 inches by t-inch angle combined, section 10.00 square inches.

5. Two bars 12 inches by 4 inch, and four bars 2 by 2 inches by 7-inch angle combined, section 10.00 square inches.

The top plates upon which rests the floor girdors shall be three-eighths inch thick, and secured to post by angle (L) iron brackets.

The posts shall be accurately drilled and re-enforced for pin holes with pin bearings the same as given before for top chord. In posts 1, 2, and 3, the 6-inch, 8-inch, and 10-inch plates shall be omitted in section of post above top chord, the angle being latticed by 11 by t-inch lacings, with one five-eighths-inch rivet in each end as shown on detail drawings.

Web ties.—The web ties shall be formed of round bars of following sizes and sections:
Second panel, main ties two bars 18-inch round, section 2.96 square inches.
Third panel, main ties two bars 18-inch round, section 2.96 square inches.
Fonrth panel, main ties three bars 17-inch round, section 3.68 square inches.
Fifth panel, main ties three bars 15-inch round, section 4.45 square inches.
Second panel, counter ties two bars 14-inch round, section 2.00 square inches.
Third panel, counter ties two bars 17-inch round, section 2.45 square inches.
Fourth panel, counter ties two bars 17-inch round, section 2.45 square inches.
Fifth panel, counter ties two bars 17-inch ronnd, section 2.45 square inches.
Sixth panel, counter ties two bars 14-inch round, section 3.53 square inches.

They shall be made with loop eyes of square iron so as to give good bearings on the pin, and all screw ends shall be upset so that the diameter of the bar under the thread shall be one-sixteenth inch greater than in the body. They shall be adjusted by sleeve nuts with right and left hand threads.

Wind braces. There shall be a lattice brace placed between each panel of lower chord, and between each panel of upper chord except the two center panels, composed at ends of four bars 2 by 3 inches by t-inch angles, latticed at first panel point four bars 2 by 2 inches by t-inch angles latticed, and at other panel points of four bars 14 by 14 inches by 4-inch angles, latticed, connected direct to chord-pins by three-eighthsinch hitch-plates of a width to accommodate the connecting detail, but in no case narrower than the smallest diameter of the connected brace.

Sway rods.—The vertical cross-ties between the trusses shall connect direct with braces as shown in drawings, and shall be 17 inch round bars at ends 1-inch round bars at first panel, and 4-inch round bars in all other points. The horizontal lateral rods shall be for upper or roadway truss

Square inches. First panel, 27-inch round, section...

3.97 Second panel, 2-inch round, section.

3. 14 Third panel, 14-inch round, section

2. 40 Fourth panel, 14-inch round, section

1.76 Fifth panel, 18-inch round, section

1.00 Sixth panel, 1-inch round, section

For lower chord sway system: First pane), 17-inch round, section..

1.00 Second panel, 1-inch round, section.

.78 Third panel, {-inch round, section

60 Fourth panel, I-inch round, section. Fifth panel, 8-inch round, section Sixth panel, 4-inch round, section

44 Those in floor truss shall be adjusted by means of thread and nut at each end janming against a wrought-iron level plate securely riveted to floor beams as shown in drawings. The lower chord sway rods shall attach direct to lower chord pins and be provided with sleeve-nut adjustment with right and left hand threads.

Floor line chord.—The floor line chord shall be composed of plates and angles of following sizes and sections for different panels:

First panel, two bars 6 inches by 1 inch, and four bars 2 inches by 2 inches by l-inch ang'•;, aggregate, section 7.00 square inches.

Second panel, two bars 6 inches by 1 inch, and four bars 2 inches by 2 inches by 7-inch angles, aggregate, section 7.00 square inches.

Third panel, two bars 10 inches by 1 inch, and four bars 2 inches by 2 inches by -inch angles, aggregate, section 9.00 sqnare inches.

Fourth panel, two bars 12 inches by 1 inch, and four bars 2 inches by 2 inches by 7-inch angles, aggregate, section 10.00 square inches.

Fifth panel, two bars 12 inches by 1 inch, and fjar bars 2 inches by 2 inches by 7-inch angles, aggregate, section 10.00 square inches.

Sixth panel, two bars 12 inches by 4 inch, and four bars 2 inches by 2 inches by 7-inch angles, aggregate, section 10.00 square inches.

.78

They shall be latticed together by 17 inches by 7-inch lacing bars with one fiveeighth-inch rivet in each end. They shall be placed between the floor beams and attached to same by gusset bitch-plates and securely bolted, all as shown in detailed drawings.

The nuts on connecting bolts shall be riveted down after being drawn up snug to prevent working loose.

Floor beams.—There shall be a wrongbt-iron floor beam at each panel point having a capacity of 100 pounds per square foot of roadway and walks, or a wheel load of 6 tous on each pair of wheels for each wheelway. The floor beam shall be so proportioned that the chord strains are resisted by the upper and lower flanges and the shearing strains by the web plates. It will be constructed of 24 inches by 7-inch plate, with four bars 3 by 34 inches by 8-inch angles riveted to the flanges and 2 by 2 inches by 1 inch, and 2 by 3 inches by t-inch angle iron stiffeners riveted to the web, two of the latter on each side over the points of support aud one of the former on each side, 6 feet from the points of support all by five-eighths-inch rivet. The floor beams shall be secured to web post top-plates by four five-eighths-inch rivets on each end, and, omitting the plate ontside of the trusses, the lower flange shall level up to 7 inches, all as shown on detail drawings.

Rirets.-All rivets shall be made of best quality of soft fibrous iron which sball be capable of bending 180 degrees upon itself without fracture. They shall, as far as possible, be driven by machinery and completely fill the holes; the heads shall be bemispherical directly opposite and shall be formed in a neat and workmanlike manDer. All rivet boles shall be carefully spaced and punched by a die not over one-sixteenth inch larger than diameter of rivet, and must match in different pieces to be riveted together, so that hot rivets can be readily inserted without using the driftpin to strain the iron. The pitch of rivets shall not exceed 5 inches (except for open lattice work), nor to be less than three times the diameter of the rivet (which will generally be five-eighths incb to seven-eighths inch diameter); where practicable rivet holes shall be two diameters from the edge of the piece.

The use of drift-pins will in no case be allowed after the work has been once assembled ready for riveting, and only to hold parts in place ready for bolting up. Within two diameters of the end of riveted compression members, the pitch of rivets shall not exceed four times the diameter of the rivets.

Pins.-All top chord pins shall be :}} inches in diameter, the bottom chord pins 5 inches in diameter, and the end connection pins 6 inches in diameter. They shall be tuned straight and smooth and to exact size as given, and shall be provided, as far as possible, with cast-iron end caps, set screws, and chamfered ends, all as shown on detail drawings. No variation of more than one-sixty-fourth of an inch will be allowed between the diatueter of pins and pin-holes. Cast-iron packing-rings or washers are to be used whenever required to make joints snug and tight. Pins are to be proportioned so as to resist bending as well as shearing strains. "The diameter to be not less than twothirds the width of the largest tension member attached.

Railing.–The sidewalk railing shall be made of open lattice work 34 feet high with projecting pickets, and shall be secured to floor beams at each panel point by wrought angle-iron posts. General. - All abutting surfaces must be planed or dressed so as to insure even bearings, taking light cuts so as not to injure the end fibers of the piece, and must be proteeted by white lead and tallow. Pieces where abntting shall be brought into close contact by the use of clamps or other approved means before being riveted together. In all built struts or posts the segments must be all of one length without break and inust be rigidly riveted together so as to act collectively as one solid post.

All rivets in pin re-enforce plates shall have the same bearing on the plate that the plate has on the pin. They shall be so placed as to utilize the full section of the plate metal, but in no case shall their distance apart exceed 5 inches nor be less than the diameter of the rivet.

All bed plates must be of such dimensions that the pressure on the masonry shall not exceed 250 ponnds per square inch. Rollers shall be not less than 2 inches in diameter and shall be so proportioned that the pressure per linear inch of roller shall not exceed the product of the square root of the diameter of the roller in inches multiplied by 500 pounds. The roller shall be placed between planed surfaces. The ends of all sqnare ended members shall be planed smooth and exactly square to the center line of strain. No lateral or diagonal rods shall have a less area than three-fourths square inch, Eyr-bars which are to be placed side by side in the bridge shall be bored at the

All iron work shall be neatly and accurately fitted up in a thorough and workmanlike manner. It shall be painted with one good coat of metallic paint and boiled liu

same temperature.

seed oil before shipment from the works, and all bright parts shall be protected by a coat of tallow and white lead.

After erected in place it shall be painted two good coats of lead and oil of such color as the engineer in charge shall direct.

Quality of the iron.-All iron used in the bridge shall be “best best" quality of double retined iron with an elastic limit not less than 25,000 pounds per square inch, and an ultimate strength as great as can be attained with that elastic limit in the best iron for bridge purposes.

All wrought iron must be tough, fibrous, and uniform in character. Finished bars must be thoroughly welded in rolling, and free from injurious seams, blisters, buckles, cinder spots, or imperfect edges.

For all tension members the muck-bars shall be rolled into flats and again cut, piled, and rolled into finished sizes. No scrap shall be used. They shall stand the following tests:

Tension tests.-When tested in specimens of uniform sectional area of not less than half nor more than one square inch for a length of ten inches, taken from members to be used in the bridge, the iron shall show an ultimate strength and elongation as follows:

Specimens from

per Ultimate strength,

pounds square inch.

Elongation.

Bar iron less than 3 square inches
Bar iron over 3 square inches
Angle iron
Plate iron

51, 000 18 per cent. in 8 inches. 50, 000 15 per cent. in 8 inches. 50,000 15 per cent. in 8 inches. 48,000 15

per cent. in 8 inches.

Full sized pieces of flat, round, or sqnare irou used for tension members, and not over 3 square inches in sectional area shall have an ultimate strength of 50,000 pounds per square inch, and bars of larger sectional area will be allowed a reduction of 1,000 pounds per square inch, down to a minimum of 46,000 ponuds per square inch.

Bending tests.-All iron for tension members must bend cold, for about 90 degrees to a curye whose diameter is not over twice the thickness of the piece, without cracking. At least one sample in three must bend 180 degrees to this curve without cracking. Then nicked on one side, and bent by a blow from a sledge, the fracture must be nearly all fibrous, showing but few crystalline specks.

Specimens from angle, plate, and shaped iron must stand bending cold through 90 degrees, and to a curve whose diameter is not over three times its thickness, without cracking

When nicked er bent its fracture must be mostly fibrous.

All facilities for inspection of iron and workmanship shall be furnished by the contractor. He shall furnish, without charge, such specimens, or full sized pieces of the several kinds of iron to be used as may be required to determine their character.

Sizce of iron.--In case the sizes of iron or members herein specified, or stated on the strain sheets, shall be found by the engineer to be insufficient to meet the strains arising from the specified loads, the sizes of such iron or member shall be increased so as to meet the required strain per square inch.

Wood work.--All luniber shall be of sound, well-seasoned, Georgia or North Carorina long-leaved pitch pine, to be all heart-wood, free from shakes, large or unsound knots, or any other defects.

Roadway plank.-The roadway plank shall be 3 inches thick, 6 to 12 inches wide, and laid diagonally. They shall be spiked to each joist by two 7-inch spikes, and with two spikes at each end.

Sidewalk plank.—The sidewalk plank shall be 2 inches thick, 6 to 12 inches wide, laid crosswise, with two 5-inch spikes at each intersection with joist, and two in each end. The grade of the sidewalks shall be 4 inches above that of the roadway.

Roadway joist.—The roadway joist shall be 15 inches deep, 4 inches wide, placed 2 feet apart.

Sidewalk joist.—The sidewalk joist shall be 3 inches thick, 15 inches deep, and placed 2 fret apart.

Wheel guard.—To the end of roadway plank shall be spiked a 6 by 8-inch wheel guard, raised on blocks, placed 4 feet apart to a level of the sidewalk plank. The inner edge of wheel guard to be bound with an 1 inch by 1 inch flat bar of iron secured to same by 14-inch wood screws driven after wheel guard is set, In case the floor system above

specified shall be found insufficient to bear the specified panel and wheel loads the sizes of beams shall be increased as required by the engineer. If in case it shall be deemed best by the contractor, upon a further examination of the natural conditions of the site, to change the location of the bridge, within the limits specified in the original advertisement, from the site herein noted, or to make any changes in the length of the spans from those herein stated, they shall base their unit strains the same as herein specified, and the capacity per square foot of roadway and walks as per the following table, subject in all cases to the approval of the engineer in charge :

Length of span.

Load.

Under 60 feet
60 feet to 100 feet.
100 feet to 200 feet.
200 feet to 400 feet.

100 90 75 65

Provided that the loads per square foot herein indicated are to be taken for a width of bridge of 30 feet. In case the width is reduced to 25 feet the loads per linear foot of bridge shall be the above units multiplied by 30 feet.

85 feet and 55 feet spans.—The sizes and section for 85 feet and 55 feet spans are given on strain diagram sheet, and in all respects they shall conform in quality to that specified above for the 187-foot spans.

False works.—The false works for the bridge shall be erected by and at the expense of the contractor, and upon the completion of the bridge shall be entirely removed.

APPROACHES.

Virginia shore.—The approaches to the bridge on the Virginia side are to be of such extent and length as will permit a connection to be readily made therewith by the county roads. The width of the approach shall not be less than the combined width of the footways and roadways, and the grade shall not exceed 3 feet in 100 feet.

The slopes of the embankment or excavation of the approach shall not be less than 11 horizontal to 1 vertical.

The character of the road-bed shall be fully equal to that of the roads connecting therewith.

Georgetown approach.- The north or Georgetown end of the bridge will cross the canal and terminate at the north abutment, to be built as already specified on the north side of the canal, so as to make a direct connection with the canal road by raising the grade of the same.

The grade of the road will be raised to the level of the bridge at the end of the same, and the approaches to a grade of 2 feet in 100 in either direction from this level.

The filling shall be made in layers, with suitable material such as is found in the immediate vicinity, and the work is to be done so as not to interfere with travel. The width of the roadway will be 50 feet, and the side slopes 11 to 1, and the roadway will be macadainized to the same depth as the existing canal road.

The wall along the canal is to be raised so as to be at the same height above the new grade as it is above the present grade of the road.

On the north side of the embankment of approach a suitable wooden railing shall be put up, if deemed necessary by the engineer, to prevent accidents to vehicles.

B.

CORRUGATED METAL COMPANY TO MR. S. T. ABERT, UNITED STATES CIVIL ENGI

NEER.

BINGHAMTON, N. Y., February 13, 1882. SIR: Referring to your esteemed favor 31st ultimo, would say: We beg to decline to accept the modified specifications therewith inclosed to us, as a basis for a contract for building the proposed bridge at Georgetown, D. C., in the particular matter of the height of the pier8.

It is not necessary to the stability of the structure to carry up the masonry of the piers to the center of the trusses.

The iron end part and braces, which you prefer to omit, are amply sufficient for the purpose as designed, for the particular reason that the brace (acting as a strut or tie)

H. Ex. 156 -3

affords a sufficient safe resistance as against wind or other force longitudinally applied to the extent and amount of a force which would overturn the pier. The exact amount of strain exerted under various conditions upon the foot brace is not determinable, but the amount of force required to overturn the pier, when applied to its top

and longest side is determinable in amount, and the foot brace is in design and

section sufficient to resist that amount of strain, whether acting as a strut or tie.

We deem it quite unnecessary to provide for a condition of resistance of the character under consideration greater than the resistance offered by the piers themselves.

With the exception of the height of the piers (they to be as proposed by us as to height) and their thickness at top (to be reduced by i foot) from that stated in your specifications, we accept all of the conditions named in your specifications of January 31, 1881, as the basis of a contract to build the bridge.

Referring to the postscript of yonr favor of January 31, 1880, would say, the weight per linear foot or yard determines the net section of an angle or channel bar.

Referring to your favor of 4th instant would say, in calculating strains graphical method has been used. We waive any error in calculations, and will submit detailed calculations if desired and if contract is awarded to us. We are, sir, very respectfully, your obedient

servants, THE CORRUGATED METAL COMPANY,

By WM. O. DOUGLAS, Agent. Mr. S. T. ABERT,

United States Civil Engineer. P. S.-We herewith return your specifications of 31st ultimo, as requested. The piers to be 7 feet wide, measured on top of coping.

C.

CORRUGATED METAL COMPANY TO THE CHIEF OF ENGINEERS.

BINGHAMTON, N. Y., February 16, 1882. GENERAL: We regret that under date of the 14th instant we were compelled to decline the final specifications concerning the proposed free bridge, submitted by Mr. Abert, principally in the matter of the increased height of the piers, which were increased from 26 feet to 46 feet above low-water.

This increased amount of masonry would cost $50,000, for which amount, in addition to our former bid of $140,000, we would subscribe to Mr. Abert's last specifications in full, and in every particular, as the basis of a contract to do the whole work. We are, general, very respectfully, your obedient servants,

THE CORRUGATED METAL COMPANY,

By WILLIAM O. DOUGLAS, Agent. Bvt. Maj. Gen. HORATIO G. WRIGHT,

Chief of Engineers, U. S. A.

D.

THE KING BRIDGE COMPANY TO MR. S. T. ABERT, UNITED STATES CIVIL ENGINEER.

CLEVELAND, OHIO, January 28, 1882. DEAR SIR: Your favor of 23d received. We also have received a Washington paper, with inclosed clipping. We presume there is some mistake about it, and that we will be allowed to modify our bid if Corrugated Company are allowed to modify theirs. We think we should have that privilege. As we understand Mr. Lewis, our bid is for a bridge such as we understood you desired for the place, and nearly twice as wide as the Corrugated Metal Company's plan. If we are allowed to bid on a bridge no wider than theirs, our price, of course, would be considerably less than on the plan we submitted last fall.

We think the fair plan would be to readvertise on a specified width, and length of spans and load, which would put all bidders on same footing. We think more companies would now compete, and the bids be lower, Yours truly,

JAS. A. KING. Col. S. T. ABERT,

United States Engineer.

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