k i i ; STROUD Report upon a Highway Bridge Civil Engineering B. S PM3VIRSITT OF Via,. XMctsici

Transcription

1 k i STROUD i ; Report upon a Highway Bridge Civil Engineering B. S PM3VIRSITT OF Via,. XMctsici i

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5 REPORT UPON A HIGHWAY BRIDGE.BY. Smith Leroy Stroud THESIS FOR THE DEGREE OF BACHELOR OF SCIENCE IN CIVIL ENGINEERING COLLEGE OF ENGINEERING UNIVERSITY OF ILLINOIS PRESENTED JUNE, 1904

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7 UNIVERSITY OF ILLINOIS May 27, 1904 l«jo THIS IS TO CERTIFY THAT THE THESIS PREPARED UNDER MY SUPERVISION BY SMITH LIROY STROUD entitled REPORT UPON A HIGHWAY BRIDGE IS APPROVED BY ME AS FULFILLING THIS PART OF THE REQUIREMENTS FOR THE DEGREE of Bachelor of Science in Civil Engineering HEAD OF DEPARTMENT OF 89

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9 / INVESTIGATION OE A HIGHWAY BRIDGE. It is proposed to investigate a highway "bridge at Danville, Illinois, and it is assumed that this thesis is a report to the City Engineer. The bridge in question is known as the Woolen Mill Bridge, and spans the west fork of the Vermilion River. It is situated at the western limits of the city of Danville, a place of about inhabitants. The bridge carries a large amount of heavy travel between the business center and the brick-yards and coal mines just west of the city. It was built in 1339 by the LaFayette Bridge Company of LaFayette, Indiana

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13 3. Fig 1, page 2, shows in outline the eletation of the bridge. The roadway consists of a 17-foot carriage-way with a 4 l/2-foot sidewalk on either side. The west approach consists of ten trestle "bents each of 20-foot span. The span crossing the river is a Whipple, or double intersection, deck truss of ten panels, each 17 feet 3 inches long. The east approach is composed of five deck Pratt trusses of four panels, each 17 l/2 feet long, resting upon iron posts, and four trestle bents, each 17 l/2 feet long supported by iron posts. The roadway of the west approach has a rise of three feet per 100 feet, while the remainder of the bridge is level. The floor beams are built-up sections. The joists are 3" x 12" oak, spaced 1.5 feet from center to center. A lattice fence runs the entire length of the bridge. All the trestles posts and the west pedestals of the river span rests upon sandstone piers. The east pedestals of the river span rest upon two wrought-iron cylinders. These cylinders are braced together by lateral ties and struts. In this investigation "Waddells Specification for Highway Bridges, Edition 1893" will be taken as the standard, and it will be assumed that this bridge is, or rather should be, a Class A bridge

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17 5. I. WEST APPROACH. This approach is a viaduct of ten trestle Dents, each having a span of 20 feet and resting upon iron posts. The highest trestle will be investigated as that is the one that will "be most likely to fail The dead load was found to "be 12,996 lbs. per span. The live is taken as 100 lbs. per sq. ft., or a total for the span of 52,000 lbs. Therefore the total dead and live load is 64,990 lbs. The horizontal wind load is assumed as 500 lbs. per lineal ft. of span. Tig. 2, shows the composition of the several members of the tallest trestle bent, the stresses in each member, and also the percent of efficiency of each in terms of what it should A be according to Waddell's Specification. ITotice that the minimum efficiency is 61 percent for the legs

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21 Floor Beam.- The form of the floor-"beam is shown in Fig. 3. The efficiency of the "beam for bending when subject to a live load of 100 lbs. per sq. ft. of roadway and sidewalk, and to the dead load of 32.7 lbs. per sq. ft. is only 24 percent. The A loading to give an efficiency of 100 percent would be only 40 lbs. per sq. ft. The efficiency of the beam for shearing stress, when subject to the above loading of 100 lbs. live load and 32.7 lbs. dead load is 65 percent. Joists.- The joists are 3" x 12" x 20" oak and will be investigated as if they were new. They are spaced 1.5 ft. A heavy traction engine and the dead load will produce the greatest stress. The engine used in this investigation is a traction engine weighing 15,800 lbs. of which 2/3 is assumed to be carried on the rear axle and 1/3 on the front. Center to center of front wheels is 4 '-7 l/2"; u. to c of rear wheels is 5' -10"; and c. to c. of axles is 8 -l l/2" f. width of front wheel is 6 inches, and of rear wheel 12 inches. It is assumed that the front and rear wheels are on a line parallel with joists and that the weight coming on the front and rear wheel is taken by two joists. It is found that for new joists the efficiency is 108 percent, but as many of them are now badly decayed, the efficiency is undoubtedly a great deal less

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25 7. II. MAIN SPAN The length of the main span is 170 feet, the depth 25 feet and the panel length 17 feet 3 inches. The driveway is 17 feet wide, and there is a 4 l/2-foot sidewalk on each side. The dead load per panel is 8000 lbs. The live load is according to Waddell ' s Specifications 86 lbs. per sq.. ft. or 22,360 lbs. per panel. The efficiencies are found by taking into consideration: the direct stresses of the members, the eccentricity, the bending due to the weight of the member, the stresses due to direct wind and to the wind moment. Fig. 4 shows the outline of the main span, the maximum stresses, the composition of members and the efficiencies.

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31 Plafe 17. ^ufs ide View of Pedestal and End Po s f. in S fc/ e V j e w of Ped e 5 fa / a nd End Poet.

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35 Loweral Laterals.- Fig. 5 shows the lower lateral system. It is seen that the efficiencies are satisfactory, although the rods have bent eyes, which is contrary to the specifications and to common practice. The design of the strut is shown in Pig. 8. It is fastened to the lower chord pin "by a stirrup. The design is not very good, but since it shows no sign of buckling, it is probably strong enough for this case. Top Laterals.- The efficiencies according to Fig. 6 range from 105 per cent to 106 per cent, which shows that they are satisfactory. The design of the top lateral rods and connection to the top chord is shown in Fig. 9. Portal.- The portal, shown in Fig. 7, gives an efficiency of 130 per cent which is sufficient. Pedestals.- The pedestals are almost entirely covered with earth and consequently the rollers do not act, because of the dirt which is between them. The pedestals so far as the main span is concerned fulfill the requirement of the specification both for thickness of shoe plate and the pressure upon the stone masonry. In the connection between the western approach and the main span the allowance for the expansion of the bridge is not provided for and consequently there is a buckling. There is a leg, shown in Plate 3, which extends from the lower end of end post to the floor-beam of the bridge. This leg has been moved out of line vertically something like three inches, caused by the expansion of the main span.

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37 Loitcra I and M a / i P o r f a System. mum Stresses, Composition of Eff.c e/icies. Boffom L d f e rd I. rto/5 s \/ <,*f/ c.a 2fVv r x N / \ / \ Load = 83o /bs./oer Panel Top Ld te r d I. \ ^ s o) v' x o) \ / / ' x jr s /ft V/ / S / \ s Live Load = 15 o / bs, per f 7 of Bridcje D& <=<d Lo dd - isolbsperii of Bridge. Po r T a ) S y st He,, r.

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39 LoWer L d fe ra I Strut.

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41 l(o. III. East Approach. The east approach is composed of five deck Pratt trusses of four panels each, 17 l/2 feet long resting upon iron trestle posts. The dead load was found to be 6000 lbs. per panel. The live load is taken as 100 lbs. per sq. ft., or a total of lbs. per panel. Pig. 10 page 18, shows the composition of the several members of the east span, the stresses in each member, and also the per cent of efficiency of the members. Prom the figure it is seen that the efficiencies range from 55 to 66 per cent. Pig. 11 page 17, shows the trestle bent upon which the span rests- It will be observed that the legs have only 68 per cent efficiency.

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47 II. IV. Piers. The iron cylinder piers seem to be in very good condition, and no weakness of any kind can "be detected. The masonry piers are built of squared sandstone, and all are in good condition with the exception of one. This one seems to have been badly damaged by cracking; but it has been repaired so that it is as good as new. The bearing area on the stone masonry is sufficient. V. Conclusion. In order to have a bridge that is satisfactory, every member should have at least an efficiency of 100 per cent. It will be seen from the preceding discussion that very few of the members fulfill this requirement. The bridge is of poor design in many respects, and probably was not intended to carry the live load which is required for a Class A bridge. The traffic is very heavy, as a great deal of brick and coal is hauled over it to the city; and it is important that the bridge should be entirely safe. The investigation shows that the design is none too heavy for the lightest of highway bridges; but unquestionably the traffic is not of this class, and consequently the bridge is unsafe. Therefore I would recommend that it be condemned and be replaced by a Class A structure.

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