The first structure investigated is located at Danville, Illinois, and is locally known as the Woolen Mill Bridge. It is 776 feet long and spans the North Fork of the Vermillion river and connects Vermillion Heights with Danville.
It is made up of 19 trestle bents, a ten panel deck Whipple truss and 5 four panel deck Pratt trusses. It was built about 1885 by the Lafayette Bridge Company of Lafayette, Indiana. The trusses are on a level grade, while the west approach is on a 3% grade as are also the three short spans at the east end. The east end of the Whipple truss is carried on two steel cylinders filled with concrete and about 25 feet high. The bents are set on square stone bases, as is also the west end of the Whipple truss. The trusses are 17 feet center to center and the roadway is 18 feet wide with a 4 foot walk on each side.
Cooper's Highway Bridge Specifications, 1909, were used in the investigation of this structure, which is rated as a Class A 1 bridge.
This bridge carries a considerable amount of heavy traffic, due to the fact that there are coal mines and brick yards located in and near Vermillion Heights. At a wagon scale located near the end of the bridge there are records of loads of about 16,000 pounds which were hauled across this bridge. At each end of the bridge there is a sign, "Not more than four teams allowed on this bridge at one time", but there is no one there to enforce the rule.
The investigation of the stresses in this bridge showed that the efficiencies of the various members vary greatly. In the Whipple truss it was noted that the bottom chord, intermediate posts and hangers, and the diagonals were fully up to the required cross sectional area. The end post showed an efficiency of 84% and the top chord showed an efficiency as low as 77%, but these efficiencies are not so low as to be dangerous if the bridge was in good physical condition. The sway bracing is ample.
The Pratt trusses have about the same efficiencies as the Whipple truss. The lower chords, posts and diagonals have ample section, while the top chord has a low efficiency at the middle of the truss.
The bents in the approaches have very low efficiencies. In one of the posts the efficiency was only 46 1/2%.
The floor system consists of 3 inch plans laid on 3x12 in. joists, spaced 2 feet center to center. These joists rest on the Hooii beams composed of four angles and a web plate. The joists have an efficiency of 60% and the floor beams an efficiency of 83 1/2.
The physical condition of this bridge is very poor. Apparently it has not been painted since erection, and consequently some parts of the bridge are badly corroded. The top chords of the trusses have corroded until the cover plates are practically of no value. The floor beams are in almost as bad condition, which reduces their efficiencies to a dangerous point. The wood joists are in a serious condition. Where the plank floor rests on them they have decayed to a depth of 2 inches. Many of these joists, after they have rotted until they do not hold the nails, have been taken out and turned upside down and put back in the floor.
One of the diagonal tension members in the north Whipple truss is broken, as is also a similar member in the south truss. These members have a calculated efficiency of 119%. Attempts were made to splice these members, but the splices, which were less efficient than the members, were also broken. A bottom lateral in one of these trusses was also found broken.
Many of the details are of a very poor design, are in bad condition, and would not be tolerated in a new structure if in charge of a competent engineer.
The long bents that support the Pratt trusses have low efficiencies and in addition are badly corroded. They are in an unsafe condition.
There is one expansion joint in the structure, and that is at the west end of the Whipple truss. Theoretically it has an efficiency of 130%, but practically it has no value whatever. Dirt has filled in around the shoe until it has clogged the rollers. The roller nest has been crowded out until it is only partially on the 1 bearing plate. Apparently, little effort has has been made to put this bridge into even a moderately safe condition.
This bridge should be condemned and a new one constructed in its place.
August 16, 1889 - Mr. A.S. Markley, superintendent of bridges for the C&EI railroad presented a report in writing to the effect that he had examined Short's Bridge (then the current bridge across the North Fork in Ellsworth Park, and named for an adjacent land owner) and found it to be in unsafe condition. The city council recommended it be "nailed up at both ends", and that was done.
August 30, 1889 - Alderman Beard suggested an expenditure of $75 to put the Short's bridge in good condition for 90 days while plans would be made on a new bridge at the site. A committee was appointed who would report to the city council at the next meeting.
Sept 13, 1889 - The commissioners of highways of the town of Danville presented a petition praying for an appropriation to aid in the construction of a bridge and approaches thereto over the North Fork of the Vermilion River, where the same is crossed by the road leading from Danville to Urbana. The total cost of said bridge to be $18,000. Prayer granted and Messrs. Jones, White and Dickson were appointed a committee to represent the county in the construction of said bridge.
(All Bridges over the North Fork and Vermilion River at that time were of dual ownership, one half owned by the city of Danville and the other by Danville Township. It wasn't always a happy marriage)
Sept 20, 1889 - The Board of Supervisors made an appropriation of $6,000 for the bridge, committees had met and an individual from the C&EI was seen in regard to furnishing plans and specifications.
Oct 25, 1889 - 19 bids were received for the new bridge, but none met with approval. Lafayette Bridge, a previous bidder, ask to meet with the councils to present plans for a bridge. Plans and specifications from the Lafayette Iron Bridge Company were presented to the city council. Proposed to build a bridge of iron and steel for $14,600. Channel span 175', west end to rest on solid stone abutment, east end on 2 tubular piers, each 4 1/2 " in diameter, 5 short spans of 70", 5 pairs of trestle bents, total length of bridge 585'. Carrying strength 70 pounds/square foot.
Alderman Beard objected saying that the bridge would be too light, and it would be better to pay $20-$25,000 for a bridge that would last longer. Also said not a single bridge in the township would be as light as this one. He said he would vote for it, nonetheless. The matter was laid over til the next meeting.
Nov 8, 1889 - Contract let for the bridge to Lafayette Bridge
May 7, 1890 - A worker for Lafayette Bridge was killed when a traveling crane used to lift ironwork fell from the structure. He had climbed up to clear a fouled line when he inadvertently knocked out a key that held the jib together.
May 13, 1890 - The trestling at the new bridge over the North Fork floated away from the bridge last night and the cofferdam is under water. How long this state of affairs will last no one can tell.
On account of high water in the North Fork there is no way of getting over the river with wagons except by Sutherland ford, and persons on that side of the river are practically cut off from all traffic in the city. Persons can cross the river on the foot-bridge at the park.
May 19, 1890 - We understand the present contractor for the bridge over the North Fork will make the western approach for the sum of $1100, the said approach to be of the most substantial character and of iron and stone. If the city is determined to build the approach, it would be better to accept the proposition of the present contractors and have the bridge open to travel as soon as possible.
- A gentleman who has an opportunity to be fully posted, says that the statement made in regard to the insecurity of the foundations of the new bridge over the North Fork at Bridge Street is incorrect, that on the contrary the rock are of the best quality of sandstone.
Just when you think the bridge should be about finished...
June 2, 1890 - The two iron piers of the new Bridge Street bridge are in position, the wooden trestle work (falsework?) is over the water and the work of putting in the iron frame work has begun, and it is possible that it will be finished in two weeks.
June 20, 1890 - The committee on bridges reported that they, with the committee from the supervisors, had inspected the Bridge Street bridge and found it completed and recommended that the bridge be accepted and that the mayor and council borrow $8,838.10, the balance due, and pay the bridge company.