The Ashtabula River railroad disaster (also called the Ashtabula horror, the Ashtabula Bridge disaster, and the Ashtabula train disaster) was caused by the collapse of a bridge over the Ashtabula River near the town of Ashtabula, Ohio, in the United States on Friday, December 29, 1876. The Pacific Express, a train of the Lake Shore and Michigan Southern Railway, was passing over the bridge as it collapsed, falling into the icy river. All but the lead locomotive plunged into the river. The train's oil lanterns and coal-fired heating stoves set the wooden cars alight. Firefighters declined to extinguish the flames, leaving individuals to try to pull survivors from the wreck. Many who survived the crash burned to death in the wreckage. The accident killed approximately 92 of the 160 people aboard. It was the worst rail accident in the U.S. in the 19th century and the worst rail accident in U.S. history until the Great Train Wreck of 1918. It remains the third-deadliest rail accident in U.S. history.
The coroner's report found that the bridge, located about from the railway station, had been improperly designed by the railroad company president, poorly constructed, and inadequately inspected. As a result of the accident, a hospital was built in the town and a federal system set up to formally investigate fatal railroad accidents.
Design and construction of the bridge
In 1863, officials of the Cleveland, Painesville and Ashtabula Railroad (CP&A; one of the predecessors of the Lake Shore and Michigan Southern Railway), decided to replace the wooden bridge over the Ashtabula River just east of the village of Ashtabula, Ohio, with an iron structure. Amasa Stone was president of the CP&A. His construction firm had built the CP&A main line from 1850 to 1852, and Stone had purchased the patent rights to brother-in-law William Howe truss bridge in 1842. Stone resolved to construct a Howe truss bridge, a commonly used type of railroad bridge, and personally designed the new bridge. The longest span was long and above the river below.
Stone also decided to award the contract for the ironwork to the Cleveland Rolling Mill (then known as Stone, Chisholm & Jones Company), an iron and steel company based in Cleveland, Ohio, which was managed by his older brother, Andros Stone. The I-beams were made by the mill. The mill also provided raw iron to the CP&A, which then made the cast and wrought iron elements according to the fabrication plans. Shop master mechanic Albert Congdon oversaw this latter work.
Design
thumb|Amasa Stone, the bridge's designer
Amasa Stone's bridge was, by his own admission, experimental. He had constructed only one all-iron Howe truss bridge before, a high, long railroad bridge over the Ohio and Erie Canal in Cleveland.
Joseph Tomlinson, a well-known bridge builder and designer, was hired to flesh out Stone's design and create the fabrication drawings for all the bridge components. Tomlinson designed the bridge's lower chord to have a camber of . When the falsework supporting the bridge was removed and the dead load of the bridge came into play, the camber would drop to between . Tomlinson was alarmed when Stone demanded that the bridge be constructed completely of iron, rather than a combination of wood and iron. An all-iron bridge would have a much greater dead load, reducing the bridge's live load (its ability to carry trains). He also concluded that the beams and posts Stone intended to use were undersized. Tomlinson proposed riveting plates to the I-beams to strengthen them, but Stone angrily refused. Stone demanded that Tomlinson make the changes he required. Tomlinson refused, and was fired from the design effort. Stone then ordered the CP&A's chief engineer, Charles Collins, to make the desired changes to the bridge design. Collins refused, and was fired from the design effort. Stone then made the changes to the design.
Stone made additional changes to the design. In a Howe truss bridge, the vertical posts connect the upper and lower chords (main parallels) in the truss. The deck on which the train travels usually hangs from these posts; the greater the live load, the greater the tension on the posts. The bracing reacts in compression, counteracting the tension. Amasa Stone inverted this design so that only the upper chord (now at the bottom of the bridge) provided tension. Where diagonal braces did not receive the extra compression from a live load, inverted Howe truss bridges had a tendency to buckle where the vertical posts were attached to the deck with cast iron angle blocks. Stone's other major change involved the end panels. In the traditional Howe truss bridge, the end panel on each side of each end of the bridge has three vertical posts and three diagonal braces. Only five Howe truss bridges ever built by 1863 had just one vertical post and two diagonal braces in the end panels. These were known as "Single Howe" bridges. Amasa Stone used the "Single Howe" design for the end panels at Ashtabula. Thus, the bridge's entire structure relied on just 12 beams and posts (three at each end).
Design of the angle blocks
thumb|The chord, diagonals, angle blocks, and vertical posts of the Ashtabula Bridge, as drawn from original plans by Charles MacDonald in 1877
Gasparini and Fields claim that the exact design of the angle blocks and the ends (the "bearings") of the diagonals are lost to history.
Civil engineer Charles MacDonald, who inspected the bridge's original plans in 1877, described and made drawings of part of the angle blocks. He noted that the vertical posts were made of iron pipe in diameter with a wall thick. Inside the pipe ran an iron rod thick. The top of the rod passed through the space between the members of the chord at the top of the bridge and then through a gib-plate. A nut and washer screwed onto the upper end of the rod, creating tension as well as securing the gib-plate in place. Those angle blocks at the top of the bridge had vertical, squarish lugs. Those members of the chord which ended atop an angle block had their bearings placed against the lug. These lugs served to transmit stress from the chord to the angle block and thence to the diagonals. These upper angle blocks also had lugs facing inward, to which were attached (by means MacDonald did not describe) the lateral braces. The interior side of each upper angle block also had a recess to accept a lug and a tap bolt. The tap bolt was used to connect the lug on the end of the sway rod to the angle block.
MacDonald described (but did not publish a drawing of) the angle blocks at the bottom of the bridge. The bottom of the rod in the vertical posts screwed into these angle blocks.
The members of the chord at the bottom of the bridge were flat bars, not I-beams, each bar measuring . Where a member of the chord ended at an angle block, a lug was forged at the base of the bar. This lug fit into a slot in the angle block. The angle blocks which made up the chord at the bottom of the bridge also had lugs facing inward, to which were attached (by means MacDonald did not describe) the lateral braces.
MacDonald and Gasparini and Fields noted that the diagonal I-beams were designed to connect to both the upper and lower angle blocks with the flanges of the I-beam in a vertical position. The web of the I-beam fit into a horizontal slot between two lugs.
It is also known that, at the ends of the bridge, only half of each angle block received load because Stone used only a single diagonal in the end panel. This put enormous shear stress on the bridgeward side of these angle blocks.
Construction
thumb|One design for a half-angle block. The attached chord puts immense downward (shear) stress on one side of the block only, for which the block is not designed.
The Ashtabula River bridge was erected in 1865 using Stone's design and plans and partly under his supervision. Tomlinson was the bridge's original construction supervisor, but Stone said he fired him for "inefficiency" at some point during the bridge's construction. Tomlinson was replaced by A. L. Rogers.
When construction began, Tomlinson observed that the I-beams intended for use as diagonals were smaller than the fabrication plans called for.
The amount of camber created a problem during construction. At Congdon's suggestion, Rogers built falsework to support construction of a bridge with a camber. Stone, now himself supervising Rogers' work, ordered the camber reduced to . With the members of the upper chord now too long, Rogers had the bearings shaved down. It is clear Rogers ordered other changes as well, but it is uncertain what these included. Gasparini and Fields suggest he had the lugs atop the angle block planed down as well. When the falsework began to be removed, the dead load caused the bridge to bend about below horizontal. The bridge was jacked up and the falsework put back in place. Stone then ordered the chord members to be returned to their original lengths, restoring Tomlinson's intended camber. Rather than ordering new I-beams, Rogers used shims to close the space between the bearings and the lugs.
When the falsework was removed a second time, the bridge buckled where the vertical posts connected to the deck. Several diagonals also buckled. Once more, the falsework went back in place.
To correct this problem, Stone added more iron I-beams to the diagonals to strengthen them. The placement, size, and number of beams added is not clear, but Stone likely added two I-beams to the brace in the end panel, two I-beams to the brace in the first panel from the end, and one I-beam to the second panel from the end. This worsened the bridge's dead load problem. Collins, Congdon, Rogers, and Stone all later testified that the I-beams making up the diagonals were now turned 90 degrees, so that the flanges were horizontal. Congdon says that he realized the I-beams would carry more live load if they were rotated. Collins, Rogers, and Stone believed workers had installed the beams incorrectly (on their sides). To make the change, Stone had workers cut away portions of each diagonal I-beam's web at the bearing, enabling the web to fit over the lugs. This weakened the new diagonals. There is also some evidence that the angle blocks were damaged while the braces and counter-braces were rotated.
The bridge was prestressed again. In every other panel connection, the diagonal braces were fitted to the angle blocks using shims rather than by tightening the vertical posts and putting the diagonals under compression. This meant that the shims carried the weight of a live load, rather than the braces themselves. It is also possible that the shims created uneven contact, causing angle blocks to undergo both bending and shear stress. Nevertheless, the bridge did not sag this time.
Upon completion, the bridge was tested by having three locomotives run over the bridge at speed. A second test had the three engines stand still on the bridge. Deflection was minimal and the bridge rebounded satisfactorily. Its two locomotives, Socrates and Columbia, were hauling two baggage cars, two day-passenger coaches, two express coaches, a drawing room car (the Yokohama), three sleeper cars (the Palatine, which originated in New York City and was bound for Chicago; the City of Buffalo, which originated in Boston and was bound for Chicago; and the Osceo, a sleeper for passengers going to St. Louis), and a smoking car with about 150 to 200 passengers and 19 crew aboard.