Broughton Suspension Bridge was a suspended-deck suspension bridge built in 1826 to span the River Irwell between Broughton and Pendleton, now in Greater Manchester, England. It was one of the first suspension bridges constructed in Europe. On 12 April 1831 the bridge collapsed, reportedly owing to a mechanical resonance induced by troops marching over the bridge in step. A bolt in one of the stay-chains snapped, causing the bridge to collapse at one end, throwing about forty of the men into the river. As a result of the incident the British Military issued an order that troops should "break step" when crossing a bridge. The bridge's construction has been attributed to Samuel Brown, but this has been questioned; some sources have suggested that it may have been built by Thomas Cheek Hewes, a Manchester millwright and textile machinery manufacturer. The bridge was rebuilt and used until 1914, when it was replaced by a Pratt truss pedestrian bridge, which is still in use.
In 1826 John Fitzgerald, the wealthy owner of Castle Irwell House (later to become the site of the Manchester Racecourse), built at his own expense a 144-foot suspension bridge across the River Irwell between Lower Broughton and Pendleton. The bridge was a source of great local pride, as the Menai suspension bridge had only opened that year and suspension bridges were the considered the "new wonder of the age".
On 12 April 1831 the 60th Rifle Corps carried out an exercise on Kersal Moor under the command of Lieutenant P. S. Fitzgerald, the son of John Fitzgerald. As a detachment of 74 men returned to barracks in Salford by way of the bridge the soldiers, who were marching four abreast, felt it begin to vibrate in time with their footsteps. Finding the vibration a pleasant sensation some of them started to whistle a marching tune, and they began to "humour it by the manner in which they stepped", causing the bridge to vibrate even more. The head of the column had almost reached the Pendleton side when they heard "a sound resembling an irregular discharge of fireams". Immediately, one of the iron columns supporting the suspension chains on the Broughton side of the river fell towards the bridge, carrying with it a large stone from the pier to which it had been bolted. The corner of the bridge, no longer supported, then fell 16 or 18 feet into the river, throwing about forty of the soldiers into the water or against the chains. As the water was only about two feet deep at that point none of the men were killed, but twenty were injured, including six who suffered severe injuries including broken arms and legs, severe bruising, and contusions to the head.
An investigation found that a bolt in one of the stay-chains had snapped at the point where it was attached to the masonry of the ground anchor. There was criticism of the construction method used, as the attachment to the ground-anchor relied on one bolt rather than two, and the bolt itself was found to have been badly forged. A number of other bolts were also bent but had not broken. It emerged that three years previously the distinguished Manchester engineer, Eaton Hodgkinson, had expressed some doubt about the strength of the stay-chains, as compared with that of the suspension chains. He had said that they should be rigorously tested, but they were not. It also came to light that some time before the accident one of the cross bolts had started to bend and crack, although it was believed to have been replaced by the time of the accident. The conclusion was that, although the vibration caused by the marching had precipitated the bolt's failure, it would have happened sooner or later anyway.
The collapse of the bridge caused something of a loss of confidence in suspension bridges, with one newspaper report at the time commenting: From what happened on this occasion we would greatly doubt the stability of the great Menai Bridge (admirable as its construction is), if a thousand men were to be marched across in close column, and keeping regular step. From its great length, the vibration would be tremendous before the head of the column had reached the further side, and some terrific calamity would be very likely to happen. This did not stop the building of more suspension bridges, and the main consequence of the collapse was that the British military introduced the order to "break step" when soldiers were crossing a bridge. However, the lessons from this incident were clearly not applied universally, as Angers Bridge in France collapsed in similar circumstances in 1850, killing over 200 soldiers. Broughton Suspension Bridge was rebuilt and strengthened but, according to the Imperial Gazetteer of England and Wales (1870-72), it was propped with temporary piles whenever a large crowd was expected. The suspension bridge remained in use until 1914, when it was replaced with a steel Pratt truss pedestrian bridge.