Loddon Bridge disaster

It is thought that a design error led part of the falsework, transitioning between the deck and the supporting towers, to be understrength and it failed by buckling or twisting.

The collapse was investigated by Her Majesty's Factory Inspectorate and the contractor, Marples Ridgway pleaded guilty to a breach of the construction regulations at a trial in Bracknell, being fined £150 (equivalent to £2,291 in 2023).

The committee, whose final report was published in 1975, made a number of recommendations for changes in how falsework was designed, constructed and dismantled.

[1]: 111 The deck was formed from in-situ concrete laid onto timber plank formwork which was supported by a system of falsework.

These measured 98 feet 4 inches (29.97 m) in length (extending into an adjacent span) and were made of four lattice sections connected together by scaffolding.

[1]: 116  The investigation was difficult as the falsework had collapsed into the river bed and been covered by the concrete which had set on top of it.

[1]: 111  Inspectors found that the steel beam support grillages at the eastern end were badly twisted and buckled.

Tests determined that the grillage arrangement had a factor of safety of just 1.3 when ideal conditions and vertical loads only were considered.

[1]: 115  The inspectors noted that the same falsework arrangement had sufficed for the westbound deck pour, which was under a heavier load.

[1]: 115–116 As secondary matters they found that some bolts used in assembling the falsework were missing or too short to accept a full nut.

They also found that the ends of some of the grillage I-beams had been tapered by flame cutting, reducing their effective web area by around 30 per cent.

The pads below the bearings were only lightly attached to the universal columns in the grillage, not ideal when horizontal loading was expected.

[1]: 116–117 Marples Ridgway were prosecuted under the construction regulations of the Factory Acts at Bracknell magistrates court.

[4][2] A consultant giving evidence stated that the loading imposed on the grillage was particularly difficult to assess and the designers should have recognised this and strengthened the beams, for example with stiffener plates welded to the web.

Its terms of reference were to advise on all aspects of the design, manufacture, erection and maintenance of falsework, particularly in the construction of bridges.

[1]: 3  The committee was chaired by Stephen Bragg, vice-chancellor of Brunel University, and included Danish engineer Povl Ahm of Ove Arup and Partners, F M Bowen of Scott Wilson Kirkpatrick and Partners, S Champion a consulting engineer in the scaffolding industry, L C Kemp national secretary of the Transport and General Workers' Union, J C S Mott of French Kier, Christopher J Wilshere head of temporary works department at John Laing Design Associates Ltd., and secretaries seconded from the Health and Safety Executive (W E J Greville) and the Department of the Environment [1] (I J Hume): 4 The committee issued an interim report in April 1974 and its final report (commonly known as the Bragg Report) in 1975.

The three A329(M) crossings of the Loddon, pictured in 2011. The eastbound carriageway, here the right-most, was the one that collapsed under construction. The River Loddon can be seen in the foreground.
2016 photograph of the A329(M) Loddon crossing, taken from the railway bridge to the south. The eastbound carriageway is the furthest of the three bridges constructed in the 1970s, masked by the westbound on-slip and westbound carriageway structures.