Structural design failures
The Ronan Point Building collapse 1968
The 22 storey Ronan Point building in London was of ‘large panel’ construction i.e. the structure consisted of large precast concrete wall and floor units with no beams or columns. In 1968, a gas explosion at the 18th storey near a corner of the building resulted in local walls being blown out. The fall of the now unsupported panels directly above the explosion then took away the corner panels below the explosion - Figure 1. Four people died.
This was a wake-up call for the need to consider progressive collapse in structural design and resulted in important changes in structural design philosophy.
A post-accident investigation into the condition of all UK high-rise large panel buildings showed many major structural design deficiencies. Structural designers in the UK used Code of Practice CP114: The structural use of reinforced concrete in buildings for the technical assessment of large-panel buildings. Many of these designers had not asked the validation question: “Does CP114 address all the issues that need to be considered for the design of large-panel buildings?” The answer to that question would have been “No!”. CP114 was written mainly for cast-in-situ beam and column structures and did not address important issues for large-panel buildings, particularly abot how the panels should be connected.
The 1968 Report on the inquiry into the collapse of flats at Ronan Point is model of good reporting. The collapse occurred on 16 May and the Committee first met on 30 May,1968. By the beginning of August 1968, the Report was mainly complete.
The Cleddau Bridge collapse
In 1970 a section of a steel box girder bridge intended to span the River Cleddau in Wales collapsed when under construction - Figure 2; four construction workers were killed. While there were other important factors, the analsis modelling used in the design for the structure was inadequate for prediction of the collapse. The main cause of the failure was buckling of a diaphragm at a pier. In order to predict the collapse, a shell element model with non-linear material and non-linear geometry effects should have been used. Such features were difficult to implement in 1970 as compared with the potential of modern software.
A major issue in the behaviour of the structure was not included in the validation of the analysis model and was not covered in the code of practice rules.