Ronan Point: The Collapse That Defined Progressive Collapse

Early on the morning of 16 May 1968, a resident on the eighteenth floor of Ronan Point, a new 22-storey tower block in Canning Town, east London, struck a match to light her cooker. Gas that had leaked from a faulty connection ignited. The explosion was modest in itself, but it blew out a load-bearing wall panel at the corner of the building, and the floors above, then the floors below, collapsed in sequence. Four people died and seventeen were injured. The resident who lit the match survived.

The partial collapse of Ronan Point is the event that gave engineers the vocabulary of progressive and disproportionate collapse, and it changed building regulations in the United Kingdom and, in time, around the world. This article explains the structural system, what the official inquiry found and why the lessons still shape how buildings are designed today.

The large panel system

Ronan Point was built using a large panel system, one of several industrialised methods adopted in post-war Britain to deliver housing quickly. Instead of a frame of beams and columns, the building was assembled from storey-height precast concrete wall panels and floor slabs, made in a factory and lifted into place by crane. The wall panels were load-bearing: each one carried the floors and walls stacked above it.

The panels were held together largely by gravity and friction, with connections at the joints formed by bolts and in-situ concrete or grout. There were no continuous ties running through the structure to bind it into a single robust whole. In normal service this was adequate. The structure carried its own weight and its occupants without difficulty. What it lacked was the capacity to cope with the loss of any single panel.

Precast construction is not inherently weak. Modern precast concrete construction is widely used, including extensively in Singapore. The difference lies in how the elements are connected and tied together, a lesson learned directly from this collapse.

What happened at Ronan Point

The building had been occupied for only about two months. The explosion on the eighteenth floor pushed out the external flank wall panel of the corner flat. Without that panel, the floor slab above lost its support and fell. The impact of that floor and the wall panels above it, falling onto the floor below, overloaded each successive floor in turn. The entire south-east corner of the building collapsed from the top storey down to the podium.

The outcome was out of all proportion to the cause. A domestic gas explosion of the kind that might damage a single room in a conventionally framed building had removed one corner of a 22-storey tower.

What the inquiry found

The government appointed a tribunal of inquiry chaired by Hugh Griffiths QC. Its report, published later in 1968, concluded that the accident was caused by a domestic gas explosion that blew out load-bearing panel walls, and that the collapse of part of the building that followed was inherent in its design.

The tribunal noted that the design had complied with the building regulations then in force. The problem was that those regulations had not anticipated the vulnerability of a structure built from load-bearing panels with weak connections and no alternative load path. The inquiry also raised concerns about the building’s performance under wind loads and fire, and its recommendations led to the strengthening of existing large panel blocks and to the gas supply being removed from many of them.

Ronan Point itself was repaired and strengthened and reoccupied. Later investigations into the quality of the original construction, including defects found at panel joints during dismantling, added to concerns about such buildings, and the block was taken down in the 1980s.

Progressive and disproportionate collapse

Ronan Point gave a name and a definition to a type of failure. Progressive collapse is the spread of an initial local failure from element to element, resulting in the collapse of an entire structure or a disproportionately large part of it. The key idea is proportion: damage should be broadly in proportion to its cause.

The defence against progressive collapse rests on a few principles that designers still apply:

Ties. Horizontal and vertical ties running through floors, walls and columns hold the structure together, so that if an element is lost the structure above can hang or span across the gap rather than fall.
Alternative load paths. The structure is checked for the notional removal of a key element, such as a column or a length of load-bearing wall, to confirm that it can bridge the loss.
Key elements. Where an alternative load path is not possible, the element is designed to resist a specified accidental pressure.
Continuity and ductility. Connections are designed to hold together and deform without snapping, so that load can redistribute.

How the regulations changed

The UK responded quickly. Amendments to the Building Regulations introduced a requirement that buildings above a certain height be designed so that an accident would not cause collapse disproportionate to its cause. That requirement lives on in Part A of the Building Regulations in England and Wales, and the tying and alternative load path methods were written into the British Standards for concrete and steel.

Today, Eurocode 1 Part 1-7 and its UK National Annex deal with accidental actions and robustness, with requirements scaled to the consequence class of the building. Singapore, which adopted the Eurocodes for structural design, applies the same approach. Robustness requirements in other national codes around the world can be traced, directly or indirectly, to the lessons of 1968.

Why Ronan Point still matters

The collapse is a reminder that a structure can be perfectly adequate for every load its designer considered and still be dangerous, because the designer did not consider what happens when something goes wrong. Robustness is the quality that makes a building tolerant of the unexpected: an explosion, an impact, a construction error or a deteriorated element.

It also reminds owners that removing or altering load-bearing walls is never a minor matter. In panel or load-bearing wall buildings, each wall may be part of the structure’s defence against collapse. Ronan Point sits at the centre of our overview of famous structural failures because so much of modern robustness design grew from it.

Frequently asked questions

What happened at Ronan Point?

On 16 May 1968, a gas explosion in an eighteenth-floor flat of the 22-storey Ronan Point tower in Canning Town, London, blew out a load-bearing wall panel. The floors above and below collapsed in sequence, bringing down the whole south-east corner of the building. Four people died and seventeen were injured.

Why did Ronan Point collapse so extensively?

The building was made of precast concrete load-bearing panels with weak connections and no continuous ties, so there was no alternative path for the loads when one panel was lost. The inquiry found that the collapse that followed the explosion was inherent in the design.

What changed after the Ronan Point collapse?

UK building regulations were amended to require that buildings be designed to avoid collapse disproportionate to an accidental cause. Methods using ties, alternative load paths and key element design were introduced into codes of practice and are still used today, including through the Eurocodes.

Is precast concrete construction safe?

Yes, when it is designed with proper connections and ties. Modern precast buildings are designed to robustness requirements that did not exist when Ronan Point was built, so that the loss of a single element does not lead to disproportionate collapse.

Planning to remove or alter a wall in a panel or load-bearing wall building? Talk to our consultancy or get in touch for accountable structural advice.