Failure Knowledge Database / 100 Selected Cases

Chain Reaction Collapse of a High-rise Apartment due to a Gas Explosion
May 16, 1968 in Ronan Point, East London, England
Masayuki Nakao (Institute of Engineering Innovation, School of Engineering, The University of Tokyo)
A gas explosion on th e 18th fl oor caus ed th e collapse of an en tire cor ner of a 24-story block of flats called
Ronan Point in east London . Three were killed and 11 people were injured after t he 22-story southeast cornercame crashing down. A gas explosion triggered the domino style collapse of the structurally unsound building
which was an assembly of prefabricated concrete panels.
1. Event
A gas explosion on the 18th floor caused the collapse of an entire corner of a 24-story block of flats called
Ronan Poi nt in eas t London. Three wer e killed and 1 1 people wer e i njured after the 2 2-story s outheast
corner came crashing down. Photo 1 shows the collapsed building.

Photo 1. Collapsed 22-Story Southeast Corner [1]2. Course
Prefabricated co nstruction tech niques kn own as “system building” wer e dev eloped in early 1960’s. Asystem-built structure was assem bled from prefabricated concrete panels lifted into position by cranes andheld together by bolts to form the walls, floors and roof slabs. It had a benefit of reducing construction time1

Failure Knowledge Database / 100 Selected Cases
and the number of skilled workers required for housing construction. Ronan Point, a 23-story block of flatsin the east end of London, was one of more than 3,000 new flats and houses system-built by 1968.
In the early mor ning of May 16, 1968, a g as ex plosion oc curred i n the so utheast corner flat on t he 18thfloor of Ronan Point. The pressure of the gas explosion blew out the pre-cast concrete panels which formed
the side of the building, then ripped through four flats above and sent all th e floors below crashing down
like falling dominoes. The entire corner of Ronan Point collapsed as shown in Photo 1, killing 3 people andinjuring 11.
3. Cause
The force of the explosion knocked out external walls of the southeast corner flat on the 18th floor, leaving
the panels above unsupported. This created a chain reaction in which the 19th floor collapsed, then the 20thfloor and so on, propag ating upward. Th e collaps e o f four flo ors on to th e 18 th f loor ini tiated a second
phase of progressive collapse. The sudden impact loading on the 18th floor caused it to give way, smashingthe 17th floor and progressing until it reached the ground (Figure 1). The collapse of Ronan Point was due
to its lack of structural r edundancy. The struc ture had no f ail-safe mechanisms, and no alternative l oad
paths for the upper floors when a lower level gave way.
The investigation panels reported that gas leaks, which had caused the explosion, occurred too frequently
in high-rise homes than expected.
The public inquiry into the collapse publicized a report that quoted a general building code that states it isabsolutely neces sary to ef fectively joint all components so that t he buil ding w ould not be like a “h ousebuilt of cards,” h owever, t he building co des b ack th en d id not h ave thorough ev aluation of th is“system-building”.

Figure 1. Domino Style Collapse
4. Immediate Action
The investigation panels determined that the explosion from the gas leak had initiated the collapse of thebuilding. Du e t o f requent g as leaks in hi gh-rise ho mes an d work by unlicen sed g as fitt ers, gas and gas
2Failure Knowledge Database / 100 Selected Cases
cylinders for cooking or heating the air were banned from high-rise buildings.
5. Countermeasure
Since the Ronan Point collapse, the public confidence in safety of high-rise homes had largely disappeared,
and few subsequent developments included high-rise blocks of flats. The Greater London Council (GLC)
admitted in late 19 70’s t hat the post-war housing solution wi th hi gh-rise homes a nd redevelopment offaltering areas within the conurbation was not adequate.
The B uilding Regulations a nd the C ode of P ractice f or concr ete des ign ad ded sp ecial th at the str ucture
would provide a certain minimum resistance to special load conditions, like gas explosion, and progressive
collapses.
During the reinforcement efforts made to the structure of the Ronan Point and 600 other similar buildings,
poor workmanship was discovered. The architect who examined the structure found that joints within thestructure were filled with newspapers rather than concrete, and walls rested on leveling bolts instead of ona conti nuous bed of mortar, allowin g r ainwater to seep in to the j oints. Det ermined t o be u nsafe, Ronan
Point and other similar buildings were demolished. The last of the kind was demolished 20 years after theRonan Point collapse.
6. Summary
Prefabricated constr uction t echniques known as “system building” gai ned popu larity during the pos t war
era, be cause they offered che aper, easier and quic ker cons truction of high-rise flats th an tr aditional
construction. Prefabricated concrete pan els w ere al l m anufactured at f actories, w hich enabled throughquality control of building material and components.
However, the Ronan Poin t c ollapse revealed vulnerability of system bui lding. Post-accid ent inquiries
proved that the large panel construction system, in which panels of prefabricated concrete formed the walls,floors a nd ro of sl abs, wa s particularly v ulnerable to progressive collapse du e to gas explosion o r o ther
accidental damage. The incident revealed a fundamental error in the design concept.
In addition to th e des ign fault, the f ollowing repair construction revealed p oor work manship (a prob lem
still occasionally found today), which is a sign of poor organization.
7. Knowledge
New construction tech niques poten tially have th e devil in side. Peo ple tend t o lo ok at on ly the m erits o f
new designs, however, checking the design if anything may go wrong is absolutely necessary.
Design errors are of ten revealed for the first time when the wr ong id ea was accepted in the pas t and not
found to be wr ong until a cat astrophe hits. Structural safety, perfor mance, in tegrity and stability must beassured by means including simulations and model testing assuming abnormal (loading) events of a generalnature. We must also study facts of past structural failures and turn them into knowledge to pass them on tothe next generation.
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Failure Knowledge Database / 100 Selected Cases

8. Background
The U.K., which led the w orld in the Industrial Revolution during the 18th century, had to deal with social
issues related to concentration of the population into industrial areas. The pressure for decent housing arosefrom over crowding in the large cities in the 19th century. D uring the l atter half o f 19th ce ntury, s everal
charitable housing projects begun to provid e housing in tenement blocks. Redevelopment and re-housing
efforts were also laun ched to bu ild m ulti-unit dwel lings and provide b etter ho mes f or those wh o live indamp, overcrowded slum conditions The housing issue led to the Housing of the Working Classes Act 1890,
which enc ouraged local a uthorities to i mprove the hou sing in their a reas. As a c onsequence, many loca lcouncils began building flats and houses in the early 20th century.
There was a major boom in housing construction in ar eas badly mauled by the World War II with several
areas approaching sl um co nditions. In the 1 960’s the adm inistration pu t priority on redeveloping t healready bu ilt urban ar eas. Many m ulti-story tower blocks were built to ac commodate the n eeds ofthousands of people, transforming the former factory sites and overcrowded slum areas. While local people
were hesitant about new non-traditional high-density housing, high-rise flatted blocks were easy and quick
to provide new homes for many.
9. On the Side
There are increasing areas forested with high-rise multi-unit dwellings in Ja pan. High-rise structures havehigher n atural fr equency than s everal-story st ructures. Gusty wind makes them sway l aterally, whic hsometimes cause motion sickness among those who are inside. If a structure’s natural vibration frequency
coincides w ith se ismic waves of the s ame f requency, th en even more of the se ismic ki netic energy canenter th e str ucture, ca using gr eater po tential for da mage. Seismic vibration may possibly be a mplified,resulting the structure to sway several meters laterally. One can only imagine what it is like to be on the top
floor when the structure is swaying violently.
High-rise st ructures may need some dynamic damping systems to c ontrol vibrations so thatseismicvibration does not trans fer to the s tructure, like the Akashi Bridge active control that sways the roof-top
water tank in the phase opposite to the seismic vibration.
References[1] Yotaro Hatamura (Editor) (2003) Shippai-ni Manabu Mono Zukuri (Applying Lessons Learned fromFailures), Kodansha, Ltd.
[2] Hideto Nakajima (Translator), Hiroyuki Ayano (Translator), Henry Petroski (2001) Why did the bridgefall? (Design Paradigms: Case Histories of Error and Judgment in Engineering), The Asahi Shimbun
Company.
[3] Geneva Association Information Newsletter.
[4] Takemasa Sato (President, Ichiura Housing & Planning Associates Co., Ltd.) “Danchi Saisei-o Kangaeru 4

Failure Knowledge Database / 100 Selected Cases
Abunai Danchi-no Saisei II (Redevelopment of Housing Complex – Safer Environment II)”, Wendy-Net
Column, http://www.wendy-net.com/nw/news&view/danchi5.html

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