Photos obtained by NK News of the construction area of North Korea’s flagship Changjon Street apartment complex have revealed “shocking” structural flaws that indicate a recent building collapse in Pyongyang “will not be an isolated incident”.
The photos, taken in August 2011, suggest the techniques used to build the prestige complex in less than a year could pose both short and long-term risks to the structural integrity of the buildings, several engineering experts told NK News.
“The pictures you sent me which purport to be of [a] high rise block in North Korea are truly shocking,” said Chartered Structural Engineer Prof. John Nolan, former President of the London-based Institution of Structural Engineers.
“Quality control appears to be an alien concept with many examples of accidental misalignment of structural members above each other and very poor steel reinforcement fixing,” Nolan said.
The Changjon Street complex, which opened in June 2012 and was built as part of a major construction boom initiated by Kim Jong Il, comprises three 47 floor buildings and 15 buildings of between approximately 20-36 floors.
Its rapid construction surprised many observers, some of whom expressed astonishment at how North Korea was able to complete the complex so quickly without the use of modern, heavy-duty equipment and limited access to crucial ingredients such as reinforced steel.
Notably, historical satellite imagery of the complex shows that the construction of the Changjon tower-blocks significantly overlapped that of a 23 floor building widely suspected as being the one North Korean media said collapsed on May 13.
With state media saying the May 13 collapse had been caused by construction carried out in a “slipshod manner,” the pictures of the Changjon complex site indicate that building safety both there and around North Korea could be a serious issue.
“If this is a genuine example of the general standard of high rise construction in North Korea, it is no surprise to me that the [recent] collapse occurred and there is a serious risk that it will not be an isolated incident,” Professor Nolan said.
Close-ups of the photos analyzed by a second structural engineer – who request anonymity for commercial reasons – illustrate multiple issues that could pose short and long term risks to the building’s safety.
For apartment blocks that reach up to 47 floors in height, close-up photographs of the Changjon complex site indicate that the steel bars used to reinforce the structure’s main concrete appear flimsy, lightweight and insufficiently ‘caged’, the engineer told NK News.
In addition, the form work panels used to set the reinforced concrete walls appear structurally weak, of low grade fabrication, and variable quality:
Notably, the structure also lacks sufficient number and sizes of reinforcing bars, with slab edges being visibly cast after completion of the main walls and no evidence of tie-bars or reinforcement.The lightweight nature of the main structure’s reinforcement and the lack of proper reinforcement caging could present risks for the building’s structural integrity, the engineer said.
Clearly visible joints in concrete walls further indicate irregular and inconsistent concrete supplies, an issue that undermines the structural integrity of supporting walls, increasing the risk of matrix fractures appearing in walls over time:
The engineer also noted that the concrete batching (or mixing) process was seen to take place at the base of the site, showing no protection from the elements, a clear indicator that the batching process has limited quality control procedures.
In contrast, concrete at modern construction sites is typically mixed at factories or in a highly controlled environment and carried by spinning mixer trucks before being piped up and set on location.
The photographs also show primitive hoists, small scale concrete buckets, timber ramps to formwork, and the manual placement of concrete within the forms, the engineer pointed out:
“Issues such as cube testing for concrete strength which would normally be done per batch do not appear to have been carried out, evidenced by the varied wall colour, pour joints, repairs etc,” the engineer said.
Walls on another side of the building showed a similar lack of alignment, which could pose further problems:
“The columns and slabs will not be designed to cope with the increased stresses,” the engineer said.
Another expert who looked at the pictures – Construction Engineering Professor Karl Vincent Høiseth of the Norwegian University of Science and Technology – said that alignment issues could have resulted from “not letting the concrete cure before filling/setting up a new unit on top of it.”
“Normally, you’re supposed to wait a week before starting the next unit, because you need to let the concrete cure,” Høiseth said.
In contrast, historical satellite imagery shows that the bulk of the highest buildings of the Changjon Street complex being raised in under four months, which would equate to a complete floor level being completed in between 3-6 days.
Despite the photos showing evidence of “poor concreteing practice” and “poor geometric control of the construction,” founder of engineering consultancy Benaim Group Robert Benaim told NK News that the defects shown “do not give rise to an obvious risk of collapse”.
Benaim said that stability of the building would likely be assured by stair-cases and lift-shafts in the building, not the walls visible in the photos.
“Usually a building like that has a central core which provides the stability. And then the walls around the outside have got a very simple propping role. So the fact that they don’t look very precisely built doesn’t mean they’re unsafe.
“In the 1960’s many blocks of flats were built with unreinforced concrete walls, the stability for the building being provided by staircases/lift shafts,” Benaim added.
However, the engineering expert who requested anonymity expressed a different opinion.
“I disagree that these buildings can be construed as being safe. The consistency in the rebar, signs of burst shutters, and limited quality control in mixing and placing concrete do not instill confidence”.
FLAGSHIP HOUSING PROJECT
Changjon Street, or known by foreigners living in Pyongyang as “mini-Dubai,” was ordered to be completed in record time by the late Kim Jong Il as part of his effort to build a “strong and prosperous nation” in time for the 100 year celebration of founding leader Kim Il Sung’s birth.
Known in Korean as ‘kangsong taeguk,’ the modernization campaign saw numerous apartments being constructed and refurbished throughout Pyongyang, as well efforts to modernize infrastructure and leisure facilities.
During the opening ceremony of the complex, North Korean state media outlet KCNA reported that DPRK Premier Choe Yong Rim delivered a keynote speech, in which he “called upon the builders and officials to further glorify the heyday of Pyongyang and the military first Songun era through their energetic efforts to turn into a more magnificent and fashionable world class city”.
Several senior party members visited the complex in June 2012, with Kim Jong Un personally visiting residents on September 4, 2012.
Additional reporting by Leo Byrne and Ole Jakob Skåtun
Main picture: NK News
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