Royal Plaza Hotel Collapse – Korat, Nakorn
Ratchasima Province, Thailand
Summary
This tragic collapse, of what was once considered the most luxurious hotel in Nakorn Ratchasima,
occurred on the late morning of Friday the 13th August 1993. The collapse was swift and almost
complete with the 6 storey building being reduced to nothing more than a pile of rubble in less than
10 seconds and leaving only the front elevator hall standing, which was structurally independent of
the rest. 379 unsuspecting occupants were inside. The sights of the rubble, the pitiful victims, and
the strenuous rescue operation will remain forever in the memory of most Thai people of this
generation.
After the incident, which took the lives of 137 people and injured 227, a technical investigation
under the Civil Engineering Chapter of the Engineering Institute of Thailand (EIT) commenced
immediately upon the arrival of the Task Force at the site on August 15, 1994. On-site inspections,
technical data which was collected and subsequent laboratory and model tests resulted in the
conclusions of what led to the Royal Plaza collapse.
History
The original building, built in 1983, was used as a massage parlour but was swiftly changed from this
to be used as a hotel in 1985, according to the construction permits granted over these periods. The
original building was 3 stories high with an underground level also. The building remained this way
for 3 years when, in 1990, a permit was sought to add 3 more storeys on top of the previous ones.
During the construction of these new levels, there is no record of any extra foundation or column
strengthening. There was no explanation how the modified structure could retain the same safety
standard after the addition of 3 more storeys. However permission for the extension was granted.
Investigation
People were confused about why the structure collapsed so suddenly. This collapse was very
uncommon as, typically, structures collapse during or just after construction or are regularly caused
by unexpected forces of nature such as earthquakes or storms. However with the Royal Plaza, the
collapse occurred 3 years after the final modification had been done to the building and there was
no report of any harsh environment, nor report of any misuse of the building to an extent that can
generate a devastating force of this scale that causes the swift and total collapse.
Many independent teams investigated the disaster. All of these teams agreed on one thing. The
structure of the Royal Plaza was substandard. This meant that the factors of safety for the building
were way below standard after the addition of the three stories. With three extra stories of dead
and live loads added without the addition of any foundation or column strengthening meant that the
original margins for safety were reduced to approximately zero.
Normally structural engineers place a high factor of safety on most buildings. This is so that even if
one section of the building is overloaded and fails, you will only get a local failure in that instance as
the other loads will be redistributed over the rest of the structure. This is not what was done in the
Royal Plaza. In this case most, if not all, columns were close to failure point at all times.
Most of the investigating teams concluded that the cause of the collapse was due to a sort of
domino effect in the structure. This process is well known as a “progressive failure”. The columns in
the building were so overloaded and close to failure at all times that small cracks and shifting in the
weight distribution occurred. When one column was close to failure the load from that column
would be shifted to another and then that column would begin to crack and break and then that
load again would be shifted to another. This repetitive motion happened over and over again until
finally one of the columns failed. A failure of one column could easily trigger the rest as the load
carried by this column would be redistributed to the rest. This subsequently caused them to fail, one
after another, within a very short time. Within seconds all the columns on the ground floor had
failed and this caused the remaining floors above them to fall the 5metres under its own weight.
This sudden and devastating movement sent a compressive wave throughout the building causing
the remaining columns in the upper floors to buckle quickly and fail completely.
Fig 1
Fig 2
Fig 1: Progressive column failure. Diagram shows 1st
column failure due to explosive but mode of failure is
analogous to the Royal Plaza Hotel collapse.
Figure
Fig 2:3 Picture showing shear stresses
and shear failure in a short strut under
a compressive load.
Survivors of the collapse did describe hearing two loud noises during the event. We suspect that
these noises were due to, firstly, the bursting of all ground floor columns and secondly the impact of
the upper-floor hitting the bottom floor.
The investigation team carried out three tests to determine if there were any other key factors in the
sudden destruction of the Royal Plaza.
1. A test of concrete strength: On-site testing of the concrete found its compressive strength to
be between 10 and 15 MPa with a 95% reliability. This led to the result that the concrete had
no deficiency which may have led to the collapse.
2. A test on the Rebars: Some rebars were collected from the site and test in lab conditions.
These were then found to conform to standards.
3. A test of soil Strength: A boring hole of the soil from the vicinity of the Royal Plaza was
tested in the lab to find its bearing strength. When this was done it was discovered that,
even with the addition of the 3 extra stories of the building, the bearing capacity was
sufficient.
After eliminating other likely causes, it was concluded that creep deformation was the main culprit
for the collapse. It occurred in the ground floor columns which were under huge stresses with low
factors of safety due to the addition of three stories onto the original building without any structural
reinforcement.
Lessons Learned
This disaster shocked the Thai nation as a whole. The Royal Plaza was one of the regions most lush
and expensive hotels. It was clear that, in Thailand at that time, economic consideration outweighed professionalism. The consideration of saving a bit of extra money at the cost of losing a bit
of safety needed to be changed. More Engineers who cared more about their standard of work than
saving the client money at the expense of safety, needed to be introduced.
The Thai Prime Minister ordered that all buildings under suspicion of being lacking in safety be
reviewed throughout the country. 218 buildings were forced to renovate their construction due to
this. This measure was able to reduce public concerns over the safety of existing buildings. In
addition, a data base of buildings around the country was established in the process.
Conclusion
This building disaster was one of the worst in Thai history. It was caused by Engineering and
Architectural mistakes, probably in the effort of trying to save money. Because of this, 137 people
lost their lives and hundreds of others were deeply affected by it.
This collapse changed a lot of engineer’s outlooks. Before, it was thought that if a building withstood
the construction period without collapse, then only improper use or natural disasters were thought
to be able to cause the building to collapse. Factors of safety in Engineering had now become more
important than ever.
Some good things have come from this tragic event however. Construction practices in Thailand
have become safer. A council of Engineers was also established which was run and managed by
Engineers for Engineers. All qualified Engineers who wished to work in Thailand were required to
register firstly with this council and their work ethics, practices and moral obligation were
scrutinised regularly.
References:
http://www.thaiengineering.com/viewtext.php?id=250&&id_cate=33
http://www.ingentaconnect.com/content/iabse/sei/1995/00000005/00000001/art00018
http://www.nytimes.com/1993/08/15/world/death-toll-rises-to-88-in-thailand-hotel-collapse.html