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The Royal Plaza Hotel Collapse
Korat, Nakorn Ratchasima
Introduction
On the 13th Of August 1993, the six storey Royal Plaza Hotel in Korat collapsed suddenly
and according to witness reports took less than 10 seconds; killing 137 and seriously
injuring 227 others. The collapse was almost vertical with little lateral displacement
resulting in the floor slabs being stacked neatly on top of each other. The cause was
unknown; speculation from the nature of the collapse alone drew comparisons with
professional demolition with the aid of explosives.
Design
The Hotel was originally according to building permits dating to 1983 a massage parlour
consisting of three stories above ground and an underground car park. In 1985 the owners
applied for a permit to convert the building into a hotel. In 1990 however further plans
were submitted and an additional three stories were added to the structure.
Investigation of Collapse
The Building failed under no external forces caused by the weather (i.e. earthquakes,
strong winds etc.) nor were there other observations of deliberate tampering with the
structure.
Taking this into account along with the sudden collapse and mode of failure, the
investigators concluded that the structure was inadequate and very poorly constructed.
With the addition of three extra stories, the original structures margins of safety on the
ground floor columns were effectively eradicated and failure of these columns triggered
the collapse. The following tests were conducted to prove this.
1) Concrete strength
Non-destructive testing of concrete samples from the site found them to range
from 10-15 MPa with 95% reliability. This was within reason and so material
deficiency could be ruled out as the cause. Subsequent cylinder tests on core
samples further validated this.
2) Rebar tests
Reinforcing bars were collected from site and were also found to be within
acceptable limits of strength.
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3) Soil test
Soil samples taken from the surrounding area showed that the bearing capacity of
the soil was adequate for the foundations even after modification. Analysis of the
soil structure ruled out failure by consolidation due to subgrade water out along
with failure due to settlement by the above structure. Post investigation by the
Public Works department found the foundation to also be in good condition.
Collapse
Investigators into the collapse pin pointed the failure at the ground floor columns, due to
the vertical collapse. The columns had to have failed one after another in a very short
space of time – this is known as progressive collapse (see Fig 1). Normally this is
accounted for and failure of one member in structure should lead to a local collapse only,
however the increased load from the extra stories would have been shared among the
columns putting them all close to their ultimate capacity.
Any cracks present in the ground floor columns would eventually develop and enlarge (as
a result of sustained load of the extra stories). Creep deformation in the columns made
this worse by shortening the columns, causing the loads to redistribute themselves among
the others. This caused the other columns to become overloaded and creep too thus
creating a cycle of deterioration. The increased loading on the columns continued until
one of the cracks became long enough to become self propagating – this lead to shear
failure of the column and eventually the rest followed (see Fig 2). Post analysis of the
rubble showed that the ground floor columns had in fact burst into small particles –
similar to the failure of concrete cylinder/cube tests.
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.
Fig 2: Picture showing shear
stresses and shear failure in a short
strut under a compressive load.
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Once this occurred the unsupported bulk of the hotel fell to the ground under its own
weight causing compressive shockwaves to travel to the columns on the upper floors.
The force of the shockwave caused upper columns to buckle. Eye witness and survivor
reports mentioned two loud bangs at the start of the collapse. The first is assumed to be
the collapse of the ground floor columns and the second from the impact of the upper
hotel structure on the surface.
Failures
The major failure is apparent as the negligence of the structural engineers, architects and
officials for checking the calculations and applying the appropriate safety margins.
Technically this amounts to the lack of extra column strengthening or additional
structural support. Likewise the cracks later developing on the columns should have been
identified and acted upon by maintenance personnel.
Korat is in a small rural province and as such the quantities of inspectors were low.
Additionally the economic growths of the province lead to increases in new construction,
redevelopments and inevitably a deluge of permits to be processed. Pressures to process
applications and the lack of manpower accentuated this problem but the main fault lies as
a matter of ethics with the chief architect/contractor/engineer that didn’t perform the
adequate safety checks in order to save time and money.
Conclusions
To prevent such failures from happening again, it is vital to ensure that inspectors are
widely available and conduct routine inspections on new and developing structures.
Likewise maintenance should be carried out by appropriate personnel on existing public
buildings at suitable timescales. Thailand had no Engineering council up until the
collapse; in the midst of other similar disasters the call for tighter regulation of engineers
and architects by fellow professionals was made. If this cannot be achieved cross
checking by third party engineers should be carried out.
In the end engineers and professionals are responsible for their actions but mistakes will
happen. All steps however must be taken to minimize this risk through education, help
and enforced regulation to prevent any more disasters.
References
http://www.ce.berkeley.edu/~astaneh/1-Publications/Astaneh-9ASEC%20%20Blast%20Paper%202003.pdf
http://www.thaiengineering.com/demo/viewnew.php?id=250
J.E. Gordon – “Structures or Why Things Don’t Fall Down”
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