Group 24 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. 1 Group 24 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. 2 Group 24 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” 3