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