By Nam Sang-so
Modern structures are dividers and collectors of a superabundance of static and mobile matter architecturally abstracted as ``loads.”
Dead loads include all architectural construction as well as mechanical equipment, utility installations, sprinkler systems, and any other permanent or immovable matter. Live loads include all movable weights the structure may carry; occupants, furnishings, machinery, movable partitions, forces due to climatic disturbances (rain, snow, ice, and wind), lateral subsoil and hydrostatic pressures, and even temporary loads applied during construction or maintenance.
Like an organism whose muscles intermittently sag and rise as the weights imposed move about, whose joints creak in their sockets as winds press against its skin, whose bones swell and shrink as the temperature rises and falls, so do structures.
Buildings are alive. Each ``bone” in supportive frameworks may be considered as a bundle of longitudinal fibers that carries various loads from its ends to where the collected weight is transferred to larger members or into the ground or onto the bedrock. It’s called stress lines that contain elastic, plastic and yield stresses. Just like human senses a symptom of sickness before getting sick, a presage appears on a building before a structural failure occurs.
A 39-story commercial building called Techno Mart in northeastern Seoul shuddered for 10 minutes on July 5. Ten minutes is a long time for a tall building to tremble. There was no earthquake or strong wind on that day. The engineers of the government run structural facility safety organization declared that the building is so far safe to occupy after conducting a cursory visual inspection, adding that a detailed structural evaluation and investigation should also be made.
I should refrain from making a prediction at this stage on the presage on the steel structured building since I’m not involved with it but let me jog your memory of the notorious collapse of Sampoong Department Store once located in Seocho-gu, Seoul, which killed 501 people and injured 937 in June 1995. The original four floor building was built in 1990 as an office building and was changed to a large department store. The owner added a fifth floor for restaurants (corruption involved), plus an air conditioning unit on the roof, exceeding four times the designed dead load and live load.
In April 1995, cracks began to appear in the fifth floor ceiling along with squeaking noises and some vibrations. On the morning of June 29, the number of cracks in the area increased dramatically. The store management failed to shut the building down or issue an evacuation order as the number of customers in the store was unusually high. They didn’t want to lose the day’s revenue.
The Sampoong executives themselves, however, left the premises as a precaution, if you can believe it. Some five hours before the collapse, the first of several loud bangs was heard emanating from the top floors, as the vibration of the air condition caused the cracks in the slabs. When the building started to produce cracking sounds at about 5:50 p.m., the management began to sound the alarm and evacuate the building, but by then it was too late. The roof gave way and the air conditioning unit crashed through onto the already overloaded fifth floor. Within 20 seconds, all of the building’s columns gave away, trapping more than 1,500 people.
Architects and engineers concluded that it was unbalanced loading that created ``concentrated load bearing.” The whole building collapsed in a domino effect, just like the World Trade Center buildings in New York.
The Techno Mart building showed a clear premonitory sign of misbehavior. It should be treated as sick until after the trembling symptom is architecturally and structurally clarified. We’ve learned enough from the Sampoong disaster, and the infamous Seongsu Bridge that collapsed into the Han River in 1994 with a bus load of school girls.
The writer is a retired architect-specifications writer, who shuttles back and forth between Seoul and New Jersey. He can be reached at sangsonam@gmail.com.