Posted on 07/20/2011 4:38:38 AM PDT by TigerLikesRooster
Aerobics Blamed for Mysterious Shopping Mall Tremor
Strenuous group exercise has been fingered as the culprit for the mysterious tremors that led to the evacuation of a shopping mall in Seoul earlier this month. On Tuesday, investigators probing the incident noticed that the vibrometer on the 38th floor of the TechnoMart building in eastern Seoul suddenly started moving violently as a group of 23 men and women in the fitness center on the 12th floor had started jumping energetically around.
An office worker in the 38th floor of the building said, "When we were evacuating on July 5, that’s how much the building trembled." The Architectural Institute of Korea and Prime Center, the owner of the Techno Mart building, on Tuesday held a press conference to explain what caused the tremor. "It is most likely that unusually intense exercise movement in the fitness center caused the building to shake," a spokesman said.
Based on a hypothesis by the Korea Infrastructure Safety and Technology Corporation, the institute recreated the situation in the fitness center on July 5. It asked 23 people to engage in Tae Bo exercise, a dynamic aerobic exercise that combines taekwondo and boxing movements. As predicted, the vibrometer on the 38th floor detected tremors 10 times more intense than usual.
(Excerpt) Read more at english.chosun.com ...
P!
Probably not enough rebar in the concrete.
I’d be a little scared to work in the office below that
Compared with other buildings, it is said to have more steel and less concrete.
This is a prank waiting to happen. Just use Twitter or Facebook to do a flash mob inside the building where everyone gathers on a particular floor and at a very specific time everyone just starts jumping up and down for one minute. Then go down or up ten or so stories and do the same the again. The people monitoring the building would certainly close the building again.
Consider yourself working in a ship on the sea.:-)
I wonder if it has something to do with the resonant frequency of the building. This is one of the reasons that you don’t march an army over a bridge.
That’s quite possible.
If a group of exercisers can induce such strong vibrations in a building, I’d be very concerned about the building stability. I wonder if they are having engineers examine it?
Probably got billed for it, it just never made its way into the concrete.
Technomart... huh. I think I won’t be visiting their cinema megaplex anytime soon.
That said, Korean concrete is mixed with a *LOT* more sand than what is allowed in concrete mixed in the US. Also, their construction companies do not let it cure before building around it.
Funny, I had a motor home like that. But that’s another story.
South Korea had a huge building boom a while back. I’ve seen other stories where the developer couldn’t get enough rebar but had to meet deadlines, so they put the building up anyway.
There was the shopping mall which collapsed a few years ago there. There was another massive project where they were putting up enough apartments for 300,000 people. In both cases the developers went to jail.
I’ve felt buildings shake before due to people. The floors quiver in parking garages as cars go by. This sounds to more pronounced.
If This Mall Is A'Rockin', Don't Come A'Knockin'!
The local mall, Galleria at Crystal Run, flexes rather oddly on the upper deck if people walk ‘hard’ on the floors.
Saw a bridge flex from foot traffic when a bunch of soldiers wandered across it.
Rather trippy stuff.
I recall reading several years ago about how San Francisco's Golden Gate Bridge flexed and apparently received some structural damage during some sort of marathon or mass pedestrian event when the bridge was closed to vehicle traffic. Apparently, the weight per square foot floor loading is considerably greater than a vehicle and greater than what a bridge's design will accommodate when a great number of people are packed closely together. It seems reasonable that a similar excessive floor loading might exist within a building, but I would think that in an aerobics class people would be spread out more over the floor. But, if they're jumping up & down the landing impact could make up for being spread out.
I'm no aerobics expert, however, so I could be wrong.
It is possible to add energy to a natural vibration incrementally.
If their jumping jacks equal a natural harmonic, the building will begin to shake.
And then begin to shake worse.
Kinda like making a large wave in a bathtub by making smaller waves and then adding a little energy to the wave every time it returns.
That all sounds quite logical and a sound enough principle to encourage exercise classes involving large numbers of people jumping simultaneously to do that particular activity outdoors ;-)
Outside or on teh ground floor on a large cement slab that is firmly rooted to the ground with no space below it at the least depending on group size.
For a comparison, I'm noticing that the curb weight of a WW2 era Jeep is 2,293 lb(1040 kg).
http://en.wikipedia.org/wiki/Willys_MB
I wouldn't want to continuously & rhythmically drop a Jeep onto an interior floor of a high-rise, or any building for that matter! ;-)
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