Monday, December 3, 2012

Sasago Tunnel Accident: Concrete Ceiling Panels Fell When the 35-Year-Old Metal Bolts Securing the Panels Fell Off from the Tunnel Ceiling

This is the silliest design I've ever seen. But then I'm no engineer.

9 people were killed when the concrete ceiling panels in Sasago Tunnel in Yamanashi Prefecture suddenly caved and fell on the motorists who happened to be in the tunnel.

The media reports try to explain how the ceiling panels were secured by metal brackets, no, they were hanging from the ceiling, oh wait, no they were attached to the dividing wall in the middle, no they were secured by metal bolts. I guess the reporters aren't engineers either.

I finally found this drawing which seems to be more or less accurate.

From the news site "Iza":

Since the tunnel opened in 1977, there has been no maintenance, no testing of the bolts that secure and hang the concrete ceiling panels (1.2 tonne a piece). There is no record of the bolts ever replaced. All they have done every five years is visual inspection. Why? Because physical inspection was not required by law, and since the bolts are anchored at the highest part of the tunnel they are inaccessible.

After I tweeted I wanted to see the detailed diagram of the tunnel, my twitter followers sent me the graphics that show how the bolts and metal suspensions were attached to the concrete panel.

16 bolts, 1.6 centimeter in diameter and 23 centimeters long, secures the metal plate to the ceiling, using chemical anchor. The metal plate secures the 5.3-meter long metal bar that is connected to another metal plate securing two concrete panels, each weighing 1.2 tonnes and measuring 5 meters x 1.2 meters x 8 centimeters (thick). The middle divider is not connected to the ceiling, but the purpose seems to be to secure the metal bar that suspends the ceiling panels. (The image is from Tokyo Shinbun.)

Now, why did they need this strange ad-hoc-looking structure? (It is not actually ad-hoc, as this structure was in place when the tunnel opened for business in 1977.) It turned out that the air in the tunnel tended to stagnate, and with heavy traffic with motorists having to sit in the tunnel for an extended period of time the risk of carbon monoxide poisoning was high. So they needed a structure that would allow effective air flow. So they decided to create air ducts by dividing the tunnel by concrete panels suspended from the ceiling by metal bars which would be supported by concrete divider wall that would separate the duct space in two, and the metal gars would be bolted to the ceiling.

Who were the general contractors who did this job? I looked all over, and there are only rumors. No major news outlets mention the names of the general contractors.

Rumors or no rumors, share prices of Japan's 1st-tier and second-tier general contractors jumped in the stock market in Japan on Monday. Kumagai-gumi, one of the most skilled contractors in tunnels, jumped more than 10 percent.

Why? Because the market thinks it is now extremely certain that the Japanese government will spend another borrowed fortune on public works, in response to citizens' fear and outrage that their infrastructure has deteriorated rapidly. As one of my followers said, it's not that the top-tier general contractors are good at maintenance (they aren't).

Well, 35 years of deferred maintenance does wonders. Like generating fat profits for general contractors who will throw work down their construction subcontractor pyramids. Dango anyone?

(H/T Kontan_Bigcat, Morimorikids, dr_masa_, 110rin, mwuema)


Anonymous said...

Uhhh. I'm not an engineer either, but that looks pretty stupid to me. I bet the real reason it was built like that is probably because "they had small metal plates and didn't want to waste money on large ones".

I've heard that stuff is falling apart all over the U.S. too because of lack of maintenance.

Anonymous said...

We live in a very, very sloppy world, my friends...
Maintenance is everything with metal corrosion.
I guess the French might be good at it, if I judge from the Eiffel Tower, kept in a very good state after more 120 years !

Niigata said...


The difference between the Eiffel Tower and the tunnel is simply the lack of maintenance of the latter. This is because it is not specifically French ...

Maintenance of the Eiffel Tower:
The Eiffel Tower is a work going maintenance because it must constantly deal with worn metal parts, but the most important works are represented by the painting.
The Eiffel Tower, the painting surface is about 20,020 m², is the size of 30 football pitches.
The amount of paint required is about 60 tonnes per layer. The duration of each coat of paint is about half a year is.

Since the wear of the upper part of the tower is faster than the bottom, now to the first floor, the paint is renewed every 10 years, and for the 2nd and 3rd floor every 5 years.

The Eiffel tower is constructed using very pure iron because if we had used steel, wear metal structures under the effect of external aggressive elements (humidity, temperature changes, wind, more snow, and pollution) would be faster and require much more maintenance and cleaning work.

The color used to paint the tower has undergone many changes throughout history, golden yellow, rusty red and currently it is the three-tone brown with dark brown for the lower part, medium brown in the middle and brown clear to the upper part. These three degrees of brown are necessary to ensure that the tower appears to be monochrome, with respect to an outside observer, because using the same degree of color to the entire structure, parts of which metal parts are too close together other, that is to say the upper parts, seem darker.

Anonymous said...

If all they were making was a ventilation plenum why did it need to be made of panels that weight tons? It seems to me the false ceiling could have been made of a lighter material and smaller panels in the name of safety.

This reminds me of the Boston Big Dig tunnel collapse back in 2006. The tunnel's "chemical anchors" experienced epoxy creep and failed.

"On August 8, 2007, a Suffolk County Grand Jury indicted epoxy company Powers Fasteners, Inc., on one charge of involuntary manslaughter, with the maximum penalty in Massachusetts being a fine of one thousand dollars."

WOW a whole $1000 that will teach them (to add $1000 surcharge to their next order).

Anonymous said...

>I've heard that stuff is falling apart all over the U.S. too because of lack of maintenance.

You have heard right here's a list of some of the problems US infrastructure is facing I'm sure the complete list would make people poop their pants.

Be afraid, be very afraid

Anonymous said...

General Contractors = cement.

That is the material they know how to use and to charge.
Structurally, those slabs do not have a load to bear.
It appears to me, that they wanted to pour the thing in and get on with the job. It is an old design. Newer tunnels have huge fans which keep the air moving.
I hope they make the decision to remove all the slabs and supports and gradually install the large duct fans.

Anonymous said...

Anyone who has driven the affected road will understand my outrage that maintenance was not performed on this infrastructure. This tunnel is on a high-priced toll road. 100KM toll from Kofu, capital of Yamanashi prefecture, toward the outskirts of Tokyo is about US$20, each way. It's a little over an hour's drive when traffic is moving at the speed limit.

kintaman said...

Improper design and no maintenance leads to death and disaster? Unthinkable! Its not as though we didn't have a similar but much worse situation just about 1.5 years ago in Fukushima to have learned from right? Idiots.

Anonymous said...

Right! That's is supposedly why we pay the ridiculous tolls to use these roads! Let me guess where all that toll money has gone???? Right down the rat hole....

kintaman said...

Yes, right down the rat hole in to some fat pigs pockets. They must audit to see how this money was misappropriated and take the necessary actions against those responsible.

Anonymous said...

like that will ever happen....TIJ

Dpat said...

I am an engineer and I can say that the comments are, for the most part, way off base. The author must not have spoken to any engineers before writing the blog or he would have been told that this is a relatively common design using plenums of concrete slabs above the roadway.

So, why concrete and not something lighter like, say plastic? Well when there's a fire in the tunnel concrete will not burn but steel, plastic, and most other materials will catastrophically fail, right when fresh air is needed the most.
The problem wasn't really maintenance either, but the article does touch on the actual issue. Until the Boston "Big Dig" tunnel failure, the phenomena of epoxy "creep" wasn't a significant consideration. This creep is where the epoxy acts like a very thick viscous liquid and over time flows and stretches. The design issue, most likely- as I haven't inspected it, was the epoxy anchors creeping out of their holes over many years and allowing the panels to fall. Another design issue is the panel weight, which was mentioned in the comments. A panel that is 15' x 3.9' x 3" made of normal weight concrete (145 PCF) would weigh about 2,200 lbs, but if lightweight concrete was used it would weigh around 1,800 lbs, still heavy, but 15% lighter.
Ultimately this is a tragedy because the Japanese didn't learn from the epoxy creep failure mechanism at the Boston tunnel.

Atomfritz said...

Such incidents are common in the nuclear industry, too.

Just a single example. When in 1978 a cooling tower of the Byron NPP partially collapsed in a similar manner, two men died.

May I add that epoxy glue gets soft when heated.
In 1988 a hot gas duct in the German pebble bed reactor THTR-300 collapsed when 36 epoxy-glued bolts got overheated and dropped loose.
In the consequence thousands of bolts had to be replaced in several German nuclear plants, leading to many years of unplanned outage in total.

In case of a tunnel fire the ceiling would have widely collapsed when the bolts started creeping when being heated somewhat above 100 degrees C.

Please note that such kinds of accidents are impossible in pre-war buildings where the bolts have been integrated into the concrete by including them into the concrete formwork.
This is a bit more expensive than drilling holes after construction and glueing the bolts into them. But, today all things must be cheap. Quality and durability seems obsolete today, even though the cheapo way usually becomes very expensive in the end.

Anonymous said...

design the roof panels to serve as an arch with small pylons at the corners

far easier and far more reliable, as opposed to glued up panels.

Unknown said...

Wow, I hope whoever was injured hired a motor vehicle accident lawyer. That sounded terrible! I can't believe they would let something that old go unrepaired. I guess you live and you learn.

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