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Grade Separation with a “Magic” Box: reality and myths

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 The Magic Box is in the news especially in Bangalore for good and bad reasons. This is not because it is the magic box which is good or bad but it is the design using the magic box is good or bad. When people ridicule the magic box it is invariably because the inherent design using the magic box happens to be faulty. 

Let us analyze why is the magic box is called a magic box? The reasons as per my understanding would be 

  1. It is an ordinary RCC box like load bearing structure which is open at both ends.
  2. It is applied to provide practical solution for grade separating at any traffic at the crossing.
  3. Providing this grade separation does not involve traffic hold up in one of the legs. 

The 3rd point above is the main reason for the naming of the ordinary open ended RCC box structure as a “magic” box. 

Praja could probably analyze the many examples of magic box bungling all along the BIAL road right from Vidhana Soudha to the airport. I remember a Praja discussion on one such case. 

Here I would like to discuss one good successful design from the IISc campus. Here are the pictures taken by me on the occasion of first Praja meet with CiSTUP on Saturday the 18th July 2009. 

I would like to list what I liked about the design, from a layman’s point of view: 

  1. The two ways under pass has narrow width each way. This allows only one vehicle to traverse at a time. Reason the underpass is meant only for vehicles inside the campus to cross a heavy traffic road above. No regular traffic AT THE UNDER PASS  as such is expected.
  2. A well designed walk path and a barricaded exclusive walk at the under pass.
  3. All Communication / power cables taken care of.
  4. Storm water drains in place for preventing any flooding in the under pass itself.
  5. The existence of the under pass is not  visible from the road above.
  6. The design was executed without disrupting the heavy traffic above. 

It is a worthy “Magic box” design by the “academic” people, I would say.



blrsri's picture

Magic waning?

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The boxes made using precast reinforced cement concrete (RCC) have shrunk by half-an-inch, resulting in cracks developing along the structure at Sanjay Nagar underpass, en route to the Bengaluru International Airport.

..Though the BBMP took up repairs on Tuesday, it is not up to the mark, according to a traffic constable, who was present at the spot. 

...But a senior BBMP official had a different take. “The underpass is only five months old. It requires a season to set properly. We have now levelled the underpass and there’s no need to panic. We will also fill the cracks with water-proof plastering,” he said. 

more here

was reading on the web that when the shrinkage is restrained--tension stress develops in the concrete and as soon as the tension stress becomes greater than the tension strength of the concrete, the concrete cracks. So the problem is the "shrinkage cracks" not the shrinkage itself...

What if the magic boxes caves in not able to take further stress?

Is it time to stop the natak and build a good bridge from HMT office to Hebbal flyover?

psaram42's picture

Designs can be faulty. Murphy’s law

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 Murphy’s Law “If any thing can go wrong it will” is a well known law. It is not the fault of Magic Box concept. 

Magic box or magic of life cannot wane per say. 

Yes magic box designs can also go wrong. Like many buildings in Chennai last far less than they would have lasted in Bangalore. This is due to the humid salty weather of Chennai. The steel used in the RCC slabs have to be specially coated to resist corrosion. Thus in Chennai you can’t build RRC as one does in Bangalore. 

Of course you may like to go for regular designs if so desired. The IISC design did not block heavy traffic above while the underpass was constructed. In fact it was like a magic that when people realize about the existence of this under pass at IISC like we experienced the other day. comment guidelines

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