Saturday, October 15, 2011

Rising of roof - Heathrow air port

     Design of Heathrow terminal 5 air port is deceptively simple , but constructing it was an extremely complex job. The site was trapped between two run ways, some of busiest in the world. This makes the building very complex to build.

     The engineer design 40meter tall terminal and to make most of the space it was designed with single-spine roof of size five football fields.


        But raising these monster roof was the biggest challenge for the engineers as one single piece of the roof weighs 6 jumbo jacks. lifting it up 40 m with tower cranes will create a problem as the cranes are so tall that they might disturb the Heathrow radar system. so it was required to conceive a design which can build the roof from ground.

 

       The construction team assembled the roof on the ground using small cranes. Then they used a clever lifting technique to pull the roof of the ground. It is called strand jacking.



      They suspend the section of the roof with steel wires. These wires are pulled by the strand jacks, powerful hydraulic rams , each lifting 185 tons.16 of these jack was used to lift the roof 40m high. It took almost a year to lift the complete roof.

      Terminal 5 has much more space compared to other 4 terminals combined.


Sunday, September 25, 2011

Palm Island













                                The Palm Islands are an artificial archipelago(a chain or cluster of islands) in Dubai, United Arab Emirates one of the major commercial and residential infrastructure. Crown prince Shekh Mahamad bin rashid ahmad 2 wants to increase tourists to Dubai. He want to make Dubai No. 1 luxurious tourist destination in the world. 5 million tourist visit annually and prince wants to increase it by 15. Coast of Dubai is 72km which is not enough for 15 million people. So the crown prince plan is to build massive islands into the sea.
Palm Islands are constructed by Nakheel Properties, a property developer in the United Arab Emirates, who hired Belgian and Dutch dredging and marine contractor Jan De Nul and Van Oord, some of the world's specialists in land reclamation (Land reclamation is the process to create new land from sea or riverbeds). The Dutch had increased Holland’s land by 35%.
The crown price wanted the island in the shape of palm tree and to be built by only sand and rocks. The construction started in August 2001. Arabian gulf is a perfect place to build such a mega structure. It is on average only 30m deep and 160km wide. It is too short for catastrophic waves to build up. But it should bear with massive waves in winter and a worst case scenario storm which hit once in 100 years should also be considered.


 

              To protect the island break water around the palm tree shaped island must be built. The team do the final calculation to built a break water 3m above sea level and 11.5 km long. 9 barges, 15 tank boats,  4 dredgers, 30 heavy land base machines and 10 floating cranes were needed to construct the massive island.



                        First step of building break water was to construct sea floor. 3 massive dredger dump the sand up to 7.4m thick. To keep it in place floor of rocks were dropped on it up to 3m above sea level, total thickness of 7m. 5.5 million cubic meter of rock was required by the 11.5m long break water which is enough to build two Egyptian pyramids. The heavy land base machines put 14000 cubic meters of rock in place per day. These rocks must interlock with each other to bear with sea waves. The constant check to ensure the break water is in place and standing firm was done by sending divers.

                March 2002 storm hits and a section of break water is in the sea. For 3 weeks work had to be stopped. But the break water stands firm. Crown prince wanted the island and city on it to be build by2006. Only way to meet the deadline is to build break water and island at same time. But this is not an ideal situation. The island will have bad effects of sea waves without complete break water. But the deadline had to be met.


               The island construction team had to find 94 million cubic meters of sand to build the palm tree island. Dubai has more sand, but desert sand is not the suitable for constructing island. Its particles are too fine and won’t stick together firmly. It means it will be easily washed away. The best sand was found 6 nautical miles(11km) out of sea. This was the best suitable sand. It packs densely and more resistant to waves.




                Dredgers scoop up 8000 ton of sand less than an hour and spray the sand into the place. The process is called rain bowing. But it was difficult to say that sand was falling at right place.  It was achieved by GPS technology. Dubai has access to only privately owned satellite in the world, the Ikonos. 







Mobile receivers on the island make grid reference and receiving signals from satellite and from a fixed position on land, height and position of island is recorded. With these records dredgers rainbow the sand at place with pin point accuracy.

                October 2002, 2/3 of break water and 9 palm fronds rise above the sea level. But then engineers discovered a problem that could put the whole project in danger. The water inside the sea wall (break water) was not circulating resulting in dirty water being stored inside.







 Luckily the solution is found just in time. Making two breaks in sea wall (break water) made it easy for sea to push clean water inside.
                
                 August 2003 break water completes. Two months later island reclamation completes. 94 million cubic meter of sand and 5.5 million cubic meters of rock holds back full force of sea. Now to fulfil crown prince’s dream  4500 houses and apartments, 200 hotels and shopping malls are to be build on the island.

The sand island must support an entire city on it. But sand is not an easy platform to build on. Because the sand is sprayed it is loose and not compactable. Over time sand will compact naturally, but it will take time.



 The solution was to use process called vibro-compaction. January 2004 fifteen vibro-compacting machines work around the clock to firm up the land. These shafts vibrate shaking the ground around it and compact the land. As the land compacts and sink more sand is poured in.  It took 8 months to stabilize the land. March 2004, the palm Jumairah is ready to be and building site.

When the palm first released to the public all the houses were sold just in 3 days. Most expensive go for 1.2 million dollars. 






         
           There was another problem, beach erosion. Normally sea current push the beach sand evenly. By building massive structure on shore line current will change its shape resulting in at some place shore will extend and other place it will erode.  Naturally problem will be solved but it will take time. Mean time developers used dredgers to suck up sand where it has deposited and pour into place where it had erode. 





London traffic servillance Technology



           London has one of the most advanced traffic surveillance system in the world. London traffic control centre(LTCC) servile spooling network of roads. London is circled by Britons most expensive roads, worlds biggest ring roads, 6 lane M25. Every rush hour M25 feeds equivalent of 25 free way lanes into the city.
More traffic into the same constrained space result in grid lock.  LTCC's job is to avoid grid locks. 

          On 80 screens it get the real time view of streets of London. Other cities monitor traffic jam after they form. But London can predict and even head them off. It is all done with central office management of integrated traffic(COMIT) system.


Embedded in London streets are 3000 electronic sensors. Sensor detects when a vehicle passes over and measures time travel to next sensor. Average time of travel between adjacent sensor is stored 100 times a minute. When traffic speed falls to lower average the system alerts and feeds to COMIT map in control centre. Green means no congestion, light blue means congestion has increased by 10%, dark blue up to 50%, red more than 50% congestion(grid lock). The LTCC team then can manipulate computer operated traffic signals and reduce the congestion.
                Most of the time there is no need for LTCC team to do anything. The traffic lights are so smart that they constantly monitor the traffic at their intersection and reset the timing for ideal flow.

 

To keep traffic rolling this city relies on more than sensors and traffic lights with minds of their own. At very heart of the city the volume of traffic exceeds capacity of streets. The solution is not improving flow but subtracting cars. Today motorists in central London are travelling in another dimension. The dimension not of space or time but of cash. There is a sign board - next stop congestion zone. Don't even think of entering the congestion zone if you haven't paid. That’s the solution to reduce crowd by hitting motorists where it hurts, in the wallet. 5 pounds per day to enter congestion zone.
But with the quarter million vehicle entering a day how do you keep track of who has paid and who is cheating? The zone is servile at 174 entry points. two cameras at each point.  Whenever a vehicle passes one camera records the licence plate and other background. With vehicles moving in and out of the congestion zone cameras takes million pictures a day. With the picture finding freeloaders is done at secret place in east London. In real time the system reads the plate as numbers and letters and sort out legal drivers from cheaters.  The technology is so good that you can take it to the court. The fine for not paying congestion charge is 100 pounds.


Wednesday, August 24, 2011

Engineering for relocating Abu Simbel temple

        The colonial temple of Abu Simbel is set on the shores of river Nile in southern Egypt. It was built by Ramesses II. His architects and engineers bestowed the temple with special power. They carefully aligned entrance of temple so that twice a year(on 21 Feb. and 21 Oct., 61 days before and 61 days after the winter Solstice) sun rays would penetrate inner century to light up the faces of gods inside. Egyptians feared that this phenomenon will not be seen in future as Abu Simbel was under the threat of very geographical condition, floods of Nile. Egypt government had to harness the power of Nile by building Aswan high dam. This massive structure almost 4km long would be providing electricity to half of Egypt. But the floods due to the dam would be destroying 20 monuments on the shores of Nile and the largest of them was Abu Simbel. It was a great challenge for engineers to save the temple maintaining its spectacles.


         The entrance of the temple was 33m high. Hidden behind is the temple with many chambers.


Statues and pillars were lined in hallway, then the inner century had statue of Ramesses seated along with three gods beside. The rays of the sun twice a year would light three of the statues keeping one in dark which is god of underworld(Ptah). Preserving this unique spectacle was the engineers toughest challenge.



       Experts over 50 nations put their head to find the best way to preserve the temple. One idea was to let the temple flood and construct an aquarium.

         But as the entrance statues were made of mud it would break eventually due to water. Then engineers realized that the only way is to move the temple to other location. They calculated that Aswan high dam will raise water level of Nile by 60m. So to safe the temple it has to be raised by at least 65m high and 200 m away from river shore.



        One idea was to move the temple in a single piece. It would be done with 650 hydraulic jacks lifting the temple to some level. Then the jacks will be replaced by concrete pillars and platform. Again lift the temple with jacks on this platform. It was required to repeat this 200 times.
          But the temple was too heavy to stand on these pillars. 


          There was another way, using rising water to lift the temple. It was proposed to encase the temple with concrete walls and the rising water would lift the temple. But the risk was storm in the river would damage the temple.







          Then engineers realized that Abu Simbel is too heave to lift. The only practical way is to cut the temple into pieces and move. In 1964, about 2000 engineers and contractors from Sweden, Italy, France, Germany and Egypt working together under UNESCO banner began to dismantle the temple, lift and reassemble. Between 1964 and 1968 the entire temple was moved 65 m high and 200 m back from the river. Due to the displacement of the temple and/or the accumulated drift of the Tropic of Cancer during the past 3,280 years, it is widely believed that the phenomenon is moved one day closer to the Solstice, so they would be occurring on October 22 and February 20 (60 days before and 60 days after the Solstice, respectively).