Reference of task 4-6

1.building process of Tsing Ma bridge, RTHK - https://www.youtube.com/watch?v=i_19XlwnO9I
2.Sustainable Development in the Project Management of the Tsing Ma Bridge in Hong Kong, Ir Dr Lau, C.K. - http://www.psdas.gov.hk/content/doc/2003-2-6/20_Nov_Dr_C_K_Lau.pdf
3.The bridge engineering 2 conference, Polly Ng Pui Yu , Department of Civl Engineering, University of Bath, United Kingdom - http://www.bath.ac.uk/ace/uploads/StudentProjects/Bridgeconference2007/conference/mainpage/Ng_Tsing_Ma.pdf
4.Tsing Ma  Bridge, Highways Department Hong Kong - http://www.hyd.gov.hk/en/publications_and_publicity/publications/hyd_factsheets/doc/e_tsing_ma_bridge.pdf
5. Tsaing Ma bridge, structures - http://structurae.net/structures/tsing-ma-bridge
6. King of bridge Lau Ching Kong - http://qkzz.net/article/02ac677d-878b-4735-bbde-7c670e6ba8da.htm
7. Reinforced concrete, Encyclopaedia Britannica - http://www.britannica.com/EBchecked/topic/496607/reinforced-concrete

loads of Tsing Ma Bridge

The dead load of Tsing Ma bridge is mainly from the deck and railway.

The live load is mainly from the train pass thought and the vehicles on the deck.

Last but not least, the wind load is one of the largest load of the suspension bridge.

Is Tsing Ma, a bridge built almost 20 years, a green building?

As a bridge, Tsing Ma bridge is a quite a green building based on the sustainability of materials and management. The Wind and Structural Health Monitoring System (WASHMS) is a sophisticated bridge monitoring system used in Tsing Ma bridge.

There are more than 350 sensors on the Tsing Ma bridge, the structural behavior of the bridges is measured 24 hours a day, seven days a week.

The sensors include accelerate meters, strain gauges, displacement transducers, level sensing stations, anemometers, temperature sensors and dynamic weight-in-motion sensors. They measure everything from tarmac temperature and strains in structural members to wind speed and the deflection and rotation of the kilometres of cables and any movement of the bridge decks and towers.

These sensors are the early warning system for the bridges, providing the essential information that help the Highways Department to accurately monitor the general health conditions of the bridges. Once when there is any problem is found on the bridge, the engineers can fix it as soon as possible.

Material using for Tsing Ma Bridge

The two anchorages are gravity structures and take the load from the main suspension cables at either end of the bridge as high as 521,000kN. The two towers of 206m high are of reinforced concrete. Each of them was slip formed in about 3 months. Total volume of concrete in towers is 46,000m3.

The successful contractor has decided to adopt conventional aerial spinning method. Each cable consists of 80 strands of 368 no. 5.38mm and 11 strands of 360 no. 5.38mm galvanized high tensile steel wires. Some 28,000 tons of galvanized steel wire are required. After spinning, the wires are compacted into a circular shape approximately 1.1 metres in diameter using special cable compacting machines. The cables are then wrapped and painted. The total length of wires is 160,000km, enough to circle the earth four times.

The bridge is mainly build with reinforced concrete and galvanized steel. Both of them are the common building materials nowadays, they both have their advantages and disadvantages.

Reinforced concrete, concrete in which steel is embedded in such a manner that the two materials act together in resisting forces. The reinforcement is usually, though not necessarily, steel reinforcing rebar) and is usually embedded passively in the concrete before the concrete sets. Thus, it has High relative strength, High toleration of tensile strain, Good bond to the concrete, irrespective of pH, moisture, and similar factors, Thermal compatibility, not causing unacceptable stresses in response to changing temperatures and Durability in the concrete environment, irrespective of corrosion or sustained stress for example.
Galvanized steel is steel that has gone through a chemical process to keep it from corroding. The steel gets coated in layers of zinc oxide because this protective metal does not get rusty as easily. Zinc protects steel in two ways. First, it is highly resistant to rust; iron, a major component of steel, reacts very easily with oxygen and moisture and will eventually disintegrate. The layer of zinc on the surface prevents those elements from reaching the steel so quickly. It also develops a patina — a layer of zinc oxides, salts, and other compounds — that offers further protection. Zinc is also extremely durable and scratch resistant, and has a satiny appearance that many find attractive.

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However, this common material does have it weakness. First and the main factor that increase the cost of project is the “time of construction”. Construction time increases in case of reinforcement. Second, reinforced concrete can corrode easily because of the presence of steel. Steel is heterogeneous material while concrete is a homogeneous material. Therefore, if both materials will be used in combination than quality control will be very difficult. Third, due to reinforcement, probability of cracking in concrete increases, because of shrinkage and creep in freshly lay concrete and hardened concrete. Last but not least, if spacing in aggregates will not be proper, then weak links increases in between steel and concrete and now if either steel or concrete fails then whole structure will be failed.

Galvanized steel that is cooled too slowly or stacked together before they have cooled completely can also have the outer zinc layer peel away. In some cases, small gaps can form between the zinc and the underlying alloy, which can also cause peeling. When a very thick coat of zinc is applied, it can also become brittle and flake off.

Comparing to the others materials, these two king of materials are still the most common building material, due to the cost and sustainability. Reinforced concrete is obviously the most suitable material for the above sea tower as it is hard and corrosion-proof. But the galvanized steel may replace by stainless steel as the main purpose is to resist from corrosion of water. But the cable size have to be changed as they have different hardness and ductility.

The "soul" of Tsing Ma bridge - Lau Ching Kong

Lau Ching Kong was born in September 1942, Guangdong Taishan. He finish his degree in the Hong Kong Polytechnic University and received his master degree of bridge construction in Surrey University. He have been called as “king of bridge” in Hong Kong construction industry and he has worked on more than a hundred of engineering designs or constructions in his career. He was the Chief engineer for the Tsing Ma Bridge project in Hong Kong, Director of Civil Engineering Department and consultant engineer of Hong Kong Disneyland project. Currently, he is the president of the Hong Kong Institute of Highway, China Highway Association and a part-time professor at Tsinghua University, Hong Kong Academy of Engineering Sciences and other duties.

In 1969, Lau was sent to England in order to do a master degree of bridge construction. After that he is back to Hong Kong. In September 1996, Lau became the Deputy Director of the Hong Kong Highways Department. He was the first to receive a Ph.D. from Tsinghua University in Hong Kong. In May 1997, under the auspices of Dr Lau, the Tsing Ma Bridge project is completed. It is the world's longest dual carriageway railway bridge, which can be used under typhoon climate in large span Suspension Bridge. This bridge building won many domestic and international awards like "British architectural award."1997 and "Top Ten Construction Achievements of the 20th century." in 1999U.S.
In the Tsing Ma bridge project, he is the man in charged. He have to check and manage the whole process of construction and do the quality control. Besides, he do site visit frequently for checking the bridge. If any problem is found, he have to organize and fix it.

Tsing Ma Bridge Introduction

Tsing Ma Bridge is a bridge connecting Tsing Yi Island and Man Wan Man-Made Island, which also where the name comes from. It was one of the infrastructural works of the Hong Kong Airport Core Program. This Tsing Ma Bridge is an important link between Hong Kong mainland and the Hong Kong International Airport. Initially, it was planned to have an under-water tunnel to carry the airport traffics. However, the channel was thought to be too deep and the heavy shipping traffics at the surface would make the under-water construction too dangerous to under-go. Therefore, a suspension bridge was built instead which is the Tsing Ma Bridge.

Tsing Ma Bridge is the world’s sixth largest suspension bridge but the world longest span suspension bridge which carrying both road and rail traffic. The bridge is supported by gravity-anchor in the form of reinforced concrete. It is situated in Hong Kong and it is 2.2km long. It was first constructed in May 1992 and finished in May 1997. It costs US$ 1 billion.

Tsing Ma Bridge is a double-decked suspension bridge and carries a total of 8 lanes of road traffic and 2 MTR rail lines. Its main span has a length of 1,377metres which makes Tsing Ma Bridge the largest of all bridges in the world carrying rail traffic. It has the width of 41m with a height of 206m. The clearance height of the bridge is 62m so the bridge does not interrupt barges going through the Ma Wan Channel.

The major problem of Tsing Ma Bridge was to withstand the excessive wind, typhoon. To overcome the excessive wind, bridge design had changed from one single deck into two level decks. The whole construction of the longest rail and road suspension cable bridge was completed within five years. There were five major construction components which are anchorages, approach span, foundations and construction of bridge tower, main cables and suspended deck. There is a Wind and Structural Health Monitoring System (WASHMA). This system is used to monitor the bridge closely to make sure the bridge is safe. With this system, quick decisions can be made.