Editing Tsing Ma Bridge (section)

== Design ==
[[File:Park Island Aerial.jpg|thumb|Ma Wan abutment]]
[[File:Tsing ma bridge.png|thumb|Tsing Ma bridge viewed from Ma Wan under [[Fog|dense fog]]]]
The bridge was designed by [[Mott MacDonald]].<ref>{{cite news|last1=Clarke|first1=Rachel|title=Construction 'Oscars' go to Tsing Ma span|work=South China Morning Post|date=25 October 1997|page=4}}</ref> The firm designed an early iteration of the bridge in 1982, with a two lane dual carriageway on the top deck, and a light railway on the lower deck.<ref name="dream">{{cite news|title=New bridge a dream come true|work=South China Morning Post|date=28 May 1992|page=35}}</ref> The bridge was redesigned beginning in 1989 to account for the three lane dual highway and the heavier airport railway. The designers were inspired by the [[Forth Bridge]] in Scotland and the [[Severn Bridge]] in England.<ref name="dream"/>

=== Wind tunnel testing ===
The objectives of the [[wind tunnel]] studies were to demonstrate the safety of the structure under construction and once completed, both with respect to [[aerodynamic]] [[flight dynamics|stability]] as well as the possible effects of extreme typhoon wind speeds. A further objective was to provide dynamic response data at several key locations to compare with full scale data from the ongoing monitoring program, conducted by the [[Highways Department]] of Hong Kong.

A 1 to 80 scale section model of the deck in the erection stage, and a 1 to 400 scale full aeroelastic model of the entire bridge were constructed. It is a [[Monte Carlo method|Monte-Carlo]] simulation of the typhoon wind climate. The full model was tested in different stages of construction in turbulent boundary layer flow, complete with the local [[topography]] to model the wind conditions at the site. The model tests identified critical stages of erection that allowed the construction schedule of the bridge to be tailored to avoid the typhoon season. The comparison of model test results and the full scale monitoring will assist engineers to better understand the behaviour of long span bridges in wind and to improve current design methods.

=== Major components ===
[[File:Cable band for Tsing Ma Bridge.jpg|upright|thumb|left|Cable band for Tsing Ma Bridge undergoing dimensional inspection]]

There is one tower located on [[Wok Tai Wan]] of Tsing Yi side and another on a man-made island {{convert|120|m|ft}} off the coast of Ma Wan.<ref>{{cite web |url=http://www.cityu.edu.hk/CIVCAL/book/bridge.html |title=Tsing Ma Bridge |publisher=Cityu.edu.hk |access-date=2013-04-29 |archive-date=16 May 2019 |archive-url=https://web.archive.org/web/20190516221456/http://www.cityu.edu.hk/CIVCAL/book/bridge.html |url-status=dead }}</ref> Both towers are {{convert|206|m|ft}} above sea level and founded on relatively shallow bedrock. The towers are two-legged with trusses at intervals, in the form of portal beam design. The legs were constructed with high-strength concrete of 50 MPa (concrete grade 50/20) strength, using a slipform system in a continuous operation.

The pulling force in the main suspension cables is taken up by large gravity anchorages located at both ends of the bridge.<ref>{{cite web |url=http://www.geo-design.co.uk/projects/foundations/tsing-ma-bridge-anchorages-hong-kong/ |archive-url=https://archive.today/20130420110230/http://www.geo-design.co.uk/projects/foundations/tsing-ma-bridge-anchorages-hong-kong/ |url-status=dead |archive-date=2013-04-20 |title=Tsing Ma Bridge Anchorages, Hong Kong |publisher=Geo-Design |access-date=2013-04-29 }}</ref> They are massive concrete structures deeply seated on bedrock on the landside of Tsing Yi and Ma Wan island. The total weight of concrete used in the Tsing Yi anchorage is 200,000 tonnes, and Ma Wan Anchorage has 250,000 tonnes of concrete.

The cables were constructed by an aerial spinning process. The process involved drawing wires from a constant-tension supply, and pulling loops of these wires from one anchorage to the other, passing through a 500-tonne cast-iron saddle on top of each bridge tower seating the cable. A total of 70,000 galvanised wires of {{Convert|5.38|mm|in|adj = on}} diameter were placed and adjusted to form the two {{convert|1.1|m|ft|adj = on}} diameter main cables.

The steelwork for the deck structure was fabricated in Britain and Japan. After delivery, they were further processed and assembled in [[Dongguan]], China into standard deck modules. A total of 96 modules, each {{convert|18|m|ft}} long and about 480 tonnes in weight, were prepared. These deck modules were brought to the site by specially designed barges and raised into the deck position by a pair of [[strand jack]] gantries that could manoeuvre along the main cable.

The approach span on the Tsing Yi side is similar in form and cross-section to the suspended deck, but is supported on piers instead by cables. The first span was assembled on the ground and raised into position using strand jacks. Further construction then proceeded in cantilever in smaller sections, using derrick cranes stationed on the deck level. An [[expansion joint]] which allowed for a maximum thermal movement of ± {{convert|835|mm|in}} was also provided and located inside the approach span.

The bridge parapets are of a special design by Hong Kong standards, comprising high-tension steel strands anchored on metal posts.<ref name=20030716legco>{{cite web|title=Tuen Mun Road Traffic Incident – The Use of Vehicular Parapets and Proposed Way Forward|url=http://www.legco.gov.hk/yr02-03/english/panels/tp/papers/tp0717cb1-2218-1e.pdf |archive-url=https://ghostarchive.org/archive/20221009/http://www.legco.gov.hk/yr02-03/english/panels/tp/papers/tp0717cb1-2218-1e.pdf |archive-date=2022-10-09 |url-status=live|publisher=Legislative Council Panel on Transport|date=16 July 2003}}</ref>

===Ship impact protection===
The rock seawalls around the base of each bridge tower are capable of halting a 220,000 tonne ship moving at eight knots.<ref name="gateway">{{cite news|title='Gateway to China' plan moves ahead|work=South China Morning Post|date=27 November 1992|page=62}}</ref>