Sky Gate Bridge
Sky Gate Bridge, located in Izumisano, crosses the River Tyne next to the famous Kansai international airport in Osaka Japan and is used as an access to the airport.
Considered a great example of military engineering, Sky Gate Bridge is the longest double- decked truss bridge designed for use by military units to bridge up to 60 meters (200 ft) gaps.
A large part of what makes Sky Gate Bridge which was constructed at a cost of 202 million USD, as successful and unique is the modular design, and the fact that it was assembled with minimal aid from heavy equipment this is according to Oscar G Meyer an engineer at Dorman Long.
Truss Bridge.
A truss bridge composed of connected elements (typically straight) which may be stressed from tension, compression, or sometimes both in response to dynamic loads. A truss bridge is economical to construct owing to its efficient use of materials.
The nature of a truss allows for an analysis of the structure by using a few assumptions and application of Newton's laws of motion according to a branch of physics known as statics. For purposes of analysis, truss is assumed to be pin jointed where the straight components meet. This assumption means that elements of the truss (chords, verticals and diagonals) only act in tension or compression.It required no special tools or heavy equipment for construction, the bridge elements are small enough to be carried in trucks yet the bridge is strong enough to hold military tanks.
Type of Truss
The type of truss used while constructing the bridge was the Pegram truss. The Pegram truss consists of a Parker type design with the vertical posts leaning towards the center at an angle between 60 and 75°. The variable post angle and constant chord length allowed steel in the bridge to be recycled into a new span using the truss design. This design also facilitated reassembly and permitted the bridge to be adjusted to fit different span lengths. The Pegram truss is a hybrid between the Warren and Parker trusses where the upper chords are all of equal lengths while the lower chords being longer than the corresponding upper chord. Because of the difference in upper and lower chord length, each panel was not square. The chords which are vertical in a Parker truss vary from near vertical in the center of the span to diagonal near each end (like a Warren truss).Oscar G Meyer chief engineer claims that this is the toughest truss to make a strong double-deck bridge unlike the truss used in the Quebec Bridge in Canada which crossed the lower Saint Lawrence River to the west of Quebec City, and Levis. Prior to its collapse, Quebec was the longest bridge in this category before the construction of the Sky Gate Bridge.
Construction
Sky Gate Bridge was constructed by Dorman Long, at a total length of 3,770 feet (1,150 metres).The total weight of fabricated steelwork used was 51,000 tonnes with a weight of steel in the arch of 38,000 tonnes.
The bridge consists of three main parts: The "floor" of the bridge which consists of a number of 19 ft (5.8 metres) wide transoms that run across the bridge, with 10 feet long stringers running between them on the bottom, forming a square. The bridge's strength is provided by the panels on the sides, which are 10 ft (3 metres) long cross-braced rectangles. They were then placed standing upright above the stringers, with clamps running from the stringers to the panels to hold them together. Ribands were placed on top of the completed structural frame, with wood planking being placed on top of the ribands to provide a roadbed.
Sky Gate has a solid deck and a lattice of pin-jointed girders for the sides. The Sky Gate Bridge has three lanes of automobile traffic on top deck, and on the lower decks there are two lanes and a pair of tracks for metro trains.
Each unit constructed created a single 10 ft (3 metre) long section of the bridge, with a 12 ft (4 metre) wide roadbed. After one section was completed it was typically pushed forward over rollers on the bridgehead, and another section built behind it. The two were then connected together with pins pounded into holes in the corners of the panels.
For added strength several panels (and transoms) were bolted on either side of the bridge. A useful feature of the Sky Gate Bridge was its ability to be "launched" from one side of a gap. In this system the front most portion of the bridge was angled up with wedges into a launching nose with most of the bridge being left without the roadbed and ribands. The bridge was placed on rollers and simply pushed across the gap, using manpower. (With the help of jacks). On the Sky Gate Bridge, groups of strain gauges were installed in carefully selected locations to obtain information concerning the behaviour of the structure under in-service loading. From these, time-series results from standard freight trains of known configurations and axle weights were obtained
Cycling on the Bridge
Cyclists are prohibited from using the bridge except for special bicycle events. The sky gate Punt is a ferry that runs directly below the bridge taking cyclists and pedestrians across the Yarra between a jetty at Fisherman's Bend near Westgate Park - Bayside Trail and a jetty adjacent to Science works Museum - Hobson’s Bay Coastal Trail.
CONCLUSION
The inclusion of the elements shown is largely an engineering decision based upon economics, being a balance between the costs of raw materials, off-site fabrication, component transportation, on-site erection, the availability of machinery and the cost of labour. In other cases the appearance of the structure may take on greater importance and so influence the design decisions beyond mere matters of economics.
Professional Team
Client Kansai International Airport
Main Engineer Oscar G Meyer
Engineering Companies Weicon And Dorman Long Company Limited
Construction Company John Hollan Construction
Designers Freemann Fox And Partners
Steel Suppliers Broken Hill Proprietory Limited
